1.b Ventilation And Respiration Flashcards
What is the forced vital capacity (FVC) maneuver?
The forced vital capacity (FVC) maneuver occurs when one takes a maximal inspiration and then forcefully exhales, usually over a period of 6–12 seconds. This is the primary test used in spirometry.
What are compliance and elastic recoil? How do they affect the FVC? Give examples of disease conditions that affect compliance and recoil.
The mechanical properties of the lung include compliance and elastic recoil. Compliance is the degree of stiffness, or distensibility, of the lung tissue. When the lung is very stiff, as with asbestosis, increased pressure is required to change the volume. In this case, compliance is low. Therefore, compliance represents the ratio of volume change to pressure change.
Elastic recoil pressure, like a balloon, is greatest at maximum inflation. With conditions that produce pulmonary fibrosis, such as asbestosis and silicosis, compliance of the lung is reduced and elastic recoil is increased. In conditions such as emphysema, where the lung shows increased compliance (floppiness), there is less elastic recoil.
How does airflow resistance affect the FVC? Give examples of disease conditions that affect airflow.
Airflow resistance is determined by the number, length, and cross-sectional area of the conducting airways. Remember that as the diameter of the conducting airways decreases, the total cross-sectional area of the airways increases. Thus, resistance to airflow actually decreases. However, when you forcefully inhale, intrathoracic pressure increases, which causes narrowing of the airways and a subsequent increase in airway resistance on expiration.
In other words, when you inspire maximally, your normal lung tissue exerts maximum elastic recoil at the end of inspiration. Then, as you forcefully exhale, airway resistance increases and elastic recoil is diminished.
Diseases that affect airflow include emphysema, asthma, and chronic bronchitis. Because of increased airflow resistance on expiration, the flow rate is decreased. In other words, an affected lung can’t exhale the air as quickly as a normal, healthy lung can.
