Table 1.

Variables and human parameter values used in the modeling

Abbreviation	Parameter	Value
Sc	Fraction of oxygenated hemoglobin in the capillary
fc	Fractional distance down capillary
pOi	Partial pressure of O2 in the capillary
r	Radial distance from the center of the capillary
pOr	Partial pressure of O2 in tissue along the capillary radius
Sa	Fraction of oxygenated hemoglobin in the artery*	0.975
OEF	Extracted O2 divided by total available O2†	0.40
p50	Partial pressure of O2 for half occupied hemoglobin‡	26 mmHg
h	Hill constant‡	2.8
J	O2 consumption§	8.20 × 10−4 cm3 O2/cm3/s
RT	Tissue radius¶	32 μ**
D	O2 diffusivity‖	1.8 × 10−5 cm2/sec
C	O2 solubility‖	2.6 × 10−5 cm3O2/cm3/mmHg
RC	Capillary radius¶	3 μm**

^*S_a = 0.975 yields an arterial pO₂ of 96.2 mmHg with the Hill constant and p50 listed below. 

^† See Powers et al. (21) and Carpenter et al. (22). 

^‡ Common textbook values, e.g. Voet and Voet (23). 

^§ Global CMRO₂ of 2.93 ml/min/100 g (24) was multiplied by 8/5 to convert to gray matter CMRO₂ and 1.05/6000 to convert units. 

^¶ Hunziker et al. (25) measured seven groups of human cerebral cortexes (total n = 38) and found intercapillary distances and SD that varied from 54.90–60.52 μm and 1.81–5.73 μm, respectively. We chose one-half of the higher intercapillary distance for the tissue radius. 

^‖ Clark et al. (26). 

^**For use in Eq. 5, the radii must be expressed as cm to be compatible with other parameters.