Pulmonary function values in Friesian and double-muscled calves during acute poikilocapnic hypoxia

The effects of an acute non-isocapnic hypoxia on ventilation and pulmonary mechanics were investigated in 6 healthy unsedated Holstein-Friesian (HF) calves and in 7 double-muscled calves of the Belgian White and Blue (BWB) breed known to develop more severe hypoxemia during exercise and respiratory diseases. Data were collected at 1 min intervals throughout the following protocol: breathing air (FIO2 = 21%), then breathing hypoxic gas mixture (FIO2 = 10%) for 5 min, and, finally, breathing air again for 5 min of recovery. Arterial blood was sampled at rest and at the 4th min of hypoxia for blood gas analysis. In HF and BWB calves, hypoxia induced a significant increase in tidal and minute volume, but did not change respiratory rate, dynamic lung compliance and total pulmonary resistance. However, with regard to their ventilation during normoxia at rest, BWB calves showed a comparatively greater rise in ventilation than HF calves during the first 4 min of hypoxia. On the contrary, by the 5th minute of hypoxia, ventilation of BWB calves declined to the normoxic level while HF calves largely sustained hyperventilation. This hypoxic ventilatory depression in BWB calves could be explained by the proportionately greater initial increase in ventilation. It was concluded that BWB calves supported this hypoxic challenge less easily than HF calves.