Disparities in circulatory adjustment to standing between young and elderly subjects explained by pulse contour analysis

Abstract

1. The circulatory adjustment to standing was investigated in two age groups. Young subjects consisted of 20 healthy 10–14-year-old girls and boys. Elderly subjects consisted of 40 70–86-year-old healthy and active females and males. Continuous responses of blood pressure and heart rate were recorded by Finapres. A pulse contour algorithm applied to the finger arterial pressure waveform was used to assess stroke volume responses. 2. During the first 30 s (initial phase), an almost identical drop in mean blood pressure was found in both age groups (young, 16 ± 10 mmHg; old, 17 ± 10 mmHg), but the initial heart rate increase was attenuated in the elderly subjects (young, 29 ± 7 beats/min; old, 17 ± 7 beats/min). 3. During the period from 30 s to 10 min of standing, mean blood pressure increased from 96 ± 12 to 106 ± 12 mmHg in the elderly subjects compared with almost no change in the young subjects (from 82 ± 8 to 84 ± 7 mmHg). In the elderly subjects a progressive increase in total peripheral resistance (from 114 ± 14% to 146 ± 29%) was found, compared with an initial rapid increase in total peripheral resistance (126 ± 18% after 30 s) with no further change during prolonged standing (124 ± 17% after 10 min) in the young subjects. In this age group the decrease in stroke volume and the increase in heart rate after 10 min of standing were large (young, −37 ± 11% and 27 ± 11 beats/min; old, −31 ± 9% and 7 ± 6 beats/min, respectively). 4. In conclusion, young subjects adjust to orthostatic stress mainly by a marked increase in heart rate. In healthy elderly subjects an attenuation of the heart rate response during orthostatic stress is compensated by a pronounced increase in total peripheral resistance resulting in an increase in blood pressure.