The physiology of coughing. Differentiation of the constrictor and dilator reflexes of the laryngeal sphincter

Abstract

In an earlier study it has been demonstrated by us that the classical description of coughing is not exact. In those investi- gations we made use of a singular method of registering the va- riations in resistance of the glottis. This method consists in passing a constant flow of air through the sepárate glottis, measuring the resistance. In the lower part of the trachea an ordinary tracheal canula is placed. In the upper part a canula at right angles is fastened. A constant flow of air is passed through this canula being directed to the glottis, the pressure being recorded. The pressure is always in proportion to the re­ sistance of air passing through cords. While resting with light anesthesia or without it, generally a rhytmical oscillation is recorded, increasing with expiration and decreasing with inspi- ration.

We arrive ab the conclusión that the comnion description of cough is not admisible and that we can not accept the differentia- tion betweeen cough and rough expirations by the existence in the cough of a glottis contraction which closes respiratory ways. And 011 the othcr hand, this notion although usually admitted had no adecúate demonstration. The effect of the tracheal sti- mulation on the resistance of the glottis in our experiments

shows that the response of the glottis cannot be taken as a datum of experimental evaluation of antitussives.

In later investitions we have confirmed that the closing of the glottis does not particípate in the act of coughing. Duringthe access provoked by excitation of the trachea, the glottis ge- nerally remains in ampie dilatation. In the mayority of cough- ings — as we have been able to check in numerous experien- ces — unlike control respiration, the glottis remains widely openned during the whole of the respiratory cycle : it dilates in the inspiration as much, as or more than in normal respi­ ratory cycle ; and the convulsive contraction of expiratory mus- culature presents itself, the glottis being dilated. When a cer- tain degree of constriction is produced, it is not greater than on a calm expiration, always beginning after the expiration starts. In general this constriction isn’t greater than in the con­ trol expiration (fig. 1, n.°3 and 4). But it’s evident that interrup- tion of the flow through the glottis, previous to the expiration, never appears. When —in exceptional cases —, a rise in the expiratory resistance, notably greater than the control expira­ tion, is recorded, it always begins after the expiratory curve of the neumotachogram (fig. 1, n.° 2). That is, we never observethe so-called compressive phase. The inspiratory phase is direc- tly followed by the expulsive phase. We fundament this defini- tive conclussion in records obtained in a considerable number of animáis.

We have completed the observation upon obtaining a film of the image of the entrance of larynx during the cough and in the spontaneous respiration. It’s evident that the dilation of the laryngeal sphincter at the end of the inspiration continúes in the expiration, without an intermedíate closing phase, as can be seen in figure 2. The photographic observation reveáis iden- tical images in the experiences with intact respiratory tracts or with isolated glottis. It is a guarantee that in this last case there are no influences of ertefacts. The fundamental charac- teristics of coughing are cleardy magnified upon comparing the records of cough with oder very different movements in the same animal (fig. 3).

Constriction reflexes of the glottis are responses that are completely different from cough, although they can appear amid coughing access. Some results over constrictor reflexes are exposed in order to make notable the aspects which define coug­ hing. A sharp glottis increase of resistance may appear by la- ringeal or tracheal excitation, and it coincides with an inspira­ tory pleural pressure curve, showing that the inspiration which appears iminediately before the closing of the glottis, is shortcr and finishcs with a slower relaxation and besidcs, the expiration is characterized by an air flow acceleration lower than tliat typical of the cough, that is very notable because this respiratory movement does not correspond to the description of the cough. It is not coughing, but an intralaringeal sphinter closure with wjiich a very different protective function is accomplished.