Author(s): OGOH, S., FEELEY, M., KUNIMATSU, N., LIU, J., KATAYAMA, K., MIYAMOTO, T., Institution: TOYO UNIVERISTY, Country: JAPAN, Abstract-ID: 373

INTRODUCTION:
When cerebrovascular carbon dioxide (CO₂) reactivity (CVR) is assessed using the Douglas bag method, ventilation increases gradually and requires time to reach a steady state. We hypothesized that temporal and inter-individual differences in respiratory responses influence CVR estimation, and that accurate assessment requires attainment of a respiratory steady state during CO₂ inhalation.
METHODS:
To test this hypothesis, we applied an 8-minute CO₂ inhalation protocol (0%, 3.5%, and 5%) and evaluated the effects of chemoreflex-driven ventilatory changes and inter-individual variability on CVR using minute-by-minute analyses.
RESULTS:
Among 25 participants, 8 (32%) exhibited an overshoot in middle cerebral artery mean blood velocity (MCA Vm) immediately after CO₂ inhalation onset. CVR reached a steady state within 2–3 min on average; however, in overshoot individuals, MCA Vm and end-tidal CO₂ (PETCO₂) fluctuated until 6–7 minutes. The overshoot was associated with central respiratory chemoreflex sensitivity (r = 0.59, P = 0.019), but not with CVR sensitivity, indicating a respiratory origin of CVR variability.
CONCLUSION:
CVR assessment during the onset of CO₂ inhalation may be over- or underestimated due to inter-individual differences in MCA Vm responses to PETCO₂. Therefore, at least 6–7 minute of CO₂ inhalation is recommended to achieve a steady-state MCA Vm across participants.