Do respiration rate and tidal volume significantly affect respiratory sinus arrhythmia (RSA) measures used to assess cardiac vagal tone?
Respiration rate and tidal volume must be controlled when using respiratory sinus arrhythmia as a measure of cardiac vagal tone, as both substantially affect RSA variance.
Respiratory sinus arrhythmia (RSA) or high-frequency heart rate variability has been widely used as a noninvasive measure of cardiac vagal tone. However, their dependency on both respiration rate and tidal volume is largely ignored. Only a minority of studies published in Psychosomatic Medicine in recent years has implemented precautions for controlling respiration rate in RSA measures, and tidal volume effects were only rarely addressed. We discuss methodologic issues related to respiratory control methods and present data that demonstrate that both respiration rate and tidal volume contribute substantially to the within-individual RSA variance under conditions of variable breathing, with tidal volume contributing up to one third beyond respiration rate. Finally, we outline a respiratory control method for the time-domain index of RSA and review research pertaining to its reliability, validity, and experimental application. HRV = heart rate variability; pCO2 = partial pressure of carbon dioxide; RSA = respiratory sinus arrhythmia; RR = respiration rate; TTOT = total respiratory cycle time; VT = tidal volume.
Ritz et al. (Sat,) studied this question.