Pulmonary mechanics. A unified analysis of the relationship between pressure, volume and gasflow in the lungs of normal and diseased human subjects.

Abstract A three-dimensional graphic representation of the mechanical aspects of pulmonary ventilation has been developed from experimental data obtained in man, in which transpulmonary pressure, respiratory flow and lung inflation have been uniquely related. The basic element of this representation is the isovolume pressure-flow curve. The behavior of a simple lung model is described to emphasize the general determinants of these isovolume pressure-flow curves. The broad inferences drawn from analysis of this model are applied to the pressure-flow-volume (P-F-V) relationship of the human lung. The three-dimensional surface representing the P-F-V relationship has had certain conceptual value. The concept of the α F-V curve evolved from consideration of this surface. This curve has been studied in man and found to have certain unique characteristics that suggest that it may become a valuable clinical tool. The α F-V curve is quite reproducible, is only moderately dependent upon effort, is essentially unaffected by wide variations in upper airway resistance, is determined by the physical properties and dimensions of the intrathoracic pulmonary system, is greatly altered in emphysematous subjects and is relatively easily obtained. In the light of this three-dimensional analysis it has been possible to evaluate a number of the commonly used indices of ventilatory mechanics. The interrelationship between these tests has been demonstrated and an understanding of their potential variability gained. Certain areas meriting further experimental exploration are suggested from considerations of the surface. It is not our intent to suggest that thorough study of ventilatory mechanics requires construction of such a surface for each person. Although certain limitations of the approach are stressed, it nevertheless has proved extremely useful in visualizing these three variables simultaneously.