customed calculates 2 basic parameters during a stress test: MET and PWC.
Below you will find an explanation on how we do it.
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MET (Metabolic Equivalent)
MET reflects the oxygen consumption during rest and sitting. It is 3,5ml O2 /kg body weight/min.
The metabolic equivalent is used to determine the energy expenditure during the maximum load. The metabolic equivalent in custo diagnostic is calculated as follows:
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MET = 1 + (12 * L): (3.5 * G)
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PWC (Physical Work Capacity)
The PWC value describes the physical performance of a patient at a certain heart rate. The indication of the PWC value is in Watt / kg
(Body weight). In custo diagnostic the PWC value is determined for heart rates of 130bpm, 150bpm and 170bpm. If those heart rates are not achieved the PWC value is calculated by interpolation or extrapolation.
Example: If a patient weighing 100 kg, the heart rate of 170 achieved at 200 watts, the PWC value is calculated as follows:
PWC170 = 200 W: 100 kg = 2 W / kg
The PWC reference values are set in custo diagnostic and can be changed.
The MET values, which are calculated in the custo diagnostic are correct according to the formula that is given for the Bruce protocol.
You could compare our results with public available tables like: http://en.wikipedia.org/wiki/Bruce_protocol
Here you see, that our results are within the range of the published values.
Please be aware that the Bruce protocol has not only advantages but also some disadvantages, as illustrated in the slide from the University of Texas.
Heinz Lowis also stated, that there is a big difference between walking and running, which is clearly reflected in physiological parameters (e.g. hear rate, breathing rate, O2-uptake and therefore also MET).
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The translation of exercise duration or workload into METs (oxygen uptake expressed in multiples of basal oxygen uptake, 3.5 O2 mL/kg per minute) has the advantage of providing a common measure of performance regardless of the type of exercise test or protocol used. Although such translations are based on approximations and are not as accurate for individual patients as measured maximum oxygen uptake (VO2max), VO2maxhas not been studied for prognostic purposes in large series of patients with chest pain.
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