Comparing the compensatory reserve metric obtained from invasive arterial measurements and photoplethysmographic volume-clamp during simulated hemorrhage.

Purpose: The compensatory reserve metric (CRM) is a novel tool to predict cardiovascular decompensation during hemorrhage. The CRM is traditionally computed using waveforms obtained from photoplethysmographic volume-clamp (PPG), yet invasive arterial pressures may be uniquely available. We aimed to examine the level of agreement of CRM values computed from invasive arterial-derived waveforms and values computed from PPG-derived waveforms.

Methods: Sixty-nine participants underwent graded lower body negative pressure to simulate hemorrhage. Waveform measurements from a brachial arterial catheter and PPG finger-cuff were collected. A PPG brachial waveform was reconstructed from the PPG finger waveform. Thereafter, CRM values were computed using a deep one-dimensional convolutional neural network for each of the following source waveforms; (1) invasive arterial, (2) PPG brachial, and (3) PPG finger. Bland-Altman analyses were used to determine the level of agreement between invasive arterial CRM values and PPG CRM values, with results presented as the Mean Bias [95% Limits of Agreement].

Results: The mean bias between invasive arterial- and PPG brachial CRM values at rest, an applied pressure of -45mmHg, and at tolerance was 6% [-17%, 29%], 1% [-28%, 30%], and 0% [-25%, 25%], respectively. Additionally, the mean bias between invasive arterial- and PPG finger CRM values at rest, applied pressure of -45mmHg, and tolerance was 2% [-22%, 26%], 8% [-19%, 35%], and 5% [-15%, 25%], respectively.

Conclusion: There is generally good agreement between CRM values obtained from invasive arterial waveforms and values obtained from PPG waveforms. Invasive arterial waveforms may serve as an alternative for computation of the CRM.