(1459) Relationship Between Perfusion Indicator and Finger Height on Healthy Volunteers

Introduction: Perfusion Indicator (PI) (or % mod), a surrogate for perfusion at a specific measurement site, is not widely recognized to vary with geometry although theoretical modeling has suggested this (1). This variation reduces the ability to compare PI between measurement sites in an individual or between individuals. The current study explores this relationship using measurements of PI over a range of oxygen saturation (SpO2) and measured finger thickness (FT).

Methods: Post hoc data analysis was performed from data collected prior to an IRB approved laboratory desaturation study on 20 healthy subjects (10 M, 10 F, mixed ethnicity). Disposable and reusable finger SpO2 probes, clip and wrap styles, were placed on 6 fingers of the left and right hands (warmed), randomized to finger and hand. Data from each 6 probes was collected using Philips picoSAT boards. Before each study, FT of each finger (palmar to dorsal) on both hands was measured at the distal interphalangeal joint with a caliper. The average PI for each finger with a probe for each subject was computed.

Results: Mean (1 SD) FT (in mm) for the thumb (Th), index (In), middle (Mi), ring (R) and pinky (Pi) fingers are 17.3(1.9), 13.3(1.4), 13.7(1.3), 12.3(1.6), and 10.7(1.0) respectively. SpO2 ranged from 70 to 98% across subjects. Average PI and FT are positively related for all fingers (p < 0.05). Average PI values for each finger vs FT, showed a weak linear relationship (r2= 0.43,0.41,0.24,0.23,0.45 for the Pi, R, Mi, In and Th respectively) with this relationship significantly different for the thumb than the other fingers (p < 0.05).
Average PI tends to be larger for thicker fingers than for thinner fingers within and between subjects. PI variation between subjects is greater than within subjects. The difference in slope for the thumb may be attributed to differences in blood supply.
The middle finger tends to have the highest value of PI for all the fingers on the same hand and may be related to finger thickness. (2)

Conclusions: PI is dependent on the thickness of the tissue at the measurement site and methods to reduce this dependency should also be considered to better allow comparisons between sites and subjects.
Refs: 1. Mendelson Y, IEEE Trans Biomed Eng.1988;35(10):798-805. 2. Swain SM et al. Cureus. 2022 May 9;14(5):e24853.