L289 Exercise Physiology - Oxygen, Heat and Fluids

Question 1

O2 uptake is ______ dependent

Answer 1

Intensity-dependent

Question 2

Describe O2 uptake + ex intensity relationship

Answer 2

Linear increase until reach plateau - VO2max

Question 3

Equation for VO2 max

Answer 3

• VO2 = Q x (CaO2 – CvO2) = CO x AVO2 difference

Question 4

Describe O2 uptake at the beginning of exercise

Answer 4

• O2 deficit: lag between O2 uptake needed for workload and actual O2 uptake
- In this time, anaerobic energy sources help supplement energy needs

Question 5

CO + intensity relationship

Answer 5

↑ intensity, ↑CO

Question 6

With increasing intensity, describe the BF to muscle, kidneys, heart, skin, brain and gut.

Answer 6

• ↑BF to muscle, heart, ↑/= BF to brain
• ↓BF to kidneys, gut
• ↑ then ↓ to skin

Question 7

Why does BF to kidneys and gut decrease?

Answer 7

• Compensatory VC to redistribute BF where needed

Question 8

Why does BF to skin increase then decrease?

Answer 8

• Initially ↑BF with ↑ intensity to lose heat

- Until the point where muscle requires BF going to skin - skin then VC ∴ potential for overheating

Question 9

Hierarchy of BF importance during ex

Answer 9

brain > muscle > skin

Question 10

What does the hierarchy of BF importance mean for BF to the muscle?

Answer 10

muscle can have ↓BF (VC) if brain perfusion is at risk

Question 11

small muscle group vs dynamic body ex effect on BP

Answer 11

Small muscle group exercise → ↑↑ BP cw. dynamic all body exercise - because of the ↑ VC

Question 12

↑BF during exercise is called…

Answer 12

ex hyperaemia

Question 13

4 plausible mechanisms for exercise hyperaemia

Answer 13

1. Metabolic vasodilators from contracting skeletal muscle, endothelium and/or RBCs
2. Muscle pump
3. “Conducted vasodilation”
4. Functional sympatholysis

Question 14

Muscle pump during ex: important for maintaining what?

Answer 14

VR cw BF

Question 15

Explain conducted vasodilation

Answer 15

• Local relaxation of smooth muscle through smooth muscle gap junctions
• Relaxation is conducted proximally

Question 16

Explain functional sympatholysis

Answer 16

• SNS-mediated VC is desensitised in response to metabolic vasodilators
• ↑SNS activity at rest → significant ↑ VC at muscle, but ↑SNS activity during exercise → less significant ↑ VC at muscle

Question 17

What occurs to HR and systole during incremental ex?

Answer 17

↑HR, ↑SV that plateaus

Question 18

Explain the increased and levelled off SV during incremental ex

Answer 18

• ↑HR during exercise → shortened diastole
- Because systole relatively fixed
∴ ↑ SV eventually level off, due to impact on diastolic filling

Question 19

During ex, SBP and DBP mimic what?

Answer 19

SBP mimics CO and DBP mimics peripheral resistance

Question 20

Therefore, what happens to SBP and DBP during ex?

Answer 20

• ↑CO → ↑SBP

- DBP maintained/falls slightly if TPR falls

Question 21

What happens to MAP during ex, and why?

Answer 21

exercise → ↑MAP: because of ↑SBP + ↓DBP (i.e. systole becomes larger component of equation)

Question 22

Why can MAP and HR increase simultaneously during ex?

Answer 22

Because baroreceptors reset to a higher level in exercise

Question 23

CV responses to prolonged exercise

Answer 23

• CV drift: = ↑HR and ↓SV over time

Which comes first is chicken or egg debate!

Question 24

Reasons for CV drift during prolonged exercise (4)

Answer 24

1. Hyperthermia
2. Dehydration
3. ↑ plasma [adrenaline]
4. Peripheral displacement of BV due to cutaneous vasodilation

Question 25

Peripheral displacement of BV due to cutaneous vasodilation: how might this cause CV drift?

Answer 25

• Skin circulation is quite compliant esp. venous circulation
  ∴ blood going to skin can ↓ systemic circulation flow → ↑HR

Question 26

Neural control of the circulation: interaction between..

Answer 26

• Central command
- Powerful pre-anticipatory control over body before exercise
• FB from peripheral sensors
- Mechanical and chemical muscle sensors, baroreceptors, thermoreceptors etc.

Question 27

Explain the early increase in HR during ex

Answer 27

Early ↑HR during exercise due to withdrawal of vagal (PNS) control and thus SNS domination of control
- Remembering basal HR actually driven by SNS

Question 28

Mechanisms of ↑CO following training (4)

Answer 28

1. Expanded blood volume
   
   2. ↑ heart size(↑ LV mass and chamber size)
   3. ↑ adrenergic sensitivity?
   4. Microvascular adaptations - ↑capillary density and recruitment

Question 29

Ventilation during incremental exercise: describe relationship

Answer 29

• Linear increases between VO2 and Ve

	- Initial gradient b/n rest VO2 and VT1 in response to CO2 from aerobic resp.
	- 2nd ↑ gradient b/n VT1 and VT2 in response to need to buffer lactic acid
	- 3rd ↑↑ gradient after VT2 in response to ↑↑ CO2 from aerobic resp. and metabolism → hyperventilation

Question 30

Pulmonary gas exchange during exercise: describe

Answer 30

• ↑CO during exercise → transit time ↓ as blood velocity ↑

Question 31

When can pulmonary gas exchange become a problem?

Answer 31

1. At altitude with ↓PO2

2. Well trained athletes with ↑↑CO

Question 32

Main driver for respiration

Answer 32

CO2 - not hypoxia!

Question 33

↑ ventilation during exercise is called …

Answer 33

Exercise hyperpnea

Question 34

Mechanisms of exercise hyperpnea (5)

Answer 34

1. Motor cortical activation
2. Muscle afferents (spindles, type III & IV)
3. CO2 flux to the lung
4. Increased K+, H+, lactate?
5. Elevated catecholamines and temperature

Question 35

Exercise ventilation following training (5)

Answer 35

1. Reduced blood lactate/H+
2. Lower plasma K+
3. Lower plasma catecholamines
4. Reduced activation of muscle afferents?
5. Reduced central drive?

Question 36

Main mechanism of heat loss during ex and when in particular

Answer 36

Evaporation of sweat -at high temperatures in particular

Question 37

Skin BF and CO at rest in heat

Answer 37

Skin already VD and CO increased (CO matches exercising at 5-6 mets at cooler temperature)

Question 38

Skin BF and CO with exercise in heat

Answer 38

• Almost immediately ↓ skin BF because blood needed somewhere else
• ∴ ability to dissipate heat decreased

Question 39

Exercise-induced dehydration affects which body fluid compartments?

Answer 39

Exercise-induced dehydration affects all body fluid compartments
- Plasma volume reasonable well protected, but marked IC and EC dehydration occurs

Question 40

Dehydration and heat stress effect on performance

Answer 40

Both impair performance

Question 41

Heat production during ex directly determined by…

Answer 41

ex intensity

Question 42

VO2 max closely correlates with…

Answer 42

O2 delivery