Pfl igers Archiv
Pfltigers Arch. 366, 107-114 (1976)
EuropeanJournal of Physiology 9 by Springer-Verlag 1976
The Role of' the Fusimotor System with Respect to the Contribution of the Diaphragm and the Intercostal Muscles to the Respiratory Tidal Volume H. TH. FOLGERING, F. D. J. SMOLDERS, and J. A. BERNARDS Department of Physiology,Universityof Nijmegen, Geert Grooteplein Noord 21a, Nijmegen, The Netherlands
Summary. The efferent electrical activity in the phremc nerve can be quantified in such a way that it gives a good correlation to tidal volume. After administration of the drug benzoctamine this relationship changes: more phrenic nerve activity is needed for the same tidal volume. No changes were found in the neuro-muscular transmission from the phrenic nerve to the diaphragm. There was no alteration in dynamic compliance of the lungs or in airway resistance. The afferent phrenic nerve activity from proprioceptors in the diaphragm did not change. It seems unlikely that respiratory neurons in the brainstem were affected since the sensitivity of the respiratory system to CO2 did not change. It is known that the tonic fusimo~.oneuron activity is suppressed at a supraspinal level by benzoctamine. Since intercostal muscles have muscle spindles and the diaphragm hardly has any, the intercostal muscle activity will be affected more than diaphragmatic activity by benzoctamine. This could actually be shown by quantifying the electromyogram of inspiratory external intercostal muscles. The tidal volume regulation is controlled by the vagal feedback loop. In order to reach a certain tidal volume after administration of benzoctamine, the contribution of the diaphragm has to increase because the activity of the intercostal muscles is diminished. Key words." Phrenic nerve activity -
Respiratory m u s c l e s - Benzoctamine -- Fusimotoneurons -Muscle spindles.
INTRODUCTION It is possible to quantify the electrical activity of the phrenic nerve in such a way that it gives a good correlation with respiratory tidal volume. This can be very useful if, in experiments with paralyzed animals, one
wants to be informed about the efferent part of the central respiratory activity (Eldridge, 1971 ; Fitzgerald, 1973 ; Smolders et al., 1975). The relationship between tidal volume and quantified phrenic nerve activity has been investigated in several experimental conditions such as hypercapnia and hypoxia (Fitzgerald, 1973), vagotomy (Eldridge, 1971), and different levels of FRC (Cherniack, 1973; Smolders et al., 1975). Most of these studies concern the effects of the vagal feedback from the lungs. Mostly the control of tension and length of the intercostal muscles and diaphragm in this respect is disregarded. Furthermore the balance between the contributions of the diaphragm and the extra-diaphragmatic muscles gets very little attention. Bergofsky (1964) found in conscious man that the "partition of the tidal volume between rib cage and diaphragm remained unaltered" during stimulation of the ventilation with hypercapnia. Konno and Mead (1967) found linear relationships between the displacement of the thoracic wall and the displacement of the abdominal wall versus tidal volume. Wade (1954) assumed a linear relationship in conscious man between fluoroscopically measured movements of the diaphragm versus tidal volume, and using this assumption, obtained good results in his experiments on the movements of the thoracic cage and diaphragm in respiration. Viljanen (1967) found a logarithmic relation between tidal volume and the impulse frequency in the EMG of the external intercostals at the end of inspiration. Mognoni et al. (1969), working with anesthetized rabbits, also found a linear relationship between volume displacement by extradiaphragmatic muscles and tidal volume. The relative contribution of the extra-diaphragmatic muscles to the tidal volume changes however with the depth of respiration. Certain kinds of sedatives and probably most of the anesthetics have a distinct influence on the fusimotoneuron system. Since intercostal muscles have
]08 muscle spindles and the d i a p h r a g m hardly has any, these drugs must have different effects on either g r o u p o f muscles; consequently these drugs also influence the relationship between quantified phrenic nerve activity and tidal volume, and m a k e it possible to study the effects of the fusimotor system. This study mainly deals with benzoctamine (Tacitin | Ciba-Geigy) in this respect. Benzoctamine (chemical n a m e : dibenzobicyclooctadiene) used as a psychoactive drug is k n o w n to suppress the tonic f u s i m o t o n e u r o n activity. The fusim o t o r system still responds to stimulation but the response is diminished. So apparently the gain o f the system regulating the g a m m a activity is changed due to the effects o f this drug at a supraspinal level (Baltzer and Bein, 1973). F u r t h e r m o r e the drug causes a small reduction in blood pressure and has an e - s y m p a t h o lytic effect (Jaques and Rtiegg, 1971). These authors described a spectrum o f peripheral effects in vivo and in vitro, similar to that o f chlorpromazine. Benzoctamine has no effects on the Sensitivity o f the respiratory regulating system to CO2 (Geissler, 1970). Oral doses o f 3 m g / k g caused no change in blood gas values (Stepanek, 1973). W h e n testing this drug we f o u n d a very consistent change in the relationship between tidal volume and quantified phrenic nerve activity. The same effects were also seen after deepening the anesthesia o f chloralose-urethane or o f pentobarbital. The purpose o f this study is to investigate whether the effects o f the drug benzoctamine on the relationship between tidal volume and quantified phrenic nerve activity is due to the suppression o f the fusim o t o n e u r o n activity o f the intercostal muscles.
METHODS Twenty-four cats of either sex, weighing 2.5-3.5 kg, were used. After premedication by 25 mg ketamine HC1 and 0.5 mg atropine, anesthesia was induced by chloralose 25 mg/kg and urethane 125 rag/ kg. A tracheal cannula was inserted, and the femoral artery and vein were cannulated for recording the blood pressure (Statham P23) and administration of drugs respectively. In 8 experiments an esophageal balloon was inserted for the measurement of intrapleural pressure. The animal was placed on the table in supine position. The rectal temperature was kept constant at 38.0 _+0.1~C. One of the phrenic nerves was dissected in the neck region and cut at the site of its entry into the thorax. The sheath of the central stump was retracted and the nerve was placed on a bipolar platinum electrode. Electrical activity of the phrenic nerve was amplified and filtered between 80 c/s and 10000 c/s (Tectronix RM 122). The whole preparation was immersed in a pool of warm paraffin oil. The Fleisch head of a pneumotachograph (Elema Schoenander) was connected to the tracheal cannula. A gas sample was withdrawn from the trachea for CO2 analysis (Godart infrared analyzer). At the beginning of the experiment a balloon filled with approximately 300 ml of oxygen was connected to the tracheal cannula, and the animal started rebreathing its own CO2 without
Pfltigcrs Arch. 366 (1976) getting hypoxic. When the endtidai CO; reached about 60 - 65 Torr the ballon was disconnected and the experiment was stopped. The rebreathing experiment was done before and after administration of benzoctamine 1 mg/kg i.v. Recordings were made on a 7-channel tape recorder (Philips, Analog 7). Respiratory airflow, integrated airflow (VT), phrenic nerve activity, respiratory CO2, and blood pressure were recorded. Calculations of the relationship between tidal volume and quantified phrenic nerve burst activity were done by a PDP9 computer. The phrenic nerve burst activity was quantified by calculating the root of the mean pulse rate (RMPR) during inspiration (Smolders et al., 1975). In order to evaluate the afferent phrenic nerve activity, 5 animals were paralyzed by slow infusion of succinylcholine(0.25 rag/ rain). Artificial respiration was performed by a Harvard Constant Volume Respirator. Endtidal Po2 and Pco2 as well as tidal volume and frequency of the respirator were kept constant before and after administration of benzoctamine. The electrical activity in the distal stump of the phrenic nerve was recorded and quantified by calculating ~he impulse rate.
RESULTS A linear relationship Vr = A + B. R M P R was f o u n d between tidal volume (Vx) and quantified phrenic nerve activity ( R M P R ) with correlation coefficients f r o m 0.72 to 0.99 obtained by the least-square m e t h o d (Table 1). In 19 out o f 20 experiments, after benzoctamine a different relationship (90 ~o confidence limits) was f o u n d between tidal volume and quantified phrenic nerve activity (Fig. 1). A significant (P < 0.01) change in slope (B) was f o u n d in 14 out o f 20 experiments. In 11 cases there was a significant decrease, in 3 cases a significant increase in slope after benzoctamine. The intercept (A) showed a significant (P < 0.01) decrease in 11 experiments; there were 2 significant increases, and in 7 cats no significant effect could be f o u n d after benzoctamine. In 2 experiments (1 and 7) there was no significant change in b o t h parameters A and B. A coincidence o f a rise in b o t h A and B did not occur. In some cases, however, there is an overlap o f the 90 ~o" confidence limits o f the two lines at the intercept with the ordinate (A) outside the measured ranges, i.e. no significant change in A, so that the shift o f the line after the drug c a n n o t be expressed by a change in A. Consequently the effect o f administration o f benzoctamine on the relationship between tidal volume and quantified phrenic nerve activity could be shown in a decrease o f the slope or increase o f the intercept, or both. In the measured ranges o f tidal volume, the regression line o f tidal volume versus phrenic nerve activity after administration was always located to the right o f the regression line before administration o f the drug and the lines did not cross with the only exception o f experiment 7. This means that m o r e electrical activity is needed in the phrenic nerve in order to reach the same tidal volume. The same effect was also f o u n d after deepening the anesthesia b y
H. Th. Folgering et al. : Respiratory Muscles and Fusimotor Innervation t'able 1. Vr = A + B x R M P R . Parameters and correlation coefficients (r) of regression lines of tidal volume versus quantified phrenic nerve activity ( R M P R : Root of Mean Pulse Rate [Smolders et al., 1975]) before and after administration of benzoctamine, or chloralose-urethane in experiments 17, 23, 25, or pentobarbital in experiment 27. All experiments were performed on different cats. Significant changes (P < 0.01) are indicated by * + : 90 % confidence limits overlap (Exp. Nr. 7) Exp.
1 2 3 4 5 6 7+ 8 9 10 I1 12 13 14 i5 16 18 20 22 26 17 23 25 27
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r
8.6 19.4 10.9 8.2 31.2 5.6 8.5 - 4.7 - 4.5 -I2.6 14.6 -34.9 1.7 33.0 47.9 27.8 15.2 8.3 3.3 68.4 -19.3 - 6.2 1.2 -18.1
0.8 0.5 0.9 1.0 0.9 1.1 0.3 0.6 0.6 0.9 1.4 2.6 0.6 0.6 0.7 1.5 0.9 1.2 1.8 1.9 1.7 1.5 1.5 1.8
0.97 0.9/ 0.99 0.90 0,96 0.98 0.93 0.98 0.94 0.97 0.88 0.97 0.98 0.93 0.99 0.94 0.98 0.96 0.98 0.94 0.99 0.98 0.95 0.98
4.6 8.9* 2.2* 7.6 20.9* - 6.0 11.2 -17.9" 3.9 -13.8 16.3 -67.3* -- 6.4* --19.5" 6.0* 45.7* -- 13.9' 29.8* -20.2* --56_7* --11.6 --38.7* -48.8* -49.5*
0.8 0.6 0.9 0.6* 0.8* 0.9* 0.2 0.7* 0.5* 0.7* 0.6* 2.3* 0.5* 1.1" 0.8* 1.0" 1.0 0.6* 1.2' 2.0 1.4" 1.4 1.9" 1.6
0.98 0.96 0.99 0.99 0.99 0.98 0.72 0.95 0.97 0.97 0.73 0.93 0.99 0.96 0.98 0.93 0.96 0.95 0.97 0.98 0.97 0.97 0.98 0.93
chloralose-urethane (3 cats) or after administration of pentobarbital (1 cat). Similar to the results of Geissler and Rost (1970) we found no change of the respiral;ory response to CO2 as determined by this rebreathing method, indicating that the sensitivity of the respiratory regulating system did not change after administration of benzoctamine (Fig. 2). The arterial blood pressure changed from 156 +_ 21/128 +_ 16 before to 140 _+ 17/114 ___ 14 mmHg after administration of the drug (n -- 10). No animal became hypotensive. In order to prove that the drug effect is caused by the depression of the fusimotor system, other sites of its action had to be excluded. The neuro-muscular transmission from the phrenic nerve to the diaphragm might be inhibited by benzoctamine. This was checked in 4 cats by stimulating the intact phrenic nerves at several frequencies. The forces of the auxotonic contractions of the diaphragm were measured using the experimental set-up described by Van Rossum and Elstrodt (t965). These
109
forces were not influenced by the administration of benzoctamine (Fig. 3). The cats were hyperventilated artificially in order to diminish the spontaneous contractions of the diaphragm. After administration of benzoctamine an increased spontaneous activity can be seen. This is in agreement with the findings of Geissler and Rost (1970) and Utting (1975). A change in the dynamic compliance of the lungs might cause a rise in phrenic nerve activity at the same tidal volume. This possibility was tested in 8 cats by plotting tidal volume versus intrapleural pressure and thus taking dynamic compliance loops before and after administration of benzoctamine. There was no significant change in this dynamic compliance (Fig. 4). There was no change in airway resistance following administration of benzoctamine either. Since the dynamic compliance of the lungs does not change, the airway resistance may be approximated by plotting intrapleural pressure versus respiratory airflow measured by the pneumotachograph. A change in afferent feedback in the intact phrenic nerve might be a cause of the increased efferent activity. Recordings were made from the distal stump of the phrenic nerve in paralyzed, artificially ventilated cats. The diaphragm was stretched by inflating a pneumatic cuff around the abdomen of the cat, thus pressing the abdominal contents against the diaphragm. Afferent phrenic nerve activity still changed phasically with the respirator. It was quantified by calculating the instantaneous impulse rate. No change in afferent phrenic nerve activity was found after administration of benzoctamine (Fig. 5). So a feedback loop within the phrenic nerve is not affected and cannot be responsible for the changes in efferent activity. DISCUSSION The main finding of this paper is a shift of the Vvphrenic nerve activity curve to the right after benzoctamine (Fig. 1). This shift is effected either by a decrease in slope, or an increase in intercept, or both. Cutting one of the phrenic nerves might also cause a shift in this relationship. But when taking this shift as a new starting situation, the administration of benzoctamine induces an additional shift. The transsection of one of the phrenic nerves is of no consequence for the total ventilation, which is primarily regulated by the blood gas values and the vagal feedback. Campbell (1958) states that "the diaphragm is not however an essential muscle and can be paralysed on both sided without significant respiratory embarrassment". Pentobarbital and chloralose-urethane might have a different site of action in the reticular formation.
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Pflfigers Arch. 366 (1976)
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H. Th. Folgering et al. : Respiratory Muscles and Fusimotor Innervatioa
t 1t
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O u r results, however, suggest they eventually also suppress f u s i m o t o n e u r o n activity. A c c o r d i n g to Jaques and Rfiegg (1971), benzoctamine has some peripheral activities similar to chlorpromazine. The latter drug disrupts temperature regulatory mechanisms. This would m e a n that benzoctamine would also decrease b o d y temperature, and m o r e energy would be needed to m o v e a cooler diaphragm. However, since both thoracic and a b d o m i n a l cavities were not opened and b o d y temperature was controlled, this c a n n o t be the explanation for our findings. The effects f o u n d on the relationship between tidal volume and quantified phrenic nerve activity were not due to a splaying o f the nerve on the electrode. The time interval between the two measurements was only 15 min. F u r t h e r m o r e , the whole preparation was immersed in paraffin oil, so that the weight o f the nerve on the electrode was negligible. U n d e r constant experimental conditions, the relationship between VT and quantified phrenic nerve activity remains very constant (Smolders et al., 1975).
Fig. 3. Effectsof benzoctamine on the auxotonic contractions of the diaphragm (arbitrary units) and on the blood pressure in an artificially ventilated cat. The intact phrenic nerves were stimulated with stimuli of pulse trains (pulses 1 ms, 5 V, train duration 200 ms, train frequency 0.06 c/s, pulse frequencies indicated in the figure). The cat was hyperventilated in order to diminish the spontaneous diaphragmatic activity. It may be noted that the spontaneous activity (irregular low activity in the tracing "contraction of diaphragm") increases after administration of benzoctamine
After the start o f a phrenic nerve burst, the firing frequency o f the active fibers increases and m o r e fibers are recruited. Thus, the longer a burst lasts, the stronger is the electrical activity (Gesetl et al., 1940; Pitts, 1942; Gill, t963). Benzoctamine is a muscular relaxant. It is possible that the d i a p h r a g m is so m u c h relaxed that the initial part o f the contraction is isometric. This would m e a n that at the beginning o f an inspiration there is phrenic nerve activity without inspiratory air flow. The phrenic nerve activity goes on till it is stopped by vagal afferent activity. In case o f an initial isometric contraction the phrenic nerve burst has to last longer in order to reach a certain tidal volume, and consequently the quantified phrenic nerve activity has to increase. A n initial isometric contraction after administration of benzoctamine would also mean that there has to be a greater
Fig. 1. Relationships between tidal volume and quantified phrenic nerve activity in 24 cats. These relationships are plotted before and after suppressing the fusimotoneurons by benzoctamine, chloralose-urethane, or pentobarbital. After administration of the drugs the relationships are shifted to the right; consequently more electrical activity is needed in the phrenic nerve in order to reach the same tidal volume. The electrical activity in the phrenic nerve is quantified by calculating the root of the mean pulse rate in a burst (Smolders et al., 1975). The solid lines indicate the 90 ~ confidence limits in the measured ranges of tidal volume. Experiments 17, 23, 25 were experiments with chloraloseurethane, experiment 27 shows the effect of pentobarbitai. Vertical scaIe ranging from 0 - 200 ml: horizontal scale from 0 - J00 (arbitrary units)
112
Pfltigers Arch. 366 (1976) Fig. 4 Dynamic compliance loops taken at the same respiratory frequency before and after suppressing the fusimotor system by benzoctamine. Both loops are almost identical, indicating no significant change in dynamic compliance of the lungs. This example is representative for all 8 cats tested in this way
(ml) 0
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Fig. 5. Quantified afferent activity (RNP, Smolders et al., 1975) in the distal stump of the phrenic nerve versus pressure in the cuff around the abdomen of the cat. No difference is seen before and after administration of benzoctamine
time lag between the start o f the phrenic nerve activity and the start o f the inspiratory air flow. But there is no change in time lag. So this explanation does not a c c o u n t for the higher electrical activity in the phrenic nerve after administration o f benzoctamine. It might be that benzoctamine also influences respiratory neurons in the brainstem. Since the blood gas values do not change (Stepanek, 1973) and the response to CO2 remains unaltered (Fig. 2; Geissler, 1970; Utting, 1975)the remaining unlikely possibility would be a suppression o f those neurons which ac-
X ~ S.D.
O
iOO
Int. EMG 2nd intercost. (Arbitrary Units)
Fig. 6. QuantifiedEMG of the second external intercostal muscle in the anterior axillary line versus tidal volume. The relationship was calculated before and after suppressing the fusimotor system by benzoctamine. The plot shows that the electric activity in the intercostal muscles is markedly reduced after administration of the drug. One point represents the mean of 10 breaths of one animal, which was representative for the whole group
tivate the ~ - m o t o n e u r o n s of the intercostal muscles, and an enhancement o f those activating the c~-motoneurons o f the diaphragm, resulting in the same ventilation. It was not possible to confirm or to refute this theory definitely. It was shown by Baltzer and Bein (1973) that benzoctamine suppresses tonic f u s i m o t o n e u r o n activity at a supraspinal level. Since both tonic as well as phasic f u s i m o t o n e u r o n activity determine the activity o f the Ia afferents, the latter activity will also be sup-
H. Th. Folgering et al. : Respiratory Muscles and Fusimotor Innervation
pressed (Campbell et al., 1970; Flandrois, 1965). According to Baltzer and Bein (1973) after administration of benzoctamine: "The (gamma) system retains its ability to respond to stimulation and thus also its capacity for regulation ... the diminution (of the response to stimulation) being proportional to the discharge frequency prior to stimulation." Apparently the gain within the y-activating system is changed by benzoctamine. The Ia afferents of the muscle spindles monosynaptically excite the :~-motoneurons of the same muscles (Eccles, 1963). Campbell et al. (1970) state that the activity of the c~-motoneurons of the intercostal muscles highly depends on this excitation. This excitatory effect is suppressed by benzoctamine. Thus only the intercostal muscles, having a considerable amount of muscle spindles, are affected and decrease their activity. Inspiration stops when a certain vagal afferent activity is reached in a certain time (Clark and yon Euler, 1972), i.e. tidal volume is regulated by the vagal feedback loop. Since the intercostal muscle activity is suppressed, the diaphragm has to act more in order to reach a lung volume sufficient for the required vagal feedback activity. The final proof of this hypothesis was secured in 3 experiments in which the quantified EMG was taken from the second and third external intercostal muscles which clearly showed inspiratory activity. The quantified electrical activity of' these intercostal muscles decreased after administration of benzoctamine (Fig. 6). The EMG, quantified by calculating the mean impulse rate per burst, appears to be linearly related to tidal volume in the measured range, although according to Viljanen (1969), who used another method, there is a logarithmic relationship. It cannot be excluded that our linear relationship is spurious; the important point here was to show that there is a consistent and significant difference between the two lines. Froese and Bryan (1974) described changes in position and in pattern of the contraction of the diaphragm after barbiturate anesthesia in humans. These changes were ascribed to "effects of the anesthetic agents and muscle relaxants on the diaphragm". However, a primary change in muscle ~:one of the intercostal muscles, and subsequently a shift of the position of the diaphragm towards the thoracic cavity might explain their findings as well. Westbrook et al. (1973) suggested: "The initial effect of our anesthetic procedure (pentothal and meperidine) was to cause a change in the P-V characteristic of the chest wall such that a reduction in FRC occurred." This reduction of FRC and stiffening of the chest wall measured in static condition in a body plethysmograph is fully compatible with a decrease in activity of the external
113
intercostal muscles. As a matter of fact the "intercostal paralysis" had already been used as a "sign of anesthesia" by John Snow in 1858. In conclusion, the electric activity in the phrenic nerve, quantified correctly, is a useful parameter for measuring the neural output of the respiratory centers. However, when using this parameter the fusimotor system should not k~e interfered with, because depression or enhancement of the fusimotor activating system has different effects on diaphragm and intercostals. Acknowledgements. The authors wish to express their gratitude to Mr. J. Evers for technical assistance during the experiments; to Mrs. E. Crul-Sluyters (Dept. of Anesthesiology) for testing the drug in an experimental set-up for measuring the auxotonic contractions of the diaphragm; and to Mrs. S. Engels for preparing the manuscript.
REFERENCES Baltzer, V., Bein, H. J. : Pharmacological investigations with benzoctamine (Tacitin), a new psycho-active agent. Arch. int. Pharmacodyn. 201, 25-41 (1973) Bergofsky, E. H. : Relative contribution of the rib cage and the diaphragm to ventilation in man. J. appl. Physiol. 19, 689-706 (1964) Campbell, E. J. M.: The respiratory muscles and the mechanics of breathing, p. 13. London: Lloyd-Luke 1958 Campbell, E. J. M., Agostoni, E., Newsom Davis, J, : The respiratory muscles, mechanics and neural control. Chapters 1, 6, 7, 1i. London: Lloyd-Luke 1970 Cherniack, N. S., Stanley, N. N., Tuteur, P. G., Altose, M. D , Fishman, A. P.: Effects of lung volume changes on respiratory drive during hypoxia and hypercapnia. J. appl. Physiol. 35, 635-641 (1973) Clark, F. J., von Euler, C.: On the regulation of depth and rate of breathing. J. Physiol. (Lond.) 222, 267-295 (1972) Eccles, R. M., Sears, T. A., Shady, C. N.: Intraceltular recording from respiratory motoneurones of the thoracic spinal cord of the cat. Nature (Lond.) 193, 844-846 (1962) Eldridge, F. L.: Relationship between phrenic nerve activity and ventilation. Amer. J. Physiol. 221, 535-543 (1971) Fitzgerald, R. S. : Relationship between tidal volume and phrenic nerve activity during hypercapnia and hypoxia. Acta Neurobiol. exp. 33, 419-425 (1973) Flandrois, R., Lacour, J. R., Chabanne, J. P., Hernandez, J. P.: Action d'une diminution de l'activit+ fusoriale sur l'hyperventilation r6flexe au cours de la mobilisation passive chez le chien. J. Physiol. (Paris) 57, 611-612 (1965) Froese, A. B., Bryan, A. C.: Effect of anesthesia and paralysis on diaphragmatic mechanics in man. Anesthesiology 41,242255 (1974) Geissler, L., Rost, H. D. : Untersuchungen fiber den Einflul3 yon Tacitin auf die Atmung des Menschen. In : Entspannung, neue therapeutische Aspecte. St, Moritz Symposium 1970, Vorsitz. P. Kielholtz, pp. 54--58. Basel: Ciba AG 1970 Gesell, R., Kearney-Atkinson, A., Brown, R. C.: The gradation of the intensity of inspiratory contractions. Amer. J. Physiol. 113, 659-673 (1940) Gill, P. K. : The effects of end-tidal CO2 on the discharge of individual phrenic motoneurones. J. Physiol. (Lond.) 168, 239-257 (1963) Jaques, R., Rfiegg, M.: Some peripheral pharmacologic characteristics of benzoctamine. Pharmacology 6, 89-98 (1971)
114 Konno, K., Mead, J. : Measurement of the separate volume changes of rib cage and abdomen during breathing. J. appl. Physiol. 22, 407 - 422 (1967) Mognoni, P., Saibene, F., Sant Ambrogio, G.: Contribution of the diaphragm and other inspiratory muscles to-different levels of tidal volume and static inspiratory muscles to different levels of tidal volume and static inspiratory effort in the rabbit. J. Physiol. (Lond.) 202, 517-534 (1969) Pitts, R. F. : Excitation and inhibition of phrenic motoneurones. J. Neurophysiol. 5, 75-88 (1942) Van Rossum, J. M.~ Elstrodt, J. M.: A potentiometer transducer. Arch. int. Pharmacodyn. 154, 63-68 (1965) Smolders, F. D.J., Folgering, H. Th., Bernards, J.A.: Phrenic nerve activity as a measure of ventilation in the paralysed cat. Pfltigers Arch. 359, 157-169 (1975) Snow, J.: On chloroform and other anaesthetics. London, p. 42, 1858. Quoted in: The signs of anaesthesia. N.A. Gillespie. Curr. Res. Anesth. 22, 275-282 (1943)
Pflfigers Arch. 366 (1976) Stepanek, J. : Changes in acid-base balance, respiration rate and heart rate upon oral administration of benzoctamine and diazepam in conscious dogs. Arch. int. Pharmacodyn. 202, 135 - 152 (1973) Utting, H. J., Pleuvry, B. J. : Benzoctamine: a study of the respiratory effects of oral doses in human volunteers and interactions with morphine in mice. Brit. J. Anaesth. 47, 987-992 (1975) Viljanen, A. A. : The relation between the electrical and mechanical activity of human intercostal muscles during voluntary inspiration. Acta physiol, scand., Suppl. 295 (1967) Wade, O. D.: Movements of the thoracic cage and diaphragm in respiration. J. Physiol. (Lond.) 124, 193--212 (1954) Westbrook, P. R., Stubbs, S. E., Sessler, A. D., Rehder, K., Hyatt, R. E. : On respiratory mechanics in normal man. J. appl. Physiol. 34, 81-86 (1973)
Received May 6, 1976
Pfltigers Arch. 366, 107-114 (1976)
EuropeanJournal of Physiology 9 by Springer-Verlag 1976
The Role of' the Fusimotor System with Respect to the Contribution of the Diaphragm and the Intercostal Muscles to the Respiratory Tidal Volume H. TH. FOLGERING, F. D. J. SMOLDERS, and J. A. BERNARDS Department of Physiology,Universityof Nijmegen, Geert Grooteplein Noord 21a, Nijmegen, The Netherlands
Summary. The efferent electrical activity in the phremc nerve can be quantified in such a way that it gives a good correlation to tidal volume. After administration of the drug benzoctamine this relationship changes: more phrenic nerve activity is needed for the same tidal volume. No changes were found in the neuro-muscular transmission from the phrenic nerve to the diaphragm. There was no alteration in dynamic compliance of the lungs or in airway resistance. The afferent phrenic nerve activity from proprioceptors in the diaphragm did not change. It seems unlikely that respiratory neurons in the brainstem were affected since the sensitivity of the respiratory system to CO2 did not change. It is known that the tonic fusimo~.oneuron activity is suppressed at a supraspinal level by benzoctamine. Since intercostal muscles have muscle spindles and the diaphragm hardly has any, the intercostal muscle activity will be affected more than diaphragmatic activity by benzoctamine. This could actually be shown by quantifying the electromyogram of inspiratory external intercostal muscles. The tidal volume regulation is controlled by the vagal feedback loop. In order to reach a certain tidal volume after administration of benzoctamine, the contribution of the diaphragm has to increase because the activity of the intercostal muscles is diminished. Key words." Phrenic nerve activity -
Respiratory m u s c l e s - Benzoctamine -- Fusimotoneurons -Muscle spindles.
INTRODUCTION It is possible to quantify the electrical activity of the phrenic nerve in such a way that it gives a good correlation with respiratory tidal volume. This can be very useful if, in experiments with paralyzed animals, one
wants to be informed about the efferent part of the central respiratory activity (Eldridge, 1971 ; Fitzgerald, 1973 ; Smolders et al., 1975). The relationship between tidal volume and quantified phrenic nerve activity has been investigated in several experimental conditions such as hypercapnia and hypoxia (Fitzgerald, 1973), vagotomy (Eldridge, 1971), and different levels of FRC (Cherniack, 1973; Smolders et al., 1975). Most of these studies concern the effects of the vagal feedback from the lungs. Mostly the control of tension and length of the intercostal muscles and diaphragm in this respect is disregarded. Furthermore the balance between the contributions of the diaphragm and the extra-diaphragmatic muscles gets very little attention. Bergofsky (1964) found in conscious man that the "partition of the tidal volume between rib cage and diaphragm remained unaltered" during stimulation of the ventilation with hypercapnia. Konno and Mead (1967) found linear relationships between the displacement of the thoracic wall and the displacement of the abdominal wall versus tidal volume. Wade (1954) assumed a linear relationship in conscious man between fluoroscopically measured movements of the diaphragm versus tidal volume, and using this assumption, obtained good results in his experiments on the movements of the thoracic cage and diaphragm in respiration. Viljanen (1967) found a logarithmic relation between tidal volume and the impulse frequency in the EMG of the external intercostals at the end of inspiration. Mognoni et al. (1969), working with anesthetized rabbits, also found a linear relationship between volume displacement by extradiaphragmatic muscles and tidal volume. The relative contribution of the extra-diaphragmatic muscles to the tidal volume changes however with the depth of respiration. Certain kinds of sedatives and probably most of the anesthetics have a distinct influence on the fusimotoneuron system. Since intercostal muscles have
]08 muscle spindles and the d i a p h r a g m hardly has any, these drugs must have different effects on either g r o u p o f muscles; consequently these drugs also influence the relationship between quantified phrenic nerve activity and tidal volume, and m a k e it possible to study the effects of the fusimotor system. This study mainly deals with benzoctamine (Tacitin | Ciba-Geigy) in this respect. Benzoctamine (chemical n a m e : dibenzobicyclooctadiene) used as a psychoactive drug is k n o w n to suppress the tonic f u s i m o t o n e u r o n activity. The fusim o t o r system still responds to stimulation but the response is diminished. So apparently the gain o f the system regulating the g a m m a activity is changed due to the effects o f this drug at a supraspinal level (Baltzer and Bein, 1973). F u r t h e r m o r e the drug causes a small reduction in blood pressure and has an e - s y m p a t h o lytic effect (Jaques and Rtiegg, 1971). These authors described a spectrum o f peripheral effects in vivo and in vitro, similar to that o f chlorpromazine. Benzoctamine has no effects on the Sensitivity o f the respiratory regulating system to CO2 (Geissler, 1970). Oral doses o f 3 m g / k g caused no change in blood gas values (Stepanek, 1973). W h e n testing this drug we f o u n d a very consistent change in the relationship between tidal volume and quantified phrenic nerve activity. The same effects were also seen after deepening the anesthesia o f chloralose-urethane or o f pentobarbital. The purpose o f this study is to investigate whether the effects o f the drug benzoctamine on the relationship between tidal volume and quantified phrenic nerve activity is due to the suppression o f the fusim o t o n e u r o n activity o f the intercostal muscles.
METHODS Twenty-four cats of either sex, weighing 2.5-3.5 kg, were used. After premedication by 25 mg ketamine HC1 and 0.5 mg atropine, anesthesia was induced by chloralose 25 mg/kg and urethane 125 rag/ kg. A tracheal cannula was inserted, and the femoral artery and vein were cannulated for recording the blood pressure (Statham P23) and administration of drugs respectively. In 8 experiments an esophageal balloon was inserted for the measurement of intrapleural pressure. The animal was placed on the table in supine position. The rectal temperature was kept constant at 38.0 _+0.1~C. One of the phrenic nerves was dissected in the neck region and cut at the site of its entry into the thorax. The sheath of the central stump was retracted and the nerve was placed on a bipolar platinum electrode. Electrical activity of the phrenic nerve was amplified and filtered between 80 c/s and 10000 c/s (Tectronix RM 122). The whole preparation was immersed in a pool of warm paraffin oil. The Fleisch head of a pneumotachograph (Elema Schoenander) was connected to the tracheal cannula. A gas sample was withdrawn from the trachea for CO2 analysis (Godart infrared analyzer). At the beginning of the experiment a balloon filled with approximately 300 ml of oxygen was connected to the tracheal cannula, and the animal started rebreathing its own CO2 without
Pfltigcrs Arch. 366 (1976) getting hypoxic. When the endtidai CO; reached about 60 - 65 Torr the ballon was disconnected and the experiment was stopped. The rebreathing experiment was done before and after administration of benzoctamine 1 mg/kg i.v. Recordings were made on a 7-channel tape recorder (Philips, Analog 7). Respiratory airflow, integrated airflow (VT), phrenic nerve activity, respiratory CO2, and blood pressure were recorded. Calculations of the relationship between tidal volume and quantified phrenic nerve burst activity were done by a PDP9 computer. The phrenic nerve burst activity was quantified by calculating the root of the mean pulse rate (RMPR) during inspiration (Smolders et al., 1975). In order to evaluate the afferent phrenic nerve activity, 5 animals were paralyzed by slow infusion of succinylcholine(0.25 rag/ rain). Artificial respiration was performed by a Harvard Constant Volume Respirator. Endtidal Po2 and Pco2 as well as tidal volume and frequency of the respirator were kept constant before and after administration of benzoctamine. The electrical activity in the distal stump of the phrenic nerve was recorded and quantified by calculating ~he impulse rate.
RESULTS A linear relationship Vr = A + B. R M P R was f o u n d between tidal volume (Vx) and quantified phrenic nerve activity ( R M P R ) with correlation coefficients f r o m 0.72 to 0.99 obtained by the least-square m e t h o d (Table 1). In 19 out o f 20 experiments, after benzoctamine a different relationship (90 ~o confidence limits) was f o u n d between tidal volume and quantified phrenic nerve activity (Fig. 1). A significant (P < 0.01) change in slope (B) was f o u n d in 14 out o f 20 experiments. In 11 cases there was a significant decrease, in 3 cases a significant increase in slope after benzoctamine. The intercept (A) showed a significant (P < 0.01) decrease in 11 experiments; there were 2 significant increases, and in 7 cats no significant effect could be f o u n d after benzoctamine. In 2 experiments (1 and 7) there was no significant change in b o t h parameters A and B. A coincidence o f a rise in b o t h A and B did not occur. In some cases, however, there is an overlap o f the 90 ~o" confidence limits o f the two lines at the intercept with the ordinate (A) outside the measured ranges, i.e. no significant change in A, so that the shift o f the line after the drug c a n n o t be expressed by a change in A. Consequently the effect o f administration o f benzoctamine on the relationship between tidal volume and quantified phrenic nerve activity could be shown in a decrease o f the slope or increase o f the intercept, or both. In the measured ranges o f tidal volume, the regression line o f tidal volume versus phrenic nerve activity after administration was always located to the right o f the regression line before administration o f the drug and the lines did not cross with the only exception o f experiment 7. This means that m o r e electrical activity is needed in the phrenic nerve in order to reach the same tidal volume. The same effect was also f o u n d after deepening the anesthesia b y
H. Th. Folgering et al. : Respiratory Muscles and Fusimotor Innervation t'able 1. Vr = A + B x R M P R . Parameters and correlation coefficients (r) of regression lines of tidal volume versus quantified phrenic nerve activity ( R M P R : Root of Mean Pulse Rate [Smolders et al., 1975]) before and after administration of benzoctamine, or chloralose-urethane in experiments 17, 23, 25, or pentobarbital in experiment 27. All experiments were performed on different cats. Significant changes (P < 0.01) are indicated by * + : 90 % confidence limits overlap (Exp. Nr. 7) Exp.
1 2 3 4 5 6 7+ 8 9 10 I1 12 13 14 i5 16 18 20 22 26 17 23 25 27
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8.6 19.4 10.9 8.2 31.2 5.6 8.5 - 4.7 - 4.5 -I2.6 14.6 -34.9 1.7 33.0 47.9 27.8 15.2 8.3 3.3 68.4 -19.3 - 6.2 1.2 -18.1
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chloralose-urethane (3 cats) or after administration of pentobarbital (1 cat). Similar to the results of Geissler and Rost (1970) we found no change of the respiral;ory response to CO2 as determined by this rebreathing method, indicating that the sensitivity of the respiratory regulating system did not change after administration of benzoctamine (Fig. 2). The arterial blood pressure changed from 156 +_ 21/128 +_ 16 before to 140 _+ 17/114 ___ 14 mmHg after administration of the drug (n -- 10). No animal became hypotensive. In order to prove that the drug effect is caused by the depression of the fusimotor system, other sites of its action had to be excluded. The neuro-muscular transmission from the phrenic nerve to the diaphragm might be inhibited by benzoctamine. This was checked in 4 cats by stimulating the intact phrenic nerves at several frequencies. The forces of the auxotonic contractions of the diaphragm were measured using the experimental set-up described by Van Rossum and Elstrodt (t965). These
109
forces were not influenced by the administration of benzoctamine (Fig. 3). The cats were hyperventilated artificially in order to diminish the spontaneous contractions of the diaphragm. After administration of benzoctamine an increased spontaneous activity can be seen. This is in agreement with the findings of Geissler and Rost (1970) and Utting (1975). A change in the dynamic compliance of the lungs might cause a rise in phrenic nerve activity at the same tidal volume. This possibility was tested in 8 cats by plotting tidal volume versus intrapleural pressure and thus taking dynamic compliance loops before and after administration of benzoctamine. There was no significant change in this dynamic compliance (Fig. 4). There was no change in airway resistance following administration of benzoctamine either. Since the dynamic compliance of the lungs does not change, the airway resistance may be approximated by plotting intrapleural pressure versus respiratory airflow measured by the pneumotachograph. A change in afferent feedback in the intact phrenic nerve might be a cause of the increased efferent activity. Recordings were made from the distal stump of the phrenic nerve in paralyzed, artificially ventilated cats. The diaphragm was stretched by inflating a pneumatic cuff around the abdomen of the cat, thus pressing the abdominal contents against the diaphragm. Afferent phrenic nerve activity still changed phasically with the respirator. It was quantified by calculating the instantaneous impulse rate. No change in afferent phrenic nerve activity was found after administration of benzoctamine (Fig. 5). So a feedback loop within the phrenic nerve is not affected and cannot be responsible for the changes in efferent activity. DISCUSSION The main finding of this paper is a shift of the Vvphrenic nerve activity curve to the right after benzoctamine (Fig. 1). This shift is effected either by a decrease in slope, or an increase in intercept, or both. Cutting one of the phrenic nerves might also cause a shift in this relationship. But when taking this shift as a new starting situation, the administration of benzoctamine induces an additional shift. The transsection of one of the phrenic nerves is of no consequence for the total ventilation, which is primarily regulated by the blood gas values and the vagal feedback. Campbell (1958) states that "the diaphragm is not however an essential muscle and can be paralysed on both sided without significant respiratory embarrassment". Pentobarbital and chloralose-urethane might have a different site of action in the reticular formation.
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H. Th. Folgering et al. : Respiratory Muscles and Fusimotor Innervatioa
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O u r results, however, suggest they eventually also suppress f u s i m o t o n e u r o n activity. A c c o r d i n g to Jaques and Rfiegg (1971), benzoctamine has some peripheral activities similar to chlorpromazine. The latter drug disrupts temperature regulatory mechanisms. This would m e a n that benzoctamine would also decrease b o d y temperature, and m o r e energy would be needed to m o v e a cooler diaphragm. However, since both thoracic and a b d o m i n a l cavities were not opened and b o d y temperature was controlled, this c a n n o t be the explanation for our findings. The effects f o u n d on the relationship between tidal volume and quantified phrenic nerve activity were not due to a splaying o f the nerve on the electrode. The time interval between the two measurements was only 15 min. F u r t h e r m o r e , the whole preparation was immersed in paraffin oil, so that the weight o f the nerve on the electrode was negligible. U n d e r constant experimental conditions, the relationship between VT and quantified phrenic nerve activity remains very constant (Smolders et al., 1975).
Fig. 3. Effectsof benzoctamine on the auxotonic contractions of the diaphragm (arbitrary units) and on the blood pressure in an artificially ventilated cat. The intact phrenic nerves were stimulated with stimuli of pulse trains (pulses 1 ms, 5 V, train duration 200 ms, train frequency 0.06 c/s, pulse frequencies indicated in the figure). The cat was hyperventilated in order to diminish the spontaneous diaphragmatic activity. It may be noted that the spontaneous activity (irregular low activity in the tracing "contraction of diaphragm") increases after administration of benzoctamine
After the start o f a phrenic nerve burst, the firing frequency o f the active fibers increases and m o r e fibers are recruited. Thus, the longer a burst lasts, the stronger is the electrical activity (Gesetl et al., 1940; Pitts, 1942; Gill, t963). Benzoctamine is a muscular relaxant. It is possible that the d i a p h r a g m is so m u c h relaxed that the initial part o f the contraction is isometric. This would m e a n that at the beginning o f an inspiration there is phrenic nerve activity without inspiratory air flow. The phrenic nerve activity goes on till it is stopped by vagal afferent activity. In case o f an initial isometric contraction the phrenic nerve burst has to last longer in order to reach a certain tidal volume, and consequently the quantified phrenic nerve activity has to increase. A n initial isometric contraction after administration of benzoctamine would also mean that there has to be a greater
Fig. 1. Relationships between tidal volume and quantified phrenic nerve activity in 24 cats. These relationships are plotted before and after suppressing the fusimotoneurons by benzoctamine, chloralose-urethane, or pentobarbital. After administration of the drugs the relationships are shifted to the right; consequently more electrical activity is needed in the phrenic nerve in order to reach the same tidal volume. The electrical activity in the phrenic nerve is quantified by calculating the root of the mean pulse rate in a burst (Smolders et al., 1975). The solid lines indicate the 90 ~ confidence limits in the measured ranges of tidal volume. Experiments 17, 23, 25 were experiments with chloraloseurethane, experiment 27 shows the effect of pentobarbitai. Vertical scaIe ranging from 0 - 200 ml: horizontal scale from 0 - J00 (arbitrary units)
112
Pfltigers Arch. 366 (1976) Fig. 4 Dynamic compliance loops taken at the same respiratory frequency before and after suppressing the fusimotor system by benzoctamine. Both loops are almost identical, indicating no significant change in dynamic compliance of the lungs. This example is representative for all 8 cats tested in this way
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time lag between the start o f the phrenic nerve activity and the start o f the inspiratory air flow. But there is no change in time lag. So this explanation does not a c c o u n t for the higher electrical activity in the phrenic nerve after administration o f benzoctamine. It might be that benzoctamine also influences respiratory neurons in the brainstem. Since the blood gas values do not change (Stepanek, 1973) and the response to CO2 remains unaltered (Fig. 2; Geissler, 1970; Utting, 1975)the remaining unlikely possibility would be a suppression o f those neurons which ac-
X ~ S.D.
O
iOO
Int. EMG 2nd intercost. (Arbitrary Units)
Fig. 6. QuantifiedEMG of the second external intercostal muscle in the anterior axillary line versus tidal volume. The relationship was calculated before and after suppressing the fusimotor system by benzoctamine. The plot shows that the electric activity in the intercostal muscles is markedly reduced after administration of the drug. One point represents the mean of 10 breaths of one animal, which was representative for the whole group
tivate the ~ - m o t o n e u r o n s of the intercostal muscles, and an enhancement o f those activating the c~-motoneurons o f the diaphragm, resulting in the same ventilation. It was not possible to confirm or to refute this theory definitely. It was shown by Baltzer and Bein (1973) that benzoctamine suppresses tonic f u s i m o t o n e u r o n activity at a supraspinal level. Since both tonic as well as phasic f u s i m o t o n e u r o n activity determine the activity o f the Ia afferents, the latter activity will also be sup-
H. Th. Folgering et al. : Respiratory Muscles and Fusimotor Innervation
pressed (Campbell et al., 1970; Flandrois, 1965). According to Baltzer and Bein (1973) after administration of benzoctamine: "The (gamma) system retains its ability to respond to stimulation and thus also its capacity for regulation ... the diminution (of the response to stimulation) being proportional to the discharge frequency prior to stimulation." Apparently the gain within the y-activating system is changed by benzoctamine. The Ia afferents of the muscle spindles monosynaptically excite the :~-motoneurons of the same muscles (Eccles, 1963). Campbell et al. (1970) state that the activity of the c~-motoneurons of the intercostal muscles highly depends on this excitation. This excitatory effect is suppressed by benzoctamine. Thus only the intercostal muscles, having a considerable amount of muscle spindles, are affected and decrease their activity. Inspiration stops when a certain vagal afferent activity is reached in a certain time (Clark and yon Euler, 1972), i.e. tidal volume is regulated by the vagal feedback loop. Since the intercostal muscle activity is suppressed, the diaphragm has to act more in order to reach a lung volume sufficient for the required vagal feedback activity. The final proof of this hypothesis was secured in 3 experiments in which the quantified EMG was taken from the second and third external intercostal muscles which clearly showed inspiratory activity. The quantified electrical activity of' these intercostal muscles decreased after administration of benzoctamine (Fig. 6). The EMG, quantified by calculating the mean impulse rate per burst, appears to be linearly related to tidal volume in the measured range, although according to Viljanen (1969), who used another method, there is a logarithmic relationship. It cannot be excluded that our linear relationship is spurious; the important point here was to show that there is a consistent and significant difference between the two lines. Froese and Bryan (1974) described changes in position and in pattern of the contraction of the diaphragm after barbiturate anesthesia in humans. These changes were ascribed to "effects of the anesthetic agents and muscle relaxants on the diaphragm". However, a primary change in muscle ~:one of the intercostal muscles, and subsequently a shift of the position of the diaphragm towards the thoracic cavity might explain their findings as well. Westbrook et al. (1973) suggested: "The initial effect of our anesthetic procedure (pentothal and meperidine) was to cause a change in the P-V characteristic of the chest wall such that a reduction in FRC occurred." This reduction of FRC and stiffening of the chest wall measured in static condition in a body plethysmograph is fully compatible with a decrease in activity of the external
113
intercostal muscles. As a matter of fact the "intercostal paralysis" had already been used as a "sign of anesthesia" by John Snow in 1858. In conclusion, the electric activity in the phrenic nerve, quantified correctly, is a useful parameter for measuring the neural output of the respiratory centers. However, when using this parameter the fusimotor system should not k~e interfered with, because depression or enhancement of the fusimotor activating system has different effects on diaphragm and intercostals. Acknowledgements. The authors wish to express their gratitude to Mr. J. Evers for technical assistance during the experiments; to Mrs. E. Crul-Sluyters (Dept. of Anesthesiology) for testing the drug in an experimental set-up for measuring the auxotonic contractions of the diaphragm; and to Mrs. S. Engels for preparing the manuscript.
REFERENCES Baltzer, V., Bein, H. J. : Pharmacological investigations with benzoctamine (Tacitin), a new psycho-active agent. Arch. int. Pharmacodyn. 201, 25-41 (1973) Bergofsky, E. H. : Relative contribution of the rib cage and the diaphragm to ventilation in man. J. appl. Physiol. 19, 689-706 (1964) Campbell, E. J. M.: The respiratory muscles and the mechanics of breathing, p. 13. London: Lloyd-Luke 1958 Campbell, E. J. M., Agostoni, E., Newsom Davis, J, : The respiratory muscles, mechanics and neural control. Chapters 1, 6, 7, 1i. London: Lloyd-Luke 1970 Cherniack, N. S., Stanley, N. N., Tuteur, P. G., Altose, M. D , Fishman, A. P.: Effects of lung volume changes on respiratory drive during hypoxia and hypercapnia. J. appl. Physiol. 35, 635-641 (1973) Clark, F. J., von Euler, C.: On the regulation of depth and rate of breathing. J. Physiol. (Lond.) 222, 267-295 (1972) Eccles, R. M., Sears, T. A., Shady, C. N.: Intraceltular recording from respiratory motoneurones of the thoracic spinal cord of the cat. Nature (Lond.) 193, 844-846 (1962) Eldridge, F. L.: Relationship between phrenic nerve activity and ventilation. Amer. J. Physiol. 221, 535-543 (1971) Fitzgerald, R. S. : Relationship between tidal volume and phrenic nerve activity during hypercapnia and hypoxia. Acta Neurobiol. exp. 33, 419-425 (1973) Flandrois, R., Lacour, J. R., Chabanne, J. P., Hernandez, J. P.: Action d'une diminution de l'activit+ fusoriale sur l'hyperventilation r6flexe au cours de la mobilisation passive chez le chien. J. Physiol. (Paris) 57, 611-612 (1965) Froese, A. B., Bryan, A. C.: Effect of anesthesia and paralysis on diaphragmatic mechanics in man. Anesthesiology 41,242255 (1974) Geissler, L., Rost, H. D. : Untersuchungen fiber den Einflul3 yon Tacitin auf die Atmung des Menschen. In : Entspannung, neue therapeutische Aspecte. St, Moritz Symposium 1970, Vorsitz. P. Kielholtz, pp. 54--58. Basel: Ciba AG 1970 Gesell, R., Kearney-Atkinson, A., Brown, R. C.: The gradation of the intensity of inspiratory contractions. Amer. J. Physiol. 113, 659-673 (1940) Gill, P. K. : The effects of end-tidal CO2 on the discharge of individual phrenic motoneurones. J. Physiol. (Lond.) 168, 239-257 (1963) Jaques, R., Rfiegg, M.: Some peripheral pharmacologic characteristics of benzoctamine. Pharmacology 6, 89-98 (1971)
114 Konno, K., Mead, J. : Measurement of the separate volume changes of rib cage and abdomen during breathing. J. appl. Physiol. 22, 407 - 422 (1967) Mognoni, P., Saibene, F., Sant Ambrogio, G.: Contribution of the diaphragm and other inspiratory muscles to-different levels of tidal volume and static inspiratory muscles to different levels of tidal volume and static inspiratory effort in the rabbit. J. Physiol. (Lond.) 202, 517-534 (1969) Pitts, R. F. : Excitation and inhibition of phrenic motoneurones. J. Neurophysiol. 5, 75-88 (1942) Van Rossum, J. M.~ Elstrodt, J. M.: A potentiometer transducer. Arch. int. Pharmacodyn. 154, 63-68 (1965) Smolders, F. D.J., Folgering, H. Th., Bernards, J.A.: Phrenic nerve activity as a measure of ventilation in the paralysed cat. Pfltigers Arch. 359, 157-169 (1975) Snow, J.: On chloroform and other anaesthetics. London, p. 42, 1858. Quoted in: The signs of anaesthesia. N.A. Gillespie. Curr. Res. Anesth. 22, 275-282 (1943)
Pflfigers Arch. 366 (1976) Stepanek, J. : Changes in acid-base balance, respiration rate and heart rate upon oral administration of benzoctamine and diazepam in conscious dogs. Arch. int. Pharmacodyn. 202, 135 - 152 (1973) Utting, H. J., Pleuvry, B. J. : Benzoctamine: a study of the respiratory effects of oral doses in human volunteers and interactions with morphine in mice. Brit. J. Anaesth. 47, 987-992 (1975) Viljanen, A. A. : The relation between the electrical and mechanical activity of human intercostal muscles during voluntary inspiration. Acta physiol, scand., Suppl. 295 (1967) Wade, O. D.: Movements of the thoracic cage and diaphragm in respiration. J. Physiol. (Lond.) 124, 193--212 (1954) Westbrook, P. R., Stubbs, S. E., Sessler, A. D., Rehder, K., Hyatt, R. E. : On respiratory mechanics in normal man. J. appl. Physiol. 34, 81-86 (1973)
Received May 6, 1976
