A refrigerated treadmill apparatus for exercising dogs.

To prevent overheating and panting in exercising dogs, a refrigerated enclosure was constructed on a standard laboratory treadmill to regulate skin and body temperature of exercising beagles. The enclosure temperature is controlled by a computer software algorithm that analyzes the exercising dog's skin and rectal temperatures and stabilizes rectal temperature to within +/- 0.1 degree C of a preselected resting level. Refrigeration is activated depending on the skin and rectal temperature dynamics lowering enclosure temperature as skin temperature and rectal temperature increase. The system has been used extensively to inhibit panting in exercising beagles, maintaining a mean and standard deviation respiratory frequency of 32 +/- 5 breaths/min during exercise at 5 km/h, 0% grade. These respiratory rates can be compared with reported respiratory frequencies of 95 +/- 57 breaths/min for beagles exercising at the same work load but at room temperature (Mauderly and Pickrell, Research Animals in Medicine, DHEW Publ. 72-333, 1973). This reduction in respiratory frequency is also accompanied by a reduced and repeatable expired minute ventilation and O2 consumption of 9.40 +/- 1.0 1/min (BTPS) and 0.331 +/- 0.031 1/min (STPD), respectively, and can be compared with 24.84 +/- 6.44 1/min (BTPS) and 0.440 +/- 0.0831 1/min (STPD) reported for beagles exercising at room temperature.

End-tidal CO2 response to low levels of inspired CO2 in awake beagle dogs.

The steady-state end-tidal CO2 tension (PCO2) was examined during control and 1% CO2 inhalation periods in awake beagle dogs with an intact airway breathing through a low dead-space respiratory mask. A total of eight experiments were performed in four dogs, comprising 31 control observations and 23 CO2 inhalation observations. The 1% inhaled CO2 produced a significant increase in the steady-state end-tidal PCO2 comparable to the expected 1 Torr predicted from conventional CO2 control of ventilation. We conclude that 1% inhaled CO2 results in a hypercapnia. Any protocol that is to resolve the question of whether mechanisms are acting during low levels of inhaled CO2 such that ventilation increases without any change in arterial PCO2 must have sufficient resolving power to discriminate changes in gas tension in magnitude predicted from conventional (i.e., arterial PCO2) control of ventilation.