A systolic blood pressure measurement of 140 mmHg or higher and a diastolic measurement of 90 mmHG or higher (140/90 mmHg) is considered high. Blood pressure is usually assessed using either a manual (auscultatory) or automatic (oscillometry) meter in a doctor’s office or hospital. However, these measurements can be affected by “white coat syndrome” — a patient’s fear or anxiety in a doctor’s office causes their blood pressure to measure above normal levels. To avoid the white coat effect, at-home automatic measurements taken by the patient may be required, but available oscillometry-based automatic meters offer a low level of accuracy.
“The automatic oscillometric technique is less accurate than the manual auscultatory technique, when both are used in the clinician’s office,” Meir Nitzan, PhD, the new study’s first author, said. Currently available automatic blood pressure measurement devices are commonly off by 10 to 15 mmHg. This is mainly due to indirect determination of the blood pressure from the oscillometric air-pressure wave measurements taken by automatic devices.
A patient with an incorrect high blood pressure diagnosis may be prescribed blood pressure-lowering medication unnecessarily. These medications can cause patients’ blood pressure to dip too low (hypotension); elderly patients are especially at risk. Side effects of hypotension can include short-term symptoms such as dizziness and fainting and long-term problems such as insufficient blood supply to vital organs, which can lead to acute kidney injury and cognitive impairment.
The research team has developed a device — using a technique called photoplethysmography — to more accurately measure systolic blood pressure. The device uses a pressure cuff wrapped around the arm and an electro-optic probe on the finger. “The finger probe is similar to that of pulse oximeter: It includes a light-source emitting light into the finger and a detector, which measures the light transmitted through the finger,” Nitzan explained. “The transmitted light exhibits pulses at the heart rate, due to cardiac-induced blood volume changes in the finger tissue. When the cuff pressure increases to above systolic blood pressure these pulses disappear, and when the cuff pressure decreases to below systolic blood pressure they reappear. This effect enables the determination of systolic blood pressure.”