Abstract P058: Regional Sympathetic Activation Induced by Obstructive Apnea

Abstract

Obstructive sleep apnea increases muscle sympathetic nerve activity (SNA) in humans that contributes to cardiovascular dysfunction including hypertension. The purpose of the present study was to determine if there are regional differences in apnea-induced sympathetic activation in rodents. Male Sprague Dawley rats (n: 8, 270-350 g) were anesthetized with urethane (1.2 g/kg i.v.) and prepared for recordings of renal, splanchnic, and lumbar SNA, phrenic nerve activity (PNA), mean arterial pressure (MAP) and heart rate (HR). Animals were exposed to 10 apneas performed by clamping a tracheal tube during 20 s each 2 min in room air. Changes in rectified and integrated (20 ms time constant) SNA were calculated by subtracting background noise after death. Basal MAP and HR were 89 ± 3 mmHg and 402 ± 14 bpm. Apneas in room air produced similar increases in SNA across various nerves (Δ renal: 96 ± 16%; Δ splanchnic: 109 ± 30%, and Δ lumbar: 93 ± 7%). These bursts increase in amplitude and the maximum response occurred in the end of 20 s of obstruction. Apnea also induced hypertension (Δ: 10 ± 2 mmHg), bradycardia (Δ: - 51 ± 25 bpm) and increased in PNA (Δ: 791 ± 194%). To test the contribution of chemoreceptors, obstructive apnea was repeated when animals were breathing 100% oxygen. Basal MAP and HR were 89 ± 3 mmHg and 402 ± 14 bpm. Hyperoxia reduced the sympathetic responses induced by apnea in renal, splanchnic and lumbar SNA (Δ renal: 40 ± 7%, Δ splanchnic: 68 ± 32%, and Δ lumbar: 52 ± 8%). The cardiovascular and respiratory response were also reduced (ΔMAP: 6±1; ΔHR: -22±8 and ΔPNA: 586 ± 149%). Therefore, obstructive apnea induces similar changes in SNA across various end-organs that depend in part of hypoxia stimulus.