Chamber Pilot Studies Plan

Purpose of this RFI: 

The objective of the pilot chamber testing is to validate chamber facility and test team capabilities to support NASA decompression sickness (DCS) studies supporting NASA’s development of the Aerospace Estimation Tool for Hypobaric Exposure Risk (AETHER).  Facilities are requested to perform 3 test days, collecting and recording data each day as they would for a research protocol.  The first day of testing may be considered practice session with the recognition that some facilities and/or hardware integration issues may arise.  The second day of testing should be scheduled after issues from the previous run have been resolved, and testing should be completed without interruption, unless otherwise indicated.  The third day of testing should occur in the same work week as the second test day to demonstrate the facility’s capability to perform multiple runs in short order.  This last capability is important because NASA’s main objectives in engaging other facilities include an increased tempo of data collection to develop a comprehensive model of DCS risk during spaceflight across a range of conditions that will inform requirements for future vehicles, habitats, suits, and mission planning.  At the discretion of NASA, a fourth test day may be required if unresolved deficiencies in performance persist after the third test day. 

NASA’s own facilities will support this work in part but are shared with other operationally relevant tasks/programs, limiting NASA facilities’ overall availability and impacting scheduling and completion of critical work.  Identification and validation of non-NASA resources to support these DCS research objectives are important steps to facilitating safe and successful prebreathe procedures and extravehicular activity (EVA) in weightlessness and during exploration missions.

Budget for this work is firm fixed price.  Budget quotes can include payments for interim milestone completion.  Dates for each interim milestone should be set by the supplier.

Subjects

Facilities will recruit and screen applicants to provide at least 3 subjects and up to one test operator (tinder/ultrasound technician) per day to participate in at least 3 test days to fulfill the requirements described above.  Each test day is anticipated to last approximately 12 hours.  Each of the three single day runs will have unique subjects.  Screening back-up subjects in case of subject availability issues, withdrawal, or disqualification is highly recommended. 

Facilities should screen subjects per their standard protocols, and the subject pool should include females to demonstrate their capabilities to recruit and test this important population.  NASA will provide inclusion and exclusion criteria for a population demographic similar to the astronaut corps.  As part of the screening process, subjects must pass a medical exam similar to a private-pilot flight physical and complete a peak (maximal) oxygen consumption (VO2pk) test using a cycle ergometer protocol with metabolic gas analysis.  NASA will provide the VO2pk cycle ergometry test protocol.  To qualify for participation, subjects must achieve VO2pk >27.5 ml/kg/min.

Following the screening, subjects will participate in a familiarization session during which they will receive verbal and written description of the test protocol, be encouraged to ask questions, and will provide written informed consent before proceeding to participation.  Thereafter, subjects will be familiarized with the chamber protocol and safety procedures, the appropriate mask size will be determined, and the subjects will practice mask breathing.  Subjects also will be familiarized with the EVA simulation workstations, and metabolic rate will be measured while performing the arm ergometry and stepping exercises at several low work rates (submaximal exercise intensity) to verify the cadence or work rates required for the in-chamber exercise prescription.

Standardized Test Day

Facilities will implement a test plan that includes a 6.5-hour prebreathe followed by a simulation of EVA lasting 6 hours, or until signs and symptoms that require test termination (per NASA and facility standards), test termination by subject request, or facility or monitoring capabilities malfunctions.  These sessions will include successful mask operations and demonstration of safety procedures.  An additional 30 minutes should be allotted for repressurization and post-test monitoring.

Medical Monitoring

The facility will provide the appropriate medical support to perform pre-chamber physical examination before ingress, during the protocol, for treatment and management of subjects as needed, clearance of subjects after the protocol is completed, and follow-up in the days after the chamber run, as required.  Responsibilities of the medical personnel include monitoring and interpretation of 2-D ultrasound and Doppler as well as monitoring of the subject’s self-report and symptoms of DCS or intolerance.

Prebreathe Conditions

Facilities will demonstrate the capabilities to perform 100% O2 prebreathe durations up to 6.5 hours.  Subjects will begin mask breathing at the start of the prebreathe and remain on mask through decompression and until repressurization is completed.  Subjects should be provided fluids ad libitum without a break in prebreathe (using drink port).  NASA will provide breathing masks and/or design for their construction or provide approval for a suitable substitution.  Food will be allowed prior to start of mask prebreathe but not during the test protocol (for 12 hours).  Subjects also are not allowed to sleep during the test protocol.

EVA Simulation

Facilities will demonstrate their capacity to perform a simulated 6-hour EVA and maintain standardized monitoring practices.  To simulate the suit environment, the chamber will depress to 5.2 psia before initiating the EVA simulation tasks described below.  The start time of the EVA is defined by the arrival at the desired level of decompression, and the end time of the EVA is defined by the start of repressurization.

EVA simulation will include rotation of each subject through a repetitive series of tasks at predetermined intervals in a pre-determined order using NASA-defined or NASA-provided workstations (Figure 1). The EVA is simulated using eight stations, nominally performed in 2 cycles of 4 stations, with subjects rotating between stations every 5 minutes.  In one cycle, subjects will rotate through stations that simulate ambulation (low step), upper body technical tasks (standing board), and load carrying (weight transfer), and 2-D ultrasound while subjects are lying left-lateral decubitus on a cot.  In the second cycle, subjects will rotate through stations that simulate more vigorous ambulation (high step), upper body physical exertion (arm ergometry), technical tasks performed in a kneeling position (kneeling board), and 2-D ultrasound while subjects are lying left-lateral decubitus on a cot.  Thus, in each cycle subjects will perform 15 minutes of low- to moderate-intensity exercise followed by 5 minutes of monitoring and rest.  Work rates during arm ergometry (cadence and resistance) and stepping (cadence) will be prescribed based upon the results of the VO2pk test and the pre-test EVA simulation familiarization with metabolic gas analysis.  During ultrasound imaging, at least 10 cardiac cycles will be monitored and recorded in each of three conditions in sequential order: rest, flexing/bending of the arms and legs, and rest.  Compliance of the subjects with the prescribed procedures should be documented, including the time at each station, work rates (cadence and load), symptoms reported by the subjects, and test operator observations.

Standardized Measures
Facilities will use a standardized set of measurements to monitor and document test subjects during the prebreathe, decompression, and recompression.

Logging of symptoms and definition of DCS
Test operators will record all symptoms reported by the test subjects throughout the duration of the protocol, whether in response to prompting by the test operators or spontaneous self-reporting.  Subjects will be removed from the chamber and repressurized (airlock or chamber) at the onset of DCS (Type I or Type II).

NASA (JPR 1800.3 E) defines DCS severity with the following criteria:
•    Mild DCS (Type I), Uncomplicated: Symptoms involving joint pain, peripheral nervous system, or simple skin bends that resolve upon repress or within the first 20 minutes of treatment.
•    Mild DCS (Type I), Complicated: Symptoms involving joint pain, peripheral nervous system, or simple skin bends that DO NOT resolve upon repress or within the first 20 minutes of treatment.
•    Mild DCS (Type I) – Repetitive: Mild DCS symptoms involving joint pain, peripheral nervous system, or simple skin bends that occur after a successful treatment and within 30 days of a prior case of DCS for ground-based exposure. These are considered discrete occurrences of DCS in response to chronologically discrete exposures.
•    Serious DCS (Type II): Symptoms involving the Central Nervous System (CNS), cardiovascular system (circulatory collapse/shock), pulmonary system (chokes).

NOTE: Previous studies using similar procedures at other facilities had rates of Type I DCS between 16% and 50% when simulated extravehicular activities were conducted at 4.3 psi for 6 hours. All cases of DCS were resolved with ground-level oxygen treatment.

Questionnaires
Test operators will query subjects for responses to standardized questionnaires during each rotation through the resting/ultrasound station.  Subjects will report a rating of perceived exertion (RPE) and pain using NASA-defined scales at the end of each exercise bout (i.e., after 5 minutes of arm ergometry, stepping).  

Cardiac Ultrasound
2-D imaging for detection of venous gas emboli will be performed by a qualified test operator or subjects trained to self-scan during each rotation through the resting/ultrasound station while the subject is at rest and following exercise. 2-D ultrasound will be recorded and stored electronically with relevant metadata (e.g., subject ID) for post-exposure review and analysis. Ultrasound will be scored using the NASA-modified Eftedal-Brubbak (EB) scale (0-7) (1).

Pulse Oximetry (Recommended)
Oxygen saturation (SaO2) should be monitored during the decompression, EVA simulation, and recompression. Test operators must be able to observe the current SaO2 from the device as needed and will record SaO2 at frequent intervals. 

Heart Rate (Recommended)
Heart rate should be continuously monitored and recorded using chest-worn devices (e.g., Polar heart chest strap) from which data can be downloaded and stored electronically with relevant metadata (e.g., subject ID, date, time) for post-exposure analysis.  Test operators must be able to observe the current heart rate from the device as needed and will manually record heart rate at the end of each 5-minute rotation through the EVA simulation stations.

Data Validation
At the conclusion of each test day, the facility will deliver electronic records to NASA using a secure, NASA-approved method.  The data package will include subject metadata, console and/or operator’s logs (including chamber event time, prebreathe records, EVA time, EVA station schedule), chamber pressure recordings (demonstrating depress and repress rates as well as sustained chamber pressure), chamber environmental conditions (partial pressures of O2, CO2, and N2, temperature, humidity), questionnaires, medical monitoring logs, heart rate and pulse oximetry records (if recorded), Doppler and ultrasound recordings, in-chamber video of EVA workstations, and DCS case descriptions.

Each facility will have ultrasound images scored by 3 independent reviewers (i.e., not aware of the other reviewers’ scoring) and blinded to the subject and time/pressure profile.  NASA can provide a template for the documentation of these. 

Test Plan Verification, Training, and Reporting
NASA will meet with each facility to discuss the test plan before submission of required documents to facility’s governing IRB (and NASA, as required) to verify expectations of the chamber pilot runs (Figure 2) and the  notional schedule (Table 1). NASA will provide limited real-time technical beyond that support for this work beyond that described in this section. Suppliers should include costs for a virtual technical interchange meeting (TIM) for final data coordination and summary of lessons learned.

Note: Providers will coordinate the actual schedule for this work with NASA.  Schedule above is only notional. After selection, plans will be made to loan hardware (e.g., breathing masks, ultrasound), if needed, and scheduling for operator training. 

NASA plans to have capability to loan the following equipment:

• Ultrasound (GE Vivid IQ)

• Masks (EATON POM Plus)

For each facility, NASA also will provide training in:

• Mask fitting procedures,
• EVA task simulation, and
• operation of loaner equipment (if required). 

NASA will monitor at least one chamber run, preferably one of the first two, to answer any questions in real-time and recommend any changes to the procedures.  At the completion of the chamber runs, NASA will coordinate a meeting with each facility to discuss results of these pilot runs and forward plans.

Work described above must be completed within 5 months of IRB approval.

Optional Work:

Vendors will provide optional work costs for the following efforts:

Note:  With Boots on the Moon by 2028, proposals must complete  effort above plus the Option before calendar 2028.  Therefore, each vendor is anticipated to only be awarded one option due to that aggressive schedule requirement.  Base effort describes the measures and number of hours with possibility of one additional hour in the chamber that might be required.

Detailed protocols provided by NASA after base study underway.  Assume measures match base effort.

Cost drivers provided below:

Option 1:

• N = 24 with three different average metabolic rate profiles for the 6h simulated EVA for each subject.  Each subject is exposed to three different average metabolic rate EVAs, on different days.

Option 2:

• N = 24 with three different pharmaceutical countermeasures for DCS for each subject.  Each subject is exposed to three different pharmaceuticals on three different days/EVA exposures.

Option 3:

• N = 24 with three different temperatures for each subject.  Each subject is exposed to three temperatures as proposed countermeasure on different days.

REFERENCES

1.  Eftedal O, Brubakk AO. Agreement between trained and untrained observers in grading intravascular bubble signals in ultrasonic images. Undersea Hyperb Med 24: 293–299, 1997.