Heart rate normalized pulmonary transit time (nPTT) is an indicator for global cardiac function and describes the relationship between pulmonary blood volume and stroke volume. The first study of this thesis indicates that nPTT measurement is practicable in healthy cats using echocardiography and the blood pool contrast agent Sonovue®.
It was the first study concerning nPTT in cats and it shows that contrast echocardiography is a safe and feasible technique in healthy cats. For determining the transit time of Sonovue® through the pulmonary circuit (pulmonary artery to left atrium) the right parasternal short axis view was used. The nPTT’s were calculated independently by three investigators with different levels of experience in echocardiography.
The observer’s experience had no influence on nPTT measuring results. In our population nPTT was 4.12 +/- 1.0 (mean +/- standard deviation). The median within-day variability for each observer was within reasonable limits for clinical purpose. The median interobserver variability across this population was 6.8 %. In our study no effect of age, body weight or gender on nPTT could be identified. In the second study nPTT, pulmonary blood volume (PBV) and stroke volume (SV) were measured in three groups of cats: Healthy cats (group 1), cats with asymptomatic cardiomyopathy (group 2) and cats with congestive heart failure (CHF) due to cardiomyopathy (group 3). Correlations between nPTT, PBV, SV, and echocardiographic variables were determined by univariate and multivariate analysis. The median nPTT in group 1, group 2 and group 3 were 3.63 (interquartile range (IQR) 3.20 to 4.22), 6.09 (IQR 5.0 to 7.02) and 8.49 (IQR 7.58 to 11.04), respectively. The values between these three groups were significantly different. The median pulmonary blood volumes in group 1, group 2 and group 3 were 27.94 ml (IQR 21.02 ml to 33.17 ml), 42.83 ml (IQR 38.46 ml to 50.36 ml) and 49.48 ml (IQR 38.84 ml to 64.39 ml), respectively. The pulmonary blood volume in group 2 and group 3 were not significantly different. SV, PBV and FS were significant predictors of nPTT. Both nPTT and LA: Ao (left atrial to aortic root ratio) had a high predictive value for the presence of congestive heart failure (AUC = 0,956). This thesis shows that nPTT is a useful clinical test for the existence of CHF in cardiomyopathic cats.
Higher nPTT-values in cats with cardiomyopathy were caused by both an increased pulmonary blood volume, and a decreased stroke volume. There was no significant difference between PBV in cardiomyopathic cats with and without CHF.