CO 2 diffuses into the alveoli and is exhaled. In the capillaries, oxygen binds to hemoglobin in erythrocytes or dissolves into the plasma (oxygenation). The gases diffuse across the barrier following pressure gradients. Gas exchange occurs via simple diffusion across the blood-air barrier. Diseases that affect the perfusion (e.g., pulmonary embolism) or ventilation (e.g., foreign body aspiration) can cause a V/Q mismatch. The Euler-Liljestrand mechanism regulates the perfusion of nonventilated alveoli: if a lung section is perfused but not ventilated, there will be a drop in the oxygen concentration in the blood, resulting in hypoxic vasoconstriction. The ventilation-perfusion ratio is higher in the apex of the lung than at its base. Perfusion of the pulmonary capillaries is closely regulated to match ventilation in order to maximize gas exchange. The physiologic dead space is the volume of inspired air that does not participate in gas exchange. Ventilation is the movement of air through the respiratory tract into (inspiration) and out of (expiration) the respiratory zone ( lungs). VC-Vital capacity the largest volume measured on complete exhalation after full inspiration.The main function of the respiratory system is gas exchange (O 2 and CO 2). TLC-Total lung capacity the volume of air in the lungs at maximal inflation. IC-Inspiratory capacity the maximal volume of air that can be inhaled from the resting expiratory level. V T -Tidal volume the volume of air inhaled or exhaled during each respiratory cycle.įRC-Functional residual capacity the volume of air in the lungs at resting end-expiration. RV-Residual volume the volume of air remaining in the lungs after a maximal exhalation. IRV-Inspiratory reserve volume the maximal volume of air inhaled from end-inspiration. These tests can further define lung processes but require more sophisticated equipment and expertise available only in a pulmonary function laboratory.įVC-Forced vital capacity the total volume of air that can be exhaled during a maximal forced expiration effort.įEV 1-Forced expiratory volume in one second the volume of air exhaled in the first second under force after a maximal inhalation.įEV 1/ FVC ratio-The percentage of the FVC expired in one second.įEV 6 -Forced expiratory volume in six seconds.įEF 25–75%-Forced expiratory flow over the middle one half of the FVC the average flow from the point at which 25 percent of the FVC has been exhaled to the point at which 75 percent of the FVC has been exhaled.ĮRV-Expiratory reserve volume the maximal volume of air exhaled from end-expiration. ![]() In some patients, additional tests such as static lung volumes, diffusing capacity of the lung for carbon monoxide, and bronchodilator challenge testing are needed. If a ventilatory pattern is identified, its severity is graded. Next, the determination of an obstructive or restrictive ventilatory patten is made. The first step is determining the validity of the test. ![]() ![]() A simplified and stepwise method is key to interpreting spirometry. ![]() However, interpreting spirometry results can be challenging because the quality of the test is largely dependent on patient effort and cooperation, and the interpreter's knowledge of appropriate reference values. Technology advancements have made spirometry much more reliable and relatively simple to incorporate into a routine office visit. Spirometry is a powerful tool that can be used to detect, follow, and manage patients with lung disorders.
0 Comments
Leave a Reply. |