1 - Respiratory Mechanics ( II ) Flashcards
Objectives: Define specific and total compliance of lungs
Specific Compliance = Compliance / FRC
Compliance = F(size); FRC accounts for this, e.g. child vs adult
Normalizes the compliance (C) value to the FRC
Objectives: Explain airway resistance in the lungs
- Two Types of Flow:
- Laminar - Ordered, Slower, Quiet
- Turbulent - Disorderd, Faster, Noisy
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Poiseuille: R α 1/radius4
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R = 8nl / r4
- R = Resistance
- r = Radius
- ONLY APPLIES TO LAMINAR FLOW
-
R = 8nl / r4
- Greatest Resistance = Large Airways
-
Smallest Resistance = Small Airways
- Due to parallel arrangement
Objectives: Explain airway collapse during forced expiration
In a healthy individuals, what prevents collapse?
- Rib cage pushes in; abdominal muscles push against diaphragm; Pleural Pressure (PPL) become Positive
- Alveolar pressure (PAlv) positive
- Pressure Outside Airway > Inside, results in Dynamic Compression
- Tracheal Rings prevent collapse in healthy individuals;
- Emphysema degrades these as tissues become “soft”;
- Asthma causes airway restriction, increasing flow velocity (smaller hole), lowering airway pressure, increasing resistance; leading to collapse and shunt
Objectives: Explain tethering of alveoli
Alveoli attached to their neighbors, preventing collapse
In emphysema, these are degraded, leading to collapse
Same relationship exists for smaller airways
Objectives: Know about lung volumes and capacities (maybe focus on terminology here)
Tidal Volume (TV)
Dead Space Volume (VD)
Residual Volume (RV)
Total Lung Capacity (TLC)
Forced Vital Capacity (FVC)
FEV1
Functional Residual Capacity (FRC)
TV = Volume of air inspired/expired with each breath (Not Forced)
VD = Air which person breathes not used for gas exhchange, fills respiratory passages
RV = Air in lungs which can’t be exhaled
TLC = Volume of lungs after max inspiratory effort
FVC = Amount of air exhaled as quickly during forced exhalation
FEV1 = Air exhaled in first second, should be 80% of FVC
FRC = Air in lung when lung and chest wall are in equilibrium (at rest)
Objectives: What is a spirometer and how is it used in lung disease?
Direct Measure: TV, FVC, FEV1, FEF
Cannot Measure: RV, FRV, TLC (all have RV component)
Objectives: What is FRC, how is it measured, and what factor affect it?
- FRC = Functional Residual Capacity = Volume of air in lungs at equilibrium (rest)
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Healthy Measure: Helium Dilution Technique
- PBag x VBag = PHE x (VBag + FRC)
- Lung Disease Patients: Body Box Plethysmography
How do you measue compliance?
How can you measure lung compliance alone, and how would you calculate chest wall compliance?
Compliance = Spirometry (Lung + Chest)
Esophageal Balloon (Lung Only)
1/Total Compliance = 1/Lung Compliance + 1/Chest Wall Compliance
Tissue destruction in emphysema?
Alveolar Simplification
Loss of entire alveoli, replaced by big open spaces
Clinical: Emphysema
Cause
Compliance
FRC
Gas Transfer
Unchecked loss of elastic tissues
Compliance increase (softer, easier to inflate)
FRC = Larger (loss of tissue opens space up)
Gas Transfer = Decreased (you’re losing alveoli)
Centrilobular vs Panacina Emphysema
- Centrilobular - Most Common, central portion of secondary lobules, superior portion, spreads peripherally; cigarettes/chemicals; upper half of lungs
- Panacinar - Lower half of lungs; AAT deficiency/Ritalin Lung;
Explain the PV Curve for Lung Volume and Pressure?
What can increase or decrease this curve (or its slope) + examples?
- Non linear; Slope = Compliance (ΔV / ΔP)
- Compliance α 1/Stiffness
- Decrease in Compliance: Stiff Lungs
- Fibrosis - More difficult to inflate
- Decreased Surfactant
- Removal of one lobe (or lung)
- Obesity
- Pulmonary vascular congestion (destruction of surfactant)
- Increase in Compliance: Soft lungs
- Emphysema
- Age (loss of elastic fibers)
Where is air velocity highest during expiration?
- ΔP α Flow Rate (Q)
- Greatest Flow Rate = Large Airways (also greatest resistance)
- Lowest Flow Rate = Small Airways (also least resistance)
Why is the airway normally held open during Passive Exhalation?
- Negative Intrapleural Pressure, Positive Airway Pressure creates expanding force
- Diaphragm relaxed, Volume Decreases and Pressure Increases (intrapleural)
- Airway subjected to expansile forces during normal exhalation (passive)
If you decrease airway diamter (Dynamic Compression) by 50%, how much does resistance increase?
Decrease by 1/2
Resistance α 1/r4
24 = 16
Increase Resistance by 16-fold
