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CO2 homeostasis during periodic breathing: predictions from a computer model
D M Rapoport1, R G Norman, R M Goldring
1Department of Medicine, New York University Medical Center, New York 10016.
Journal of Applied Physiology (Bethesda, Md. : 1985)
|November 1, 1993
Summary
Periodic breathing patterns can elevate carbon dioxide levels (CO2) by mismatching ventilation and CO2 delivery. Increased ventilation is needed to prevent hypercapnia during such breathing, impacting CO2 homeostasis.
Area of Science:
- Physiology
- Computational Biology
- Respiratory System Mechanics
Background:
- The Bohr/Riley model explains CO2 homeostasis, assuming ventilation and CO2 delivery are well-matched.
- Periodic breathing patterns, unlike normal breathing, exhibit temporal mismatches between ventilation and CO2 delivery.
Purpose of the Study:
- To develop a computer model simulating lung CO2 clearance during various breathing patterns.
- To investigate the impact of periodic ventilation on arterial PCO2 (PaCO2) and CO2 homeostasis.
Main Methods:
- Developed a computer model of lung CO2 clearance using CO2 transfer equations.
- Generated iterative solutions for PaCO2 in multiple body compartments over time.
- Simulated both continuous and periodic ventilatory patterns.
Main Results:
- The model predicted steady-state PaCO2 consistent with the Bohr model during continuous ventilation.
- Periodic ventilation led to elevated mean PaCO2 unless ventilation was increased beyond Bohr model requirements.
- Factors like variable tidal volumes and low lung volumes potentiated hypercapnia, while in-phase cardiac output oscillations minimized it.
Conclusions:
- Periodic ventilation can cause sustained hypercapnia due to ventilation-perfusion mismatch.
- This suggests a novel mechanism for hypercapnia development, independent of absolute hypoventilation or lung disease.
- Optimizing ventilation timing and cardiac output phase may be crucial for maintaining CO2 homeostasis during altered breathing patterns.