Gas tension profile of the lung of the viper, Vipera xanthina palestinae.

Oxygen and carbon dioxide concentrations along the lung of five awake, resting Palestine vipers were continuously measured by mass spectrometry. Ventilatory volumes, body wall movements and heart rate were also measured. In the anterior part of the faveolar (respiratory) lung, oxygen and carbon dioxide concentrations returned to within 1% of inspired composition with each inspiration. Between breaths, changes of 0.5-2% in gas concentrations were seen in the faveolar region but practically no changes occurred in the caudal, non-respiratory lung (air sac) where mean oxygen and carbon dioxide concentrations of 16.4% and 2.5% respectively were recorded. The respiratory exchange ratio dropped from near 1.5 in the anterior faveolar region to zero in the transition zone to the air sac. Instantaneous R values declined with breath-holding time in each location along the length of the lung. Gas exchange appears greatest in the posterior faveolar region near the heart and there is evidence of cardiogenic gas mixing in this region. The posterior air sac may either passively respond to air movements in the anterior lung or it may participate in ventilation. During periods of extended breath-holding (10-15 min) pronounced body wall movements were seen but there was no air flow from the mouth and gas exchange continued in the lung with rapidly decreasing R.