Abstract
In this work, we evaluated a non-linear approach to estimate morphological variations in ECG depolarization, in the context of intermittent hypoxia (IH). Obstructive apnea sequences were provoked for 15 minutes in anesthetized Sprague-Dawley rats, alternating with equal periods of normal breathing, in a recurrent obstructive sleep apnea (OSA) model. Each apnea episode lasted 15 s, while the frequency used for each sequence was randomly selected. Average heartbeats obtained before the start and at the end of each episode, were delineated to extract only the QRS wave. Then, the segmented QRS waves were non-linearly aligned using the dynamic time warping (DWT) algorithm. Morphological QRS changes in both the amplitude and temporal domains were estimated from this alignment procedure. The hypoxic and basal segments were analyzed using ECG (lead I) recordings acquired during the experiment. To assess the effects of IH over time, the changes relative to the basal QRS wave were determined, in the intervals prior to each successive events until the end of the experiment. The results showed a progressive increase in the amplitude and time-domain morphological markers of the QRS wave along the experiment, which were strongly correlated with the changes in traditional QRS markers (r ≈ 0.9). Significant changes were found between pre-apnea and hypoxic measures only for the time-domain analysis (p<0.001), probably due to the short duration of the simulated apnea episodes.Clinical relevance Increased variability in ECG depolarization morphology during recurrent hypoxic episodes would be closely related to the expression of cardiovascular dysfunction in OSA patients.
Highlights
Repeated episodes of apnea during sleep in patients with obstructive sleep apnea (OSA), can result in a sustained exposure to intermittent hypoxia (IH)
In this work, we evaluated a non-linear approach to estimate morphological variations in ECG depolarization, in the context of intermittent hypoxia (IH)
Obstructive apnea sequences were provoked for 15 minutes in anesthetized Sprague-Dawley rats, alternating with equal periods of normal breathing, in a recurrent obstructive sleep apnea (OSA) model
Summary
Repeated episodes of apnea during sleep in patients with obstructive sleep apnea (OSA), can result in a sustained exposure to intermittent hypoxia (IH). This chronic condition has been linked to some cardiovascular consequences of OSA, including systemic hypertension, myocardial infarction, and stroke among others [1], [2], [3]. To figure out the association between OSA and cardiovascular diseases, many studies have developed experimental models of acute/chronic IH. Cardiovascular functions and the control handled by the autonomic nervous system (ANS) have been widely studied in this setting, through the heart rate variability (HRV) analysis [5], [6] or evaluating ECG markers for characterizing both repolarization and depolarization intervals in both amplitude and temporal domains. Apart from conventional markers, there have been proposed other ECG markers able to robustly quantify morphological changes of the ECG waveforms (QRS complex and T wave), such as the QRS slopes and angles [7] and non-linear measures derived from dynamic time warping (DTW) analysis [8]
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