Role of mechanoreflex control of breathing during formation of compensatory response to antiorthostatic load in anesthetized rats

The work objective is to study the role of mechanoreceptor boundary in control of breathing during formation of respiratory system compensatory response to head-down tilt position. Material and Methods. The study was performed on 15 anesthetized Wistar rats in supine (baseline) and head-down tilt positions at a -30° angle. The pneumotachograph method was used to register the basic parameters of external breathing (time and volume). The reflex responses of the respiratory system to head-down tilt position were estimated before and after bilateral cervical vagotomy. The respiratory system spare capacity was evaluated according to maximum (peak) values of inspiratory esophageal pressure during short postinspiratory airway occlusion. Results. The data obtained showed that in vagotomized animals (head-down tilt position) deceleration of inspiratory flow, tidal volume and minute ventilation occurred more often than in vagal-intact animals. The increase in peak inspiratory esophageal pressure in response to postinspiratory occlusion was twice as little in vagotomized animals than that in intact-vagal ones. It was found out that one of the main components of respiratory system compensatory response to anti-orthostatic load is a mechanoreflex control of breathing, which is implemented through afferent impulses from pulmonary stretch receptors and provides feedback between lung volume change and central inspiratory activity. Reflex mechanism causing compensatory increase in the total inspiratory effort during transition to head-down tilt position is weakening of inhibitory afferent input coming into the respiratory center from the pulmonary stretch receptors, due to lung volume decrease. Conclusions. The data obtained indicate the decrease in spare capacity of the respiratory system in head-down tilt position as a result of inhibition of reflex mechanisms that are implemented through the lung afferent system.