Validation of impulse oscillometry in Friesian and Blue Belgian calves with respect to changes in extrathoracic upper airway resistance

Impulse oscillometry (IOS) was compared with conventional pulmonary function techniques (using oesophageal balloon and airflow measurements). Healthy Friesian (FR) and Blue Belgian (BB) calves were examined in different conditions of extrathoracic airway resistance (physiological and vertical head position). Higher resistance values were detected in BB calves compared with FR calves with both conventional and forced oscillation techniques in both head positions. Upper airway narrowing was characterised by increasing resistance values without changes in frequency dependence. Measuring input impedance in animals using a face mask, a considerable capacitive shunt of the upper airways (including the capacitive components of the mask) has to be taken into account. Even if the absolute value of this capacitive component is constant, its influence on the measurement results increases with growing frequency and with an increase in upper airway resistance. In conclusion, (1) impulse oscillometry is sensitive to upper airway resistance changes and (2) face mask capacitance is important and has frequency dependent effects on the respiratory impedance