1 - Pulmonary Circulation Flashcards
Objectives: Explain bronchial and pulmonary circulation
- Two circulatory systems associated with the lung
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Bronchial Circulation: Similar to coronary arteries, bronchial circulation is part of systemic circulation
- Most of its venous blood drains into pulmonary vein; in absence of perfusion may act as shunt
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Pulmonary Circulation: Driven by right ventricle through lungs; blood spends < 1sec in capillaries of lungs
- Cardiac Output in R/L heart is equal; pulmonary flow = systemic flow
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Bronchial Circulation: Similar to coronary arteries, bronchial circulation is part of systemic circulation
Objectives: Explain the anatomy of pulmonary capillaries
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Pulmonary Capillaries have Low Vascular Resistenace
- Vessel walls thinner
- Vessel walls contain less smooth muscle
- Easily distended/compressed
- Results in lower intravascular pressures vs systemic
- Anastomoses exist, but mostly relevant during disease states
Objectives: Compare the anatomical and physical features of the pulmonary to the systemic circulation
- Pulmonary Circulation - Main Differences vs Systemic
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Lower resistance
- Lack of arteriole networks
- Vessels Soft, Easily Distended/Compressed
- Driven by Right Ventricle
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Low Perfusing Pressures
- (ΔPPulmonary = 10 mmHg)
-
Lower resistance
- Avg Pulmonary Arterial Pressure = 25/8
- Systemic Circulation: Blood pumped uphill and through solid organs; requires greater force and pressure; high pressure allows redistribution under stress
Objectives: How does gravity influence the pulmonary circulation?
- At Top of Lung: Working against Gravity
- Lowest Parterial
- Lowest blood flow
- At Bottom of Lung: Working with Gravity
- Highest Parterial
- Greatest blood flow
Objectives: Define Zones 1, 2, 3 of the lungs
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Zone 1: Higher pressures (gravity) collapse capillaries
- NOT perfused
- PA > Pa > PV
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Zone 2: Perfused intermittently at systolic P
- Pa > PA > PV
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Zone 3: Always perfused; highest blood flow and perfusion due to gravity effects
- Capillaries “bulge”; radius increases, decreasing resistance
- Pa > PV > PA
Objectives: How does one measure Blood Flow?
- Regional Blood Flow:
- Pulmonary Angiography
- 133Xe Technique
- Lung Perfusion: Microaggregates of Albumin (black/white lung screen)
Objectives: What is PVR and what affects PVR?
- Pulmonary Vascular Resistance (PVR): Resistance to flow
- Defined by Poiseuille’s: R=(8ηL) / (πr4)
- Radius has inverse relationship to resistance
- Two Types of Control:
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Active Control - Increase PVR
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Alveolar Hypoxia - Pulmonary vascular contracts in low PO2
- This is opposite systemic
- Beneficial in normal lungs, bad in sick lungs
- Right Side Heart Failure
- Altitude Sickness - Low O2 leads to vasoconstriction
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Alveolar Hypoxia - Pulmonary vascular contracts in low PO2
-
Passive Control - Decrease PVR
- __Recruitment of unperfused capillaries (increase Zone 1)
- Distension of existing pulmonary capillaries (increase radius, decrease resistance)
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Active Control - Increase PVR
Objectives: Explain pulmonary edema and explain the use of the Starling equation
- Pulmonary Edema: Accumulation of fluid in the lung; result is impaired gas transfer (O2)
- Governed by Starling Law:
- Qf = Kf [(Pc - Pis) - σ(πc - πis)]
- (Pc - Pis) = Capillary P driving fluid towards alveoli
- (πc - πis) = Oncotic P driving fluid away from alveoli
- Kf = Membrane Coefficient (fluid)
- σ = Membrane Coefficient (protein)
- Qf = Kf [(Pc - Pis) - σ(πc - πis)]
- Two Type:
- Hydrostatic (Cardiogenic)
- Permeability (Non-Cardiogenic)
How does resistance change from top to bottom of the lung?
Greatest at top (small radius, -gravity influence)
Least at bottom (large radius, +gravity influence)
How does body position affect blood flow?
“Top” and “Bottom” of the lung (Zones 1, 2, 3) are not fixed anatomical positions
These will change with gravity’s force vector
How do the following change lung Zone workloads?
Hemorrhage / General Anesthesia
Exerise (high Cardiac Output)
Positive Pressure Ventilator with PEEP
- Hemorrhage / General Anesthesia: Low systolic pressure
- Increase Zone 1; reduced pressure driven resistance
- Exerise (high Cardiac Output)
- Zone 1 increases greatly (most room to change)
- Zone 2-3 increase somewhat (less room to change)
- Positive Pressure Ventilator with PEEP
- Increase Zone 1; positive pressure decreases vessel collapse
Explain how changes in lung volumes and PVR are different in Inter-Alveolar and Extra-Alveolar Pulmonary vessels
- Inter-Alveolar: Inhalation causes increased PVR
- Alveoli expands, compressing internal vessel (decreasing radius, increasing resistance)
- Extra-Alveolar: Inhalation causes decreased PVR
- Transmural pressure gradient and radial traction cause distension
- Increase radius, decrease resistance
What can be a difference in intra/extra alveolar vessels during mechanical ventilation with PEEP?
What is a downstream risk to the cardiac system?
- Alveolar Pressure (PA) and Intrapleural (PPL) are positive during inspiration
- Both intra/extra alveolar vessels are compressed (decreased radius, increased resistance)
- Result: Increase in PVR in both vessel locations
- Right Ventricle must work harder; right side heart failure is possible
What is the perfusion/ventilation case of Pulmonary Embolus?
- Poor Perfusion
- Adequate Ventilation
- Nothing is “wrong” with the air in/out of the lungs, however there is a blockage (emboli)–and no blood perfusion to alveoli; thus oxygen (perfusion limited) can not move into the blood
