Term
| What are the 3 major pathophysiological categories of restrictive disorders? |
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Definition
All involve decrease in Vt, FRC, RV, TLC and VC.
1) Increased elastic recoil (opposite of emphysema)
- insterstial disease and pulmonary fibrosis
2) Limiting expansion of chest wall
- kyphoscoliosis, morbid obesity, and massive ascites
- decrease equilibrium volume
3) Impaired respiratory muscle function (Normal FRC)
= CNS, Peripheral nerves, NMJ or muscular disease |
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Term
| What is the affect of interstitial inflammation and fibrosis on gas exchange in pulmonary fibrosis? |
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Definition
1) Decreased perfusion of diseased regions and increased perfusion of spared regions (V-Q mismatch with drop is PAO2 and increased AA gradient)
2) With capillary damage, CO increases in spared regions and there is less residency time for gas exchange
3) Increase in Vd and decrease in Vt increase Vd/Vt ratio, which leads to increased PCO2 (see hyperventilation) |
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Term
| Why might a patient with pulmonary fibrosis be hyperventilating? |
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Definition
1) V/Q mismatching increases Vd and decreases Vt, leading to increased Vd/Vt and increased PCO2
2) To compensate for respiratory acidosis, patient breathes harder. |
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Term
| How do disorders affecting the chest wall and the respiratory muscles impair gas exchange? |
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Definition
1) Low Vt may cause focal atalectasis of lung parenchyma, leading to V/Q mismatch, shunt and arterial hypoxemia
2) PCO2 may also increase because of excessive load or impaired function. |
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Term
| What PFT results do you see in restrictive lung disease? |
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Definition
Decreased FEV1, FVC with NORMAL/ELEVATED FEV1/FVC
1) FEV1 decreases because of low VC (contrast with high VC in obstructive)
2) FEV1/FVC is normal, because their is no obstruction to expiration (in fact, increased elastic recoil might even make it faster!).
3a) FRC and RV are low in parenchymal disease
3b) FRC is normal and RV is high in muscle disease |
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Term
| How can you distinguish between interstitial restrictive lung disease, restrictive chest wall disorders and restrictive lung disease due to respiratory muscle dysfunction based upon PFT? |
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Definition
BOTH will have decreased FVC, FEF25-75 and FEV1, with normal/increased FEV1/FVC ratio (>0.7).
BOTH will have decreased TLC and normal DLco
1) Interstitial and Chest wall disorders have
- Low FRC and low RV
2) Muscle disorders have
- Normal FRC and high RV |
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Term
| What is the pathophysiological basis for dyspnea and exercise limitation in interstitial restrictive lung disease? |
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Definition
Interstitial Thickening and Alveolar/Capillary Destruction
1) Interstitial thickening produces diffusion impairment and increased elastic recoil
- elastic recoil puts stress on muscles and decreases Vt
- diffusion impairment lowers PaO2 (hypoxemia)
2) Alveolar/capillary destruction produces V/Q mismatch (increased Vd/Vt and decreased PaO2) and diffusion impairment
3) Ultimately, decreased PaO2 and Vt, along with increased dead space ventilation from high V/Q units produces dyspnea and exercise limitation. |
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Term
| How can interstitial thickening produce dyspnea in interstitial restrictive disease? |
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Definition
1) Increased elastic recoil increases muscle load, leading to fatigue and decreased Vt
2) Diffusion impairment drops PaO2 |
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Term
| How can alveolar/capillary destruction produce dyspnea in interstitial restrictive disease? |
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Definition
1) Diffusion impairment drops PaO2
2) V/Q mismatch generates Vd and increases Vd/Vt, which increases PCO2 and drops PaO2 |
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Term
| How is emphysema different from pulmonary fibrosis? |
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Definition
Emphysema DECREASES elastic recoil, increasing expiration time and increasing VC and TLC
Pulmonary fibrosis INCREASES elastic recoil, decreasing expiration time and decreasing VC and TLC |
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Term
| What interstitial disorders cause increased elastic recoil? |
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Definition
Interstitial thickening increases muscle work/stress to inspire and lowers VC, despite increasing the "force" drive expiration.
1) Idiopathic pulmonary fibrosis
2) Sarcoidosis
3) Pneumoconioses |
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Term
| What restrictive disorders limit chest wall expansion? |
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Definition
Look for normal FEV1/FVC and low RV and FRC
1) Obesity
2) Ascites
3) Kyphoscioliosis |
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Term
| What restrictive disorders are caused by respiratory muscle dysfunction? |
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Definition
Look for normal FEV1/FVC with normal FRC and high RV
1) CNS
2) Peripheral
3) NMJ
4) Muscle |
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Term
| Why is DLco unchanged in restrictive disease due to muscle dysfunction? |
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Definition
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