Distribution of ventilation in the turtle Pseudemys scripta

Spontaneously ventilating turtles, Pseudemys scripta, were allowed to rebreathe 133Xe to equilibrium. Frequent gamma camera images were obtained and processed to allow regional evaluation of ventilation. The distribution of ventilation was markedly inhomogeneous, with washin to equilibrium most rapid in anterior lung compartments and slowest in posterior lung compartments. Similarly washout from equilibrium was most rapid in anterior compartments and slowest in posterior compartments. During apnea intercompartmental gas exchange occurred rapidly during spontaneous activity of the limbs or, more slowly, during episodes ascribed to regional contraction of lung smooth muscle. Despite inhomogeneous ventilation, overall washout of 133Xe could be monoexponential. A simple series model of the turtle lung is consistent with the inhomogeneous ventilation observed.