ACUTE PHYSIOLOGICAL RESPONSES TO HEAT STRESS - PowerPoint PPT Presentation

Loading...

PPT – ACUTE PHYSIOLOGICAL RESPONSES TO HEAT STRESS PowerPoint presentation | free to download - id: 6f8c56-ZDYxZ



Loading


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation
Title:

ACUTE PHYSIOLOGICAL RESPONSES TO HEAT STRESS

Description:

Title: ACUTE PHYSIOLOGICAL RESPONSES TO HEAT STRESS Author: Department of Human Performance Last modified by: Craig Cisar Created Date: 2/8/2010 9:46:09 PM – PowerPoint PPT presentation

Number of Views:25
Avg rating:3.0/5.0
Slides: 89
Provided by: Departm125
Learn more at: http://www.sjsu.edu
Category:

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: ACUTE PHYSIOLOGICAL RESPONSES TO HEAT STRESS


1
ACUTE PHYSIOLOGICAL RESPONSES TO HEAT STRESS
2
Basic Mechanisms of Thermoregulation
  • Core temperature maintained between 35 to 41o C
    despite environmental extremes which fluctuate
    between -88 to 58o C via
  • 1. Behavioral temperature regulation such as
    choice of clothing, shelter, ventilation, air
    conditioning, heating, humidifiers, and
    dehumidifiers.
  • 2. Physiological temperature regulation
    controlled by rate of metabolic heat production,
    heat flow from core to skin, and sweating.

3
(No Transcript)
4
Basic Mechanisms of Thermoregulation
  • Physiological control systems operate on a graded
    or proportional response in which changes in
    controlled variables (e.g., sweating and skin
    blood flow) are proportional to displacements of
    the regulated variable (e.g., core temperature)
    from a threshold value.
  • Note each physiological response has a core
    temperature at which the responses start to
    increase and the actual response is
  • dependent on mean skin temperature the lower
    the skin temperature, the higher the increase in
    core temperature before the response is
    initiated.

5
Basic Mechanisms of Thermoregulation
  • Thus, thermoregulatory responses are related to
    both core and mean skin temperature and hence,
    (1) at any given skin temperature each response
    is proportional to core temperature and (2) an
    increase in skin temperature will decrease the
    core temperature threshold and increase the
    response at any given core temperature.

6
(No Transcript)
7
(No Transcript)
8
(No Transcript)
9
CORE TEMPERATURE
  • Temperatures within body regions are dependent
    on
  • 1. The metabolic rate of surrounding tissues.
  • 2. The source and magnitude of blood flow.
  • 3. The temperature gradients between
    contiguous body regions.

10
SKIN TEMPERATURE
  • Determination of skin temperature is useful for
  • 1. Estimating the input of skin temperature
    receptors into the hypothalamus for
    thermoregulatory control.
  • 2. Predicting core temperature.
  • 3. Calculating mean body temperature for
    heat storage determination.
  • 4. Calculating sensible (radiation and
    convection) heat exchange.

11
Exercise Intensity and Core Temperature
  • At rest, 70 of metabolic heat comes from
    internal organs and viscera within the body core.
    During dynamic exercise, metabolic rate
    increases rapidly by 5-15 fold with 70-90 of
    metabolic rate released as heat (humans are least
    efficient at slow and fast speeds of movement).
    Thermoregulatory effectors for heat dissipation
    respond more slowly.
  • Core temperature increases rapidly, then
    gradually leveling off at a steady-state value
    when heat production equals heat loss.

12
(No Transcript)
13
Exercise Intensity and Core Temperature
  • Magnitude of core temperature at steady-state is
    largely independent of environmental conditions
    within a fairly wide prescription zone.
    Increases in core temperature are proportional to
    increases in metabolic rate. 1 watt 6 kgm/min
    .01433 kcal/min.
  • The prescription zone is smaller at higher
    exercise intensities.

14
(No Transcript)
15
Exercise Intensity and Core Temperature
  • If exercise intensity is expressed in absolute
    terms (L/min), large individual differences exist
    in steady-state core temperature however, if
    exercise intensity is expressed in relative terms
    (VO2max),the inter-individual differences
    disappear.

16
(No Transcript)
17
Exercise Intensity and Core Temperature
  • There is a curvilinear relation between
    steady-state core temperature and relative
    workload. The prescription zone is smaller at
    higher relative exercise intensities and it is
    more difficult to reach steady-state core
    temperature as core temperature and relative
    exercise intensity increases.
  • Note An increase in VO2max from training would
    decrease relative workload and hence, reduce core
    temperature, particularly in a heat acclimated
    person.

18
(No Transcript)
19
Exercise Intensity and Core Temperature
  • An increase in ambient air temperature increases
    the metabolic rate (energy requirements) and
    hence relative workload of an absolute exercise
    task as well as the relative contribution of
    anaerobic energy metabolism to the total energy
    requirements.

20
(No Transcript)
21
Effects of Mode of Exercise on Relative Workload
  • Although VO2max of upper body exercise (e.g., arm
    cranking) is lower than lower body exercise
    (e.g., leg cycling) and consequently relative
    work intensity is much higher when performing the
    same absolute exercise task during arm cranking,
    core temperature responses appear to be quite
    similar when working at the same absolute
    metabolic workload.

22
(No Transcript)
23
Acute Metabolic and Muscular Effects of Heat
  • 1. Decreased VO2max due to diversion of blood
    to the skin (cutaneous) vasculature.
  • - Decreased blood flow ( Q) to muscle.
  • - Increased peripheral pooling of blood,
    which decreases central blood volume and hence
    end- diastolic volume (EDV).
  • SV EDV - ESV, Q SV X HR,
  • and VO2 Q X A - V O2 Diff

24
Acute Metabolic and Muscular Effects of Heat
  • 2. The decreased muscle blood flow increases
    tissue hypoxia and the
  • relative contribution of anaerobic metabolism
    to total energy
  • requirements.
  • 3. Increased carbohydrate utilization, primarily
    from blood glucose.

25
(No Transcript)
26
Acute Metabolic and Muscular Effects of Heat
  • 4. Increased blood lactate levels, due to
    increased lactate production as
  • well as reduced lactate removal due to
    splanchnic vasoconstriction and hence, decreased
    hepatic clearance of lactate.
  • 5. Decreased free fatty acid utilization as an
    energy source.

27
Acute Metabolic and Muscular Effects of Heat
  • 6. Increased blood glucose levels, as glucose
    is released from the liver.
  • 7. Decreased blood triglyceride levels, due to
    decreased mobilization of fat.

28
Acute Metabolic and Muscular Effects of Heat
  • Increased reliance on fast-twitch motor units.
  • 9. Decreased efficiency of skeletal muscle
    contraction as fast-twitch motor units expend
    greater energy than ST motor units to develop the
    same tension.

29
Acute Metabolic and Muscular Effects of Heat
  • 10. Increased expired ventilation rate,
    primarily due to an increase respiratory rate
    (i.e.,breathing frequency) with minimal
    changes in respiratory (i.e.,tidal) volume.

30
Effector Mechanisms of Acute Heat Exposure
  • Vasodilation of Cutaneous Vasculature (Increased
    Skin Blood Flow)
  • Increased Sweat Rate

31
Vasodilation of Cutaneous Vasculature (Increased
Skin Blood Flow)
  • There is threshold above which skin blood flow
    will increase. Skin blood flow carries heat by
    convection from the deep body tissues to the
    skin, which may lead to sensible and/or
    insensible heat loss.

32
Vasodilation of Cutaneous Vasculature (Increased
Skin Blood Flow)
  • Skin blood flow is dependent on both core
    temperature and skin temperature as
  • - Increased skin blood flow is proportional to
    core temperature at any given skin temperature.
  • - Increased skin temperature will decrease the
    core temperature threshold.

33
(No Transcript)
34
Heat Transfer by Skin Blood Flow
  • Dependent on the rate of blood flow and on the
    differences in temperature between arterial blood
    leaving the core on its way to the skin and
    venous blood returning to the core from the skin.
    Increases in the rate of blood flow, conduction
    of tissues, and the difference between core and
    skin temperatures will increase the heat
    transfer.

35
  • As ambient temperature increases, there is an
    increased dependence on insensible (evaporative)
    heat loss mechanisms and a decreased dependence
    on sensible (convection and radiation) heat loss
    mechanisms to minimize exercise-induced increases
    in core temperature.
  • Evaporative heat loss is dependent on skin blood
    flow (provides latent heat for the evaporation of
    sweat) and on secretion of perspiration from the
    sweat glands.

36
(No Transcript)
37
Types of Sweat Glands
  • 1. Apocrine glands - nervous or emotional sweat
    due to neurochemical stimuli secretion is a
    watery substance that contains lipids, trace
    of color, and odor most commonly found on the
    palms of the hands, soles of
  • the feet, arm pits, groin area, face, and
    upper lip.

38
Types of Sweat Glands
  • 2. Eccrine glands - respond to thermal stress
    by secreting a watery substance which contains
    electrolytes and is generally colorless and
    odorless there are 1.6 to 4 million eccrine
    glands and are most numerous on the sole of the
    feet and least numerous on the back, although
    the back eccrine glands are the first to
    respond to increases in core temperature.

39
(No Transcript)
40
(No Transcript)
41
Sweat Rate
  • People who sweat more (1) have larger sweat
    glands, (2) have a greater amount of sweating per
    gland, (3) have a higher sweating rate per unit
    of tubular length or unit volume of secretory
    coil, (4) have a reduced hidromeiotic effect, and
    (5) the sweat glands have a greater cholinergic
    (AcH) sensitivity.
  • Hidromeiotic Effect - increased skin wettedness
    decreases sweating.

42
Sweat Rate
  • Sweat rate is dependent on both core temperature
    and skin temperature as
  • - Increased sweat rate is proportional to core
    temperature at any given skin temperature.
  • - Increased skin temperature will decrease the
    core temperature threshold.

43
(No Transcript)
44
  • Generally, the heat dissipating responses are
    sufficient to meet the rise in core temperature
    during exercise if not however, hyperthermia may
    occur leading to heat strain and/or other
  • heat-related illnesses.

45
Heat Strain
  • Heat strain results in a decrease in
    end-diastolic volume as blood pools in the
    peripherally dilated veins and/or plasma volume
    decreases, which leads to a decrease in stroke
    volume and thus heart rate must increase to
    maintain cardiac output. Plasma volume decreases
    due to an increased movement of fluid from the
    plasma to tissue (affected by temperature,
    exercise intensity and mode, hydration level, and
    status of heat acclimation) and an increased
    fluid loss through sweating.

46
(No Transcript)
47
(No Transcript)
48
Compensation of Heat Strain
  • Decreased splanchnic (visceral) and renal blood
    flow, which is proportional to relative exercise
    intensity and skin temperature.

49
Compensation of Heat Strain
  • Decreased skin blood flow at high intensities as
    cardiovascular strain is increased (i.e., skin
    blood flow is proportionally lower than expected
    for a given skin or core temperature) this
    response occurs more quickly in the upright
    position as compared to the supine position and
    is probably controlled by cardiopulmonary
    baroreceptors.

50
(No Transcript)
51
Compensation of Heat Strain
  • 3. Venoconstriction of cutaneous (i.e., skin)
    veins during intense exercise.
  • 4. Increased water and sodium retention by the
    kidneys.

52
(No Transcript)
53
Heat Illnesses
  • Heat Cramps
  • Heat Syncope
  • Water Depletion Heat Exhaustion
  • Salt Depletion Leading to Heat Exhaustion
  • Heat Hyperpyrexia Leading to Heat Stroke
  • Skin Lesions

54
(No Transcript)
55
(No Transcript)
56
(No Transcript)
57
(No Transcript)
58
(No Transcript)
59
(No Transcript)
60
HYPOHYDRATION AND HYPERHYDRATION
61
Hypohydration and Body Fluids
  • SWEAT LOSS OF 5 BODY WEIGHT WILL DECREASE TOTAL
    BODY WATER (TBW) BY AS MUCH AS 8.

62
Hypohydration and Body Fluids
  • Body Weight 75 kg
  • TBW 45 kg (60 of BW)
  • Sweat Loss of 5 BW 3.75 kg
  • 3.75 kg/45 kg 8 Decrease in TBW

63
Hypohydration and Body Fluids
  • PROPORTIONATELY, WHEN TOTAL BODY WATER IS
    REDUCED
  • INTRACELLULAR, INTERSTITIAL, AND PLASMA FLUID
    VOLUMES DECREASE.

64
Hypohydration and Body Fluids
  • IN GENERAL, THE GREATEST DECREASES TEND TO OCCUR
    IN THE INTERSTITIAL AND INTRACELLULAR FLUID
    VOLUMES.

65
Hypohydration and Body Fluids
  • PERCENT PLASMA VOLUME DECREASES STAY ABOUT THE
    SAME REGARDLESS OF THE DECREASE IN TOTAL BODY
    WATER.

66
(No Transcript)
67
Effects of Heat Adaptation on Hypohydration
  • 1. ADAPTED PERSON HAS A SMALLER PLASMA VOLUME
    REDUCTION AT A GIVEN BODY WEIGHT LOSS DUE TO
    HYPOHYDRATION.

68
(No Transcript)
69
Effects of Heat Adaptation on Hypohydration
  • 2. ADAPTED PERSON HAS MORE TBW THEREFORE,
    ABSOLUTE FLUID LOSS WOULD REPRESENT A
    SMALLER PERCENTAGE OF TBW.

70
GENERAL EFFECTS OF HYPOHYDRATION
  • 1. INCREASED CORE TEMPERATURE (INCREASE TENDS TO
    BE LINEAR).
  • 2. INCREASED HEAT STORAGE DUE TO REDUCED HEAT
    LOSS THROUGH BOTH SENSIBLE AND INSENSIBLE
    MECHANISMS.
  • 3. NO AFFECT ON RATE OF AEROBIC AND ANAEROBIC
    METABOLISM.

71
GENERAL EFFECTS OF HYPOHYDRATION
  • 4. DECREASED SWEAT RATE FOR A GIVEN CORE
    TEMPERATURE DUE TO HYPEROSMOLARITY
    (HIGH CONCENTRATION OF OSMOTICALLY ACTIVE
    PARTICLES IN A SOLUTION) AND/OR HYPOVOLEMIA
    (LOW PLASMA VOLUME) OF PLASMA.

72
(No Transcript)
73
GENERAL EFFECTS OF HYPOHYDRATION
  • NOTE HYPEROSMOLARITY OF PLASMA VOLUME HAS ALSO
    BEEN SHOWN TO INCREASE CORE TEMPERATURE DUE TO
    REDUCED CONVECTIVE HEAT TRANSFER (DECREASED SKIN
    BLOOD FLOW) AS WELL AS THE DECREASE IN SWEAT RATE
    THAT LEADS TO AN INCREASE IN CORE TEMPERATURE.

74
HYPOHYDRATION AND EXERCISE
  • 1. HYPOHYDRATION DURING SUBMAXIMAL EXERCISE
    WITHOUT THERMAL STRESS
  • A. INCREASED HEART RATE.
  • B. DECREASED STROKE VOLUME AS REDUCED
    PLASMA VOLUME DECREASES END-DIASTOLIC
    VOLUME.

75
HYPOHYDRATION AND EXERCISE
  • C. NO CHANGE IN CARDIAC OUTPUT.
  • D. NO CHANGE IN VO2MAX.
  • DECREASED PHYSICAL WORK CAPACITY DUE PRIMARILY TO
    THERMOREGULATORY STRESS.
  • THERMOREGULATORY STRESS
  • INCREASED CORE TEMPERATURE AND HEAT STORAGE AS
    INTERNAL CONVECTIVE HEAT TRANSFER AND SWEAT RATE
    IS DECREASED (I.E., DECREASED HEAT LOSS).

76
(No Transcript)
77
HYPOHYDRATION AND EXERCISE
  • 2. HYPOHYDRATION DURING SUBMAXIMAL EXERCISE
    WITH THERMAL STRESS.
  • A. INCREASED HEART RATE
  • B. DECREASED STROKE VOLUME
  • C. DECREASED CARDIAC OUTPUT AS DECREASE IN
    STROKE VOLUME IS GREATER THAN INCREASE IN
    HEART RATE.

78
HYPOHYDRATION AND EXERCISE
  • D. DECREASED MAXIMAL OXYGEN OXYGEN UPTAKE RATE.
  • E. DECREASED PHYSICAL WORK CAPACITY DUE TO
    THERMOREGULATORY STRESS AND CARDIOVASCULAR
    STRAIN.

79
(No Transcript)
80
FITNESS LEVEL, ADAPTATION LEVEL, AND HYPOHYDRATION
  • 1. IN A HYDRATED STATE, AN ADAPTED PERSON
    WITH A HIGH FITNESS LEVEL WILL HAVE LESS BODY
    HEAT STORAGE AND BETTER PERFORMANCE THAN
    UNADAPTED PERSON WITH LOW FITNESS LEVEL.

81
FITNESS LEVEL, ADAPTATION LEVEL, AND HYPOHYDRATION
  • 2. HOWEVER, HYPOHYDRATION MAY NEGATE THE
    THERMOREGULATORY ADVANTAGE OF THE HIGHLY
    TRAINED, ADAPTED PERSON, DESPITE THE FACT
    THAT THE HIGHLY FIT PERSON IS CAPABLE OF
    TOLERATING HIGHER CORE TEMPERATURES.

82
FITNESS LEVEL, ADAPTATION LEVEL, AND HYPOHYDRATION
  • 3. ADDITIONAL RESEARCH IS NEEDED IN THIS AREA.

83
HYPERHYDRATION
  • 1. HYPERHYDRATION CAN DELAY THE DEVELOPMENT OF
    DEHYDRATION DURING HEAT STRESS.
  • 2. HOWEVER, EXCESS FLUIDS BY THEMSELVES MAY NOT
    PROVIDE A CLEAR EXERCISE ADVANTAGE.

84
HYPERHYDRATION
  • 3. ADDITIONAL RESEARCH IS NEEDED IN THIS AREA.

85
GLYCEROLPERFORMANCE AIDOR FAD?
86
HYPERHYDRATION USING GLYCEROL
  • RAPIDLY ABSORBED WHEN INGESTED ORALLY AND EVENLY
    DISTRIBUTED TO ALL FLUID COMPARTMENTS.
  • ATTRACTS AND HOLDS WATER LIKE A SPONGE.
  • INCREASES PRE-EXERCISE HYDRATION LEVELS AS URINE
    PRODUCTION IS DECREASED.

87
HYPERHYDRATION USING GLYCEROL
  • DURING EXERCISE
  • INCREASED SWEAT RATE AT A LOWER CORE
    TEMPERATURE.
  • GREAT SWEAT CAPACITY.
  • LOWER HEART RATE AND CARDIOVASCULAR
    STRAIN.
  • IMPROVED ATHLETIC PERFORMANCE IN HOT, HUMID
    ENVIRONMENTS.

88
QUESTIONS?THE END!
  • AND THAT WINDS UP MY PRESENTATION TONIGHT AT
    SJSU WHERE THE WOMEN ARE STRONG, THE MEN ARE GOOD
    LOOKING, AND ALL OF THE STUDENTS ARE ABOVE
    AVERAGE!!
About PowerShow.com