A noninvasive measure of baroreflex sensitivity without blood pressure measurement

Baroreflex sensitivity (BRS) and heart rate variability (HRV) are attenuated in cardiovascular disease and can give important prognostic information. Conventional measures of BRS require expensive or invasive equipment for the beat-to-beat measure of blood pressure (BP). We examined the possibility of developing a simple protocol that would provide a relatively standardized BP stimulus, which might obviate the need to measure BP beat-by-beat.

Fifty-five patients with chronic heart failure (mean age 59 [SD 11] years) and 20 healthy control subjects (mean age 53 [SD 14] years, P not significant) underwent 5-minute recordings of BP (by photoplethysmograph) and R-R interval during 0.1-Hz controlled breathing. The size of the oscillations in BP was the same in the 2 groups (3.6 mm Hg vs 4.1 mm Hg, P =.5). There was, however, a significant difference in the amplitude of the R-R interval oscillations (77 ms vs 31 ms, P <.0001). The amplitude of the R-R interval oscillations correlated strongly with BRS (r = 0.81, P <.0001 with controlled breathing BRS, and r = 0.51, P <.0001 with alpha index). There was no correlation with the size of BP oscillations (r = -0.13, P not significant with controlled breathing BRS, and r = -0.15, P not significant with alpha index). In a separate study, a group of 22 young patients (mean age 36 years) with type I diabetes mellitus and 28 healthy control subjects (mean age 39 years) underwent measurement of resting HRV and amplitude of R-R interval oscillations during 0.1-Hz breathing. There was no significant difference in triangular index or low-frequency R-R interval power between the 2 groups. There was, however, a significant difference in the amplitude of R-R interval oscillations during controlled breathing between patients with diabetes and healthy control subjects. Total and high-frequency RR interval variability was also significantly different between the 2 groups.

During 0.1-Hz breathing, the marked difference in BRS between patients with CHF and age-matched control subjects is the result of smaller R-R interval oscillations. In young patients with diabetes, these R-R interval oscillations are significantly smaller than age-matched control subjects, even when some measures of spontaneous HRV are not different between groups. Breathing at 0.1 Hz provides a standard BP stimulus and concentrates spectral power of heart rate at one frequency, enabling simple evaluation of BRS even when BP measurement is not available.