Chapter 4 Flashcards
What is the equation for vascular resistance?
Vascular Resistance =(Input pressure - output pressure) / blood flow
What is the Fick Principle Equation?
Q = VO2 / (CaO2 - CVO2)
Q = Cardiac Output
VO2 = O2 consumption per minute
CaO2 = O2 concentration of blood leaving lung
CvO2 = O2 concentration of blood entering lung
What is pulmonary vascular resistance normally?
- Small
When does pulmonary vascular resistance decrease? why?
On Exercise
- Recruitment of capillaries
- Distension of Capillaries
some compounds
When does Pulmonary Vascular Resistance Increase?
- High lung volume
- Low lung volume
- Alveolar Hypoxia
- some compounds
What compounds cause pulmonary vascular resistance to increase?
- Endothelin
- Histamine
- Serotonin
- Thromboxane A2
What compounds cause Pulmonary Vascular Resistance to Decrease?
- Acetylcholine
- Calcium-channel Blockers
- Nitric Oxide
- Phosphodiesterase Inhibitors
- Prostacyclin (PGI2)
What does gravity do to the lung?
- Causes large differences in Distribution of Blood Flow
How many zones are in the lung? (blood flow zones)
- 3
What happens in Zone 1 of blood flow in the lung? When is this not seen?
Zone 1
- No flow
- Pulmonary artery pressure is less than alveolar pressure
Not Seen
- Under normal conditions
What happens in Zone 2 of blood flow in the lung?
- Flow is determined by the difference between arterial and alveolar pressure
What happens in Zone 3 of blood flow in the lung?
- Flow is determined by difference in arterial and venous pressure
Where does flow increase in Zone 2 and 3 of blood flow in the lung?
- down each zone (due to gravity)
What does Alveolar Hypoxia do to small pulmonary arteries? Why?
Constricts them
- Direct effect of low PO2 on vascular smooth muscle
What is Critical at Birth during the transition from placental to air breathing?
Release of Alveolar Hypoxic Vasoconstriction
- Reduces constriction of small pulmonary arteries
When can Alveolar Hypoxic Vasoconstriction be used in the adult lung?
- To direct blood flow away from poorly ventilated areas of a diseased lung in an adult
What is the difference between pulmonary circulation and systemic circulation?
- Pressure on Pulmonary Circulation is much lower
What is the difference between pulmonary capillaries and extra-alveolar vessels?
Capillaries
- exposed to alveolar pressure
Extra-Alveolar Vessels
- Pressure around them is lower
Why is there uneven blood flow in the lung?
- Gravity: Higher blood flow at base than apex in upright lung
- Random Variation of blood vessels: any given level
What is fluid movement across the capillary endothelium governed by?
- Startling Equilibrium
What is a main metabolic function of pulmonary circulation?
- Conversion of Angiotensin I to Angiotensin II by Angiotensin-Converting Enzyme
What are the walls of pulmonary arteries and branches made up of?
- little smooth muscle
how much blood does the lung receive?
4-6L/min
how much blood does the lung receive?
4-6L/min
What is the average pulmonary artery pressure? what about aortic pressure?
Pulmonary Artery
- 15mmHg
Aortic
- 95-100mmHg
What is the left atrial pressure?
- 5mmHg
Compare Systemic Circulation to Lung Circulation
Systemic
- Regulates blood supply to various organs
- Directs blood from one region to another
Lung
- Accepts entire output
- Keeps Pressure low
- Minimize RT heart work
- Allow Efficient Gas Exchange
What is a Pressure Gradient?
- Blood Flow from region of high pressure to region of low pressure
What is the Pressure gradient across the entire cardiovascular system?
- 100mmHg
Do Blood Vessels and Blood itself provide resistance to flow?
- YES
What is the Equation for Resistance to Flow?
Resistance = [nL/r^4]
n = viscosity of blood
L = length of vessel
r^4 = radius of the vessel to the 4th power
What is the equation for blood flow? (in terms of pressure and resistance)
Blood Flow = Change in Pressure/Resistance
How can blood flow change?
Changes in
- Pressure
- Resistance
- Combination of both
Why does changing resistance have a larger effect on blood flow?
- Fourth power relationship between resistance and vessel radius
How does Vasoconstriction impact Blood Flow?
- Radius decreases
- Resistance Increase
- Blood Flow Decreases
How would vasodilation impact blood flow?
- Increase Radius
- Decrease Resistance
- Increase Blood Flow
What do Extra-Alveolar Vessels include? How are they affected by lung volume?
Arteries and Veins that run through the lung parenchyma
- lung volume determines the expanding pull of the parenchyma on their walls
What happens to Alveolar and Extra-alveolar vessels at different lung volumes?
High Lung Volume
- Alveolar vessels: compressed
- Extra-alveolar vessels: distended due to low pleural pressure
Low Lung Volumes
- Alveolar Vessels: Distended
- Extra-alveolar vessels: compressed from pleural pressure
What is the equation for Vascular resistance?
VR = Input P - Output P / Blood Flow
VR = (15-5) / 6 (average at rest)
VR = 1.7mmHg/L/min
How does Resistance lower as pressure rises?
- Recruitment: Closed vessels conduct blood
- Distension: Increase in Caliber
Does resistance increase or decrease with exercise?
- Decrease
What is the force that tends to push fluid out of the capillary?
Capillary Hydrostatic pressure minus interstitial hydrostatic pressure (Pc-Pi)
What is the force tending to pull fluid in the capillary?
Colloid Osmotic Pressure of Protein of blood minus COP of Protein in interstitial fluid (πc - πi)
What does σ mean?
- Indicates the effectiveness of the capillary wall in preventing the passage of protein across it
What is the Starling Equation that determines fluid exchange?
Net Fluid Out = K[(Pc – Pi) – σ(πc – πi)]
What happens if there is Pulmonary Edema? (build-up of pressure)
First
- Engorgement of peribronchial and perivascular spaces (interstitial edema)
Later
- Fluid cross alveolar epithelium
- Fluid in alveolar space
- Gas exchange impairment
What substances are metabolized in the lung? What one is important?
Vasoactive and Bronchoactive Substances
- Arachidonic Acid Metabolites
