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Related Experiment Videos

Hypoxemic threshold for lung ventilation in the toad.

N H West1, Z L Topor, B N Van Vliet

  • 1Department of Physiology, College of Medicine, University of Saskatchewan, Saskatoon, Canada.

Respiration Physiology
|December 1, 1987
PubMed
Summary

In toads, low oxygen (hypoxemia) and high carbon dioxide (hypercapnia) levels together stimulate lung ventilation. Carotid labyrinth chemoreceptors contribute to this response but are not the sole drivers.

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Area of Science:

  • Comparative Physiology
  • Respiratory Physiology

Background:

  • Lung ventilation in amphibians is complex and influenced by various physiological factors.
  • Understanding the interplay of oxygen and carbon dioxide levels on ventilation is crucial for respiratory control research.

Purpose of the Study:

  • To investigate the relationship between buccal force pump activity and partial pressure of oxygen (PaO2) in conscious toads.
  • To determine the hypoxemic thresholds for lung ventilation under different partial pressure of carbon dioxide (PaCO2) conditions.
  • To assess the role of carotid labyrinth chemoreceptors in mediating ventilatory responses to hypoxia.

Main Methods:

  • Conscious toads (Bufo marinus) were unidirectionally ventilated at a high flow rate to create an open-loop system.
  • Partial pressure of oxygen (PaO2) and partial pressure of carbon dioxide (PaCO2) were manipulated and measured.

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  • Pulmonary ventilation was monitored, and bilateral denervation of carotid labyrinths was performed in some subjects.

    • Main Results:

    • The hypoxemic threshold for lung ventilation increased significantly with rising PaCO2: 54.2 mm Hg (hypocapnia), 82.6 mm Hg (normocapnia), and 137.9 mm Hg (hypercapnia).
    • Ventilation ceased under normoxic, hypocapnic conditions (20% O2 in N2).
    • Carotid labyrinth denervation reduced overall pulmonary ventilation but did not abolish the proportional increase during normocapnic hypoxia.

    Conclusions:

    • Hypoxic and hypercapnic stimuli interact and summate to drive lung ventilation in toads.
    • Carotid labyrinth chemoreceptors play a role in the hypoxemic ventilatory drive but are not exclusively responsible for it.