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Human Spaceflight Capabilities

Noninvasive Biosensor Algorithms for Continuous Metabolic Rate Determination

Completed Technology Project

Project Introduction

NASA is designing new spacesuits to meet the needs of future space exploration. Real-time measurement of metabolic rate during astronaut activity is a key function of the biosensor suite which is planned for the new spacesuit. This project is developing novel near infrared spectroscopic (NIRS) algorithms and sensors for real-time assessment of metabolic rate (measured as the rate of oxygen consumption, VO2). This capability is intended to be incorporated into a smart system advising astronauts on their use of consumables during extravehicular activity (EVA). The specific aims of this project include the development of algorithms to calculate VO2 from NIRS spectra and validation of the algorithms during exercise in two different ground-based protocols which simulate plasma volume reduction during spaceflight. An additional aim of this project is to support the EVA suit testing program by developing small, lightweight and robust sensors which can be used within the spacesuit to evaluate metabolic cost of the suit itself, on individual muscles.

Over the last year we have made significant progress in developing the components of the algorithm to calculate VO2 from NIR spectra. We have completed the initial algorithm to estimate stroke volume and made advancements in improving the accuracy of our hematocrit calculation. We have further optimized our measurement of muscle oxygen saturation and demonstrated its high degree of accuracy under a number of potential confounding factors. Most important for space application, we demonstrated accuracy under conditions that simulate factors that occur during fluid shifts, i.e., variation in blood and water fraction, as well as changes in blood vessel size.

We completed data collection for a study of pharmacologically induced hypovolemia, one of the validation studies we will use to assess performance of our VO2 algorithms. Initial data analysis showed that noninvasively determined NIRS parameters, muscle oxygen saturation, and hydrogen ion threshold were not different between the hypovolemia and normovolemia exercise sessions. This result is in agreement with the finding that lactate at peak exercise was not different between the 2 groups.

With synergistic funds from the US Army Medical Research Command we continued to develop the solid state sensor and software to support it. The first systems were delivered to Johnson Space Center (JSC) for testing in the Exercise Physiology lab. Hardware and software usability was greatly improved over the fiber optic system according to the users.

This project has produced a prototype wearable sensor that terrestrial doctors and their patients can use to track and optimize exercise in the management of health and fitness, as well as during related applications in the care of critically ill patients. A company has been formed to commercialize the sensor. The company is on target to submit a 510(k) application to the FDA (Food and Drug Administration) in early 2011.

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This is a historic project that was completed before the creation of TechPort on October 1, 2012. Available data has been included. This record may contain less data than currently active projects.