Altitude/Hypoxia/Exercise

Question 1

high altitude causes what changes to Pa_O2

Answer 1

hypoxemia (decreased Pa_O2)

Question 2

what is the most significant response to high altitude

Answer 2

increase in ventilation rate

• **hypoxemia will stimulate the peripheral chemoreceptors in the carotid and aortic bodies -> increase breathing rate

Question 3

polycythemia

Answer 3

an abnormally increased concentration of hemoglobin in the blood

Question 4

how does high altitude cause polycythemia

Answer 4

1. high altitude produces increased RBC
   
   1. thus, increased [Hb]

Question 5

what is advantagous and disadvantagous of polycythemia created at high altitude?

Answer 5

• advantagous: increase in [Hb] will increase O2-carrying capacity which will increase total blood O2 content
• disadvantagous: increase in blood viscosity due to increased # RBC which will increase the resistance to blood flow

Question 6

how does the body create polycythemia in times of hypoxemia

Answer 6

1. increased synthesis of erythropoietin in the kidney
2. erythropoietin acts on bone marrow to increase RBC production

Question 7

altitude has what affect on 2,3-DPG concentration? What affect does that have on O2-Hb dissociation curve

Answer 7

• altitude results in increased synthesis of 2,3-DPG concentration by the RBC
• causes Right shift in the O2-Hb dissociation curve
  
  • bc 2,3-DPG binds to Hb and decreases its affinity for O2

Question 8

when the O2-Hb dissociation curve shifts to the right? is there an increase or decrease in P50? What does this mean in terms of O2 loading and unloading

Answer 8

• increased P50
• decreased affinity of Hb for O2
• increased unloading of O2 in tissues

Question 9

at high altitude, what happens to pulmonary vasculature? What is this process known as?

Answer 9

• vasoconstricts
• hypoxic vasoconstriction

Question 10

at high altitue, the pulmonary vasculature vasoconstricts, what does this do to vascular resistance? As a result, what happens to pulmonary arterial pressure?

Answer 10

• vascular resistance increases
• thus, pulmonary arterial pressure must also increase (to maintain constant BF)

Question 11

in high altitude, what changes are made to right venticle?

Answer 11

hypertrophy

• due to increased pulmonary arterial pressure from pulmonary vasculature vasoconstriction

Question 12

at high altitude, what changes are made to pH

Answer 12

• respiratory alkalosis
• due to hyperventilation

Question 13

what is the A-a gradient?

Answer 13

A-a gradient = PA_O2 - Pa_O2

Question 14

what does the A-a gradient tell us?

Answer 14

whether there has been equilibration of O2 between alveolar gas and pulmonary capillary blood (systemic arterial blood)

Question 15

what is the other equation for A-a gradient that takes into account PI_O2

Answer 15

A-a gradient = (PI_O2 - (PA_CO2 / RQ)) - Pa_O2

• RQ = respiratory quotient

Question 16

the A-a gradient is normally what value

Answer 16

A-a gradient = 0

• if not zero, signifies a defect in O2 equilibrium

Question 17

what happens to A-a gradient at high altitude

Answer 17

• A-a gradient = normal
  
  • high altitude barometric P decreases which decreases PI_O2 and PA_O2
  • but equilibration across the alveolar/pulmonary capillary barrier is normal
  • so arterial blood achieves the same (lower) P_O2 as alveolar air

Question 18

what happens to A-a gradient at hypoventilation

Answer 18

• A-a gradient = normal
  
  • hypoventilation: PA_O2 is decreased due to decreased PI_O2
  • but equilibration across the alveolar/pulmonary capillary barrier is normal
  • thus, arterial blood achieves the same (lower) P_O2 as alveolar air

Question 19

what happens to A-a gradient in fibrosis and pulmonary edema

Answer 19

• A-a gradient increases
  
  • **diffusion distance increases
  • equilibration across the alveolar/pulmonary capillary barrier is impaired
    
    • PA_O2>Pa_O2

Question 20

with diffusion defects, will breathing supplemental O2 increase Pa_O2

Answer 20

• yes, it will increase the driving force for O2 diffusion and the increase in PA_O2 will result in an increase in Pa_O2

Question 21

what happens to A-a gradient in a right to left shunt (e.g. ventricular septal defect)

Answer 21

• A-a gradient increases
  
  • shunted blood bypasses ventilated alveoli and is not oxygenated
  • shunted blood mixes with and dilutes normally oxygenated blood - the P_O2 of blood leaving the lungs is therefore lower than normal

Question 22

does supplemental O2 has an effect on Pa_O2

Answer 22

• limited effect since it can only raise the P_O2 of non-shunted blood

Question 23

how does arterial P_O2 and P_CO2 change with exercise? why

Answer 23

• no change
• due to
  
  • increase in ventilation rate and
  • increased efficiency of gas exchange

Question 24

why does the ventilation rate increase in exercise

Answer 24

• P_CO2 increases during exercise because the skeletal muscle is adding more CO2 than usual to the venous blood
• since average Pa_CO2 stays constant, ventilation rate must increase to remove the excess CO2

Question 25

how is ventilation increased during exercise

Answer 25

• muscle and joint receptors stimulate meduallary inspiratory center

Question 26

what happens to pulmonary resistance during exercise

Answer 26

• decreases due to perfusion of more capillary beds

Question 27

what happens to ventilation/perfusion ratio and physiologic dead space during exercise

Answer 27

becomes more even or uniform thus resulting in a decrease in physiologic dead space

Question 28

exercise causes what change to O2-Hb dissociation curve?

Answer 28

curve shifts to right

• get increased unloading of O2 at skeletal muscle