Pulmonary gas exchange in panting dogs.
Pulmonary gas exchange during panting was studied in seven conscious dogs (32 kg mean body wt) provided with a chronic tracheostomy and an exteriorized carotid artery loop. The animals were acutely exposed to moderately elevated ambient temperature (27.5 degrees C, 65% relative humidity) for 2 h. O2 and CO2 in the tracheostomy tube were continuously monitored by mass spectrometry using a special sample-hold phase-locked sampling technique. PO2 and PCO2 were determined in blood samples obtained from the carotid artery. During the exposure to heat, central body temperature remained unchanged (38.6 +/- 0.6 degrees C) while all animals rapidly switched to steady shallow panting at frequencies close to the resonant frequency of the respiratory system. During panting, the following values were measured (means +/- SD): breathing frequency, 313 +/- 19 breaths/min; tidal volume, 167 +/- 21 ml; total ventilation, 52 +/- 9 l/min; effective alveolar ventilation, 5.5 +/- 1.3 l/min; PaO2, 106.2 +/- 5.9 Torr; PaCO2, 27.2 +/- 3.9 Torr; end-tidal-arterial PO2 difference [(PE' - Pa)O2], 26.0 +/- 5.3 Torr; and arterial-end-tidal PCO2 difference, [(Pa - PE')CO2], 14.9 +/- 2.5 Torr. On the basis of the classical ideal alveolar air approach, parallel dead-space ventilation accounted for 54% of alveolar ventilation and 66% of the (PE' - Pa)O2 difference. But the steepness of the CO2 and O2 expirogram plotted against expired volume suggested a contribution of series in homogeneity due to incomplete gas mixing.
Meyer
M
M
Department of Physiology, Max Planck Institute for Experimental Medicine, Göttingen, Federal Republic of Germany.
Hahn
G
G
Buess
C
C
Mesch
U
U
Piiper
J
J
D000075:Acepromazine / Q000494:pharmacology; D000818:Animals; D002245:Carbon Dioxide / Q000097:blood*; D004285:Dogs / Q000502:physiology*; D004329:Droperidol / Q000494:pharmacology; D005260:Female; D008168:Lung / Q000187:drug effects / Q000502:physiology*; D008297:Male; D010100:Oxygen / Q000097:blood*; D010313:Partial Pressure; D011652:Pulmonary Circulation; D012016:Reference Values; D012119:Respiration / Q000187:drug effects
D002245:Carbon Dioxide; D000075:Acepromazine; D004329:Droperidol; D010100:Oxygen