The Pressure - Volume Diagram of the Thorax and Lung 1 Hermann

It is remarkable that physiologists have paid so little attention in the past to the mechanics of breathing that no adequate data are now on record concerning the pressure-volume characteristics of the chest and lungs in normal men. The literature contains innumerable investigations of the various fractions of the lung volume and the vital capacity and also a number of observations concerning the positive and negative pressures that can be exerted but these two sets of data have not been correlated. There is little indication of how the vital capacity or other lung volumes vary with pressures nor, conversely, of how the pressures vary with the volume at which they are developed. Likewise there is little information concerning the relaxation pressures at different lung volumes and the relation between these data and the venous pressure. In this paper data are presented concerning the positive and negative pressures which can be produced by voluntary effort, and a diagram which gives a comprehensive picture of all these mechanical factors. Since completing this work we have discovered similar diagrams from papers by Rohrer (1916) and Senner (1921) each based upon measurements on a single individual as well as a partially similar effort by Jacquet (1908) and Bernouilli (1911). Three types of measurement were used for the pressure-volume diagram of the lung : (1) maximum expiratory and inspiratory pressures at different lung volumes, (2) relaxation pressures at different lung volumes, (3) vital capacities, tidal air, and inspiratory and expiratory reserves at different lung pressures. METHODS. (1) M aximum inspiratory and expiratory pressures. Measurements were made with a recording mercury manometer connected to a one hole rubber stopper cut to fit one nostril. The other nostril was held closed while the subject expired or inspired with maximum force. The nose was used in preference to the mouth in order to avoid all possibility of using the cheeks. It was found to be important to keep the subject from bending over in his effort to