Mapas conceptuales y organizadores gráficos:

BP decreases during sleep, and reduced dipping of BP during sleep increases cardiovascular risk.⁶⁹ Calhoun et al reported that during normal sleep, there is a decrease in BP relative to wakefulness and partly is attributable to decrease in sympathetic output.⁶⁹ While Ogawa et al showed that diastolic blood pressure was significantly higher after total sleep deprivation than after control sleep (66.5 ±1.7 vs 57.4 ± 3.3 mm Hg) and this was due to increase in sympathetic activity.¹²⁶ This showed that maintaining and improving sleep will reduce blood pressure and improve blood pressure control in hypertensive patients. The Sleep Heart study showed that a night of sleep restriction to a mean of 3.6 hours due to working overtime was associated with a 6mmHg increase in mean SBP and a 3-mm Hg increase in mean DBP, compared with a night of 8 hours sleep. Lusardi and colleagues found that a single night of experimental sleep restriction of 4 hours of sleep in the home setting resulted in a 4mmHg and 7mmHg increase in mean morning SBP in normotensive and hypertensive subjects respectively. Smaller increases in mean morning DBP was also observed.²³ The same group reported increases of 22mmHg in mean SBP and 17mmHg in mean DBP across 10 days of

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partial sleep deprivation to 4hours per night in four experimental subjects, but this was not significantly different from the 10mmHg increase in mean SBP and 13mm Hg increase in mean DBP observed in the 5 control subjects.²³ On the other hand, study by Haack and colleagues demonstrated that increasing average nightly sleep duration by approximately 30 min over a 6-week period led to a significant reduction of beat-to-beat SBP and DBP in hypertensive and pre-hypertensive subjects, while the control group who maintained their habitual sleep duration did not show a significant reduction in BP.⁴⁵ The findings suggested that behavioral interventions designed to increase sleep duration may serve as an effective strategy in the treatment of high BP.⁴⁵ The study also showed that when compared with standard behavioral intervention strategies, such as exercise and dietary interventions, the BP reduction in response to increased sleep duration appears to be of comparable magnitude.⁴⁵ Systolic and diastolic beat-to-beat blood pressure averaged across the 24-hour recording period significantly decreased from pre- to post-intervention visit in the sleep extension group that had improved by 14 + 3 and 8 +3mmHg, respectively (P < 0.05). Though the reduction of 7 + 5 and 3 + 4mmHg in the sleep maintenance group was not significant, it did not differ from the blood pressure reduction in the sleep extension group (P = 0.15 for interaction effect).⁴⁵

Improving sleep by increasing sleep extension in the study reduced systolic blood pressure by 14mmHg and the arm without sleep extension had a reduced SBP by 7mmHg.⁴⁵ This reduction of BP in the sleep maintenance group may reflect habituation to the Clinical Research Centre environment, but may also reflect the fact that the sleep maintenance group was an “active” Control (i.e. subjects in this group, as well as in the sleep extension group, were asked to follow a set of sleep hygiene instructions, such as maintaining regularity of bedtimes).While total sleep deprivation over 3 days in healthy volunteers showed an average increase of 7 and 4mmHg for SBP and DBP, respectively.¹²⁷ Haack et al showed that

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elevating effect of short sleep duration is reversible by increasing habitual sleep duration.

This BP-lowering effect of sleep extension was evident after an intervention period of 6 weeks.⁴⁵ The time course of this effect is unknown; that is whether the change in BP was a function of successive days of sleep extension, because the study was designed with only a single visit.⁴⁵ On the other hand, Kubo et al failed to find a BP-lowering effect of sleep extension of 2 hours per weekend day over a period of one week in workers with habitual sleep durations of less than 6 hours.¹²⁸ Comprehensive lifestyle interventions over a 9-week period, including dietary and exercise interventions, reduced 24-hour ambulatory SBP and DBP by 10 and 5mmHg, respectively.¹²⁹ Compared with these standard behavioral interventions, it appears that the sleep extension approach to improve sleep may serve as an effective strategy in the treatment of high BP, either alone or in combination with standard lifestyle modification.⁴⁵

Vgontzas and colleague showed that chronic insomniacs (individual with sleep difficulty) who slept five or less hours or 5-6 hours, respectively, for more than one year had a high risk of hypertension than subjects who slept > 6 hours and had no sleep complaint.¹²⁴ In contrast, insomniacs who slept ≥ 6 hours did not show an increased risk for hypertension compared to the control group. Subjects with the milder form of insomnia (difficulty falling or staying asleep) had a significantly higher risk for hypertension when they slept ≤ 5 hours and a non-significantly increased risk when they slept 5-6 hours compared to the control group.¹²⁴ Gangwisch et al found that progressively, older age groups had increasingly lower percentages of subjects who reported 7-hour sleep durations and increasingly higher percentages who reported long and short sleep durations. The most likely explanations for this finding are a cohort effect and changes in sleep durations over time, whereby, as individuals age, they become less likely to sleep 7 hours and more likely to sleep 5 hours or less or 9 hours or more.¹³⁰

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