Chronic intermittent hypoxia increases sympathetic responsiveness to hypoxia and hypercapnia

Division of Pulmonary and Critical Care Medicine, Long Island Jewish Medical Center, Long Island Campus for the Albert Einstein College of Medicine, New Hyde Park, New York 11040 We sought to determine whether chronic exposure to intermittent hypoxia (CIH) increases sympathetic responsiveness to subsequent chemoreflex stimulation. Sprague-Dawley rats were exposed to 30 days of CIH: exposure chamber %O 2 [fractional concentration of chamber O 2 (Fc O 2 )] nadir 6.5-7% with return to 21% each minute for 8 h/day during the diurnal sleep period (Exp group). Sham controls (SC group) were similarly handled but kept at 21% Fc O 2 and compared with unhandled controls (UC group). Rats were then anesthetized with urethan, and preganglionic cervical sympathetic activity (CSA), diaphragm electromyogram, arterial pressure, and electrocardiogram were recorded while the rats were spontaneously breathing 100% O 2 , room air, 10% O 2 , 12% CO 2 , and 10% O 2 -12% CO 2 . CSA and heart rate were also recorded during phenylephrine infusion to assess baroreceptor function. Mean arterial pressure was significantly greater in Exp than in SC and UC rats during all conditions ( P