Physiological mechanism of digital vasoconstriction training

The thermophysiological cascade leading to sleep initiation in relation to phase of entrainment

This article reviews circadian thermoregulation in relation to sleep induction and phase of entrainment in the light of the comprehensive thermophysiological and chronobiological concepts of Jürgen Aschoff. The idea that temperature and sleep are interrelated is based on evolutionary history. Mammalian sleep developed in association with endothermy, and all species, independent of temporal niche, usually sleep during the circadian trough of their core body temperature (CBT) rhythm. The circadian pattern of CBT results from the balance between heat production and heat loss, the latter being relevant for sleep induction. Sleep under entrained conditions is typically initiated on the declining portion of the CBT curve when its rate of change and body heat loss is maximal. Body heat loss before lights off, via selective vasodilatation of distal skin regions, promotes sleepiness and the rapid onset of sleep. This thermophysiological effect represents the cement between the circadian clock and the sleep-wake cycle, and in turn determines phase of entrainment (Psi) and sleep onset latency (SOL). These interrelationships have been recently studied in a particular subset of the general population, mainly women, who suffer from cold hands and feet (the so-called vasospastic syndrome, VS). Women with VS exhibit not only a lower capacity to lose heat during the daytime but also a prolonged SOL, a disturbed Psi of the circadian clock with respect to the sleep-wake cycle and psychologically, a disposition to turn experienced anger inwards. This naturalistic model leads us to a more general conclusion that regulation of distal skin blood flow may have clinical relevance for insomnia, in particular sleep onset insomnia.

The human sleep–wake cycle reconsidered from a thermoregulatory point of view

Sleep is typically initiated on the declining portion of the circadian rhythm of core body temperature (CBT) when its rate of change, and body heat loss, is maximal. Distal vasodilatation plays a primary role in the circadian regulation of body heat loss and is strongly associated with sleepiness and sleep induction. In contrast, sleep (i.e. non-REM sleep and slow-wave activity, SWA) has no or only a minor thermoregulatory function. Two lines of evidence support this statement. First, detailed analyses of thermoregulatory changes before and after lights off show clearly that they start before stage 2 sleep begins. Second, accumulation of sleep pressure with increasing time awake, increases subjective sleepiness and SWA during the succeeding recovery night, but does not influence the thermoregulatory system. Taken together, the circadian modulation of sleepiness and sleep induction is clearly associated with thermoregulatory changes, but the thermoregulatory system seems to be independent of the sleepiness/sleep regulatory system. A simplified model is presented which attempts to explain the relationship between these two systems. It is based on the main hypothesis that all thermoregulatory effects which lead to an increase in the core/shell ratio (e.g. a reduced shell by increased distal skin temperature) lead to increased sleepiness and, as a consequence, to increased sleep propensity. However, the sleepiness/sleep regulatory system feeds back onto the thermoregulatory system only indirectly via sleep-related behaviors (e.g. relaxation, lying down).

Thermophysiologic aspects of the three-process-model of sleepiness regulation

The following overview reconsiders the three-process model of sleepiness regulation (homeostatic, circadian, and sleep inertia) from a thermophysiologic point of view. Our results gathered over the last decade indicate that the homeostatic aspect of sleepiness regulation (ie, buildup of sleepiness during wakefulness and its decay during sleep) is not related to the thermoregulatory system, whereas the two other processes of sleepiness regulation (ie, circadian and sleep inertia process) are clearly related to thermoregulation in humans. Distal skin temperature of hands and feet seems to be the crucial variable for the association between thermophysiology, sleepiness, and sleep. Increased distal skin temperature before a nocturnal sleep episode is a good predictor for short sleep-onset latency. The disappearance of sleep inertia after sleep or a nap episode shows very similar kinetics as distal vasoconstriction. Furthermore, relaxation-induced sleepiness (eg, after lying down, at lights-off, with thermal biofeedback training) also evokes an increase in distal skin temperatures. The reverse effect occurs at lights-on or a posture change from supine to standing, Therefore, in terms of thermophysiology, sleep inertia can be explained as the reverse of a relaxation process (ie, decrease in distal skin temperatures). Our results reinterpret the so-called "sleep-evoked" reduction of core body temperature as a consequence of relaxation-induced vasodilatation after lights-off. Sleep per se has no further thermoregulatory effect. Taken together, a thermophysiologic approach may provide a successful strategy to treat sleep-onset insomnia and alleviate sleep inertia.

Development of a multi-channel exploratory battery for psychophysiological assessment: the Stress Profile

OBJECTIVE

As the expanding field of psychophysiology is currently demanding applied methodologies to be used in the clinic, this study aimed to develop a practical multi-channel exploratory battery for psychophysiological evaluation of stress (the Psychophysiological Stress Profile; PSP). The PSP records 6 psychophysiological variables and it is designed to be mainly used in the daily clinic. Moreover, the PSP was intended to be 'the method' to obtain normative and individual psychophysiological patterns, providing relevant information for the therapeutic process.

METHODS

Two hundred and three subjects were evaluated with the PSP in two different contexts: the natural environment and the laboratory. Factorial analysis was applied to obtain psychophysiological profiles. These profiles are based on the covariation among different system responses. The Burt and Tucker Congruence Coefficient was used to compare factorial structures.

RESULTS

A 3-factor structure was obtained in both contexts, Congruence Coefficient indicates that these factorial structures are very similar, indicating the existence of a unique and consistent psychophysiological pattern that characterizes the sample.

CONCLUSIONS

The identified factorial structure shows relevant activation patterns, offering a comprehensive view of the subject's functioning. The structure is consistent through samples and can be considered as normative data for the studied population. PSP has turned out to be a quick and easy-to-use psychophysiological battery that has shown adequate internal consistency for all the recorded variables. In this way, the PSP methodology shows its practical value and usefulness in the assessment process.

Physiological problems of biofeedback control of the pulse rate

Data are presented in this article on the voluntary control of the heart rate in man as a function of individual typological differences in adaptive attributes, in the ecological features of the milieu of habitation and work, as well as in the presence of deviations in the state of health (neuroses, vegetovascular dystonias, etc.). The key significance of training of the rhythmic regulatory processes in the course of biofeedback control is substantiated.

Effects of feedback on the control of skin temperature using the tension-relaxation experiment

The effects of feedback on the control of peripheral skin temperature were examined using a tension-relaxation experiment. Sixteen male undergraduates were assigned to feedback or no-feedback groups and asked to increase the temperature of the right index finger immediately after decreasing with (in the feedback group) or without (in the no-feedback group) feedback during 10 training sessions. A no-feedback transfer session (post-test) followed these sessions. During the training sessions, skin temperature corresponded to instructions in the feedback group, whereas it did not in the no-feedback group. Feedback control did not transfer to the no-feedback condition. These results were discussed in terms of the ceiling-effect hypothesis in the baseline-relaxation type experiment and of the subjects' cognitive events, including strategies.

Physiological mechanisms of temperature biofeedback

Research on the physiological mechanisms of finger temperature biofeedback with normal subjects and Raynaud's disease patients is reviewed. Studies conducted in the author's laboratory have shown that feedback-induced vasodilation is mediated through a non-neural, beta-adrenergic mechanism rather than through reductions in sympathetic nervous system activation. In contrast, feedback-induced vasoconstriction is mediated through the traditional, sympathetic nervous pathway. When used with primary Raynaud's disease patients, feedback-induced vasodilation has achieved reductions in reported symptom frequency ranging from 66% to 92% in controlled investigations. Future research directions are discussed.