Mechanism of cough. Tracheal excitation and glottic resistance

Abstract

An experimental study with dogs has been carried out to investigate the functional c h a n g e s of the glottis when cou- ghing, by using a new method which permits the changes of resistance in the separate glottis to be recorded. This method consists of passinga constant flow of air through the glottis, measuring the resistance (fig. 1). mI the lower p a r t of the trachea an ordinary trachealcanula (a) of the exact diameter necesary so that it remains steady by the light expansion of the tissue without ligating. In the upper part acanula at right angles b)( is festenedby adevice consisting of elastic membrane and a spring as shown in the scheme. The tube (b) connects with the recording manometer b ya side tube. A constant flow of airis passed through this canula being directed to the glot- tis, the pressure being recorded. The pressureis always in proportion to the resistance of t h e air passing through cords. While resting, with light anesthesia o rwithout it, generally a rhythmical oscillation is recorded increasing with expiration and decreasing with inspiration. When beginning the experi- ment the flow is graduated, increasing graduallyuntil thein- crease of pressure in the expiration beginsto be wel recorded. The seizure elicited by tracheal excitation is a serie of res- piratory movements characterized by the aceleration of the air flow with a strong positive expiratory pleural pressure (fig. 2 and 3).

The glottis resistance changes in a charactetistic form. The resistance decrease atthe beginningof the seizure is very often (fig.2 , I Iand 3). The resistance increase at the expiration, which is always registered in the narcoseless animals, usually desappears completly. Sometimes the beginning of the mecha- nic excitation is remarked by a rough closing expiratory of the glottis, but we observe this with much lessfrecuency than employingthe powder soap technic. There is then an inverse rate between pleural expiratory pressure an resistance of the glottis: the maximun decrease of resistance comes during the coughs of highest pleural expiratory pressure. I f we take as seazure sign of intensity the number of rough expirations, the time of the glottis dilatation - by its paralelism with the strong expiratory contractions - may be also considered, in a cer- tain way as an appraisal of the intensityof the response. Usually the glottis expiratory enlargement -as w e l l

as the strong expiratory contractions — does not last, more than the time of mechanic excitation. But when the excitatin of the respiratory center is increased by analeptic actions, the seazure may be much longer than the excitation time

(fig. 6, III).
In order to relate the glottis wide with the tracheal excita-

tion, a comparation of seizures elicited by mechanic tracheal excitation with seizures aroused by other kind of excitation is sugestive (fig. 5). AVe observe that in cough elicited by lobe- line does not appear the glottis dilation. The same thing hap- pens in burst of strong expirations, observed after the Micoren

injection, which are going with expiratory contractions of the glottis. (fig. 6, II). On the other hand, it is remarkable that when the tracheal excitation is done in the momcnt when strong expiratory contractions of the glottis are being recordcd — cha-

racteristic of the Micoren — the obtained scizure is al so charac- terized by the whole decreasing of the glottis expiratory resis- tance (fig. 6, III).

A rate between tracheal excitation and glottis dilation is also evident in the obtained records during very short excita- tions, of tenths of a second, acting only during the inspiration or the expiration (fig. 4). In each both cases always appear an

expiratory contraction going with a sharp decreasing of the glottis resistance. And in this experimental conditions may be observed that when the expiratory contraction is very short and it starts when the glottis resistance in the same expiratory fase has arrived to the maximun, the glottis roughly relaxes, to come back again to increase the glottis resistance before the end of the expiration.

The results show the sharp closing of the glottis may not be considered as a cough characteristic caused by the excita­ tion of the respiratory ways. Such a sharp glottis increase ofresistance may appear toward the end of the seizure, uíˆsually when the tracheal mechanical action has stoped, and itcoincides with an inspiratory pleural pressure curve, showing that the inspiration which appear immediately before to the closing of the glottis, is shorter and finishes with a slower relaxation (fig. 3). Besides, the expiration is characterized by an air flow aceleration lower than the forme'r, which is very interestmg because the respiratory movements of this kind seems to corrcspond with the elassie descriptions of the cough.

\ve amve to the conclusión that it is not admisible the description of the cough, and that we can not accept e dnferentiation between cough and rough expirations by the existence in the cough of a glottis contraction which closes respiratory ways. And on the other hand, this notion although usually admitted mad not adecuate demostration.
The effect of the tracheal excitement on the resistance of the glottis in our experiments shows that the response of the glottis cannot be taken as a datum of experimental valuation of antitussives. 'The lack of relation between the contraction of expiratory muscles and changes in the resistance of the glottis is evident. In some cases, doses which noticeably diminish the expiratory contraction and the number of coughs, hardly in- fluence the resistance of the glottis either in the spontaneous respiration or during the access. In other cases, when the phar- macological action is able to reduce to the maximum the resis- tance of the glottis in the spontaneous respiration, the tra- cheal excitement still provokes accesses of cough with noticea- ble expiratory contractions without a marked change in the resistance ofthe glottis. And other times when the resistance of the glottis wasreduced to the maximum also coinciding with the depression of the respiratory rhythm, the tracheal exci- tement then provokes sharp increases in expiratory resistance in the glottis which does not coincide with any changei nthe activity of the expiratory muscles. In fig. 7 the record of pleu- ral pressure a n d resistance of the glottis is represented, in relation with a tracheal excitement applied several times with the same intensity: a not very strong stimulus brings only one spasmotic contraction of the glottis, in the control (1) as wel as after the antitussive (2), which forms a contrast with the evident decrease in the cough which may be noticed on account of the decrease in the maximum of pleural expiratory pressure and the mumber of coughs; a stimulus somewhat more intense, each time it is repeated - 3, 4, 5, 6 and 7 - , brings on accesses approximately the same if they are evaluated by the maximum of pleural pressure and the number of expiratorycontractions,and, on the otherhand the spasmodiccon- traction of the glottis appears only in some cases (7) or even spasmodically (4) without relation to the tracheal excitement.