EVALUATION OF PULMONARY ARTERY STIFFNESS IN ASTHMA AFFECTED HORSES

The present research evaluated Pulmonary Artery Stiffness (PAS) and right ventricular systolic time intervals (RVSTIs) in horses with mild/moderate (MEA) and severe (SEA) equine asthma and in healthy horses. In human medicine, PAS is a pulsed-wave (PW) Doppler echocardiographic parameter useful in assessing an increase in pulmonary artery stiffness due to remodeling of the vessel wall caused by chronic diseases. Moreover, PAS in humans is used as an early indicator of pulmonary hypertension. RVSTIs, such as acceleration time (AT), ejection time (ET) and acceleration time index (AT/ET), are other PW Doppler parameters useful for the evaluation of changes in the pulmonary vascular bed. Like human asthma, equine asthma is able to induce remodeling of the pulmonary artery wall even in horses, leading to a decreased pulmonary artery elasticity and consequently pulmonary hypertension. Therefore, it is conceivable that PAS could be a useful parameter also in horses. However, there are no studies on PAS in veterinary medicine. The aims of this research were: to assess feasibility of PAS in horses, to evaluate possible influence of age, bodyweight, sex and heart rate on PAS and RVSTIs, to investigate possible differences between healthy, MEA and SEA horses regarding those parameters, to evaluate possible correlation between PAS and RVSTIs and ratio of pulmonary artery diameter to aorta diameter (PAD/AOD) and to determine PAS and AT cut-off values for diagnosis of SEA. Echocardiographic examination and PW Doppler of the pulmonary flow were performed in 23 MEA affected horses, 15 SEA affected horses and 15 healthy horses. Results demonstrated that PAS can been measured consistently in horses and that, as well as RVSTIs, it is not influenced by age, bodyweight, sex and heart rate. Moreover, a significant higher PAS and lower RVSTIs were detected in SEA affected horses compared to healthy subjects and MEA affected ones. In addition, considering the whole sample, a positive correlation between PAS and PAD/AOD and a negative correlation between AT or AT/ET and PAD/AOD were found. These findings, in association with several similarities between equine asthma and human asthma, suggest that these parameters could be correlated to pulmonary pressure even in horses. Finally, this study determined that a PAS value of 8.18 kHz/sec and a AT value of 0.202 sec are the best cut-off values, with a very high sensitivity (PAS: 93.33%; AT: 86.67%) and specificity (PAS: 86.84%; AT: 89.47%), for the diagnosis of SEA.