Microvascular vasodilatory capacity in skeletal muscle is impaired following 10-days of bed rest in older adults with and without metabolic impairment

Background Periods of inactivity can have catastrophic consequences for physical function in older adults. While a reduced peak cardiac output is an established physiological response to inactivity, the associated peripheral vascular adaptations in skeletal muscle are poorly delineated and the impact of metabolic dysregulation on these effects remains unclear. Purpose The purpose of this work is to establish how microvascular vasodilatory capacity in the skeletal muscle changes across 10 days of bed rest and 4 weeks of ambulatory recovery and to assess whether this change differs in older adults with type-2 Diabetes Mellitus (T2DM) or pre-T2DM compared to metabolically healthy older individuals. Methods Older adults with T2DM/pre-T2DM (MET) or who were metabolically healthy (CON) completed 10 days of horizontal bed rest followed by 4 weeks of ambulatory recovery. Microvascular vasodilatory capacity was assessed using near infrared spectroscopy (NIRS) to capture the post-occlusive reactive hyperaemia (PORH) in the tibialis anterior (TA) and gastrocnemius (GN) muscles following a 5-minute cuff-induced arterial occlusion. Measurements were performed pre-bed rest, days 1, 3, 5 and 10 of bed rest and weekly during ambulatory recovery. Linear mixed-effects models were used to determine the effect of time (day for bed rest or week for recovery) on each measure of PORH. A random intercept for participant was included to account for repeated measures. An interaction term for metabolic status was also included. Where interactions were observed (p<0.10), time effects were stratified by metabolic status. Results In total, 21 participants (52% men, 58% MET, age 64[63, 67]) completed bed rest and recovery. Time to 95% and peak PORH increased and the rate of PORH response decreased across bed rest (Table 1). There was evidence for a greater effect of bed rest on PORH in the MET group, but this was only observed in the GN. All measures of PORH recovered with ambulatory recovery in both metabolic status groups (Table 1). Conclusion These data show that muscle microvascular vasodilatory capacity of older adults is reduced following 10 days of bed rest, an effect that appears to be greater in the GN of metabolically impaired individuals. Vasodilatory capacity improved with ambulatory recovery at a similar rate in both healthy and metabolically impaired individuals.