Integrative Physiology Flashcards
Compare definitions of hypoxic and hypobaric
hypoxic/hypoxia
- condition in which body tissues are deprived of oxygen
- physiological
hypobaric
- condition of less than normal atmospheric pressure
- physical
hypobaric hypoxia
- condition of low atmospheric pressure = low oxygen supply
- change atmospheric pressure
normobaric hypoxia
- condition of low oxygen concentration in air = low oxygen supply
- change [O2]
Oxygen pressure
Pgas = Tp x [gas]
- Pgas = partial pressure of individual gas
- Tp = total barometric pressure
- [gas] = concentration of individual gas
PaO2 = (FiO2 x (Patm - Ph2o)) x (PaCO2/RespQ)
- PaO2 = partial pressure of alveolar oxygen
- FiO2 = fraction of inspired oxygen, 0.21 in room air
- Patm = 760mmHg at sea level
- Ph2o = H20 vapour pressure in alveolus, usually 47mmHG at 37*C
- PaCO2 from ABG
- RespQ = respiratory quotient, usually 0.8
Oxygen pressure and saturation
- diffusion gradient between tissues acts as a driving force fo O2 delivery to the muscle
- decrease in driving force as altitude increases
- fall in PO2 reduces driving pressure for gas exchange in lungs
- produces a cascade of effects down to mitochondria
Impact of altitude on health
0-500m - sea level/near sea-level
500-2000m low altitude
- minor impairments in aerobic performance
2000-3000m moderate altitude
- AMS starts to occur and acclimatisation becomes important for performance
3000-5500m high altitude
- AMS, HAPE, and acclimatisation become clinically relevant and performance is considerably impaired
> 5500m extreme altitude
- prolonged exposure leads to progressive deterioration and potentially to HACE
AMS: acute mountain sickness - breathlessness, headache, nausea, dizziness, tiredness
HAPE: high-altitude pulmonary edema - fluid released in pulmonary cavity, coughing, wheezing, general weakness
HACE: high-altitude cerebral edema - brain swells due to fluid accumulation, confusion, fatigue, coma, paralysis
AMS treatment
- go no higher until symptoms resolve, if not resolved, descend (500m descent can improve symptoms)
pharmacological measures
- ibuprofen/paracetamol (headache, pain, fever)
- diamox (acetazolamide) (hastens acclimatisation, helps prevent high altitude disorders, inhibits carbonic anhydrase enzyme that counteracts respiratory alkalosis during ascent, facilitates excretion of bicarbonate in urine)
Performance
world records:
- 100, 200 and 400 (men), 100 and 200m (women)
- triple jump, top 6 jumpers beat previous WR
- long jump bob beamon 8.9m
- reduced air density
distance events
- only events without world/olympic record (marathon, walk, steeplechase)
- reduced O2 availability
Oxygen cascade
ambient air
- breath in air with O2
lungs
- transfer of O2 from pulmonary alveoli to blood
haemoglobin
- carriage of O2 in the blood
cardiac output
- pumping of blood by the heart
muscle blood flow
- distribution of oxygenated blood to working muscle
oxygen extraction
- extraction of O2 by working muscle
cellular metabolism
- utlisation of O2 by working muscle
max performance
- acute altitude exposure affects all facets of oxygen cascade
- increased relative exercise intensity for a given absolute workload
- delayed recovery between high-intensity intervals
- moderate altitude AMS symptoms that contribute to increase RPE
acute acclimatisation
inc sympathetic activity leads to inc heart rate
inc Ve to dec PaCO2
inc PaO2 and pH
plasma vol dec
inc Hb conc
inc RBC production due to inc EPO
altitude acclimatisation
dec HRmax of 1bpm per 100m>3000m due to inc vagal tone (parasympathetic activity) and downregulation of B receptors
dec SV possibly due to lower plasma and blood volume
fick equation
Q = HR x SV
VO2max = Q x a-vO2diff
what to do
- athletes who must perform at altitude should do so within 24h of arrival while the detrimental changes that occur have not become too great
- notion of a ‘physiological window’ for exercising immediately after arrival at altitude unsupported
- longer acclimatisation more beneficial than ‘fly in, fly out’
high altitude natives
tibetans
- incidence of CMS 1%
- 4000m+
- decreased hgb conc in blood, lower arterial oxygen saturation, compensate with a higher breathing rate and larger lung volume
- higher Ve and normal Hgb (move more O2 via lungs
- higher capillary density (improves perfusion and O2 delivery due to shorter diffusion distance)
andeans
- incidence of CMS up to 18%
- 4000m+
- increased hgb conc and better arterial oxygen saturation
ethopian highlanders
- incidence of CMS 0%
- 2500m-4100m
- living at higher altitudes, show no difference in hgb conc and arterial oxygen saturation compared with people living at sea level
CMS: chronic mountain sickness
Core temp
- usually between 36-37.5*C in thermoneutral conditions
- large range of interindividual variability
- defended by various thermoregluatory process to maintain this tight range irrespective of environments
- increases and decreases for various reasons
Skin temp
- between 34-35*C in thermoneutral conditions
- rises and falls much easier than core temperature and dependent on environment
- responsible for perceptions of hot/cold especially when at rest
Heat balance
body constantly strives to maintain heat balance
heat production
- basal metabolic rate
- muscle activity
-hormone and neurotransmitter stimulation
- thermogenic effect of food (digestion, absorption, storage)
heat loss
- how rapidly heat can be conducted from body core to skin surface
- how rapidly heat can be transferred from skin to environment
Heat balance equation
S = M - Wk - R - C - K - E (W)
- S = body heat storage
- M = metabolic rate
- Wk = external work rate
- R = radiative heat transfer
- C = convective heat transfer
- K = conductive heat transfer
- E = evaporative heat loss
biophysics of heat transfer
heat stress
- radiation
- evaporation
- convection
- conduction
- radiation from sun
cold stress
- radiation
- convection
- conduction
heat always transferred down a gradient from hot to cold temps
what affects heat transfer
- air velocity
- air temperature
- water vapour presure
- thermal insulation of clothing
- vapor permeability of clothing
role of hypothalamus
- coordinating centre
- specialised neurons that sense and regulate temperature
- responds to feedback from central and peripheral thermoreceptors
- activates specific mechanisms to retain or dissipate heat
afferent feedback to hypothalamus
- temperature change detected at skin or central thermoreceptors
- signal transmitted through nerve to dorsal horn of spinal cord
- warm or cold sensitive sensory neurons are activated
- neurons transmit nerve impulse to lateral parabrachial nucleus in brainstem
- triggers signals to the preoptic area of the hypothalamus and then to median preoptic nucleus (dedicated to thermoregulation in mammals)
efferent control to the effector
- brown adipose tissue metabolism (cold stress)
- skin blood flow responses (cold or heat stress)
- sweating responses (heat stress)
- increase muscle activity/shivering thermogenesis (cold stress)
autonomic thermoeffector
1) autonomic thermoeffector activation is involuntary
2) autonomic thermoeffector capacity is finite
cold stress
- cold ambient temp affects skin, brain and visceral temp
- hypothalamic integration causes somatic and sympathetic responses from the nervous system
- somatic: shivering thermogenesis
- sympathetic BAT/beige thermogenesis and vasoconstriction
- increase core body temperature which affect skin, brain and visceral temp
vasoconstriction
- sympathetic response
- blood vessels distributed profusely beneath skin
- continuous venous plexus supplied by inflow of blood from skin capillaries
- in most exposed areas of body (ears, hand and feet), blood supplied to plexus through arteriovenous anastomoses
- rate of blood flow to skin can vary to barely above zero during cold stress
- control of the flow of blood from core to skin is an effective way to transfer heat (skin is a heat radiator system)
shivering thermogenesis
- somatic response
- generates some metabolic heat but is limited
- max rates of heat produced = 5x resting metabolic rate
- if core temp continues to fall, shivering will eventually cease
non shivering thermogenesis
- sympathetic response
- brown adipose tissue (BAT) activation
- BAT have very high levels of mitochondria
- aids temp regulation by breaking down glucose for energy and releasing heat
- adult humans have very little BAT, however in babies BAT thermogenesis likely to play a greater role in heat production
voluntary muscular activity
- somatic response
- greatest contribution in defending against cold extremes
- actually a behavioural response, not truly autonomic
heat stress
hot abient temp/exercise affects skin, brain and visceral temp. sends signals to the hypothalamus, hypothalamic integration sends sympathetic signals such as vasodialtion and sweating from the nervous system which lowers core body temperature, affecting skin, brain and visceral temp.
vasodilation
- sympathetic response
- blood vessels distributed profusely beneath skin
- continuous venous plexus supplied by inflow of blood from skin capillaries
- in most exposed areas of body (ears, hands, feet), blood supplied to plexus through arteriovenous anastomoses
- rate of blood flow to skin can reach upwards of 50% total cardiac output
- fully vasodilated vessels can reach eight-old increase in heat conductance compared to vasoconstrictred vessels
sweating
- sympathetic response
- most powerful heat loss effector
- 2-4 million sweat glands on the body surface (dependent of age, sex, body morphology)
- 1L vaporised water (sweat/respiration) transfers 580kcal to the environment
- important to replace fluids and electrolytes during heat stress
behavioural thermoeffector
- sustains human life
- activation is voluntary
- capacity is essentially unlimited
types of behaviours
simple and complex
hypothermia avoidance
- put a layer of clothing on
- seek shelter
hyperthermia avoidance
- seek shade
- take a break
- drink cold water
dictated by conscious perception
discriminative component
- thermal sensation
- object evaluation of skin temp (hot or cold)
hedonic component
- thermal comfort
- subject indifference to thermal environment
- thermal pleasantness
- perceived when a stimulus aims to restore thermal comfort
pathways of behavioural thermoregulation
peripheral nervous system
- temperature sensitive transient receptor ion channels
- dorsal root ganglion
spinal cord
- lamina 1
brain stem
- lateral parabrachial nucleus
hypothalamus
- preoptic area
- sympathetic nervous system
- sweating, metabolic rate (shivering/non shivering), skin blood flow
thalamus (from lamina 1)
- posterior ventromedial nucleus
cortex
- insula (thermal sensation)
- orbitfrontal, cingulate (thermal discomfort
- medial prefrontal area 10 (decision to behave)
- supplemental motor
- motor area 4 (thermal behaviour)
orderly recruitment of thermoeffector activation
skin blood flow 1st order
thermal behaviour 2nd order
sweating and shivering 3rd order
abnormalities of body temp regulation
heatstroke
- if unable to escape heat or reduce levels of activity, body temp continues to inc
- leads to greater demands on other physiological systems
- heatstroke = body temp inc upwards of 40-42*C
- various symptoms: dizziness, abdominal distress, vomiting, delirium, eventually loss of consciousness
- inflammatory response that can lead to critical organ failure
fever
- set point becomes higher than normal allowing body temp to reach new point
- all mechanisms of raising body temp stimulated especially vasoconstriction, shivering, non-shivering thermogenesis (if a baby)
physiological effects of heat stress
- increased core body temp
- peripheral vasodilation
- increased sweating response
can lead to…
- dehydration
- greater demands on the heart
- renal damage
- critical organ failure
