Sources of error

Physical quantities can be measured. However, measured values have the property that they scatter around the true value. When dealing with a measurement method, it is essential to be aware of the extent of the scattering of the measured values, the error. While the error in physical measurements, e.g. the height of a person, is quite small, the unavoidable error in a hormone determination, for example, can be well over 10 %. The error is strongly dependent on the hormone concentration.

In addition to errors caused by the measurement method, influences originating from the person being tested can also distort the assessment of a measured value.

Hyperventilation

Hyperventilation triggers a large number of changes in the body; increases the heart rate, reduces the CO2 concentration in the blood, makes the blood alkaline and much more.

Because of the importance of hyperventilation for our well-being, I will soon be adding a corresponding page to this homepage. (to follow)

At this point, the influence of hyperventilation on the methods described in the diagnostics chapter will be explained.

Influence on physical working capacity

When determining the Physical Working Capacity, it is determined how many watts a person is able to produce at a defined heart rate of 110, 130, 150 or 170. The value is given as PWC110; 130, 150 or 170 in watts / kg body weight.

Since the maximum achievable heart rate (_HRmax ) can be described quite well with the formula _HRmax=(220 – age) x 0.9, it is clear that, for example, an 80-year-old could at best aim for a PWC of 110, and a 70-year-old could just about reach a PWC of 130. For younger people, the heart rate can certainly be increased to 150, or even 170 beats per minute, depending on how you define “younger”.

It is generally assumed that the PWC can be determined quite objectively and is even superior to the _VO2max when assessing a person’s performance, because the PWC is not subject to the subject’s voluntary influence. In contrast, anyone being assessed can claim that they cannot do any more and therefore stop the test well before reaching the actual maximum exercise capacity, the _VO2max.

When determining the PWC, it is assumed that physical stress increases the heart rate via the release of catecholamines. However, stress in general and anxiety in particular are also able to cause a release of catecholamines. The result is palpitations and a rapid pulse. Hyperventilation with an increase in pressure in the lungs plays a significant role in the release of catecholamines.

In any case, the result is a considerable acceleration of the heart rate regardless of the physical exertion. The next figure shows a case in which a test subject had considerable stage fright before the lactate test. First the data as a table:

Even at the lowest load level (inherent resistance of the ergometer 20 watts), the test subject had a heart rate of 122 beats/minute. Since he managed a load of 220 watts with only a moderate increase in lactate, it can be assumed that he was in good training condition, and the high initial heart rate is clearly due to the excitement of the examination.

The figure above shows the data in the table. The solid blue line shows the progression of the heart rate as the load increases. You can clearly see two different slopes in the heart rate curve. The curve rises more steeply at around 160 beats per minute. If you interpolate the slope > 160 / min back to the resting state, you arrive at the resting heart rate that the test person had on the day before the test!

The actual PWC130, as it is usually determined (blue rectangle, solid line), results in an extremely poor value of 0.76 W/kg (50 watts / 66 kg)! If you read off the interpolated straight line (blue rectangle, dashed line), a value of 1.8 W/kg (120 W / 66 kg) would be determined, which is clearly more realistic. The differences for the PWC 150 (green rectangles) are only slight. The influence of lamp fever can no longer be shown for the PWC170.

Generally speaking, it can be said that at resting heart rates below 100 bpm, the influence of stage fright or other psychological factors on PWC130 is negligible. However, resting heart rates above 100 bpm must be taken into account – either corrected, as shown here, or the value must be marked as unreliable.

Influence on the lactate test

As described in the previous paragraph, hyperventilation triggers various effects in the body, including an influence on the determination of the PWC. The values in the table from the course of a lactate test in an 18-year-old who had considerable stage fright before the test also show the effects on the lactate test.

If you look at the watts versus heart rate curve in this evaluation, you will see – as with the determination of the PWC in the previous paragraph – that there is no even approximate linearity between the increase in load (in watts) and the heart rate (brown line). The high heart rate in the lower load levels is not caused by the load but by stage fright. This means that the evaluation reads a much too high heart rate as _LT1 (134 b/min).

If the same corrections are made in the figure as in the PWC130 evaluation, realistic data is obtained for _LT1. _LT2 is not affected. Without correction, a somewhat high training heart rate would be recommended for the test person, but without entering a problematic range.

Influence on spiroergometry

follows after the description of spiroergometry