Proceedings of The Physiological Society
University College Dublin (2009) Proc Physiol Soc 15, PC76
The response to hypoxia: a refined Human Patient Simulator (HPS) model to demonstrate high altitude physiology
R. Helyer1, E. Lloyd1
1. University of Bristol, Bristol, United Kingdom.
The Human Patient Simulator (HPS; METI, Sarasota, Florida) has a computer driven mechanical lung and gas exchange mechanism, designed to model the human respiratory system. We have previously demonstrated that the HPS is a useful educational tool for demonstrating physiological responses to changes in the environment such as hypoxia, but that the model requires some adjustment in order to more accurately represent human data (Helyer et al, 2008). The aim of this study was to refine the response of the HPS to hypoxia to improve the correspondence with human data in order to improve the validity of the HPS for teaching high altitude human physiology. In our previous study we constructed an Oxygen-Carbon Dioxide diagram for the HPS that demonstrated a linear relationship between PAO2 and PACO2 over the entire range investigated (Helyer et al, 2008). In comparison unacclimatised humans show a linear relationship between PAO2 and PACO2 over a PAO2 range of 60-100 mmHg but below this range there is a non-linear relationship (Fenn et al, 1946; Rahn & Otis, 1949; O’Brien, 1995). This is due to hyperventilation resulting in a respiratory alkalosis when PAO2 decreases below approximately 60mmHg (Fenn et al, 1946). In this study we found that the relationship between PAO2 and minute volume was linear (between PAO2 = 30 to 100 mmHg) in the HPS whereas humans show an increase in gain when PAO2 decreases below 60 mmHg. We changed the gain of the HPS ventilatory response incrementally and this resulted in a more accurate representation of the human data. This produced an improved correspondence between the HPS and human O2-CO2 diagrams. Subsequent refinement allowed demonstration of equivalent responses for acclimatised humans as well as appropriate changes in Oxygen saturation, arterial pH and heart rate. We conclude that the HPS response to hypoxia can be refined to increase its validity as an educational tool to illustrate high altitude physiology.
Where applicable, experiments conform with Society ethical requirements