MUSCLE VENOUS PO₂ AND V.O₂ ARE LINEARLY RELATED IN REPETITIVE TETANIC CONTRACTIONS OF CANINE MUSCLE DURING HYPOXIC HYPOXIA

Abstract

1. It has previously been shown that perfusion with high O2-affinity-erythrocytes decreases venous PO2 (PVO2) and decreases O2 uptake (VO2) in contracting muscle at the same O2 delivery (arterial O2 concentration x flow). A linear VO2-PVO2 relationship has been obtained with a VO2-axis intercept, suggesting that, during this type of hypoxia, VO2 is composed of a PVO2-dependent and -independent VO2. However, the VO2-PVO2 relation during hypoxic hypoxia has not been examined. 2. To clarify this relation, PVO2 and VO2 have been measured in contracting gastrocnemius (1 Hz trains of 0.2 s isometric tetani) under both normoxic and hypoxic conditions during 5 min of stimulation. 3. Venous O2 changes proportionally with O2 delivery. Each VO2-PVO2 relation was linear, with the mean described by the equation VO2 = 5.06 + 0.41 x PVO2 (n = 6, r = 0.81, P < 0.05). The VO2-axis intercept was significantly different from zero (P < 0.05). 4. These results were similar to those obtained during hypoxia induced by high O2-affinity-erythrocytes. We conclude that there is a linear relationship between PVO2 and VO2 above the VO2-axis intercept, regardless of the type of hypoxia.

Increase in O2 Delivery with Hyperoxia Does Not Increase O2 Uptake in Tetanically Contracting Dog Muscle.

“…However, the PvO 2 increased by hyperoxia did not augment the VO 2 level as compared with normoxia, and the VO 2 /PvO 2 ratio during hyperoxia was decreased significantly (Table 1). This suggests that hyperoxia affects muscle VO 2 through a mechanism other than O 2 diffusion limitation as manifested by the VO 2 /PvO 2 ratio [3][4][5][6][7][8].…”

“…A thermostatically controlled infrared lamp was used to keep the surface of the muscle at 37°C. The isolated gastrocnemius was perfused by blood using methods described previously [6]. The perfusion pressure at the inlet of the arterial supply to the muscle was measured using a pressure transducer.…”

“…The animals were ventilated by a respirator with room air except for hyperoxia. The left gastrocnemius-plantaris muscle group in the 8 dogs was surgically prepared using a method similar to that described by us previously [5,6]. The right femoral artery and vein were exposed, and heparin (1,000 IU kg Ϫ1 ) was administered intravenously.…”