Interaction Between the Heart and Lungs
The heart and the lung (H-L) interaction can be defined as the effects of airway pressure and volume on venous return, ventricular function and arterial outflow. The main reason for the heart and lungs to interact physiologically is that they share the sa
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Fabio Guarracino and Rubia Baldassarri
16.1 Introduction The main reason for the heart and lungs to interact physiologically is that they share the same space within the chest (Fig. 16.1), and their physiologies are both submitted to and driven by the interaction among different pressures (viz. airways, intrathoracic and intracardiac pressures). The heart and lung (H-L) interaction can be defined as the effects of airway pressure and volume on venous return, ventricular function and arterial outflow [1]. Such effects are summarised in Fig. 16.2. H-L interactions are different in healthy and diseased conditions and between spontaneous and positive pressure ventilation. Under normal conditions and in spontaneous ventilation, the H-L interaction is subtle. In the presence of cardiac and respiratory disease states, or when the compensatory reserve is limited, such as in critically ill patients, and under positive pressure ventilation (either invasive either non-invasive), H-L interactions are elicited, and the cardiovascular function can be affected by respiratory changes. As ARDS (Acute Respiratory Distress Syndrome) pathology involves both alveoli and pulmonary capillaries, as reported long ago [2], it represents a typical predisposing situation for the H-L interaction to influence the circulation.
F. Guarracino (*), R. Baldassarri Department of Anaesthesia and Critical Care Medicine, Azienda Ospedaliero Universitaria Pisana, Via Paradisa, 2, Pisa 56123, Italy e-mail: [email protected] © Springer International Publishing Switzerland 2017 D. Chiumello (ed.), Acute Respiratory Distress Syndrome (ARDS), DOI 10.1007/978-3-319-41852-0_16
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F. Guarracino and R. Baldassarri
Fig. 16.1 A CT scan of human chest showing the close spatial relationship between the heart and the lungs
Fig. 16.2 Effects of increase in airway pressure and volume on the heart
Effects of increase in airway pressure and volume Right ventricle Decreased preload Increased afterload Reduced contractility Compression of heart in cardiac fossa
Left ventricle Decreased preload Decreased compliance Variable effects on (autonomous nervous system control of) contractility Decreased afterload compression of heart in cardiac fossa
16.2 H -L Interactions: The Impact of Cardiorespiratory System Characteristics The description of the anatomy and function of the heart and lungs is basic knowl edge that is beyond the scope of this chapter. Therefore, only some key aspects of the cardiorespiratory system relevant to the H-L interaction issue of the ARDS patient will be addressed here. The human heart shows the interesting combination of physiologically consisting of a double pump system where the two pumps, the left and right ventricles, work in series, with each pump ejecting the blood received from the other pump, and anatomically consisting of two pumps sharing the interventricular septum and the pericardium, thus being anatomically in parallel (Fig. 16.3). One more important aspect to underline in this contest is the anatomic and funct
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