A small study has shown that a doctor’s presence during a blood pressure measurement skews the results, according to researchers who studied the effect by measuring nerve activity.
The phenomenon known as ‘white coat hypertension‘ is where the mere presence of a medical professional can raise blood pressure. Known about for decades, it occurs in about a third of patients.
In a small study published in the journal Hypertension, researchers probed the effect by measuring blood pressure, heart rate and nerve traffic in the skin and muscles with and without a doctor present.
The researchers found a “drastic reduction” in the body’s alarm response when a doctor was not present, said co-lead author Dr Guido Grassi, professor of internal medicine at the University of Milano-Bicocca.
Blood pressure and heart rate increases in response to a perceived threat, said Dr Meena Madhur, associate professor of medicine in the divisions of clinical pharmacology and cardiology at Vanderbilt University.
“If you’re out in the wild and a bear was charging after you, you’d want your blood vessels in your skin, for example, to constrict and the blood vessels in your muscles to dilate to provide more blood flow to those organs so that you can run really fast,” said Prof Madhur, who was not involved in the new research.
The study included 18 people, 14 of them men, with untreated mild to moderate hypertension. Each participant was examined in a lab, where an electrode measured nerve activity in the skin and muscles. Readings were taken twice in the presence of a doctor and twice without.
Both blood pressure and heart rate rose when the doctor was present, with nerve traffic patterns to the skin and skeletal muscle suggesting a classic fight or flight reaction.
Without the doctor’s presence, cardiovascular and neural responses were “strikingly different,” the researchers wrote. Fight or flight response indications were “entirely absent”.
Peak systolic blood pressure was an average of 14 points lower when the participant was alone than when a doctor was present, and peak heart rate was lowered by nearly 11 beats per minute.
This was the first study to actually measure sympathetic nervous system responses to doctors supervising a blood pressure measurement, the researchers wrote.
The study’s findings illustrated the complexity of blood pressure measurement and how it is affected by involuntary nervous system reactions, Grassi said. “Measurements without the doctor’s presence may better reflect true blood pressure values.”
White coat hypertension is not a new concept, Prof Madhur said, “this just drives home the fact that we should be more conscious of how the blood pressure is taken in the clinic.”
Last year, the American Medical Association and AHA issued a joint report endorsing more blood pressure measurement at home.
Limitations included the small study size due to the complexity of the measurements, the researchers said. Subsequent research would need to examine blood pressure medication as they could affect the fight or flight response, said Orof Madhur.
The work needs to be repeated with more women to examine possible sex differences. And she’d be interested in seeing whether people have the same response to nurses and other medical professionals as they did to doctors in this study.
Previous work shows that when nurses take blood pressure measurements, the white coat effect is reduced.
This latest research emphasises the need for people to handle blood pressure measurements with care, Prof Madhur said.
“I always tell my patients that we really can’t rely on a single office blood pressure measurement, because that’s just a random point in time,” she said.
Prof Madhur said that to take an accurate reading at home, a patient should sit still, with their back straight and supported and feet on the floor, waiting at least a few minutes before recording blood pressure. They should take multiple readings at the same time of day over the course of a week, and bring that log to their doctor’s appointment. Those at-home readings should be the ones used for planning treatment, she said.
“But,” Prof Madhur added, “if we are going to do an office blood pressure reading, it should be taken with the doctor not in the room.”
Source: American Heart Association
