Respiratory Sinus Arrhythmia

When the respiratory oscillator frequency-modulates the cardiac drive, a high-frequency heart-rate-variability peak appears at the respiratory frequency (≈ 0.28 Hz) inside the cited 0.15–0.40 Hz vagal band — and only when the two oscillators are coupled. The peak tracks the breathing frequency as it is scaled. Grade [V].

Respiratory modulation of cardiac drive yields an HF-HRV peak at f_resp ≈ 0.28 Hz inside the cited 0.15–0.40 Hz band, present only when coupled and tracking f_resp. [V].

Respiration modulates the heart

Respiratory sinus arrhythmia is reproduced by letting the respiratory oscillator frequency-modulate the cardiac drive, drive = drive₀ + ε·r(t). The diagnostic is the heart-rate-variability spectrum computed from inter-beat intervals.

The lock is defined inside the cited high-frequency HRV window, 0.15–0.40 Hz, which is the standard vagal RSA band. This matters: strong coupling pushes a harmonic outside the band, so the peak must be read within the band to match the physiological definition.

Lock only when coupled

Decoupled, the HRV spectrum shows no in-band peak at the respiratory frequency. Coupled, an HF peak appears essentially at f_resp = 0.2811 Hz (measured peak 0.2784 Hz), and it tracks the respiratory frequency as that frequency is scaled.

Grade

Coupling creates an HF-HRV peak at the respiratory frequency that is absent when decoupled and that tracks f_resp: grade [V]. The band itself is the cited Task-Force window [L].