This extra volume into the lung after a normal tidal inspiration is referred to as inspiratory reserve volume. Our patient (figure 3.1) returns to normal tidal breathing for two breaths before taking a full breath in, filling the lungs as much as they can. This also means that residual volume can never be measured with a spirometer. Even with maximal efforts, this volume cannot be exhaled, so at no point can the lung be fully emptied. Once a normal expiration is complete, however, the lung is far from empty, and when instructed, this patient (figure 3.1) breathes out as far as they can this excess that comes out the lung is referred to as the expiratory reserve volume.Įven at this point, however, some air remains in the lung, and this is referred to as residual volume. The amount of volume inspired during each breath is referred to as tidal volume. The initial part of the trace shows resting or “tidal” breathing. Let us work through the trace from left to right. Figure 3.1: Lung volumes detected by spirometry. This trace from a spirometer (figure 3.1) shows the change in lung volume as a patient breathes normally and then performs some specific maneuvers. Lung Volumesįirst let us look at lung volumes. We will then see how breathing pattern is generated to improve the efficiency of the lung and reduce the work of breathing. We will also begin to look at the work of breathing and what factors affect how easy or hard the lung is to inflate, that is, lung compliance. In this section we will look at some of the nomenclature for a variety of lung volumes and how these are clinically pertinent and can change in disease. Describe the ramifications of dead space on the pattern of breathing during hyperpnea. Describe the factors that determine lung compliance as the lung inflates from residual volume to total lung capacity.Describe the lung volumes that can be determined by spirometry.
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