A Simple In-flight Method to Test the Risk of Fainting on Return to Earth After Long-Duration Spaceflights (BP Reg) - 09.05.18

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ISS Science for Everyone

Science Objectives for Everyone
A Simple In-flight Method to Test the Risk of Fainting on Return to Earth After Long-Duration Space Flights (BP Reg) tests the effectiveness of an in-flight manipulation of arterial blood pressure (BP) as an indicator of post-flight response to a brief stand test, since spaceflight negatively impacts the regulation of BP on return to upright posture on earth. A Leg Cuff test induces a brief drop in BP following the release of a short obstruction of blood flow to the legs; the change in BP from pre-flight to in-flight is used to predict those crew members who might be susceptible to experience the greatest drop in BP in the post-flight stand test. A second objective of this investigation 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.
Science Results for Everyone
Check your heart health the right way. According to this study, there is a better way to monitor cardiac function during spaceflight. Two different techniques used to track cardiac output (i.e., rebreathing and pulse contour analysis) were compared to see which one measured cardiac health more accurately in astronauts. It was revealed that the rebreathing technique is a better approach for detecting elevated cardiac output aboard the ISS. Therefore, using the right tools for measuring cardiac output is crucial for obtaining accurate data and effectively monitoring astronaut health.

The following content was provided by Richard Lee Hughson, Ph.D., and is maintained in a database by the ISS Program Science Office.
Experiment Details

OpNom: BP Reg

Principal Investigator(s)
Richard Lee Hughson, Ph.D., University of Waterloo, Waterloo, Ontario, Canada

Information Pending

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

Sponsoring Space Agency
Canadian Space Agency (CSA)

Sponsoring Organization
Information Pending

Research Benefits
Space Exploration, Earth Benefits

ISS Expedition Duration
September 2012 - September 2015

Expeditions Assigned

Previous Missions
Information Pending

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Experiment Description

Research Overview

  • Spaceflight affects blood pressure functioning in a way that causes returning crew members to be more likely to faint when they return to Earth. A sensitive test was developed to identify whether or not crew members need countermeasures to prevent them from fainting upon return to Earth. A Simple In-flight Method to Test the Risk of Fainting on Return to Earth After Long-Duration Space Flights (BP Reg) verifies 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 represents an interesting alternative non-invasive measurement.
  • Equipment that is currently on board the International Space Station (ISS) is 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 simulates the challenges experienced by the body on return to Earth, to identify those crew members 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 helps identify the crew members 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 the testing of individuals on Earth, especially the elderly, who are at risk for fainting. The research also allows the demonstration of the feasibility of obtaining a set of indicators of overall cardiovascular regulation from the non-invasive measurement of continuous blood pressure.


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, or fainting, 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. A Simple In-flight Method to Test the Risk of Fainting on Return to Earth After Long-Duration Space Flights (BP Reg) seeks to gain further insight into finding this mechanism.
It is important to develop an approach that yields 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) it was 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, mean blood pressure, 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 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 tests 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, allows researchers to examine whether the in-flight leg cuff test can accurately predict those crew members who might experience orthostatic intolerance upon return to Earth, and the effectiveness of any countermeasures.

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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 crew member to danger of injury during the fall. The tests conducted in this investigation provide additional insight into the degree of cardiovascular deconditioning and identifies the primary causes. Results from this investigation 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, is the development of appropriate countermeasures so that astronauts returning from long-duration space flights have a 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 can provide additional insight into the degree of cardiovascular deconditioning, and provide a better identification of the primary causes.

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Operational Requirements and Protocols

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.


  • Leg Cuff: Occurs twice in-flight if countermeasures (end-of-flight, gravity like countermeasures; e.g. CHIBIS or other LBNP) 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.

During flight, two protocols are 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 instrument themselves with continuous blood pressure device and leg cuffs on both thighs and perform 3 repetitions of the inflation/deflation cycle. If end-of-flight, gravity like countermeasures (e.g. CHIBIS or other LBNP) 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 is conducted once during flight, using the PFS simultaneously with the continuous blood pressure device.

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Decadal Survey Recommendations

Information Pending

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Results/More Information

The use of non-invasive techniques for the assessment of cardiac function during human spaceflight is important in astronaut health monitoring. Cardiac output can be measured using different techniques; such as, arterial pulse contour analysis and rebreathing. While scientists agree that cardiac output tends to be elevated in spaceflight relative to baseline (i.e., sitting upright on Earth), different techniques have reported widely different cardiac output values in the past. For example, a study using rebreathing reported that astronauts embarking on long-duration missions experienced 35% to 41% increases in stroke volume, whereas a study using arterial pulse contour analysis reported only about a 10% increase. It is possible that the discrepancy between the values reported by each technique is a consequence of unanticipated changes related to the measurement of cardiac output in spaceflight.
The goal of this study was to compare the 2 techniques (i.e., rebreathing and pulse contour analysis) by contrasting the estimates obtained for cardiac output under each method during preflight baseline and long-duration spaceflight aboard the International Space Station (ISS). Nine male astronauts participated in the study with preflight data collected 2-3 months before launch and in-flight data collected during the last month before return. Arterial pulse contour analysis recorded arterial pressure from astronauts’ fingers, whereas rebreathing consisted of breathing through a mouthpiece while wearing a nose clip. At the start of rebreathing, astronauts exhaled to a normal end point, and then followed a visual display that prompted a smooth inhale-exhale rhythm. In the rebreathing maneuvering, blood flow through the pulmonary capillaries was used to estimate cardiac output. Rebreathing measurements were taken while sitting upright during pre-flight and in-flight, and the pulse contour was also measured pre-flight in the supine position.
Results showed cardiac output estimated by pulse contour analysis was systematically different from rebreathing. When pulse contour analysis was compared to rebreathing in the baseline seated position and in spaceflight, there was a significant main effect of spaceflight and an interaction of spaceflight and technique. The estimate of cardiac output reported by rebreathing increased by 46.6 ± 18.2 % from seated baseline to inflight, while the estimate reported by pulse contour analysis was unchanged from supine to seated to spaceflight. These results, thus, revealed that the rebreathing technique was a better approach for detecting significantly elevated cardiac output aboard the ISS, compared to the seated-upright posture on Earth.
The current study unveiled an important limitation with the pulse contour analysis technique to estimate cardiac stroke volume and cardiac output during spaceflight. Previous measurements obtained during spaceflight using this technique have probably underestimated the change in cardiac output. The results presented here strongly suggest that rebreathing, or some other method not reliant on pulse contour analysis, is necessary to properly monitor cardiac function during spaceflight.

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Results Publications

    Hughson RL, Peterson SD, Yee NJ, Greaves DK.  Cardiac output by pulse contour analysis does not match the increase measured by rebreathing during human spaceflight. Journal of Applied Physiology. 2017 August 10; epub. DOI: 10.1152/japplphysiol.00651.2017. PMID: 28798205.

    Hughson RL, Shoemaker JK, Arbeille P.  CCISS, Vascular and BP Reg: Canadian space life science research on ISS. Acta Astronautica. 2014 November; 104(1): 444-448. DOI: 10.1016/j.actaastro.2014.02.008.

    Hughson RL, Yee NJ, Greaves DK.  Elevated end-tidal Pco2 during long-duration spaceflight. Aerospace Medicine and Human Performance. 2016 October 1; 87(10): 894-897. DOI: 10.3357/AMHP.4598.2016. PMID: 27662353.

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Ground Based Results Publications

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ISS Patents

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Related Publications

    Hughson RL, Shoemaker JK.  Autonomic responses to exercise: Deconditioning/inactivity. Autonomic Neuroscience: Basic and Clinical. 2015 March; 188: 32-35. DOI: 10.1016/j.autneu.2014.10.012. PMID: 25458429.

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Related Websites

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NASA Image: ISS035E040478 - Commander Chris Hadfield, Canadian Space Agency (CSA) Astronaut, is the first subject to perform the Canadian experiment BP Reg during Increment 35-36.

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NASA Image: ISS035E022360 - Commander Chris Hadfield, Canadian Space Agency (CSA) Astronaut, is wearing the Continuous Blood Pressure Device (CBPD) and the leg cuffs for the BP Reg experiment during Increment 35/36.

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NASA Image: ISS038E041880 - NASA Astronaut Mike Hopkins takes part in the Canadian experiment BP Reg during Increment 37/38.

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NASA Image: ISS038E041883 - NASA Astronaut Mike Hopkins performs the rebreathe procedure with the Pulmonary Function System (PFS), part of the Human Research Facility-2, for the BP Reg experiment.

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NASA Image: ISS037E014706 - Italian Space Agency (ASI) Astronaut Luca Parmitano, geared up to perform the Canadian experiment BP Reg during Increment 35/36.

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