A rapid, non-invasive method for measuring total respiratory impedance in the horse

Total respiratory impedance was measured rapidly and noninvasively in conscious horses over the frequency range 3 to 40 Hz by the forced random noise method. The shape of curve of impedance versus frequency in horses was markedly different from that of humans. Respiratory resistance was readily found as the real part of impedence and both its absolute value and frequency dependence are useful indices of pulmonary function. It was difficult to obtain meaningful results in intubated animals with the method because of the mechanical properties of the endotracheal tube itself.