Work of breathing When there is increased gas flow resistance, the optimal respiratory rate decreases. This work (generally during the inhalation phase) is stored as potential energy which is recovered during exhalation. A pressure difference is required to overcome the frictional resistance to gas flow due to viscosity, and to provide non-elastic components of movement of the airway tissues to accommodate pulmonary volume change. Total work done against non elastic forces is 35% of total. Work is defined as a force applied over a distance. The SI unit of work is the Joule, equivalent to a force of 1 Newton exerted along a
Elastic energy of compressible fluids, and especially gases, demonstrates the essence of elastic energy with negligible complication. The simple thermodynamic formula: formula_2 where dU is an infinitesimal change in recoverable internal energy "U", "P" is the uniform pressure (a force per unit area) applied to the material sample of interest, and "dV" is the infinitesimal change in volume that corresponds to the change in internal energy. The minus sign appears because "dV" is negative under compression by a positive applied pressure which also increases the internal energy. Upon reversal, the work that is done "by" a system is the negative of the