Pupillography

The Pupillograph Sleepiness Test (PST) from Amtech (Weinheim) reflects the fatigue waves of the pupil described by Löwenstein. Normally, the pupil size will be constant in normal central nervous system activation in the dark for a long time. However, occur with increased daytime sleepiness after a few minutes spontaneous fluctuations (oscillations) on the pupil, which are recorded with infrared videography. Cause of fluctuations in pupil size is a mechanism of the autonomic nervous system. With reduced central nervous system activating two divisions acting simultaneously, which inhibit the Edinger-Westphal nucleus. This leads to instability of the central sympathetic activation and consequently fluctuating in an inhibition of parasympathetic activity and the Edinger-Westphal nucleus (Löwenstein et al. 1963, Yoss et al. 1970).

Fig. 1. Experimental setup for the pupillography. The patient wears an infrared protective goggle, has propped his chin on a device and looks toward the infrared camera.

Evaluation

The average Pupil Unrest Index (PUI) is the average pupil size fluctuations in millimetres per second over a period of 11 minutes. Higher PUI values indicate a clinically significant daytime sleepiness in (Table 2). In a normal population (n = 349) between 20 and 60 years, was found a mean value for ln PUI of 1.50 ± 0.39 mm/min. Thus, abnormal values are obtained from ln PUI > 1.89 and pathological values from ln PUI > 2.28. The cut-off value of > 6.64 was found for 84.1% of a healthy sample (Wilhelm et al 2001), which was established that this is independent of gender and age (r = .85 to .94). The PUI correlated low, but significantly with the subjective estimates of daytime sleepiness in SSS (r = .29, p < .010). The implementation objectivity and evaluation objectivity seem to be sufficiently given, because the change in pupil size can be deliberately manipulated. The reliability was tested in healthy control subjects and is satisfactory (r = .64, p < .001) (Weefi et al. 2000).

Value range

Mean-2SD

Mean-SD

Mean

Mean+SD

Mean+2SD

ln PUI (mm/min)

0.73

1.11

1.50

1.89

2.28

Percentile

2.3%

15.9%

50.0%

84.1%

97.7%

PUI (mm/min)

2.07

3.05

4.50

6.64

9.80

Table 2. Percentile of the normal reference range for ln PUI and PUI 2.7 Reading test (Fig. 2)

In the first version of the Reading test, it was up to the patients and healthy controls, to select a passage according to their interests. Therefore, it was possible that the individual level of activation of OSAS patients may have influenced the excitement level of the books. For this reason, the story "One day, maybe one night" by Arnold Stadler (2003) was selected. This is a retrospective narrative. Due to the low excitement level of the narrative it was assumed that the degree of tonic activation would remain constant.

Table 2. Percentile of the normal reference range for ln PUI and PUI 2.7 Reading test (Fig. 2)

In the first version of the Reading test, it was up to the patients and healthy controls, to select a passage according to their interests. Therefore, it was possible that the individual level of activation of OSAS patients may have influenced the excitement level of the books. For this reason, the story "One day, maybe one night" by Arnold Stadler (2003) was selected. This is a retrospective narrative. Due to the low excitement level of the narrative it was assumed that the degree of tonic activation would remain constant.

A B

Fig. 2. In 2A is seen as the patient reads in a semi-recumbent position, the modified form of the story "One day, maybe one night" by Arnold Stadler (Fischer paperback 2003). In the face of the electrodes are glued EOG, EEG and the EMG and its right to recognize a polysomnography. In 2B, the patient is asleep and the book has resigned.

The text was justified, typed in the font "Times New Roman" and the size 12. The pages were not numbered and included 36 lines with 11 cm length. A lamp (40 watts) was used for lighting, placed at a distance of one meter above the patient's head. At the beginning of the Reading test, the patient was informed by a verbal instruction, to read the text as possible in the normal reading speed and without interruptions. Patients were asked to keep the book at a distance of 40 cm. Lack of vision and of reading ability has been excluded by spontaneous, aloud reading of few sentences, if the patient was able to read 3-5 sentences correctly and fluently. About the intention and the period of reading, the patients were not informed in order to allay apprehensions and expectations.

Evaluation

The reading movements are simultaneous eye movements, which are characterized by either internal or external amplitude deflections in the EOG. It occurs while reading a specific rhythm EOG, as the eyes "jump" at the end of the line to the next line start. The reading movements can be distinguishing well visually by small and big eye movements (Fig. 3). All reading movements were counted that occurred after a minimum interval of 3 seconds.

Fig. 3. On display are the reading movements of the left and right eye (LEOG and REOG) as a rhythmic, blue wave pattern. The reading movements occur during reading, when the eyes "jump" at the line end of the text (right) to line beginning (left). Large eye movements (e.g. view movements) are characterized by large amplitude fluctuations.

Fig. 3. On display are the reading movements of the left and right eye (LEOG and REOG) as a rhythmic, blue wave pattern. The reading movements occur during reading, when the eyes "jump" at the line end of the text (right) to line beginning (left). Large eye movements (e.g. view movements) are characterized by large amplitude fluctuations.

In the present study, the following variables were used and calculated: the average, the highest and the lowest reading frequency (read line per epoch), sleep latency (in minutes) and the number of read pages.

Results

The average reading rate of the patients (n = 75) was 7.0 +/- 3.5 lines per epoch. In healthy volunteers (n = 16) it was 9.4 +/- 4.0 lines per epoch. All healthy subjects were evaluated for daytime sleepiness than normal, since neither sleep onset tendencies nor decreasing reading frequencies were observed. In 32 of the 70 OSAS patients (45.5%), however, sleep latency was found within 60 minutes. Also the reading frequency decreased over time. Rühle and colleagues calculated for the first time, the sensitivity and specificity of the Reading test, finding a cut-off value of greater than 11 for a pathological daytime sleepiness (Rühle et al. 2007). The standardized Reading test achieved a sensitivity of 76.2% and a specificity of 66.7% (Erle et al. 2009).

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