Lung capacity and study lung functions

Abstract

Lung capacities and lung volumes refer to the volume of air associated with different phases of the respiratory cycle. Some important lung capacities are defined as follows. •Tidal Volume (TV) is the volume of air that is inhaled or exhaled in a single normal, resting breath. •Vital capacity (VC) is the maximum volume of air that a person can exhale from the lungs after maximum inhalation, which can be measured with a spirometer. In combination with other physiological measurements, the vital capacity can help make a diagnosis of underlying lung disease. •Residual Volume (RV) is the amount of gas remaining in the lung at the end of a maximal exhalation. •Total Lung Capacity (TLC) is the amount of gas contained in the lung at the end of a maximal inhalation. It is composed of VC and RV. The total lung capacity depends on the person’s age, height, weight, sex, and normally ranges between 4 to 6 L. •Functional Residual Capacity (FRC) is the volume of air present in the lungs, specifically the parenchyma tissues, at the end of passive expiration. Various attempts have been made to study lung functions. Invasive methods such as using surgically implanted markers to study lung mechanical functions have been discussed. Standard CT imaging has been commonly used to help diagnose and evaluate lung diseases because it can provide high-resolution images of the lung structures. But it is static and we can not assess lung ventilations from a single CT image. Another imaging modality which is able to directly assess lung function is xenonenhanced CT. It measures regional ventilation by observing the gas wash-in and wash-out rate on serial CT images. Imaging allows non-invasive study of lung behavior and image registration can be used to examine the lung deformation. Pulmonary diseases may change the tissue material and thus change the mechanical properties of parenchymal tissues. An example of obstructive pulmonary diseases, emphysema, is a long-term, progressive disease of the lungs that primarily causes shortness of breath. In people with emphysema, the tissues necessary to support the physical shape and function of the lungs are destroyed. Since the destruction of alveoli makes these air sacs unable to hold their functional shape upon exhalation, emphysema is characterized by loss of tissue elasticity (increased compliance). Another example of restrictive pulmonary diseases, idiopathic pulmonary fibrosis (IPF), is a chronic, progressive form of lung disease characterized by fibrosis of the supporting framework (interstitium) of the lungs. The pulmonary fibrosis increase the lung tissue thickness and stiffness (reduced compliance), which leads to increased lung elastic recoil. Therefore, pulmonary diseases cause tissue material change, which results to its mechanical function change from normal tissue. Based on this fact, finding effective methods to understand ventilation patterns of lung parenchyma and quantify the regional lung mechanical function is desirable to help disease diagnosis.