Tonometers were caught in understating the pressure
Denis Strigun, Naked Science
Researchers from the University of Alberta have shown for the first time that the vast majority of home sphygmomanometers do not provide the necessary measurement accuracy.
Arterial hypertension is considered one of the key risk factors for diseases of the cardiovascular system - the main cause of death worldwide, according to The World Health Organization (WHO). The likelihood of hypertension increases with age and is often diagnosed in elderly (over 65 years old) people; tobacco smoking, oral contraceptives and obesity can also provoke a violation. To simplify the diagnosis and monitoring of hypertension, sphygmomanometers are often used. Regardless of the hardware, the operation of these portable and affordable devices is based on the registration of pressure fluctuations in the cuff, which is worn on the shoulder or wrist.
Since the detection of hypertension requires a steady increase in pressure in a certain range – from 140/90 millimeters of mercury and above – the accuracy of the tonometer largely determines the diagnosis and course of treatment. Meanwhile, mathematical modeling conducted by the American physiologist Charles F. Babbs in 2012 showed that the physiological parameters themselves, characteristic of people with suspected hypertension, can influence the measurement result. So, in the case of elderly patients, arterial rigidity (thickening of the walls of the arteries) and increased pulse pressure (normally, an increase in pressure in response to stress or heat) can distort the data.
Until now, the accuracy of home sphygmomanometers has not been evaluated experimentally. To fill the gap, Canadian scientists examined 85 healthy volunteers over the age of 18. At the first stage, the authors studied the sociodemographic parameters, anamnesis and calculated the body mass index (BMI) of the participants. Then six pre-trained assistants, under the supervision of an expert in the field of hypertension, measured everyone's blood pressure 18 times. Measurements were carried out in pairs using the mercury (most accurate) sphygmomanometer Baumanometer and 79 different commercial devices. The mercury tonometer was put on the shoulder with an accuracy of 0.1 millimeters.
All home sphygmomanometers were classified by brand (Omron – the largest Japanese manufacturer – and others), type of measurement (shoulder or wrist), approval status from inspection organizations and cuff stiffness. In accordance with the generally accepted technique, to clarify the measurement results, the researchers also used the ausculatory method: simultaneously with the use of the sensor, they monitored the pulsation of the brachial artery of the volunteers using a stethoscope. Four millimeters of mercury were taken as the maximum permissible error between ausculatory measurements. At the same time, such an assessment of pressure was used as a standard.
In 69 percent of cases, the discrepancy between the auscular method and home tonometers was more than five millimeters of mercury. A third of measurements by commercial devices were characterized by an error of more than 10 millimeters of mercury, for seven percent – 15 millimeters of mercury. The authors estimated the average pressure level at 125.7±14/73,9±10.4 and 129±14.7/72.9±9.3 millimeters of mercury for sensors and stethoscope, respectively. Thus, most tonometers underestimated the indicator. According to scientists, this indicates the need for validation of independent measurements with the help of professional equipment and specialists.
Article by Ringrose et al. An Assessment of the Accuracy of Home Blood Pressure Monitors When Used in Device Owners is published in The American Journal of Hypertension.
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09.06.2017