Table 3.

Microvascular Oxygen Transport from Rest to Contractions

	O2 Sat (%)	Hct (%)	Q̇m (ml min−1 100g−1)	Q̇O2mv (ml O2 min−1 100g−1)	V̇O2mv (ml min−1 100g−1)	DO2mv-mito (ml O2 min−1 mmHg−1 100g−1)	Q̇O2mv/V̇O2mv
SOL Rest	35	16	27	5.35	4.65	0.156	1.149
SOL End	17	20	85	16.83	15.52	0.761	1.084
PER Rest	23	16	8	1.58	1.45	0.061	1.095
PER End	6	20	46	9.11	8.83	0.659	1.031
MG Rest	24	16	6	1.19	1.08	0.045	1.098
MG End	6	20	42	8.31	8.06	0.602	1.031
WG Rest	19	16	8	1.58	1.47	0.067	1.078
WG End	12	20	45	8.91	8.42	0.484	1.058

Microvascular oxygen delivery (Q̇O₂mv), utilization (V̇O₂mv) and diffusing conductance (DO₂mv-mito) at rest and at the end of 120 s of twitch contractions. The Fick equation was used to calculate V̇O₂mv (i.e., V̇O₂mv = Q̇m × (CaO₂ − CvO2)) assuming the present PO₂mv is analogous to venous PO₂ (McDonough et al. 2001) and, by extension from the O₂ dissociation curve, venous blood O₂ content (Roca et al. 1992). Thus venous O₂ contents (CvO₂) were calculated [(1.34 ml O₂ (gHb)⁻¹ × (Hct/3) × %O₂ Saturation) + (PO₂mv × 0.003)] based on the constructed rat O₂ dissociation curve with Hill coefficient (n) of 2.6 to obtain O₂ saturation (O₂ Sat) from the present PO₂mv (see Table 2), an O₂ carrying capacity of 1.34 ml O₂ (gHb)⁻¹, haemoglobin (Hb) concentration using capillary haematocrit at rest and during contractions (Kindig et al. 2002), and a P₅₀ of 38 (the PO₂ at which Hb is 50% saturated with O₂). Q̇O₂mv (i.e., Q̇O₂mv = Q̇m × CaO₂) and V̇O₂mv utilizing extant blood flow (Q̇m; Behnke et al. 2003, McDonough et al. 2005) and capillary haematocrit during rest and contractions (Hct; Kindig et al. 2002). DO₂mv-mito was defined as V̇O₂mv/PO₂mv and provides an index of diffusive O₂ transport per unit of O₂ driving pressure. Q̇O₂mv/V̇O₂mv emphasizes the degree of O₂ delivery relative to O₂ utilization (i.e., higher values suggesting greater muscle perfusion per unit of intramyocyte V̇O₂).