[Influencing respiratory gas analytical lung function parameters by intravenous injection of clenbuterol in horses with chronic lung diseases].

The research study investigated how intravenous injection of clenbuterol, a medication often used to treat chronic lung diseases in horses, affects several respiratory gas analytical lung function parameters. The researchers found this treatment increased the functional dead space (the part of the lung where gas exchange is reduced or absent) but only temporarily, and it also temporarily decreased the amount of oxygen in the bloodstream while carbon dioxide levels remained unchanged.

Methodology

• The study was a placebo-controlled drug trial involving 13 horses with chronic obstructive pulmonary disease.
• The researchers analyzed lung properties like flow, volume, and expiratory CO2-concentration, before and for up to 2.5 hours after the horses were administered an intravenous injection of clenbuterol.
• The tools used included an ultrasonic flow measuring device and an infrared CO2-analyzer.
• Parameters like functional dead space, expiratory mixed volume, the partial pressure of oxygen (PaO2), and carbon dioxide (PaCO2) in arterial blood were calculated and evaluated. Furthermore, the alveolo-arterial oxygen difference (AaDO2) was ascertained.

Findings

• Shortly after the injection of clenbuterol, the volume of the functional dead space was found to be 24% larger than the placebo. The difference was no longer significant 45 minutes post-injection.
• The PaO2 showed a decline at 45 minutes post-injection, the maximum difference being 11.6 mmHg compared to the baseline level. However, there was no significant change in PaCO2 levels, leading to an increased AaDO2 of up to 15 mmHg at this time.
• All these changes were temporary and approached baseline values around 45 minutes post-injection, except for the PaO2 level, which did not return to its initial level even after 150 minutes.
• The changes in the expiratory mixed volume were not consistent.

Interpretation and Conclusion

• The research showed that the functional dead space could be an important factor in understanding the pathophysiology of lung diseases.
• The observed changes in the blood gas tension and dead space volume following the clenbuterol injection may suggest that the initial increase in anatomic dead space caused by bronchospasmolysis and prolonged opening of previously unventilated alveoli are responsible for the initial drop in PaO2.
• However, the study discusses potential alternative explanations for these results.