Pulmonology Flashcards
Where does surfactant come from
- type II pneumocytes synthesize pulmonary surfactant
What is tidal volume?
- Tidal volume (Vt) is about 500mL and includes the volume of air that fills the alveoli plus the volume of air that fills the airways
What is residual volume?
the volume of gas remaining in lungs after maximal forced expiration. about 1200mL. Can’t be measured by spirometer.
What is inspirational capacity (IC)?
tidal volume plus inspiratory reserve volume - about 500mL plus 3000mL for 3500mL total
What is the functional residual capacity (FRC)?
expiratory reserve volume (1200mL) plus residual volume (1200mL) for 2400mL total. FRC is the volume remaining in the lungs after a normal tidal volume is expired. Called the equilibrium volume of lungs
What is vital capacity (VC)?
inspiratory capacity plus expiratory reserve volume. approx 4700mL (3500+1200). VC is the volume that can be expired after maximal inspiration. Value increases with body size, male gender, and physical conditioning. Decreases w age.
What is total lung capactiy (TLC)?
all lung volumes - vital capacity plus residual volume for about 5900mL (4700+1200). Includes residual volume, so can’t be measured by spirometry.
How do we measure FRC?
helium dilution or body plethysmograph
How do you sample alveolar air?
sample end expiratory air. First air exhaled is dead space air that has not undergone gas exchange
What is anatomical dead space?
volume of conducting airways that don’t participate in gas exchange - nose, mouth, trachea, bronchi, bronchioles (does not include respiratory bronchioles or alveoli)
What is physiologic dead space?
total volume of lungs that doesn’t participate in gas exchange. includes anatomic dead space plus any functional dead space of alveoli. In normal people, physiological and anatomical dead space are about equal.
What is a ventilation/perfusion defect?
cause of functional dead space. mismatch of ventilation and perfusion where ventilated alveoli are no perfused by pulmonary capillary blood. In healthy people, functional dead space is minimal.
What are elastic forces?
Lungs & chest wall are elastic structures that resist stretch
They passively return to state of equilibrium after they are expanded or compressed
Elastic properties of the lungs or chest wall determine elastance
What are resistive forces?
Viscosity of inhaled air Airway diameter (flow-dependent)
What forces combine to create net negative intrapleural pressure?
Lungs tending to collapse inward and chest wall springing outward - opposing elastic forces.
What is compliance?
A measure of stiffness. A change in volume per unit change in pressure (delta V/delta P). Inversely correlated with elastance.
What is hysteresis?
A feature of the PV loop for an air filled lung where the slope is different for expiration vs. inspiration due to difference in compliance. The lung is more compliant on expiration than inspiration. Surface tension at liquid-air interface of lung causes hysteresis
Surface tension = Force of attraction between liquid molecules at the surface > force between liquid and air
What is the Law of Laplace?
P=2T/r where T is surface tension and r is radius. Describes collapsing pressure on alveolus. Small alveolus will have high collapsing pressure/inward force
Why surfactant?
Breaks up surface tension so we can keep alveoli small, reduces collapsing pressure, and improves compliance. AMPHIPATHIC
When is surfactant first produced?
after 24 weeks gestation
How can you change functional rsidual capacity?
By exhaling forcefully. Can change FRC, can’t change residual volume.
how does emphysema change lung compliance? how about fibrosis?
Emphysema: increase in lung compliance: due to loss of elastic fibers (decrease in lung elastance)
Fibrosis: decrease in lung compliance: due to excessive stiffness of fibrotic tissue
Where in the respiratory tract is resistance the highest?
medium sized bronchi
How does airways resistance change with disease?
Airways are tethered by the surrounding lung tissue, thus airway diameter varies with lung volume. Loss of surrounding lung parenchyma, as occurs in emphysema, will lead to loss of radial traction on the airways, narrowing them, increasing airway resistance (COPD) . Pulmonary fibrosis increases radial traction, which may result in larger airway diameters at a given lung volume and decreased airway resistance