Automated blood pressure measuring devices

In 1890, Roy and Adami demonstrated arterial oscillations at different pressures by applying a tight-fitting water chamber to the wrist. The mean arterial pressure was represented at the point of maximum oscillation (Hill and Barnard, 1897) and changes in the amplitude of these oscillations could be used to detect systolic and diastolic pressures (Howell and Brush, 1901).

Initially it was thought that an increase in the amplitude of the oscillations corresponded to the systolic pressure, while the diastolic pressure was represented by the lowest point of the maximum oscillations (Erlanger, 1903). Subsequent studies showed that diastolic pressure was in fact below the maximum oscillations.

Most automated devices available today use oscillometry to determine the blood pressure. Their accuracy and suitability as a replacement for the mercury sphygmomanometer have been the subject of research and discussion for more than two decades. Although they address some of the errors associated with mercury sphygmomanometry, their accuracy cannot be assumed without evaluation against mercury sphygmomanometry.

The need for a standardized protocol became apparent in the late 1980s after the widespread introduction of automated devices to the market. Various protocols have since been published with the aim of establishing a minimum standard of accuracy. The Association for the Advancement of Medical Instrumentation (1993), the British Hypertension Society (O'Brien et al., 1993a) and the European Society for Hypertension (O'Brien et al., 2002) all published protocols and both Germany and Australia have unpublished recommended national standards.

The need to evaluate devices in an obstetric population specifically is well-documented. Various devices deemed accurate in adults have been shown to underestimate blood pressure in a hypertensive pregnant population by clinically significant amounts (Franx et al., 1997; Gupta et al., 1996; Hehenkamp et al., 2002; Natarajan et al., 1999; Quinn, 1994; Reinders et al., 2003). Revised protocols of the AAMI and BHS now make specific provision for the evaluation of automated devices in pregnancy, although it does not address pre-eclamptic women in particular.

Device accuracy also varies depending on whether it is compared to mercury sphygmomano-metry or intra-arterial readings. Automated auscul-tatory devices have shown decreased accuracy in pre-eclampsia despite passing the protocol in a pregnant population (Nataranjan etal., 1998; Penny et al., 1996) and the same has been found for oscillometric devices (Gupta et al., 1996; Penny etal., 1997).

It is thought that the accuracy of automated devices might be influenced by the altered compliance in pre-eclampsia. Care should be taken when interpreting blood pressure measurements taken with automated devices in women with pre-eclampsia.

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Blood Pressure Health

Blood Pressure Health

Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...

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