Ventilatory response in metabolic acidosis and cerebral blood volume in humans

The relationship between alterations in cerebral blood volume (CBV) and cen tral chemosensitivity regulation was: studied under neutral metabolic condi tions and during metabolic acidosis. Fifteen healthy subjects (56 +/- 10 ye ars) were investigated. To induce metabolic acidosis, ammonium chloride (NH 4Cl) was given orally. CBV was measured using Near Infrared Spectroscopy du ring normo- and hypercapnia and related to inspired ventilation ((V) over d ot(i)). A mean acute metabolic acidosis of Delta pH - 0.04 was realized wit h a mean decreased arterialized capillary Pco(2) (P(c)co(2)) of 0.20 kPa (1 .5 mmHg) (both P<0.001). During normocapnia, CBV was 3.51+/-0.71 and 3.65 /- 0.56 mi 100 g(-1) (mean +/- S.D.), measured under neutral metabolic cond itions and during acute metabolic acidosis, respectively (ns). Correspondin g values of (V) over dot(i) were 7.6 +/- 1.4 and 10.0 +/- 2.4 l min(-1) (P< 0.01), respectively. The slopes of the CO2-responsiveness (Delta CBV/dP(c)c o(2) and Delta (V) over dot(i)/DeltaP(c)co(2)). were not significantly diff erent Juring both metabolic conditions. A significant correlation between D elta CBV/DeltaP(c)co(2) and Delta (V) over dot(i)/DeltaP(c)co(2) was found during metabolic acidosis (P<0.01), but not under neutral metabolic conditi ons. CBV does not contribute in a predictable way to the regulation of cent ral chemoreceptors, (C) 2001 Elsevier Science B.V. All rights: reserved.