ABSTRACT
One of the most exciting human dreams has been the exploration and conquest of the underwater world. However, for centuries, underwater excursions have been limited to depths of a few meters. A compilation of the processes used by divers of old, including rigid diving bells, hypothetical respiratory apparatus, and breath-hold diving, may be found in De Re Militari by Vegece (sixteenth century). A large number of physiological problems associated with the investigation of the underwater environment take place during breath-hold diving. Until the experiments with barometric pressure by Pascal (L' equilibre des Liqueurs, 1648), the consequences of elevated ambient pressure on an immersed individual, principally on chest wall mechanics, were totally ignored. Based on the knowledge of the necessity to equilibrate pressure between the inspired air and the medium surrounding the chest, several inventors proposed models for diving helmets connected via an umbilicus to a pump delivering compressed air (Freminet, 1774; K.lingert, 1797; Siebe, 1819).
