Low long-term heart rate variability (HRV), often observed in obstructive sleep apnea (OSA) patients, is a known risk factor for cardiovascular diseases. However, it is unclear how the type or duration of individual respiratory events modulate ultra-short-term HRV and beat-to-beat intervals (RR intervals). We aimed to examine the sex-specific changes in RR interval and ultra-short-term HRV during and after apneas and hypopneas of various durations. Electrocardiography signals, recorded as a part of clinical polysomnography, of 758 patients (396 men) with suspected OSA were analysed retrospectively. Average RR intervals and time-domain HRV parameters were determined during the respiratory event and the 15-s period immediately after the event. Parameters were analysed in three pooled sex-specific subgroups based on the respiratory event duration (10–20 s, 20–30 s, and > 30 s) separately for apneas and hypopneas. We observed that RR intervals shortened after the respiratory events and the magnitude of these changes increased in both sexes as the respiratory event duration increased. Furthermore, ultra-short-term HRV generally increased as the respiratory event duration increased. Apneas caused higher ultra-short-term HRV and a stronger decrease in RR interval compared to hypopneas. In conclusion, the respiratory event type and duration modulate ultra-short-term HRV and RR intervals. Considering HRV and the respiratory event characteristics in the diagnosis of OSA could be useful when assessing the cardiac consequences of OSA in a more detailed manner.
Obstructive sleep apnea (OSA) causes e.g. intermittent blood oxygen desaturations increasing the sympathetic tone. Yet, the effect of desaturations on heart rate variability (HRV), a simple, non-invasive method for assessing sympathovagal balance, has not been comprehensively studied. We aimed to study whether the desaturation severity affects the immediate HRV. We retrospectively analysed the electrocardiography (ECG) signals in 5-minute segments (N=39 132), recorded during clinical polysomnography, of 642 suspected OSA patients. HRV parameters were calculated for each segment. The segments were pooled into severity groups based on the desaturation severity (DesSev, the integrated area under the blood oxygen saturation curve) and the respiratory event rate within the segment (Ev). Covariate-adjusted regression analyses were performed to investigate the possible confounding effects of e.g., comorbidities. With increasing Ev, the normalized high-frequency band power (HFNU) decreased from 0.517 to 0.364 (p<0.01), the normalized low-frequency band power (LFNU) increased from 0.483 to 0.636 (p<0.01), and the mean RR interval decreased from 915 to 869 ms (p<0.01). Similarly, with increasing DesSev, the HFNU decreased from 0.499 to 0.364 (p<0.01), the LFNU increased from 0.501 to 0.636 (p<0.01), and the mean RR interval decreased from 952 to 854 ms (p<0.01). DesSev-related findings were confirmed by considering the confounding factors in the regression analyses. In conclusion, the short-term HRV response differs based on the desaturation severity and the respiratory event rate in suspected OSA patients. Therefore, a more detailed analysis of the HRV and desaturation characteristics could enhance the OSA severity estimation.
Obstructive sleep apnea (OSA) is related to the progression of cardiovascular diseases (CVD); it is an independent risk factor for stroke and is also prevalent post-stroke. Furthermore, heart rate corrected QT (QTc) is an important predictor of the risk of arrhythmia and CVD. Thus, we aimed to investigate QTc interval variations in different sleep stages in OSA patients and whether nocturnal QTc intervals differ between OSA patients with and without stroke history. 18 OSA patients (apnea-hypopnea index (AHI)≥15) with previously diagnosed stroke and 18 OSA patients (AHI≥15) without stroke history were studied. Subjects underwent full polysomnography including an electrocardiogram measured by modified lead II configuration. RR, QT, and QTc intervals were calculated in all sleep stages. Regression analysis was utilized to investigate possible confounding effects of sleep stages and stroke history on QTc intervals. Compared to patients without previous stroke history, QTc intervals were significantly higher (β = 34, p<0.01) in patients with stroke history independent of age, sex, body mass index, and OSA severity. N3 sleep (β = 5.8, p<0.01) and REM sleep (β = 2.8, p<0.01) increased QTc intervals in both patient groups. In addition, QTc intervals increased progressively (p<0.05) towards deeper sleep in both groups; however, the magnitude of changes compared to the wake stage was significantly higher (p<0.05) in patients with stroke history. The findings of this study indicate that especially in deeper sleep, OSA patients with a previous stroke have an elevated risk for QTc prolongation further increasing the risk for ventricular arrhythmogenicity and sudden cardiac death.
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