Pulmonary Circulation

Question 1

*** A 56-year-old man presents to the Emergency Department with severe abdominal pain and a temperature of 103°F. The patient is in severe respiratory distress. Moderate amounts of pulmonary edema fluid are aspirated during suctioning. The patient is placed on a ventilator with an FIO2 of 0.5 and an arterial blood gas sample reveals a PO2 of 160 mmHg and a PCO2 of 40 mmHg. His alveolar oxygen tension, at a barometric pressure of 747 mmHg (P H2O = 47mmHg) and a respiratory exchange ratio (R) of 0.8.

Calculate A-a Gradient.

Answer 1

PaO2 = 160mmHg

PAO2 = (747-47) * 0.5 - (40/0.8)
= 300mmHg

A-a Gradient
= 300 - 160
=140

[normal = 5-10]

Question 2

Pulmonary vascular resistance

Answer 2

↑ pulmonary vascular resistance

↑ work load on right side of the heart & constriction of pulmonary vein

↑ the pulmonary capillary pressure

↓pulmonary blood flow

Question 3

pulmonary vascular dilators

Answer 3

↑PA O2
↓P A CO2
↑pH
B adrenergic agonists
Bradykinin
Acetylcholine
NO
Histamine, H2 agonists

Question 4

pulmonary vascular constrictors

Answer 4

↓ PA O2 
↑ P A CO2 
↓pH 
alpha adrenergic agonists 
Serotonin
Angiotensin II

Question 5

Fetal pulmonary vascular resistance is very high. Why??

Answer 5

Fetal lungs are without air and no PAO2 causing generalized hypoxic vasoconstriction

Question 6

Apex of the lung

Answer 6

Less blood flow

↑ pulmonary vascular resistance

intrapleural pressure is more negative (-10)

Question 7

Base of the lung

Answer 7

Greater blood flow

↓pulmonary vascular resistance

intrapleural pressure is less negative (-2.5)

alveoli have a greater tendency to expand

Question 8

V/Q ratio

Answer 8

approximately 0.8 ( 4/5=0.8)

If V/Q < 0.8 – under ventilation,↑PaCO2, ↓PaO2, ↓pH

If V/Q > 0.8 – over ventilation,↓PaCO2, ↑PaO2, ↑pH

Question 9

COPD V/Q ratio

Answer 9

In chronic obstructive pulmonary diseases V/Q ratio reduces greatly

Question 10

V/Q in zone 1 (apex)

Answer 10

↓V
↓↓Q

↑↑ V/Q

Question 11

V/Q in zone 3 (base)

Answer 11

↑V
↑↑ Q

↓↓ V/Q

Question 12

Why is Tuberculosis cavity more often seen at the apex of the lungs???

Answer 12

Tubercle Bacilli is an Aerobic Organism.

As apex of lung is overventilated, it favors growth of organisms

Question 13

Perfusion rate in airway obstruction

Answer 13

V/Q = 0

PO2 = 40
PCO2 = 46

arterial blood is same as venous blood

Question 14

Perfusion rate in Pulmonary Embolism

Answer 14

V/Q = infinite

PO2 = 150
PCO2 = 0

Question 15

P(A-a)O2 Gradient

Answer 15

5-10mmHg

Question 16

alveolar gas equation

Answer 16

PAO2 = PIO2 - (PACO2 / R)

Question 17

alveolar gas equation (using barometric pressure and water)

Answer 17

PAO2 = FIO2 * (PB- PH2O) - (PACO2 / R)

Question 18

Left-to-right shunts

Answer 18

less dangerous

VSD (ventricular septal defect)
ASD (atrial septal defect)

PaO2 is normal, (A-a) gradient is normal

Question 19

Right-to-left shunts

Answer 19

DANGEROUS

Fallot’ tetralogy
Hypoxia

PaO2 is always low, widening of (A-a) gradient

PaO2 will not improve by breathing 100% oxygen

Question 20

Fallot’ tetralogy

Answer 20

1. narrowing of the pulmonary valve
2. thickening of the wall of the right ventricle
3. displacement of the aorta over ventricle septal defect
4. ventricular septal defect - opening between the left and right ventricles

Question 21

*** Which of the following occurs with the baby’s first diaphragmatic respiration?

Answer 21

PaO2 increases