Evaluation of cardiac function using heart-lung interactions
Heart lung interactions can be used clinically to assist in the evaluation of cardiac function. Application of these interactions and understanding of the physiology underlying them has formed a focus of research over a number of years. The changes in preload induced by changes in intrathoracic pressure (ITP) with the respiratory cycle, have been applied to form dynamic tests of fluid responsiveness. Pulse pressure variation (PPV), stroke volume variation (SVV), end expiratory occlusion test, pleth variability index (PVI) and use of echocardiography are all clinical assessments that can be made at the bedside. However, there are limitations and pitfalls to each that restrict their use to specific situations. The haemodynamic response to treatment with continuous positive airway pressure (CPAP) in left ventricular failure is explained by the presence of heart lung interactions, and works predominately through afterload reduction. Similarly, in other disease states such as acute respiratory distress syndrome (ARDS), the effects of a change in ventilation can provide information about both the cardiac and respiratory system. This review aims to summarise how assessment of cardiac function using heart lung interactions can be performed. It introduces the underlying physiology and some of the clinical applications that are further explored in other articles within the series.