Author(s): GIUSTI, L., MARCIANO, A., NERI, M., BOTTINELLI, R., PORCELLI, S., Institution: UNIVERSITÀ DI PAVIA, Country: ITALY, Abstract-ID: 2381

INTRODUCTION:
Inactivity is an important and independent risk factor for all-cause mortality, and there is increasing evidence of the importance of minimizing sedentary behavior to reduce the risk of cardiovascular diseases (1). Endothelial dysfunction plays an important role in the pathogeneses of cardiovascular diseases, and impaired endothelium dependent dilation is directly linked with cardiovascular morbidity and mortality (2). Bedrest, which is a classical model utilized to study the physiological effects of severe inactivity, showed a negative impact on endothelial function (3,4). The effects of steps reduction, a milder form of inactivity, on microvascular responsiveness are currently unclear. In the present study, we investigate the effects of 14 days of steps reduction on microvascular function, evaluating acute post-occlusive reactive hyperemia by near-infrared spectroscopy (NIRS).
METHODS:
Eighteen young subjects (12 males and 6 females; age: 22±3y, weight: 69.1±11.9kg, height: 172±7cm) were assessed before (PRE) and after 14 days of steps reduction (SR). Their physical activity was monitored through an accelerometer worn on the waist. Microvascular function was estimated by monitoring changes of tissue saturation index (TSI) during a prolonged ischemia followed by a reperfusion phase. The rate of muscle deoxygenation during the first minute of occlusion (Slope1) was used as proxy of resting muscle oxygen uptake. Time of ischemia (t-isch) and the lowest TSI value reached during occlusion (TSImin) were calculated to estimate the ischemic vasodilatory stimulus. The rate of muscle reperfusion during 10s (Slope2-10s) post-ischemia and the magnitude of reperfusion (TSIpeak) were calculated.
RESULTS:
Steps count was effectively reduced by 82% from PRE to SR. Slope1 was not different between PRE (-0.11±0.07%*s-1) and SR (-0.12±0.10%*s-1; p=0.436). TSImin was lower after SR compared to PRE (46.2±7.1% vs 43.2±8.5%, respectively; p<0.05). Slope2-10s was similar between PRE (1.16±0.59%*s-1) and SR (1.12±0.38%*s-1; p=0.573) but it resulted significantly reduced after SR (-13%) when normalized for the ischemic vasodilatory stimulus.
CONCLUSION:
After 14 days of steps reduction, resting muscle oxygen uptake did not change whereas endothelial function was impaired. Thus, a mild reduction of daily activity induced alterations at microvascular level, which are probably due to lower nitric oxide (NO) bioavailability and partial structural vascular modifications.