Blood pressure variation in response to changing arm cuff height cannot be explained solely by the hydrostatic effect

Abstract

To challenge the widely accepted explanation of hydrostatic effect for blood pressure (BP) variation in response to arm elevation by testing the hypothesis that SBP and DBP measurements in the same individual vary differently with cuff height, and to evaluate the potential deviation of these measurements from the value predicted by the hydrostatic theory. Arm BP was measured in 37 individuals from the general population in the sitting position using a digital BP monitor. Measurements included nine consecutive BP readings at four cuff heights. The height dependence of BP was derived using reduced major axis regression. The variation in systolic and diastolic pressure had a highly linear correlation with cuff height (r = -0.90 and -0.93, respectively), with the systolic rate lower than the diastolic one by -0.13 ± 0.20 mmHg/cm (P = 0.0003) for all individuals. Systolic and diastolic rates were more negative in hypertensive individuals (P < 0.001 and P < 0.05, respectively). Significant deviation from the hydrostatic prediction of -0.77 mmHg/cm was observed in 30% of the individuals. This study assesses for the first time the inappropriateness of the hydrostatic theory as the sole explanation for the effect of gravity on BP. The phenomenon may be associated with mechanical properties of arteries in individuals known to have prognostic significance. The potential of the change in systolic and diastolic pressure with cuff height to be used as a novel type of clinical variable and vascular marker that can be determined by a simple test remains to be explored.