The relationship between maximal ventilation, breathing pattern and mechanical limitation of ventilation

1. The extent to which the pattern of breathing at maximal ventilation in man is affected by the mechanical properties of the respiratory pump has been studied. 2. The maximal effort flow volume (MEFV) loop has been used to calculate the shortest possible inspiratory (TI) and expiratory (TE) durations associated with the highest ventilation for all tidal volumes (VT). These minimal TIS and TES hve been plotted on a VT-TI-TE diagram. 3. Such predicted minimal TIS and TES were compared with observed minimal values from five healthy subjects who tried to reach their maximal ventilations during three experimental conditions: maximal voluntary hyperventilation, rebreathing, and graded exercise. 4. We have found that exercise increases the maximal flows at all lung volumes and confirmed that rebreathing has no such effect. 5. During hyperventilation the mechanical limits were followed closely for all VTS. During exercise and rebreathing the VT-TI and the VT-TE relationships showed a definite maximum of VT at submaximal ventilation in half the cases. The calculated minimal TIS and TES were approached but not reached. This indicates that maximal ventilation is not entirely limited by the mechanical properties of the respiratory pump, but that mechanical factors influence the regulation of breathing pattern when ventilation approaches the maximal capacity of the respiratory pump.