Lowerbody Negative Pressure Counteracts Simulated Microgravity Effects On Tibial Microvascular Flow
- Paper number
IAC-15,A1,2,4,x28004
- Author
Dr. Jamila Siamwala, University of California, San Diego, United States
- Year
2015
- Abstract
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) can be used 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) simulates microvascular flow responses to microgravity. We hypothesized that HDT induced changes in tibial microvascular flow and leg girth is prevented by LBNP. Tibial bone microvascular flow, oxygenation and calf circumference were measured during 5min sitting, 5min supine, 5min of 15o HDT, 10min HDT with 25mmHg LBNP using photoplethysmography (PPG), near infrared spectroscopy (NIRS) and strain gauge plethysmography (SGP), respectively. All the measurements were taken simultaneously and in a balanced order. Peak to peak averages measured in Volts demonstrated that tibial microvascular flow increased by 70% with 5min HDT (2.9±2.5V; RMANOVA p<0.0001) from sitting (0.9±0.8V). With 10min of LBNP in the HDT position, tibial microvascular flow returned to sitting levels (1.4±1.2V; RMANOVA p<0.001). Calf circumference decreased with 5min HDT (-0.7±0.4V; RMANOVA p<0.0001) compared to the sitting. In contrast, calf circumference increased with LBNP (-0.4±0.1V; RMANOVA p=0.002) compared to the HDT position (-0.7±0.4V). Further tibial blood flow was twice as low in females compared to males for all the positions. These data, establish that simulated microgravity increases tibial microvascular flow, reduces calf girthand 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).
- Abstract document
- Manuscript document
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