Short reflex expirations (expiration reflexes) induced by mechanical stimulation of the trachea in anesthetized cats

Abstract

Fifty spontaneously breathing pentobarbital-anesthetized cats were used to determine the incidence rate and parameters of short reflex expirations induced by mechanical stimulation of the tracheal mucosa (ERt). The mechanical stimuli evoked coughs; in addition, 67.6% of the stimulation trials began with ERt. The expiration reflex mechanically induced from the glottis (ERg) was also analyzed (99.5% incidence, p < 0.001 compared to the incidence of ERt). We found that the amplitudes of abdominal, laryngeal abductor posterior cricoarytenoid, and laryngeal adductor thyroarytenoid electromyograms (EMG) were significantly enhanced in ERg relative to ERt. Peak intrathoracic pressure (esophageal or intra-pleural pressure) was higher during ERg than ERt. The interval between the peak in EMG activity of the posterior cricoarytenoid muscle and that of the EMG of abdominal muscles was lower in ERt compared to ERg. The duration of thyroarytenoid EMG activity associated with ERt was shorter than that in ERg. All other temporal features of the pattern of abdominal, posterior cricoarytenoid, and thyroarytenoid muscles EMGs were equivalent in ERt and ERg.In an additional 8 cats, the effect of codeine administered via the vertebral artery was tested. Codeine, in a dose (0.03 mg/kg) that markedly suppressed cough did not significantly alter either the incidence rate or magnitudes of ERt.In the anesthetized cat the ERt induced by mechanical stimulation of the trachea was similar to the ERg from the glottis. These two reflex responses differ substantially only in the frequency of occurrence in response to mechanical stimulus and in the intensity of motor output.

Figure 1

The reflex responses to the mechanical stimulation (stim) in the trachea. Two quiet breaths (slight inspiratory increase in the records of laryngeal abductor posterior cricoarytenoid – PCA and parasternal muscles – PS EMG moving averages with a depression in esophageal pressure – EP) followed by a short reflex expiration (ERt) at the beginning of stimulation (steep elevations in EMG moving averages of laryngeal adductor thyroarytenoid muscle – ThAr, PCA, and abdominal muscles – ABD, as well as in EP). The ERt was then followed by 3 coughs in which the expulsions caused slight elevations of blood pressure (BP). Moderate post-inspiratory activity was present at the inspiratory-expiratory transition of quiet breathing in ThAr. The ERt was markedly shorter compared to the cough expulsions (see ABD and EP) leading to the lower amplitude of EP compared to that in coughs, although the amplitudes of ABD EMG moving averages remained comparable.

Figure 2

Mechanical stimulation of the trachea (stim) with short reflex expiration (ERt) during the inspiratory period of breathing. The stimulation immediately terminated an inspiration (rapid suppression of PCA and PS) and induced the ERt (abrupt activation of ThAr, PCA and ABD). Two much weaker ERt were detectable in the record of ABD, before the initial cough inspiration began (activation of PCA at the end of the record). See Fig. 1 for abbreviations.

Figure 3

Motor pattern of short reflex expiration (ERt) induced by mechanical stimulation of the trachea (stim). See Fig. 1 for abbreviations.