PHYS: Pulmonary Blood Flow

Question 1

Which has a higher pressure, the pulmonary artery or the aorta?

Answer 1

Aorta! PVR is a ninth of systemic vascular resistance

Question 2

Why is low pulmonary arterial pressure especially important during exercise?

Answer 2

RBCs pass through capillaries slowly in a low pressure system (maximize oxygen exchange because O2 is perfusion limited). During exercise, pressure increases in the pulmonary artery, so RBCs pass through more quickly. However, as pressure increases, the apex of the lung becomes better perfused, which increases the cross sectional area and attenuates the effect that decreased time at the capillary would have on oxygen saturation.

Question 3

What are the two reasons why blood flow increases from the apex to the base of the lungs?

Answer 3

1) Vascular resistance decreases

2) Pressure drop increases

Question 4

Increases in pulmonary artery pressure do what to vessels at the base of the lung?

Answer 4

Distends them! (get more blood flow)

Question 5

Which part of the lung has a higher blood pressure, the apex or the base?

Answer 5

the base

Question 6

What factors favor fluid flow OUT of capillaries?

Answer 6

1) Capillary hydrostatic pressure
2) Interstitial fluid pressure
3) Osmotic pressure of interstitial fluid proteins

Question 7

What factors favor fluid flow INTO capillaries?

Answer 7

ONLY the osmotic pressure of plasma proteins

Question 8

Why do you get edema more commonly at the base of the lungs?

Answer 8

Pressure at the base of the lung is highest, so you would expect hydrostatic pressure to increase over osmotic pressure here (if it happens at all), which leads to pulmonary edema

Question 9

What happens to vasculature if the Po2 in the alveoli is lowered (hypoxia) OR if the CO2 increases (hypercapnia/acidosis)?

Answer 9

Vessels will constrict in order to shunt blood into better ventilated areas

Question 10

Hypoxia leading to increased pulmonary vascular resistance can lead to what condition?

Answer 10

chronic pulmonary hypertension

Question 11

Chronic pulmonary HTN has what effect on the heart?

Answer 11

leads to increased RV load and EDP–> right ventricular hypertrophy–> cor pulmonale (right sided heart failure)

Question 12

What are the 3 main functions of the lung?

Answer 12

1) increase O2, decrease CO2
2) Filter blood
3) Vasoactive substances (ex. activation of angiotensin)

Question 13

What is a normal A-a gradient?

Answer 13

around 5

Question 14

What is worse, a higher or lower A-a?

Answer 14

HIGHER A-a gradient indicates hypoxia, because blood with a lower Po2 is in the systemic circulation

Question 15

Where is the V/Q ratio the highest?

Answer 15

at the APEX of the lung (very well ventilated but poorly perfused)

Question 16

If you get increased ventilation, the Pao2 will look more like what?

Answer 16

inspired air

Question 17

If you get increased flow, the Pao2 will look more like what?

Answer 17

blood

Question 18

Is V higher at the apex or base?

Answer 18

base

Question 19

Is Q higher at the apex or base?

Answer 19

base

Question 20

If V and Q are both higher at the base, why is the V/Q ratio higher at the apex?

Answer 20

because blood flow is so much lower at the apex than the base

Question 21

Which has a higher Po2, the apex or base of the lung?

Answer 21

apex! (also has a lower Pco2)

Question 22

What are the 5 main causes of hypoxemia?

Answer 22

1) low FiO2 (barometric pressure)
2) Hypoventilation
3) Low diffusing capacity
4) V/Q mismatch
5) Shunt