Chronic intermittent hypoxia alters ventilatory and metabolic responses to acute hypoxia in rats

We determined the effects of chronic exposure to intermittent hypoxia (CIH) on chemoreflex control of ventilation in conscious animals. Adult male Sprague-Dawley rats were exposed to CIH [nadir oxygen saturation (SpO(2)), 75%; 15 events/h; 10 h/day] or normoxia (NORM) for 21 days. We assessed the following responses to acute, graded hypoxia before and after exposures: ventilation ((V) over dotE, via barometric plethysmography), (V) over dotO(2) and (V) over dotCO(2) (analysis of expired air), heart rate (HR), and SpO(2) (pulse oximetry via neck collar). We quantified hypoxia-induced chemoreceptor sensitivity by calculating the stimulus-response relationship between SpO(2) and the ventilatory equivalent for (V) over dotCO(2) (linear regression). An additional aim was to determine whether CIH causes proliferation of carotid body glomus cells (using bromodeoxyuridine). CIH exposure increased the slope of the (V) over dotE/(V) over dotCO(2)/SpO(2) relationship and caused hyperventilation in normoxia. Bromodeoxyuridine staining was comparable in CIH and NORM. Thus our CIH paradigm augmented hypoxic chemosensitivity without causing glomus cell proliferation.