The Circadian Rhythm of Thermoregulation Modulates both the Sleep/Wake Cycle and 24 h Pattern of Arterial Blood Pressure

Abstract

Borbély proposed an interacting two-component model of sleep regulation comprising a homeostatic Process S and a circadian Process C. The model has provided understanding of the association between core body temperature (CBT) as a key element of Process C that is deterministic of sleep onset and offset. However, it additionally provides a new perspective of the importance of the thermoregulatory mechanisms of Process C in modulating the circadian rhythm of arterial blood pressure (ABP). Herein, we examine the circadian physiology of thermoregulation, including at the end of the activity span the profound redistribution of cardiac output from the systemic circulation to the arteriovenous anastomoses of the glabrous skin that markedly enhances convective transfer of heat from the body to the environment to cause (i) decrease of the CBT as a pathway to sleep onset and (ii) attenuation of the asleep ABP mean and augmentation of the ABP decline (dipping) from the wake-time mean, in combination the strongest predictors of the risk for blood vessel and organ pathology and morbid and mortal cardiovascular disease events. We additionally review the means by which blood perfusion to the glabrous skin can be manipulated on demand by selective thermal stimulation, that is, mild warming, on the skin of the cervical spinal cord to intensify Process C as a way to facilitate sleep induction and promote healthy asleep ABP.

Inverse Association of Skin Temperature With Ambulatory Blood Pressure and the Mediation of Skin Temperature in Blood Pressure Responses to Ambient Temperature

“…Meanwhile, the circadian pattern of core body temperature, resulting from the endogenous circadian rhythm of heat production and loss, 32 affects the 24-hour pattern of BP through vasomotor modulation of the AVAs. 12 The clinical implication of our findings is that ST manipulation can contribute to BP regulation, such as by lowering BP variability and nighttime BP. Our results suggested that smaller changes in ST, especially in DST during the daytime, may lead to lower ambulatory BP variability.…”

“…Meanwhile, the circadian pattern of core body temperature, resulting from the endogenous circadian rhythm of heat production and loss, 32 affects the 24-hour pattern of BP through vasomotor modulation of the AVAs. 12…”

“…13 AVAs modulate vascular resistance to regulate body temperature through the homeostatic and circadian system, resulting in BP changes. 12,14 Skin temperature (ST), which results from thermoregulatory responses to our external and internal thermal environment, 14 reflects the effect of thermal exposure on our bodies. Direct ST regulation with heat retention or passive heating may prevent BP elevation and excessive BP fluctuation by modulating the effect of ambient temperature on BP.…”

“…Skin has the potential to receive enormous blood flow, which can exceed 7 L/minutes. 10–12 Arteriovenous anastomoses (AVAs), which exchange heat via glabrous skin regions of the hands and feet, are direct connections between arterioles and venules that bypass high-resistance capillaries. 13 AVAs modulate vascular resistance to regulate body temperature through the homeostatic and circadian system, resulting in BP changes.…”

Estimation of Heart Rate Variability Parameters by Machine Learning Approaches Applied to Facial Infrared Thermal Imaging

“…Particularly, the venous return and the cardiac output are also modulated by the heat transfer from skin to blood, and subsequently to the body core ( 56 ). However, it is worth to highlight that the superficial microcirculation is influenced also by local factors, hence, it could be licit to suppose that the not optimal correspondence between the estimated and measured HRV metrics is related to different physiological mechanisms underlying the cardiac rhythm and the skin temperature modulations ( 57 ). In addition, it is useful to highlight that PPG signals could vary based on the measurement site and the skin temperature.…”