Analysis of blood pressure-heart rate feedback regulation under non-stationary conditions: beyond baroreflex sensitivity.

The feedback regulation of blood pressure and heart rate is an important indicator of human autonomic function usually assessed by baroreflex sensitivity (BRS). We suggest a new method yielding a higher temporal resolution than standard BRS methods. Our approach is based on a regression analysis of the first differences of inter-heartbeat intervals and blood pressure values. Data are recorded from 23 patients with hypertension and sleep apnoea, 22 patients with diabetes mellitus and 23 healthy subjects. Using the proposed method for 3 min data segments, we obtain average regression coefficients of 9.1 and 3.5 ms mmHg(-1) for healthy subjects in supine and orthostatic positions, respectively. In patients with hypertension, we find them to be 3.8 and 2.6 ms mmHg(-1). The diabetes patients with and without autonomic neuropathy are characterized by 3.1 and 6.1 ms mmHg(-1) in the supine position compared with 1.7 and 3.3 ms mmHg(-1) in the orthostatic position. The results are highly correlated with conventional BRS measures; we find r > 0.9 for the dual sequence method. Therefore, we suggest that the new method can quantify BRS. It is superior in distinguishing healthy subjects from patients both in supine and orthostatic positions for short-term recordings. It is suitable for non-stationary data and has good reproducibility. Besides, we cannot exclude that other regulatory mechanisms than BRS may also contribute to the regression coefficients between the first differences.