Fig. 3. Relation between changes in cardiac output measurements obtained by thermodilution technique and those obtained by carbon dioxide rebreathing when positive end-expiratory pressure was increased. Ventilatory settings are volume-controlled and 12 ml/kg tidal volume. When positive end-expiratory pressure was increased from 4.2 to 14.0 cm H2O in average, cardiac output measurements obtained both by thermodilution technique and by carbon dioxide rebreathing decreased in almost all patients. Each point corresponds to a different patient. Note that both values moved in identical directions in all patients but one. Equations and result curves for linear regression analysis are also shown.