forced expiration

Examples of forced expiration in the following topics:

• Lung Capacity and Volume

  • The two most often used measurements are FVC (forced vital capacity) and FEV1 (forced expiratory volume in one second).
  • The inspiratory reserve volume is the extra space for air after a normal inspiration and the expiratory reserve volume is the extra air that can be exhalaed after a normal expiration.
  • RV: The amount of air left in the lungs after a maximal expiration.
  • The most widely used diagnostic application for lung capacities is the ratio between forced expiratory volume (FEV1) and forced vital capacity (FVC).
  • FEV1: The volume of air exhaled in one second of forced expiration.

• Aging and the Respiratory System

  • This forced expiration increases pressure across walls of airways and may lead to narrowing or even wheezing.

• Expiration

  • Exhalation (or expiration) is the flow of the respiratory current out of the organism.
  • While expiration is generally a passive process, it can also be an active and forced process.
  • There are two groups of muscles that are involved in forced exhalation.
  • Internal Intercostal Muscles: Muscles of the ribcage that help lower the ribcage, which pushes down on the thoracic cavity, causing forced exhalation.
  • Voluntary expiration is actively controlled.

• Chronic Obstructive Pulmonary Disease (COPD)

  • In COPD, the greatest reduction in air flow occurs when breathing out (during expiration), because the pressure in the chest tends to compress rather than expand the airways.
  • In theory, air flow could be increased by breathing more forcefully, increasing the pressure in the chest during expiration.
  • If the rate of airflow is too low, a person with COPD may not be able to completely finish breathing out (expiration) before he or she needs to take another breath.
  • The diagnosis of COPD is confirmed by spirometry, a test that measures the forced expiratory volume in one second (FEV1), which is the greatest volume of air that can be breathed out in the first second of a large breath.
  • Spirometry also measures the forced vital capacity (FVC), which is the greatest volume of air that can be breathed out in a whole, large breath.

• Inspiration

  • The force of the intrapleural pressure is even enough to hold the lungs open during inpiration despite the natural elastic recoil of the lung.
  • Eventually, the pressure inside the lung becomes less negative as the volume inside the lung increases, and when pressure and volume stabilize, the air movement stops, inspiration ends, and expiration (exhalation) will begin.
  • External intercostal muscles: muscles located in between the ribs that help the thoracic cavity (and thus pleural cavity) to expand during quiet and forced inspiration.

• Velocity and Duration of Muscle Contraction

  • The shortening velocity affects the amount of force generated by a muscle.
  • The force-velocity relationship in muscle relates the speed at which a muscle changes length to the force of this contraction and the resultant power output (force x velocity = power).
  • The force generated by a muscle depends on the number of actin and myosin cross-bridges formed; a larger number of cross-bridges results in a larger amount of force.
  • Though they have high velocity, they begin resting before reaching peak force.
  • As velocity increases force and power produced is reduced.

• Proprioceptor Regulation of Breathing

  • As inspiration stops, expiration begins and the lung begins to deflate.
  • The heart rate returns to normal during expiration when the stretch receptors are deactivated.

• Force of Muscle Contraction

  • The force a muscle generates is dependent on its length and shortening velocity.
  • The force-velocity relationship in muscle relates the speed at which a muscle changes length with the force of this contraction and the resultant power output (force x velocity = power).
  • The force generated by a muscle depends on the number of actin and myosin cross-bridges formed; a larger number of cross-bridges results in a larger amount of force.
  • As velocity increases force and therefore power produced is reduced.
  • Although force increases due to stretching with no velocity, zero power is produced.

• Pons

  • Within the pons is the pneumotaxic center, a nucleus that regulates the change from inspiration to expiration.

• Regulation of Water Output

  • Some fluid is lost through perspiration (part of the body's temperature control mechanism) and as water vapor in expired air, however these fluid losses are considered to be very minor.