Handout #2 & 3 - CV Adjustments to Exercise

Question 1

What are the three general CV responses to exercise and their values at rest vs. max exercise?

Answer 1

1. Increase CO
   – Rest = 5L/min
   
   • Max = 20L/min
2. Redistribute CO
   – Rest = 25% to muscles
   
   • Max = 85% to muscles
3. Increase Venous Return
   – Rest = 5L/min
   
   • Max = 20L/min

Question 2

_____ and ______ have to be matched precisely to continue exercise.

Answer 2

Cardiac output; venous return

Question 3

List three ways the ANS increases cardiac output?

Answer 3

1. Decrease PNA to SA node (release brake)
2. Increase SNA to SA node (foot on pedal)
3. Increase SNA to LV, which increases SV

Question 4

How does the ANS redistribute cardiac output?

Answer 4

Increases SNA to non contracting tissues to cause arterioles to restrict blood flood to those areas

Question 5

How does the ANS increase venous return?

Answer 5

Increase SNA to veins - venoconstriction to push blood back to heart

Question 6

Fick equation

Answer 6

VO2 = CO x a-VO2diff

FYI: CO = SV x HR

Question 7

VO2 is defined as…

Answer 7

The rate of which you are delivering and utilizing O2

Question 8

VO2 max is defined as…

Answer 8

Max capacity to consume O2 and produce ATP

Question 9

Average VO2max values for active college males/females are…

Answer 9

1. Males - 45 ml/kg/min
2. Females - 38 ml/kg/min

Question 10

How is VO2 expressed in non weight bearing exercise vs weight bearing exercise?

Answer 10

1. Non weight bearing - L/min
2. Weight bearing - ml/kg/min

Question 11

What causes the initial HR increase and further increase of HR?

Answer 11

1. Initial - vagal withdrawal increases HR to ~100bpm
2. Further increases in HR - Increases in SNA

Question 12

List two ways SV increases with exercise intensity?

Answer 12

1. Increased preload due to increased venous return
2. Increased LV contractility due to SNA

Question 13

______ doesn’t help increase SV.

Answer 13

Afterload

(Pressure LV must overcome to eject blood)

Question 14

Preload is the initial ______ of _____ ventricle prior to contraction.

Answer 14

stretch; left

Question 15

As SV increases preload ______, which increases _______ formation and ____ sensitivity.

Answer 15

Increases; cross bridge; calcium

Question 16

Contractility is the ____ of contraction at a given _____.

Answer 16

Contraction; preload

Question 17

How does the SNS increase contractility?

Answer 17

1. Increased SNA to myocytes increases contractility due to increased intracellular Ca++
2. Ca++ also comes from extracellular sources and SR

Question 18

a-vO2 represents…

Answer 18

The amount of oxygen extraction

Arterial O2 content > muscles extract O2 > venous O2 content

Question 19

a-vO2 difference increases due to…

Answer 19

1. Increased muscle fiber recruitment
2. Increased O2 extraction by tissues

Question 20

What is the mean arterial pressure and right atrial pressure at rest and during exercise?

Answer 20

1. Mean Arterial Pressure (blood flow to tissues)
   – Rest = 90 mmHG
   
   • Max = 120-150 mmHg
2. Right Atrial Pressure (blood flow heart)
   – Rest = 0 mmHG
   
   • Max = 0 mmHg

Question 21

Why does the right arterial pressure remain at 0 mmHg at rest and exercise?

Answer 21

To increase the pressure gradient from aorta to RA favors blood flow back to the heart.

Question 22

Venous return increases during exercise from what four mechanisms?

Answer 22

1. Increased pressure gradient from aorta to RA
2. Venoconstriction via SNS
3. Muscle pump - muscle contraction squeeze veins to push blood back to heart
4. Respiratory pump

Question 23

SVR stands for…

Answer 23

Systemic vascular resistance

Question 24

What happens to SVR during exercise?

Answer 24

Decreases due to dilation of arterioles in active muscles.

Question 25

Will arterioles continue to dilate during exercise?

Answer 25

No, at some point, usually during high intensity exercise, SNA will eventually oppose dilation to protect BP

Question 26

What are the three mechanisms that regulate SVR during exercise?

Answer 26

1. Decrease concentration of constrictors (O2, endothelium) 2. Skeletal muscles produce dilators (CO2, K+, H+) 3. EC produce dilators (NO, PGI2, EDHF)

Question 27

MSNA stands for...

Answer 27

Muscle sympathetic nerve activity

Question 28

What happens to MSNA during exercise?

Answer 28

Increases. NE levels increases as well.

Question 29

If increases in MSNA and NE that cause constriction, how can BF increase?

Answer 29

Functional Sympatholysis (FS), a local control mechanism

Question 30

What are the three mechanisms of Functional Sympatholysis (FS) that promote arteriole dilation?

Answer 30

1. Pre-Synaptic inhibition – Dilators (NO is most important) act on SN reducing NE release 2. Post-synaptic inhibition – Dilators make a receptors less responsive to NE 3. Vasodilators act on vascular smooth muscle to cause relaxation of muscles.

Question 31

Vasodilators are produced by...

Answer 31

Endothelial cells and skeletal muscle cells

Question 32

Endothelial cells produce what dilators?

Answer 32

Nitric oxide (NO) - most important EDHF

Question 33

Skeletal muscle cells produce what dilators?

Answer 33

K+, H+, increased CO2, adenosine

Question 34

What is the significance of FS?

Answer 34

FS allows muscle BF to increase during exercise despite increases MSNA.

Question 35

Describe the dog study that proves evidence for FS.

Answer 35

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.

Question 36

Describe the human study that proves evidence for FS.

Answer 36

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.