Sacral Microvascular Response in Older Adults Following Mechanical Loading Assessed by Photoplethysmography and Infrared Thermometry

Pressure injuries in institutionalized older adults with reduced mobility represent a relevant clinical problem due to their impact on quality of life and health costs. <b>Purpose:</b> This study aimed to describe the behavior of blood flow and tissue temperature in the sacral region and the significance of interindividual conditions in the post-load recovery of tissue in the context of pressure injuries. <b>Methods:</b> An observational study was conducted in 55 older adults living in a geriatric institution. Photoplethysmography and temperature signals were recorded at four times: at baseline (preload) and 15 s, 5 min, and 10 min post-load. The perfusion index was calculated, and two dichotomous variables were defined, Return b (flow) and Return t (temperature), to evaluate the physiological capacity to return to baseline conditions. Associations with clinical, functional, and diagnostic variables were explored. <b>Results:</b> The perfusion index showed usefulness as an indicator of microvascular recovery, but with variability between individuals. Return b was significantly associated with BMI and diagnosis of cardiovascular disease, while t-return was associated with body temperature and basal perfusion index. No significant associations were observed with sex, age or functional scales, state of consciousness, or risk of pressure injury. <b>Conclusions:</b> The study shows heterogeneous physiological responses to external load influenced by individual characteristics. Flow and temperature monitoring allows a functional approximation of injury risk, although more complex models are required to understand the nonlinear dynamics of tissue responses.