In equine medicine lung function measurements provide an additional diagnostic approach to investigate lung diseases, especially those associated with exercise intolerance. Furthermore the effect of different drugs on respiratory mechanics can be analysed. The forced oscillation technique which employs pressure oscillations superimposed on the spontaneous breathing has the advantage over conventional lung function tests that it is a non-invasive and easy-to-use method.
In this study lung function of a mixed group of six horses comprising healthy animals and horses with clinical signs of respiratory disorders was measured over a period of one month twice a day using the forced oscillation technique. The first measurement run started at 8 a.m. and the second one at 3 p.m. The respiratory impedance described by the two components resistance (Rrs) and reactance (Xrs) was measured over 1, 1.5, 2 and 3 Hz. The mean coherence value was >= 0.8. In addition in- and outdoor temperature and humidity were recorded.
Mean resistance in the morning, mean resistance in the afternoon and over-all resistance were 0.93 ± 0.15 cmH2O/l/s, 0.82 ± 0.12 cmH2O/l/s and 0.87 ± 0.14 cmH2O/l/s, respectively. Mean reactance in the morning, mean reactance in the afternoon and over-all reactance were -0.18 ± 0.11 cmH2O/l/s, -0.15 ± 0.09 cmH2O/l/s and -0.17 ± 0.10 cmH2O/l/s, respectively.
There was no evidence of negative frequency dependence of the resistance. Resistance values at 1 Hz were significantly lower than at 3 Hz both in the morning and in the afternoon.
Reactance values at 3 Hz were significantly higher than at other frequencies. Horses with clinical signs of respiratory disorders showed a noticeable negativity of the reactance values and a marked right shift of the reactance-frequency-curves.
Resistance values in the morning as well as in the afternoon exhibited significant daily and animal-individual variations. Only reactance values at 1 Hz (in the morning as well as in the afternoon) showed no clear daily effects. Resistance values were higher while reactance values were lower in the morning than in the afternoon over the whole frequency range.
Environmental conditions, especially temperature, besides individual influences have little but significant effect on the variation of measured data.