Influence Of Hypoxia, Hypercapnia And Inspiratory Efforts On Sympathoexcitation During Apnea

Abstract

Obstructive Sleep Apnea (OSA) is characterized by frequent periods of apnea resulting in hypoxia, hypercapnia and fluctuations of intrathoracic pressure (inspiratory efforts). Hypoxia, hypercapnia and inspiratory efforts lead to stimulation of peripheral chemoreceptors, central chemoreceptors and baroreceptors, respectively, which in turn influence Muscle Sympathetic Nerve Activity (MSNA). We hypothesized that hypoxia and hypercapnia result in an elevated MSNA response, while inspiratory efforts result in a reduced MSNA response during apnea. To test the hypothesis, we determined the contributions of hypoxia (at 12% O2), hypercapnia (at 3% CO2) and inspiratory efforts (mueller maneuvers at 20 mmHg) to MSNA (using microneurographic techniques) during simulated apnea, respectively. Six healthy subjects and four OSA patients participated in this study. We found that, hypoxia and hypercapnia during apnea resulted in a significant increase in MSNA response from 88.5 ± 9.8 AIU for room air conditions (simulated apnea after breathing room air) to 116.4 ± 9.0 AIU for hypoxia and 121.1 ± 7.4 AIU for hypercapnia, respectively. However, inspiratory efforts during apnea resulted in a significant decrease in MSNA to 78.8 ± 9.3 AIU. Further, it was also found that hypercapnia had a significantly greater influence on MSNA response during apnea as compared to hypoxia and inspiratory efforts. These findings indicate that central chemoreceptors are more sensitive during apneic episodes than peripheral chemoreceptors and baroreceptors.