Interaction of Humoral Ventilatory Stimuli at High Altitude

Abstract

The effects of individual and combined ventilatory stimuli have been studied by most respiratory physiologists and by many others. It would be impossible to describe all the methods used. Many studies have utilized the well-known steady state method described by Lloyd et al. ¹. However, with this method it is inconvenient to study simultaneously arterial peripheral and central chemoreceptor activity. Dejours² introduced a transient method to test the peripheral chemoreceptor activity. In this method, the subject inhales a tidal volume of a given gas mixture, and the transient change in ventilation observed within 10–15 seconds is related to the change in alveolar gases. This method has been developed in different ways; some authors have preferred to use 2 or 3 tidal volumes to increase the stimulation of the chemoreceptors³ while others have used the inhalation of a vital capacity of a gas at the concentration of 15% of CO₂ to obtain the maximal firing of peripheral chemoreceptors4. The two methods have been compared ⁴,⁵,⁶, but the data obtained were not really comparable. Still other authors have combined steady state and transient methods. They have studied the increase of breathing versus time observed after inhalation of a hypercapnic mixture and the decrease of breathing at the removal of the mixture.