The Difference in Peripheral Chemosensitivity Between Trained and Untrained Individuals during Exercise

Abstract

Hypercapnic chemosensitivity is the ventilatory response to increased partial pressure of CO2 and is the result of central and peripheral chemosensor stimulation. The hypercapnic chemosensitivity of the peripheral chemoreceptors is potentially impacted by exercise, fitness, and sex, but this is not conclusive. This thesis sought to determine the difference of the peripheral chemoresponse to a transient hypercapnic test at rest and during exercise in individuals of various fitness. We hypothesized that 1. People that are trained will have a lower hypercapnic chemosensitivity compared to those that are untrained. 2. Individuals without mechanical limitations, with a lower V̇E than a participant of similar V̇O2, will have a lower hypercapnic chemosensitivity. Twenty-nine healthy participants (n=16 males) participated in one test day involving transient hypercapnic chemosensitivity testing and a maximal exercise test. Chemosensitivity testing involved two breaths of 10% CO2 repeated five times (30-45 sec between repeats) at rest and during the first two stages of exercise. Stage 1 of exercise started at 60W and 80W for females and males respectively, and both increased by 20W for stage 2. After stage 2, intensity increased in 20W increments every 1.5 minutes for both sexes. Overall, there was no significant difference between males and females, flow limited and nonflow limited, or high and low fitness groups during each stage of chemosensitivity testing (p>0.05). We did however see an effect of acute exercise, where there was a significant increase in the hypercapnic response during exercise compared to the response at rest (p<0.05). When the male and female participants were compared at an iso-V̇CO2, at 80W, the male participants had a significantly higher hypercapnic chemoresponse compared to females (p<0.05); however, this difference was absent when the response was scaled for BSA. These results suggest that fitness and sex do not influence hypercapnic chemosensitivity. These results also demonstrate the importance of taking these measurements both at rest and during exercise. Finally, the results of this study suggest that the mechanisms that lead to different hypercapnic chemosensitivities are not affected by fitness and that differences in the hypercapnic chemosensitivity between individuals do not have implications for those that develop flow limitations.