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Journal of Experimental Biology 47,1-20 (1967)
Published by Company of Biologists 1967

The Mechanism of Lung Ventilation in the Tortoise Testudo Graeca Linne

C. GANS ¹ and G. M. HUGHES ²

¹ Department of Zoology, University of Bristol; Department of Biology, State University at Buffalo, N.Y. 14214, U.S.A.
² Department of Zoology, University of Bristol

1. An account is given of the gross structure of the respiratory system and of the principal muscles involved in ventilation of the tortoise, Testudo graeca.

2. The mechanism of ventilation was investigated by electrophysiological methods. Cannulae inserted into the lung through holes drilled in the shell recorded pressure changes during the cycle of ventilation and simultaneous recordings were made of the forelimbs movements. The pressure changes were triphasic in form, consisting of an initial increase in pressure followed by a fall to a level of 7 cm. water below atmospheric, and again returned to the atmospheric level or usually slightly above. During the pause between individual ventilation cycles, any overshoot gradually declined to the base-line.

3. Electromyograms showed that all phases of the respiratory cycle were active. The increase in pressure was accompanied by activity in the transversus abdominis and in the pectoralis muscle which draws the shoulder girdle back into the shell. These activities increase the pressure in the peritoneal cavity, which is transmitted to the lung. During the opposite phase of the cycle, the obliquus abdominis and serratus major muscles are active. This increases the volume of the peritoneal cavity and leads to the reduction in intrapulmonary pressure below atmospheric.

4. Activity recorded from the opener and closer muscles of the glottis showed that the glottis is dilated during the first two parts of the cycle but not during the final recompression phase.

5. The respiratory rhythm does not appear to be composed of brief periods of ventilation activity followed by prolonged pauses, as supposed by many authors. These differences may relate to the species investigated.

6. No evidence was found for significant differences in pressure between the right and left lungs or between the anterior and posterior chambers of the lung on one side.

7. It is concluded that the mechanism producing ventilation in the tortoise takes advantage of the only possible way of changing the volume of the thoracico-peritoneal cavity, namely by altering the position of the limb flanks. Both expiratory and inspiratory movements are active.

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