Exercise Phys: Oxygen, Heat, & Fluids Flashcards
T/F At a given PO, oxygen uptake differs between trained and untrained individuals on a cycle ergometer
False; mechanical efficiency for cycling is about the same tf oxygen uptake is the same
What is the maximal oxygen uptake?
Point at which an increase in PO does not result in ay further increase in oxygen uptake
Oxygen uptake is dependent on
exercise intensity; slow increase to steady state, then no further increase beyond maximal O2 uptake
What is the cardiovascular response to exercise?
increase O2 supply to skeletal and cardiac muscle; facilitate CO2 and heat removal (generated in aerobic metabolism); maintain MAP
Fick equation
VO2 = Q x (CaO2 - CvO2) = whole body O2 uptake is equal to whole body CO times difference between arterial and venous concentrations of O2 (AvO2 difference)
Only ___% of O2 consumption is used in mechanical work; extra energy is ____________
20%; dissipated as heat
Which tissues increase metabolic rate during exercise?
Skeletal and cardiac muscle
Increase in CO is about _____ per L of O2 uptake increase
5-6L
What happens to muscle blood flow in exercise?
Increases; 90% of CO at max exercise
What happens to coronary circulation during exercise??
Increases
What is the purpose of vasoconstriction of vascular beds during exercise?
increase in muscle bloodflow occurs via peripheral vasodilation; CO increases to maintain MAP but because MAP = CO x TPR, TPR must also be increased to maintain MAP - this is achieved by vasoconstricting other vascular beds to oppose peripheral vasodilation to muscles
What happens to splanchnic blood flow during exercise?
decreases; vascular bed can be severely constricted and endanger the GIT
What happens to renal blood flow during exercise?
decreases; kidney is vasoconstricted tf reduced urine concentration; GFR is also reduced to decrease urine production and conserve water
What happens to skin blood flow during exercise?
increased early on (vasodilation) to dissipate heat; reduced approaching max CO/intensity (vasodilation) to maintain TPR - can no longer dissipate heat!!
T/F Muscle blood flow is a target of vasoconstriction in exercise
True; approaching max, muscles can become a target for vasoconstriction - muscle wins out over skin but brain wins out over muscle
Why do we get an increase in muscle blood flow during exercise?
Metabolic vasodilators from contracting skeletal muscle, endothelium (NO), and/or RBCs; muscle pump; conducted vasodilation; functional sympatholysis
What role does the endothelium play in vasodilation?
Initial increase in flow causes shear stress on the endothelium that stimulates NO release
What role do RBCs play in vasodilation?
as Hb becomes desaturated, red cells release ATP which binds to purinergic receptors on vascular smooth muscle causing vasodilation
What is conducted vasodilation?
local depolarisation releases ACh which depolarizes local vascular smooth muscle causing proximal spread via gap junctions leading to upstream dilation in resistance arterioles in larger vessels
What is functional sympatholysis?
Giving a vasoconstrictor stimulus to a muscle is much less effective if the muscle is contracting and much more effective if it is at rest - some dilators desensitize sympathetic nerve endings and receptors such that the sympathetic vasoconstrictor effect is blunted
What is the difference in CO between trained and untrained individuals during exercise?
CO increases similarly but trained individuals reach a much higher CO
What is the difference in A-VO2 difference between trained and untrained individuals during exercise?
Similar; even at max trained is only slightly higher
What is thought to be the reason for increased VO2 max in trained individuals vs untrained?
Increase in CO - trained can reach a higher CO
How is a higher CO attained in trained individuals?
lower HR and higher SV due to larger chamber size and expanded blood volume
Systolic blood pressure reflects
CO
Diastolic blood pressure reflects
TPR
What happens to DBP as you approach maximum intensity?
relatively stable, may fall slightly due to vasodilation
What happens to SBP as you approach maximum exercise intensity?
increases bc CO is increasing
What happens to MAP as you approach maximum exercise intensity?
increases slightly bc increase in SBP is greater than decrease in DBP and bc length of time in diastole is decreasing (due to increased HR)
Does MAP track more with SBP or DBP?
SBP
What is unique about MAP and HR in exercise?
only situation where MAP and HR both increase; normally baroreflex will decrease the HR but this is reset during exercise to a higher operating level
What happens to HR in prolonged exercise?
Increases
What happens to TPR in prolonged exercise?
increases to offset the big decrease in SV, meaning CO falls slightly
What happens to blood volume in prolonged exercise?
decreases due to sweating and volume loss but is reasonably protected; interstitial and intracellular volumes are challenged to a greater extent
What happens to MAP in prolonged exercise?
might fall slightly; if this drops when you stop exercising you get postural hypotension
What is meant by cardiovascular drift?
MAP and SV decrease while HR increases; HR increases due to reduction in SV and displacement of blood to the periphery - decrease in SV may also be due to shorter diastole w/increased HR tf shorter filling tf less blood is ejected
Cardiovascular drift (inc HR, decreased SV) is related to
hyperthermia, dehydration, increased plasma adrenaline, and somewhat to peripheral displacement of blood volume due to cutaneous vasodilation
What is the risk of exercising in water in cardiac failure?
Hydrostatic pressure opposes peripheral displacement of blood volume to the skin - this causes an increase in central blood volume and tf can volume overload the patient
How is circulation controlled neurally?
central command - HR and MAP increase in anticipation of exercise; feedback from peripheral sensors about muscle etc.; feed-forward command resets baroreceptor to a higher level to allow some increase in BP
How does the ANS affect HR in exercise?
Initial increase in HR is due to vagal (PSNS) withdrawal; then an increase in SNS activity
What are the mechanisms of increased CO following training?
expanded blood volume (= diluted haematocrit, hence EPO doping); Frank-Starling mechanism; increased heart size; increased LV mass and chamber size; increased adrenergic sensitivity (SA node may change intrinsic properties = lower HR)
What is considered to be the hallmark of training?
Decreased HR
What microvascular adaptations occur in response to exercise training?
increased capillary density and increased capillary recruitment
How is oxygen delivery enhanced in trained muscle?
increased capillary density and recruitment - even though AvO2 doesn’t change much from UT to T, the total mass of O2 delivered is enhanced bc of this
What are the respiratory responses to exercise?
maintain arterial O2 saturation; CO2 removal; acid-base balance compensating for metabolic acidosis; fluid and temperature balance (heat and fluid are lost in hyperventilation)
What happens to ventilation with increasing exercise intensity?
early exercise: VE tracks with increasing O2; ventilatory threshold 1 (VT1): VE increases slightly, starting to get metabolic acids; at higher intensities (VT2) further stimuli increase VE =relative hyperventilation
How do arterial paO2 and paCO2 change during incremental exercise?
Until VT2, arterial paO2 and paCO2 are constant at resting levels; once you start hyperventilating paO2 increases a little while paCO2 drops significantly due to hyperventilation = relative hyperventilation
At rest, mixed venous PvO2 is
~40mmHg
At rest, arterial PaO2 is
~100mmHg
Alveolar PAO2 is
~150mmHg
PiO2 is
~100mmHg
What happens to PvO2 with exercise?
drops because more O2 is extracted
How is ventilation controlled?
chemical inputs from central and peripheral chemoreceptors; stretch receptors in the lung; mechanoreceptors in muscle
What drives ventilation during exercise?
motor cortical activation (same as +HR); muscle afferents from spindles and type III & IV fibres; CO2 flux to the lung (mixed venous chemoreceptor?); increased K+, H+, lactate, catecholamines, and temperature; NOT O2
What happens to exercise ventilation with training?
ventilation is lower for a given PO; reduced lactate/H+, K+, plasma catecholamines, activation of muscle afferents, and central drive; can achieve same arterial saturation for relatively less VE input
What factors determine VO2 max potential?
training, genetics
Sedentary VO2max
30mL O2/kg body mass/minute
Normally active-conditioned VO2max
40-50mL O2/kg/min
Endurance VO2max
80mL O2/kg/min
What factors determine VO2 max in exercise?
primarily by O2 delivery (respiration, ventilation, ventilation-perfusion matching, diffusion); central circulation (Hb, BP, max CO); peripheral circulation (local BF, capillary density); metabolism in muscle (mitochondria)
VO2 max is primarily determined by
O2 delivery
T/F O2 consumption in the muscle is the major determinant of VO2 max
False; O2 delivery is the major determinant of VO2 max
What are the mechanisms of heat exchange during exercise?
conduction (major heat loss in water), convection, radiation, evaporation of sweat (major heat loss mechanism in air)
T/F Sweating causes heat loss
False; the evaporation of sweat causes heat to be lost - there MUST be a phase change - tf in humidity sweating is not an effective mechanism, lose fluid but not heat
What happens to heat loss in humid environments?
Fluid is lost to sweating but not heat because it cannot be evaporated
At lower temperatures, heat is primarily lost by
convection and conduction, some radiation
As temperature increases, heat is predominantly lost by
evaporation of sweat; less of a contribution from convection & conduction, and radiation
T/F Respiration contributes significantly to heat loss
False, relatively less significant than evaporation, convection, conduction, radiation
Heat is transferred from muscle via
overlying skin and via cardiovascular system (vasodilation)
What is the risk of heat to elderly people with cardiac problems?
In the heat, skin vascular beds vasodilate - tf a lot of CO is going to the skin, so CO is increased, but as activity increases the muscle demands more blood flow and you get vasoconstrction at the skin, making it harder to lose heat
How does the brain auto-regulate body temperature and power output?
The brain reduces power output in hotter temperatures to maintain body temperature
What is the benefit of pre-cooling?
Can lower the core body temperature so it takes longer to get to a temperature that is too hot to sustain exercise - maintain bloodflow to muscles for longer, longer duration before flow has to be diverted to the skin to lose heat
T/F Blood volume decreases in dehydration
False; blood volume is reasonably well protected but interstitial and intracellular dehydration occurs
What are the benefits of fluid ingestion relative to no fluids?
increased blood volume; decreased HR; increased SV and CO; lower core temperature; lower plasma sodium and osmolality; reduced muscle glycogen use; enhanced exercise performance
How is blood volume maintained or restored following exercise?
during exercise renal BF and GFR are reduced to retain fluid; in recovery, RAAS is activated which increases plasma aldosterone (salt retention), renin (Na and fluid), and ADH (fluid retention)
What is critical to restoring water balance?
Restoring Na balance
Sodium is the main cation of ECF or ICF?
ECF
What is the importance of diuretics in exercise?
Need to closely monitor fluid replacement if exercising while taking diuretics because fluid is being lost through sweat
