Differences in oscillometric blood pressure readings between unsupported and supported back conditions

Appropriate body posture is important for accurate blood pressure (BP) measurement. However, the impact of an unsupported back on BP readings is currently controversial. This study included 224 subjects (18-86 years old, 54.5 ± 15.5 years old, 105 males). BP was measured with an oscillometric BP device randomly following one of two protocols for back support conditions: (1) supported-unsupported-supported-unsupported, or (2) unsupported-supported-unsupported-supported. The average of the two systolic BP (SBP) and diastolic BP (DBP) readings in the same position was recorded as the final BP value. The differences in BP between the unsupported and supported back conditions were calculated as delta BP. Moreover, the percentage variation in BP (PV) was calculated with the formula delta BP/BP with an unsupported back. Multivariable regression analysis evaluated the impact of age, sex, hypertension history and supported BP level on PV. The SBP/DBP levels measured with an unsupported back were slightly higher than those when the back was supported (132.7 ± 19.5/79.6 ± 12.9 mmHg vs. 130.3 ± 20.0/78.5 ± 14.3 mmHg), and the delta SBP (2.3 mmHg) was statistically significant. The multivariable regression analysis showed that age was a positive factor but supported SBP level as a negative factor for systolic PV, while age and supported DBP level were positive factors, but hypertension history was a negative factor for diastolic PV. For a group participant, the mean difference in oscillometric SBP/DBP in the unsupported back position was 2.3/1.0 mmHg higher than that in the supported back position.