Work of breathing in dog during exercise

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Abstract
In 6 dogs trained to wear a mask and to swallow an esophageal balloon, the dynamic work of breathing (.ovrhdot.Wdyn) was measured while the animals ran on a treadmill at different intensities (7-13 km/h, +10%). .ovrhdot.Wdyn (kg .cntdot.m/min-1) increased with ventilation (.ovrhdot.VE, 1/min) according to .ovrhdot.Wdyn = 0.308 .cntdot. 10-2 .ovrhdot.VE + 0.0098 .cntdot. 10-2 .cntdot. .ovrhdot.VE3. If the exercise was prolonged so that the body temperature rose above .apprx. 39.degree. C, .ovrhdot.Wdyn, for a given ventilation, decreased; and hence .ovrhdot.Wdyn = 0.253 .cntdot. 10-2 .cntdot. .ovrhdot.VE2 -0.0011 .cntdot. 10-2 .cntdot. .ovrhdot.VE3. Similar observations were made on another dog heated from an external source. During exercise, when the temperature rises and the ventilation increases to dissipate heat, the airway size in some portion of the respiratory tract increases markedly and greatly diminishes the cost of breathing. This mechanism would save O2 for the exercising limb muscles when exercise had to be continued for an extended time.