Noninvasive measurement of vascular compliance by a photoplesythmographic technique

Abstract

We describe a simple and robust alternative to ultrasonic methods for the measurement of pulse propagation velocity (PWV) which detects the passage of the diameter wave as it passes two sites a known distance apart. Two probes each containing an infra-red emitting diode and a phototransistor are placed on the skin near to the vessel of interest. The energy returning to each probe depends on the amount of blood the beam has passed through, and this varies as the vessel pulsates. The output from each probe is displayed in real time on a portable PC. PWV is estimated beat-by-beat from the delay between the start ofthe systolic upswing in the signals from the two sites.In order to verify that our device measures changes in arterial diameter its signals were compared to those obtained simultaneously from an echo tracking pulsed ultrasound system. Transit time measurements from the two devices on the radial and femoral arteries in 6 subjects agreed closely. Additional validation experiments on 2 1 subjects undergoing cardiac catheterization have shown that transcutaneous measurements of PWV using the infra-red device agree well with intra-arterial measurements obtained with a cannula and pressure transducer.We conclude that the optical technique for measuring PWV is a useful addition to the methods available for determining blood vessel elasticity. Its simplicity and ease of use make it suitable for large scale measurements in the 'field'. Three such studies are currently in progress.

Effect of a COL1A1 Sp1 Binding Site Polymorphism on Arterial Pulse Wave Velocity

“…PWV is inversely related to the square root of vessel wall compliance, so a high PWV indicates a stiffer arterial wall. This method yields results 29,30 similar to those of Doppler ultrasonography, 28 which provides reproducible estimates of arterial compliance. 31 PWVs were measured in 3 arterial segments: aortoiliac (PWVA), from the proximal common carotid into the femoral artery at the inguinal ligament; aortoradial (PWVB), from the carotid into the radial artery; and aorto-dorsalis-pedis segment (PWVF), from the carotid into the posterior tibial artery posterior to the dorsalis-pedis artery.…”

“…27 The technique was a modification of that developed by Greenwald et al 28 to determine the transit time of the wave of dilatation propagating from the pressure wave generated by left ventricular contraction. PWV is calculated as the time taken to travel a known distance, timed from the ECG R wave, to the arrival of the pressure wave at a distal site, using a photoplethysmographic probe.…”

Vascular dysfunction after repair of coarctation of the aorta

“…PWV was calculated as the ratio of the distance between the 2 probes and the transit time. The accuracy and reproducibility of photoplethysmographic assessment of PWV have been validated, 13 and this measure is considered to be a robust index of arterial stiffness being inversely related to the square root of distensibility (PWVϭ1/͌distensibility). 14 Femoral-dorsalis pedis PWV was also assessed by similar methodology.…”

“…13 Two photoprobes, each containing an infrared-emitting diode and a phototransistor, were placed over the brachial and radial arteries and secured without compression. The infrared beam was scattered by the skin and other soft tissues and strongly absorbed by the blood as it flowed along the blood vessels.…”

Early Changes in Vascular Dynamics in Relation to Twin-Twin Transfusion Syndrome

“…This is a non-invasive technique using two probes, each containing an infra-red emitting diode and a photo-transistor, that are placed over the artery of interest, a known distance apart, to measure the pulse transit time (Figure 1; Greenwald et al, 1997). The PWV is derived by dividing the distance between the two probes, measured to the nearest millimetre, by the transit time.…”