Chapter 9: Circulatory Responses to Exercise Flashcards
purposes of the cardiorespiratory system
1) transport O2 and nutrients to tissues
2) removal of CO2 and wastes from tissues
3) regulation of body temperature
two major changes to blood flow during exercise
1) increased cardiac output
2) redistribution of blood flow from inactive organs to active muscle
describe the pulmonary circuit, which side of the heart is it?
right side of the heart, pumps deoxygenated blood to the lungs via pulmonary arteries and returns oxygenated blood to the left side of the heart via pulmonary veins
describe the systemic circuit, which side of the heart is it?
left side of the heart, pumps oxygenated blood to the whole body via arteries and returns deoxygenated blood to the right side of the heart via veins
what is the liquid portion of blood? what does it contain?
plasma; contains ions, proteins, hormones
3 cells found in blood and their functions
1) red blood cells- contain hemoglobin to carry O2
2) white blood cells- prevent infection
3) platelets- important in blood clotting
define hematocrit
percentage of blood composed of packed RBCs
how do we define blood flow? what is it directly and inversely proportional to?
directly proportional to the pressure difference between the two ends of the system and inversely proportional to resistance (blood flow = change in pressure/ resistance)
what is pressure proportional to?
the difference between MAP and right atrial pressure (change in pressure)
describe diastole, when are atrioventricular valves open?
pressure in ventricles is low, filling with blood from atria, AV valves open when ventricular P < atrial P
describe systole, when are semilunar valves open?
pressure in ventricles rises, blood ejected in pulmonary and systemic circulation, semilunar valves open when ventricular P > aortic P
at rest, how do diastole and systole compare?
diastole is longer than systole
during exercise, how do diastole and systole compare?
systole is longer than diastole, but both are shorter
define cardiac output
amount of blood pumped by the heart each minute (Q = HR x SV)
what does cardiac output depend on?
training state and sex
what inputs regulate heart rate?
sympathetic and parasympathetic input
what inputs regulate stroke volume?
sympathetic nervous system
how does the parasympathetic nervous system regulate HR?
postganglionic nerve (vagus nerve) releases acetylcholine onto mAch (muscarinic cholinergic) receptors on autorhythmic cells of the SA and AV node —> hyperpolarization of the cell —> inhibits SA and AV node —> slows HR
how does the sympathetic nervous system regulate heart rate?
postganglionic nerves (cardiac accelerator nerves) release norepinephrine (catecholamines) onto B1-ADR receptors of autorhythmic cells on the SA and AV node —> depolarizes cell —> stimulate AV and SA node —> increases HR
what is the increase in heart rate at the onset of exercise due to? up to what HR?
parasympathetic withdrawal, up to 100 bpm
what is the increase in HR due to later on (after onset)?
sympathetic input
what does a wide variation in resting HRV indicate?
good index of “healthy” balance between SNS and PNS
what does a low variation in resting HRV indicate?
imbalance in autonomic regulation —> excellent predictor of cardiovascular dysfunction
why is high heart variability good?
indicates both sympathetic and parasympathetic are active; low variability shows a take over of sympathetic
3 factors influencing stroke volume
1) end diastolic volume
2) average aortic blood pressure
3) strength of ventricular contractility
what is EDV? how does it affect SV?
EDV is the volume of blood in the ventricles at the end of diastole, increased EDV increases SV
describe the Frank-Starling mechanism , what is it dependent on?
greater EDV results in a more forceful contraction due to stretch of ventricles and it is dependent on venous return
3 factors increasing venous return
1) venoconstriction
2) skeletal muscle pump
3) respiratory pump
how is venoconstriction accomplished?
via SNS input
how does the skeletal muscle pump increase venous return?
rhythmic skeletal muscle contractions force blood in the extremities toward the heart (one way valves in veins prevent back flow)
how does the respiratory pump increase venous return?
changes in thoracic pressure (in the diaphragm) pull blood toward the heart
besides venous return, what else might affect EDV?
filling time
what is filling time affected by? how does lying supine affect filling time?
increased heart rate decreases filling time therefore decreasing EDV; lying supine rather than standing allows for more filling which increases EDV
what is afterload? how does it affect SV?
pressure the ventricles must pump against to eject blood during contraction; increased afterload decreases SV
how does ventricular contractility (ionotropy) increase SV?
catecholamines bind B1-ADR on contractile cells of the heart —> depolarizes cell —> more forceful contraction —> decreased ESV —> increased SV
what is increased SV during exercise due to?
increased EDV (preload) and increased ventricular contractility
how does oxygen command during exercise compare to at rest?
15-25x greater
what two factors increase oxygen delivery during exercise
1) increased cardiac output
2) redistribution of blood flow
what is increased cardiac output due to at intensities up to 40-60% VO2 max?
increased heart rate and increased stroke volume
what is increased cardiac output due to at intensities greater than 40-60% of VO2 max?
increased heart rate
how does stroke volume change during exercise in untrained subjects?
increases linearly until high heart rates cause decreased filling time (decreased EDV and SV) and stroke volume plateaus
how do changes in stroke volume during upright and supine exercises differ?
during supine exercise, peak stroke volume is higher and still plateaus with higher intensities because of higher heart rates
how does % cardiac output to working skeletal muscles change from rest to exercise?
15-20% of cardiac output to skeletal muscle at rest, and 80-85% of cardiac output to skeletal muscle during maximal exercise
which organs get decreased blood flow during exercise?
liver, kidneys, GI tract
what does redistribution of blood flow depend on? what kind of factors mediate blood flow?
metabolic rate; local factors mediate blood flow (autoregulation)
what local factors increase blood flow? via what mechanism?
local metabolites (e.g. nitric oxide, prostaglandins, ATP, adenosine, and endothelium-derived hyperpolarization) promotes vasodilation to increase blood flow to the working muscles
how does arteriovenous oxygen difference increase during exercise?
increases due to higher O2 uptake in tissues for oxidative ATP production, not higher O2 content in arteries
how do emotionally charged environments affect HR and BP? via what mechanism?
elevate HR and BP due to increases in SNS activity
can emotional influence increase peak HR or BP during exercise?
no, just increases pre-exercise HR and BP
what does the rest to exercise transition look like for HR, SV, and CO?
rapidly increase until there is a plateau (during submaximal exercise that is below lactate threshold)
during graded exercise, how do heart rate and cardiac output change?
increases linearly with increasing work rate and reaches a plateau at 100% VO2 max
how does blood pressure change during graded exercise?
mean arterial pressure increases linearly (systolic increases and diastolic remains fairly constant)
at the same oxygen uptake, what does arm work result in compared to leg work?
higher blood pressure due to vasoconstriction of large inactive muscle mass and higher heart rate due to sympathetic stimulation
3 factors that recovery of heart rate and blood pressure depend on
1) fitness level
2) temperature and humidity
3) duration and intensity of exercise
during prolonged exercise, how does cardiac output, heart rate and stroke volume change?
cardiac output is maintained:
1) gradual decrease in stroke volume due to dehydration and reduced plasma volume
2) gradual increase in heart rate (cardiovascular drift- particularly in heat)
how can you prevent cardiovascular drift during prolonged exercise?
lower intensity, drink water, cooler environments
what does the decrease in HR, SV, and CO toward resting depend on?
1) duration and intensity of exercise
2) training state of subject
