The aim of this study was to show that changes from baseline in the TAA(Thoraco-abdominal Asynchrony), caused by CO2, induced hyperventilation can be used to differentiate between healthy, IAD(Inflammatory Airway Disease) and RAO(Recurrent Airway Obstruction) affected horses.
The TAA from 34 horses was calculated, using the measured RUP(Respiratory Ultrasound Plethysmography) signals, first during breathing at rest and second during CO2 induced hyperventilation.
Additionally, a BAL(Bronchoalveolar Lavage) cytology was taken, a clinical examination and endoscopic examination were performed and arterial blood gases were analyzed.
According to the percentage of PMN(polymorphonuclear) cells in the BAL cytology the horses were assigned to one of the following 3 groups:
Healthy horses, horses with IAD or RAO affected horses.
The TAA during normal tidal breathing and during CO2 induced hyperventilation was calculated using the Pearson Correlation Coefficient (PCC). The changes in the TAA were determined via the Quotient of the Pearson Correlation Coefficient (PCCQ). Horses with RAO showed significantly higher median PCCQ than healthy horses (1.06 vs.
0.88; p=0.08), whereas the results for IAD affected horses were significantly larger than those found in control horses (1.035 vs. 0.88; p= 0.045). No significant difference could be detected in the median PCCQ of horses with RAO and IAD affected horses (1.06 vs. 1.035; p= 0.779). To determine the accuracy of PCCQ we compared it with a Clinical Scoring System. We found no significant difference between the Clinical Score and PCCQ when differentiating healthy from sick horses (difference of AUCs 0.137, 95% CI -0.0602 to 0.333, p=0.174).
The hypotheses could be confirmed with the results found in this study:
Horses suffering from an obstructive pulmonary disease decrease the TAA during stimulated breathing. Therefore, abdominal compartment and rib cage compartment moved more similar to each other and with a lower mean amplitude difference.
In this study, we were able to confirm that measuring the TAA with RUP and calculation of the Quotient of the Pearson Correlation Coefficients (PCCQ) provides a useful tool to differentiate horses with RAO and IAD from a healthy control group. Thus, RUP is a good non-invasive method for lung function testing in horses.