Key words: 

hypoxia, chemoreflex control of breathing, acid-base balance, strong ion difference, 2,3 DPG.

Introduction: 

Our interactive personal computer based mathematical model for the oxygen transport uses clinical and laboratory data for the purpose of simulation of physiological and pathophysiological states, and is based on the known kinetic principles to describe transport of blood gases in human body from the outer atmosphere to different tissues¹. Recently, the model was upgraded to include the influence of acid-base balance in the chemoreflex control of breathing², as well as the influence of hypoxia on the peripheral blood flow³. With such model we simulated adaptation of breathing to the prolonged hypoxia to find which of the known compensatory mechanism is most effective.

Material and methods: 

The model is composed of four compartments for transport of blood gases (O2 and CO2): airways, alveolo - capillary interface, the blood and the blood vessels, and the Krogh cylinder for blood gas exchange in tissues. With the model, it is possible to change interactively in real-time different parameters that are accessible from clinical and laboratory measurements to monitor the arterial oxygen saturation and blood CO₂ levels. Thus, it is possible to vary the gas composition and the barometric pressure, alveolar ventilation, diffusion capacity of the lungs, blood hemoglobin concentration, plasma protein concentration (both affect pH), blood perfusion of different tissues (so far we use 6 different tissues), specific tissue metabolism and the tissue capillary density. In addition, it is possible to vary strong ion difference (SID) in the blood plasma and cerebrospinal liquor, or to change the concentration of 2,3DPG in the erythrocytes.

Results: 

The most effective adaptation measure to reduce effects of hypoxia were found to be changes of brain SID and acidification of blood due to bicarbonate excretion by kidneys, whereas substantial changes in 2,3 DPG in the blood inexpectedly reduced the efficincy oxygen transport to tissues, particularly after acid-base adaptation has already reached

Conclusions: 

The model enables understanding of integrative function of respiratory adaptation and suggests direction of the experimental studies connected with hypoxia.

References:

1. Starc V. Interaktivni model prenosa kisika po telesu ya simulacijo nekaterih fiziolo[scaron]kih stanj. In: Fras Z, Poredo[scaron] P, editors. Zbornik prispevkov 47. Tav[ccaron]arjevi dnevi; 2005; Portoro[zcaron]. Ljubljana: Medicinska fakulteta, Katedra za interno medicino, 2005; 203-11.

2. Starc V. Effects of myogenic and metabolic mechanisms on the autoregulation of blood flow through muscle tissue: a mathematical model study. Cardiovasc Eng 2004; 4(1):81-8.

3. Duffin J. Role of acid-base balance in the chemoreflex control of breathing. J Appl Physiol 2005; 99: 2255-2265