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

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Abstract
The extent to which the pattern of breathing at maximal ventilation in man is affected by the mechanical properties of the respiratory pump was studied. The maximal effort flow-volume (MEFV) loop was used to calculate the shortest possible inspiratory (TI) and expiratory (TE) durations associated with the highest ventilation for all tidal volumes (VT). These minimal TI and TE were plotted on a VT-TI-TE diagram. Such predicted minimal TI and TE were compared to observed minimal values from 5 healthy subjects who tried to reach their maximal ventilations during 3 experimental conditions: maximal voluntary hyperventilation, rebreathing and graded exercise. Exercise increased the maximal flows at all lung volumes. Rebreathing had no such effect. During hyperventilation the the mechanical limits were followed closely for all VT. 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 TI and TE 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 the breathing pattern when ventilation approaches the maximal capacity of the respiratory pump.