Flashcards in Exam #3: Pulmonary Circulation Deck (28):
How do pulmonary arteries structurally compare to the systemic arteries?
2) More compliant
3) Thinner walled
This allows them to accomodate the entire cardiac output
What is the bronchial circulation?
Circulation to the lung parenchyma itself
- Bronchial arteries provide oxygenated systemic blood to the lungs
- Bronchial veins carry 1/3 of the bronchial circulation back to the RA
- Remaining 2/3 goes to the LA via the pulmonary veins, which is responsible for the "physiological shunt" of blood
What is the effect of bronchial circulation?
Physiological shunting of blood & drop in partial pressure of oxygen in systemic circulation compared to alveolar oxygen
What is hypoxic pulmonary vasoconstriction (HPV)?
- Decreased alevolar Po2 i.e. alveolar hypoxia (<70 mmHg) causes local vasoconstriction, which is the OPPOSITE of what happens in systemic circulation
- Blood redistribution to better aerated alveoli i.e. serves to match ventilation & perfusion by redirecting perfusion to better oxygenated alveoli
What causes HPV?
Failure of ventilation
Acute lung damage
What is the long term effect of HPV?
Pulmonary arterial hypertension (PAH)
What are the effects of gravity on the distribution of pulmonary blood flow? What is the clinical significance?
- Blood flow is greater in the bases of the lungs than the apex in the standing individual.
- Clinically, this is why you look for evidence of edema at the bases of the lungs
Describe the structure of the pulmonary capillaries.
Leaky to protein
Form a sheet of flow
Summarize the pulmonary capillary & interstitial fluid dynamics.
1) Normal outward forces are greater than inward forces, which provides a filtration pressure out of the pulmonary capillaries into the interstitial space
2) Pulmonary lymphatic pressure is negative relative to interstitial, which results in the recycling of fluid
What causes an increased in interstitial hydrostatic pressure?
What conditions will increase intravascular hydrostatic pressure?
Increased blood volume
Poor heart function
What will decrease capillary osmotic pressure?
What conditions will change capillary permeability?
What is the ventilation- perfusion relationship?
Matching ventilation (V) to perfusion (Q) is essential for ideal gas exchange
What is the average normal for V/Q?
Draw the V/Q graph.
Note that ventilation & perfusion decrease from the base of the lung to the apex, but perfusion decreases FASTER
How do V & Q change from the base to the apex of the lung?
BOTH drop, but there is a higher V than Q at the apex than the base
What pathological condition favors high V at the apex of the lung?
What is a V/Q defect?
Mismatch between V & Q.
What is the V/Q relationship at the dead space? What pathologic condition results in dead space?
Infinity b/c no perfusion
- Pulmonary embolism; there is ventilation but no perfusion because the region is occluded by the emboli
What does it mean that there is a high VQ?
- There is high ventilation relative to perfusion (high V compared to Q)
- Usually due to a decrease in blood flow
What does it mean that there is low V/Q?
- There is low ventilation relative to perfusion, usually because ventilation is decreased
What is the term for VQ= 0?
"Shunt," this is a portion of the lung where the CO has been diverted
What is a right to left shunt? What are the clinical features of a right to left shunt?
Shunting of blood from right heart to left heart e.g. in cases of LATE stage VSD or ASD
- Hypoxemia always occurs because blood is not going through the lungs
- Cannot be corrected with having the person breathe high O2 gas
What is Eisenmenger Syndrome?
Refers to late stage septal defects that essentially have a reversal of shunting from left to right, to right to left
- Left to right shunting causes increased pressure to be pumped into the pulmonary arteries
- Vascular remodeling occurs that increases the thickness of these arteries, transmitting pressure back into right heart
- Eventually right pressure is greater than left & shut reverses direction
Describe the pathophysiology of PE.
Right ventricular failure
Right to left shunting
What is the physiologic shunt?
This refers to roughly 2% of the CO that NORMALLY bypasses the alveoli