The National Science Foundation's (NSF) Tokyo Office periodically receives and disseminates reports on research developments in Japan that are related to the Foundation's mission. NSF-sponsored researchers currently working in Japan prepare many of these reports. These reports present information for use by NSF program managers and policy makers; they are not statements of NSF policy.
Special Scientific Report #00-10 (October 11, 2000)
Ms. Kathleen Sienko, a graduate student in both the Massachusetts Institute of Technology /Harvard University Health Science and Technology Division and Massachusetts Institute of Technology Department of Aeronautics and Astronautics, prepared the following report. Ms. Sienko was a participant in the 2000 Monbusho Summer Program sponsored in the United States by NSF and in Japan by the Ministry of Education and Science (Monbusho). Dr. Satoshi Iwase of the Department of Autonomic Neuroscience in the Research Institute of Environmental Medicine at Nagoya University hosted Ms. Sienko. Ms. Sienko can be reached via email at: sienko@mit.edu.
Long-duration exposure to microgravity results in broad-spectrum physiological deconditioning. Despite significant flight experience in both the US and Russian space programs, the fundamental mechanisms triggering the degradation of wide-ranging physiological subsystems remain unclear. Long-duration exposure to the stimulus of microgravity, and to some extent, short-term exposure, results in alterations to bone physiology, skeletal muscle, sensorimotor integration, cardiovascular and pulmonary systems, endocrine and immune systems, autonomic function, and sociological behavior. The physiological response to the absence of gravity is both appropriate to the immediate environmental requirement and demonstrative of human adaptability. The issue is not whether these changes are appropriate, but rather if the changes will detrimentally affect the safe return to and productivity in a gravito-inertial environment. Such responses, if left untreated, could lead to serious problems following the return from microgravity. For example, reduced orthostatic tolerance (the ability to function normally while standing upright) poses serious hazards to the health and safety of crewmembers during re-entry and emergency egress following landing.
The Department of Autonomic Neuroscience in the Research Institute of Environmental Medicine at Nagoya University investigates the human autonomic nervous system’s adaptive mechanisms during exposure to various environmental conditions including real and simulated microgravity, gravitational stress, high altitude, and extreme temperatures; the primary focus of the department, however, is space and gravitational physiology. Several ground-based analogues have been developed to partially simulate the physiological effects resulting from exposure to microgravity. Simulated microgravity exists in the form of head down tilt bed rest, water immersion, dry immersion, and parabolic flight. My research experience as a Monbusho Summer Fellow included participating in a simulated microgravity experiment aimed at clarifying the underlying mechanisms associated with autonomic deconditioning of cardiovascular and thermoregulatory functions following two weeks of 6 head down tilt bed rest.
The Department of Autonomic Neuroscience specializes in microneurography, a technique used to record nerve action potentials from human peripheral nerves in situ using tungsten microelectrodes. Direct observation of sympathetic efferent nerve activity outflow to the muscles (muscle sympathetic nerve activity-MSNA) and skin (skin sympathetic nerve activity-SSNA) can be recorded by properly inserting the microelectrode into the median, ulner, or radial nerves in the upper extremities, and tibial, peroneal, or sural nerves in the lower extremities. Sympathetic efferent nerve activity plays an important role in maintaining homeostasis of blood pressure and body temperature by regulating the cardiovascular and thermoregulatory systems, respectively.
Nagoya University’s bed rest facility is capable of accommodating a maximum of 20 subjects and is equipped with a full-time nursing staff, pre-/post-bed rest experimental facilities, and the new National Space Development Agency of Japan (NASDA) funded short-radius human centrifuge (Figures 1 and 2).
Figure 1: Nagoya University’s bed rest facility
Figure 2: National Space Development Agency of Japan short-radius human centrifuge
This summer, thirteen college-aged male students were subjected to two weeks of 6° head down tilt bed rest. The primary objective of this study was to investigate the mechanisms associated with autonomic deconditioning resulting from simulated microgravity; specifically, cardiovascular deconditioning (orthostatic intolerance) and thermoregulatory deconditioning (reduced sensitivity to heat loss) following two weeks of 6° head down tilt bed rest. This investigation focused on the effect of bed rest on the cardiovascular and thermoregulatory systems during exercise (static hand grip and static plantar flexion) and graded head-up tilt in both normal and hyper-thermal conditions (Figures 3 and 4). The bed rest study was spearheaded by Nagoya University’s Autonomic Neuroscience Department. Research collaborators included Nihon University School of Medicine, Aichi Medical University, and Asahi Chemical Industry Company.
Pre- and post-bed rest data collection sessions occurred two weeks prior to bed rest and during the two days following the completion of bed rest, respectively. Data collection sessions included the recording of MSNA and SSNA signals, heart rate, blood pressure, respiration, peripheral venous pressure, stroke volume, cardiac output, chest and calf impedance, core body temperature, skin surface temperatur, sweat rate, venous compliance, capillary filtration rate, and calf blood flow during two minutes of exercise (static hand grip-30% of maximum force, static plantar flexion-70% of maximum force) and graded head-up tilt (-10° to 60° tilt via tilt table) both prior to and following approximately one hour of heating. Additionally, cerebral blood flow, calf circumference, balance/posture, weight, and body fat percentage were recorded. During the two-week bed rest period, skin temperature, skin blood flow, blood pressure, R-R interval, venous compliance, capillary filtration rate, calf blood flow, mental stress tests, psychological evaluations, and weight were examined.
Figure 3 & 4: Pre-/post-bed rest experiments focusing on cardiovascular and thermoregulatory interactions during graded head-up tilt in both normal and hyper-thermal conditions
The pre-/during-/and post-bed rest data collection sessions spanned mid-July through August. Consequently, results are not yet available at this time.
During my stay in Japan I conducted several site visits to various research laboratories at Nagoya University, University of Tokyo, Nihon University School of Medicine, Kyushu Institute of Technology, Gifu University, and Toho Gas Company. I continued my study of Japanese by enrolling in the Nagoya University intensive 12-day Japanese language course.
This summer’s research experience provided me with a unique opportunity to participate in a large-scale bed rest study, develop a fundamental understanding of the plasticity exhibited by the autonomic nervous system in response to simulated microgravity, and apply integrated physiology principles to understand specific physiological subsystem deconditioning. The Monbusho Summer Program also allowed me to build friendships and professional relationships with numerous Japanese colleagues, offered insight on a culturally varied approach to research, provided exposure to the Japanese culture and language, and enabled future participation in scientific collaborations. I hope to return to Nagoya University in the near future to examine the effects of short-radius centrifugation as a potential countermeasure to both simulated microgravity and long-duration space flight.
I would like to extend my sincere gratitude to the National Science Foundation, the Japanese Ministry of Education and Science (Monbusho), the Graduate University for Advanced Studies (Soken-dai), and the Department of Autonomic Neuroscience at Nagoya University for extending me this incredible opportunity.
Special thanks to Dr. William Blanpied, Director of the National Science Foundation's Tokyo Regional Office; Director Keisuke Yoshio, Director of the Monbusho Division of International Affairs; and my hosts, coworkers and friends at Nagoya University's Department of Autonomic Neuroscience: Professors Tadaaki Mano and Satoshi Iwase, Fu Qi, a postdoctoral fellow, A. Kamiya and D. Michikami, research associates; Yuki Niimi, MD, T. Shibata, a medical student, J. Kawanokuchi, a graduate student, K. Ohmori, a research assistant, and the departmental secretaries Keiko Kato, Rico Aoi, and Ai Sugiyama.
Click here to return to top of this report