Circadian variations in cardiovascular parameters during sleep deprivation

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Abstract
Twelve subjects were kept awake for 64 h under conditions of isolation from external time cues. Activity was sedentary and kept as constant as possible over time, as was intake of food and drink. Cardiovascular variables — blood pressure, heart rate, contractility (IJ-amplitude from ballistocardiogram), T-wave amplitude, QRS, PQ and QT intervals — were assessed every 3 h. At the same intervals, urine samples for catecholamine analysis were obtained. Data were analyzed by analysis of variance and cosinor techniques. Adrenaline excretion showed a pronounced circadian rhythm. Noradrenaline excretion and IJ amplitude showed much weaker rhythmicity, statistically significant only with the cosinor technique. The remaining variables showed no rhythmicity with either technique. It was concluded that constant conditions (including sleep deprivation) markedly disturb or even obliterate the circadian rhythms of cardiovascular variables and urinary noradrenaline excretion. It was also concluded that most of the amplitude of cardiovascular circadian rhythms measured under habitual sleep/wake conditions must be due to the alternation between sleeping and waking. The present data do not, however, rule out the existence of selfsustained circadian rhythmicity in cardiovascular variables; a design including continuous wakefulness may well have concealed endogenous low-amplitude rhythms.