Development of a new method for assessing the cardiac baroreflex: response to downward tilting in patients with diabetes mellitus

OBJECTIVE: To investigate the clinical value of a new non-invasive method for assessing baroreflex sensitivity using downward tilting. PATIENTS: 34 patients with diabetes mellitus, mean (SD) age, 53.6 (11.8) years. DESIGN: Arterial blood pressure and ECG were recorded simultaneously while the patients were on a tilt table. After 20 minutes at a 70 degrees upright tilt, the patients were returned to the supine position at a speed of 3.2 degrees /s (downward tilting baroreflex sensitivity test, DT-BRS). A beat to beat systolic blood pressure increase associated with a corresponding lengthening of the RR interval was noted during downward tilting. Baroreflex sensitivity was also assessed using the conventional method of an intravenous injection of phenylephrine (Phe-BRS). Heart rate variability was analysed during rest and tilting. RESULTS: The slope of the regression line for systolic blood pressure v RR interval during downward tilting was highly correlated with Phe-BRS (r = 0.83, p < 0.0001). Both DT-BRS and Phe-BRS were correlated with the high frequency (HF) component of resting heart rate variability (p < 0.005) and with the ratio of the low frequency to the high frequency component (LF/HF) during upright tilting (p < 0.005). DT-BRS and Phe-BRS were also correlated with the difference between rest and tilting values of HF and LF/HF (p < 0.005). CONCLUSIONS: DT-BRS provides a physiological, non-invasive method for determining baroreflex sensitivity and may be a useful index of reflex cardiac vagal and sympathetic function in patients with diabetes mellitus.