Who will bell the cat? A call for a new approach for validating blood pressure measuring devices


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Blood pressure (BP) measurement should be the foundation stone on which all decisions in hypertension, be they in practice or in research, are dependent. If BP measurement is inaccurate, it follows that all decisions will be flawed. Yet the history of clinical practice and scientific research is replete with examples of disregard for the accuracy of BP measurement. Recognizing that the commonest measurement in medicine is often inaccurate, clinical scientists and the scientific hypertension organizations have made recommendations over the years to improve the technique of measurement and the accuracy of BP measuring devices. The discipline of validating BP measuring devices has developed from primitive origins with ad-hoc protocols to the latest revision of the European Society of Hypertension International Protocol (ESH International Protocol), which is now available on-line (www.dableducational.org) [1].In this issue of the Journal Turner [2] asks: ‘ Can we trust automatic sphygmomanometer validations?’ The essence of his case is that, as hypertension is an undisputed leading risk for cardiovascular morbidity and mortality, the devices used to measure BP should be accurate. However, he questions the present policy of trusting the quality control of sphygmomanometer validations to peer review of published reports, which is not without its limitations. He argues that patients, whose health may depend on accurate BP measurements, are surely entitled to expect that the quality control of validation of sphygmomanometers is at least as good as the quality control of the scales used in the sale of potatoes by a greengrocer. Is it not logical then to apply external accreditation of laboratories that validate sphygmomanometers as is done for other measurements that are important to society? It is perhaps timely to review the history of BP device validation before addressing the implications of this reasonable proposal.Humble beginnings with ad-hoc protocolsWhen the technique of BP measurement was introduced into clinical medicine during the early years of the twentieth century, the importance of accuracy and the limitations of the technique were well recognized [3]. However, the standards called for by the clinicians and scientists who pioneered the technique were relaxed as the twentieth century progressed. During the 1960s and 1970s, individual groups, frustrated by the failure of manufacturers to produce evidence to match their often extravagant claims, began to validate BP measuring systems according to a variety of ad-hoc protocols and so illustrated the need for independent validation of devices [4–6]. However well intentioned such protocols may have been, they had the serious disadvantage of not permitting comparison of one device against another because of the differing methodologies of validation [7].International protocolsIn 1987, the Association for the Advancement of Medical Instrumentation published a standard for electronic and aneroid sphygmomanometers, which included a protocol for the evaluation of the accuracy of devices [8]. In 1990, the British Hypertension Society (BHS) published a more detailed protocol devoted solely to the validation of devices in the clinical setting [9] and both protocols were revised in 1993 [10,11]. These protocols, which differed in detail, had a common objective, namely the standardization of validation procedures to establish minimum standards of accuracy and performance, and to facilitate comparison of one device with another.A large number of BP measuring devices were evaluated according to one or both protocols, but experience soon demonstrated that the conditions demanded for validation were extremely difficult to fulfill because of the large number of individuals that needed to be recruited and the ranges of BP required.

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