Magnetic field fluctuations detect arterial pulse

Researchers from the Indian Institute of Technology Madras have proposed a magnet-based sensor that would allow scientists to measure the velocity of blood pulse waves within the carotid artery. Each heart beat pumps blood at a high pressure through the arteries, and parameters such as the pulse speed provide useful pathophysiological information (IEEE Trans. Biomed. Circuits Syst. 11 1065).

Pulse wave velocity (PWV) – the velocity of blood propagating through the arterial tree – is a strong indicator of cardiovascular events. Calculation of blood pressure using PWV, based on the fundamental biomechanical equations, holds true only for smaller sections of an artery. But existing cuffless blood pressure monitoring technologies measure PWV across a large arterial section. Current techniques for measuring local PWV, such as Doppler ultrasound and MRI, are expensive and operator dependant.

Magnet-based sensor

To determine PWV from small arterial sections, the electrical and biomedical engineering researchers propose a magnetic plethysmograph (MPG) transducer, based on the modulated magnetic signature of blood (MMSB) principle, to measure blood pulse velocity across small sections of arteries. This consists of a permanent magnet producing an ambient field and a Hall-effect sensor that provides a voltage measurement corresponding to volumetric change in the artery.

When the transducer is placed on the skin above an artery, the magnetic sensor measures magnetic fluctuations due to skin surface motion caused by the pulsatile blood flow. Analysis of the arterial blood pulse is possible because the output voltage of the sensor is directly proportional to the amplitude of the pulse. After the acquisition and digitization process, the data are analysed by custom designed algorithms to identify characteristic points in each waveform and calculate the local PWV.

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