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Experiment Overview


Brief Summary

This investigation will test the efficacy of an in-flight manipulation of arterial blood pressure (BP) as an indicator of post-flight response to a brief stand test. Space flight negatively impacts the regulation of BP on return to upright posture on earth. A Leg Cuff test will induce a brief drop in BP following the release of a short occlusion of blood flow to the legs. The change in BP from pre-flight to in-flight will be used to predict those astronauts who will experience the greatest drop in BP in the post-flight stand test. A second objective is to determine whether cardiac output calculated from the analysis of the finger blood pressure waveform provides an accurate estimate both pre-flight and in-flight by comparison with a rebreathing method.

Principal Investigator(s)

Richard Lee Hughson, Ph.D., University of Waterloo, Waterloo, Ontario, Canada

Co-Investigator(s)/Collaborator(s)

Information Pending

Developer(s)

Canadian Space Agency (CSA), Saint-Hubert, Quebec, Canada

Sponsoring Space Agency

Canadian Space Agency (CSA)

Sponsoring Organization

Information Pending

Research Benefits

Information Pending

ISS Expedition Duration:

September 2012 - September 2014

Expeditions Assigned

33/34,35/36,37/38,39/40

Previous ISS Missions

Information Pending

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Experiment Description

Research Overview

• Space flight affects blood pressure functioning in a way that causes astronauts to be more likely to faint when they return to Earth. A sensitive test has been developed to identify whether astronauts need countermeasures to prevent them from fainting on return to Earth. This research will verify the accuracy of this test. Direct measures of venous pressure or use of multiple Doppler ultrasound probes to quantify blood flow requires considerable operator expertise and multiple pieces of equipment. The proposed method for quantifying indicators of overall cardiovascular regulation from the finger blood pressure waveform will represent an interesting alternative non-invasive measurement.



• Equipment that is currently on the Space Station will be used to evaluate return of blood to the heart, the pumping capacity of the heart, and the ability of the blood vessels to maintain blood pressure. An in-flight test will simulate the challenge experienced by the body on return to Earth, to identify those astronauts who show large reductions in return of blood to the heart or poor constriction of blood vessels and are at high risk for fainting after landing.



• The test will help to identify the astronauts who could benefit from countermeasures before returning to Earth. Thus, this method has great potential for astronaut health monitoring during future long-term space flights and it also has important implications for testing of individuals on Earth, especially the elderly, who are at risk for fainting. The research will also allow demonstrating the feasibility of obtaining a set of indicators of overall cardiovascular regulation from the non-invasive measurement of continuous blood pressure.

Description

Dizziness with the risk of fainting (orthostatic intolerance) remains a critical problem for the return of astronauts to the gravitational forces of Earth, especially after long-duration space flight (Meck et al. 2001). Mechanisms contributing to this orthostatic intolerance on return to Earth have not yet been fully identified. Evidence points to an important role for reductions in cardiac output contributing to the fall in blood pressure due to some combination of reduced blood volume (Hargens et al. 1996; Fortney et al. 1996), reduced cardiac muscle mass (Perhonen et al. 2001), and impaired venous properties that reduce return of blood to the heart (Butler et al. 1991; Convertino et al. 1989). Mechanisms may include a reduction in total circulating blood volume (Hargens et al. 1996; Fortney et al. 1996), however orthostatic intolerance has been seen when blood volume has been maintained or restored (Hargens et al. 1996) and after short- (Buckey, Jr. et al. 1996; Fritsch-Yelle et al. 1996) or long-duration space flights even when saline loading was administered as a countermeasure (Meck et al. 2001). There is definitely impairment of the rapid parasympathetic nervous system-mediated heart rate component of the arterial baroreflex (Fritsch et al. 1992; Hughson et al. 1994). Various results have been found with regard to changes in the activity of the sympathetic nervous system after bed rest and space flight, although for those individuals who failed a stand test after space flight impaired vasoconstriction clearly implied reduced sympathetic vasoconstrictor responses (Buckey, Jr. et al. 1996; Waters et al. 2002; Fritsch-Yelle et al. 1996; Arbeille et al. 1995; Mano and Iwase 2003). Because of these different observations and the lack of conclusive evidence, there are different opinions about the most likely mechanism for orthostatic intolerance.

It's important to develop an approach that can yield critical information about the extent of deconditioning before return to Earth, provide rationale for prescription of countermeasures, and evaluate the effectiveness of these countermeasures before return from long-term sojourns on ISS and with future missions to the moon and Mars. Our recent research demonstrates the feasibility of a simple non-invasive measurement of cardiovascular function and the benefits to be gained from quantification of the venous return (VR), stroke volume (SV), heart rate (HR), cardiac output (Q) and total peripheral vascular resistance (TPR) responses to leg cuff deflation in-flight. The continuous blood pressure device (CBPD) is a non-invasive finger blood pressure cuff that provides continuous, real-time estimates of arterial blood pressure. With the finger cuff it is possible to monitor changes in the arterial blood waveform as if there were a needle placed directly in the artery (Imholz et al. 1990; Bow et al. 1996). Developments by the group of Wesseling and colleagues have enabled the non-invasive blood pressure signal to generate an estimate of beat-by-beat cardiac SV from the pulse waveform with "Modelflow" calculations (Wesseling et al. 1993). Many studies have been published comparing the Modelflow method with direct or indirect alternatives. In a recent bed rest study (Fischer et al. 2007) we observed that the relationship between CVP and SV was linear and unchanged after short-duration head-down bed rest although there was a shift to lower CVP and SV after bed rest. The non-invasive continuous blood pressure device therefore gives: continuous estimates of arterial systolic, diastolic and mean blood pressure and beat-by-beat stroke volume and heart rate. From these data it is possible to derive cardiac output (Q) = HR * SV; total peripheral resistance (TPR) = mean arterial pressure (MAP) / Q; and an estimate of change in CVP from the change in SV. The non-invasive pulse waveform provides indices of the effectiveness of venous return and of arterial vasoconstriction. However, there are currently several unknowns for any transfer of these concepts to space flight. First, it is not known if the relationship between Modelflow SV and SV by other more direct measurements (rebreathing) is maintained in zero gravity. As well, while our research suggests no change in the relationship between SV and CVP for short-term bed rest, this has not been clearly established for space flight. The present project will test the relationship between CBPD with Modelflow and a standard method to estimate SV on the ISS. Furthermore, the device used post-flight during a simple 3-min stand test will allow us to examine whether the in-flight leg cuff test can accurately predict those astronauts who will experience orthostatic intolerance upon return to Earth and the effectiveness of any countermeasures.

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Applications

Space Applications

Astronauts returning from long-duration space flights risk experiencing dizziness or fainting when they stand immediately after returning to Earth. This has an important health risk as it reduces the potential for astronauts to safely escape from an emergency situation. Other health risks include falls which could expose the astronaut to danger of injury during the fall. The test conducted in this investigation will provide insight into the degree of cardiovascular deconditioning and will identify the primary causes. It could identify the need for countermeasures for astronauts prior to return from space missions, including the moon or Mars, and guide the specific requirements of individual astronauts. The long-term outcome of research such as this will be the development of appropriate countermeasures so that astronauts returning from long-duration space flights will have very low risk of experiencing dizziness or fainting when they return to Earth.

Earth Applications

For the general population, dizziness and fainting (syncope) are major health problems accounting for 1-3% of visits to hospital emergency rooms. These problems become especially important for elderly, where falling is a major contributor to bone fracture. A better understanding of the mechanisms responsible for fainting could reduce risk of injury. Astronauts returning from space flights risk experiencing dizziness or fainting when they stand immediately after returning to Earth. The test conducted in this investigation will provide insight into the degree of cardiovascular deconditioning and will identify the primary causes.

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Operations

Operational Requirements

Subjects: 8+1 astronauts
Pre-flight: L-60 to L-30

• Stand Test


• Cardiac Output


• Leg Cuff


• Data sharing: Heart rate at designated rate during MEDB4.1, pre-flight closest to BDC.

In-flight:

• Leg Cuff: Occurs twice in-flight if countermeasures are used (before countermeasure at R-30 ± 7d and also at R-7 to R-0) or once in-flight if no countermeasures are used at (R-30 ± 7d).


• Cardiac Output: and once in-flight (at R-30 ± 7d)


• Data sharing: Medication & Exercise Logs; Information on Specific End-of-Flight Countermeasures

Post-flight: R+1:

• 3-min Stand Test with continuous BP and ECG: at R+1 or R+0


• Data sharing: Heart rate at designated rate during MEDB4.1 during post-flight session closest after landing. Medication logs.

Operational Protocols

During flight, two protocols will be executed as one follow-through procedure: 1) the Leg Cuff with continuous BP monitoring and 2) Cardiac Output with continuous BP monitoring. During the Leg Cuff protocol subjects will instrument themselves with continuous blood pressure device and leg cuffs on both thighs and perform 3 repetitions of the inflation/deflation cycle. If countermeasures are used this test should be administered at R-30 ± 7 d and R-7 to R-0. If there is no specific end-of-flight countermeasure (e.g. centrifuge, lower body negative pressure) then this test should be done only at R-30 ± 7 d. The Cardiac Output will be conducted once during flight, using the PFS simultaneously with the continuous blood pressure device.

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Results/More Information

Information Pending

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Related Websites

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Imagery