Hypoxia-induced vasodilation and effects of regional phentolamine in awake patients with sleep apnea.

Obstructive sleep apnea (OSA) is associated with increased sympathetic nerve activity, endothelial dysfunction, and premature cardiovascular disease. To determine whether hypoxia is associated with impaired skeletal muscle vasodilation, we compared femoral artery blood flow (ultrasound) and muscle sympathetic nerve activity (peroneal microneurography) during exposure to acute systemic hypoxia (fraction of inspired oxygen 0.1) in awake patients with OSA (n=10) and controls (n=8).

Venous but not skeletal muscle interstitial nitric oxide is increased during hypobaric hypoxia.

Systemic hypoxia leads to peripheral vasodilation that serves to counteract the decrease in peripheral oxygen (O(2)) delivery. Skeletal muscle vasodilation associated with hypoxia is due to release of vasodilator substances such as adenosine and/or nitric oxide (NO). We hypothesized that skeletal muscle may act as a source of NO during exposure to hypoxia.

Short-term intermittent hypoxia enhances sympathetic responses to continuous hypoxia in humans.

Short-term intermittent hypoxia leads to sustained sympathetic activation and a small increase in blood pressure in healthy humans. Because obstructive sleep apnea, a condition associated with intermittent hypoxia, is accompanied by elevated sympathetic activity and enhanced sympathetic chemoreflex responses to acute hypoxia, we sought to determine whether intermittent hypoxia also enhances chemoreflex activity in healthy humans. To this end, we measured the responses of muscle sympathetic nerve activity (MSNA, peroneal microneurography) to arterial chemoreflex stimulation and deactivation before and following exposure to a paradigm of repetitive hypoxic apnea (20 s/min for 30 min; O(2) saturation nadir 81.

Sympathetic chemoreflex responses in obstructive sleep apnea and effects of continuous positive airway pressure therapy.

Background: Sympathetic nerve activity is increased in awake and regularly breathing patients with obstructive sleep apnea (OSA). Over time, repetitive hypoxic stress could alter sympathetic chemoreflex function in OSA.

Methods: We determined the responses to acute hypoxia (fraction of inspired oxygen of 0.

Muscle sympathetic nerve activity responses to dynamic passive muscle stretch in humans.

It is suggested that mechanoreceptors in muscle play an important role in the exercise pressor reflex. However, it has not been verified whether isolated stimulation of the mechanoreceptors can induce responses in muscle sympathetic nerve activity (MSNA) in young healthy individuals. We tested the hypothesis that passive stretch of muscle can evoke an increase in MSNA in healthy individuals.

Effects of intermittent hypoxia on sympathetic activity and blood pressure in humans.

Sympathetic nerve activity and arterial pressure are frequently elevated in patients with obstructive sleep apnea (OSA). The mechanisms responsible for chronic sympathetic activation and hypertension in OSA are unknown. To determine whether repetitive apneas raise sympathetic nerve activity and/or arterial pressure, awake and healthy young subjects performed voluntary end-expiratory apneas for 20 s per min for 30 min (room air apneas).

Aging and the exercise pressor reflex in humans.

Background: Blood flow limitation to exercising muscles engages the muscle reflex during exercise, evoking an increase in heart rate (HR), blood pressure (BP), and muscle sympathetic nerve activity (MSNA).

Methods And Results: In the current study, we examined forearm flow and autonomic responses to ischemic handgrip in young and older subjects. We studied 6 younger subjects (mean age 23.

Attenuated sympathetic nerve responses after 24 hours of bed rest.

Bed rest reduces orthostatic tolerance. Despite decades of study, the cause of this phenomenon remains unclear. In this report we examined hemodynamic and sympathetic nerve responses to graded lower body negative pressure (LBNP) before and after 24 h of bed rest.

Obstructive apnea during sleep is associated with peripheral vasoconstriction.

Obstructive apnea during sleep is associated with a substantial transient blood pressure elevation. The mechanism of this pressor response is unclear. In this study we measured muscle sympathetic nerve activity (MSNA), mean arterial pressure (Psa), and mean limb blood velocity as an index of blood flow (MBV, Doppler) and calculated changes in limb vascular resistance during and after apneas during both wakefulness and sleep in patients with the obstructive sleep apnea syndrome.