The ambulatory measurement of posture, thigh acceleration, and muscle tension and their relationship to heart rate

We compared the relative ability of continuous accelerometric, electromyographic (EMG), and hydrostatic posture measurements to discriminate tasks involving variations in motor activity and posture and to predict heart rate (HR) variability. EMG was a more sensitive measure than accelerometry in differentiating the tasks. However, accelerometry and EMG explained comparable amounts of HR variance. The hydrostatic posture was a stable measure that clearly differentiated postures and explained a significant amount of HR variance but less than accelerometry or EMG. Accelerometric and EMG measures of motor activity used either alone or in combination with the hydrostatic posture are valuable in discriminating activities and in controlling for the effects of motor activity and posture on HR during ambulatory measurement.

The relationship between cardiovascular reactivity in the laboratory and heart rate response in real life: active coping and beta blockade

Earlier studies suggest that cardiovascular responses in the laboratory and in the field are likely to be related when the laboratory tasks involve active coping, when the field measure is taken continuously, and when there is allowance for the effects of autocorrelation and physical activity on the ambulant cardiovascular measure. These studies lead to the hypothesis that the hyperreactivity common to the laboratory and to the field has a beta-adrenergic basis. We examined the heart rate variability of 16 hyperreactive and 16 hyporeactive subjects over an 8-hour period while they were receiving either a placebo or a cardio-selective beta-blocking drug (Bisoprolol) in a double-blind crossover design. Subjects were classified on the basis of their heart rate and systolic blood pressure responses to a complex self-paced, reaction-time task. Response in the field was assessed from the standard deviation of the raw heart rate series, after allowance for the serial dependency in the data using autoregressive methods and, when allowance was made for physical activity, assessed from the muscle activity of the thigh. As predicted, on placebo hyperreactive subjects had markedly more variable heart rates, particularly when allowance was made for physical activity. Although not confirmed by a significant interaction effect, this difference largely disappeared under beta-blockade.

Twenty-four-hour ambulatory noninvasive continuous finger blood pressure measurement with PORTAPRES: a new tool in cardiovascular research

PORTAPRES model 1 is a portable 24 h continuous noninvasive blood pressure recorder based on the same principles as FINAPRES, the volume-clamp method of Peñaz and the physiocal criteria of Wesseling. In addition, PORTAPRES measures two adjacent fingers in alternation every 30 min and automatically corrects hydrostatic effects due to height changes of the measured fingers. The device measures 255 x 210 x 60 mm and weights about 3,000 g, including a lithium battery pack and a TEAC cassette FM instrumentation tape recorder to record the finger pressure wave form, the height signal, and beat-to-beat derived systolic, mean and diastolic pressure as well as heart rate. It appears to be an excellent new tool for cardiovascular research in humans. In a randomized, placebo-controlled, double-blind, crossover study the effect of oral administration of 2.5 mg cilazapril, a new potent long-acting, nonsulfhydryl-group angiotensin converting enzyme (ACE) inhibitor, given once daily for 7 days, was investigated in 16 healthy young men (mean age 25.3 +/- 1.6 years). Finger blood pressure and heart rate were measured with PORTAPRES for 24 h during everyday life and during standardized laboratory tasks, once about 1 to 2 h A.M. and once about 10 to 11 h P.M. once about 1 to 2 h A.M. and once about 10 to 11 h P.M. after drug administration. Physical activity was controlled by integrated thigh-EMG. Using stepwise multiple linear regression analysis it was shown that based on 64 s mean values, this measure of physical activity explains 34-77% of the heart rate variance within 24 h (median 53%), 10-52% (31%) of systolic, and 4-38% (25%) of diastolic blood pressure variance when up to 20 time lags of the EMG signal were introduced as possible predictors. This indicates that varying degrees of physical activity have a great impact on everyday blood pressure and heart rate. After one week cilazapril did not alter 24-h means of systolic and diastolic blood pressure or heart rate significantly, but reduced 30 min averages of both systolic and diastolic blood pressure by 6-10 and 4-6 mm Hg between 1 1/2 and 4 or 6 h after drug administration respectively during everyday life (p = 0.0067-0.066) without changing heart rate. On adjusting cardiovascular variables for the effects of physical activity, this blood pressure reduction was confirmed.(ABSTRACT TRUNCATED AT 400 WORDS)