Exercise physiology

Question 1

Describe the Fick equation and how its components relate to the circulatory responses to dynamic exercise.

Answer 1

VO2 = Cardiac Output x CaO2 – CMVO2 VO2 = Cardiac output x a-v O2
Cardiac Output – Blood Flow (L/min)
CaO2 = [Hgb] x 1.36 x O2 saturation (%)
CMVO2 = [Hgb] x 1.36 x venous O2 saturation (%)
VO2 = Cardiac Output x CaO2 – CMVO2 VO2 = Cardiac output x a-v O2
Cardiac Output – Blood Flow (L/min)
CaO2 = [Hgb] x 1.36 x O2 saturation (%)
CMVO2 = [Hgb] x 1.36 x venous O2 saturation (%)

Question 2

Describe the phases of the cardiac cycle and the effect of heart rate on ventricular filling and contraction. How does increasing the heart rate with exercise differ from artificially increasing heart rate on stroke volume?

Answer 2

Increase in HR during exercise decreases diastolic time most, and also decreases systolic time at high HR. Ventricular filling is preserved, venous return increases, vasodilation and venoconstriction occur and stroke volume increases. Increased heart rate at rest causes decreased ventricular filling time, decreased stroke volume.

Question 3

Describe the heart rate response to exercise and the influence of the autonomic nervous system on heart rate during exercise.

Answer 3

During rest, parasympathetic control of HR. Anticipatory response occurs just prior to exercise due to sympathetic stimulation from central command of CNS. During exercise, there is a linera increase in HR up to maximal response as exercise intensity increases. Max HR : 220-age. during early exercise there is parasympathetic withdrawal. Then during moderate to heavy exercise, sympathetic stimulation occurs

Question 4

Describe the factors responsible for changes in stroke volume during exercise. What is the Frank Starling relationship?

Answer 4

Stroke volume: EDV - ESV. EDV aka preload (is influenced by venous return, ventricular distensibility and pericardial constraint), strength of contraction and afterload (EDV). Starling’s Law of the Heart:Force of contraction proportional to initial resting length
Stroke volume: EDV - ESV. EDV aka preload (is influenced by venous return, ventricular distensibility and pericardial constraint), strength of contraction and afterload (EDV). Starling’s Law of the Heart:Force of contraction proportional to initial resting length

Question 5

factors influencing venous return

Answer 5

venoconstriction (Reflex sympathetic control of vascular smooth muscle), muscle pump brings blood back to heart, respiratory pump (negative thoracic pressure increases venous return)

Question 6

Factors causing inhanced contractility

Answer 6

enhanced sympathetic stimulation via direct innervation or circulating catecholamines (NE, or epi), and frank starling effect

Question 7

Major adjustments of circulatory system during exercise

Answer 7

increased blood flow (CO and muscle blood flow), redistribution of flow, maintain blood pressure (maintains flow to vital organs such as brain)

Question 8

How does the stroke volume response during exercise differ between untrained persons and elite athletes?

Answer 8

Endurance atheletes have a leftward shift on the starling curve. They have a greater stroke volume than non athletes at the same EDV or pressure. In elite athletes, SV does not plateau and continues to rise until maximal exercise. In untrained people, SV plateaus at 40-60% of maximal exercise. This is due to increased EDV at lower workloads, and increased contractility with lower ESV at higher workloads

Question 9

compare SV during upright vs supine exercise

Answer 9

upright SV doubles. Supine: SV increases 20-40%

Question 10

Describe the cardiac output response to exercise in untrained and trained persons.

Answer 10

No difference in resting cardiac output between untrained and trained person b/c trained person has greater SV with slower HR. At maximal exercise, CO is higher in trained persons b/c SV is greater, even though max HR is roughly the same.

Question 11

Describe the response of blood pressure during exercise.

Answer 11

Mean arterial pressure: Diastolic +0.33 (systolic-diastolic BP). During exercise, systolic pressure rises with CO and HR, there is little change in diastolic pressure, thus there is an increase in mean arterial pressure.

Question 12

Explain how the redistribution of blood flow during exercise contributes to an increase in muscle blood flow.

Answer 12

The non exercising vascular beds vasoconstrict (SNS activity) while the exercising muscle vasodilates(metabolic control via PO2, PCO2, etc) and has near 100% recruitment of capillaries (capillaries are open). MAP is maintained. During very high workloads, the amount of vasodilation becomes too large and MAP drops, so some vasoconstriction occurs to maintain MAP>

Question 13

How does the coronary circulation differ from the systemic circulation?

Answer 13

•Coronary blood flow increases during exercise due to increase in cardiac output. Coronary oxygen saturation is lower at rest than systemic, and further decreases with exercise.

Question 14

Potential Mechanisms to Increase Availability of Oxygen to Exercising Muscle

Answer 14

Increase oxygen delivery (supply), Increase in Oxygen Extraction (utilization), Increased metablic efficiency of skeletal muscle

Question 15

Describe the concept of oxygen delivery and approaches to increase oxygen delivery.

Answer 15

O2 delivery: flow x oxygen content. Ways to increase oxygen delivery during exercise is exercise training (increases CO and leg blood flow), blood doping (increases concentration of oxygen with EPO or blood transfusion), high altitude exposure (increases Hgb)

Question 16

What is the role of the arterial-venous O2 content difference at maximal exercise? How does the increase in a-v O2 difference compare to the increase in cardiac output during exercise?

Answer 16

At rest, a-v O2 is 4-5vol%. During exercise, a-v O2 is 15vol%. This is a 3-fold increase in a-v O2 with exercise, compared to the 5-fold increase in CO with exercise.

Question 17

Factors leading to increased muscle oxygen extraction (increased a-v O2 diff)

Answer 17

•Increase in skeletal muscle microcirculation, Increase in aerobic activity of skeletal muscle, Increase in size and number of mitochondria, Local vascular and metabolic improvements in skeletal muscle, Increase in arterial O2 content not a factor!