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The sections in this article are: Lung Volumes Volume‐Pressure Relations of Respiratory System During Relaxation Total Respiratory System Chest Wall and Lung Effects of Gravity and Posture Changes Throughout Life Span Volume‐Pressure Relations of Respiratory System During Static Muscular Efforts Alveolar Pressure Abdominal and Thoracic Pressures Factors Limiting Volume Extremes Upper Volume Extreme Lower Volume Extreme

The abdominal (gastric) pressures as well as the intrathoracic pressures were recorded in man during various respiratory maneuvers such as complete relaxation, moderate inspiratory and expiratory efforts, maximal inspiratory and expiratory efforts, and during maximal abdominal pressure efforts. Each maneuver was systematically carried out at various lung volumes. From these measurements it is possible to determine the transdiaphragmatic pressure difference and thus obtain information concerning the activity of the diaphragm during these various maneuvers. During relaxation pressure maneuvers and during moderate expiratory pressure efforts the transdiaphragmatic pressure difference is zero. During maximal inspiratory efforts the pressure is about 100 cm H2O more positive on the abdominal side than on the thoracic side of the diaphragm regardless of the lung volume. A similar difference is found during a maximal abdominal contraction whether during this maneuver the alveolar pressure is zero or whether a high alveolar expiratory pressure is developed. These findings are discussed in terms of reflex contractions of the diaphragm which limit the pressures and volumes that can be obtained in the lung. Submitted on May 2, 1960

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