Calibrated photoplethysmographic estimation of digital pulse volume and arterial compliance

Abstract

Digital pulse volume and arterial compliance have been estimated by using the finger arterial pressure and volume waveforms when performing measurements at rest and during local cold exposure in 17 volunteers. The amplitude-based algorithm determines compliance as a ratio of finger volume and pressure pulses. Cooling was conducted by immersion of the contra-lateral arm in water at 11 degrees C for 2 min. Continuous non-invasive finger blood pressure was measured by the Finapres monitor, while the finger volume pulses were recorded by the UT9201 physiograph, which provides a photoplethysmographic registration of volume changes in a large range of transmural pressures (P(transm)). The photoplethysmographic signal was calibrated by applying a graded modulation to the cuff. The study demonstrated that contra-lateral arm cooling induced a statistically significant (P<0.001) reduction in the digital arterial compliance at P(transm) approximately 0 as well as at P(transm) = 50 mmHg. The median compliance diminished during cooling from 0.67 mm(3 )mmHg(-1) to the level of 55% at P(transm) approximately 0, and from 0.14 mm(3 )mmHg(-1) to the level of 42% at P(transm) = 50 mmHg respectively. The observed changes were mostly due to the reduction in the pulse volume. Digital arterial pressure and volume waveforms recorded by the Finapres monitor combined with a calibrated photoplethysmograph can be used in estimating the absolute values of the dynamic compliance of finger arteries. A quantitative estimation instead of the non-calibrated recording of the digital pulse volume allows shortening the variability and widening the scope of finger arterial compliance measurements.