Handout #2 & 3 - CV Adjustments to Exercise Flashcards
What are the three general CV responses to exercise and their values at rest vs. max exercise?
- Increase CO
– Rest = 5L/min- Max = 20L/min
- Redistribute CO
– Rest = 25% to muscles- Max = 85% to muscles
- Increase Venous Return
– Rest = 5L/min- Max = 20L/min
_____ and ______ have to be matched precisely to continue exercise.
Cardiac output; venous return
List three ways the ANS increases cardiac output?
- Decrease PNA to SA node (release brake)
- Increase SNA to SA node (foot on pedal)
- Increase SNA to LV, which increases SV
How does the ANS redistribute cardiac output?
Increases SNA to non contracting tissues to cause arterioles to restrict blood flood to those areas
How does the ANS increase venous return?
Increase SNA to veins - venoconstriction to push blood back to heart
Fick equation
VO2 = CO x a-VO2diff
FYI: CO = SV x HR
VO2 is defined as…
The rate of which you are delivering and utilizing O2
VO2 max is defined as…
Max capacity to consume O2 and produce ATP
Average VO2max values for active college males/females are…
- Males - 45 ml/kg/min
- Females - 38 ml/kg/min
How is VO2 expressed in non weight bearing exercise vs weight bearing exercise?
- Non weight bearing - L/min
- Weight bearing - ml/kg/min
What causes the initial HR increase and further increase of HR?
- Initial - vagal withdrawal increases HR to ~100bpm
- Further increases in HR - Increases in SNA
List two ways SV increases with exercise intensity?
- Increased preload due to increased venous return
- Increased LV contractility due to SNA
______ doesn’t help increase SV.
Afterload
(Pressure LV must overcome to eject blood)
Preload is the initial ______ of _____ ventricle prior to contraction.
stretch; left
As SV increases preload ______, which increases _______ formation and ____ sensitivity.
Increases; cross bridge; calcium
Contractility is the ____ of contraction at a given _____.
Contraction; preload
How does the SNS increase contractility?
- Increased SNA to myocytes increases contractility due to increased intracellular Ca++
- Ca++ also comes from extracellular sources and SR
a-vO2 represents…
The amount of oxygen extraction
Arterial O2 content > muscles extract O2 > venous O2 content
a-vO2 difference increases due to…
- Increased muscle fiber recruitment
- Increased O2 extraction by tissues
What is the mean arterial pressure and right atrial pressure at rest and during exercise?
- Mean Arterial Pressure (blood flow to tissues)
– Rest = 90 mmHG- Max = 120-150 mmHg
- Right Atrial Pressure (blood flow heart)
– Rest = 0 mmHG- Max = 0 mmHg
Why does the right arterial pressure remain at 0 mmHg at rest and exercise?
To increase the pressure gradient from aorta to RA favors blood flow back to the heart.
Venous return increases during exercise from what four mechanisms?
- Increased pressure gradient from aorta to RA
- Venoconstriction via SNS
- Muscle pump - muscle contraction squeeze veins to push blood back to heart
- Respiratory pump
SVR stands for…
Systemic vascular resistance
What happens to SVR during exercise?
Decreases due to dilation of arterioles in active muscles.
Will arterioles continue to dilate during exercise?
No, at some point, usually during high intensity exercise, SNA will eventually oppose dilation to protect BP
What are the three mechanisms that regulate SVR during exercise?
- Decrease concentration of constrictors (O2, endothelium)
- Skeletal muscles produce dilators (CO2, K+, H+)
- EC produce dilators (NO, PGI2, EDHF)
MSNA stands for…
Muscle sympathetic nerve activity
What happens to MSNA during exercise?
Increases.
NE levels increases as well.
If increases in MSNA and NE that cause constriction, how can BF increase?
Functional Sympatholysis (FS), a local control mechanism
What are the three mechanisms of Functional Sympatholysis (FS) that promote arteriole dilation?
- Pre-Synaptic inhibition
– Dilators (NO is most important) act on SN reducing NE release - Post-synaptic inhibition
– Dilators make a receptors less
responsive to NE - Vasodilators act on vascular smooth muscle to cause relaxation of muscles.
Vasodilators are produced by…
Endothelial cells and skeletal muscle cells
Endothelial cells produce what dilators?
Nitric oxide (NO) - most important
EDHF
Skeletal muscle cells produce what dilators?
K+, H+, increased CO2, adenosine
What is the significance of FS?
FS allows muscle BF to increase during exercise despite increases MSNA.
Describe the dog study that proves evidence for FS.
Researchers wanted to know if the adrenergic receptors become less responsive, so they infused drugs into dogs that caused arteriole constriction.
At rest, blood flow was reduced by 80%, which proved the adregenic stimulation caused constriction. As exercise intensity increased, blood flow reduction decreased, which proved SNS mediated constriction was blunted.
Describe the human study that proves evidence for FS.
Researchers wanted to know if the constrictor response would be blunted and to what level during various exercise intensities.
They gave subjects three different doses of a drug (low, med, high) that stimulated the release of NE and compared their percent change in blood flow at rest, moderate and high exercise intensities. At rest, blood flow was reduced, which proved the drug caused constriction. Regardless of the dosage, the blood flow increased, which proved the constrictor response was blunted during exercise. They also found that the higher the intensity, the more the constrictor response was overriden.
