Journal of Applied Physiology, Vol 66, Issue 3 1258-1263, Copyright © 1989 by American Physiological Society
Pulmonary gas exchange in panting dogs
M. Meyer, G. Hahn, C. Buess, U. Mesch and J. Piiper
Department of Physiology, Max Planck Institute for Experimental Medicine, Gottingen, Federal Republic of Germany.
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.
