HPHE 6710: Section 05 - Exercise Performance and Environmental Stress (Chapter 25,24,26,27)

7/30/2019 HPHE 6710: Section 05 - Exercise Performance and Environmental Stress (Chapter 25,24,26,27)

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Section 05:

Exercise Performance and

Environmental Stress

Chapter 25 Exercise and Thermal Stress

Chapter 24 Exercise at High and Medium Altitude

Chapter 26

Sport DivingChapter 27 Microgravity: The Final Frontier

HPHE 6710 Exercise Physiology II

Dr. Cheatham


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Chapter 25

Exercise and Thermal Stress


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Chapter Objectives

Understand the physiological mechanisms inresponse to heat and cold exposure

Understand the physiological responses during

exercise in the heat and the cold Understand heat and cold acclimatization

Understand the different types of heat illness

Understand factors that modify the responses

to heat and cold


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Introduction


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Part 1

Mechanisms of Thermoregulation


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Thermal Balance

E-RCCMS dV


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Hypothalamic Regulation of Temperature

Hypothalamus Central coordinating center for temperature

regulation

Activation of bodys heat-regulatingmechanisms

Thermal receptors in the skin

Changes in blood temperature perfusing thehypothalamus


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23C, 74F

TCORE = 37.1C

TSET = 37.1C

0C, 32F

TCORE = 37.1C

36C, 97F

TCORE = 37.1C

Skin

Temp

Skin

Temp

TSET = 37.5CIm

cold!

TSET = 36.5C

Im

hot!


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Thermoregulation in Cold Stress: Heat Conservation

and Heat Production


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and Heat Production


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and Heat Production

h l i i ld i


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and Heat Production

Vascular adjustments Cutaneous cold receptors constrict peripheral blood

vessels. 250 mL/min at thermoneutral; approaches zero with severe

cold stress

Begins when skin temperature < 35C and is maximal when skintemperature < 31C

Skin temperature declines

Muscular activity Shivering

Maximal rates have been shown to be around 46% VO2max

Hormonal output Epinephrine and norepinephrine (short term)

Thyroxine (long term)

Th l i i C ld S H C i


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and Heat Production


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Individual Factors Modifying Responses to Cold

Anthropometric Characteristics

Surface area to mass ratio

Body Composition


and Heat Production


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Thermoregulation in Heat Stress: Heat Loss


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Radiation

Electromagnetic heat waves

Conduction

Direct contact between molecules Convection

Movement of adjacent air or water molecules

Evaporation Vaporizing water

Evaporative heat loss at high ambient temperatures

Heat loss in high humidity



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Integration of Heat Dissipating Mechanisms Circulation

Body can control dry heat loss by varying skin blood flow

and thus skin temperature

After sweating has begun, skin blood flow serves

primarily to deliver to the skin the heat that is being

removed by sweat evaporation.

Skin blood flow is affected by temperature in two ways:

Local effect on smooth muscle

Reflexes operating through the SNS



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36C (97F), 60% RH, 105 Watts


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Integration of Heat Dissipating Mechanisms Evaporation

Sweating begins within several seconds of the start of vigorous

exercise.

The onset time of thermoregulatory sweating is influenced by skin

temperature, acclimatization status, hydration status, and non-

thermal stimuli.

Sweating closely parallels increase in body temperature

First, recruitment of sweat glands increases

Second, sweat secretion per gland increases Chest and back sweat first, followed by limbs

Cooled blood returns to core to absorb additional heat.

Hormonal adjustments

Vasopressin and aldosterone help maintain blood volume.



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36C (97F), 60% RH, 105 Watts


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Effects of Clothing on Thermoregulation

Clothing Insulation (CLO Units) Index of thermal resistance

A clo unit of 1 maintains a sedentary person at 1MET indefinitely in an environment at 21C (68.8F)

and 50% RH

Factors: Wind speed

Body movements

Chimney effect baggy clothes Bellows effect movement increases ventilation of air

layers

Water vapor transfer

Permeation efficiency factor clothes absorb sweat


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Cold-weather clothingLayers trap air

Moisture properties Warm-weather clothing

Light in color

Moisture properties


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Part 2

Thermoregulation and Environmental

Stress During Exercise


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Core Temperature During Exercise

Exercise in the Heat


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36C (97F), 60% RH, 105 Watts

h


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i i h


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i i h


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Circulatory Adjustments Two competing cardiovascular demands:

Adequate muscle blood flow for metabolism

Adequate peripheral blood flow for thermoregulation

Also, maintenance of blood pressure

E i i h H


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E i i h H


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E i i h H


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Cardiovascular Responses

E i i th H t


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Cardiovascular Responses

E i i th H t


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Exercise in the HeatCardiovascular Responses

E i i th H t


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Exercise in the HeatCardiovascular Drift

E i i th H t


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HR Higher in heat

SV Lower in heat

Q At low intensity will increase

At higher intensities usually maintained

a-vO2 difference Usually higher in heat

Blood Pressure Lower in heat

TPR Usually lower in heat


E i i th H t


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Exercise Performance

Limitations

Performance Effects

VO2max is lower in hot

compared to temperateenvironments

0.25 L/min lower in 49C

compared to 21C

Why? Decrease in muscle blood flow

Decrease in central blood flow

and thus maximal CO


E i i th H t


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E ercise in the Heat


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Water Loss in the Heat: Dehydration Magnitude of fluid loss

The more prolonged or intense the exercise, the greaterthe loss.

Sweat rates can exceed 3 L/hour Significant consequences

Dehydration may threaten health.

Physiologic and performance decrements occur.

For every liter of sweat loss, HR can increase by 8 b/minwith a corresponding 1.0 L/min decrease in Q

Diuretics

Cause greater fluid loss from plasma than sweating




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Water Loss in the Heat: Dehydration Dehydration by more than 2% of body weight will

negatively impact endurance exercise

Increased hyperthermia

Core temperature elevations ~ 0.2C for every 1% decrease in

BW

Lowers the core temperature that can be tolerated before heat

exhaustion from heat strain

Sweating is reduced Increased cardiovascular strain

Altered metabolic function

Altered CNS function


Maintaining Fluid Balance


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Factors That Modify Heat Tolerance


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Acclimatization Physiologic changes that improve heat tolerance

Optimal acclimatization requires adequaterehydration.

Three classical signs:

Lower HR

Lower core temperature

Higher sweat rate

After acclimatization, the threshold for sweatingoccurs at a lower core temperature

Lower skin temperatures decrease cutaneous BFrequirements for heat balance



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Training status Increased sensitivity and capacity of sweating response

Plasma volume increases

Greater skin and GI blood flow

Larger volumes of more dilute sweat Age

Age-related differences in heat tolerance

Some age-related factors affect thermoregulatory

dynamics. Children

Lower sweating rate and higher core temperature

Sweat is more concentrated.




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Gender When studies control for fitness level and relative

exercise intensity, no gender differences are observed.

Sweating Women Sweat less prolifically than men despite having more heat-activated

sweat glands

Sweat smaller volumes

Begin sweating at higher skin and core temperatures

Compared to men, women tend to cool faster. Menstrual cycle alters skin blood flow and sweating response.

Body fat insulates body, retards heat dissipation, and adds to

metabolic cost of weight-bearing activities.


Complications from Excessive Heat Stress


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Heat Cramps (Involuntary Muscle Spasms) Core temperature typically in normal range

Due to an imbalance in fluid levels and electrolyte

concentrations

Those at risk tend to have high sweat rate and high

sweat sodium concentrations

Prevention

Adequate fluid and electrolyte intake before and during

exercise



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Heat Exhaustion Ineffective circulatory adjustments, depletion of extracellularvolume (especially PV)

Peripheral pooling occurs, central blood volume decreases,cardiac output usually decreases

Symptoms: Weak, rapid pulse

Low blood pressure

Dizziness, headache, overall weakness

Possible decrease in sweat rate

Core temperature is elevated but not to dangerous levels (i.e.> 40C or 104F)

Treatment Move to cooler location, rapid body cooling, fluids (possibly

intravenously)




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Heat Stroke The failure of the heat-regulating mechanisms from

an excessively high core temperature

Classic Form:

Environmental heat overloads the bodys heat dissipatingmechanisms.

Symptoms:

Core temp > 105F, altered mental status, absence of sweating,multisystem organ dysfunction.

Exertional Heat Stroke:

Extreme hyperthermia from:

Metabolic heat load in exercise

Challenge in heat dissipation from a hot-humid environment




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Heat Stroke (contd) ExertionalHeat Stroke (contd):

Symptoms:

Core temp > 41.5C

Sweating diminishes, skin becomes dry and hot

Inordinate strain on the CV system

Rapid breathing

Altered mental status

Treatment: Rapid cooling: ice packs, alcohol rubs, whole-body immersion in

cold water or ice, intravenous fluids, EMS medical attention,

drug treatment (endotoxins)




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Exercise in the Cold


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Cardiovascular Responses At Rest:

Higher Q

Higher SV

No change in HR

Higher BP and TPR

a-vO2 diff

Lower if muscle temp decreases Similar between cold and neutral if muscle temp remains the

same



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Cardiovascular

Responses

During Exercise:

Increased Q

Increased SV

No change or slight

decrease in HR

Increased BP and TPR


Note to self: Get better figure for this slide



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Oxygen Uptake andSystemic OxygenTransport

Man in the cold is not

necessarily a cold man If cold stress is sufficient

to decrease coretemperature or muscle

temperature, then: VO2max may be reduced

Impairment of myocardialcontractility




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VO2max in the Cold Matsui et al. (1978)

Acute exposures to 5C, 18C, and 35C

No differences in VO2max

Astrand and Saltin (1961)

20C and -5C

No difference in VO2max

Bergh (1980)

5 to 6% decrease for every 1C drop in core

Probably related to decrease in max HR and thus

maximum Q




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Individual Factors Modifying Responses to Cold Anthropometric Characteristics

Surface area to mass ratio

Body Composition


Acclimatization to Cold


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Chapter 24

Exercise at Medium and High Altitude

Chapter Objectives


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Chapter Objectives

Fill in

The Stress of Altitude


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Reduced PO2 creates a metabolic challenge. Oxygen transport cascade

Progressive change in environments oxygen

pressure and in various body areas Acclimatization

Adaptations occurring due to a change in the

natural environment

Acclimation

Adaptations produced in a controlled laboratory

setting



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e St ess of t tude



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f



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149

104

9640

23

40

84

53

40

25

159 94Sea Level 4300 m

f



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Oxygen Loading at Altitude No meaningful change in Hb saturation until an

elevation of 3048 m

Examples At 1981 m (6500 feet)

PAO2 at sea level = 100 mmHg (97.2% saturated)

PAO2 at 6500 feet = 78 mmHg (~ 94% saturated)

Mexico City Olympics (1968) (2300 m, 7546 feet) PaO2 = 120 mmHg (80% saturated)

Performance decrement

Sudden exposure to 4300 m VO2max decreases by 32%

Mt. Everest VO

2max

decrease of 70%

f



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Acclimatization


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Acclimatization


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Immediate Response to Altitude Increase in respiratory drive to produce hyperventilation

Increase in blood flow during rest and submaximal exercise

Hyperventilation Low PaO2 sensed by peripheral chemoreceptors

When PIO2 drops below 110 (normal = 150) or PaO2 is less than60 (normal = 96) ventilation increases

Beyond these levels, ventilation increases in proportion tolevel of hypoxia

Increase in ventilation increases PAO2 and decreases PACO2

What happens during rapid exposure to low O2 First few minutes = dramatic increase in VE After initial minutes = slight blunting of VE but still more than

normal

Why? Ventilation induced hypocapnia

Acclimatization


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Acclimatization


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Immediate Response to Altitude (contd) Increased cardiovascular response

Resting SBP increases

Submaximal exercise heart rate and cardiac output can rise to50% above sea level values (no change in SV)

At a given absolute workload:

Q is increased at altitude

HR is increased at altitude

SV is the same

Compensation for lower a-vO2 difference

However, a given absolute workload is a greater relativeworkload because VO2max is reduced at altitude

If same relative workload is performed, no difference betweennormoxia and hypoxia

Acclimatization


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Acclimatization


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Catecholamine Response Plasma and urine catecholamines are higher at

altitude

Mostly due to increase in NE not E

During first few minutes, no difference in NE

Production is increased, but removal is also increased

Within 14-18 hours, an increase in NE is observed

Production is increased, but removal is decreased Splanchnic removal is proportional to arterial

concentration

Acclimatization


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Acclimatization


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Acclimatization


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Longer-Term Adjustments to Altitude Regulation of acid-base balance altered by

hyperventilation

Synthesis of hemoglobin and red blood cells

Elevated sympathetic neurohormonal activity

Acid-Base Readjustment

Hyperventilation causes a decrease in PCO2 Increase in pH

Kidneys begin to excrete bicarbonate

Acclimatization


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Longer-Term Adjustments to Altitude (contd) Hematologic Changes

Initial plasma volume decrease

Shift from intravascular space to interstitial and intracellular

space Increases red blood cell and hemoglobin concentration

Diuresis

Maintains fluid balance between the compartments even

though total body water is reduced

Red blood cell mass increases

Acclimatization


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Acclimatization


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Longer-Term

Adjustments toAltitude (contd)

Cellular Changes

Capillaryadjustments

Increasedmyoglobin

Increased

mitochondrialdensity

Increased 2,3-DPGlevels

Altitude Training and Sea-Level Performance


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Performance upon return is not improved if usingVO2max as the criteria

Altitude acclimatization improves ability to perform at

altitude.

Decrement in absolute training level at altitude

Athletes cannot train as intensely while at altitude.

Altitude Training and Sea-Level Performance


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Combine Altitude Stay with Low-Altitude Training


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Live hightrain low appears to be

the best scenario for improvingperformance.

Capitalize on stress of altitude andacclimatization

Train lower so intensity can bemaintained

At-Home Acclimatization

Methods of simulating hypobaricconditions

Cause altitude-induced physiologicadaptations

Gamow hypobaric chamber

Wallace altitude tent

Simulated Altitude


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Simulated Altitude


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http://www.youtube.com/watch?v=RRCBbAKW1DU&feature=player_embedded

Simulated Altitude
http://www.youtube.com/watch?v=RRCBbAKW1DU&feature=player_embeddedhttp://www.youtube.com/watch?v=RRCBbAKW1DU&feature=player_embeddedhttp://www.youtube.com/watch?v=RRCBbAKW1DU&feature=player_embedded


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http://www.youtube.com/watch?v=izuDBEu4BhY&feature=player_embedded

Simulated Altitude
http://www.youtube.com/watch?v=izuDBEu4BhY&feature=player_embeddedhttp://www.youtube.com/watch?v=izuDBEu4BhY&feature=player_embeddedhttp://www.youtube.com/watch?v=izuDBEu4BhY&feature=player_embedded


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http://www.youtube.com/watch?v=p6WHPd7yHdk
http://www.youtube.com/watch?v=p6WHPd7yHdkhttp://www.youtube.com/watch?v=p6WHPd7yHdkhttp://www.youtube.com/watch?v=p6WHPd7yHdk


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Chapter 26

Sport Diving (Hyperbaria)

Chapter Objectives


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Fill in

Introduction


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Pressure-Volume Relationships and Diving Depth


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Diving Depth and Pressure Hyperbaria

Water is noncompressible.

As a diver descends, the pressure increases.

Two forces produce this external pressure Weight of the column of water above the diver

Weight of the atmosphere at the waters surface

Every 33 feet of sea water represents anotheratmosphere of pressure.



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Diving Depth and Gas Volume Boyles law

At a given temperature, the volume of a gas

varies inversely with its pressure.

Greater pressure compresses the gas into a

smaller volume. So, volume of air underwater is less than that same amount of

air measured at sea level

P1V1 = P2V2



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Diving Depth and

Gas Volume(contd)

Example:

What is thevolume of 1 liter

of gas (measured

at sea level) at a

depth of 100 feet(4 ATM)?

(1)(1) = (4)(X)

X = 1/4 Liter



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Diving Depth and Gas Volume (contd) If a rigid container was submersed underwater, the

pressure in the container would not change

But, the human body is not a rigid container

Therefore, the contents of the human body will

compress as the pressure increases as water depth

increases

Water cannot compress (but the pressure of watercan increase), so the air spaces within the body will

compress



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Diving Depth and Gas Volume (contd) Which air spaces are susceptible to damage?

Natural Air Spaces

Lungs

Middle Ear Sinuses

Gastrointestinal Tract

Artificial Spaces

Cavities within teeth Face Mask

Air spaces within diving suit



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Diving Depth and Gas Volume (contd) What happens to the lungs?

A breath hold diver with a TLC of 6L and a RV of 1.5L

takes a full inspiration and dives downward

At 100 feet, pressure equals 4 ATM and lung volumeequals:

(6L)(1ATM) = (X)(4ATM)

X = 1.5 L

Residual volume has been reached and lung volume can

decrease no further



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Diving Depth and Gas Volume (contd) What happens if the diver goes deeper?

Pulmonary capillary and venous congestion displaces air

in thorax decreasing RV and equalizing pressure

Problem with this:

The increase in vascular pressures may lead to ruptures of the

microvasculature

Pulmonary edema and hemorrhage



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Diving Depth and Gas Volume (contd) What happens to diver during ascent?

At 100 feet, diver is running out of air

He fills his lungs with air from the tank

As he ascends, pressure decreases Volume of air expands because pressure is decreasing

Volume of air is too large to occupy lung space

Lung bursts

Only happens if breath holding during ascent



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Snorkeling and Breath-Hold Diving


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Limits to Snorkel Size Inspiratory capacity and diving depth

Pressure of water reduces lung expansion

Snorkel size and pulmonary dead space

The snorkel adds to the dead space.

Larger snorkel sizes are not effective due to too much

dead space, which limits alveolar ventilation.



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Breath-Hold Diving Duration depends on

Time to CO2 build-up reaches breath-hold breakpoint(PCO2 ~ 50 mmHg)

Relationship between divers TLC and RLV Hyperventilation

Decreases PCO2, increases breath-hold time

Increases susceptibility to blackout

Thoracic squeeze Limits depth of breath-hold diving to about 100 FSW



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A Diving Reflex in Humans? Physiologic responses to water immersion

Bradycardia

Decreased cardiac output

Increased peripheral vasoconstriction

Lactate accumulation



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Scuba Diving


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Open vs. Closed Circuit Scuba

Special Problems With Breathing Gases at High Pressure


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Henrys law Gas dissolved in a liquid at a given temperature

depends upon pressure differences between the

gas and liquid and gas solubility in the liquid.

Air must be delivered at sufficient pressure toovercome force of water against divers thorax.



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The Bends At high pressures, the partial pressure of all gases

increases

The partial pressure of Nitrogen especially increases

Nitrogen is fat soluble and thus enters the fattytissues

Upon ascent, the pressure decreases and thus thegases must be released

The lungs cannot get rid of the nitrogen quicklyenough

Thus, the nitrogen begins to bubble out of thetissues and the nitrogen content of the bodyincreases



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The Bends (contd) Treatment

Recompression allows

the nitrogen to enter

into solution again

The pressure is then

gradually decreased

This allows time forthe nitrogen to escape

through the

respiratory system



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Oxygen Poisoning

Exposure to a high partial pressure of oxygen can

have severe effects on the lungs and the CNS

A high PO2 causes much oxygen to be dissolved insolution

The O2 dissolved in solution is the first O2 to be

used by the tissues Because the dissolved O2 is high, it is sufficient to

supply the tissues with O2



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Oxygen Poisoning (contd) Thus, O2 does not have to dissociate from

hemoglobin

Hemoglobin in venous blood contains high amountof O2

What problem does this cause?

Hemoglobin normally binds CO2 in the venous circulation

CO2 builds up since it cannot bind to hemoglobin



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Oxygen Poisoning (contd) Symptoms of O2 poisoning

The high PO2 can cause cerebral blood vessels to constrict

Visual distortion Rapid and shallow breathing

Convulsions

Irritation of the respiratory tract leading to pneumonia



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Nitrogen Narcosis Nitrogen is not metabolically active

Can act like an anesthetic gas

Diver develops symptoms similar to alcohol

intoxication

Every 15 meter descent is equal to the consumption of

one martini on an empty stomach

Impairment of judgment and diver may not recognize aproblem exists

Divers who dive below 30 meters will use a helium

mixture


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Chapter 27

Microgravity: The Last Fronteir

Chapter Objectives


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Fill in

Introduction


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Microgravity and Weightlessness

Microgravity: Gravitational forces acting on the

long axis of the body are minimized.

Gravity depends on the:

Persons mass, earth mass, and distance from the centerof the earth (increases 5% during spaceflight)

So, gravity is only slightly decreased in space

Weightlessness:

Caused in space due to the fact that the spacecraft is in

free fall.

The crafts centrifugal force counterbalances the force of gravity.

Therefore, the perception is weightlessness

Introduction


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Introduction


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Space Flight

Microgravity unloads body tissues and

redistributes body fluids

Light and dark cycles are altered

Very little ultraviolet radiation

Carbon dioxide levels are elevated

Psychological stress

Vigorous physical activity

Introduction


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Simulated Microgravity

Bed Rest

Loss of muscle mass and strengthwithin 2 weeks

Decrease in bone mineral density(~12 weeks)

Decrease in cardiac mass (~6weeks)

Exercise impairment (~ few days)

Decrease in maximal exercisecapacity (~ few weeks)

Immersion

Suspension and Immobilization

Introduction


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Physiologic Adaptations to Microgravity


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Cardiovascular System

Decrease in plasma volume

Lower resting heart volume

Cardiac atrophy

May actually be negative caloric balance and body weight

Cardiac contractility probably not affected

Increases in cardiac compliance

But, these decrease after two weeks of bed rest

Increased venous compliance (decrease VR)

Decreased PNS, increased HR, increased SNS



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Musculoskeletal adaptations

Increased calcium loss

Skeletal muscle adaptations

Concentric and eccentric strength

Muscle ultrastructural changes Altered muscular coordination

Delayed-onset muscle soreness

General weakness and fatigue

Max explosive leg power decreases.



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HPHE 6710: Section 05 - Exercise Performance and Environmental Stress (Chapter 25,24,26,27)

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Transcript of HPHE 6710: Section 05 - Exercise Performance and Environmental Stress (Chapter 25,24,26,27)