ABSTRACT
Wall ace Fenn compared the performance of respiratory and limb skeletal muscles in situ, with regard to pattern of contraction, operating lengths, the extent of maximum shortening, and the force-velocity relationship (Fenn, 1963). He pointed out that the resting length of the respiratory muscles is set by the balance between the inward recoil of the lung and the outward recoil of the chest wall. Based on its dimensions, Fenn suggested that the diaphragm could shorten by 50%, in agreement with the Weber-Fick law. He developed equations for respiratory muscle contractile force as functions of both the velocity and the extent of muscle shortening. Fenn calculated diaphragmatic wall tension per unit of thoracic circumference, based on transdiaphragmatic pressure (P di) and thoracic cross-sectional area (TCSA). He calculated the volume swept by the diaphragm as the product of TCSA and diaphragmatic excursion. This chapter about the performance of the respiratory muscles in situ in intact animals and humans owes much to Fenn 's landmark review and insightful ideas.
