Effect of caffeine on the ventilatory response to inhaled carbon dioxide

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Abstract

We investigated the effect of caffeine on the hypercapnic ventilatory response (HCVR) using steady state (SS) and rebreathing (RB) methods in 6 subjects. They received caffeine (5 mg/kg) or saline intravenously in a randomized, double-blind, crossover manner, with measurement of serum caffeine levels. PetCO2 and (V̇e), normalized for vital capacity (VC), were measured continually during RB and during the last 5 min of SS runs. The slope of the V̇e-PetCO2 response increased from 0.21 ± 0.14 to 0.38 ± 0.14 and from 0.23 ± 0.12 to 0.59 ± 0.45 VC·min−1·mmHg−1, measured by RB and SS respectively (P<0.05). Plotting Vt vs PetCO2 revealed a parallel shift (additive effect) in the response measured by RB after caffeine; but an increased slope (multiplicative effect) in the Vt-PetCO2 relation measured in SS. We conclude that caffeine acts as a respiratory stimulant and increases the HCVR, but that assessment of the caffeine-CO2 interaction is dependent on the methodology employed.

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