The role of potassium in postural hypotension: electrolytes and neurohumoral factors in elderly hypertensive patients using diuretics.

OBJECTIVE

To study the association between postural hypotension and (i) electrolyte levels and (ii) neurohumoral factors in elderly hypertensive patients using diuretics.

DESIGN

Cross-sectional study of patients and controls.

SETTING

The subjects were gathered from senior citizen clubs or they were referred to the study by general practitioners. The subjects were examined on a geriatric ward in Turku City Hospital.

SUBJECTS: Seven subjects with postural hypotension and 13 controls.

MEASUREMENTS: Plasma electrolyte levels and neurohumoral response to head-up tilt.

RESULTS

There were significantly more hypokalaemic subjects in the postural hypotension group (5/7) than in the control group (1/13) (P < 0.01). The plasma potassium level was negatively correlated to plasma aldosterone (r = -0.57; P < 0.01) and renin activity (r = -0.69; P < 0.001). Subjects with postural hypotension had higher levels of noradrenaline, both supine (P < 0.05) and during tilt (P < 0.05). There were no significant differences in supine or tilt levels of plasma adrenaline, vasopressin, atrial natriuretic peptide, aldosterone and renin activity between the groups.

CONCLUSION

The results suggest that potassium depletion is associated with postural hypotension in elderly hypertensive patients using diuretics. However, it is unclear whether there is a causative link between potassium depletion and postural hypotension or whether they are both caused by some other factor, e.g. volume contraction.