Cardiac activity during sleep onset.
Level 4 - case-series / case-control
Small observational physiological repeated-measures study without a control group
PubMed 10352553 · doi:10.1017/s0048577299980198
What was done
Cardiac and respiratory activity was evaluated during sleep onset in 6 participants over 3 experimental nights. Sleep onset was categorized into four sequential phases: wakefulness, mixed alpha and theta activity, stage 2 NREM sleep with arousals, and stable stage 2 sleep. Outcomes measured were heart rate (HR), respiratory sinus arrhythmia (RSA), pre-ejection period (PEP), T-wave amplitude (TWA), and respiration rate (RR).
What was found
HR and RR were lower in stable Stage 2 sleep than during wakefulness, while PEP, TWA, and RSA did not change significantly. HR decreased during transitions into sleep and increased following spontaneous arousals, resolving back to sleep levels within 12 beats post-arousal. The abstract does not report exact numerical values or effect sizes.
Why it matters
This study provides descriptive detail on the rapid autonomic adjustments and heart rate recovery kinetics that occur during micro-arousals and the transition into stable non-REM sleep.
Limits
The sample size is extremely small (n = 6), which severely limits statistical power and generalizability. Participant demographic characteristics are not reported in the abstract, and no quantitative values or variance metrics are provided.
Cited by
- contradicts A resting heart rate of 60 beats per minute or below is required to fall into sleep and enter unconsciousness.