Tidal Breathing Analysis

After completing this article, readers should be able to: 1. Explain why tidal breathing mechanics differ between infants and adults. 2. Describe the results of compensatory mechanisms used in infancy. 3. Explain the value of the ratio of time to peak tidal expiratory flow to expiratory time and how it can be performed. 4. Link the direction of movement of the rib cage and abdominal wall on a Konno-Mead plot with the cause of muscle failure. 5. Explain why respiratory inductance plethysmography values do not correlate well with those obtained with a pneumotachograph. Tidal breathing refers to inhalation and exhalation during restful breathing. The range of tidal breathing is determined both by the depth of inspiration and by the end point of passive exhalation at functional residual capacity (FRC), the point at which the outward elastic recoil of the rib cage (RC) is balanced by the inward elastic recoil of the lungs (Fig. 1). Although tidal breathing often is maintained within a relatively narrow range in a quietly breathing person who does not have lung disease, lung disease not only can change the normal character of breathing, but it can create change within a series of breaths. Therefore, for patients who have respiratory disease, it would be helpful to identify these alterations and follow their change during therapy. The breathing pattern should be altered as little as possible during measurement. Before discussing the methods of studying tidal breathing, understanding the mechanics of tidal breathing is important. Figure 1. Functional residual capacity (FRC) is the volume in respiration at which the outward elastic recoil of the rib cage is balanced by the inward elastic recoil of the lungs. ### Tidal Thoracic Motion Volume excursion during tidal breathing is initiated and primarily determined by downward diaphragmatic motion, which creates the negative intrathoracic pressure that drives inspiration. There also is a series of other …