Short-Term Cardiovascular Compensatory Responses to Varying Levels of Orthostatic Stress During Active Standing in...

Background: The cardiovascular system of older adults is significantly impacted by aging, contributing to blood pressure (BP) dysregulation, particularly during postural transitions. This study compared the short-term cardiovascular compensatory responses of younger adults (YA) and older adults (OA) during sit-to-stand and lie-to-stand. Methods: Participants underwent two active standing orthostatic stress tests, involving 5 min of sitting or 10 min of lying, followed by up to 7 min of standing. Beat-to-beat cardiovascular parameters were assessed using a Finometer (Finapres Medical Systems). Systolic (SBP), diastolic (DBP), mean arterial pressure (MAP), cardiac output (CO), stroke volume (SV), systemic vascular resistance (SVR), and HR were measured at baseline, immediately on standing, and throughout four specific phases after standing: phase 1 (0-30 s), phase 2 (30-60 s), phase 3 (60-80 s), and phase 4 (300-420 s). CO-SVR matching was evaluated to assess BP regulation timing. Results: Compared to YA, OA exhibited higher SBP, DBP, MAP, and SVR but lower HR, CO, and SV at baseline. Immediately on standing, OA experienced a greater drop in SBP, DBP, MAP, and SVR, blunted HR, reduced CO, and higher SV. The short-term compensatory responses were delayed (30-60 s), particularly in lie-to-stand, due to a transient CO and SVR mismatch observed in phase 1 and subsequent BP stabilization from phases 2-4. Conclusions: OA exhibited short-term compensatory cardiovascular dysregulation, particularly during the transition from a lying to a standing position.