1. Blood pressure, heart rate and plasma catecholamine responses were examined in two groups of elderly subjects distinguished by blood pressure responses to standing. Subjects in the control group showed a fall of less than 15 mmHg in systolic blood pressure on standing; subjects in the orthostatic hypotension group had falls of more than 20 mmHg systolic and 10 mmHg diastolic blood pressure on standing.

2. The heart pressure response on standing showed no significant difference between the two groups.

3. The orthostatic hypotension patients had lower plasma noradrenaline concentrations than the control patients (P < 0.01) in the supine position, but during 10 min standing there was no significant difference in noradrenaline levels between the groups, and the percentage increase of noradrenaline levels in the orthostatic hypotension group was greater (P < 0.05) than in the control group.

4. in the supine position, diastolic blood pressure was higher (P < 0.05) in the orthostatic hypotension group than in the control group.

5. We conclude that impairment of baroreceptor function is not involved in most cases of orthostatic hypotension in the elderly, nor is there reduction of sympathetic nervous activity. We suggest that mechanical changes or adrenoreceptor dysfunction are more likely to be important factors in orthostatic hypotension in the elderly.

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