The relationship between the photoplethysmographic waveform and systemic vascular resistance

The objective of this study was to determine the relationship between systemic vascular resistance (SVR), finger & ear photoplethysmographic measurements in 14 adult patients undergoing coronary artery bypass grafting (CABG).

Patients were monitored with photoplethysmographs of the finger and ear and continuous cardiac output (QT) via thermodilution catheter. The relationship between SVR, finger plethysmographic amplitude, width and ear plethysmographic amplitude, width was assessed with linear regression.

The finger plethysmographic amplitude had a low correlation r value = -0.15, while finger plethysmographic width had a better correlation r value = 0.56. The correlation between SVR and ear plethysmographic amplitude and width were -0.24 and 0.62 respectively. Using receiver operating characteristic analysis the ear plethysmographic width had both better sensitivity and specificity than the finger plethysmographic width in identifying high and low SVR. Using a multiple regression analysis, SVR was estimated from the pulse oximeter waveforms: SVR calculated = 27.27 + (3978.53 x Ear pulse oximeter width) - (8.91 x Ear pulse oximeter area) + (1986.3 x Finger pulse oximeter width). Bland-Altman analysis was used the bias was 29.8 dynes s cm(-5), standard deviation was 587.3, upper and lower limit of agreement were 1204.45, and -1144.8 dynes s cm(-5) respectively.

The data indicate that pulse width of finger and ear plethysmographic tracing are more sensitive to changes in SVR than the other indices. An appreciation of changes in pulse width may provide valuable evidence with respect to changes in peripheral vascular tone.