Respiratory Physiology

Question 1

What effect does anemia have on the O2 saturation curve?

a. Shifts it upwards
b. Shifts it downwards
c. Shifts it to the left
d. Shifts it to the right

Answer 1

B = Shifts it downward - there is less oxygen carrying capacity in the blood overall, therefore at ALL PO2 values along the x axis will not pick up as much O2, so the O2 concentration on the y axis is lower. See the attached pic.
Upward shift caused by Polycythemia (opposite of anemia) - Increased oxygen carrying capacity overall.

• Right shift caused by increased H+, increased PCo2, increased temp- aka all the things that increase with exercise. Also increased 2,3 DPG with chronic hypoxia, high altitude, chronic lung diz. Right shift = increased unloading at peripheral tissues.
• Left shift caused by low H+, low PCO2, low temp. Also low 2,3 DPG from prolonged storage in blood bank. Left shift = increased uptake at lungs.

Question 2

Why does administration of 100% oxygen NOT improve hypoxemia during shunting?

a. Worsens vasoconstriction + shunting, therefore worsening the degree of shunting in the lungs
b. Not true - it DOES improve hypoxemia during shunting.
c. Depresses respiratory drive, causing decreased respiratory rate and worsening hypoxemia
d. The shunted blood does not get exposed to ventilated alveoli and the blood exposed to ventilated alveoli is already saturated.

Answer 2

D .. Usually increases respiratory drive because the chemoreceptors detect increased arterial PCO2 from the shunted blood and icnrease the ventilation. This lowers PCO2 but has no effect on the PO2.

Question 3

What drives the mechanism for hypoxic pulmonary vasoconstriction?

a. Central chemoreceptors detect low arterial PO2 –> systemic catecholamines –> constriction of smooth muscles in small arterioles of hypoxic region
b. Central chemoreceptors detect low arterial PO2 –> systemic vasoactive substances (nitric oxide, endothelin-1) –> constriction of smooth muscles in small arterioles of hypoxic region
c. Low alveolar PO2 causes changes in local perivascular tissue –> local catecholamines –> constriction of smooth muscles in small arterioles of hypoxic region
d. Low alveolar PO2 causes changes in local perivascular tissue –> local vasoactive substances (nitric oxide, endothelin-1) –> constriction of smooth muscles in small arterioles of hypoxic region

Answer 3

D – everything here happens locally. Get clinical improvedemnet with inhibitors of NO synthase and blockers of endothelin receptors.

Question 4

What are the two qualities controlled in the inspiratory ramp?

Answer 4

1. Rate of increase of ramp signal
2. Limiting point at which ramp stomp sudddenly decreases

Rate of increase of ramp signal - during heavy respiration, ramp increases rapidly, fills the lungs rapidly

Limiting point of ramp cessation - earlier ramp ceases the shorter the duration of inspiration – and ultimately, increases respiration frequency.

Ramp - weak and stead increase of action potential to inspirator muscle, then ceases.

Question 5

What is typically the percent saturation of systemic arterial blood?

Answer 5

97% (95 mmHg)

Question 6

What is typically the percent saturation of venous blood?

Answer 6

75% (40 mmHg)