Table 1. Physiologic measurements at all four levels of PETCO2 manipulation (mean±s.d.); statistically significant differences are denoted by asterisks (*).
| Challenge | Level | N | ΔPETCO2 (mm Hg) | ΔCBF (%) | ΔY (%) | ΔCBF:ΔPETCO2 (%/mm Hg) | ΔY:ΔCBF (%/%) | Ψ (%/%) | ΔCMRO2 (%) |
|---|---|---|---|---|---|---|---|---|---|
| Hypercapnia | Mild | 10 | 4.7±0.3 | 23.6±3.0 | 4.9±2.0 | 5.2±0.7 | 0.26±0.05 | 0.30±0.17 | 5.0±3.0 |
| Moderate | 11 | 9.0±0.3 | 53.3±3.1 | 16.9±2.1 | 5.9±0.3 | 0.36±0.05 | −0.21±0.16 | −6.8±8.0 | |
| Hypocapnia | Mild | 10 | −2.9±0.2 | −13.2±2.1 | −7.5±3.0 | 4.7±0.8 | 1.40±0.57 | 0.18±0.60 | 10.2±3.0 |
| Moderate | 9 | −5.8±0.3 | −16.9±2.0 | −12.7±2.0 | 5.2±0.7 | 0.76±0.25 | −0.24±0.60 | 12.5±9.1 | |
| Hypocapnia versus hypercapnia | P=0.004* | P=0.01* | P>0.99 | P=0.04* | |||||
| Mild versus moderate challenges | P=0.29 | P=0.18 | P>0.99 | P=0.21 | |||||
CBF, cerebral blood flow; ΔCMRO2, cerebral oxidative metabolism change; PETCO2, end-tidal partial pressure of CO2.
The means were weighted by the inverse of the measurement uncertainties. No significant difference in Ψ was found between mild and moderate hypercapnia (P>0.99), or between mild and moderate hypocapnia (P>0.99). Moreover, the Ψ estimates computed from all hypercapnic (Ψ=−0.12±0.11, mean±s.d.) and from all hypocapnic (Ψ=0.06±0.30) cases did not differ significantly (P>0.99).