Restrictive lung disease basics Flashcards
Definition of restrictive physiology
TLC <80% predicted
compare compliance and airway resistance in obstructive and restrictive lung diseases
obstructive: increased complianc (less stiff) and increased resistance. Restrictive: decreased compliance (more stiff) and decreased resistance
What two components determine total pressure to begin airflow and which parts do obstructive/restrictive disease affect
Ptotal= Pressure to overcome elastic recoil of lung + pressure to overcome resistance to airflow. Obstructive disease primarily increases resistive pressure. Restrictive disease increases the work required to distend the lung (elastic recoil)
Equation for elastance
elastance (1/total compliance) = 1/ lung compliance + 1/ chest wall compliance
Mechanisms that change lung compliance
decreased lung compliance can occur via 1. Increased thickness of the lung interstitium 2. Increased lung water 3. increased alveolar surface tension
Causes of increased thickness of lung interstitium
increased deposition of elastic/connective tissue in many forms of chronic interstitial lung disease, excessive collagen and elastin production by lung fibroblasts in response to injury and increase in inflammatory cells in interstitium.
Causes of increased lung water and how it decreases compliance
Congestive heart failure- fluid escapes the capillary and fills the interstitium (which thickens the interstitium and increases elasticity. Next, fluid fills the alveoli which disrupts the surfactant and increases surface tension
How does increased alveolar surface tension reduce lung compliance and causes of increased alveolar surface tension
Increases in alveolar surface tension tend to cause alveoli to collapse and remain closed which reduces compliance. Caused by pulmonary edema (water dilutes surfactant) or abnormal surfactant production (respiratory distress syndrome)
lung volumes and P-V curve in restrictive lung disease
TLC, FRC and RV are all decreased. The PV curve is flatter and shifted down
airflows in restrictive disease
Airflows for any given volume are higher than normal b/c airways are dilated (due to traction applied from adjacent parenchyma called traction bronchiectasis). FEV/FVC ratio is normal and peak expiratory flow is low.
Gas exchange in restrictive disease
Gas exchange is impaired b/c decreased lung volumes with subsequent decrease in alveolar capillary surface area. Diffusion can also be impaired as the thickness of the alveolar-capillary wall increases (most prominent during exercise when capillary transit time decreases)
Mechanisms that decrease chest wall compliance
Burns, obesity, kyphoscoliosis, ankylosing spondylitis, respiratory muscle weakness, pleural fibrosis/thickening, pleural effusion
How do abnormalities of chest wall affect lung volumes and airflow, P-V curve and gas exchange
decreased lung volumes (including FRC) and normal airflow. P-V curve will have normal slope but down shifted. Gas exchange is normal functioning, but reduced lung volume reduces DLCO b/c alveolar capillary membrane surface area is reduced
How do you distinguish btw restrictive physiology caused by lung disease vs chest wall pathology
Pressure-volume curve: Manometer is inside the chest wall so any restrictive effects of chest wall are eliminated. Restriction due to chest wall (restrictive physiology) will have a similar slope to normal, but down shifted. Restriction due to lung disease will have a decreased slope plus down shifted. Also DLCO/Va is reduced in restrictive disease but not in restrictive physiology
Describe PFTs in someone with combination of obstructive and restrictive lung disease
Decreased lung volumes (indicative of restrictive disease) PLUS decreased FEV/FVC (obstructive). Usually combo leads to markedly decreased DLCO
