Baroreflex sensitivity in the elderly: influence of age, breathing and spectral methods

Baroreflex sensitivity (BRS) has been proposed as a diagnostic parameter fo r neurological disorders and as a survival-prognosis parameter in diabetic and cardiac patients. Therefore reference values and the reproducibility of BRS were assessed, taking into account the possible influence of age, gend er, test conditions and some analysis variants. Healthy subjects (n = 191) were randomly selected from the 50-75-year-old general population (the Hoor n Study). Variations in blood pressure and heart rate were recorded non-inv asively during three breathing modes: spontaneous (3 min), slow metronome ( 1 min; 6 breaths/min = 0.1 Hz) and fast metronome (1 min; 15 breaths/min = 0.25 Hz), all in a supine position. From these recordings, BRS was assessed as the transfer gain between changes in blood pressure and heart period, a nd as the GI coefficient. BRS values ranged from 5.0 to 8.9 ms.mmHg(-1). Sl ow metronome breathing resulted in higher BRS values than fast breathing, w hile during spontaneous breathing BRS in the low-frequency band was lower t han that in the high-frequency band (respiratory origin). BRS values decrea sed with lower coherence criteria. BRS-ce was significantly higher than BRS -gain. While regression analysis showed no gender differences, BRS decrease d with age. Therefore age-specific reference values were calculated. The re producibility of BRS values was in general moderate, with reliability coeff icients ranging from 43 to 81% and coefficients of variation ranging from 3 4 to 59%. In conclusion, this study shows age, breathing mode, frequency an d coherence threshold to affect measures of BRS. Therefore these factors sh ould be considered in clinical studies; appropriate reference values are gi ven.