Abstract Body (Do not enter title and authors here): Introduction. Sleep duration is now recognized as an important determinant of cardiovascular (CV) health. Recently, the CV implications of day-to-day variability in sleep duration have become apparent, with irregular sleep duration associated with increased risk of CV disease, including hypertension. However, the relationship between sleep duration variability and ambulatory blood pressure (BP) patterns in the general population or in patients with CV disease is unknown.
Research Questions. We sought to investigate whether irregular sleep duration is associated with aberrant ambulatory BP or heart rate (HR) profiles in patients undergoing cardiac rehabilitation (CR).
Methods. We recruited a sample of 42 patients with coronary artery disease enrolled in CR at Mayo Clinic Rochester. Participants underwent 24-hour ambulatory BP monitoring and sleep assessment including one week of wrist actigraphy and sleep diary prior to entering CR. Twenty-four hour, awake, and asleep averages were calculated for systolic BP, diastolic BP, and HR. Nocturnal dipping and morning surge were also computed for BP and HR. Sleep regularity was quantified by SD of actigraphy-derived sleep duration and irregular sleep duration was defined as SD >1 hour. Chi-square tests and Mann-Whitney U tests were used to compare groups.
Results. Thirty-six participants (22% females, median age [25^th,75^th IQR] 66.5 [61,75.8] years, body mass index 31.7 [26.9,35.1] kg/m²) had valid actigraphy and ambulatory BP recordings. We found sleep duration SD >1 hour in 36% of them. Demographics and average sleep duration were similar between those with irregular and regular sleep duration (all Ps>0.11). Twenty-four-hour, awake and asleep HR values were comparable between groups (all Ps>0.26). Participants with irregular sleep duration exhibited lower nocturnal HR dipping (9.2 [3.1,11.6] % vs 12.9 [8.9,18.2] %, P=0.019) than their counterparts with regular sleep. Morning HR surge was also attenuated in patients with irregular sleep duration (3 [-1,9] bpm vs 10 [7,14] bpm, P=0.006). Ambulatory SBP and DBP measures did not differ significantly between groups (all Ps>0.17).
Conclusions. High day-to-day variability in sleep duration is linked to blunted nocturnal dipping and morning surge in HR in patients with coronary artery disease enrolled in CR. Because altered ambulatory HR profile predicts unfavorable CV outcomes, evaluation of sleep patterns in the CR setting may yield important prognostic information.