Heart Rate Variability · 心率变异性 "A healthy heart is not a metronome" · 健康的心脏不是节拍器[10]
Mean HR 75 bpmMean RR 800 msSDNN — msRMSSD — mspNN50 —%LF power — ms²HF power — ms²LF/HF —
RR tachogram · RR间期趋势图
Each dot is one heartbeat. Y-axis = RR interval (ms). A healthy heart shows natural variation; a rigid one flatlines.
ECG strip (multi-beat) · 心电图
Notice how the R–R spacing varies beat-to-beat — wider during expiration (slower HR), narrower during inspiration (faster HR). This is respiratory sinus arrhythmia.
Power spectral density · 功率谱密度
LF peak (~0.1 Hz) = baroreflex (mixed ANS). HF peak = vagal / respiratory. LF is NOT "sympathetic" — that's a common misconception.[4][5]
Poincaré plot · 庞加莱图
Each dot: (RRn, RRn+1). Width along the diagonal (SD2) = long-term variability. Width perpendicular (SD1) = vagal beat-to-beat variability. More spread = healthier.
What drives beat-to-beat variation? · 什么驱动逐搏变化？
The autonomic nervous system 自主神经系统
Sympathetic 交感神经
Parasympathetic (vagal) 副交感/迷走神经
Transmitter
Norepinephrine 去甲肾上腺素
Acetylcholine 乙酰胆碱
Receptor
β1 adrenergic
M2 muscarinic
Effect on HR
↑ (speeds up)
↓ (slows down)
Latency
1–3 seconds (slow)
~200 ms (fast, beat-to-beat)
Why?
NE reuptake is slow (seconds)
AChE degrades ACh in ~1 ms
Because parasympathetic response is ~10× faster, it dominates the rapid beat-to-beat HRV you see in the HF band. Sympathetic effects are too slow to modulate HR above ~0.15 Hz.[13]
Frequency bands 频率带
Band
Range
Driver
ANS
HF
0.15–0.4 Hz
Respiratory sinus arrhythmia 呼吸性窦性心律不齐
Parasympathetic
LF
0.04–0.15 Hz
Baroreflex (Mayer waves) 压力感受性反射
Mixed (NOT purely sympathetic)[4]
VLF
0.003–0.04 Hz
Thermoregulation, RAAS
Sympathetic + hormonal
Frank-Starling connection · Frank-Starling联系
Variable RR intervals directly modulate stroke volume: longer diastole → more filling → higher EDV → greater stretch → stronger contraction → bigger SV. HRV produces stroke-volume variability that optimises cardiac output to changing conditions — without any neural command for each individual beat.[10]