Interactions of body temperatures and modulators of human pulmonary ventilation

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Mechanisms underlying the control of exercise ventilation remain an anomaly in human physiology. Numerous hypotheses on the function of this control system are unable to fully explain the disproportionate increases in pulmonary ventilation relative to metabolic needs during intense exercise. We hypothesized that during exercise core temperature (Tc) is a significant influence on pulmonary ventilation. Evidence supporting this novel view was from our demonstration of Tc thresholds for pulmonary ventilation in both passively (i.e. hot immersion at rest) and actively warmed (i.e. exercise) humans and proportional relationships between Tc and pulmonary ventilation during more pronounced hyperthermia. This proportionality suggested a causal relationship that was supported by our further studies that indicated positive interactions between Tc and known modulators (i.e. arterial PCO2/pH & PO2) of pulmonary ventilation. An emerging view became that elevated Tc stimulates ventilation and this is followed by a second phase or vestigial panting response when thermo- is prioritized over chemo-regulation. The objective of the proposed research is to further explore the nature and mechanisms underlying this hyperthermia-induced hyperventilation. To attain this objective we will assess how modulators of ventilation and Tc interact in their influences on thermo- and chemo- regulation during hyperthermia. A breath-by-breath end-tidal forcing system will be employed to allow clamping of partial pressures of end-tidal carbon dioxide and oxygen. The novelty and significance of this research will be to contribute to the resolution the long-standing anomaly of how and why humans hyperventilate heavy exercise. Elucidating how modulators of ventilation and temperature interact in thermo- and chemo- regulation of will help broaden the understanding of the function of these two physiological control systems in humans.