Metabolism
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Breathless after sprinting
WS is a sprinter; he weighs 75 kg. At the end of a 100 m race he is breathing rapidly and deeply, and continues to do so for several minutes. His plasma lactate and pyruvate were measured before and immediately after the race, and again 30 min later, when his breathing had returned to normal.
lactate (mmol /L) |
pyruvate
(mmol /L) |
|
| before the race | 0.5 |
0.11 |
| immediately after | 11.5 |
0.09 |
| 30 minutes later | 1.0 |
0.12 |
Can you explain why he was hyperventilating at the end of the race?
For reasons that we will be exploring in the exercise, he is acidotic, with a high plasma concentration of lactate. Note, however, that unlike the cases of PC and BD, who were considered in the exercise on Life-threatening acidosis in an alcoholic - and in a hunger striker given intravenous glucose, WS's plasma pyruvate is within the normal range at all times.
The usual response to acidosis is to increase the rate of breathing, so as to expel carbon dioxide, and so shift the equilibrium below to the left, lowering the hydrogen ion concentration in the bloodstream, and so raising plasma pH.
His oxygen consumption was also measured for 10 minutes before the race, and over the 30 minutes after the race. At rest he was consuming 0.5 L oxygen per minute. Over the 30 minutes after the race his average oxygen consumption was 14% higher, with a total consumption over 30 minutes of 17.12 litres of oxygen.
What we have to consider is where the lactate has come from, how it disappears during the 30 minutes after the race and why he consumes 14% more oxygen over the thirty minutes after he has completed the race.
In a series of experiments with anaesthetised fasting dogs cannulae were placed in the femoral artery and popliteal vein to permit measurement of metabolites taken up, or put out, by the gastrocnemius-plantaris muscle group after gentle electrical stimulation (1 twitch per second) and after vigorous electrical stimulation (5 twitches per second). Cannulae were also placed in the hepatic artery and hepatic vein, to permit measurement of metabolites taken up and put out by the liver. The result are shown as the arterio-venous difference as nmol /g tissue /minute; positive values indicate output from the tissue, negative values indicate uptake by the tissue. Figures show mean ± sd for 3 x replicate experiments.
muscle |
liver |
|||
gentle stimulation |
vigorous stimulation |
gentle stimulation |
vigorous stimulation |
|
| glucose | -215 ± 12 |
-885 ± 15 |
+100 ± 12 |
+660 ± 20 |
| oxygen | -4515 ± 50 |
-6912 ± 50 |
-1150 ± 50 |
-1800 ± 50 |
| lactate | +20 ± 5 |
+1112 ± 50 |
-50 ± 10 |
-1100 ± 40 |