“Blood pressures measured by an arm or wrist will give you ‘brachial pressures’ instead of the central pressure,” Kan explained. “Brachial pressures can be similar if the cuff is maintained at the height of the heart, but it is an indirect measurement together with the arm condition.”
Cuff-based measurements provide an estimate of an average blood pressure over a number of heartbeats, while the Kan group’s RF-based method gives an estimate for every heartbeat.
Patients in hospital whose blood pressure needs to be periodically checked will often have their rest interrupted by cuff-based measurements. The new method can be done over clothing, without rolling up sleeves or putting on a Velcro wrap, and without disturbing the patient.
The RF method also collects data that an arm-cuff cannot provide.
“The heartbeat has two circulations,” Kan said. “One goes through most of the body (systemic circulation) and the other through the lungs (pulmonary circulation). Therefore, the heartbeat contains four pressure points in the central blood pressures: systolic and diastolic pressures in systemic and pulmonary circulation. The arm cuff provides no information about pulmonary circulation.”
Pulmonary artery hypertension (PAH), one of the pre-existing conditions that increases COVID-19 fatality risk, currently has to be measured using catheters or estimation from ultrasound imaging. Measuring pulmonary blood pressures using a far less invasive method has become even more important today.
“Additionally, blood pressure variations (like heart rate variation, HRV) per heartbeat are indicators for stress and wellness states, which is not possible in cuff-based measurements,” Kan said.
If sensors can be integrated into garments, healthcare professionals could receive continuous monitoring of at-risk patients’ complete blood pressure data in the coming era of telemedicine.