Unanesthetized dogs with increased respiratory dead space

¹ Departments of Medicine and Surgery, University of North Carolina School of Medicine, Chapel Hill, North Carolina

A method is described for maintaining a permanent tracheostomy in dogs. This animal preparation has been used to study the effects of artificially increased respiratory dead space. Trained dogs with tracheostomies have made possible measurements of ventilation without anesthesia. It has been found that additions to the respiratory dead space in the form of tubing of in. i.d. result in an increase in physiologic dead space of the same magnitude as the volume of tubing added. Increasing the dead space in this manner resulted in an increased minute volume which was accomplished principally by an increase in tidal volume without a significant or consistent change in respiratory rate. Alveolar ventilation remained unchanged even with large additions to the dead space (20–30 cc/kg of animal wt.). Arterial pCO₂ was significantly higher in these animals than in the controls. The CO₂ tension was similarly elevated when extra dead space of lesser volume (5–20 cc/kg) was allowed to remain on the dogs for more than 48 hours.

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