This experiment was designed to develop novel algorithms for existing near infrared spectroscopy (NIRS) platform for real-time assessment of metabolic rate (measured as the rate of oxygen consumption, VO2) and muscle temperature. This capability was intended to be incorporated into biosensors which were part of a smart system to advise astronauts regarding their usage of consumables during lunar surface activities.
The following specific aims were proposed:
1. Develop and validate algorithms to accurately calculate VO2 from NIR spectra collected from muscle
2. Develop and validate algorithms to simultaneously calculate muscle temperature
3. Support incorporation of the sensor algorithms into the EVA suit testing program, where practical.
The feasibility was demonstrated by determining VO2 with the Fick equation and data that was collected solely through a NIRS system. The accuracy of this technique was currently limited at high exercise intensities, primarily due to inaccuracies in the stroke volume estimate. Improvements were made on the accuracy of the NIRS measurements used to calculate oxygen content. These improvements were tested with the data collected from the bed rest subjects, as well as the data collected from a hypovolemia study, which looked at the effects of plasma volume changes alone on these measurements.
Collaboration efforts, supported by non-NASA funds, was initiated to develop a solid-state, low profile spectroscopic sensor which had the potential to provide a prototype unit with appropriate characteristics which was used for ground testing within the extra-vehicular activity (EVA) suit.
The proposed biosensor system had built-in redundancy through easy application to both limbs. The biosensor also provided system redundancy in the measurement of heart rate and temperature to further ensure astronaut safety. The proposed technology was expected to result in wearable sensors that terrestrial doctors and their patients could use to track and optimize exercise in the management of both health and fitness, as well as during related applications for the care of critically ill patients.
The same cycle ergometer, ECG, blood pressure, and metabolic gas analysis devices/techniques were used for all NIRS tests as per the Standard Measure cycle ergometer test (MR080G).
This experiment has concluded in ground-based studies sponsored by the National Space Biomedical Research Institute (NSBRI). This experiment was conducted during the Head Down Tilt 30 Day Study. LSDA does not expect to receive results from this study.
Publication results indicate that interstitial hydrogen ion concentration and muscle tissue oxygenation (SO2) are aggregate measures of local metabolite production and the cardiovascular response. Inferred from simultaneous SO2 and [H+] measures in the vastus lateralis (VL) and gastrocnemius (LG) muscles, muscle perfusion is well matched to VL and LG work during walking, but not running. More information can be found in the cited publications below.