Evaluation of Oxygen Concentrators at Altitude
Principal Investigator:
Jay A. Johannigman, M.D.
Organization:
University of Cincinnati
Oxygen is often needed when treating a major illness or injury on Earth. It is likely oxygen will be needed if injury or trauma occurs during a space mission. The question is, though, how to best provide oxygen if it is needed for emergency health care during a spaceflight.
Dr. Jay Johannigman is leading a project to determine the feasibility of using oxygen concentrators during an emergency health care situation in space. Oxygen concentrators extract and concentrate oxygen from the air. Oxygen concentrators are commonly available and are often used in home health care of patients with lung disease and other respiratory disorders. There are many potential advantages to the use of oxygen concentrators including the reduction of weight from oxygen tanks, and their ability to supply long term oxygen needs with relatively low power.
Dr. Johannigman and his team will test two types of oxygen concentrators that were previously identified as having the highest output of oxygen. These investigations will take place in an altitude chamber to evaluate oxygen concentrator abilities to perform in space or flight environments.
NASA Taskbook Entry
Original Aims The management of major illness and/or trauma in space will likely result in the need for delivery of oxygen. On-orbit delivery of oxygen relies on oxygen stores which also provide environmental oxygen. A major concern of oxygen delivery is the elevation of ambient oxygen concentration and increased risk of fire.
Our previous work has found that in previously healthy individuals (similar to NASA astronauts) oxygen requirements can be met by oxygen at three-to-four liters per minute. This finding suggests that oxygen on orbit could be provided by an oxygen concentrator. This device has the advantage of operating solely from electric power. Since it concentrates oxygen from ambient air, it does not result in increases in environmental oxygen concentration, reducing fire risk. The waste gas from a concentrator is nitrogen, resulting in a net environmental change of zero.
Oxygen concentrators are used in home applications for patients with chronic lung disease and other respiratory disorders. This project is evaluating the SeQual Eclipse and SeQual Integra oxygen concentrators in an altitude chamber up to 30,000 feet. The investigators all have certifications for altitude chamber use, and we will use the chamber at Brooks Air Force Base in San Antonio, Texas.
Key Findings
We evaluated currently on-the-shelf portable concentrators. Testing results demonstrated the following important findings:
- The volume of oxygen produced per minute varied from 0.5 to three liters.
- As respiratory rate increases, concentrator performance follows one of three characteristics;
- Oxygen concentration remains constant.
- Oxygen concentration remains constant, but only every other breath is rewarded with oxygen (the net effect being less oxygen to the patient).
- Oxygen concentration falls precipitously with increasing breath rate (60-70 percent).
- The SeQual Eclipse produces nearly three times more oxygen than the second-best performing device (Respironics EverGo).
The delivered fraction of inspired oxygen (FIO2) from the concentrators was highest at sea level. FIO2 diminished as barometric pressure decreased. The Eclipse II failed to operate above 22,000 feet. Power consumption was reduced at higher altitudes. At the highest flow settings, power consumption diminished by 30 percent during continuous flow and 31 percent during pulse dose in the Eclipse II and 19 percent in the Integra comparing sea level to 8,000 feet. Battery duration on the Eclipse II at 8,000 feet and 3 liters per minute was 1 hour, 48 minutes compared to 1 hour, 22 minutes at sea level.
Oxygen is a finite commodity, which is cumbersome and hazardous to transport. The relatively high FIO2 delivered by the portable oxygen concentrators makes this method of oxygen delivery a viable alternative to compressed oxygen in select situations. However, portable oxygen concentrators cannot deliver an FIO2 of 1.0, necessitating complementary compressed gas for these scenarios. At operational barometric pressure, portable oxygen concentrators function remains equivalent to operation at sea level. The FIO2 available to the patient however, remains constrained by lower barometric pressure as altitude increases. At sea level (barometric pressure of 750 mmHg), an FIO2 of 0.90 produces an alveolar oxygen level of 582 mmHg. At 8,000 feet (barometric pressure of 564 mmHg), an FIO2 of 0.90 produces an alveolar oxygen level of 415 mmHg. Whereas, at an altitude of 32,000 feet (barometric pressure of 206 mmHg), an FIO2 of 0.90 produces an alveolar oxygen level of 93 mmHg.
Impact
The findings suggest that even at extremes of altitude, oxygen concentrators are a safe alternative to compressed or liquid oxygen. At the extremes of mission altitudes, the device continues to operate with only a slight tail off in delivered oxygen concentration. An unsuspected finding was that at lower density, the devices became more energy efficient owing to reduced resistance through the sieve beds, resulting in a longer battery life. Oxygen concentrators provide oxygen as long as there is sufficient electricity. In space, an oxygen concentrator is attractive as additional stores of oxygen are not required and use does not raise the oxygen concentration of the ambient environment. In austere environments (aircraft at altitude, remote areas, far forward military operations), oxygen concentrators provide a safe alternative to traditional oxygen sources.
Oxygen concentrators are capable of providing oxygen whenever electricity is available. Oxygen concentrators can be used instead of compressed oxygen in cylinders or liquid oxygen in a number of scenarios where transport of oxygen is hazardous or logistically challenging. This work supports the use of oxygen concentrators in far-forward situations, in the back of aircraft, in extreme environments (climbing to altitude), and in emergency and mass casualty situations. This work has initiated new research into combining an oxygen concentrator with a ventilator for military and mass casualty operations. The use of concentrators in ground ambulances in the current conflict in the Middle East has been spurred by the success of this project.
