Neurocirculatory consequences of negative intrathoracic pressure vs. asphyxia during voluntary apnea

To investigate the mechanisms responsible for fluctuations in arterial pressure and sympathetic nerve activity that occur during obstructive sleep apnea, we studied neurocirculatory responses to Mueller maneuvers and breath holds in conscious humans. During 20-s Mueller maneuvers at -40 mmHg, mean arterial pressure fell initially (-11 +/- 3 mmHg) and then rose above baseline (+8 +/- 3 mmHg) on release of the inspiratory strain. Sympathetic outflow to skeletal muscle was almost completely suppressed during the initial moments of the maneuver and rose to more than three times the baseline level at the termination of the maneuver. Simple 20-s breath holds were accompanied by time-dependent increases in both arterial pressure (+11 +/- 3 mmHg) and sympathetic nerve activity (> 3 times baseline). The administration of supplemental O2 greatly attenuated the increases in arterial pressure and sympathetic nerve activity during Mueller maneuvers and breath holds. We conclude that carotid chemoreflex stimulation is the primary mechanism responsible for apnea-induced sympathetic activation during wakefulness and that it may contribute importantly to the sympathetic activation that accompanies sleep-disordered breathing.