Effect of Mild, Asymptomatic Obstructive Sleep Apnea on Daytime Heart Rate Variability and Impedance Cardiography Measurements

Abstract

Dysregulation of autonomic nervous system dynamics is important in the pathophysiology of cardiovascular risk in obstructive sleep apnea (OSA). Heart rate variability (HRV) and impedance cardiography measures can estimate autonomic activity but have not gained traction clinically. We hypothesized that, even in a cohort of mild, asymptomatic OSA patients without overt cardiovascular disease, daytime HRV metrics and impedance cardiography measurements of pre-ejection period (PEP) would demonstrate increased sympathetic and decreased parasympathetic modulation compared with matched controls. Obese individuals (BMI ≥30 kg/m2) without any known cardiovascular or inflammatory comorbidities were recruited from the community. Subjects underwent standard in-laboratory polysomnograms (PSG), followed by simultaneous electrocardiography (ECG) and impedance cardiography recordings while supine, supine with paced breathing, and after standing. 74 subjects were studied, and 59% had OSA (apnea-hypopnea index (AHI) ≥10episodes/hr) with a median AHI of 25.8/hr. OSA subjects had significantly decreased daytime time- and frequency-domain HRV indices, but not significantly different PEP, when compared to controls. AHI was a significant independent predictor of time-domain HRV measures in all awake conditions, after controlling for age, gender, blood pressure, fasting cholesterol levels and hemoglobin A1C. In conclusion, our results demonstrate reductions in cardiac vagal modulation, as measured by multiple daytime time-domain markers of HRV, among asymptomatic OSA patients versus controls. Further prospective outcomes-based studies are needed to evaluate the applicability of these metrics for noninvasive screening of obese asymptomatic OSA patients, prior to the onset of overt cardiovascular disease.

Heart Rate Variability in Obstructive Sleep Apnea.

“…Our findings regarding the heart rate variability in patients with OSAS need to be considered in the light of findings of other researchers like Balachandran et al who studied heart rate variability (HRV) and even found evidence of decrease in cardiac vagal modulation in asymptomatic OSA subjects using time-domain and frequency-domain HRV indices 15 . They proposed conducting further studies to explore the possibility of using heart rate variability for the noninvasive screening of obese asymptomatic OSA patients before they develop overt cardiovascular disease 15 .…”

“…They proposed conducting further studies to explore the possibility of using heart rate variability for the noninvasive screening of obese asymptomatic OSA patients before they develop overt cardiovascular disease 15 . Narkiewicz et al even felt that there may be a link between the degree of alteration in cardiovascular variability and the severity of OSA 16 .…”

“…HF, LF, and VLF); they found that HRV improves in the first night of CPAP use in severe OSA patients and suggested that CPAP treatment should not be delayed in such patients 14 . Balachandran et al studied HRV in asymptomatic OSA patients and controls and found that daytime time-domain and frequency-domain HRV indices were significantly decreased in asymptomatic OSA subjects demonstrating a decrease in cardiac vagal modulation and suggested that further studies should be done to evaluate these indices for the non-invasive screening of obese asymptomatic OSA patients before they develop overt cardiovascular disease 15 . Narkiewicz et al found that altered cardiovascular variability in patients with OSA is seen even in the absence of other diseases like hypertension and heart failure and that there may be a link between the degree of alteration in cardiovascular variability and the severity of OSA 16 .…”

Contribution of Autonomic Nervous System to the Hypertension Induced by Obstructive Sleep Apnea

“…HF power reflects the activity of parasympathetic nervous system activity, whereas LF power reflects a combination of sympathetic and parasympathetic activity [92,105]. OSA patients showed increased sympathetic and reduced vagal modulation of HRV in comparison with controls [2,4]. This symphato-vagal imbalance is modified with CPAP therapy; in OSA patients with hypertension CPAP administration reduced the LF power [11,114].…”

Impedance cardiography: Recent advancements

“…Balachandran et al [22] used heart rate variability (HRV) and pre-ejection period (PEP) derived from ICG traces, to estimate autonomic activity. The hypothesis of their study was that even in a cohort of patients with mild, asymptomatic obstructive sleep apnoea without overt cardiovascular disease, daytime HRV metrics and ICG measurements of pre-ejection period would demonstrate increased sympathetic and decreased parasympathetic modulation compared to matched controls.…”