Figure 17-14 The diagrams show the work done against elastic and airflow resistance separately and summated to indicate the total work of breathing at different respiratory frequencies. The total work of breathing has a minimum value at about 15 breaths/min under normal circumstances. For the same minute volume, minimum work is performed at higher frequencies with stiff (less compliant) lungs and at lower frequencies when airflow resistance is increased. (Redrawn with modification from Lumb AB: Pulmonary ventilation: Mechanisms and the work of breathing. In Lumb AB [ed]: Nunn's Applied Respiratory Physiology, 5th ed. London, Butterworths, 2000, p 128.)