Accurate blood pressure measurement

Cardiovascular disease is the leading global cause of mortality and morbidity and high blood pressure (BP) is the single greatest risk factor. Cuff measured BP is used in clinical practice to diagnose and guide management of high BP, with treatment of high BP resulting in a reduction of cardiovascular risk. For these reasons, BP measurement is among the most important medical tests performed, yet the conventional cuff method may be inaccurate. The overall aims of this research were to determine: the accuracy of cuff measured BP; if distinct BP phenotypes exist that relate to cuff BP accuracy and; haemodynamic factors that influence estimation of BP. In study 1 (Chapter 2), the accuracy of cuff measured BP compared with intra-arterial brachial and aortic BP was examined via three individual participant data meta-analyses among data from the 1950’s to 2016. Intra-arterial brachial systolic BP was higher than aortic values. Cuff BP had variable accuracy for measuring intra-arterial brachial and aortic BP, and this significantly influenced correct BP classification. Indeed, the concordance of cuff BP across hypertension categories (normal, pre-hypertension, hypertension stages 1 and 2) compared with intra-arterial brachial BP was 60%, 50%, 53% and 80%, and compared with intra-arterial aortic BP was 79%, 57%, 52% and 76%. In study 2 (Chapter 3), cuff measured BP and intra-arterial BP waveforms from the aorta, brachial and radial arteries were examined in 126 patients undergoing coronary angiography. Four novel BP phenotypes were discovered based on variability in aortic-to-brachial and brachial-to-radial systolic BP amplification. Cuff BP was unable to discriminate between the phenotypes (p>0.5 all comparisons), and among two phenotypes completely missed patients at potentially higher risk due to raised aortic BP. The key findings were confirmed by additional data in 255 patients, supplied by four independent, international collaborators. In study 3 (Chapter 4), intra-arterial BP from 107 individuals undergoing coronary angiography was used to determine the best peripheral BP waveform calibration method for the estimation of aortic BP, as well as haemodynamic factors that may influence accuracy. BP waveforms calibrated with brachial mean arterial BP/diastolic BP estimated aortic systolic BP more accurately than brachial systolic BP/diastolic BP calibration. However, systolic BP amplification had a major influence on the accuracy of estimated aortic systolic BP. In summary, this thesis revealed the extent of inaccuracy in cuff measured BP compared to intra-arterial BP. Moreover, distinct BP phenotypes were discovered which were related to cuff inaccuracy. Finally, systolic BP amplification was found to influence the accuracy of estimated aortic BP from peripheral BP waveforms. Altogether, these studies substantially advance understanding of the strengths and limitations of current BP measurement methods. Novel reasons for measurement inaccuracy have been identified that may lead to tangible improvements in the accuracy of BP measurement