European Journal of Cardiovascular Medicine

Accurate measurement of blood pressure (BP) is fundamental in diagnosing hypertension, a leading risk factor for cardiovascular diseases globally. The accurate measurement of BP is essential not only for diagnosing hypertension but also for monitoring its treatment and progression. Inaccurate BP measurements can lead to misdiagnosis, inappropriate treatment and failure to control hypertension effectively, thereby increasing the risk of cardiovascular events1. Clinical guidelines emphasize the importance of proper posture during BP measurements, including the support of the back and feet, to ensure accuracy. However, these recommendations are not consistently followed in clinical practice, potentially leading to significant inaccuracies in BP readings2.

Hypertension is a prevalent condition with profound implications for public health. It is estimated that even small inaccuracies in BP measurement can have substantial consequences at the population level3. For instance, variations of 10 mmHg in systolic BP (SBP) or 5 mmHg in diastolic BP (DBP) can lead to significant changes in hypertension prevalence (22.1% vs. 53.4%) and control rates (21.2% vs. 3.6%). These discrepancies underscore the need for precise BP measurement techniques to accurately assess and manage hypertension4.

BP measurement accuracy is influenced by various factors, including the measurement environment, the subject's behaviour, the procedures followed, the devices used, and the observer's expertise. A systematic review identified 29 factors that could affect BP readings5. Among these factors, the position and support of the back and feet are critical but often overlooked aspects.

The impact of body posture on blood pressure (BP) readings has been extensively studied, focusing on the differences when the back is supported versus unsupported. Cushman et al. found that diastolic BP was significantly higher by 6.5 mmHg without back support in hypertensive men, though systolic BP showed no significant difference6. Handler and Tolonen's reviews corroborated these findings, noting unsupported backs could increase systolic BP by 5-15 mmHg and diastolic BP by 6 mmHg7,8. Conversely, Ringrose et al. reported minimal differences in BP readings with and without back support using oscillometric devices9. Wan et al. further explored the impact of back and feet support on BP readings and found that the most significant effect was on diastolic BP when the back was unsupported. They observed that systolic BP differences were greater than or equal to 5 mmHg in a notable percentage of participants without back support10.

These studies underscore the importance of back support during BP assessments to ensure accurate readings. While some research highlights significant differences in BP readings based on back support, especially for diastolic BP, others suggest minimal effects on systolic BP when using oscillometric devices. The variability in findings points to a need for consistent evaluation of back and feet support during BP measurement, particularly as oscillometric devices are prevalent in clinical settings due to their convenience.

This study aims to address these discrepancies by evaluating the impact of back and feet support on oscillometric BP measurements in a tertiary care hospital. Through systematic comparison of BP readings under different postural conditions, this research seeks to provide clearer guidance on the significance of maintaining proper posture during BP measurement. The findings are expected to inform clinical practice, improving the accuracy and reliability of BP measurements, which is crucial for effective hypertension management. By refining BP measurement protocols, healthcare providers can enhance patient outcomes and reduce the burden of cardiovascular diseases. This study aims to fill a critical gap in understanding BP measurement accuracy and to provide evidence-based recommendations for clinical practice, ensuring more accurate and consistent BP measurements across diverse healthcare settings.

Patients above 18 years of age of both genders visiting the outpatient department of general medicine in a tertiary care hospital located in the south coastal part of Karnataka, India, from November 2024 to March 2025 who provided consent were included in the study. Patients who were pregnant and had atrial fibrillation were excluded from the study. This study was approved by the ethical committee of Age, gender, hypertension history (Patients with or without a history of hypertension (SBP > 140 mmHg and/or DBP > 90 mmHg)), and blood pressure of the patients were recorded.

BP measurement

BP measurements were recorded according to American Heart Association guidelines11 by a trained doctor using a diamond delux BPMR 120 manual BP apparatus after a 5-minute rest period. Two settings were used for the measurement: back and foot supported, and back and foot unsupported. Participants followed one protocol randomly for BP measurement, and then changed their position for 1 minute before the next measurement. The average SBP and DBP from three readings in the same position were recorded as the final BP value. The percentage variation (PV) was calculated with the formula delta (BP/unsupported BP) *100. The delta SBP and delta DBP was calculated as difference in SBP/DBP between positions.

Statistical Analysis

Data are expressed as means ± standard deviation for continuous variables. The paired sample t-test/ ANOVA was used to determine the significance of delta BP and percentage variation between different conditions, such as age, sex, and hypertension history. A P value < 0.05 was considered statistically significant. Statistical analyses were performed using R version 4.2.2, while graphs and tables were generated using Microsoft Word and Excel as needed.

Sample size and Power

To detect a 5-mmHg difference in systolic BP using a paired design with a two-tailed α of 0.05, β of 0.8, and an SD of up to 16 mmHg9, 82 patients were estimated. Rounding up to accommodate for ambiguity, 100 patients were enrolled.

The mean age of the study population was 39.2±12.6 years, ranging from 22 to 77 years. Among the 100 patients, 44 were female and 56 were male, with 38 patients having a history of hypertension. The mean SBP value for the unsupported back and feet position was 133.20±14.48 mmHg, significantly higher by 5.50±1.56 mmHg compared to the supported position. The DBP levels in the unsupported position were 82.10±7.42 mmHg, significantly higher by 4.00±1.52 mmHg than in the supported position (Table 1). Both SBP and DBP were higher in older patients, males, and those with hypertension. SBP and DBP levels were higher in the unsupported position across all subgroups, regardless of age, sex, or hypertension status. However, no significant difference in delta SBP or DBP was found between any subgroups (Table 2). The mean delta SBP and DBP of the study population was calculated to be respectively 5.5±1.56 mmHg and 4±1.52 mmHg. There were 63 and 80 patients who had higher-than-average delta SBP and delta DBP.

Table 1:  Blood pressure recordings of patients with and without support

Table 2: Influence of Age, gender and history of hypertension on delta Blood pressure

*Compared between mean BP within the same group p < 0.05; **compared between delta BP values p < 0.05

The overall percentage variation (PV) in SBP and DBP was 4.2±1.33% and 4.9±1.99%, respectively. PV differed with age, gender, and hypertension history (Figures 1 and 2). The lowest PV in SBP (3.6±0.92%) and DBP (4.5±1.5%) was seen in patients aged ≥55 years and increased with decreasing age, but this was not statistically significant (P=0.517). Female patients exhibited higher PV in SBP (4.5±1.37% vs. 3.9±1.24%; P=0.024) and DBP (5.10±2.32% vs. 4.80±1.69%) compared to male patients. Patients with a history of hypertension had lower PV (SBP=3.7±0.97%; DBP=4.7±1.6%; P=0.456) than those without hypertension (SBP=4.5±1.43%; DBP=5.1±2.2%). The difference in PV of SBP between hypertensive and non-hypertensive groups was statistically significant (P=0.003), while the difference in PV of DBP was not (P=0.333).

Our study aimed to assess the impact of back and feet support on Oscillo metric blood pressure (BP) measurements in a tertiary care hospital setting. Our results demonstrated a significant mean difference in systolic BP (SBP) and diastolic BP (DBP) between supported and unsupported positions, with unsupported readings being higher by 5.50±1.56 mmHg for SBP and 4.00±1.52 mmHg for DBP. These findings align closely with those reported by Cushman et al., 6 Handler et al.,7 and Tolonen et al.,8 who found similar increases in BP when the back was unsupported. Specifically, Cushman et al. noted a 6.5 mmHg higher DBP in unsupported conditions, Handler et al., reported SBP differences of 6–10 mmHg, and Tolonen et al. observed SBP/DBP differences of 5–15/6 mmHg.

However, our values were higher than those reported by Wan et al.10 (2.3/1.0 mmHg) and Ringrose et al.9 (0.7/1.8 mmHg). Notably, 60% and 80% of our patients exhibited above-average delta SBP and DBP, respectively, and these changes were not influenced by age, gender, or hypertension history. Ringrose et al. suggested that increased muscular tension in unsupported positions might contribute to greater BP variability, which could explain the discrepancies observed in different studies9.

Beyond mean BP and delta BP, we also explored the percentage variation (PV) of SBP and DBP, finding variations of 4.2±1.33% and 4.9±1.99%, respectively. While PV did not significantly vary with age, it was notably higher in females and those without hypertension. Male and hypertensive patients exhibited lower PV for BP, consistent with Wan et al.'s findings that hypertension history negatively impacted DBP variation10.

The underlying mechanisms for the BP differences between supported and unsupported conditions remain underexplored. Some studies suggest that back support influences physiological positioning, reducing myoelectric activity and disc pressure compared to unsupported conditions12–15. For instance, fitting a backrest during sitting reduces peak pressure under the ischia, decreases muscular activity, maintains lumbar lordosis, and increases intervertebral disc height15. Watanabe et al.16 indicated that reclining against a backrest could correct lumbar curvature, stabilize the lumbopelvic region, and reduce stress on passive structures.

Our findings have significant clinical implications. They contrast with studies by Ringrose et al.,9 and Wan et al.,10 which reported minimal effects of back and feet support on mean oscillometric BP measurements. Our results highlight that back and feet support lead to substantial differences in BP readings. The strengths of our study include a larger sample size than previous studies, the inclusion of both genders and the assessment of oscillometric BP measurement, which is increasingly utilized in clinical practice.

Given the inconsistencies in findings across various studies, further research using the oscillometric technique is essential to validate our results. This additional research should aim to clarify the physiological mechanisms behind the observed BP differences and assess the broader implications for BP measurement protocols in clinical settings.

Our study demonstrates that back and feet support significantly impact oscillometric BP measurements, with unsupported positions leading to higher SBP and DBP. These findings are consistent with some previous studies but differ from others, underscoring the need for further research to confirm these results and explore the underlying mechanisms. Clinicians should be aware of these potential variations and consider back and feet support during BP measurement to ensure accurate readings.

Conflict of interest

The authors have declared that they have no conflicts of interest.

1. Gulati, M., L. A. Peterson, and A. Mihailidou. "Assessment of Blood Pressure Skills and Belief in Clinical Readings." American Journal of Preventive Cardiology, vol. 8, 2021, p. 100280. doi: 10.1016/j.ajpc.2021.100280.
2. Hwang, K. O., A. Aigbe, H. H. Ju, V. C. Jackson, and E. W. Sedlock. "Barriers to Accurate Blood Pressure Measurement in the Medical Office." J Prim Care Community Health, vol. 9, 2018, p. 215013271881692. doi:10.1177/2150132718816929.
3. Oparil, S., M. C. Acelajado, G. L. Bakris, et al. "Hypertension." Nat Rev Dis Primers, vol. 4, no. 1, 2018, p. 18014. doi:10.1038/nrdp.2018.14.
4. Campbell, N. R. C., R. Padwal, D. S. Picone, H. Su, and J. E. Sharman. "The Impact of Small to Moderate Inaccuracies in Assessing Blood Pressure on Hypertension Prevalence and Control Rates." Journal of Clinical Hypertension, vol. 22, no. 6, 2020, pp. 939-942. doi:10.1111/jch.13915.
5. Kallioinen, N., A. Hill, M. S. Horswill, H. E. Ward, and M. O. Watson. "Sources of Inaccuracy in the Measurement of Adult Patients’ Resting Blood Pressure in Clinical Settings: A Systematic Review." Journal of Hypertension, vol. 35, no. 3, 2017, pp. 421-441. doi:10.1097/HJH.0000000000001197.
6. Cushman, W. C., K. M. Cooper, R. A. Horne, and E. F. Meydrech. "Effect of Back Support and Stethoscope Head on Seated Blood Pressure Determinations." American Journal of Hypertension, vol. 3, no. 3, 1990, pp. 240-241. doi:10.1093/ajh/3.3.240.
7. Handler, J. "The Importance of Accurate Blood Pressure Measurement." TPJ, vol. 13, no. 3, 2009, pp. 51-54. doi:10.7812/TPP/09-054.
8. Tolonen, H., P. Koponen, A. Naska, et al. "Challenges in Standardization of Blood Pressure Measurement at the Population Level." BMC Medical Research Methodology, vol. 15, no. 1, 2015, p. 33. doi:10.1186/s12874-015-0020-3.
9. Ringrose, J. S., J. Wong, F. Yousefi, and R. Padwal. "The Effect of Back and Feet Support on Oscillometric Blood Pressure Measurements." Blood Pressure Monitoring, vol. 22, no. 4, 2017, pp. 213-216. doi:10.1097/MBP.0000000000000265.
10. Wan, T. Xuan, Y. Hao Wu, Y. Qing Wu, W. Hu, and H. Su. "Differences in Oscillometric Blood Pressure Readings Between Unsupported and Supported Back Conditions." Hypertension Research, vol. 44, no. 5, 2021, pp. 528-532. doi:10.1038/s41440-020-00595-w.
11. Whelton, P. K., R. M. Carey, W. S. Aronow, et al. "2017 ACC/AHA/AAPA/ABC/ACPM/AGS/APhA/ASH/ASPC/NMA/PCNA Guideline for the Prevention, Detection, Evaluation, and Management of High Blood Pressure in Adults: Executive Summary: A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines." Hypertension, vol. 71, no. 6, 2018, pp. 1269-1324. doi:10.1161/HYP.0000000000000066.
12. Harrison, D. D., S. O. Harrison, A. C. Croft, D. E. Harrison, and S. J. Troyanovich. "Sitting Biomechanics Part I: Review of the Literature." Journal of Manipulative and Physiological Therapeutics, vol. 22, no. 9, 1999, pp. 594-609. doi:10.1016/S0161-4754(99)70020-5.
13. Andersson, B. J., R. Ortengren, A. L. Nachemson, G. Elfström, and H. Broman. "The Sitting Posture: An Electromyographic and Discometric Study." Orthopedic Clinics of North America, vol. 6, no. 1, 1975, pp. 105-120.
14. Azghani, M. R., J. Nazari, N. Sozapoor, M. Asghari Jafarabadi, and A. E. Oskouei. "Myoelectric Activity of Individual Lumbar Erector Spinae Muscles Variation by Differing Seat Pan Depth." International Journal of Occupational and Environmental Medicine, vol. 10, no. 3, 2019, pp. 137-144. doi:10.15171/ijoem.2019.1551.
15. Makhsous, M., F. Lin, R. W. Hendrix, M. Hepler, and L. Q. Zhang. "Sitting with Adjustable Ischial and Back Supports: Biomechanical Changes." Spine, vol. 28, no. 11, 2003, pp. 1113-1121. doi:10.1097/01.BRS.0000068243.63203.A8.
16. Watanabe, S., A. Eguchi, K. Kobara, and H. Ishida. "Influence of Trunk Muscle Co-Contraction on Spinal Curvature During Sitting Reclining Against the Backrest of a Chair." Electromyography and Clinical Neurophysiology, vol. 48, no. 8, 2008, pp. 359-365.