High blood pressure: Irish-US research points to major change in treatment

New study shows no evidence that diastolic blood pressure can be too low

Latest research suggests that if you suffer with  persistently high systolic blood pressure, your doctor can treat the systolic value, without being overly concerned about the diastolic reading falling too low. Photograph: iStock

Latest research suggests that if you suffer with persistently high systolic blood pressure, your doctor can treat the systolic value, without being overly concerned about the diastolic reading falling too low. Photograph: iStock

 

Are you one of the almost one million people in Ireland with high blood pressure? Hypertension affects more than one in four men and one in five women. Now some novel research led by a professor at NUI Galway looks set to change how doctors treat some patients with high blood pressure.

The study by researchers at NUI Galway, Johns Hopkins University and Harvard Medical School found no evidence that diastolic blood pressure – the bottom reading on a blood pressure test – can be harmful to patients when reduced to levels that were previously considered to be too low.

The fear was that, in driving down the systolic pressure, the diastolic pressure would also be lowered, to a point where it was thought there was a risk to health from too low a reading

Blood pressure is measured using a sphygmomanometer – traditionally a stethoscope, a cuff for the arm, a pump and a dial. It is recorded in millimetres of mercury (mmHg). These readings can be divided into two parts: systolic blood pressure is the top number and measures the force that the heart exerts on our arteries during a heartbeat. The normal range of systolic BP is 100-130mmHg. Diastolic blood pressure is the bottom number on a reading and it measures the pressure on artery walls between heartbeats. The normal range has traditionally been considered to be 70-90mmHg.

Until now, one of the challenges facing doctors treating people with high blood pressure was the person with a high systolic reading and a normal diastolic reading. The fear was that, in driving down the systolic pressure, the diastolic pressure would also be lowered, to a point where it was thought there was a risk to health from too low a reading. Blood pressure medication lowers both systolic and diastolic readings. Treatment decisions are made on the basis of a 24-hour measurement of blood pressure.

Dr Bill McEvoy, professor of preventive cardiology at NUI Galway and a consultant cardiologist at University Hospital Galway, said the findings had the potential to immediately influence the clinical care of patients.

“We now have detailed research based on genetics that provides doctors with much-needed clarity on how to treat patients who have a pattern of high systolic values – the top reading for blood pressure – but low values for the diastolic, or bottom, reading,” he said.

“This type of blood pressure pattern is often seen in older adults. Previous studies using less reliable research methods suggested that the risk for a heart attack began to increase when diastolic blood pressure was below 70 or above 90.”

The research team’s analysis of complex genetic and survival data from more than 47,000 patients worldwide, published in the medical journal Circulation, showed there appears to be no lower limit of normal for diastolic blood pressure and no evidence that diastolic blood pressure can be too low.

In particular, there was no evidence of an increased risk of heart disease when a person’s diastolic blood pressure reading is as low as 50mm Hg. And the study also confirmed established evidence that systolic blood pressure readings above 120mm Hg increase the risk of heart disease and stroke.

Although the complex analysis carried out by the researchers is not the equivalent of a fully randomised clinical trial, it does reflect findings from the Systolic Blood Pressure Intervention Trial (Sprint). A post hoc analysis of Sprint found that having low diastolic blood pressure did not have a negative effect on the lower cardiovascular and all cause mortality rates seen in the trial.

Essentially, this latest research suggests that if you are someone with persistently high systolic blood pressure, your doctor can treat the systolic value, without being overly concerned about the diastolic reading falling too low.

Noting that this scenario is a common clinical problem that causes much debate, Dr Joe Gallagher, Irish College of General Practitioners’ lead, National Heart Programme, said: “This data helps remove uncertainty about how to treat people who have an elevated systolic blood pressure but low diastolic blood pressure.”

mhouston@irishtimes.com, muirishouston.com

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