Pulmonary Circulation Flashcards
*** 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.
PaO2 = 160mmHg
PAO2 = (747-47) * 0.5 - (40/0.8)
= 300mmHg
A-a Gradient
= 300 - 160
=140
[normal = 5-10]
Pulmonary vascular resistance
↑ pulmonary vascular resistance
↑ work load on right side of the heart & constriction of pulmonary vein
↑ the pulmonary capillary pressure
↓pulmonary blood flow
pulmonary vascular dilators
↑PA O2 ↓P A CO2 ↑pH B adrenergic agonists Bradykinin Acetylcholine NO Histamine, H2 agonists
pulmonary vascular constrictors
↓ PA O2 ↑ P A CO2 ↓pH alpha adrenergic agonists Serotonin Angiotensin II
Fetal pulmonary vascular resistance is very high. Why??
Fetal lungs are without air and no PAO2 causing generalized hypoxic vasoconstriction
Apex of the lung
Less blood flow
↑ pulmonary vascular resistance
intrapleural pressure is more negative (-10)
Base of the lung
Greater blood flow
↓pulmonary vascular resistance
intrapleural pressure is less negative (-2.5)
alveoli have a greater tendency to expand
V/Q ratio
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
COPD V/Q ratio
In chronic obstructive pulmonary diseases V/Q ratio reduces greatly
V/Q in zone 1 (apex)
↓V
↓↓Q
↑↑ V/Q
V/Q in zone 3 (base)
↑V
↑↑ Q
↓↓ V/Q
Why is Tuberculosis cavity more often seen at the apex of the lungs???
Tubercle Bacilli is an Aerobic Organism.
As apex of lung is overventilated, it favors growth of organisms
Perfusion rate in airway obstruction
V/Q = 0
PO2 = 40 PCO2 = 46
arterial blood is same as venous blood
Perfusion rate in Pulmonary Embolism
V/Q = infinite
PO2 = 150 PCO2 = 0
P(A-a)O2 Gradient
5-10mmHg
alveolar gas equation
PAO2 = PIO2 - (PACO2 / R)
alveolar gas equation (using barometric pressure and water)
PAO2 = FIO2 * (PB- PH2O) - (PACO2 / R)
Left-to-right shunts
less dangerous
VSD (ventricular septal defect)
ASD (atrial septal defect)
PaO2 is normal, (A-a) gradient is normal
Right-to-left shunts
DANGEROUS
Fallot’ tetralogy
Hypoxia
PaO2 is always low, widening of (A-a) gradient
PaO2 will not improve by breathing 100% oxygen
Fallot’ tetralogy
- narrowing of the pulmonary valve
- thickening of the wall of the right ventricle
- displacement of the aorta over ventricle septal defect
- ventricular septal defect - opening between the left and right ventricles
*** Which of the following occurs with the baby’s first diaphragmatic respiration?
PaO2 increases
