The Bergen Blood Pressure Study. Estimated prevalence of postural hypotension is influenced by the alerting reaction to blood pressure measurement.

The prevalence of postural hypotension, defined as a > or = 20 mmHg decline in SBP from the sitting to the standing position, was studied in 430 subjects aged 67.2 +/- 6.8 years (mean +/- SD). Before the subjects assumed the upright position, three sitting measurements were performed. The difference between the first sitting and standing recording revealed a postural hypotension prevalence of 18.9%. However, when the mean of the two last sitting recordings was used as baseline, only 4.9% of the subjects experienced a > or = 20 mmHg drop in SBP on standing. It is well documented that the alerting reaction to conventional sphygmomanometry causes the BP to rise and that BP decreases spontaneously with repeated measurements. When postural hypotension is based on the difference between the first sitting and the standing recording, the change in BP is not caused by the change in posture alone but reflects the effect of repeated measurements and the regression-towards-the-mean-phenomenon as well. Consequently, the prevalence of postural hypotension is overestimated. Repeated baseline recordings are encouraged in the assessment of postural hypotension.