Presentation to the IOM 22 June 2015 NASA Evidence Report: Orthostatic Intolerance

Transcription

1 Presentation to the IOM 22 June 2015 NASA Evidence Report: Orthostatic Intolerance Presenter: Vic Convertino, Ph.D. Location: Keck Center Washington DC

2 1. Does the evidence report provide sufficient evidence, as well as sufficient risk context, that the risk is of concern for long-term space missions? YES The evidence report provides substantial evidence that the risk for developing some degree of orthostatic compromise is high. There is also compelling evidence presented in the report that various countermeasures may NOT be effective in many (a majority?) of astronauts. Evidence is presented that the risk is elevated with longer missions (i.e., astronauts and cosmonauts who experienced no orthostatic problems following short Shuttle missions could not complete tilt tests following ISS missions of 4 to 6-month duration).

3 2. Does the evidence report make the case for the research gaps presented? PARTLY Discusses limitations with modeling of the cardiovascular system (e.g., Guyton model). Discusses the gap in knowledge for whether exposure to lower G environments (e.g., Moon, Mars) will cause or protect/mitigate orthostatic intolerance.

4 3. Are there any additional gaps in knowledge or areas of fundamental research that should be considered to enhance the basic understanding of this specific risk? YES Significant gaps in knowledge and fundamental research is created by limitations of the tools used to assess the effects of microgravity adaptation and countermeasure effectiveness. The primary KNOWLEDGE gap for areas of fundamental research is to determine the minimum threshold for absolute compensatory reserve required to protect orthostatic competence to assure successful completion of specific mission tasks. The primary CAPABILITY gap is to develop a tool (e.g., monitor) that provides for real-time measurement of the absolute compensatory reserve of the INDIVIDUAL astronaut. This capability would provide assessment of the current orthostatic status of each crewmember and serve as a goal-directed guide for effectiveness of countermeasures. We shall return to this topic in slides 6 through 9.

5 4. Does the evidence report address relevant interactions among risks? PARTLY The report addresses the potential for impairment of operational performance such as the ability to emergency egress the vehicle or other mission tasks that require standing after landing. There is no reference to the evidence that orthostatic compromise following adaptation to simulated microgravity exposure results in greater reductions in maximal oxygen uptake (e.g., J Cardiac Rehab 3:660-63, 1983; Circulation 65: ,1982; Am J Cardiol 51: , 1983). There is no reference to the evidence that increased venous compliance is correlated to the degree of muscle atrophy following exposure to simulated microgravity (J Appl Physiol 66: , 1989).

6 5. Is the breadth of the cited literature sufficient? PARTLY => limited countermeasures There is no reference to the evidence that mechanisms associated with orthostatic compromise following exposure to simulated microgravity is ameliorated with one bout of acute maximal exercise (e.g., Am J Physiol 269:R614-R620, 1995; Am J Physiol 270:R3-R10, 1996; Am J Physiol 271:R837-R847, 1996; Med Sci Sports Exerc 33:75-80, 2001). There is no reference to the evidence that intrathoracic pressure regulation (IPR) therapy provides protection against orthostatic compromise (e.g., J Appl Physiol 104: , 2008; Aviat Space Environ Med 79: , 2008; Am J Physiol 293:R243-R250, 2007; Crit Care Med 35: , 2007). Consideration of these types of countermeasures include efficiency in use of astronaut time, equipment and resources.

7 3. Are there any additional gaps in knowledge or areas of fundamental research that should be considered to enhance the basic understanding of this specific risk? YES There exists a significant capability gap for a diagnostic tool to provide early identification of individuals at greatest risk for orthostatic intolerance Low Tolerant High Tolerant

8 3. Are there any additional gaps in knowledge or areas of fundamental research that should be considered to enhance the basic understanding of this specific risk? YES

9 Summary and Recommendations Extend countermeasure research to the use of acute maximal exercise and application of simple physiological technologies (e.g. IPR therapy). Future research should be focused on the determination of the minimum threshold for absolute compensatory reserve required to protect orthostatic competence to assure successful completion of specific mission tasks. Consider inclusion of novel state-of-the-art assessment tools for early prediction of astronauts at greatest risk of experiencing orthostatic intolerance and assessment of countermeasure effectiveness. NASA must focus future research on assessment of physiological signals that are capable of learning the dynamic, specific, and complex nature of compensation for each INDIVIDUAL astronaut.