2. Cardiorespiratory Responses to Endurance Exercise Flashcards
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
What happens to arterioles as muscles begin exercising
the arterioles serving the muscle Dilate to provide more blood flow
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
What do active muscles in exercise release and what do they cause
CO2
Pi
H+
K+
Vasodilation of arterioles
Increased blood flow
What do Precapillary
sphincters in capillaries do
Regulate blood flow
Resting HR
60-80 bpm
influenced by exercise, heat, altitude
pre-exercise hr
above normal levels
anticipatory response
sympathetic ns releases norepinephrine
Sympathetic vs Parasympathetic
s - fight or flight
p - relaxation
Autonomic NS that increases HR rest - 100 bpm
Decreased parasympathetic input to the sinoatrial (SA) node
Autonomic system that increases HR 100 bpm - HR max
Increased sympathetic
input to the SA node
at exercise onset HR :
↑ in proportion to ↑ exercise
intensity
At Maximal exercise hr:
HR begins to plateau (even if
workload continues to increase)
Maximal heart rate (HRmax) is:
highest value achieved in all-out
effort to point of volitional fatigue
from age 10-15 years, hrmax
decreases 1ish beat per year
HRmax estimation calculation
Tanaka equation
Tanaka equation
HRmax = 208 – 0.7 x age (years)
Stroke Volume
Amount of blood ejected with each contraction.
what is SV a major determinant of
cardiorespiratory endurance capacity at near maximal/maximal
exercises intensities.
SV determined by four factors:
- Venous return
- Ventricular distensibility
- Force of contraction
- Resistance to flow
what do 1. Venous return 2. Ventricular distensibility influence and determine (SV)
Influence filling capacity of ventricle
Determine end-diastolic volume (preload)
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)
Increased Stroke Volume in Exercise causes increased:
myocardial contractility
venous return
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
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.
