48
Results
Blood samples were obtained before the contractions
began and at t = 10, 30, 40 and 70 minutes. Arterial PO2
was 87  2.3 mm Hg (mean  SEM) before contractions and
did not change significantly throughout the experiments
(see Figure 8). Before contractions began, PvC>2 was
50.2  2.0 mm Hg. During the contraction period PvC>2
was lower, but none of the blood samples measured had
a P02 less than 12 mm Hg. Except for the experiments
where fatigue was caused by 2.5/sec contractions, PvC>2
was back to pre-fatigue values early in the recovery
period. Contractions were continued, 0.2/sec, during the
recovery period of these (2.5/sec) experiments; therefore,
it might be expected that PvC>2 would not be at rest levels.
Arterial PCO2 began at 31.6  0.8 mm Hg and fell
slowly during the experiments. The decrease in PaCC>2 was
statistically significant but probably is of minimal
physiological significance. Venous PCO2 was high during
the contraction period when PvC>2 was low, and returned
to pre-contraction levels early in the recovery period.
Arterial pH was 7.40 0.01 before contractions began,
and did not change significantly throughout the experiments.
Venous pH decreased from 7.37 at t = 0 minutes to 7.32
(for 2.5/sec) or 7.28 (for 5 or 10/sec) at t = 10 minutes.
By 10 minutes of recovery, venous pH had returned to pre
fatigue values (see Figure 8).