The strategy that the respiratory controller adopts in order to deliver a given VE depends upon a number of factors, especially in the presence of disease. Chapter 1 described how the respiratory controller most likely regulates ventilation and breathing pattern so as to keep the operating point of the blood at the optimum while using a minimum of energy (Priban & Fincham, 1965) Figure 2.1 illustrates how tidal volume changes as exercise intensity increases, placing it within the subdivisions of the lung volumes that are illustrated in Figure 2.1. Initially, during light exercise VT increases by the person exhaling more deeply, and utilizing the expiratory reserve volume, Inspiratory capacity Functional residual capacity