Lung volumes, pulmonary blood flow and carbon monoxide diffusing capacity of turtles

Summary

Lung volume, pulmonary blood flow and CO diffusing capacity were measured during pump-ventilation in two turtle species, the aquaticPseudemys scripta elegans (mean weight 1,550 g) and the terrestrialTestudo graeca (mean weight 980 g). Mean resting lung volumes, determined by argon dilution, were similar in both species, 160 ml/kg inP. s. elegans and 170 ml/kg inT. graeca. Argon washout curves were monoexponential and the dead space obtained from the difference between the total ventilation and the ventilation effective in Ar washout showed good agreement with anatomically estimated extrapulmonary airway volume. The dead space averaged 0.6 ml/kg inP. s. elegans and 2.6 ml/kg inT. graeca. Pulmonary blood flow was obtained from the exponential decrease of pulmonary N₂O concentration during rebreathing conditions. The mean values were 52.0 ml/(min · kg) inP. s. elegans and 34.4 ml/(min · kg) inT. graeca. Utilizing O₂ uptake determined simultaneously with pulmonary blood flow, the O₂ content difference between pulmonary venous and pulmonary arterial blood was calculated. It averaged 1.73 Vol% inP. s. elegans and 4.48 Vol% inT. graeca. The pulmonary CO diffusing capacity, obtained using a rebreathing technique, was found to decrease in both species as the rebreathing time was increased from 30 sec to 120 sec. The mean D_co values for the same rebreathing times were lower inP. s. elegans, 0.066 to 0.033 ml/(min · torr · kg), than inT. graeca, 0.114 to 0.068 ml/(min · torr · kg). The values are critically discussed and compared with available literature data on reptiles and mammals.