The siesta and ambulatory blood pressure: is waking up the same in the morning and afternoon?

We have shown previously that blood pressure (BP) reduction after the siesta is similar to that after night sleep. As cardiovascular events cluster around morning waking hours, when there is a sharp rise of BP and heart rate (HR), the double-product of which is a major determinant of cardiac oxygen consumption, we also investigated changes after the siesta. Twenty-four-hour ambulatory BP monitorings of 156 consecutive patients referred for evaluation of hypertension who reported the siesta (afternoon nap) were analysed. The mean daytime awake BP and HR were 145 +/- 18/80 +/- 10 mm Hg and 71 +/- 11 beats per minute (bpm). During night sleep and the siesta BP decreased significantly (P < 0.00001) to 126 +/- 20/67 +/- 10 and 125 +/- 17/65 +/- 10 mm Hg, respectively. HR decreased during the siesta (69 +/- 11 bpm; P < 0.00001) but even more so (P < 0.00001) during the night (62 +/- 8 bpm; P < 0.00001). When normotensive subjects (n = 38), untreated (n = 33) and treated hypertensives (n = 85) were evaluated separately, they all had similar trends. However, when percentage rise over the sleeping baseline was considered, there were no significant differences in the rise of BP after the siesta and night sleep. The rise in HR for the normotensives and treated hypertensives was 16% and 8%, respectively, higher in the morning than after the siesta (P < 0.0004 and P < 0.001, respectively). The double-product increased significantly more in the morning than after the siesta (both P < 0.0001) in the normotensives (by 20%) and treated hypertensives (by 10%). In untreated hypertensives the rise in HR and double-product was no different between the time periods. In conclusion, there is a higher rise of HR and double-product in the morning. The relatively lower rise after the siesta may indicate a lesser increase in cardiac oxygen consumption and, therefore, lesser potential for acute ischemia.