Lecture 9 Flashcards
To define and describe the different types as well as stages of physiological and behavioral adaptations to hot environments
ACCLIMATION is the physiological or behavioral adaptive changes in response to experimentally induced changes of particular climatic factors such as ambient temperature and humidity in a controlled environment.
ACCLIMATIZATION are the physiological or behavioral adaptive changes that occur within an organism that reduce strain caused by stressful changes in the natural climate (e.g., seasonal or geographical).
Focusing on heat acclimation (HA), there are two phases/stages: ACUTE and CHRONIC. Physiological adaptations (inc CV and thermoregulatory) to hot environments include improved thermal perception, fluid balance (sweat Na and Cl conc dec, renal Na and Cl conc dec).
In the ACUTE phase, there is:
- ↓ sweat
- ↑ core and skin temperatures
- ↑ heart rate, ↓ stroke volume; tachycardia to ↑ cardiac output
- ↓ thermal comfort
- ↑ Borg Rating of Perceived Exertion (BRPE)
- ↓ exercise tolerance
- ↑ electrolyte loss in sweat/urine
In the CHRONIC phase, there is:
- reversal or improvement of acute phase variables
- plateau values for sweat, Tcore, HR
- ↑ plasma volume
- ↓ electrolyte loss in sweat/urine
- ↑ improved thermal comfort/BRPE
- ↑ exercise tolerance
To describe the thermal and cardiorespiratory adaptations to hot environments.
** slide 11 says during acute phase of HA, CO dec due to redistribution of blood to skin and muscles. but slide 13 says Q inc?
Initially see:
- ↓ stroke volume
- ↑ HR to compensate for decreased cardiac filling (to ↑ CO)
- ↑ skin BF
- ↑ skeletal muscle BF w/exercise
- ↓ VR, CO, and central blood volume (due to redistribution to skin and skeletal muscle)
- Elevated core temp
- Low sweat
- ↓ liver & splanchnic blood flow
Post HA:
- Lower skin and core temp
- ↓ HR, closer to rest
- ↑ SR (from 400 to 550mL/hr)
- Start sweating at a LOWER core temp
- ↓ Skin BF
- ↑ VR, CO, and central blood volume
- ↑ Plasma volume
To describe the thermoregulatory response adaptations to hot
environments
- Lowered Tcore threshold for Esw and skin BF
- Sweat amount as well as its distribution change from mainly trunk to limbs; improves evaporation and surface cooling
To describe the changes in total body water and fluid balance as well as the hormonal changes underlying these fluid compartment adaptations to hot environments
TOTAL BODY WATER AND FLUID BALANCE:
- HA can ↑ TBW by 5-7%
- Studies are split btwn proportions of ↑ extra-(ECF) and ↑ intra-cellular (ICF) w/HA
- HA can ↑ ECF and plasma volume but lots of variability; 0-30%
- Effects of HA on ECF and PV expansion vary depending on duration of heat exposure, exercise/passive HA etc.
- Mechanisms for this ECF and PV expansion are unclear but include:
1) Na and H2O retention
2) a net fluid shift from interstitium to plasma due to higher circulating protein mass in plasma (i.e. ↑ oncotic pressure)
3) Warm skin gives venodilation that lowers post capillary resistance and mediates net fluid reabsorption into plasma as well as hemodilution
HORMONAL CHANGES with HA:
- ↑ Adrenocorticotropic hormone (ACTH) from anterior pituitary due to circulatory strain early in HA
- ACTH causes adrenal cortex to ↑ release of [aldosterone]PLASMA and [cortisol] PLASMA
- Aldosterone and cortisol contribute to renal distal tubule and collecting duct retention of Na+ in a few hours, and to sweat glands retention of Na+ in a few days.
- Some debate if aldosterone alone affects sweat Na+ retention
- An alternative hypothesis is other factors influence this absorption only in the presence of aldosterone.
- Exercise and heat stress also ↑ release of aldosterone via renin-angiotensin system
- Within a few days Na+ conserving effects of aldosterone are sufficient and [ACTH] falls
- Antidiuretic Hormone (ADH) aka vasopressin and Atrial Natriuretic Peptide are less studied and may ↑ or ↓ w/HA
To describe factors influencing the maintenance of physiological adaptations to hot environments
1) Fitness: Athletes or those with higher VO2 will adapt more quickly.
To maintain benefits of HA, avoid the following:
2) Sleep loss
3) Infection
4) Alcohol abuse
5) Salt depletion
6) Dehydration
To describe the time course of the decay and the re-acclimation to hot environments.
% loss or decay rate is = (Mean Post Acclimation value* - Mean Acclimation Value) /
(Mean Unacclimation Value - Mean Acclimation Value)
*at a given post acclimation day
- Both deacclimation and reacclimation is highly variable
- No seasonal effects
- Rule of thumb is that one day deacclimated gives you a loss of 2 days HA
To describe how heat acclimation influences aerobic performance
a
Define acclimation
Physiological or behavioral adaptive changes in response to experimentally induced changes of particular climatic factors such as ambient temperature and humidity in a controlled environment
Define acclimatization
Physiological or behavioral adaptive changes that occur within an organism that reduce strain caused by stressful changes in the natural climate (e.g., seasonal or geographical).
How many days does it take heat acclimation to complete? What % is completed in the 1st 5-7 days?
- 10-14 days to complete
- ~75-80% in first 5-7 days
What are the 2 phases of acclimation?
- Acute
2. Chronic
What are the 2 main system adaptations of heat acclimation?
CV & thermoregulatory adaptations
What exercise conditions induce is best to induce heat acclimation?
Exercise intensity (~50 - ~75% VO2max) & duration (~60 min/d)
Is heat acclimation done at low or high temp and can it be in low or high RH?
Passive heat exposure w/high temp., can be w/ low or high RH
How does heat acclimation affect thermal perception
Improved thermal perception
How does heat acclimation affect fluid balance?
Tend to retain fluid early on in HA (good cause one adaptation is inc SR)
What does the rate of heat acclimation and decay depend on?
Fitness lvl and other factors
9 things that occur during acute phase?
- dec SWEAT
- inc core and skin TEMPS
- inc HR
- dec SV (to maintain given CO)
- TACHYCARDIA to inc CO
- dec THERMAL COMFORT
- inc Borg Rating of Perceived Exertion (BRPE)
- dec EXERCISE TOLERANCE
- inc ELECTROLYTE LOSS in SWEAT/URINE
9 things that occur during acute phase?
- reversal or improvement of acute phase variables
- PLATEAU values for SWEAT, Tcore, HR
- inc PLASMA VOLUME
- dec ELECTROLYTE LOSS in sweat/urine
- improved THERMAL COMFORT/BRPE
- inc EXERCISE TOLERANCE
What are “plateau days’ of physiological adaptations during HA?
The point at which approx 95% of the adaptation occurs
What adaptation occurs during 3-6 days of HA?
- HR dec
- PV expansion
- Perceived exertion dec
What adaptation occurs during 3-8 days of HA?
Renal Na+ and Cl- conc dec
What adaptation occurs during 5-7 days of HA?
Rectal temp dec
What adaptation occurs during 5-9 days of HA?
Sweat Na and Cl conc dec
