Table 3.
Cerebrovascular response to hypercapnia and parameters from logistic model
| Variable | Caucasian Americans | African Americans | P Value | |
|---|---|---|---|---|
| Hypercapnia | ||||
| Maximal flow (CBFV; % of baseline) | 195 (17) | 170 (20) | <0.001 | |
| Maximal conductance (CVCI; % of baseline) | 178 (17) | 153 (16) | <0.001 | |
Magnitude of hypercapnia achieved ( ; mmHg) |
15 (3) | 15 (3) | 0.65 | |
| Parameters from logistic model | ||||
| Flow | a (%) | 101 (18) | 69 (23) | <0.001 |
| b | 0.34 (0.2) | 0.50 (0.3) | 0.06 | |
| x0 (mmHg) | 45 (5) | 44 (4) | 0.47 | |
| y0 (%) | 205 (24) | 169 (24) | <0.001 | |
| Conductance | a (%) | 83 (21) | 58 (21) | <0.001 |
| b | 0.34 (0.2) | 0.58 (0.4) | 0.018 | |
| x0 (mmHg) | 44 (6) | 43 (4) | 0.43 | |
| y0 (%) | 188 (28) | 154 (19) | <0.001 | |
| Estimates of CVMR | ||||
| Logistic regression | ||||
| CVMRmax − CBFV (% mmHg−1) | 8.3 (3.8) | 7.3 (2.8) | 0.35 | |
| CVMRmax − CVCI (% mmHg−1) | 6.8 (3.7) | 7.1 (2.9) | 0.82 | |
| Linear regression (Δ9 mmHg) | ||||
| CVMRmax − CBFV (% mmHg−1) | 6.6 (2) | 6.1 (2) | 0.40 | |
| CVMRmax − CVCI (% mmHg−1) | 5.6 (2) | 5.1 (2) | 0.39 | |
Values are means ± SD. Abbreviations: a, the range of change in percentage of CBFV or CVCI; b, a constant that determines the overall sigmoidal property of the curve; x0, the level of 
at which cerebral vasomotor reactivity for CBFV or CVCI is maximal; and y0, the maximal value of CBFV and CVCI during the hypercapnic rebreathing protocol; CVMRmax, the maximal cerebral vasomotor reactivity using logistic regression analysis and linear regression analysis. Other abbreviations are as for Table 2.