Short-term reduction in sleep irregularity modulates cardiac autonomic function and central hemodynamic parameters at rest.

Fluctuation in sleep/wake timing, often referred to as sleep irregularity, is associated with elevated risk for cardiovascular disease. We sought to determine the effect of reducing sleep irregularity on cardiac autonomic function and hemodynamic parameters. Sixteen adults (35 ± 10 years) were randomly assigned to 12 nights of regular sleep timing or habitual sleep (control) completed in a crossover fashion. Sleep was assessed using wrist actigraphy. Laboratory testing took place the morning after each 12-night period. Short-term EKG recordings were used to evaluate heart rate variability (HRV, index of cardiac autonomic function). Central aortic blood pressure, augmentation index, and subendocardial viability ratio (SEVR, estimate of coronary flow reserve) were also measured at rest. Sleep duration irregularity (standard deviation) was reduced following regular sleep timing as compared to habitual sleep (57 ± 14 to 31 ± 14 min, P < 0.001) despite similar average sleep duration (P = 0.27). Regular sleep timing decreased resting heart rate (65 ± 7 to 62 ± 9 bpm, P = 0.005), increased HRV (root mean square of successive differences between normal heartbeats, 34 ± 17 to 42 ± 20 ms, P = 0.009), and improved SEVR (1.54 ± 0.22 to 1.68 ± 0.30 ms, P = 0.001) as compared to habitual sleep. No significant (P > 0.05) change was observed for the other measures. These results demonstrate that a short-term reduction in sleep irregularity confers favorable cardiovascular benefits to cardiac autonomic function and coronary flow reserve but does not alter central blood pressure.