A novel algorithm has been created by Russian researchers enabling contactless measurement of the time it takes for blood to travel from the heart to a specific body location. This instrument maintains functionality even when the patient is moving, a factor that previously hindered the clinical deployment of optical sensors. The research received support from an RSF grant, and its key findings have been published in the journal Scientific Reports.
During examinations and surgical procedures, clinicians assess not only pulse rate and blood pressure; the velocity of the pulse wave is also a crucial metric. This refers to the speed at which the pressure impulse from the heart propagates to various body regions. The stiffer the vessel walls are, the greater this parameter becomes, offering insight into potential risks for heart attacks and strokes.
Traditionally, measurements of this nature rely on wearable sensors, yet these are unsuitable for infants or patients suffering from burns. Conversely, previously developed contactless optical methods lacked sufficient accuracy due to interference from patient movements and respiration.
Researchers from the G. A. Krusenstern Institute of Automation and Control Processes of the Far Eastern Branch of the Russian Academy of Sciences (Vladivostok), in collaboration with colleagues from other universities, have succeeded in refining an algorithm for processing data from optical devices to estimate pulse wave velocity without physical contact.
They employed a camera utilizing green light, aiming it at a section of skin on the forearm. Green light is effectively absorbed by hemoglobin, making monitoring blood pressure changes straightforward by observing fluctuations in its intensity. As the pulse wave reaches the microvasculature, these vessels constrict, increasing light absorption, which consequently weakens the reflected signal.
To validate the accuracy of their measurements, the experts simultaneously recorded the heart rhythm using an electrocardiograph and synchronized its signals with the camera data.
The new algorithm successfully differentiated the blood flow signals from noise generated by the patient’s breathing and motion. It has the capability to partition each video frame into minute elements and track their temporal displacements. This development allowed for the highly precise measurement of the pulse wave amplitude (the disparity between systolic and diastolic pressures) and its transit time—the interval between the heart beat and the wave’s arrival at the observation point.
Using this algorithm, the scientists measured the pulse wave velocity in 47 healthy individuals. The skin area on the subjects’ arms was heated to 41°C—a procedure designed to evaluate vascular response to increased temperature.
The experiment demonstrated that upon heating, the pulse wave amplitude in the forearm increased by up to 23 times, while the time taken for the wave to travel from the heart to the arm was 23% faster than normal. No such alterations were observed outside the heated area.
This indicates a redistribution of blood flow: the majority bypasses the capillary network. This effect must be taken into account when testing vessel elasticity to identify risks associated with cardiovascular diseases.
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