Mitral and aortic blood flows during spontaneous respiration in dogs

Left sided hemodynamic events during respiration remain a controversial subject. Left ventricular (LV) hemodynamic events were evaluated during obstructed and partially obstructed inspiration in anesthetized dogs acutely instrumented with mitral (Qm) and ascending aortic (Qa) flow probes. This allows classification of the inspiratory decrease in LV stroke volume as either a diastolic event (e.g., ventricular interdependence) in which case the LV inflow volume (integral of Qm) should decrease before the LV outflow volume (integral of Qa), or a systolic event (e.g., afterload or contractility) in which case outflow (integral of QA) should decrease before inflow (integral of Qm). During either unobstructed (n =8) or partially obstructed (n = 5 spontaneous ventilation, Qm reached both its inspiratory minimum and expiratory maximum prior to the associated minimum and maximum values for integral of in 80% or more of the respiratory cycles. Thus, a diastolic event dominates both in reducing the subsequent LV outflow during the expiratory increase in intrathoracic pressure. However, because a diastolic event did not occur first at all times, a systolic event must occur first at all times, a systolic event must also be present. If a rapid change in intrathoracic pressure occurred during diastole, integral of Qm invariably immediately increased. If a rapid in intrathoracic pressure occurred during systole, integral of Qa could change independently of the preceding integral of Qm. Both systolic and diastolic mechanisms contribute to the inspiratory fall in LV output. These mechanisms will not be clearly delineated without evaluating the effects of intrathoracic pressure within a single cardiac cycle.