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Deep diving mammals: Dive behavior and circulatory adjustments contribute to bends avoidance.
A Fahlman1, A Olszowka, Brian Bostrom
1Department of Zoology, The University of British Columbia, 6270 University Blvd., Vancouver, BC, Canada V6T 1Z4. andreas_fahlman@yahoo.com
Respiratory Physiology & Neurobiology
|January 18, 2006
Summary
A mathematical model of breath-hold diving shows that physiological adjustments, like reduced heart rate and controlled ascent, significantly lower nitrogen (N2) levels in blood and tissues. This reduces the risk of decompression sickness (DCS) in marine mammals.
Area of Science:
- Physiology
- Marine Mammal Science
- Biophysics
Background:
- Breath-hold diving presents challenges for inert gas management.
- Understanding nitrogen (N2) tension in tissues is crucial for assessing decompression sickness (DCS) risk.
Purpose of the Study:
- To develop and validate a mathematical model predicting N2 tension during breath-hold diving.
- To assess the impact of physiological adaptations and dive behavior on N2 uptake and offloading.
Main Methods:
- A mathematical model was created to predict blood and tissue N2 tension (P(N2)).
- Model predictions were compared with measured muscle P(N2) in bottlenose dolphins after 100m dives.
- Lung collapse was simulated as a 100% pulmonary shunt; dive response effects (reduced cardiac output) were also modeled.
Main Results:
- The model accurately predicted dolphin muscle P(N2) when simulating lung collapse.
- Simulating a dive response (66% cardiac output reduction) also yielded accurate P(N2) predictions without lung collapse.
- Both cardiovascular adjustments and dive behavior were found critical for minimizing N2 uptake.
Conclusions:
- Physiological adaptations, including bradycardia and controlled ascent rates, significantly reduce mixed venous P(N2) upon surfacing.
- Reductions in mixed venous P(N2) can substantially decrease the risk of decompression sickness (DCS).
- The model provides insights into safe diving practices for marine mammals and potentially humans.