[Clinical significance of blood pressure response to posture]

To assess the clinical significance of the blood pressure reaction to orthostatic posture, 55 normotensives and 369 subjects with different degrees of hypertension were studied with non-invasive 24-hour blood pressure monitoring. During the recordings blood pressure response to standing was evaluated at 8 a.m., and at 2, 4 and 7 p.m. All subjects were attributed a target organ damage score on the basis of ECG, chest x-ray and fundoscopic findings. To assess whether the orthostatic reaction may represent a marker for the severity of hypertension, subjects were divided into 4 classes of increasing blood pressure levels, and each class was further subdivided into two groups of subjects with orthostatic reaction above and below the mean value. On average, blood pressure rose by 2.7 +/- 9/7.2 +/- 7 mmHg while standing up, an increase which was inversely correlated to that of heart rate (p < 0.05). The orthostatic response was substantially constant throughout daytime hours. The systolic orthostatic change from lying to standing was directly correlated with age (p < 0.02) and average daytime blood pressure (p < 0.01), and inversely correlated with lying blood pressure immediately before standing up (p < 0.001). Both systolic (p < 0.05) and diastolic (p < 0.01) pressure responses to standing were related to the day-night blood pressure difference and to the standard deviation from mean daytime blood pressure. The degree of target organ damage was not significantly greater in the 4 groups of subjects with high orthostatic response compared to those with low response. The present results show that the pressure reaction to orthostatic stress is constant throughout daytime, even though a large intraindividual variability in the extent of the response is present. Orthostatic pressure change seems to be an important determinant of diurnal pressure rhythm, while it is not a marker for the severity of hypertension.