Gas Exchange

Question 0

What would bronchodilators do to patients with Acute Respiratory Distress Syndrome (ARDS)?

Answer 0

Worsen the V/Q mismatch. By systemically acting as vasodilator, bronchodilator will increase the blood flow to pulmonary bed, lowering the already low V/Q.

Question 1

Describe five causes of hypoxemia and its effect on PA-Pa difference for each case.

Answer 1

High altitude (normal) 
Hypoventilation (normal)
V/Q mismatch (increased)
Diffusion impairment (increased)
True shunt (increased)

Question 2

Equation for partial pressure of O2 in alveolus?

Answer 2

PIO2-PAO2=vO2/VO2 (rate of O2 removal relative to fresh O2 replacement)

Question 3

Equation for partial pressure of CO2 in alveolus?

Answer 3

PACO2=vCO2/VCO2 (rate of CO2 addition relative to fresh O2 replacement)

Question 4

Equation for anatomical dead space?

Answer 4

Vd/Vt=(PACO2-PECO2)/PACO2

Question 5

Equation for physiological dead space?

Answer 5

Vd/Vt=(PaCO2-PECO2)/PaCO2

Question 6

Equation for shunt ratio?

Answer 6

Qs/Qt=(Cc’O2-CaO2)/(Cc’O2-CvO2)

Question 7

How do you approximate for PAO2?

Answer 7

PAO2=PIO2-1.2*PaCO2, vO2/vCO2=Respiratory rate

Question 8

How does fibrosis affect diffusion of O2?

Answer 8

Thickens the alveolar wall, decreases diffusion rate, and slows equilibration rate of O2.

Question 9

What is normal value for V/Q? Also, how does high or low V/Q affect the expired gas and/or arterial blood?

Answer 9

. 8
High V/Q dilutes the expired gas
Low V/Q lowers PaO2

Question 10

Describe Hering-Breuer reflex.

Answer 10

A phenomenon in which distension of lungs and airways stimulates mechanoreceptors to initiate a reflex in the brain to decrease breathing rate via vagus nerve (CN X).

Question 11

Describe how J (juxtacapillary) receptor works.

Answer 11

These receptors near capillaries in alveolar wall detect increase in volume of blood and interstitial fluid to send the signal to increase breathing rate, in rapid shallow breathing and dyspnea pattern.

Question 12

Describe respiratory alkalosis at high altitude and what happens to the patient after a few days. Also what could be the treatment?

Answer 12

Hypoxemia as a result of high altitude leads to hyperventilation, which blows off CO2 from the blood and increases pH (Hence alkalosis). Over time, HCO3- renal excretion increases, HCO3- leaves CSF, and pH decreases again and resumes hyperventilation. Carbonic anhydrase inhibitor, which increases HCO3- excretion, is one treatment.

Question 13

Compare pulmonary vasculature effects of exercise and ascent to high altitude.

Answer 13

Exercise: although PaO2 doesn’t change, an increase in demand for oxygen delivery leads to an increase cardiac output and distends pulmonary arteries with their accompanying decrease in resistance.
High altitude: Decrease in PAO2 causes hypoxic vasoconstriction and increases pressure and resistance on pulmonary arteries. Right ventricular hypertrophy can be expected.