2. Cardiorespiratory Responses to Endurance Exercise Flashcards by Lucy Holmes

What are the Cardiovascular Responses in Exercise (3 points)

Increased muscle metabolism
Increased fuel and oxygen delivery is required
Cardiovascular system responds immediately to increase blood supply

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What happens to arterioles as muscles begin exercising

the arterioles serving the muscle Dilate to provide more blood flow

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What are arterioles (2 points)

Smooth muscle in wall can contract to constrict (narrow) the vessel or relax to dilate (widen) the vessel
Act to control blood flow

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What do active muscles in exercise release and what do they cause

CO2
Pi
H+
K+
Vasodilation of arterioles
Increased blood flow

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What do Precapillary
sphincters in capillaries do

Regulate blood flow

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Resting HR

60-80 bpm
influenced by exercise, heat, altitude

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pre-exercise hr

above normal levels
anticipatory response
sympathetic ns releases norepinephrine

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Sympathetic vs Parasympathetic

s - fight or flight
p - relaxation

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Autonomic NS that increases HR rest - 100 bpm

Decreased parasympathetic input to the sinoatrial (SA) node

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Autonomic system that increases HR 100 bpm - HR max

Increased sympathetic
input to the SA node

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at exercise onset HR :

↑ in proportion to ↑ exercise
intensity

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At Maximal exercise hr:

HR begins to plateau (even if
workload continues to increase)

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Maximal heart rate (HRmax) is:

highest value achieved in all-out
effort to point of volitional fatigue

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from age 10-15 years, hrmax

decreases 1ish beat per year

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HRmax estimation calculation

Tanaka equation

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Tanaka equation

HRmax = 208 – 0.7 x age (years)

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Stroke Volume

Amount of blood ejected with each contraction.

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what is SV a major determinant of

cardiorespiratory endurance capacity at near maximal/maximal
exercises intensities.

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SV determined by four factors:

Venous return
Ventricular distensibility
Force of contraction
Resistance to flow

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what do 1. Venous return 2. Ventricular distensibility influence and determine (SV)

Influence filling capacity of ventricle
Determine end-diastolic volume (preload)

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what do 3. Force of contraction
4. Resistance to flow influence and determine (SV)

Influence ventricle’s ability to empty
during systole (contraction)
Determine force which ejects blood & pressure which is expelled into arteries (aortic mean pressure; afterload)

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Increased Stroke Volume in Exercise causes increased:

myocardial contractility
venous return

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Increased myocardial contractility is:

Increased force of contraction due to sympathetic stimulation of ventricular muscle cells

Increased venous return is:

Increased force of contraction via Frank Starling mechanism

Frank-Starling’s Law of the heart

The more the heart muscle is stretched (filled) before contraction (preload), the more forcefully the heart will contract.

Stimulation of the sympathetic nervous system during exercise causes:

↑ venous return, stretches the heart muscle, and ↑ cardiac output

Increased venous return is due to (3):

– Respiratory pump – Skeletal muscle pump – Venoconstriction

During inspiration (respiratory pump) (pressure effect cavities)

– <-- press in thoracic cavity – --> press in abdominal cavity – Press abdominal > thoracic – Helps to squeeze blood from lower body back to heart – Greater respiratory movements (rate+depth) in exercise --> venous return

Skeletal Muscle Pump

* Muscle contraction propels blood forward through open distal valves and obstructs flow into muscle as proximal valves close during contraction. * During muscle relaxation, proximal valves open and blood fills venous segment * The net effect: cycle of compression and relaxation propels blood to heart.

Venoconstriction involves:

Involves reflex signals that cause veins to constrict.

What autonomic system sends reflex signals

the sympathetic nervous system during exercise

what do reflex signals cause

Decrease vol of blood that venous system can contain, (facilitates venous return) (causes veins to restrict)

Exercise onset effect on SV

Increases with exercise intensity up to ~40 to 60% VO2max Plateaus and remains unchanged until exhaustion.

elite athletes SV vs exercise onset

SV can continue to ↑, sometimes to maximal intensity.

Acute Cardiovascular Responses

Increase in : Blood flow HR Stroke Volume (SV) Cardiac Output (CO)

Measurements to assess cardiac output:

▪ Direct Fick ▪ Indicator dilution ▪ CO2 rebreathing

Oxygen uptake =

Oxygen uptake = cardiac output (Q) x arterio-venous oxygen difference

What equation could you use to determine cardiac output?

The Fick Equation

what is Oxygen consumption of a tissue dependent on

Blood flow to tissue and amount of 02 extracted from blood by tissue.

Product of blood flow and difference in O2 concentration in the blood between arterial blood supplying the tissue and venous blood draining out of the tissue.

Oxygen consumption (VO2) Called (a-v)O2 difference

Method that: Expresses relationships between VO2 (mL/min) , and a- vO2diff (mL/100mL blood) to determine cardiac output (mL/min)

Direct Fick Method

Cardiac output = VO2 ÷ a-vO2diff VO2 = HR x SV x (a-v)O2

what does Direct Fick require

Requires complex invasive methodology * VO2 (L/min) using open circuit spirometry * average difference between O2 content of arterial and mixed-venous blood (a-vO2diff)

pulmonary artery oxygen content

low oxygen content

pulmonary vein oxygen content

high oxygen content

Cardiac Output (Q)

Q = HR x SV

exercise effect on CO

↑ with ↑ exercise intensity.

resting CO

Q ~5.0 L/min

Ventilatory Response to Exercise equation

Ventilation (VE) = tidal volume (VT) x breathing frequency (Bf)

Pulmonary ventilation during dynamic exercise

Start of exercise accompanied by immediate increase in ventilation. Increase may occur before onset of muscle contractions (anticipatory response)

Pulmonary ventilation during dynamic exercise

2nd phase of respiratory increase more gradual (for heavy exercise). Controlled primarily by changes in chemical status of arterial blood. *↑ in pulmonary ventilation during exercise directly proportionate to metabolic needs of exercising muscle. * At higher intensities, rate of respiration also increases. * At low intensities, accomplished via ↑ in tidal volume (amount of air moved in & out of lungs).

Most commonly used measure of respiratory function with exercise

VO2 (volume of oxygen uptake)

Increase in Ventilation in Relation to Exercise Intensity

VE increases linearly with work rate up to lactate threshold * VE increases more rapidly after the lactate threshold

v02max

the amount of oxygen taken up and used by the body

why does VO2 increase linearly with increases in exercise intensity.

due to an increasing reliance on oxygen to help provide energy as exercise continues.