Figure 75-1 Schematic representation of the pathogenesis of acute respiratory failure (ARF). The ventilatory pump is composed of the chest cage, ventilatory muscles, and nervous system elements involved in respiration. The pump primarily affects carbon dioxide excretion (CO₂ ). The lung involves the elements that allow inspired gas to exchange with pulmonary blood flow and primarily affects blood oxygenation (O₂ ). The large arrow from lung to pump represents the finding that lung disease often increases the work of the pump.