University of Kentucky UKnowledge Theses and Dissertations--Biomedical Engineering Biomedical Engineering 2014 HUMAN CARDIOVASCULAR RESPONSES TO ARTIFICIAL GRAVITY VARIABLES: GROUND-BASED EXPERIMENTATION FOR SPACEFLIGHT IMPLEMENTATION Mark Howarth University of Kentucky, [email protected] Right click to open a feedback form in a new tab to let us know how this document benefits ou.y Recommended Citation Howarth, Mark, "HUMAN CARDIOVASCULAR RESPONSES TO ARTIFICIAL GRAVITY VARIABLES: GROUND- BASED EXPERIMENTATION FOR SPACEFLIGHT IMPLEMENTATION" (2014). Theses and Dissertations-- Biomedical Engineering. 14. https://uknowledge.uky.edu/cbme_etds/14 This Doctoral Dissertation is brought to you for free and open access by the Biomedical Engineering at UKnowledge. It has been accepted for inclusion in Theses and Dissertations--Biomedical Engineering by an authorized administrator of UKnowledge. For more information, please contact [email protected]. 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Mark Howarth, Student Dr. Abhijit Patwardhan, Major Professor Dr. Abhijit Patwardhan, Director of Graduate Studies HUMAN CARDIOVASCULAR RESPONSES TO ARTIFICIAL GRAVITY VARIABLES: GROUND-BASED EXPERIMENTATION FOR SPACEFLIGHT IMPLEMENTATION ____________________________________ DISSERTATION ____________________________________ A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the College of Engineering at the University of Kentucky By Mark Steven Howarth Lexington, Kentucky Director: Dr. Abhijit R. Patwardhan, Professor of Biomedical Engineering Lexington, Kentucky 2014 Copyright © Mark Steven Howarth 2014 ABSTRACT OF DISSERTATION HUMAN CARDIOVASCULAR RESPONSES TO ARTIFICIAL GRAVITY VARIABLES: GROUND-BASED EXPERIMENTATION FOR SPACEFLIGHT IMPLEMENTATION One countermeasure to cardiovascular spaceflight deconditioning being tested is the application of intermittent artificial gravity provided by centripetal acceleration of a human via centrifuge. However, artificial gravity protocols have not been optimized for the cardiovascular system, or any other physiological system for that matter. Before artificial gravity protocols can be optimized for the cardiovascular system, cardiovascular responses to the variables of artificial gravity need to be quantified. The research presented in this document is intended to determine how the artificial gravity variables, radius (gravity gradient) and lower limb exercise, affect cardiovascular responses during centrifugation. Net fluid (blood) shifts between body segments (thorax, abdomen, upper leg, lower leg) will be analyzed to assess the cardiovascular responses to these variables of artificial gravity, as well as to begin to understand potential mechanism(s) underlying the beneficial orthostatic tolerance response resulting from artificial gravity training. Methods: Twelve healthy males experienced the following centrifuge protocols. Protocol A: After 10 minutes of supine control, the subjects were exposed to rotational 1 Gz at radius of rotation 8.36 ft (2.54 m) for 2 minutes followed by 20 minutes alternating between 1 and 1.25 Gz. Protocol B: Same as A, but lower limb exercise (70% V02max) preceded ramps to 1.25 Gz. Protocol C: Same as A but radius of rotation 27.36 ft (8.33 m). Results: While long radius without exercise presented an increased challenge for the cardiovascular system compared to short radius without exercise, it is likely at the expense of more blood “pooling” in the abdominal region. Whereas short radius with exercise provided a significant response compared to short radius without exercise. More fluid loss occurred from the thorax and with the increased fluid loss from the thorax blood did not “pool” in the abdominal region but instead was essentially “mobilized” to the upper and lower leg. The exercise fluid shift profile presented in this document is applicable to not only artificial gravity protocol design but also proposes a mechanistic reason as to why certain artificial gravity protocols are more effective than others in increasing orthostatic tolerance. KEYWORDS: Artificial Gravity, Spaceflight Countermeasures, Centrifugation, Cardiovascular Regulation, Electrical Impedance Plethysmography Multimedia Elements Used: JPEG (.jpg) Mark Steven Howarth February 28, 2014 HUMAN CARDIOVASCULAR RESPONSES TO ARTIFICIAL GRAVITY VARIABLES: GROUND-BASED EXPERIMENTATION FOR SPACEFLIGHT IMPLEMENTATION By Mark Steven Howarth Dr. Abhijit R. Patwardhan Director of Dissertation Dr. Abhijit R. Patwardhan Director of Graduate Studies February 28, 2014 Freedom Is Not Free I would like to dedicate this work to those that have died in battle fighting to keep America free from terrorism. Those that volunteer their lives to protect the principles on which America was founded allow the rest of us in society to carry on our daily lives with relative ease. I was fortunate enough to remain stateside with cushy luxuries while many (including friends and family) deployed to “the suck”. It is my hope that this work will benefit society, particularly the space program, at some point in the future. Otherwise, I have published a book that will simply collect dust on a library shelf, or occupy digital space on some hard drive. If that is the case, then perhaps I should have just joined my friends and family in “the suck”. It remains to be seen if this book is the ticket for admission to a happy, successful, and meaningful career. ACKNOWLEDGMENTS First and foremost I would like to thank Dr. David Randall. Without him, it is unlikely that I would have been able to navigate the political waters of a dissertation committee. I would also like to thank Dr. Brian Jackson for our informal discussions at the gym. I would like to thank my committee members: Dr. Charles Knapp, Dr. Abhijit Patwardhan, Dr. Ken Campbell, and Joyce Evans for their knowledge, guidance, and editorial suggestions. We had some heated discussions that often left me puzzled. Post-meeting discussions with Dr. Randall allowed me to keep an even keel and keep plowing forward. I would also like to thank the outsider reviewer, Dr. Kevin Donohue, for his time. I would like to thank all of the staff members at NASA Ames Research Center that allowed this study to be possible, particularly Dr. Fritz Moore, Dr. Ralph Pelligra, Rick Ryzinga, and Russ Westbrook. I would also like to thank all of our test subjects, although, most all of them had a blast riding the centrifuge and being instrumented to the hilt. Thanks also belong to the taxpayer whose money supports NASA and also supported the NASA EPSCoR grants that helped fund this study. Dr. Mike Stenger left the University of Kentucky within a couple years of my arrival to go work at NASA. He first introduced me to MATLAB and SAS programming which gave me enough basic knowledge to pick up the rest along the way in order to complete my data analysis. Helena Truszczynska is to thank for helping me develop the exact SAS code I wanted. It would have been fun to have Mike around longer for research purposes, and as a gym partner. He was and probably still is a BAMF. I would also like to thank my friends and family that have been there at the various stages of this process. I suppose we deal with the stress and rigors of academic pursuit in different ways. My vices were my hair and the gym. I have had curly hair like Tom Jones, blonde hair like Hulk Hogan and Brad Pitt, buzz cut hair, and more recently long hair like Fabio and Troy Polamalu. Thank you for the Johnson Center at UK. I have had many a workout in there either pushing iii weights or running circles around the track blowing off stress or constructively vetting out ideas. To match the hair changes, I have weighed at times anywhere from the 170’s to 248 pounds, depending on if it was “bulking season” or not. Finally, I would also like to thank my undergraduate mentor Dr. John Watret. We had a conversation mid-way through this process and he reminded me of the importance of actually completing the dissertation so that I was not another statistic