Oxygen cost of breathing in dogs.

The O2 cost of breathing has been calculated in awake and anesthetized dogs breathing spontaneously. Respiratory variables were measured in tracheostomized dogs in the standing position, while supported in a canvas sling, at room temperatures between 20 and 23 degrees C. Minute ventilation ranged between 3 and 53 liters/min while VO2 ranged from 61 to 686 ml/min. VE, VO2 and f varied considerably from measurement to measurement even though body temperatures and experimental conditions changed very little. VO2 increased with VE: VO2 = 10.2 VE + 58.4 r = 0.94. A cubic polynomial equation was also calculated for these data: VO2 = 11.6 + 19.0 VE-0.42 (VE)2 + 0.0057 (VE)3. Awake dogs showed panting and considerable hyperventilation (PACO2 = 22.5 +/- SD of 4.5 mm Hg). Anesthetized dogs had lower average values of f, VE and VO2; while average PACO2 was 29.1 +/- 4.5 mm Hg. VO2 and VE measured when the dogs were anesthetized, paralyzed and artifically ventilated were related by this equation: VO2 = 5.9 VE + 87.5, r = 0.88. The O2 cost of breathing, calculated by subtracting the regression equation obtained while the dogs were under artificial respiration, from the cubic polynomial equation, increased with increasing VE in a curvilinear fashion. The values for O2 cost of breathing at high levels of ventilation were high because dogs' lungs are small. After correcting for lung size, values for O2 cost of breathing were similar to those in humans.