Circulatory Responses to Exercise
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100 Terms
What part of the brain contains the cardiovascular control center?
Medulla oblongata
Which nervous system regulates cardiovascular function?
Autonomic nervous system
Which division decreases heart rate?
Parasympathetic nervous system
What nerve provides parasympathetic input to the heart?
Vagus nerve (CN X)
Which cardiac structures are affected by the vagus nerve?
SA node and AV node
How does parasympathetic stimulation lower heart rate?
Hyperpolarizes SA and AV nodes
Which division increases heart rate and contractility?
Sympathetic nervous system
Where do sympathetic cardiac neurons originate?
T1-T5 spinal segments
What are cardiac accelerator nerves?
Sympathetic nerves that increase heart rate and force of contraction
What do vasomotor nerves cause?
Vasoconstriction
What do chromaffin cells release?
Norepinephrine and epinephrine
What is systole?
Contraction phase of the heart
What is diastole?
Relaxation phase of the heart
What is cardiac output?
Volume of blood ejected by the heart each minute
Units of cardiac output?
L/min
Equation for cardiac output?
Q = HR × SV
What is heart rate (HR)?
Number of heart beats per minute
What is stroke volume (SV)?
Amount of blood ejected per beat
If HR = 75 bpm and SV = 70 mL/beat, what is Q?
5.25 L/min
Why is cardiac output smaller in females?
Smaller heart size and stroke volume
At rest, how does cardiac output compare in trained vs untrained people?
Similar
Why is resting cardiac output similar in trained and untrained people?
Lower HR but higher SV in trained individuals
Who has the higher maximal cardiac output?
Trained individuals
How is stroke volume calculated?
SV = EDV − ESV
What is EDV?
End-diastolic volume
What is ESV?
End-systolic volume
What are the three regulators of stroke volume?
Preload, afterload, contractility
What is preload?
End-diastolic volume
What happens to SV when preload increases?
SV increases
What law explains preload effects?
Frank-Starling Law of the Heart
Why does increased EDV increase SV?
Greater ventricular stretch optimizes sarcomere length
What is venous return?
Blood returning to the heart
What influences venous return?
Venoconstriction, muscle pump, respiratory pump
What is afterload?
Pressure in the aorta that must be overcome before ejection
What happens to SV when afterload increases?
SV decreases
What happens to afterload during exercise?
It decreases
Why does afterload decrease during exercise?
Reduced total peripheral resistance
What is contractility?
Strength of contraction at a given preload
What increases contractility?
Norepinephrine and epinephrine
How do catecholamines increase contractility?
Increase intracellular calcium
Define blood pressure.
Hydrostatic pressure exerted by blood on vessel walls
What is systolic blood pressure?
Pressure during ventricular contraction
What is diastolic blood pressure?
Pressure during ventricular relaxation
What is MAP?
Mean arterial pressure
What is considered normal blood pressure?
Less than 120/80 mmHg
What is elevated blood pressure?
120-129 and less than 80 mmHg
What is Stage 1 hypertension?
130-139 or 80-89 mmHg
Before 2017, what was the hypertension threshold?
140/90 mmHg
Blood flow is directly proportional to what?
Pressure difference
Blood flows from what pressure to what pressure?
High pressure to low pressure
Blood flow is inversely proportional to what?
Resistance
What determines resistance?
Blood viscosity, vessel length, vessel radius
Which resistance factor has the greatest effect?
Vessel radius to the fourth power
Why must oxygen delivery increase during exercise?
Muscles need oxygen to produce ATP
How is oxygen delivery increased during exercise?
Increased cardiac output and blood flow redistribution
What is the first mechanism that increases HR during exercise?
Parasympathetic withdrawal
Parasympathetic withdrawal raises HR to approximately what value?
100 bpm
What raises HR above 100 bpm?
Sympathetic stimulation
Traditional maximum heart rate equation?
220 − age
Alternative maximum heart rate equation?
208 − 0.7 × age
Why does maximum heart rate decrease with age?
Reduced intrinsic firing rate and beta-adrenergic responsiveness
How does preload increase during exercise?
Muscle pump and respiratory pump increase venous return
How does afterload decrease during exercise?
Vasodilation decreases peripheral resistance
Why does contractility increase during exercise?
Increased sympathetic stimulation and catecholamines
How is blood redistributed during exercise?
By altering peripheral vascular resistance
What does sympathetic stimulation do to blood vessels?
Causes vasoconstriction
Which tissues receive less blood flow during exercise?
Inactive tissues
What causes vasodilation in active muscle?
Local metabolic factors
What is functional sympatholysis?
Local vasodilation overriding sympathetic vasoconstriction
What is the Fick equation?
VO2 = Q × a-vO2 difference
What is a-vO2 difference?
Amount of oxygen removed from blood by tissues
What does central command theory state?
Initial cardiovascular responses originate from higher brain centers
What fine-tunes central command responses?
Afferent feedback
Which receptors help fine-tune cardiovascular responses?
Chemoreceptors, mechanoreceptors, baroreceptors
What happens immediately at exercise onset?
HR, SV, and Q rapidly increase
When is steady state reached during submaximal exercise?
Within 2-3 minutes
What is cardiovascular drift?
HR rises while SV falls during prolonged exercise
Why does SV decrease during prolonged exercise?
Loss of plasma volume decreases venous return
What happens to cardiac output during incremental exercise?
It increases continuously
What happens to HR during incremental exercise?
It increases to maximum
What happens to SV during incremental exercise?
Increases then plateaus around 40-60% VO2max
What is HIIT?
High-intensity intervals separated by recovery periods
How does HR respond during HIIT?
Rises during work and falls during recovery
What is another name for resistance training?
Strength exercise
What happens to HR during strength exercise?
Modest increase
What happens to SV during strength exercise?
Unchanged or slightly decreased
What happens to Q during strength exercise?
Small increase
What happens to preload during strength exercise?
Decreases
What happens to afterload during strength exercise?
Increases
What happens to SBP during aerobic exercise?
Increases
What happens to DBP during aerobic exercise?
Remains unchanged or slightly decreases
Why does DBP remain stable during aerobic exercise?
Reduced peripheral resistance
What happens to MAP during aerobic exercise?
Increases
Which produces a higher blood pressure response, aerobic or strength exercise?
Strength exercise
Why is blood pressure higher during strength exercise?
Both SBP and DBP increase
What maneuver should be avoided during lifting?
Valsalva maneuver
What is another name for double product?
Rate pressure product
Equation for double product?
DP = SBP × HR
What does double product estimate?
Myocardial oxygen demand
Why is double product clinically useful?
Helps prescribe exercise below symptom threshold