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Transient cardiorespiratory events during NREM sleep: a feline model for human microarousals
J J Quattrochi1, J Shapiro, R L Verrier
1Laboratory of Neurophysiology, Program in Neuroscience, Harvard Medical School, Boston, USA. jq@hms.harvard.edu
Abstract:
Microarousals (MAs) are brief transient events that occur during normal sleep in humans and with increased frequency in disordered sleep, especially in association with sleep apnoea. In a feline model, we discovered transient cardiorespiratory events during nonrapid eye movement (NREM) sleep that exhibited consistent features with similarities to human MAs. It was observed that MAs have two distinct phases. Phase I (MAI) is characterized by an abrupt increase in electromyogram (EMG) amplitude (> 50%), increased electrooculogram (EOG) activity and accelerated frequency of hippocampal electroencephalographic (EEG) activity. MAI lasts 4.1 +/- 0.3 s. Phase II (MAII), lasting 9.8 +/- 0.8 s, is characterized by high frequency EEG activity, but EMG, EOG and hippocampal activity remain at baseline levels. Mean inspiratory rate begins to increase 15 s before the onset of the MA, followed 10 s later by the increase in mean heart rate. Mean respiratory rate decreases sharply through MAII, and returns to baseline levels 15 s after the MA. During MAII mean heart rate decreases quickly; there is increased respiratory irregularity, followed by a prolonged ventilatory overshoot. The abrupt shift in heart rate is coincident with the change in breath timing seen during MAII. Heart rate returns to baseline levels 10 s following the MA. Integrating our findings with those described previously in humans, we propose that MAs may serve as a homeostatic mechanism which is designed to restore cardiorespiratory function allowing the continuity of sleep.
Insights
Microarousals (MAs) are brief sleep events. In cats, these cardiorespiratory events during NREM sleep mirror human MAs, suggesting a role in restoring sleep continuity.
Area of Science:
- Sleep Science
- Cardiorespiratory Physiology
- Neuroscience
Background:
- Microarousals (MAs) are transient sleep events, more frequent in sleep disorders like sleep apnea.
- Previous research has primarily focused on human MAs.
Purpose of the Study:
- To investigate cardiorespiratory events during NREM sleep in a feline model.
- To compare feline MAs with human MA characteristics and functions.
Main Methods:
- Utilized polysomnography in a feline model during NREM sleep.
- Analyzed electroencephalogram (EEG), electrooculogram (EOG), and electromyogram (EMG) activity.
- Monitored cardiorespiratory parameters including heart rate and respiratory rate.
Main Results:
- Identified two distinct phases of feline MAs (MAI and MAII) with specific EEG, EOG, and EMG signatures.
- Observed significant cardiorespiratory changes preceding, during, and after MAs, including heart rate shifts and respiratory rate alterations.
- Feline MAs showed consistent features comparable to human MAs.
Conclusions:
- Feline MAs exhibit distinct phasic characteristics and cardiorespiratory changes similar to human MAs.
- MAs may function as a homeostatic mechanism to restore cardiorespiratory stability, ensuring sleep continuity.
- This feline model provides valuable insights into the pathophysiology of human sleep disorders.