Statics Volumes Capacities, Compliance, and Surface Tension

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🌱 來自: Huppert’s Notes

Statics VolumesCapacities, Compliance, and Surface Tension🚧 施工中

Statics: Volumes/Capacities, Compliance, and Surface Tension

•   Volumes and Capacities:

-   Definitions (Table 2.1)

TABLE 2.1 • Volumes and Capacities

-   Changes in pathologic states (Figure 2.3)

FIGURE 2.3: Lung volumes and capacities in health and disease. A) The four components of volume in the lung: Tidal volume (TV), expiratory reserve volume (ERV), inspiratory reserve volume (IRV), and residual volume (RV), as well as capacities which are measurements of two or more volumes. Functional residual capacity (FRC) = ERV + RV. Inspiratory capacity (IC) = TV + IRV. Vital capacity (VC) = ERV + TV + IRV. TLC (total lung capacity) is the volume of the lungs at maximal inflation. B) The changes in residual volume (RV), vital capacity (VC), and total lung capacity (TLC) in obstructive and restrictive lung diseases.

•   Obstructive lung disease (e.g., asthma, emphysema): ↑TLC, FRC, RV; ↓↓FEV1, ↓FVC, FEV1/FVC < 0.7

•   Restrictive lung disease (e.g., fibrosis): ↓TLC, FRC, RV; ↓FEV1, ↓↓FVC, ↑ or normal FEV1/FVC

•   Compliance: C = ΔV/ΔP

V = volume, P = pressure

-   Compliance = Filling term; ability of lungs to stretch

-   Elastance = Expiration term; ability of lungs to collapse from stretched position

-   Obstructive diseases = ↑ Compliance, ↓ Elastance; Restrictive diseases = ↓Compliance, ↑Elastance

•   Surface tension: P = 2T/r

P = pressure, T = surface tension, r = radius

-   Law of Laplace: Large alveoli remain open due to high radius, and small alveoli collapse, causing atelectasis

-   Surfactant:

•   Increases surface tension → Decreases pressure → Increases compliance and reduces alveolar collapse

•   Produced by Type II alveolar cells: Choline + diacylglycerol → dipalmitoylphosphatidylcholine (DPPC)

•   Surfactant contains lecithin; if lecithin:sphingomyelin ratio ≥ 2:1 in amniotic fluid = lung maturity

-   Hysteresis: Compliance (i.e., the slope of a pressure/volume curve) changes with inspiration and expiration; compliance is lower during expiration and at extreme volumes (i.e., very full lungs or very empty lungs)

FIGURE 2.4: Transpulmonary pressures by lung volume in health and disease. Transpulmonary pressure is the pressure across the lung that produces pulmonary ventilation. It is equal to the difference between pleural and alveolar pressure. At a given lung volume, transpulmonary pressures are higher in restrictive disease and lower in obstructive disease.