Membrane theory with multimodal evidence defines blood pressure measurement

Cuff-based blood pressure (BP) measurement is a cornerstone of health assessment, yet its mechanism remains unclear and measurement error remains substantial 1 . On the basis of membrane theory 2,3 , we propose that external pressure generated by cuff inflation follows a hyperbolic-cosine-shaped axial distribution along the artery, forming a pressure-peak zone (PPZ) beneath the cuff. By combining this external pressure with intra-arterial pressure, we constructed a mathematical model that systematically predicts site-specific vascular motion and hemodynamic changes during BP measurement. In humans, multimodal experiments integrating vascular imaging and synchronized invasive and noninvasive pressure measurements validated the model. The PPZ organizes distinct proximal and distal hemodynamics during cuff pressurization: at DBP, diastolic arterial collapse begins at the PPZ; near SBP, only weak residual blood flow traverses the PPZ and disappears once cuff pressure exceeds SBP. These transitions generated identifiable oscillogram features for DBP and SBP, precisely localized by wavelet scanning. The resulting method showed higher accuracy and lower variability than auscultation and conventional oscillometry and was the only method whose estimates did not differ significantly from invasive BP. This study redefines the hemodynamic basis of cuff-based BP measurement, and its mechanistic framework and accuracy may support clinical application and more reliable therapeutic decision-making. Structured Abstract Introduction Brachial cuff-based noninvasive blood pressure (BP) measurement is among the most important measurements in medicine, yet its underlying mechanism remains unclear. Current oscillometric and auscultatory techniques rely largely on empirical criteria and show substantial errors and variability when compared with invasive BP. A core theoretical basis is therefore needed to link cuff-vessel coupling mechanics to hemodynamic changes and to support a more accurate, mechanism-consistent method for BP estimation. Rationale Traditional cuff-based BP theories assume vascular compression due to a spatially uniform external force. These theories cannot explain prior observations: tourniquet studies using cuffs similar to BP cuffs showed axial central tissue injury; intratissue pressure measurements and direct measurements of cuff contact pressure all showed curvilinear axial pressure distributions. Because the cuff is intrinsically a membrane structure, we hypothesized that sub-cuff pressure distribution should follow a membrane-theory contact model and a Laplace-type equilibrium. By combining this nonuniform external pressure with intra-arterial pressure, we constructed and validated a mathematical model that systematically predicts vascular motion, hemodynamics, and oscillogram changes during BP measurement. Results The model predicted that the cuff external pressure follows a hyperbolic-cosine-like axial distribution, forming a pressure-peak zone (PPZ) at the cuff axial center, the site of minimal curvature, with external pressure decreasing toward proximal and distal edges. Sub-cuff pressure-sensor measurements and transvenous tissue-pressure measurements in supine participants verified this pressure-distribution pattern and showed that, once cuff pressure exceeded approximately 30 mmHg, cuff pressure and tissue pressure in the PPZ were nearly identical. On this mechanistic basis, we established a physically constrained mathematical framework that reproduced vascular motion and hemodynamic changes during inflation and linked vascular dynamics to oscillogram morphology. Angiography, intravascular ultrasound (IVUS), computed tomographic angiography (CTA), and multisite invasive pressure measurements in the human brachial artery showed that the model-predicted motion, hemodynamics, multisite pressure, cross-sectional area, volume, and oscillogram changes agreed with measured results. The arterial PPZ was the primary site determining key state transitions of the sub-cuff vessel and the dominant contributor to hemodynamic and oscillogram changes. When cuff pressure rose above diastolic blood pressure (DBP) during inflation, the PPZ first collapsed during diastole, gradually creating two regions with distinct vascular motion proximal and distal to the PPZ. Near systolic blood pressure (SBP), distal pulsations became markedly delayed and attenuated into distinctive low-amplitude delayed pulsations (small waves). When cuff pressure exceeded SBP, pulsations in the PPZ and distal region disappeared, whereas proximal pulsations persisted. These hemodynamic events mapped onto characteristic oscillogram morphology transitions. Using wavelet scanning analysis, we extracted local oscillatory components as reference features for SBP and DBP. Auscultation, vascular imaging, and synchronized pressure recordings during the cardiac cycle showed that Korotkoff sounds (KS) occurred during early vascular opening and were related to expansion velocity. Our model further allowed estimation of the area-derived expansion velocity near the distal cuff edge; however, KS-generation thresholds vary across individuals. When cuff pressure is close to SBP, weak blood passage produces expansion velocities below the KS threshold, causing systematic underestimation. In contrast, near DBP, mild post-collapse re-expansion may trigger KS prematurely or with delay, leading to substantial variability. The model also showed that the conventional oscillometric amplitude-coefficient method for estimating SBP and DBP can be analytically derived from our mathematical equations. However, because these parameters are numerous and case-specific, they cannot be practically determined; therefore, the maximum amplitude algorithm (MAA) must rely on empirical ratios relative to the maximum oscillogram amplitude. Consequently, MAA exhibits not only systematic bias but also substantial variability. On the basis of this mechanism, we developed the novel Morphology-Transition Oscillometry (MTO) method for noninvasive BP measurement. For SBP, MTO showed consistently much higher accuracy and lower dispersion in 175 participants (0.39 ± 6.41 mmHg) than conventional auscultation (KS) (−6.58 ± 10.30 mmHg) and oscillometry based on MAA (-6.79 ± 10.58 mmHg), with no significant difference from invasive pressure. For DBP, the bias was 0.14 ± 6.25 mmHg for MTO, −1.15 ± 7.24 mmHg for KS, and 4.85 ± 9.14 mmHg for MAA. Conclusion This membrane-theory-based framework establishes a reliable new theory of cuff-based BP measurement, accurately predicting hemodynamic transitions, vascular motion, and oscillogram morphology, as validated by multimodal in vivo measurements. The MTO method derived from this theory measured arterial BP more accurately than auscultation and traditional oscillometry.