Journal of comparative physiology

, Volume 89, Issue 2, pp 145–158 | Cite as

Respiratory adaptations to diving in the nile monitor lizard,Varanus niloticus

  • Stephen C. Wood
  • Kjell Johansen


The objectives of this study included directin vivo measurements of circulating blood gases, pH, heart rate, and blood pressure during voluntary dives of unrestrained Nile monitor lizards. A Radiometer flow-through cuvette was employed for continuous recording of arterial PO2, PCO2 and pH. Hematological properties revealed no particular adaptations for diving. Mean values were: hematocrit = 24%; hemoglobin concentration = 7.1 g %; oxygen capacity = 9.3 vol %; red cell dimensions = 22×12 μ; red cell count = 0.67 million/μl. The respiratory properties of the blood, studiedin vitro andin vivo, show distinct adaptations to habitual diving. Oxygen affinity of blood is low (P50 = 42.4 mm Hg at pH 7.45, 25 °) and the dissociation curve is markedly sigmoid (n = 3.1). These features, coupled with a Bohr factor (Δ logP50/ΔpH) of −0.48, ensure increased utilization of oxygen while maintaining relatively high tissue PO2. Arterial pH decreases during diving from about 7.5 to 7.1 due to combined respiratory and metabolic acidosis. High plasma bicarbonate (30 mM/l at PCO2 = 25 mm Hg) and a buffering capacity of ΔH C3O/Δ pH = 18.9 mM/l increase the tolerance to this acidosis and prolong diving time. Thein vivo oxygen dissociation curve shows a 90 % depletion of arterial oxygen content during typical dives. Diving elicited a rapidly developing bradycardia with maximum of 85 % reduction in heart rate. The temperature sensitivity of HbO2 binding was very low (ΔH = −3kcal). This would minimize the HbO2 affinity increase accompanying the decrease in body temperature likely to occur in lizards going from sun basking to submergence in water.


Metabolic Acidosis Dissociation Curve Typical Dive Arterial Oxygen Content Plasma Bicarbonate 
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Copyright information

© Springer-Verlag 1974

Authors and Affiliations

  • Stephen C. Wood
    • 1
    • 2
  • Kjell Johansen
    • 1
  1. 1.Department of ZoophysiologyAarhus UniversityAarhusDenmark
  2. 2.Department of Biological SciencesSouthern Illinois UniversityEdwardsvilleUSA

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