Circadian rhythms and sleep have additive effects on respiration in the rat

Oct 2, 2001The Journal of physiology

Daily Body Clock and Sleep Together Influence Breathing in Rats

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Abstract

The 24-hour mean ventilation rate was 363.5 ml min(-1) during wakefulness, significantly higher than during NREM sleep (284.8 ml min(-1)) and REM sleep (276.1 ml min(-1)).

Circadian rhythms were statistically significant in ventilation and metabolic rate across wakefulness, NREM sleep, and REM sleep.
The amplitude and phase of circadian rhythms in ventilation were similar across the different sleep-wake states.
The circadian rhythm in ventilation was linked to a change in respiratory frequency, while tidal volume remained consistent throughout the day.
Ventilation and metabolic rates decreased from wakefulness to NREM sleep and further to REM sleep.
The findings indicate that respiratory and metabolic changes associated with circadian rhythms and sleep-wake states are additive in rats.

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1. We tested two hypotheses: that respiration and metabolism are subject to circadian modulation in wakefulness, non-rapid-eye-movement (NREM) sleep and rapid-eye-movement (REM) sleep; and that the effects of sleep on breathing vary as a function of time of day. 2. Electroencephalogram (EEG), neck electromyogram (EMG) and abdominal body temperature (T(b)) were measured by telemetry in six male Sprague-Dawley rats. The EEG and EMG were used to identify sleep-wake states. Ventilation (V(I)) and metabolic rate (V(CO2)) were measured by plethysmography. Recordings were made over 24 h (12:12 h light:dark) when rats were in established states of wakefulness, NREM sleep and REM sleep. 3. Statistically significant circadian rhythms were observed in V(I) and V(CO2) in each of the wakefulness, NREM sleep and REM sleep states. Amplitudes and phases of the circadian rhythms were similar across sleep-wake states. 4. The circadian rhythm in V(I) was mediated by a circadian rhythm in respiratory frequency (f(R)). Tidal volume (V(T)) was unaffected by time of day in all three sleep-wake states. 5. The 24 h mean V(I) was significantly greater during wakefulness (363.5 +/- 18.5 ml min(-1)) than during NREM sleep (284.8 +/- 11.1 ml min(-1)) and REM sleep (276.1 +/- 13.9 ml min(-1)). V(CO2) and V(T) each significantly decreased from wakefulness to NREM sleep to REM sleep. f(R) was significantly lower in NREM sleep than in wakefulness and REM sleep. 6. These data confirm that ventilation and metabolism exhibit circadian rhythms during wakefulness, and NREM and REM sleep, and refute the hypothesis that state-related effects on breathing vary as a function of time of day. We conclude that the effects of circadian rhythms and sleep-wake state on respiration and metabolic rate are additive in the rat.

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Circadian rhythms and sleep have additive effects on respiration in the rat

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