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Continuous orthostatic responses of blood pressure and heart rate were measured in 40 healthy and active elderly subjects over 70 years of age in order to assess the time course and rapidity of orthostatic cardiovascular adaptation in old age. 2. During the first 30 s (initial phase) the effects of active standing and passive head-up tilt closely resembled those observed earlier in younger age groups. Standing up was accompanied by a drop (mean +/- SD) in systolic and diastolic blood pressures of 26 +/- 13 mmHg and 12 +/- 18 mmHg, respectively, at around 10 s, and a subsequent rise up to 11 +/- 17 mmHg and 8 +/- 6 mmHg above supine values at around 20 s. The drop in blood pressure upon standing was accompanied by a transient increase in heart rate with a maximum of 13 beats/min, followed by a gradual decrease to 7 beats/min above supine levels. These characteristic transient changes were absent upon a passive head-up tilt. 3. After 1-2 min of standing (early steady-state phase) diastolic blood pressure and heart rate increased significantly after active and passive postural changes. On average, for all subjects systolic blood pressure tended to increase from control during 5-10 min standing, reaching a significant difference at 10 min. During standing, the largest increases in systolic blood pressure were found in subjects with the lowest supine blood pressures. 4. In conclusion, for the investigation of orthostatic circulatory responses in elderly subjects the following factors have to be taken into account: active versus passive changes in posture, the timing of the blood pressure reading, and the level of supine blood pressure.
Imholz et al. (Sun,) studied this question.