The Relationship Between Central and Peripheral Chemoreflex Sensitivities and (V)over dot(E) (V)over dotCO(2) Slope Below and Above the Respiratory Compensation Point of Incremental Exercise

During incremental exercise, the ventilation (V̇ ) versus carbon dioxide production (V̇CO ) relationship exhibits a double-linear response with an inflection of slope at the transition from hyperpnea to hyperventilation (i.e., respiratory compensation point (RCP)). Whether peripheral or central chemoreflexes contribute to the hyperventilatory response to incremental exercise remains undetermined. This study tested the hypothesis that peripheral and not central chemoreflex sensitivity would relate to the magnitude of the V̇ -V̇CO slope above RCP and that neither would relate to the sub-RCP V̇ -V̇CO slope. Seven healthy, caffeine-free males (age: 27±5 years) performed a ramp-incremental test to exhaustion on a cycle ergometer, during which ventilation and gas exchange were measured by metabolic cart. The V̇ -V̇CO slope above and below RCP were determined by linear regression from the estimated lactate threshold to RCP, and from RCP to end-exercise, respectively. On four separate days, 12 modified rebreathing tests were performed: six in isoxic-hyperoxia (PO =150 mmHg) and six in isoxic-hypoxia (PO =50 mmHg). Using ensemble-average data, central chemoreflex sensitivity was measured as the mean hyperoxic V̇ versus end-tidal partial pressure of carbon dioxide (P CO ) slope (in L∙min ∙mmHgP CO ) and the peripheral chemoreflex sensitivity was determined from the difference of hypoxic and hyperoxic slopes. The mean V̇ -V̇CO slopes above and below RCP were 35.0+3.7 (range: 28.3-39.9) and 61.8+9.2 (range: 51.9-78.3), respectively. Mean peripheral and central chemoreflex sensitivities were 1.6±1.3 L∙min ∙mmHgP CO (range: 0.1-3.7) and 4.1±2.1 L∙min ∙mmHgP CO (range: 2.3-8.4), respectively. Peripheral chemoreflex sensitivity did not relate to V̇ -V̇CO slope below (r=0.44, p=0.32) or above (r=-0.02, p=0.96) RCP. No relationships were found between central chemoreflex sensitivity and V̇ -V̇CO slope below (r=0.06, p=0.90) or above (r=0.04, p=0.93) RCP. These preliminary observations suggest that neither central nor peripheral chemoreflex sensitivity factor into the magnitude of the hyperpneic or hyperventilatory response to incremental exercise.