Exercise and shock

Question 1

1. What is the definition of Shock?

Answer 1

Inadequacy of blood flow which results in inadequate delivery of oxygen and nutrients throughout the body to the extent that the tissues are damaged

Question 2

2. What are the compensatory mechanisms that are active in hemorrhagic shock?

Answer 2

• Baroreceptor Reflexes
• Chemoreceptor Reflexes
• Cerebral Ischemic Response
• Reabsorption of Tissue Fluids
• Endogenous Vasoconstrictor Substances
• Renal Salt and Water Conservation

Question 3

3. In shock where is vasoconstriction most prominent?

Answer 3

• Cutaneous vascular bed
• Skeletal muscle vascular bed
• Splanchnic vascular bed

Question 4

4. Blood flow is preferentially redistributed to which body organs in shock states?

Answer 4

Blood flow through the heart and brain is maintained essentially at normal levels as long as the arterial pressure does not fall below about 70 mm Hg.

Question 5

5. Approximately how much fluid can be reabsorbed at the capillary level to help maintain blood volume?

Answer 5

1 L of fluid/hour

Question 6

6. What are the decompensatory mechanisms that occur in progressive shock?

Answer 6

• Cardiac depression
• vasomotor failure
• acidosis
• blood clotting abnormalities
• reticulo-endothelial system
• CNS depression
• Cellular deterioration
• reduced organ perfusion from stimulation of inflammatory process, clotting

Question 7

7. What are the positive feedback decompensatory mechanisms that are triggered by severe hypotension?

Answer 7

The shock itself leads to more shock! That is, the inadequate blood flow causes the body tissues to begin deteriorating, including the heart and circulatory system. This deterioration causes an even greater decrease in cardiac output, and a vicious cycle ensues, with progressively increasing circulatory shock, less adequate tissue perfusion, more shock, and so forth until death. It is with this late stage of circulatory shock that we are especially concerned, because appropriate physiological treatment can often reverse the rapid slide to death.

Question 8

8. What occurs at the cellular level that leads to irreversible shock?

Answer 8

Depletion of cellular high-energy phosphate reserves

Question 9

1. How much can muscle blood flow be increased during extreme exercise in the well-trained athlete?

Answer 9

50 -80 ml/min/100 g of muscle (or 6-7 times)

blood flow increases to 15-20% above resting

Question 10

2. How does muscle contraction augment venous return?

Answer 10

Contracting muscles help pump blood though the system along with one way valves in veins

Question 11

3. What happens to blood flow in muscle tissues during exercise?

Answer 11

• Blood flow may increase 15-20 times above resting level
• Decreased oxygen in muscle greatly enhances flow

(intermittent blood flow during muscle contraction)

Question 12

4. How does capillary recruitment help delivery oxygen to muscle tissues during exercise?

Answer 12

• During rest, some muscle capillaries have little or no flowing blood. During strenuous exercise, all the capillaries open. This opening of dormant capillaries diminishes the distance that oxygen and other nutrients must diffuse from the capillaries to the contracting muscle fibers

• Increase surface area for diffusion
• Shorten the distance for diffusion

Question 13

5. What factors facilitate oxygen unloading from hemoglobin to the tissues during exercise?

Answer 13

• Contracting muscle avidly extracts oxygen from the blood
• A rightward shift reduces affinity of O2 to HGB
• Reduced pH
• Lactic acid
• Increased pCO2

Question 14

6. What factors enhance blood flow at the tissue level?

Answer 14

Dilation of the resistance vessels d/t reduced oxygen tension in the tissues and release of vasodilators (adenosine, lactic acid, potassium), all which increase BF

Question 15

7. What are the beta-2 effects of epinephrine on skeletal muscle?

Answer 15

Vasodilating effects

accept more blood and offload more oxygen

Question 16

8. Does cardiac output increase or decrease during exercise?

Answer 16

Increase, correlated with increased HR

Question 17

9. How is the change in cardiac output correlated to heart rate changes during exercise?

Answer 17

• CO increased in proportion to degree of exercise

* Increase CO with exercise correlates with an increase in HR

Question 18

10. Does mean arterial pressure increase or decrease during exercise?

Answer 18

• Rises tremendously at the onset of heavy exercise
• Sympathetic stimulation that contracts the veins and other capacitative parts of the circulation
• Tensing of the abdominal and other skeletal muscles of the body compresses many of the internal vessels

Question 19

11. What effect does the change in mean arterial pressure have on muscle blood flow? Why?

Answer 19

MAP rises even though there is a reduction in SVR in the body musculature

Vasoconstriction in inactive tissues is important for maintaining normal or increased BP during exercise. This provided a higher perfusion pressure which results in greater blood flow through active tissues

Question 20

12. What effect does the sympathetic nervous system have in the kidneys, splanchnic beds, and inactive muscle during heavy exercise?

Answer 20

diverts blood away from these areas

Question 21

13. What factors enhance venous return during exercise?

Answer 21

• Sympathetically-mediated constriction of the capacitance vessels
• Decreased systemic vascular resistance in the muscles
• Contracting muscles help pump blood in the veins back to the heart
• Deeper, more frequent respirations decrease intra-thoracic pressure and enhance flow of venous blood to the heart