Respiratory Alterations Due to Chronic Long-Term Intermittent Hypobaric Hypoxia in Rabbits: Importance of Peripheral Chemoreceptors

BackgroundNone of the studies carried out so far investigated the effect of denervation of peripheral chemoreceptors on basal ventilation and respiratory responses to acute hypoxia in subjects exposed to chronic long-term intermittent hypobaric hypoxia (CLTIHH). We aimed to research (i) the effect of CLTIHH (430 mmHg, 5 h/day, 5 days/week, 5 weeks) on basal ventilation and respiratory responses to hypoxia and (ii) the effects of CLTIHH on central respiratory mechanisms after peripheral chemodenervation.MethodsSixteen adult albino rabbits were divided into two groups: CLTIHH (n = 8) and control (n = 8). The tidal volume (VT) and respiratory frequency (f/min) were initially recorded in both groups and respiratory minute volume (VE) was calculated. PaO2, PaCO2, and pHa values were determined.ResultsThe initial values of f/min and VE in CLTIHH group were significantly higher than that of control group. After exposure to hypoxic gas mixture (8% O2−92% N2), the elevations in f/min, VT, and VE in CLTIHH group were significantly higher than those of control group. After denervation of peripheral chemoreceptors, the decrease in VE in CLTIHH group was found to be significantly less than that of control group. When the animals in control group were allowed to breathe hypoxic gas mixture, f/min, VT, and VE decreased significantly and hypoxic depression was obtained. In contrast, hypoxic depression did not occur in the CLTIHH group.ConclusionsOur results suggested that CLTIHH increases the basal ventilation and hypoxic respiratory responses and that enhanced ventilatory responses were due not only to the augmentation of peripheral chemoreceptor activity but also to the augmentation of central respiratory activity.