Changes in the spectral powers of finger photoplethysmographic waveform variability in hemodialysis patients

This paper reports changes in the spectral powers of finger photoplethysmographic waveform variability (PPGV) following hemodialysis compared to pre-dialysis. The results are based on data collected from 12 hemodynamically stable patients having regular hemodialysis thrice weekly. Six minutes of continuous electrocardiogram (ECG) and finger infra-red photoplethysmographic (PPG) signals were collected at pre-dialysis and at end of dialysis. A four minute artefact free segment was selected and baseline and amplitude variabilities were derived from PPG waveform. Heart rate variability was derived from ECG R-R interval. Frequency spectrum analysis was then applied to these variability signals. The spectral powers were then calculated from low frequency (LF), mid frequency (MF) and high frequency (HF) bands. The results indicate that LF (p=0.01) and MF (p=0.02) powers of baseline PPGV (expressed in mean-scaled units) and LF (p=0.006), MF (p=0.003) and HF (p=0.017) powers of amplitude PPGV (expressed in mean-scaled units) showed a significant increase at the end of dialysis compared to pre-dialysis. HRV spectral measures did not show any significant change. The increase in LF and MF powers in PPGV may suggest the recovery and further enhancement of peripheral sympathetic vascular modulation as a result of volume unloading in initially hypervolemic dialysis patients, at the same time the increase in respiratory HF power in PPGV may indicate preload reduction.