Relationship between heart rate excursion and apnea duration in patients with Obstructive Sleep Apnea

Obstructive Sleep Apnea (OSA) is a sleep disorder with a high prevalence in the general population. It is a risk factor for many cardiovascular diseases, and an independent risk factor for cerebrovascular diseases such as stroke. After an apnea episode, both arterial blood pressure and cerebral bood flow velocity change in function of the apnea duration (AD). We hypothesized that the relative excursion in heart rate (ΔHR), defined as the percentage difference between the maximum and the minimum heart rate values associated to an obstructive apnea event, is also related to AD. In this work we studied the relationship between apnea-related ΔHR and AD in a population of eight patients with severe OSA. DHR and AD showed a moderate but statistically significant correlation (p < 0.0001) in a total of 1454 obstructive apneas analyzed. The average heart rate excursion for apneas with AD ≥ 30s equation was significantly greater (p = 0.0002) than for apneas with AD ∈ (10,20)s equation. We also observed that patients with similar Apnea-Hypopnea Index (AHI) may exhibit remarkably different distributions of ΔHR and AD, and that patients with a high AHI need not have a higher average ΔHR than others with a lower severity index. We conclude that the overall apnea-induced heart rate excursion is partially explained by the duration of apnoeic episodes, and it may be a simple measure of the cardiovascular stress associated with OSA that is not directly reflected in the AHI.