Changes in chemoreflex characteristics following acute carbonic anhydrase inhibition in humans at rest

The effect of carbonic anhydrase (CA) inhibition with acetazolamide (ACZ, 1 0 mg kg(-1) I.V.) on the peripheral and central chemosensitivity and breath ing pattern was investigated in four women and three men aged 25 +/- 3 year s using a modified version of Read's rebreathing technique. Subjects were e xposed to dynamic increases in CO2 in hypoxic and hyperoxic backgrounds dur ing control conditions and following acute CA inhibition. All manoeuvres we re repeated twice and averaged For data analysis. The central chemoreflex s ensitivities, estimated from the slopes of the ventilatory response to CO2 during hyperoxic rebreathing, increased following acute CA inhibition (cont rol vs. ACZ treatment: 1.87 +/- 0.66 vs. 4.07 +/- 1.03 1 min(-1) (mmHg CO2) (-1), P < 0.05). The increased slope was reflected by an increase in the ra te of rise of tidal volume and breathing frequency. Furthermore with ACZ, t here was a left-ward shift of the ventilation vs. end-tidal P-CO2 curve dur ing hyperoxic hypercapnia but not hypoxic hypercapnia. The peripheral chemo reflex sensitivity was isolated by subtracting the hyperoxic slope (central only) from the hypoxic slope (central and peripheral). Following ACZ admin istration, the peripheral chemosensitivity was blunted (control vs. ACZ tre atment: 3.66 +/- 0.92 vs. 1.33 +/- 0.461 min(-1) (mmHg CO2)(-1), P < 0.05). In conclusion, acute CA inhibition enhanced the central chemosensitivity t o CO2 but diminished the peripheral chemosensitivity.