Physiological Responses to Prior Verbal Notice Before Passive Postural Change: A Randomized Crossover Exploratory Study of Circulatory and Autonomic Dynamics

Background/Objectives: Passive postural change from the supine position to sitting requires rapid circulatory and autonomic adjustment. This small-scale exploratory study examined whether prior verbal notice is associated with changes in cerebral and peripheral haemoglobin dynamics and heart rate variability during passive postural change in healthy middle-aged and older men. Methods: Ten healthy men completed both experimental conditions in randomized order: passive postural change with prior verbal notice and passive postural change without prior verbal notice. Each condition consisted of 10 min of supine rest, 10 min of sitting with feet on the floor, and 10 min in the supine position after return. Near-infrared spectroscopy was used to assess haemoglobin changes in the left frontal region and right gastrocnemius muscle, and heart rate variability was used to estimate autonomic modulation. Results: In both conditions, frontal total haemoglobin and oxygenated haemoglobin decreased shortly after sitting and subsequently tended to recover by approximately 5 min after postural change. The low-frequency/high-frequency (LF/HF) ratio increased earlier in the prior-notice condition, and no adverse events occurred. Because the sample was small, these findings should be interpreted as preliminary within-sample patterns rather than as confirmatory evidence. Conclusions: Prior verbal notice may be associated with earlier autonomic adjustment during passive postural change. The findings do not establish clinical benefit or causality. Larger crossover studies that include women, frail older adults, and clinical populations are needed before firm clinical recommendations can be made.