Additional resources

PowerPoint presentation 5 on the CD. Self-assessment quiz 5 on the CD.

Problem 5.1: Winston B

Winston is a 75-kg man who takes part in a 100 m sprint. His plasma lactate was 0.5 mmol/L before the race and 11.5 mmol/L immediately after the race. Thirty minutes later, when his breathing had returned to normal, it was 1.0 mmol/L.

Assuming that extracellular fluid is 20% of body weight, what is the total amount of lactate that he metabolizes during this 30 minutes?

Most of this lactate will be metabolized in the liver, undergoing gluconeogenesis, followed by release of glucose into the bloodstream and uptake into muscle for synthesis of glycogen to replace that used during the race.

What is the total cost in mol ATP and/or GTP per mol of lactate converted to glycogen?

How much ATP would be required to convert all of the lactate that is metabolized into muscle glycogen?

How much lactate must undergo total oxidation to CO2 and water (via lactate dehydrogenase, pyruvate dehydrogenase and the citric acid cycle) to provide this ATP?

The oxidation of lactate, like that of glucose, consumes 0.746 L of oxygen per gram. The molecular mass of lactate is 90.1. What is his additional oxygen requirement (in litres of oxygen) over the 30 minutes after the end of the race?

Assuming that his total energy expenditure is 14 MJ/day, and that regardless of the fuel being oxidized the energy yield is 20 kJ per litre of oxygen consumed, what is the percentage increase in his oxygen consumption during this 30 minutes?

Problem 5.2: Peter C

Peter is a 50-year-old man, 174 cm tall and weighing 105 kg. He is an engineer, and works on secondment in one of the strict Islamic states in the Gulf, where alcohol is prohibited. At the beginning of August he returned to England for his annual leave. According to his family, he behaved as he usually did when on home leave, consuming a great deal of alcohol and refusing meals. He was known to be drinking 2 L of whisky, two or three bottles of wine and a dozen or more cans of lager each day; his only solid food consisted of sweets and biscuits.

On 1 September he was admitted to the Accident and Emergency Department of UCL (University College London) Hospital, semiconscious, and with a rapid respiration rate (40/min). His blood pressure was 90/60 and his pulse rate was 136/min. His temperature was normal (37.1 °C). Emergency blood gas analysis revealed severe acidosis (pH 7.02) and base excess (—23) with a Po2 of 91 mmHg and Pco2 of 10 mmHg. He was transferred to intensive care and given intravenous bicarbonate.

His pulse rate remained high, and his blood pressure low, so emergency cardiac catheterization was performed; this revealed a cardiac output of 23 L/min (normal 4— 6). A chest radiograph showed significant cardiac enlargement.

Table 5.7 Clinical chemistry results for a plasma sample from Peter C taken in the fasting state

Concentration (mmol/L)

Peter C

Reference range

Glucose

10.6

3.5-5.0

Sodium

142.0

131-151

Potassium

3.9

3.4-5.2

Chloride

91.0

100-110

Bicarbonate

5.0

21-29

Lactate

18.9

0.9-2.7

Pyruvate

2.5

0.1-0.2

Table 5.7 shows the clinical chemistry results from a plasma sample taken shortly after Peter was admitted.

What is the likely biochemical basis of Peter's problem, which led to his emergency hospitalization?

What additional test(s) might you request to confirm your assumption?

What emergency treatment would you suggest?

This information is from the case notes of a patient in the ITU at UCL Hospital/ The Middlesex Hospital — I am grateful to Dr Hugh Montgomery for drawing my attention to this case, and for permission to repeat data from the patient's notes.

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