Autonomic nervous activity in rats can be evaluated by blood photoplethysmography-derived pulse rate variability analysis

In humans, pulse rate variability (PRV) obtained from pulse waves (PWs) is utilized to assess cardiac autonomic nervous function which normally heart rate variability (HRV) obtained from inter-beat (RR) intervals of an electrocardiogram (ECG) recording represents. However, the acceptability of PRV as an index of autonomic function in rats has not been evaluated and, therefore, was the aim of the present study. PW and ECG waveforms of normotensive Sprague Dawley (SD) rats and Spontaneously Hypertensive Rats (SHR) were recorded using photoplethysmography of the tail and radiotelemetry. The frequency component in a series of intervals between the maximum points of the second derivative photoplethysmography waveform or between the RR intervals of the ECG waveform was analyzed using the Cooley–Tukey fast Fourier transform algorithm and the correlativity of the low frequency (LF) power, high-frequency (HF) power, and LF/HF ratio were determined. The R-values for the coefficients of determination between parameters from HRV and PRV were above 0.98 in both normotensive and hypertensive rats, indicating that these two analyses provide the same results. Our findings suggest that the PRV method may be an alternative to HRV in rats with hypertension to effectively evaluate autonomic nerve function in drug discovery research. Since oscillometric tail-cuff BP analyses in rats are commonly used in pharmaceutical research, the PRV would provide additional valuable information on cardiac autonomic nervous function during the evaluation of drug efficacy and safety.