| Summary: | In summary, the mechanical integration of ventricular and pulmonary actions is determined by a number of mechanisms including airway pressure, pleural and pericardial pressure, state of the interventricular septum, and others. After this brief review of essential features, we may discuss some aspects of the interactions between heart and lung function. Influence of Intrathoracic Pressure: The Importance of Transmural Pressure It is established that blood pressure, volume and flow rates in the lesser circula tion change during each respiratory cycle. The effects of intrathoracic (Pit) and pleural (P pi) pressures, and lung volumes, were recently described in terms of ventricular preload and afterload during normal breathing, hyperventilation, and the Valsalva and Muller maneuvers [4, 7, 8]. Still, many aspects remain unsettled, mainly because of technical difficulties related to the simultaneous recording of floating respiratory and circulatory events in the intact animal or in man [9]. Some confusion arises from the clinicians' unawareness of the role played by the transmural pressure (Ptm), being the pressure gradient between the lumen of a vessel or heart chamber and the surrounding tissues (Pit for the pulmonary arteries and veins, and Ppe for the heart). Yet, an undetected change of Plm may modify vascular caliber and resistance in the pulmonary district, regardless of any changes in vasomotor activity. Consequently, a change of vascular resistance concomitant with a change of Ptm is not a reliable index of pulmonary vasomo tricity
|
|---|