Assessment of sympathetic nerve activity controlling blood pressure in the elderly using head-up tilt

In order to assess age-related changes in sympathetic nerve activity controlling blood pressure, we recorded muscle sympathetic nerve activity, blood pressure, and heart rate during head-up tilt in 10 healthy elderly (69-75 years) and 16 healthy young (19-23 years) subjects. The elderly had significantly lower responsiveness of muscle sympathetic nerve activity to postural change than did the young subjects. In the elderly, marked rise in blood pressure without increase in muscle sympathetic nerve activity was observed in nearly upright position during head-up tilt, whereas this phenomenon was not observed in the young. We conclude that neural control function of blood pressure during head-up tilt in the elderly differs from that in the young, which may be due to age-related change in baroreflex function.