Determination of Baroreceptor‐Stroke Volume Reflex Sensitivity by Power Spectral Analysis: A Quantitative Probe of Baroreceptor‐Cardiac Reflex

Abstract

Baroreceptor‐cardiac reflex, which consists of baroreceptor‐induced chronotropic and inotropic actions, is a very useful index of cardiac sympathovagal balance. Baroreceptor‐heart rate reflex sensitivity, which reflects baroreceptor‐induced chronotropic action, has been used as a marker of baroreceptor‐cardiac reflex. However, it cannot be used in patients with chronotropic incompetence and/or implanted cardiac pacemaker. We hypothesized that baroreceptor‐stroke volume (SV) reflex sensitivity, which reflects baroreceptor‐induced inotropic action, may also be a useful method for measurement of baroreceptor‐cardiac reflex, similar to the baroreceptor‐heart rate reflex sensitivity. To test this hypothesis, we measured baroreceptor‐SV reflex sensitivity expressed as ratio of low frequency (LF) power to total power of SV fluctuation (LF/TPsv: %/mmHg) by spectral analysis of mean blood pressure and SV fluctuations, the gain in low‐frequency band between two signals in supine and 60° upright positions, and compared these values to baroreceptor‐heart rate reflex sensitivity in 14 healthy subjects. Baroreceptor‐SV reflex sensitivity correlated significantly with baroreceptor‐heart rate reflex sensitivity (r = 0.73, p < 0.0001). In addition, baroreceptor‐SV reflex sensitivity correlated significantly and positively with high frequency (HF) power (r = 0.57, p < 0.005) and negatively with LF/HF ratio (r = − 0.57, p < 0.005) in power spectral analysis of R‐R interval variability. Moreover, baroreceptor‐SV reflex sensitivity in LF/TPSV correlated positively with the R‐R interval (r = 0.70, p < 0.0001) and negatively with diastolic blood pressure (r = − 0.50, p < 0.01). We conclude that baroreceptor‐SV reflex sensitivity in LF/TPSV can be used as a quantitative probe of baroreceptor‐cardiac reflex, similar to the baroreceptor‐heart rate reflex sensitivity in healthy subjects, and it may enable us to estimate inotropic aspect in baroreceptor‐cardiac reflex in patients with chronotropic incompetence and/or implanted pacemaker.