Assessing the strengths and limitations of non‐invasive blood pressure measurement

Non-invasive measurement of arterial blood pressure (BP) has traditionally been performed by auscultation of Korotkoff sounds, but semi-automated blood pressure measurements which utilize oscillometry are increasingly common in clinical practice.1 Oscillometric BP devices construct an oscillometric waveform envelope (OMWE) to determine the mean arterial pressure (MAP).2 Oscillometric BP devices are validated by comparing the measured MAP to a gold standard, which is an intra-arterial catheter connected to a pressure transducer.3 However, the systolic blood pressure (SBP) and diastolic pressure (DBP) are not directly measured by oscillometric BP devices, they are estimated from the OMWE using proprietary algorithms, such as fixed-ratio coefficients.4 SBP and DBP estimates produced by oscillometric BP devices are limited by individual variations in arterial compliance and pulse waveform.5 Given the morbidity and mortality associated with uncontrolled hypertension, an understanding of the strengths and limitations of various modalities for BP measurements is crucial. Therefore, I read with great interest the well-written article by O'Halloran et al. entitled “Blood pressure measurement and blood pressure control in Veterans Affairs medical centers”.6 The study examined Terminal digit preference (TDP), a tendency to record specific digits (e.g., 0) more frequently than others, a common measurement bias with the auscultatory methods. The authors produce data showing Veterans Affairs (VA) medical centers with the largest TDP had the highest BP control rates, and they posit auscultatory methods could have inflated BP control rates in part due to TDP. An alternative interpretation is that lower BP measurements do not imply inflated BP control rates, but rather reflect a higher specificity of auscultatory methods.7 In support of this, auscultatory methods attempt to directly measure SBP and DBP, whereas oscillometric BP devices do not.8 In addition, arterial stiffness is associated with an overestimation of SBP and DBP by oscillometric BP devices.9 Arterial stiffness is common amongst groups frequently screened for hypertension, especially patients with Diabetes and Chronic kidney disease.10, 11 The overestimation of SBP and DBP may increase sensitivity of oscillometric BP devices but limit specificity, making it reasonable to use these devices as a screening tool followed by confirmatory testing with auscultatory methods. O'Halloran et al. have ably described TDP as a potential limitation of auscultatory blood pressure measurement.6 Other forms of measurement error are common to all forms of noninvasive blood pressure measurement, such as improper cuff and arm positioning and talking during measurements.12 Increased awareness of these errors can increase development of better training programs and technologies. An understanding of the strengths and limitations of various methods of blood pressure measurement will allow for their complementary usage in clinical practice. Despite potential for errors such as TDP, an appreciation for the value of auscultatory measurements of blood pressure can encourage the development and retention of auscultatory skill, as well as guide development of new technologies to capture sound waves. Further advancements in research and technology have the potential to increase the precision and accuracy of blood pressure measurement and minimize observer error.13 Jeffrey Hanover performed the literature review and wrote the manuscript. The author has no conflicts of interest to disclose.