Gravity and the Lung: Lessons from Microgravity PDF

Preface

Although humans have been traveling in space for 40 years (since the first flight of Yuri Gagarin in 1961), for the first 20 or so years only a few scientific studies were performed in space, and those studies were limited. Given the difficulties of placing and sustaining humans in that distant and hostile environment, this is hardly surprising. However, the first flight of the European-built Spacelab module (a laboratory placed in the cargo bay of the space shuttle) in 1983 provided the opportunity for well-designed and properly controlled experiments. The pressurized Spacelab module flew 14 times during the period from 1983 to 1998. Of those 14 flights, 11 carried a significant proportion of physiological experiments, and 3 of those were dedicated to life sciences research. Many of those flights carried payload specialists-professional scientists who were recruited because of their higWy specialized knowledge and skills. Spacelab was decommissioned in 1998, following the Neurolab mission, which carried the most complex series of life sciences experiments performed in space. In the future, the International Space Station will provide the opportunity for more elaborate studies in microgravity.

Knowledge of environmental physiology comes from understanding how the organism reacts to changes in the environment. For example, thermoregulatory processes might be studied by raising or lowering ambient temperature. However, for subjects here on earth, gravity is a constant force that cannot be eliminated. We know that gravity has a large effect on the behavior between the top and bottom of the lung in an upright subject. There are substantial vertical gradients in alveolar size and ventilation, in perfusion, and in gas exchange. Therefore, we would expect to see large differences in the behavior of the lung in microgravity. In addition, because the lung presents such a large surface area to the environment (~50-100 m² ), it is vulnerable to polluted atmospheres such as might occur in the closed environment of a spacecraft. Yet none of these factors are unique to the microgravity environment. People routinely change the gravitational influence on their lungs every time they lie down, and many terrestrial dwellers are exposed to both indoor and outdoor atmospheric pollution. Thus, this volume focuses on using measurements made in the absence of gravity (or, in some cases, at high gravity levels) to understand how the lung is affected by gravity here on earth. The title Gravity and the Lung: Lessonsfrom Microgravity reflects this approach.

We had the good fortune to be closely involved with several experiments on Spacelab, and its demise provides an ideal time to summarize those findings in the field of respiratory physiology before the transition of the Space Station. We are grateful to Claude Lenfant, Executive Editor, who agreed to place this volume in the Lung Biology in Health and Disease series.

It is always challenging to perform first-class experiments in a difficult environment. Performing studies in space presents numerous difficulties, but the result is exhilarating. It has been a privilege to participate.