Abstract
Abstract only In patients with autonomic nervous system (ANS) dysfunction, compromised ANS organo- and somatotopic vascular control is poorly captured by current diagnostic and prognostic assessments (such as the Composite Autonomic Scoring Scale (CASS)). While capable of capturing hemodynamic tone during a vascular challenge (such as vascular occlusion), current commercially available photoplethysmography (PPG) sensors are typically designed to only fit “finger pad-like” interfaces – i.e. highly curved, pliable tissue. Thus, modular and customizable housings for commercial PPG sensors that can facilitate adequate affixing pressure for high-quality signal acquisition would allow for more accurate assessment of vascular control at standard sites (e.g., finger pad) and non-standard sites (e.g., mid-forearm). This study was designed to test the following hypotheses in healthy adult subjects: (1) PPG recorded from a non-standard site using a low-cost, 3D-printed custom housing is of similar quality to that recorded from the commercially standard site; (2) the deconstructed PPG signal into pulsatile and non-pulsatile components reflect blood volume indices across distinct vascular compartments (arterial vs venocapillary, respectively); and (3) vascular control displays distinct PPG changes across standard and non-standard recording sites during a proximal (upper arm) occlusive reactive hyperemia experiment. To test these hypotheses, healthy volunteers were instrumented with 2x PPG sensors (PPG100C, Goleta, CA, US) – one at the standard manufacture site (finger pad) and one at a non-standard site (mid-forearm). The non-standard site PPG was removed from its original housing and reinstalled in a custom 3D printed flat housing containing a pressure transducer – both sensors were affixed to their respective sites with Velcro. A manual sphingomanometer was placed on the upper arm ipsilateral to the sensors and inflated to a supra-systolic blood pressure (SBP + 20 millimeters of Mercury (mmHg)), mean arterial pressure (MAP), or sub-diastolic pressure (DBP – 20mmHg). The mid-forearm PPG sensor was affixed loosely, ideally, or tightly. Results from this study show that PPG signal quality improves as affixing pressure increases [at affixing pressures of 0.57 pounds/inch2 (psi), 1.12 psi, or 1.65 psi, the difference in the mean Voltage (V) peak-to-peak recorded from the forearm or finger sites were 0.39 ± 0.2V, 0.12 ± 0.03V, 0.19 ± 0.03V, respectively; ANOVA p < 0.01; data presented as mean ± SD]. Additionally, vaso-occlusive conditions show that not only do the pulsatile and non-pulsatile components of the PPG signal represent independent compartments of the underlying vascular bed, but also that vascular volume control is differential between mid-forearm and finger pad positions. Therefore, these results suggest that (1) signal quality changes as a function of affixing pressure, (2) a single PPG signal carries information about individual blood vascular compartments, and (3) vascular dynamics follow a sectionalized distribution that can be measured. Funding support: William Townsend Porter Pre-Doctoral Fellowship from the American Physiological Society awarded to Eric Albuquerque This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.