PULMONARY GAS-EXCHANGE KINETICS DURING EXERCISE - PHYSIOLOGICAL INFERENCES OF MODEL ORDER AND PARAMETERS

1. The ventilatory and pulmonary gas exchange responses during moderate exercise can be appropriately modelled with first-order dynamics. 2. A delay term, reflecting tissue-to-lung transit time, is needed for accurate characterization, however. 3. The O-2 uptake time constant (tau V-O2) reflects the enzymatically controlled tissue O-2 utilization. 4. tau V-CO2 is appreciably longer than tau V-O2 consequent to the tissue CO2 capacitance. 5. As tau V-E is typically longer than tau V-CO2, transient errors in alveolar and arterial blood gas tensions are predicted: small for P-CO2 but much larger for P-O2. 6. At work rates above the lactate threshold, a slow and delayed component of V-O2 induces an additional V-O2 component (''excess'' V-O2), leading to more rapid fatigue. 7. The ventilatory compensation for the metabolic acidemia at these work rates is slow, with compensation being poor for rapid-incremental exercise. 8. A justifiable control model of the coupling of ventilation to metabolism must cohere with these demonstrable physiological characteristics.