Lecture 8 Kin PDF

11/18/24 Microgravity Altitude stress Readings: Textbook Chapters 24 and 27 1 § Identify strategies to simulate and study microgravity § List five physiologic/anatomic responses to microgravity § Discuss countermeasures to counteract micro-gravity § Describe...

11/18/24 Microgravity Altitude stress Readings: Textbook Chapters 24 and 27 1 § Identify strategies to simulate and study microgravity § List five physiologic/anatomic responses to microgravity § Discuss countermeasures to counteract micro-gravity § Describe the short- and long-term physiological adaptations that occur with altitude stress § Understand altitude sickness 2 1  11/18/24 § Micro-gravity? § Medium and high altitude? 3 4 2  11/18/24 § An invisible attraction that makes any mass exert downward force or have weight. § Gravitational law: § “Every particle in matter in the universe attracts every other particle with a force directly proportional to the product of the masses of the particles and inversely proportional to the square of the distance separating them” § Every mass (m) on Earth requires support from a force (F) equal to its weight (w) § W (or F) = mg 5 6 3  11/18/24 § Any place where perceived gravity is less than on earth, § Moon – 0.18 g; Mars = 0.38 g, Space station = 0 g § A condition in which people or objects experience weightlessness. § In microgravity, all forces acting on body remain in balance § Force of gravity never reaches an absolute value of zero because some gravitational force still exists § The gravitational pull on a rocket decreases as it moves farther from Earth 7 § Data analysis from single flights § Data collection on space motion sickness symptoms § Validate ground-based predictive tests of susceptibility and define acceptable countermeasures § Longitudinal studies spanning several missions § Quantify effects of repeated exposure to space, mainly radiation on cancer risk and bone mineral loss § Longitudinal studies throughout careers: § Document occupational injuries and maladies during or following space missions 8 4  11/18/24 § Simulating microgravity allows researchers to manipulate experimental conditions to decide best procedure for a particular mission § Creating brief zero-g conditions: § Parabolic airplane flights with living and nonliving objects, § Use of head-down bed rest, wheelchair confinement or immobilization, water immersion, § Hindlimb suspension (animal models) 9 § Parabolic Flights § Stratotanker aircraft (“vomit comit”) climbs rapidly (45 - 50˚angle) and then follows parabolic path 10 5  11/18/24 11 EFFECTS OF NEAR-ZERO-G DURING SPACEFLIGHT § Removal of gravity force causes spinal disks to expand and stature to increase up to 5 cm 84-day Skylab 4 mission and 17 days post-flight 12 6  11/18/24 Head-down bed rest § Subjects confined to bed for weeks, months, or a year in a horizontal or head-down tilt position (-3˚ to -12˚) § Followed by measurements to positive acceleration at forces up to 3g in centrifuge 13 A) Elevate hind quarters or tail B) Partial weight bearing apparatus Reduces sensory input to motor centers Decreased stimulation of connective, muscular and osseous tissues Mimics fluid shift of anti-gravity 14 7  11/18/24 § In microgravity there is: § Reduced hydrostatic gradients § Reduced loading and disuse of weight-bearing tissues § These two factors impact the following systems: § Cardiovascular and cardiopulmonary § Hematologic § Fluid, electrolyte, and hormonal § Muscle § Bone § Neurosensory and vestibular 15 16 8  11/18/24 § Blood and fluid volumes shift upward and move into the thoracocephalic region causing: § A puffy-face appearance, § 2- to 5- cm decrease in the waist girth, § Eye redness, § Skinny legs, § Nasal congestion, headaches, and nausea § Blood volume, plasma, and red blood cell volume decrease § Increased venous pooling, blunted baroreceptor reflex, and orthostatic intolerance 17 § Rapid decrease in total fluid volume reduces heart’s total work effort § Chronic exposure, overall heart size decreases from reduced left ventricular end- diastolic volume § Adaptations represent appropriate response without compromising normal cardiovascular function 18 9  11/18/24 19 § Cells’ demand for oxygen during rest and exercise remains invariant regardless of environment § Any change in external work above resting baseline triggers immediate ventilatory responses that increase breathing rate and tidal volume § Augmented alveolar ventilation maintains adequate pressure differential for oxygen diffusion across lung tissues for delivery to site of increased energy metabolism 20 10  11/18/24 Diffusing capacity increases in laying and standing position during flight (0-g) 21 (A) Plasma volume (B) Total hemoglobin (C) Blood volume and red cell mass 22 11  11/18/24 § Greatest concern involves 1% a month loss in weight-bearing bone mass during missions § In an microgravity environment, reduced calcium intestinal absorption exacerbates calcium fecal loss, § Even with on-board physical exercise intervention, bone loss persists and can remain pathologic for a prolonged period following mission, § Solution involves selecting crewmembers with greatest resistance to bone loss 23 § Proposed parallel dynamics of calcium–endocrine response and skeletal adaptation and altered bone composition and architecture to altered gravitational loading with adequate diet and endocrine balance 24 12  11/18/24 § Bone loss during prolonged microgravity exposure coincides with considerable decrements in muscle mass and strength § Absence of gravity virtually eliminates any load-bearing effects on antigravity muscles, rendering them susceptible to impaired performance in emergencies 25 26 13  11/18/24 Different Duration Spaceflight Effects on Maximal Explosive Power (MEP) and Maximal Cycling Power (MCP) Assessed preflight and 26 days postflight for astronauts exposed to microgravity up to 180 days 27 § Permanent neuromuscular dysfunction not demonstrated during prolonged space missions § In-flight and post-flight changes during missions of nearly 1 year include: § Altered muscular coordination patterns § Delayed-onset muscle soreness § Generalized muscular fatigue and weakness 28 14  11/18/24 § Body composition variables of 10 astronauts assessed by densitometry and bioelectrical impedance analysis before and 2 days following 7- to 16-day missions: § No changes in % fat or extracellular water, § 2.3% decline in body mass attributable to a loss in FFM, § All three components of FFM (water, protein, and mineral) declined from 3 to 4% post- flight 29 Body Composition Changes in Microgravity, cont. DAYS FOLLOWING 7- TO 16-DAY 30 15  11/18/24 § Without appropriate countermeasures, microgravity’s deleterious effects mimic adverse changes with prolonged bed rest § Decrements in cardiovascular function generally parallel losses in muscle strength and size § In-flight resistance and endurance exercises show greatest potential as exercise countermeasures § Countermeasure strategies help minimize microgravity-induced orthostatic intolerance § Measures include fluid loading, G-suit inflation, pharmacologic agents, artificial gravity, short-term exercise to elicit maximal effort 31 § Four exercise modes play predominant roles during in-flight workouts aboard space missions: § Treadmill walking and running § Cycle ergometry § Leg rowing § Upper- and lower-body multi-joint dynamic resistance exercise 32 16  11/18/24 33 § Resistance training on diverse exercise equipment, while in-space § increases muscle mass § improves force-generating capacity § maintains muscle ultrastructure and complimentary neural components § Standard concentric and eccentric methods, including isokinetic loading devices and newer onboard equipment produce improvements 34 17  11/18/24 ASTRONAUTS DID NOT ATTAIN ASSIGNED TARGET HEART RANGE (60, 70, 80% VO2MAX) WHEN EXERCISING CONTINUOUSLY FOR 30 MINUTES DURING AN 11-DAY MISSION 35 § Space motion sickness (SMS) remains most persistent short-term problem during space flight § No single pharmacologic treatment prevents or cures SMS due to incomplete understanding of cause; medication provides most effective pharmacologic therapy: § Anticholinergics § Antihistamines § Sympathomimetics § Sympatholytics 36 18  11/18/24 § Within 14 days, 10% change occurs in body fluid redistribution § Within first 3 wk of microgravity, 10% change in cardiovascular function reflects deconditioning response § Within 3 months, bone mass declines by 5% § Declines to 15% between months 5 to 6; then stabilizes for several months, and then decreases to 17% after 1 year § Bone mass and muscle structure and function deteriorate at slower rate than fluid redistribution and cardiac deconditioning, but magnitude of decrement reaches higher values 37 38 19  11/18/24 39 High Altitude World map with different altitudes around the globe. Himalaya mountain range 40 20  11/18/24 § Altitude’s physiologic challenge comes directly from decreased ambient Po2 § Elevations between 3048 m and 5486 m above sea level are considered “high altitude” § O2 transport cascade = progressive changes in environment’s O2 pressure § Acclimatization refers to adaptations produced by changes in the natural environment § Acclimation concerns adaptations produced in a controlled laboratory environment that simulates high altitude § Arterial hypoxia that accompanies reductions in Po2 precipitates both the immediate physiologic adjustments to altitude and the longer-term acclimatization process 41 42 21  11/18/24 43 § Overview § Altitudes at which aerobic performance declines § 700 m (2300 ft): declines begin § 1524 m (5000 ft): declines become more obvious § 2200 m (7217 ft): declines become significant § Impaired oxygen consumption § Impaired endurance performance § Decline in oxidative metabolism § 2-15% decrease in maximal oxygen consumption 44 22  11/18/24 Altitude Stress (cont’d) Running performance predicted at different altitudes. 45 Altitude Stress (cont’d) Short-Duration Performance Responses – Only primarily aerobic activities are affected – Effect of altitude itself is likely minimal – Preparation, focus, & other psychological factors contribute Long-Duration Performance Responses – Speed is dramatically decreased in endurance running events (beginning at 400 meters) 46 23  11/18/24 § Hypoxia and Other Challenges of Altitude § Hypoxia - Compromised delivery of oxygen to target tissues. § Caused by: § Decrease in barometric pressure (hypobaric) § Reduced partial pressure of oxygen § Increased cold with altitude § Dehydration induced by cold § Increased solar radiation 47 § Physiological Responses to Altitude § Increased resting heart rate § Increased blood pressure § Increased catecholamines § Increased pulmonary ventilation § Increased depth (tidal volume) & rate of breathing § Decreased maximal oxygen consumption § Increased in hemoglobin & hematocrit blood concentrations § Acute – dehydration induced § Chronic adaptation occur in 3 weeks 48 24  11/18/24 § Hyperventilation from reduced arterial Po2 reflects the most important and clear-cut immediate response of native low-landers to altitude exposure § Once initiated, the hypoxic drive increases during the first few weeks and can remain elevated for a year or longer during prolonged exposure 49 § Submaximal exercise heart rate and cardiac output rise to 50% above sea level values, while stroke volume remains unchanged. § Resting blood pressure increases in early stages of altitude adaptation § Increased submaximal exercise blood flow at altitude compensates for arterial desaturation 50 25  11/18/24 § Sympathoadrenal activity progressively increases over time § Increased blood pressure § Increased heart rate § Regulates blood pressure, vascular resistance, and substrate mixture hypobaric exposures 51 52 26  11/18/24 53 54 27  11/18/24 System Immediate Longer Term Pulmonary Hyperventilation Hyperventilation acid-base Bodily fluids become more alkaline due Excretion of base (HCO3−) via the kidneys and concomitant to reduction in carbon dioxide (H2C03) reduction in alkaline reserve with hyperventilation Cardiovascular Increase in submaximal heart rate Submaximal heart rate remains elevated Increase in submaximal cardiac output Submaximal cardiac output falls to or below sea-level values Stroke volume remains the same or Stroke volume decreases decreases slightly Maximum cardiac output remains the Maximum cardiac output decreases same or decreases slightly Hematologic Decreased plasma volume Increased hematocrit Increased hemoglobin concentration Increased total number of red blood cells Local Possible increased capillarization of skeletal muscle Increased red blood cell 2,3-DPG Increased mitochondrial density Increased aerobic enzymes in muscle Loss of body weight and lean body mass 55 § Ambient air in mountainous regions remains cool and dry, allowing body water to evaporate as inspired air becomes warmed and moistened in respiratory passages § Fluid loss leads to moderate dehydration and accompanying dryness of lips, mouth, and throat § Fluid loss becomes pronounced for physically active people because of large daily total sweat loss and exercise pulmonary ventilation 56 28  11/18/24 § Live high–train low approach combines high-altitude stay with low- altitude training: 1. Altitude must be high enough to raise EPO to increase total red blood cell volume and VO2max 2. Athlete must respond positively with increased EPO output 3. Training must take place at low enough elevation to maintain training intensity and exercise oxygen consumption at near sea- level values 57 § In absence of a hypobaric chamber, three approaches create “altitude” environment to stimulate an altitude acclimatization response § 1. Gamow Hypobaric Chamber: person rests and sleeps in a chamber about 10 hr daily. Total air pressure decreases to simulate the barometric pressure of preselected altitude. § 2. Simulate altitude at sea level by increasing the nitrogen percentage of air within an enclosure, which reduced air’s oxygen percentage, thus decreasing inspired Po2 § 3. Hypoxico Altitude Tent: tent that continuously supplies air with oxygen at about 15%, thus lowering inspired Po2 58 29  11/18/24 59 § Medical problems associated with reduced arterial Po2 § Acute mountain sickness: a relatively benign condition resulting from acute reduction in cerebral oxygen saturation, § High-altitude pulmonary edema: when fluid accumulates in brain and lungs § High-altitude cerebral edema: neurologic syndrome that develops within hours or days in those with acute mountain sickness 60 30  11/18/24 § Acute Mountain Sickness (above 2000 meters) § A pathological condition often requiring medical attention § Symptoms: (begin 6-24 hrs after ascending) § Headache, nausea, weakness, loss of appetite, SOB, insomnia, swelling of hands, increased HR,drowsiness, dizziness § Treatment includes: § Rest and removal from altitude § Caused by reduction in partial pressure of oxygen § Can lead to pulmonary edema and high-altitude cerebral edema 61 62 31  11/18/24 63 32