PROCEEDINGS OF THE PHYSIOLOGICAL SOCIETY CHARING CROSS AND WESTMINSTER MEETiNG 10-11 January 1991 These abstracts were accepted by Mlembers of the Society present at the meeting

J. Phy.siol. (1991) l1ol. 43S8. (Charing (Cros.




DEMIONSTRATIONS Abnormal segment 'work' in the alternating heart of the anaesthetized pig .M. Moutoussis, I.B. Gartside and AI.J. Lab I)epartment of Physiology, Char ing (Cross & lVestnminster Medical School, London W6 8RF Electrical alternans at a steady heart rate has been shown to precede fibrillation in the acutely ischaemic myocardium (Dilly & Lab, 1988). AMechanical alternans probably precedes electrical alternans (Lab & Lee, 1990). We therefore studied mechanical alternans of ventricles in a quickly paced, normal, intact heart. Five Landrace/Large White pigs were deeply anaesthetized (1-2% halothane in 0) & N,O [1:1]) and the hearts exposed. Left ventricular (LVP) and arterial pressure were measured. Monophasic action potentials and the motion of small epicardial segments were recorded by suction-operated devices (Lab & Woollard, 1978) from three areas on each left ventricle. LVP was plotted against segment motion, indicating the work performed by each segment (Fig.1A).







X~ Segment Length


Segment Length

Fig.1. A, control loops (pacing interval 475 ins). B, alternating loops (325 ins). All units are arbitrary but A and B have the same units in corresponding axes.

Fast atrial pacing (interval 325-425 ms) provoked mechanical alternans in each heart and in four of the pigs fast pacing (mean stimulation interval 350 ms) caused at least one area (7 of 15 overall) to behave as shown in Fig. lB. Half the beats resembled the slow paced controls but did not proceed to complete relaxation. The alternate beats, however, showed an inability to shorten at high LVP. The consequent lengthening causes the clockwise loops and hence negative work is produced during these beats (Fig.lB). We found no electrical cause to explain this behaviour. Since each heart produced positive work as a whole on each beat, there must have been considerable mechanical spatial inhomogeneity. If this occurs in ischaemia, mechanoelectric feedback (Lab. 1982) might cause or exaggerate the electrical inhomogeneity, which is conducive to arrhythmia. Supported by the BHF and W!ellcome Trust. REFERENC'ES

Dilly, S. & Lab, M.J. (1988). J. Physiol. 402, 315-333. Lab, M.J. (1982). Circ. Res. 50, 757 766. Lab, M.A. & Lee, J. (1990). Circ. Res. 66. 585-595. Lab, M.J. & Woollard, K. (1978). Cardiovasc. Res. 12. 555-565.

J. lPhysiol. (1991) XVol. 4.38. IProceedinys of 7Te Physioloyical Society



Interval dependence of mechanically induced early afterdepolarizations in ventricle of anaesthetized pigs M.J. Lab and D.J. Dick Department of Physiology, Charing Cross & Westninster Medical School, London 1V6 8RF Mechanically induced early afterdepolarizations (EADs) are either real and potentially arrythmogenic, or perhaps artefact. We wished to determine if EADs produced by occluding the aorta (Lab, 1982) are genuine. Decreasing interbeat interval reduces the amplitude of Cs'-induced EADs recorded by microelectrodes in isolated Purkinje fibres (Damiano & Rosen, 1984). We studied interval changes in mechanically induced EADs. Pigs were anaesthetized (1-2% halothane in O.:N.)O), the heart exposed and the ascending aorta snared to give isovolumic contraction when required. The right atrium was paced. Left ventricular epicardial monophasic action potentials (Lab & Wollard, 1978) were recorded, as was intraventricular pressure. Aortic occlusion increased intraventricular pressure producing an afterdepolarization in late phase repolarization of the action potential (Fig. IA). These were sometimes associated with an ectopic beat with a short interbeat interval. The EAD amplitude of this beat is reduced in comparison with EAD of steady-state intervals. This was seen three or more times in each of fifty pigs. In one pig the aorta was occluded at different steadystate intervals. There was a correlation between steady-state interval and the amplitude of the EAD (Fig. IB). LO)



~ ~~~~Ec0 E

E clamp



< 0 300


600 400 500 Beat interval (ms)


Fig. 1. A, amplitude of EADs in the monophasic action potential at steady state and after a short interval. B, relationship between EAD amplitude (arbitrary units) and different steadx state intervals.

These results are analagous to those of Damiano & Rosen (1984) and support the possibility of the genuine nature of mechanically induced EADs. Supported by The British Heart Foundation. REFERENCES

Damiano, B.P. & Rosen. M.R. (1984). Circulation. 69, 5, 1013-1025. Lab,.M.J. (1982). Circ. Res. 50, 757-766. Lab, NI.J. & WN'ollard, K. (1978). Cardiovasc. Res. 12, 555-565.

J. Phy.5iol. (1991) XVol. 438. (haring Cross Meeting 10 11 January 1991



A device for atraumatic recording of regional electromechanical signals from the heart at surgery in man

AIM.Jd. Lab, F.G. Harrison and G. Bennet* I)epartment of Physiology, Charing Cross & Wlestmninster Medical School. Londont WO6 8RF. *National Heart & Lung Institute, Fuihan, London SIV6 Simultaneous electrical and mechanical measurements from the epicardium of man at cardiac surgery could provide a valuable research and diagnostic tool, but an atraumatic system suitable for human use is not yet available. Based on an earlier system (Lab & Woollard, 1978) we have developed a hand-held device to measure the mechanical behaviour of an area of myocardium roughly 20mm diameter, together with the 'contact' monophasic action potential (Franz 1983). Strain gauges are glued to each of 3 legs (phosphor bronze shim) and mounted on a Perspex base (Fig. 1). The feet of the tripod are knurled gold enabling frictional contact with the heart surface. Contraction deforms the transducers producing electrical outputs via isolated transducer amplifiers. Mechanical artefact is minimized by spring-loading, and by the protective skirt which rests on the moving heart. The device and leads are sterilizable by conventional ethylene oxide or exposure to low temperature steam-formaldehyde. We will demonstrate some evaluations of the instrument's ability to reflect motion of the underlying myocardium. The validations are promising and include 'Starling' type curves, and pressure-length loops from normal and abnormal myocardium. We can thus compare electrical and mechanical events in normal and pathological human myocardium with those found in experimen-

tal animals. pillar


sprng skillt

base / i0t1

strain gauge


Fig. 1. Diagram of tripodal device.

Supported by the British Heart Foundation REFERENCES

Franz, M.R. (1983). Anii J. Cardiol. 51. 1629-1634. Lab, AI.J. & W;'oollard, K. (1978). (ardiorasc. Res. 12. 5553565.

P-bronze leg

J. Physiol. (1991) Vol. 438. Proceedings of The Physiological Society



Mechanical alternans induced in isolated guinea-pig papillary muscles by a combination of hypothermia and rapid pacing C.I. Spencer, MI.J. Lab* and WV.A. Seed Departments of Medicine and *Physiology, Charing Cross & W1estminster Medical School, London W6 8RF

Mechanical alternans (MA) may be elicited in isolated mammalian ventricular muscle by stimulation at high frequencies and reducing the pH, pCa, or temperature of the bathing medium, or by combinations of these interventions. We have combined low temperature (27 ± 0.1°C) with a high rate of pacing (3-4.5Hz) to induce stable MIA in guinea-pig papillary muscles. Thus, aspects of myocardial contractility in MA such as the mechanical restitution of the small and large contractions (Lu et al. 1968) may be studied. We demonstrate the induction of AIA and the study of mechanical restitution in this preparation, and the use of a digital data acquisition system (S200, Intracel) with an IBM PC compatible computer. REFERENCE

Lu, H., Lange, G. & Brooks. C. (1968). J. Electrocardiol. 1. 7-17.

Phys4ol. (1991) Vol. 4.38. ('hariny (Cross.leetiny 10 II Janu(ar-y 1991 PROCEEDIYGS OF THE PHYSIOLOGIC AL SOCIETY J.


January 1891 - The Physiological Society at Charing Cross P.H. Ellaway*, H.R. Haguet, F. Harrison* and E.M. Tansev3

*Department of Physiology and 'The Library, Charing Cross &Wt- 'est ninster Medical School, Fuilhamn Palace Road, London W'6 8RF; 'Vellcomne Instit utefor the History of Medicine, 183 Euston Road, London NJ'I 2BN

One hundred years ago. in January 1891. the Physiological Society met for the first time at the Charing Cross Hospital at the invitation of its Lecturer in Physiology, Frederick MIott, and with the approval of the MIedical School Committee. The format of the meeting was that normal for the period: a short informal scientific session at which two demonstrations were given, followed by the main business of the Annual General Meeting (AGMI), which was held at the nearby Gatti's Restaurant on the Strand, a frequent venue for the Society's meetings. The two scientific communications reflect rather different pictures of late nineteenth century physiology: the first, by Emmanuel Klein, a Founder Member of the Society, was a bacteriological and histological presentation of cultures of tubercle and other bacilli, exemplifing the broader biological roots and interests of contemporary physiologists. In contrast Frederick MNIott described results from a study that is more resonant with present day physiology: the effect of surgical lesions to the monkey spinal cord at different levels, with a demonstration of histological material taken from the experimental animals. The AGM included the usual routine elections of the Committee, and of thirteen new members: among the former were Michael Foster, John Burdon Sanderson and Frederick Mott, with the re-elections of WI.H. Gaskell as Treasurer and C.S. Sherrington as Secretary: among the latter were L.E. Hill, H.D. Rolleston and T. Grainger Stewart, whose son became an eminent neurologist at Charing Cross. The business was varied and several ammendments to the Society's rules were proposed. E.A. Schafer suggested two alterations: that the qualifications of candidates for election should be disclosed by their proposers, and also that a delegation should approach the General MIedical Council to negotiate an increase in the amount of elementary biology included in the medical curriculum. Further details of this MIeeting, the early history of physiology at Charing Cross, and the contributions made by AMott and Grainger Stewart will be presented in this demonstration. X'e are grateful to the Honorary Archivist and the Committee for allowing the Society's Archives to be consulted.

.J. Physiol. (1991) XVol. 438. Proceedinys of The Physioloyical Society



Facilitation by mechanical cutaneous stimulation of muscle responses to transcranial magnetic stimulation in man N.J. Davey, P.H. EllawaY and D.W. AMaskill Department of Physiology, Charing Cross & Westminster iIedical School, Fulhant Palace Road, London TV6 8RF

It is well known that changes in motoneurone excitability and reflex responses to cutaneous stimulation vary with the location of the peripheral stimulus (Sherrington, 1906; Hagbarth, 1952). We find that muscle responses evoked by transcranial magnetic stimulation of the brain in man can be facilitated by cutaneous stimulation and are now examining the peripheral organization of this facilitation. A response in the relaxed adductor pollicis was elicited by magnetic brain stimulation using a Novametrix 9cm circular coil centred at the vertex. The skin overlying the dorso-lateral aspect of the base of the thumb was stimulated at points on a 1.5cm grid using circular movements of a small stiff brush. A series of twenty brain shocks during alternating periods with and without cutaneous stimulation was employed at each site. The evoked compound muscle action potentials were recorded with surface electrodes placed on the skin over the muscle. The recordings were rectified, averaged and the voltage-time integral calculated. The intensity of magnetic stimulation was adjusted to give a suprathreshold response and then kept constant during the experiment. We have observed facilitation that was maximal over the metacarpo-phalangeal joint and the first carpo-metacarpal joint, but extended over the TI dermatome. Maximal facilitatory responses were obtained from sites overlying the joint lines and this may indicate a component of capsular involvement. The facilitation was minimal or not present on the medial aspect of the long extensor tendon of the thumb. We will demonstrate that mechanical cutaneous stimulation facilitates muscle responses to transcranial magnetic stimulation and that this phenomenon may have a discrete organization that is associated with areas overlying joints involved in movements produced by the muscle. Ethical approval and informed consent was obtained for this study. REFERENCES

Sherrington. (CS. (1906). The Integrative ,4ction of theNervous Systeml. Scribner's New, York. Hagbarth. K-E. (1952). Acta Physiol. Scand. 26, Suppl. 94.

J. Physiol. (1991) V'ol. 4.38. (hariny ( Meeting 10-lo January 1991



Method for measuring the time course of twitch tension from a single motor unit in man P.H. Ellaway, I.B. Gartside, P. Romaigu6re. S.R. Raulinson and E. W1'ells Department of Physiology, Charing Cross & Westminster Medical School, Fulhain Palace Road, London WV6 8RF The technique of spike-triggered averaging of muscle tension has been used as a means of extracting the twitch tension of a single motor unit from the total force generated during a voluntary contraction in man (Alilner-Brown et al. 1973). However, it is recognized that the twitch profile will be distorted if the unit discharges at a rate high enough to cause partial summation of adjacent twitch contractions i.e. during an unfused tetanus. Thus the motor unit should fire at a sufficiently low frequency such that the interspike interval is longer than the time course of the single twitch (Nordstrom et al. 1989). It has proved difficult for a subject to maintain a low rate of firing of a single motor unit by voluntary control alone. To overcome this problem we have developed a logic circuit to allow only spikes of low discharge frequency to be used as trigger spikes. A single motor unit potential can only act as a trigger spike if the following criteria are fulfilled: (1) No other spike should occur in a preceding period equivalent to the expected motor unit twitch duration. (2) Given that condition 1 is met, no further spike should occur in a subsequent period of equal duration. If these conditions are fulfilled, then at the end of the subsequent period a pulse is generated to synchronize the averaging of the tension over the expected time course of the twitch, a technique commonly referred to as 'back averaging'. The logic circuit has been built with three options for selecting the duration of the preceding and the subsequent periods. One or other of these can be chosen according to an initial estimate of the time course of contraction of a particular motor unit. The circuit is currently being evaluated and will be demonstrated in conjunction with spike-triggered averaging of twitch contractions in forearm or intrinsic hand muscles during voluntary contractions in man. REFERENCES

AMilner-Brown, H.S., Stein, R.B. &Yemm, R. (1973). J. Physiol. 228, 285-306. Nordstrom, 'M.A., Miles, T.S. & Veale, J.L. (1989).JMuscle &.Nerve 12, 556 567.

1Proceedinys of The P'hy.sioloyical Society (HARING (SROSS AND) WESTMVISTER M,EETIN'G 10-11 JANUARY 1991

J. Phy.siol. (1991) lVol. 43N.


A computer-assisted practical class on isolated frog sciatic nerve: software and hardware Ivor B. Gartside I)epartment of Physiology. Road, London tUV6 8RF

(Charing Cross & Westninster Medical School, Fulham Palace

The program is an integrated package of software for teaching the theoretical and practical aspects of the experiments to be performed and to turn the computer into the recording device on which action potentials recorded by the students can be displayed. In order to give a reasonable picture of a compound action potential on the oscilloscope screen, a sampling rate of at least lOOkHz is desirable. This is provided by a ZN439 8-bit analog-to-digital convertor with a conversion time of 5ms. Timing and control signals are provided from an Amplicon PC26 board, and direct memory access is used for fast data transfer from the analog-to-digital converter to the memory of the computer. The stimulus is provided by a monostable circuit which is triggered at the start of data acquisition. The program is written in compiled Basic, with the sections for data gathering and display written in assembler language for speed. It begins by providing basic information on the nature of the extracellularly recorded action potential, a description of the apparatus and the theory necessary to perform an experiment. The computer then becomes an oscilloscope and enables recordings of action potentials to be obtained, measured and dumped to a printer. The computer instructs the student to discuss the results obtained with a demonstrator, before presenting further information for the performance of the next set of recordings. It has been found that this use of an 'automated' system for the nerve practical class actually increases student demands on demonstrators, hopefully due to the increased discussion of results demanded by the computer.

Mleetiny 10-11 January PROCEEDING(S OF THE PHYSIOLOGIC"AL SOCIETY' J. P/hysiol. (1991) 1'ol. 4.38. (Clhiny (Cro..



Apparatus for the production of step changes in cuff pressure for venous occlusion plethysmography in man Ivor B. Gartside and John Gamble Department of Physiology, Charing Cross & WVestmninster Medical School, Fulhamz Palace Road, London W'6 8RF

In order to differentiate between the vascular volume of fluid filtration components of the volume response to venous occlusion, the rate of the pressure change in the occlusion cuff must be significantly faster than the events to be studied. In this laboratory we use a pump delivering 2 1/s (Compton 2D/351VM) connected to a six-inlet thigh cuff (Acosson) using wide bore tubing to minimize inflow resistance. In series with this is a variable leakage resistance to bleed off air flow in excess of that needed to maintain the cuff at the desired pressure. The excess air leaks out through graduated holes drilled in a disc so the cuff pressure can be increased in steps of 10 mmHg (after an initial step of 15 mmHg) by turning the disc. The upper limit is determined by the diastolic pressure of the subject. The cuff is constrained in an inelastic corset which directs the expansion of the cuff on to the limb. We have found that the completion time for the initial pressure step is less than 4s, and less than 2s for subsequent steps. This is less than the time constant of the compliance component of vascular filling (12.65 ± 1.79 s) and very much less than the time constant of the filtration component (>>800 s). Furthermore, since the pressure increments can be applied as a stepped continuum, the time required for a six-step study is less than forty minutes. The apparatus and the results will be demonstrated.

J. Physiol. (1991) Vol. 438. Proceedings of The Physiological Society



An electronic membrane osmometer to measure the oncotic pressure of microlitre quantities of oedema fluid D.O. Bates, J.R. Levick and P.S. Mortimer Division of Physiological Medicine & Department of Physiology, St George's Hospital Medical School, London SW17 ORE

To investigate Starling forces in postmastectomy lymphoedema, we wished to measure the oncotic pressure of the oedema fluid. The volume of fluid available for osmometry was sometimes as little as 10,l. We have therefore adapted the Hansen osmometer (Hansen, 1961) by designing a new head requiring as little as 5u1. A semipermeable membrane (Amicon PM10) is clamped between the new Perspex head and a conventional base. The head contains a sample chamber (radius 2 mm, depth 0.5mm), enclosed within the Perspex block to prevent evaporation. Chamber volume is further reduced by clamping the head directly onto the membrane without an 0-ring, leaving a chamber of 3,l. Access to the chamber is by two fine cylindrical shafts (radius 0.25mm). The sample is introduced with a 25 gauge, 16mm hypodermic needle through one shaft and flushed through. Stable oncotic pressures are measured within 90-120 s. Besides the small sample volume and speed, a further advantage is that there is no need to cover samples with oil (cf. Aukland & Johnson, 1974). SCREW HOLES HEAD }




| 19 mm

24 mm



GOULD P23XL TRANSDUCER Fig. 1. Cross-section of microlitre osmometer. a, supporting block; b,-membrane; c, sample chamber; d, saline filled reference chamber; r = 0.5 mm. REFERENCES

Hansen, A.T. (1961). Acta Physiol. Scand. 53 197-213. Aukland, K. & Johnson, H.M. (1974). Acta Physiol. Scand. 90 485-90.


J. Plhysiol. (1991) 1Vol. 438. (hariny Cro,.ss Meetiny 10--l January 1991 PRO(CEEDINGr(;S OF THE PHYSIOLOGIC.AL SOCIETY

A re-assessment of the relationship between the protein concentration (CONC) and colloid osmotic pressure (COP) of fresh, heparinized human plasma (HP) and bovine serum albumin (BSA) J. Gamble Department of Physiology. Charing Cross & W1estimWinster Medical School, Fulham Palace Road, London W6 8RF It is known that orthostasis induces increases in the COP of venous blood draining from the foot (e.g. Noddeland et al. 1981). In this laboratory, analysis of the relationship between plasma protein CONC and corresponding values of COP in samples of venous blood taken from the foot during 50 min dependency gave values that were different to those anticipated from the cubic equation of Landis & Pappenheimer (1963) which suggests that COP = 2.1 C + 0.1602 + 0.0090U3, where C = protein concentration (g/100 ml). Since this equation is often used to calculate COP it seemed worth re-assessing its validity. For each study, fresh blood from at least four healthy subjects was placed in lithium heparin tubes and centrifuged. The plasma samples were pooled, placed in an Amicon Stirred Ultrafiltration Cell (Model 3) fitted with an Amicon PM30 membrane and ultrafiltered with pressure from a nitrogen cylinder. The resulting protein-free filtrate and concentrate were re-combined to give a range of concentrations; the pH of these solutions was measured. COP was measured using an oncometer fitted with an Amicon PM30 membrane and CONC measured using the BCA protein assay system (Pierce) and the Pierce protein standard (No 23210). The relationship between COP and CONC for BSA (Cohn fraction V. Sigma) was also studied. When corrected to 37°C the relationship for BSA did not differ from that described by Landis & Pappenheimer, i.e. COP = 2.8C + 0.18 02 + 0.0120C3. Miy analysis of the human plasma samples showed that the relationship was best fitted by a cubic equation COP = 0.827 + 0.47C + 0.54C2 + 0.006C3, which is significantly different from the equation given by Landis & Pappenheimer (P < 0.001). These data suggest that the Landis & Pappenheimer formula is not appropriate for the estimation of COP from protein concentration. REFERENCES

Noddeland, H., Aukland, K. & Nicolaysen, G. (1981). Acta Physiol. Scand. 113, 447 454. Landis, E.M. & Pappenheimer, J.R. (1963). Handbook of Physiol. Section 2. Vol. II, 961--1034.

J. Physiol. (1991) Vol. 438. Proceedings of The Physiological Society



A simple analogue circuit to provide a voltage proportional to 'instantaneous' minute ventilation from respiratory airflow for use in studies with targeted breathing S.H. Moosavi, L. Adams and K. Murphy Department of Medicine, Charing Cro0s & Westminster Medical School, London W6 8RF In studies on the voluntary control of breathing, it is often necessary for subjects to control ventilation (VE) in a defined manner. We have used an analogue computer with logic control (MiniAC, EAI) to construct a circuit which converts a respiratory airflow signal to a 'D.C.' voltage proportional to the prevailing V E but which is independent of the respiratory pattern. Visual feedback ofthis voltage gives subjects the straightforward task of matching their VEto a target; manipulation of this voltage allows the investigator to impose a specific experimental design. The circuit is shown schematically in Fig. 1. -------------


J .










aP tP4,

:sws B) ADIOA



The flow signal is monitored by a comparator (CP) which controls the tracking function of two track/store units (TS 1, TS2) such that TS1 will track when flow is above zero (inspiration) and TS2 when flow is below zero (expiration). The output from TS2 is inverted (INVI) and summed (SI) with that of TS1. This 'rectified' signal is fed into an integrator (2jINT1), the output of which provides negative feedback via a potentiometer (P1). The resultant output is a voltage varying linearly with IVE (up to at least 90 1 min-'; r = 0.999) independent of the pattern of breathing. The degree of smoothing of respiratory oscillations and the response time to a step change in V~E is determined by the level of feedback. The V E-dependent voltage can be modified in two ways. A switched increase or decrease in gain at the input stage (via SWI, P2 or SW2, P3, INV2 respectively), which occurs over the response time of the circuit, requires the subject to change iVE by a defined amount without this being obvious. At the output stage (S2), an immediate change in the ikE-dependent voltage can be switched in via SW3; one application of this is to add a negative voltage ramp (P4, INT2) so that the subject has to steadily increase IVE (to keep the ikE-dependent voltage matched to a fixed target) thus 'simulating' the response to exercise. Passing the primary output through a track/store unit (TS3, SW4) makes it possible to select the VkE at a specified time as the fixed target for subsequent breathing.


J. Physirol. (1991) l'ol. 4.38. (hariny (ross .Mfeetiny 10 PROCEEDING'S OF THE PHYSIOLOGICAL SOCIETY

11 Jantuary 1991

A simple technique to study human laryngeal respiratory muscle action (LRMA) during different tasks in health and disease A.K.Datta, H.Holden* and A.Guz I)epartments of Mledicine a,nd *E.N. T., Charing Cross & WTestminster Hospital Medical School, Fulham Pa,la,ce Road. London W6 8RF

In normal human subjects the larynx aets as a portal for air entry to the lungs; inspiration is accompanied by abduction of the cords to allow airflow (Semon, 1891; Brancatisano. Collett & Engel, 1983). In this demonstration we will show how the temporal relationship between cord movement and ventilation may be studied in man during different tasks. The subject is seated on a couch. After local anaesthesia of the nose and oropharynx, a fibre optic bronchoscope is inserted via the nose to view the vocal cords. The bronchoscope tip is applied to the cords and then drawn back by a known distance. This distance is used to calibrate the size of the displayed image of the cords. Respiratory volume, recorded non-invasively using DC-coupled respiratory inductance plethysmography and calibrated with a spirometer, is displayed on an oscilloscope. The laryngeal image and the respiratory volume trace recorded using two video cameras, are electrically mixed and recorded onto a video recorder running at 25 frames/s. The composite image is then visualized on a TV monitor and hard copy device. Recordings from a normal subject show the cords opening just before the onset of inspiratory airflow during a variety of respiratory tasks. In contrast, recordings from two patients will be shown where during voluntary breathing inspiration occurs against a closed glottis or supraglottis resulting in marked inspiratory stridor. During other motor tasks, e.g. panting, speech, exercise, during coughing following voluntary breath-holding and during sleep, LRMA is more coordinated resulting in greater inspiratory airflow. In one patient, neither lignocaine anaesthesia of the superior laryngeal nerves nor subsequent cryo-ablation of these nerves altered the discoordinate LRMIA. Similarly when airflow bypassed the larynx (tracheostomy) LRAIA remained discoordinate. This suggests that the discoordinate LRMIA observed in these patients is task and state dependent. The lack of response to superior laryngeal nerve anaesthesia suggests that either other, extra-laryngeal, afferents are involved or that central neural influences linked to motor task may predominate. REFERENCES

Semon, F. (1891). Proc. Roy. Soc. (Lond) Series B 48. 156 159. Brancatisano, T., Collett. P.A'. & Engel, L.A. (1983). J. App. Physiol. 54, 192-204.

J. Physiol. (1991) V'ol. 4.38. Proceedings of 7'he Physiological iS'ociety



Comparison of within-breath variations in left ventricular stroke volume during positive-pressure and spontaneous ventilation in man S.C. De Cort, J.A. Innes and A. Guz Department of Medicine, Charing Cross & Westn)inster Medical School, Fulhan? Palace Road, London W6 8RF During spontaneous breathing in normal subjects, left ventricular stroke volume, measured using pulsed Doppler ultrasound, was maximal during expiration (Guz et al. 1987), whereas during therapeutic positive pressure ventilation in a group of patients with neurological disorders, maximum stroke volumes occurred during inspiration (Innes et al. 1990). Comparison of the responses and elucidation of the mechanisms responsible in these two groups of subjects is complicated by factors such as differences in lung compliance, posture and state of consciousness. By training normal subjects to accept passive ventilation through a nasal mask, it is possible to compare respiratory variations in stroke volume in response to normal and positive-pressure ventilation within subjects. Chest expansion, measured using respiratory inductance plethysmography (Respitrace) and displayed on an oscilloscope, can be used by the subject to match the spontaneous tidal volume, respiratory rate and pattern to that generated by the ventilator. The only difference between spontaneous breathing and positive-pressure ventilation in this situation is the direction of the intrathoracic pressure swings. REFERENCES

Innes, J.A., De Cort, S.C., Kox. Xv". & Guz, A. (1990). J. 1'hysiol. 432, 37I'. Guz. A.. Innes. J.A. & Murphy, K. (1987). J. Physiol. 393, 499-512.

Chariny ( Meeting 10-11 Januiary 1991 PROCEEDILN(GS OF THE PHYSIOLOGICAL SO(IETY J. Physiol. (1991) lol. 438.


Generation and measurement of rapid changes in airway pressure in man J.A. Innes, R.L. Horner and A. Guz Department of Medicine, Charing Cross & Westminster Medical School, Ftlhani Palace Road, London 1W6 8RF For studies of the reflex effects of a pressure stimulus, it is desirable to have 'square wave' pressure changes of reproducible rates of change and magnitude. Our apparatus (Fig. LA) is designed to produce negative airway pressure (-veP) stimuli that fulfil these criteria. Subjects breathe through a tight-fitting face mask attached to an open breathing circuit made from stiff plastic tubing (15 mm internal diameter). Activation of a solenoid valve (Martonair/Beech, B/ 6SP5/122/M10, time to full opening = 10 ms) switches the circuit to a partially evacuated 501 tank causing rapid decreases in pressure. Spring-loaded valves (Vital Signs Inc.) vent the excess -veP to atmosphere and constrain the -veP to pre-determined levels. The -ve P stimuli are recorded by a transducer (AIP45-30871 Validyne Inc.) connected to the mask via a 52 cm length of manometer line; this length does not significantly damp the recording of the -veP but delays the measurement of its onset by 5 ms. The reproducibility of the rate of change and the magnitude of the stimuli is shown in Fig. 1B. Pressure changes with 0-90% rise time of < 10 ms can be achieved when applied with the glottis closed (Fig. 1B) and O applied wvith the glottis closed.

WVe thank Dr C. Clark, Department of Manufacturing and Engineering, Brunel University for advice on the measuremnent of rapid pressure changes.

J. Physiol. (1991) Vol. 438. Proceedings of The Physiological Society



Facilitation of the diaphragmatic response to transcranial magnetic stimulation with peripheral nerve stimulation K. Murphy, L. Adams, A. Mier, D. Maskill*, D. Lobo and A. Guz Departments of Medicine and *Physiology, Charing Cross & Westminster Medical School, London W6 8RF A protocol for studying the effects of changes in orthostatic pressure on the responses of the human limb to cuff inflation using mercury-in-Silastic strain gauge plethysmography J. Gamble, F. Christ and I. B. Gartside Department of Physiology, Charing Cross & Westminster Medical School, Fulham Palace Road, London W6 8RF

Proceedings of the Physiological Society. Charing Cross and Westminster meeting, 10-11 January 1991. Abstracts.

PROCEEDINGS OF THE PHYSIOLOGICAL SOCIETY CHARING CROSS AND WESTMINSTER MEETiNG 10-11 January 1991 These abstracts were accepted by Mlembers of the Soc...
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