Author(s): GULUZADE, N., DUFFIN, J., KEIR, D., Institution: UNIVERSITY OF WESTERN ONTARIO, Country: CANADA, Abstract-ID: 2579

INTRODUCTION:
During steady-state exercise, ventilation (V̇E) is tightly matched to metabolic demand (V̇CO2) but whether and how changes in V̇CO2 are detected/transmitted remains a mystery because humans lack venous/lung CO2 sensors and exercise-induced elevations in blood PCO2 are buffered before entering the arterial circulation where CO2 sensors exist. We tested the hypothesis that breath-to-breath oscillations in alveolar PCO2 increase with exercise intensity and in proportion to V̇CO2.
METHODS:
Twenty participants (10 females) completed a maximal cycling exercise protocol and three repeated, step-incremental tests involving two, 8-min stages below gas exchange threshold (GET; MOD1 and MOD2) and two, 12-min stages between GET and RCP (HVY1 and HVY2). Breath-by-breath gas exchange (V̇CO2) and ventilatory variables (V̇E and PCO2) were measured by mass spectrometer and pneumotach. For each breath, the alveolar phase of PCO2 (vs time) was identified by the Fowler method and the rate of change in PCO2 (deltaPCO2/delta t) was quantified between 25%-75% of phase 3 (mmHg∙s-1). The V̇E, V̇CO2, and deltaPCO2/deltat were determined for each intensity as the average of breaths within the final 5 minutes of each intensity (MOD & HVY).
RESULTS:
One-way repeated measures ANOVA revealed a progressive increase (p<0.001) in steady-state V̇E from 25.0±3.8 at 20 W to 33.6±3.6, 42.6±5.3, 54.0±7.8, and 65.4±10.7 L∙min-1 at MOD1, MOD2, HVY1, and HVY2 and V̇CO2 rose (p<0.001) from 0.78±0.1 to 1.1±0.2, 1.5±0.3, 1.8±0.4, and 2.1±0.5 L∙min-1 over that intensity range. The deltaPCO2/delta t steepened from 5.7±2.8 mmHg∙s-1 at 20 W to 7.1±2.7, 8.6±2.9, 10.6±3.3, and 13.1±5.2 mmHg∙s-1. Repeated-measures correlation demonstrated a positive relationship between deltaPCO2/delta t and V̇CO2 (r=0.81, p<0.001).
CONCLUSION:
Breath to breath oscillations in PCO2 relate positively to increases in V̇CO2 during steady-state exercise of increasing intensity. Alveolar oscillations in PCO2 slope and amplitude likely translate to arterial circulation and could link V̇E to V̇CO2 through chemoreflexes in arteries and brainstem.