Sympathetic and blood pressure responses to voluntary apnea are augmented by hypoxemia

Oscillations of arterial pressure during sleep are the hemodynamic hallmark of the sleep apnea syndrome. The mechanism of these transient pressure elevations is incompletely understood. To investigate the role of the arterial chemoreflex in the neurocirculatory responses to apnea, we measured mean arterial pressure (MAP; Finapres) and muscle sympathetic nerve activity (MSNA; peroneal microneurography) during voluntary end-expiratory apnea during exposure to room air, 10.5% O₂ in N₂ (hypoxemia), and 100% O₂ (hyperoxia) in 11 healthy men. While the men breathed spontaneously, MSNA (in bursts/min) rose during hypoxemia and decreased during hyperoxia and MAP remained unchanged. During room air exposure, apnea led to a rise of 94 ± 54% in MSNA total amplitude and a rise of 6.5 ± 2.1 mmHg in MAP. MSNA and MAP increased by 616 ± 158% and 10.8 ± 2.4 mmHg, respectively, during hypoxemic apnea of equal duration (time-matched responses) and by 98 ± 41% and 4.9 ± 2.0 mmHg, respectively, during hyperoxic apnea (P < 0.05 for hypoxemic vs. hyperoxic apnea for both). Thus, in awake healthy humans, activation of the arterial chemoreflex by hypoxemia appears to contribute importantly to the sympathetic and blood pressure responses to apnea.