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Biomedical devices

Magnetic field fluctuations detect arterial pulse

13 Oct 2017 Zaibaa Patel 
Proposed device for local PWV measurement
Proposed device for local PWV measurement

Researchers from the Indian Institute of Technology Madrashave 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.

Local PWV measurement using a dual MPG probe

Transducer validation

The researchers performed in vitro studies using the MPG transducer with an arterial flow phantom. The phantom represented an arm, allowing the researchers to validate the system by obtaining measurements over the radial artery. The phantom experiments demonstrated that the new MPG prototype could obtain measurements that determined the PWV of small arterial segments.

The team also performed in vivo measurements under two physical conditions (physically relaxed and post-exercise) on a group of 20 healthy volunteers. They obtained blood pressure and local PWV measurements from the left carotid artery by placing the MPG probe on the neck.

The study demonstrated the ability to obtain continuous arterial MPG data with a signal-to-noise ratio of approximately 28 dB. The study results, of carotid pulse detection and local PWV measurement, proved the efficiency of the proposed technique, which provides a promising approach for cuffless blood pressure measurements.

 

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