Non-invasive ambulatory blood pressure variability and cardiac baroreflex sensitivity

The objective of this study was to evaluate the relationship between non-invasive ambulatory blood pressure variability and cardiac baroreflex sensitivity in hypertensive patients.

Ambulatory blood pressure measurements (15-min intervals for 24 h) and continuous blood pressure measurements (Finapres, 20 min at rest after a 10-min resting period) were performed in 123 untreated hypertensives (resting diastolic blood pressure > or = 90 mmHg; 80 males, 43 females; mean +/- SD age 49 +/- 12 years, range 19-73). Fourier series were used to model 24-h blood pressure profiles (four harmonics). Ambulatory blood pressure variability was assessed by determination of the residuals in each 24-h blood pressure profile (measured minus predicted pressures). Resting blood pressure variability was defined as the SD of the mean Finapres value. Baroreflex sensitivity was evaluated by automatic detection of blood pressure and pulse interval sequences of > or = 3 beats when systolic blood pressure and pulse interval sequences changed in the same direction (increase or decrease: 1 mmHg for systolic blood pressure and 4 ms for RR interval), and was assessed as the slope of the regression line for each sequence.

Ambulatory systolic blood pressure variability increased with age (r = 0.28*) and systolic pressure (r = 0.44**). Baroreflex sensitivity (increasing systolic pressure/pulse interval) decreased significantly with age (r = -0.48**) and systolic pressure (r = -0.23**), and was significantly related to increased ambulatory blood pressure variability (r = -0.33**). In a multivariate stepwise analysis the relationship between ambulatory blood pressure variability and baroreflex sensitivity (increasing systolic pressure/pulse interval) was statistically independent of age and systolic pressure (R = 0.55, P<0.001); this relationship was not observed with the corresponding decreasing sequence.

This study shows that in uncomplicated hypertension, ambulatory blood pressure variability is related to baroreflex sensitivity independently of the blood pressure level. This finding has prognostic implications for this non-invasive measurement, which needs to be confirmed by large longitudinal studies.