Normal Heart Rate During Sleep
The normal heart rate during sleep is typically between 40-60 beats per minute, with nocturnal heart rate being assessed by using 2-hour rolling averages to detect the lowest mean heart rate during the reported sleeping window. 1
Physiological Changes in Heart Rate During Sleep
Heart rate during sleep follows distinct patterns based on sleep stages:
- Non-REM Sleep: Heart rate decreases significantly from the awake state, with the low-frequency to high-frequency ratio (LF/HF) decreasing from approximately 4 to 1.22, indicating parasympathetic (vagal) dominance 2
- REM Sleep: Heart rate increases compared to non-REM sleep, with the LF/HF ratio rising to around 3, approaching awake levels 2
- Overall Sleep: Generally characterized by vagal dominance compared to wakefulness 2
Normal Heart Rate Ranges During Sleep
- Base heart rate (minimum and stable HR during sleep): Approximately 49±4 beats per minute in normotensive subjects 3
- Age effect: Base heart rate tends to rise with increasing age (r = 0.51, P < 0.01) 3
- Trained athletes: May have resting heart rates as low as 30 beats per minute during sleep with associated pauses or type I second-degree AV block resulting in asystole as long as 2.8 seconds 1
Heart Rate Variability During Sleep
Heart rate variability (HRV) serves as an important indicator of autonomic nervous system function during sleep:
- Respiratory sinus arrhythmia: Normal phenomenon where heart rate increases during inspiration and decreases during expiration 4
- Sleep stages: Each sleep stage has a distinct pattern of heart rate response and respiratory arrhythmia 5
- Normal variations: Sinus pauses of variable duration may occur during sleep, particularly in trained athletes 1
Clinical Considerations
- Bradyarrhythmias during sleep: Predominantly exaggerated sinus arrhythmias and transient AV block, which typically occur during REM sleep 5
- Sleep apnea: Can cause significant bradycardia that worsens with increased apnea length and oxyhemoglobin desaturation 6
- Monitoring methods: Nocturnal heart rate can be assessed using continuous HR recordings, with the lowest values typically observed during sleep 1
Potential Pitfalls in Assessment
- Confounding factors: Sleep quality, sleep stage, age, fitness level, and medical conditions can all affect heart rate during sleep
- Device considerations: When using wearable devices, ensure proper calibration and be aware that some devices may adjust sampling rates based on activity level 1
- Interpretation challenges: Distinguishing between physiological bradycardia (e.g., in trained athletes) and pathological bradycardia requiring intervention 1
For accurate assessment of nocturnal heart rate, continuous monitoring during sleep is recommended, with attention to the lowest mean heart rate during the reported sleeping window, which provides valuable information about cardiovascular health and autonomic function.