Abstract Title

Effects of Acute Intermittent Hypoxia Training on Markers of Cardiac Autonomic Regulation

RAD Assignment Number

401

Presenter Name

Kaethan Bysani

Abstract

Background and Hypothesis: The intermittent episodes of hypoxia observed during apneic events of obstructive sleep apnea (OSA) increase the risk of cardiovascular disease, by altering sympathetic nervous activity (SNA); increased SNA outflow is postulated to be mediated by activation of angiotensin II receptors. Hypoxic apneic episodes were used to simulate short-term OSA with an intermittent hypoxic training (IHT) protocol, while assessing several indices of autonomic control with or without treatment with angiotensin receptor blockers (ARBs). Our hypotheses were: 1)Acute IHT training in healthy patient will increase indices of sympathetic control post-IHT compared to baseline, and 2)blockade of angiotensin II receptors with ARBs will attenuate the change in autonomic control associated with IHT.

Materials and Methods: Eight healthy subjects were studied on two days. On day 1, subjects were treated with placebo or Losartan and IHT. On Day 2, the study was repeated with the alternative treatment (ARB or placebo). The IHT protocol consisted of a 5 minute baseline, then 3 breaths of nitrogen followed by 20 second expiratory apneas with a 40 second recovery period between each apnea for a total of 20 apneas, and then followed by a 5 minute post-IHT period. Heart rate (ECG), beat-to-beat blood pressure (Finometer), and O2 saturation (pulse oximeter) recorded continuously. The following autonomic indices were derived from these measures RRI, pNN50, and HF-RRI as indices of parasympathetic control, and LF-MAP, LF-SAP, and LF-RRI as indices of sympathetic control.

Results: The IHT conditioning produced significant reductions in parasympathetic control (evidenced by RRI, pNN50 and HF-RRI, p<0.05) and increases in sympathetic control (evidenced by LF-MAP, LF-SAP and LF-RRI, p<0.05). Treatment with the ARB did not significantly alter the responses of any of these variables (although the a levels for sympathetic indices were near significance ~0.1-0.15).

Conclusions: Acute IHT training in healthy individuals significantly enhanced the indices of sympathetic control, and reduced the indices of parasympathetic control. The ARB treatment did not significantly affect these measures although the sympathetic measures trended toward significance. Coupled with our prior finding that ARBs reduced the SNA post-IHT, these data suggest that further investigation is needed that includes a larger subject number and longer stimulus period similar to actual OSA.

Research Area

Cardiovascular

Presentation Type

Poster

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Effects of Acute Intermittent Hypoxia Training on Markers of Cardiac Autonomic Regulation

Background and Hypothesis: The intermittent episodes of hypoxia observed during apneic events of obstructive sleep apnea (OSA) increase the risk of cardiovascular disease, by altering sympathetic nervous activity (SNA); increased SNA outflow is postulated to be mediated by activation of angiotensin II receptors. Hypoxic apneic episodes were used to simulate short-term OSA with an intermittent hypoxic training (IHT) protocol, while assessing several indices of autonomic control with or without treatment with angiotensin receptor blockers (ARBs). Our hypotheses were: 1)Acute IHT training in healthy patient will increase indices of sympathetic control post-IHT compared to baseline, and 2)blockade of angiotensin II receptors with ARBs will attenuate the change in autonomic control associated with IHT.

Materials and Methods: Eight healthy subjects were studied on two days. On day 1, subjects were treated with placebo or Losartan and IHT. On Day 2, the study was repeated with the alternative treatment (ARB or placebo). The IHT protocol consisted of a 5 minute baseline, then 3 breaths of nitrogen followed by 20 second expiratory apneas with a 40 second recovery period between each apnea for a total of 20 apneas, and then followed by a 5 minute post-IHT period. Heart rate (ECG), beat-to-beat blood pressure (Finometer), and O2 saturation (pulse oximeter) recorded continuously. The following autonomic indices were derived from these measures RRI, pNN50, and HF-RRI as indices of parasympathetic control, and LF-MAP, LF-SAP, and LF-RRI as indices of sympathetic control.

Results: The IHT conditioning produced significant reductions in parasympathetic control (evidenced by RRI, pNN50 and HF-RRI, p<0.05) and increases in sympathetic control (evidenced by LF-MAP, LF-SAP and LF-RRI, p<0.05). Treatment with the ARB did not significantly alter the responses of any of these variables (although the a levels for sympathetic indices were near significance ~0.1-0.15).

Conclusions: Acute IHT training in healthy individuals significantly enhanced the indices of sympathetic control, and reduced the indices of parasympathetic control. The ARB treatment did not significantly affect these measures although the sympathetic measures trended toward significance. Coupled with our prior finding that ARBs reduced the SNA post-IHT, these data suggest that further investigation is needed that includes a larger subject number and longer stimulus period similar to actual OSA.