Transit time heterogeneity of bolus flow through the heart and lungs in patients with left-to-right intracardiac shunt

Knowledge of the contributions of transit time heterogeneity to the cardiop ulmonary system is important for understanding cardiopulmonary function in patients with intracardiac shunt. We determined the heterogeneity of blood transit times occurring between the right atrium and the left ventricle. Ei ghty two patients with suspected left-to-right shunt were investigated with first-pass Tc-99m-labelled red blood cell radiocardiography at supine rest . Forty two of them had a pulmonary-to-systemic how ratio (Qp:Qs) of less t han 1.2 and they served as a control group. The remaining study subjects ha d a ep:es ratio of 1.7 +/- 0.3 (mean +/- SD), The patients with shunt had s ignificantly greater (p < 0.001) heterogeneity of transit times (49 +/- 9%) than in the controls (39 +/- 7%). Overall heterogeneity of cardiopulmonary transit times in patients with shunt showed a curvature relationship; the highest values were centred in patients with moderate to severe shunt (1.5 < Qp:Qs < 2.5). The results suggest that the increased heterogeneity of tra nsit times mainly occurs within the pulmonary capillary bed in patients wit h intracardiac shunt. This is probably due to the recruitment of the open c apillaries without vessel distension.