[Which moments in the respiratory cycle have the most influence on right ventricular dynamics?]

The performance of the right heart during respiratory activity has mostly been studied in terms of changes in flow and pressure in pulmonary circulation. The aim of this study was to identify which moments of the respiratory cycle exert the greatest influence on right ventricular dynamics. Thus, the behaviour of the right ventricular systolic time intervals and pulmonary artery pressures, expressed both as intravascular (Piv) and transmural (Ptm), were investigated to this end. Investigations were carried out on 10 anesthetized spontaneously breathing beagle dogs using high-fidelity pressure transducers (MPC 500, Millar Instr.) and by making use of a computerized system of signal recording and analysis. Changes in right ventricular systolic time intervals were evident during transition from inspiration to expiration and at the beginning of expiration. In fact, compared to spontaneous post-expiratory pause values, the so-called Rapid Ejection and Slow Ejection Phases, and therefore the Total Ejection Period, were significantly shortened (p less than 0.01 for both) only at early expiration, whereas during the same phase of the respiratory cycle the Isovolumetric Contraction Time and the total Pre-ejection Period were significantly prolonged (p less than 0.01 for both). During the transition from inspiration to expiration, the right ventricular systolic "plateau" very often presented an ascending slant, i.e., reaching maximum pressure in late instead of early systole, as usually observed in the other moments of the respiratory cycle.(ABSTRACT TRUNCATED AT 250 WORDS)