[Cardiovascular response to cerebral circulatory regulation during shifts in head position]

Cardiovascular response and its effect on cerebral regulation was examined in groups of young and old people by putting pressure on the cerebral circulatory system through rapid changes in head position. A transient increase in blood pressure was observed in both the young and old people's groups when the head was tilted up. In the old group, there was less change in both systolic blood pressure and diastolic blood pressure. A transient reduction in blood pressure was observed in both groups when the head was tilted down. However, there was less change in diastolic blood pressure in the old group. The number of heart beats before a maximum change in blood pressure was 5 to 9 beats when the head was tilted up, and there was no significant difference between the two groups. The corresponding figure when the head was tilted down was 17.1 +/- 3.51 beats in the young group, and 27.1 +/- 11.5 beats in the old group, significantly higher among the old group. All were early responses observed within 1-2 minutes. Looking at the change of pulse after the head was tilted up or down among the young group, the number of heart beats increased to reach a peak when the head was tilted up, and when the head was tilted down the number of heart beats fell to its lowest level. The affect of these two cardiovascular responses tended to compensate for cerebral perfusion pressure, which indicates the possible existence of a cerebral perfusion pressure regulatory mechanism, assisted by a carotid sinus reflex. A reduction of this function was suggested in the old group.