LOWER BODY NEGATIVE PRESSURE COUNTERACTS SIMULATED MICROGRAVITY EFFECTS ON TIBIAL MICROVASCULAR FLOW

摘要

Space poses myriad physiological problems among which is 1-2% bone loss per month compared to 1% bone loss in post-menopausal women per year. Bone loss may be caused by altered bone microvascular flow in space. The main purpose of the study is to determine if lower body negative pressure (LBNP) is feasible as a suitable countermeasure to prevent microgravity effects on the tibial blood flow. We also sought to find out if there were gender differences in tibial microvascular flow in simulated microgravity conditions. Head down tilt (HDT) simulated microvascular flow responses to microgravity. We hypothesized that HDT-induced changes in tibial microvascular flow are prevented by LBNP. Tibial bone microvascular flow wasmeasured during 5min sitting, 5min supine, 5min of 15o HDT, 10min HDT with 25mmHg LBNP using photoplethysmography (PPG), respectively. All measurements were taken simultaneously and in a balanced order. Peak to peak averages demonstrated that tibial microvascular flow increased by 70% with 5min HDT (2.9±2.5Volts; RMANOVA p<0.0001) from sitting (0.9±0.8Volts). With 10min of LBNP in the HDT position, tibial microvascular flow returned to sitting levels (1.4±1.2Volts; RMANOVA p<0.001). These data establish that simulated microgravity increases tibial microvascular flow and LBNP is an effective counter measure. Thus, our results suggest that LBNP may be a suitable countermeasure to normalize the bone microvascular flow changes in space. This study was supported by NASA grant NNX13AJ12G (ARH).