NASA Research Project

Overview

Astronauts, like divers, are exposed to changes in pressure that can lead to decompression sickness (DCS), otherwise known as "the bends". When an astronaut leaves the Space Station for Extravehicular Activity (EVA), the pressure of the space suit (4.3 psia) is one third of sea level pressure (14.7 psia), or equivalent to the pressure at an altitude of 30,300 feet. Astronauts breathe oxygen prior to an EVA ('prebreathe') to eliminate nitrogen from the body, thus decreasing the risk of developing decompression sickness. This study is designed to determine the safest procedure for protecting astronauts from DCS during the many spacewalks required for construction and maintenance of the International Space Station. Extravehicular activity is very demanding, both physically and mentally, partially due the nature of the space suit. The space suit currently in use consists of a Hard Upper Torso with flexible extremities. The resting position or maximum volume of a spacesuit is found with the arms elevated overhead in a relaxed position. Astronauts work to alter the resting position of the spacesuit in addition to the work required for the EVA. This study endeavors to simulate both the effects of the space environment on the body and the effort of spacesuit/EVA activity.

Objectives

The specific goals of this project are to:

• Measure the oxygen consumption necessary to complete prebreathe
• protocols during astronaut simulation activity.
• Determine the operational suitability of a 1.5 hr in-suit prebreathe protocol.
• Provide scientific understanding of the relationship between intermittent exercise intensity and duration and the occurrence of DCS and VGE.

Methods

Initially, prebreathe exercise and EVA simulation will be done at ground level while breathing air. Exercise levels during prebreathe will be dependent upon an individual's fitness level (indicated by the person's ability to consume oxygen at maximal exercise - aerobic capacity or VO_{2 max}). Oxygen consumption will be measured during the study to measure the effort required in different activities. Symptoms related to the exercise done during EVA simulation portion of the protocols will be recorded to develop a baseline symptom database to help astronauts differentiate between discomfort due to activity and possible DCS. Participants will complete exercises similar to those that astronauts may perform during EVA. The exercises include cross-chest pulls (simulating reaching across the body), operation of a torque wrench, hand grips (to grasp an object astronauts must exert enough force to bend the suit's glove plus that required to grip an object), sit-ups against an applied force, and pulls (simulating the work required to use a PFI or Portable Foot Insert). The exercises are grouped into four minute intervals. After three exercise intervals, a rest interval is used for doppler monitoring, use of an ultrasonic probe to determine the presence of gas bubbles associated with decompression phenomena.

Listen to Doppler Recording (WAVE Format)

Participants will be asked to come to the laboratory on five separate days (approximately three hours on the first day and eight hours on the other days (with a minimum of three days between trial days). The first day involves a study overview for the subject, followed by completion of paperwork (pre-participation questionnaire, medical history, informed consent, etc), a physical examination, and a test to determine VO_{2 max} (simultaneous arm and leg crank cycle ergometry) to determine maximal aerobic capacity. The second day begins with a brief overview of the day's events, purposes, risks, and expectations. The participants are then prepared for the prebreathe. During the prebreathe period, participants will exercise on a stationary cycle ergometer. Exercise levels will be set to 40-60% of their previously measured VO_{2 max}. Technicians will time exercise periods and adjust exercise levels as prescribed in the prebreathe protocol being tested (any one of four). After the prebreathe exercise is complete, participants will lay in the suit simulator cots. Following the rest period required by the prebreathe protocol, a TaskPrompter will be started to cue participants to the time and type of exercise to be done as part of the 240 minute EVA simulation.

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• Overview
• Objectives
• Methods
• Typical Trial Schedule
• Future Studies

Typical Trial Schedule

At least 72 hrs prior to the EVA simulation
08:00 Meet at Hyperbaric Center
08:15 Fill out paper work (Informed consent - Medical History - Compensation)
09:00 Pre-dive physical examination
09:30 VO_{2 max} test
10:00 Scheduling and Review
10:30 Orientation to equipment and procedures

VO2 Measurement and EVA Simulation
08:00 Arrive at the Center for Hyperbaric Medicine and Environmental Physiology
08:15 Medical interview
08:30 Review procedures, complete paperwork
08:45 Breathing equipment set-up
09:00 Start prebreathe protocol
11:00 Start EVA simulation
15:00 End EVA simulation / Debriefing
15:30 Release

Future Studies

Studies to resume late Fall 2005.