Validation and Reliability Testing of Blood Pressure Monitors

Abstract

The diagnosis and management of hypertension is dependent on the accuracy of blood pressure measurement which, in turn, demands that the devices used for measurement are accurate. Regrettably, this is often not the case and there is a need, therefore, for validation procedures to ensure that devices on the market are accurate and reliable. All aspects of blood pressure device validation are reviewed in this chapter. The different validation protocols and their development are outlined, namely the Association for the Advancement of Medical Instrumentation (AAMI) and the International Standards Organisation (ISO) standards, the British Hypertension Society (BHS) protocols and the International Protocols of the European Society of Hypertension (ESH). The ways in which these protocols might be harmonised and improved is discussed. Manufacturer obligations and consumer requirements are given thoughtful consideration, and finally, the need for a unified approach to the evaluation of blood pressure measuring devices is emphasised.

Appendix: Observer Blinding During Validation Procedure

This appendix provides a generalised description of the observer blinding procedure required during validation. It is an adaptation of the method described for observer training in the 1990 BHS protocol [15], the 1993 BHS protocol [17] and the 2002 ESH-IP [20].

Observer Isolation

The observers and supervisor are seated at a bench fitted with partitions so that each is isolated from each other in a “booth”. It must not be possible for an observer to have any indication of any blood pressure measurement other than by viewing his/her mercury column and listening with his/her own headset.

Booth Contents

The only objects in the observer booths are a mercury column (or other reference device), a stethoscope headset, two pens (one spare) and prepared forms to write down the observed measurements.

The supervisor booth will have space for both the supervisor and the subject. It will contain a mercury column (or other reference device), a full stethoscope, cuffs, an inflation bulb, the test device, two pens (one spare) and prepared forms.

The Pneumatic System

For sequential same-arm measurements and simultaneous opposite-arm measurements, all of the mercury columns and inflation bulb and a facility to connect a cuff are appropriate to the subject. This will not be a cuff supplied with the test device.

For simultaneous same-arm measurements, all of the mercury columns are connected to the device pneumatic system. The cuff used will be the appropriate cuff for the subject as supplied with the test device.

The system must be closed, and regardless of whether inflation and deflation are controlled by a bulb or by the test device, the system must be calibrated to test for air leaks and for stability.

The Auscultatory System

All of the stethoscope headsets must be connected to the one diaphragm. The lengths of tubing to each of the observer headsets must be the same. The system must be tested to ensure that Korotkov sounds are audible clearly on each headset.

Subject Forms

For the ESH-IP, supervisors must use the Subject Form as published. A similar form should be prepared, containing spaces for all subject details required, including observer measurements, for validations carried out according to the AAMI/ANSI/ISO standard.

Observer forms must contain a space for the subject number, spaces for the measurements and possible repeat measurements. For example, for the ESH-IP protocol, observers will record measurements A, 1, 3, 5 and 7; for the AAMI/ANSI/ISO standard with simultaneous same-arm measurements, observers will record an entry measurement and measurements 1, 2 and 3.

Procedure for Each Subject

After each observer reading, the supervisor checks the observers’ readings and, if they differ by at most 4 mmHg for both SBP and DBP, the supervisor simply states “OK” and continues. If not, the supervisor simply states “Repeat measurement n”, n being the number of the respective measurement. If there are three consecutive repeat measurement or mmm repeat measurements on the same subject, the supervisor simply states “OK” but the subject is excluded.

When the all measurements have been completed on the subject, the supervisor collects the forms and enters the observer measurements on the supervisor form. The forms are stapled together, in the order of Supervisor, Observer 1 and Observer 2. After entry into a computer, they are stored as evidence.