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FOREWORD vii

PREFACE ix

INTRODUCTION xi

CHAPTER 1:  PHYSIOLOGICAL EFFECTS 1

I. Effects of Weightlessness 2

II. Effects of Landing and Readaptation 5

III. Summary 5

References 6

CHAPTER 2:  SHORT FLIGHTS 9

I. Assessment Methods 9

II. Early Effects on Fluids and Electrolytes 15

A. Body Fluid 15
B. Blood and Urinary Osmolality and Monovalent Ions 18
C. Blood and Urinary Divalent Ions 21

III. Renal-Stone Risk 21

IV. Early Effects on Hormones Regulating Fluid and Electrolyte Metabolism 22

A. Antidiuretic Hormone 22
B. Atrial Natriuretic Peptide 24
C. Renin-Angiotensin-Aldosterone System 24
D. Cortisol and Adrenocorticotropin 27
E. Catecholamines 28
F. Stress 28

V. Hormones Regulating Calcium or Bone Metabolism 29

VI. Early Effects on Renal Function 29

VII. Readaptation 31

VIII. Conclusions 34

References 35

CHAPTER 3:  LONG FLIGHTS 41

I. Assessment Methods 41

II. Fluid and Electrolyte Metabolism on 2- to 52-Week Spaceflights: Review of Findings 42

A. Skylab 42

1. Body Fluid 42

2. Electrolytes 43

3. Hormones 44

B. Soviet and Russian Flights 47

1. Body Fluid 47

2. Blood Electrolytes 47

3. Urinary Electrolytes 50

4. Hormones 55

5. In-Flight Measurements 57

III. Physiological Responses to Long Flights: Summary and Discussion 63

A. Fluid Balance, Electrolyte Balance, and Fluid Redistribution 63

B. Hormonal Regulation of Fluid and Electrolyte Balance 67

C. Renal Responses to Fluid Loads or Deprivation After Long Flights 69

IV. Fluid and Electrolyte Status After Landing 72

References 74

CHAPTER 4:  SPACEFLIGHT SIMULATIONS 81

I. Simulation Models: Immersion and Bed Rest 81

II. Fluid Balance 82

III. Sodium and Potassium Balance 85

IV. Predicting Fluctuations in Fluid Balance During Bed Rest 88

V. Calcium Balance 91

VI. Renal Osmoregulatory Responses to Immersion and Bed Rest 93

A. Urine-Concentrating Ability/Fluid Deprivation 96

B. Urine-Diluting Ability/Fluid Load 97

VII. Electrolyte Levels in Blood 99

VIII. Fluid-Compartment Volumes 103

IX. Possible Mechanisms for Maintaining Fluid-Electrolyte Homeostasis 105

A. Immersion 105

1. Body Position 106

2. Temperature 107

B. Head-Down Bed Rest 109

1. Endocrine Effects 110

2. Circadian Influences 115

3. Prostaglandins 116

4. Glucocorticoid Receptors 116

5. Insulin Secretion and Metabolism 117

6. Changes in Potassium and Calcium Storage Capacities 118

X. Summary 123

References 124

CHAPTER 5:  ANIMAL EXPERIMENTS: THE KOSMOS BIOSATELLITES 133

I. Fluid and Electrolyte Balance 134

II. Renal Response to Fluid or Potassium-Chloride Loads 136

III. Electrolyte Content in the Rat Kidney Cortex and Medulla 140

IV. Fluid and Electrolyte Content of Rat Reproductive Organs and Fetuses 144

A. The Male Reproductive System 144

B. Pregnancy and Reproduction 145

1. Maternal Characteristics 145

2. Fetal Development 146

3. Neonatal Development 148

References 149

CHAPTER 6:  COUNTERMEASURES 153

I. Exercise 154

A. General Principles 154

B. In-Flight Exercise Devices 156

1. Other Training Devices and Techniques 156

C. Exercise Protocols During Long Flights 157

1. Phase I 157

2. Phase II 158

3. Phase III 159

D. Summary 159

II. Lower-Body Negative Pressure 159

A. General Principles for LBNP Conditioning 160

B. Protocols and Schedules for LBNP Conditioning in Spaceflight 160

C. Combinations of LBNP and Fluid-Salt Supplements 161

III. Occlusion Cuffs and Positive Pressure Garments 162

IV. Pharmacological Prophylaxis 163

V. Summary and Conclusions 163

References 164

CONCLUSIONS 171

I. Fluid and Electrolyte Regulation on Earth 171

II. Effects of Spaceflight on Fluid and Electrolyte Homeostasis 171

III. Adaptation 172

IV. Approaches to the Study of Spaceflight Effects 173

A. Integrating Different Levels 173

B. Levels of Knowledge About Antidiuretic Hormone 173

V. Physiological Mechanisms of Spaceflight Effects 175

VI. Future Studies 176

VII. Importance of Fluid and Electrolyte Homeostasis for Space Medicine 177

VIII. Earth Benefits from Fluid and Electrolyte Studies 177

References 179

APPENDICES 183

Appendix A: Summary of Human Spaceflight Experience 184

Appendix B: Publications of the American Astronautical Society 204

Advances in the Astronautical Sciences 205

Science and Technology Series 212

AAS History Series 218

INDEX 221