Published in The Hindu on February 10, 2011
Hypertensive patients, why, even normal people, sensing their blood pressure rising as the doctor prepares to measure their blood pressure is not unusual. It is called the ‘White coat effect.’
Studies have shown that a subset of about 25 per cent of hypertensive patients experience an elevation in their blood pressure “when readings are taken in treatment settings, especially by physicians.” This can lead to overtreatment.
Many studies have shown that this phenomenon is widespread. There are also concerns about the quality and accuracy of BP measurement in clinical settings. Many studies done in the past have found that automated BP measuring instruments operated by patients themselves can overcome this white coat fear.
Lower systolic values
A study published recently online in the British Medical Journal (BMJ) has once again established that the effect is real. On an average the systolic blood pressure was 5.4 mm HG lower in people who had their BP measured using an automated device compared with the manual mercury instrument. The difference was not significant in the case of diastolic blood pressure.
Another study found the difference was as much as 9 mm HG between routine manual and automated measurement. And greater reductions have been shown by other studies. But immaterial of the amount of reduction, it is becoming increasingly clear that using automated measuring devices show a lower systolic pressure.
The study included a total of 572 hypertensive patients, who were randomly split into two groups. One group continued to be tested manually with the conventional mercury instrument (sphygmomanometers). The other group had their BP measured using an automated monitor (BpTRU device). Blood pressure levels of patients in both the groups were also measured with an ambulatory blood pressure monitor.
The study was undertaken in a clinical setting, and not in a research environment.
Many readings needed
Unlike one reading taken with the conventional device, the automated one required five readings. These were taken at two-minute intervals between each reading. Other studies have also insisted on more than one reading and have used different timings between each reading. More studies are needed to know the interval between readings and the number of readings to be taken.
The latest study, however, found that the use of an automated device only reduced the white coat effect; it did not totally eliminate it. “The simple presence of an observer seems to increase blood pressure,” the authors note. The authors also attribute the increase to disturbance of patients by doctors when the readings were taken.
The authors therefore note that a reduction would be seen if patients using automated devices follow/are made to follow the three basic tenets — the patient rests alone in a quiet room, the patient is alone when the readings are taken, and multiple readings are taken.
The need for rest before readings are taken appears to be of great importance. An increase, as seen in white coat effect, can be noticed if the patient does not rest prior to readings being taken, and only one or two readings are taken.
The need for rest can be done away with if five readings are taken with only one minute interval between readings, they note.
Finally the authors conclude that automated devices are an alternative to manual readings as they can overcome the white coat fear if the patient is left alone.
This and other studies are supported by the recommendation of several associations. For instance, the American Heart Association and the European Society of Hypertension have recommended “the widespread use of home blood pressure monitoring.”
Even if conventional manual blood pressure measuring devices are not abandoned, these studies have shown that they provide “suboptimal measures of an individual patient’s blood pressure status,” the study notes.
An Editorial published in the same issue of the journal notes that “automated blood pressure measurement provides an alternative to manual and out of clinic monitoring. But its precise role depends on further evidence.”