Bit. J. Dis. Chest (1976)
70, 58
INCREASED UPPER IN PATIENTS WITH
AIRWAY AIRWAY
RESISTANCE NARROWING
ALASTA~R H. CAMPBELL, H. IMBERGER AND B. McC. JONES Repatriation General Hospital, Heidelberg, Victoria, Australia SOME patients with respiratory disease groan or produce other vocal sounds Others have noisy respiration with loud harsh breath during respiration. sounds which may be audible with the unaided ear or be heard loudly by auscultation over the larynx, particularly during expiration. The normal blowing quality of the breath sounds is often replaced by more guttural sounds. Rhonchi may be heard. These abnormal sounds could be due to narrowing of the glottis or other parts of the upper airway during respiration. Recognition of such narrowing, with associated rise of upper airway resistance and thus of total airway resistance, would be of clinical significance. Upper airway resistance has been measured in patients with airways obstruction who had signs considered to suggest increased upper airway resistance. Patients
and Methods
Patients Eleven men aged between 45 and 75 years with airways obstruction were selected for study. In these, auscultation over the glottis revealed signs suggestive of glottic narrowing as described above. From clinical, physiological and radiological evidence, airways obstruction was classified as asthma in 5 patients and chronic bronchitis with or without emphysema in 6. Control values of upper airway resistance were measured in 6 male volunteers aged 2 1-71 years who were free of respiratory symptoms. The sounds heard by auscultation over the larynx of the controls had a normal blowing quality. Measurement of @per airway resistance The upper airway resistance was me,asured by recording the air flow and pressure difference across the upper airways during mouth breathing. With the patient seated without any premeditation, the skin of the neck was prepared with 70% isopropypl alcohol. Skin and subcutaneous tissues down to the cricothyroid membrane were infiltrated with I y0 lignocaine. A I 5-gauge Dwellcath intravenous infusion needle 5 cm long was inserted by percutaneous puncture through the cricothyroid membrane at right angles to the long axis of the larynx. Its tip was positioned by feel at about the centre of the lower (Receivedfor
publication
October 1975)
INCREASED
UPPER
AIRWAY
RESISTANCE
59
larynx. The metal needle was withdrawn leaving the Teflon catheter in place. In 2 patients who had a healing tracheostomy, the needle was inserted through the tracheostomy into the trachea. The skin and deeper tissues were drawn together with strapping, sealing the tracheostomy stoma and holding the needle in position. The pressure at the mouth was measured through a needle inserted into th: lumen of a mouth-piece 1.9 cm diameter. Provided that the air velocity is approximately the same at the measuring points, the lateral pressure difference between the needle in the mouth-piece and that in either the lower larynx or the trachea will be due to the flow resistance of the upper airways. Measurements offlow characteristics of the larynx in autopsy specimens showed that with the low flow rates used in this investigation, the air velocity at the measuring points would be approximately the same. Consequently the measured lateral pressure difference can be taken as being due to the resistance of the upper airways. This pressure difference was measured with a Statham PM 6 TC pressure transducer. The flow was a measured with a Fleisch head, linear for flow rates up to 2 litres/sec, connected by tubing to a Godart pneumotachograph. With the patient seated, the upper airway pressure difference and flow rate were recorded during normal breathing in all patients and during ventilation (in all but I patient) on both an Offner Type R recorder and a Tektronix storage oscilloscope type 564, fitted with a Polaroid camera. Upper airway resistances calculated from the tracings recorded by the Offner recorder and those of the oscilloscope were similar. To obtain representative values, at least 4 respiratory cycles were used and the mean resistance calculated at flows of 0.25 litre/sec and of 0.5 litre/sec when this was reached. In some patients looping occurred during one or both phases of respiration and two values of resistance were obtained, these were averaged for the purpose of comparison with normal values. Response characteristics of pressure transducing systems The response characteristics of the pressure transducing systems, i.e. from pressure sensing point to the oscilloscope screen, were determined by applying to each a fast rising pressure step (rise time less than about I msec). The voltage responses showed some resemblance to exponential rises of varying time constants, none greater than approximately 18 msec. We endeavoured to match the response characteristic of the transducers by adding extra tubing to the faster transducer. The effect of the delayed transducer action was tested by recording the pressure-flow curves of a fixed non-linear resistance while breathing through it with various breathing patterns. The pressure-flow curve of this resistance was alinear and resembled that of a typical upper airway flow curve. With high breathing rates of 50 or more breaths per minute the tracings became less alinear and the resistance measured at 0.25 litre/sec became a little greater than at lower breathing rates. However at breathing frequencies of 35 per minute or less and maximum flow rates of I litre/sec or less the resistances
CAMPBELL
60
ET
AL.
were constant at either 0.25 litre/sec or 0.5 litre/sec. With one exception during hyperventilation, the breathing frequencies and flow rates employed in this investigation were within the above range, permitting accurate measurement of resistance values at either 0.25 litre/sec or 0.5 litre/sec. Measurement of total airways resistance
?
In 8 of the patients the upper airway resistance and the total airway resistance were measured simultaneously. With needles in position the patients were moved carefully into the body plethysmograph and recordings were made
I. With the patient in the body plethysmograph, the tracings obtained on the oscilloscope were: (I) box pressure (BP) and flow; (2) upper airway pressure difference (UAWP) and flow; (3) flow rate and tidal volume; and (4) mouth pressure (with shutter closed) and box pressure
FIG.
of the upper airway pressure difference, air flow and box pressure. The upper airway pressure difference-flow curve and the box pressure flow curve were recorded simultaneously on the oscilloscope. The mouth pressure-box pressure trace was recorded after closing the mouth shutter. The flow volume curve was recorded immediately afterwards. The recording arrangement is represented diagramatically in Fig. I. Box pressure was measured with a Statham PM 197 pressure transducer and the mouth pressure recorded with a Stratham PM 5 pressure transducer. To measure the total airway resistance using the plethysmograph during normal breathing and slight hyperventilation, corrections have to be made for the box pressure changes due to the heating and humidification of the inspired air as well as the cooling of, and condensation in, the expired air. The technique employed was similar to that described by Bargeton (I 959).
INCREASED
UPPER
AIRWAY
RESISTANCE
61
Statistical anal_ysis When appropriate the t-test was used for testing the significance between means. When the variances cri2 and c22 were very different, the method described by Walpole (1968) was employed. Results Upper airway resistance of patients and controls The mean upper airway resistance of the patients was significantly greater than that of the healthy controls during resting ventilation and slight hyperventilation. The difference was greater during expiration than during inspiration (Table I). The upper airway resistance was alinear, and. the resistance calculated
TABLE
I.
U@er airway resistance
UPPER
AIRWAY
Patients with signs
measurement
RESISTANCE*
Controls
Patients v. controls
laryngeal
At 0.25 litrelsec Resting ventilation inspiration expiration Slight hyperventilation inspiration expiration
1.04ko.56 2*16& 1.21
(II) (II)
0.63 + 0.23 0.90 2 0.58
(6) (6)
Pco.05 P < 0.025
1’50fo*g7 2.Ig+ 1.58
(10)
(10)
0.65 + 0.24 0.75 I 0.27
(6) (6)
P
70, 58
INCREASED UPPER IN PATIENTS WITH
AIRWAY AIRWAY
RESISTANCE NARROWING
ALASTA~R H. CAMPBELL, H. IMBERGER AND B. McC. JONES Repatriation General Hospital, Heidelberg, Victoria, Australia SOME patients with respiratory disease groan or produce other vocal sounds Others have noisy respiration with loud harsh breath during respiration. sounds which may be audible with the unaided ear or be heard loudly by auscultation over the larynx, particularly during expiration. The normal blowing quality of the breath sounds is often replaced by more guttural sounds. Rhonchi may be heard. These abnormal sounds could be due to narrowing of the glottis or other parts of the upper airway during respiration. Recognition of such narrowing, with associated rise of upper airway resistance and thus of total airway resistance, would be of clinical significance. Upper airway resistance has been measured in patients with airways obstruction who had signs considered to suggest increased upper airway resistance. Patients
and Methods
Patients Eleven men aged between 45 and 75 years with airways obstruction were selected for study. In these, auscultation over the glottis revealed signs suggestive of glottic narrowing as described above. From clinical, physiological and radiological evidence, airways obstruction was classified as asthma in 5 patients and chronic bronchitis with or without emphysema in 6. Control values of upper airway resistance were measured in 6 male volunteers aged 2 1-71 years who were free of respiratory symptoms. The sounds heard by auscultation over the larynx of the controls had a normal blowing quality. Measurement of @per airway resistance The upper airway resistance was me,asured by recording the air flow and pressure difference across the upper airways during mouth breathing. With the patient seated without any premeditation, the skin of the neck was prepared with 70% isopropypl alcohol. Skin and subcutaneous tissues down to the cricothyroid membrane were infiltrated with I y0 lignocaine. A I 5-gauge Dwellcath intravenous infusion needle 5 cm long was inserted by percutaneous puncture through the cricothyroid membrane at right angles to the long axis of the larynx. Its tip was positioned by feel at about the centre of the lower (Receivedfor
publication
October 1975)
INCREASED
UPPER
AIRWAY
RESISTANCE
59
larynx. The metal needle was withdrawn leaving the Teflon catheter in place. In 2 patients who had a healing tracheostomy, the needle was inserted through the tracheostomy into the trachea. The skin and deeper tissues were drawn together with strapping, sealing the tracheostomy stoma and holding the needle in position. The pressure at the mouth was measured through a needle inserted into th: lumen of a mouth-piece 1.9 cm diameter. Provided that the air velocity is approximately the same at the measuring points, the lateral pressure difference between the needle in the mouth-piece and that in either the lower larynx or the trachea will be due to the flow resistance of the upper airways. Measurements offlow characteristics of the larynx in autopsy specimens showed that with the low flow rates used in this investigation, the air velocity at the measuring points would be approximately the same. Consequently the measured lateral pressure difference can be taken as being due to the resistance of the upper airways. This pressure difference was measured with a Statham PM 6 TC pressure transducer. The flow was a measured with a Fleisch head, linear for flow rates up to 2 litres/sec, connected by tubing to a Godart pneumotachograph. With the patient seated, the upper airway pressure difference and flow rate were recorded during normal breathing in all patients and during ventilation (in all but I patient) on both an Offner Type R recorder and a Tektronix storage oscilloscope type 564, fitted with a Polaroid camera. Upper airway resistances calculated from the tracings recorded by the Offner recorder and those of the oscilloscope were similar. To obtain representative values, at least 4 respiratory cycles were used and the mean resistance calculated at flows of 0.25 litre/sec and of 0.5 litre/sec when this was reached. In some patients looping occurred during one or both phases of respiration and two values of resistance were obtained, these were averaged for the purpose of comparison with normal values. Response characteristics of pressure transducing systems The response characteristics of the pressure transducing systems, i.e. from pressure sensing point to the oscilloscope screen, were determined by applying to each a fast rising pressure step (rise time less than about I msec). The voltage responses showed some resemblance to exponential rises of varying time constants, none greater than approximately 18 msec. We endeavoured to match the response characteristic of the transducers by adding extra tubing to the faster transducer. The effect of the delayed transducer action was tested by recording the pressure-flow curves of a fixed non-linear resistance while breathing through it with various breathing patterns. The pressure-flow curve of this resistance was alinear and resembled that of a typical upper airway flow curve. With high breathing rates of 50 or more breaths per minute the tracings became less alinear and the resistance measured at 0.25 litre/sec became a little greater than at lower breathing rates. However at breathing frequencies of 35 per minute or less and maximum flow rates of I litre/sec or less the resistances
CAMPBELL
60
ET
AL.
were constant at either 0.25 litre/sec or 0.5 litre/sec. With one exception during hyperventilation, the breathing frequencies and flow rates employed in this investigation were within the above range, permitting accurate measurement of resistance values at either 0.25 litre/sec or 0.5 litre/sec. Measurement of total airways resistance
?
In 8 of the patients the upper airway resistance and the total airway resistance were measured simultaneously. With needles in position the patients were moved carefully into the body plethysmograph and recordings were made
I. With the patient in the body plethysmograph, the tracings obtained on the oscilloscope were: (I) box pressure (BP) and flow; (2) upper airway pressure difference (UAWP) and flow; (3) flow rate and tidal volume; and (4) mouth pressure (with shutter closed) and box pressure
FIG.
of the upper airway pressure difference, air flow and box pressure. The upper airway pressure difference-flow curve and the box pressure flow curve were recorded simultaneously on the oscilloscope. The mouth pressure-box pressure trace was recorded after closing the mouth shutter. The flow volume curve was recorded immediately afterwards. The recording arrangement is represented diagramatically in Fig. I. Box pressure was measured with a Statham PM 197 pressure transducer and the mouth pressure recorded with a Stratham PM 5 pressure transducer. To measure the total airway resistance using the plethysmograph during normal breathing and slight hyperventilation, corrections have to be made for the box pressure changes due to the heating and humidification of the inspired air as well as the cooling of, and condensation in, the expired air. The technique employed was similar to that described by Bargeton (I 959).
INCREASED
UPPER
AIRWAY
RESISTANCE
61
Statistical anal_ysis When appropriate the t-test was used for testing the significance between means. When the variances cri2 and c22 were very different, the method described by Walpole (1968) was employed. Results Upper airway resistance of patients and controls The mean upper airway resistance of the patients was significantly greater than that of the healthy controls during resting ventilation and slight hyperventilation. The difference was greater during expiration than during inspiration (Table I). The upper airway resistance was alinear, and. the resistance calculated
TABLE
I.
U@er airway resistance
UPPER
AIRWAY
Patients with signs
measurement
RESISTANCE*
Controls
Patients v. controls
laryngeal
At 0.25 litrelsec Resting ventilation inspiration expiration Slight hyperventilation inspiration expiration
1.04ko.56 2*16& 1.21
(II) (II)
0.63 + 0.23 0.90 2 0.58
(6) (6)
Pco.05 P < 0.025
1’50fo*g7 2.Ig+ 1.58
(10)
(10)
0.65 + 0.24 0.75 I 0.27
(6) (6)
P
