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Sarah Melville must be credited for drawing attention to what she calls the “Accuracy Crisis”. Crisis or not, the problem of accuracy in the use of home health devices is ubiquitous but has not been covered sufficiently.

Blood pressure monitors are widely-used home devices. Are they accurate?

The blood pressure monitors is one of the most commonly used home devices. As stated in a recent publication,  “An Assessment of the Accuracy of Home Blood Pressure Monitors When Used in Device Owners”, most home blood pressure devices are not accurate to within 5 mmHg.

 

Blood pressure measurements. Classic Riva Rocci method.

To analyze the situation, we must consider a classic Riva Rocci method of blood pressure measurement. A sphygmomanometer, a stethoscope and a doctor’s trained ear are the major tools. The sphygmomanometer, a device with a glass tube filled with mercury is intended to measure air pressure in the cuff, not blood pressure. The stethoscope helps the doctor to detect Korotkoff sounds. And the doctor defines the moments when the pressure in the cuff is equal to the blood pressure, systolic or diastolic, when Korotkoff sounds appear or disappear. Only non-invasive blood pressure measurements and measurements in the deflation phase are considered here.

 

Blood pressure monitors for home use.

 

Even now you can see some doctors using this method and considering it to be more reliable and accurate. The blood pressure monitors designed for home use perform the following 3 actions: measuring air pressure in the cuff, detecting the pulse signal and identifying the points in time corresponding to systolic and diastolic blood pressure. Electronic and programming components perform all 3 functions in modern blood pressure monitors for home use.

 

Errors in blood pressure measurements.

 

All 3 components contribute to overall errors in blood pressure readings. If a  classic sphygmomanometer does not in fact need calibration since mercury’s features are very stable at the same room temperature, modern pressure sensors need to be calibrated on a regular basis. The second component, pulse wave detection depends not only on the quality of the sensor but also on other  factors, one of which is the nature of a pulse wave. These factors can lead to the situation when a pulse wave of a single heartbeat can be missed and additional errors occur. The error of the third component, the decision making unit mostly depends on the deflation speed and the heart rate. Typical cuff pressure deflation speed is about 3 mmHg/sec. Therefore, if the pulse rate is 60 beats/min the measurement error cannot be smaller than 3 mmHg, and taking into account all other error factors, overall error margin can easily exceed 5 mmHg.

 

How to diminish blood pressure measurements errors?

 

What can you as a user of a blood pressure monitor do to reduce measurement errors. Firstly, choose a medical grade device. The blood pressure monitors for home use now are more consumer goods than medical devices. Therefore, the manufacturers have to pay more attention to non-medical features which make the goods more attractive but not in the sense of accuracy. Secondly, the device must be calibrated on a regular basis. Thirdly, to decrease the influence of other factors which are beyond our control, repeating measurements can be helpful. Finally, the measurement procedure must be followed. For example, the person being monitored should stay calm and relaxed for 5 min prior the first measurement; the measurement should not be repeated until 2 min has passed.

 

About blood pressure correction.

 

This last remark is not exactly about the accuracy. There is no doubt that monitoring of vital metrics has to be reliable and as accurate as possible. Blood pressure monitoring provides information for decision-making and pharmacological correction. Here, the patient faces a problem of accuracy interpretation. While an acceptable level of accuracy of blood pressure measurement must be within 5 mmHg, the dosage of medication does not match this accuracy. For example, available Coversyl doses are 2mg, 4mg, 8mg, and Coversyl plus. This means that to take the next step of correction, the dose has to be doubled.