R. Waanders, W. Studer, F. Pleh, A. Kristen

is present if there was an increase in altitude and the person has headache or at least one other symptom and a total score equal to or above 5. The minimum score indicates that the subject is healthy; the maximum score is 25. Finally, the d2 test was administered. The test consists of 14 rows with 47 characters each (total of 658 items), as shown in Figure 3. There is a time limit of 20 seconds for each row. The task is to differentiate the characters d or p with 1 to 4 dashes. Every d with 2 dashes has to be crossed out with a pencil; no other signs should be marked. Each row contains 21 or 22 targets (i.e. characters to be crossed out) in random order. Each row is a small test in and of itself and allows evaluation of performance over time. The test counts the number of items processed (TN), the percentage of errors (E%), the concentration performance (CP – the number of correctly processed items minus the incorrectly crossed items), the errors (E) and the TN minus E (TN-E) as well as the fluctuation rate (FR). About 5 minutes are needed to complete the test. An important advantage is that the test can be administered to a group.

Fig.3. First 3 lines of the d2 test showing the processed items. After arrival at a new altitude, the subjects rested at least for 1 hour prior to testing.

RESULTS

Table 1 shows the results of the d2 test for all 8 subjects at the three measurement time points. The mean CP value decreased from 242.6 at sea level (SL) to 194.1 at 3,500 m and again increased to 212.3 at 4,640 m. The same trend can be seen for female and male participants with slightly more reduced values for females at altitude, but no significance analysis was performed because of the limited number of subjects. The maximum CP at SL was achieved from S8 (283), at 3,500 m from S6 and S8 (212) and at 4,640 m from S3 (245). S4 showed a CP performance that was well under the performance of all other subjects. The most characters (TN) were processed at SL, followed by 4,640 m and 3,500 m. The most errors (E) were made at 3,500 m, followed by SL and 4,640 m.

d2 CP

TN

E

SL 3,500 m 4,640 m

S1 209 177 179 S2 228 180 186 S3 259 208 245 S4 184 158 144 S5 249 211 230 S6 282 212 244 S7 247 195 232 S8 283 212 238 Mean/STD 242.6±34.4 194.1±20.4** 212.3±37.6** Female 240.0±38.4 189.7±19.4 201.0±32.2 Male 244.2±36.4 196.8±22.7 219.0±42.5 ** p< 0.01

Mean/STD 605.6±46.2 530.3±37.2** 541.8±54.4**

Mean/STD 19±36.1 26.9±33.2** 13.1±18.9**

Table 1: Concentration performance of the d2 test at Kilimanjaro for each subject and mean and standard deviation for the group.

Table 2 shows the LLS, the SaO2

and HR response to the different altitudes at Kilimanjaro as grand average of the 8 subjects. The LLS increases from SL to 3,500 m, where it reaches its maximum of 2.0. At 3,870 m it again decreases and finally increases to 1.9 at the highest measurement point of 4,640 m. SaO2 decreases from SL to 3,500 m and slightly increases at 3,870 m before reaching its minimum at the highest point. The HR increases from SL to 3,500 m and then decreases until 4,640 m. Female subjects reached higher LLS scores, lower SaO2 values and higher HR at 3,500 m and 4,640 m than male subjects, but no significance test was performed for the male and female groups because of the small size of the group.

SL 2,509 m 3,500 m 3,870 m 4,640 m

LLS 0±0 0.5±0.8** 2.0±1.1** 0.5±0.5** 1.9±1** Female 0±0 1.0±1 2.7±0.6 0.7±0.6 2.0±0 Male 0±0 0.2±0.4 1.6±1.1 0.4±0.5 1.8±1.3 S4 0 1 2 0 3

SaO2 [%]

97.1±0.8 96.1±1.7** 88.0±3.2** 88.3±2.1** 82.0±3.5** Female 97.3±1.5 97.0±2.0 87.3±4.5 88.7±1.2 80.0±5.2 Male 97.0±0 95.6±1.5 88.4±2.6 88.0±2.5 83.2±1.9 S4 97 97 90 90 86

HR [bpm] 71.6±10.8 79.1±14.7**99.0±12.3**82.3±10.3**79.3±12.6** Female 75.3±8.1 84.7±14.7 102.0±14.7 83.0±15.4 81.3±17.2 Male 69.4±12.5 75.8±15.3 97.2±12.0 81.8±8.2 78.0±11.2 S4 62 75 83 75 78

** p<0.01

Table 2: Grand average (for all subjects) of LLS, SaO2 and HR at Kilimanjaro

Of special interest is subject S4, who had a LLS of 2 at 3,500 m and of 3 at 4,640 m, which was in the range of all other subjects. The SaO2 value was 90% and 86% at the two altitudes, which was also in the range of the other subjects or even a little higher (i.e. better). The HR of 83 bpm and 78 bpm was also in the range of the other subjects and even below the average. But interestingly, this subject had been taking Diamox‚ for several days and due to a very severe headache at 4,640 m could not attempt the summit.

DISCUSSION

Within this study, ECG parameters, the LLS and oxygen saturation were measured at different altitudes and for the first time, compared to CP of the d2 test. The former are very commonly used parameters to describe high altitude symptoms. The LLS is especially popular because unlike ECG and oxygen saturation, it does not require special equipment.

Of special interest in this study is that the d2 test is a very effective and easily administered test to evaluate concentration performance at altitude. It decreased from a score of 242.6 at SL to 194.1 at 3,500 m. This altitude was reached after only 2 days of acclimatization. It is very interesting that the CP again increased to 212.3 at 4,640 m because of the 4 days additional acclimatization. It is also noted that the CP performance at 3,500 m was still 3% above the average German CP value and 8% above that at 4,640 m (12). The test also clearly shows that subjects are not able to process the characters at altitude as fast as at sea level and that with some adaptation, the processing speed again increases. It is quite obvious that subjects made most errors at 3,500 m, but the minimum error rate was reached at 4,640 m and not at sea-level. It must be noted that the SL-recording was made after the other 2 test points, so that the training effect does not explain this situation. Also interesting is that the LLS and the HR reached their maxima and CP its minimum at 3,500 m and not at 4,640 m. But the SaO2 reached the minimum at the highest point, i.e. 4,640 m. This shows that the HR, CP and LLS react faster than the SaO2 to altitude changes and acclimatization. The parameters HR, CP, LLS and SpO2 so allow us to quantify the positive effect of the acclimatization hike up Mt. Meru (4,566 m). Subject S4 showed LLS, SaO2 and HR values in the range of the other subjects, but could not attempt the summit because of severe headache. As he had been taking Diamox from the first day on, it could be that the medicine masked the high altitudes effects on LLS, SaO2 and HR. But if the CP value is considered, the minimum can be found at 4,640 m, where the severe headache developed that stopped him from continuing the climb. Table 3 compares the HR and LF/HF values for different studies performed [1 described in this paper, Dachstein see (1), Königsbrück see (2), Pakistan see (12)]. All 4 studies have in common that the HR and LF/HF increased from the base station (Low) to the top station (High). Notably, the ascent times and adaptation times were very different. On the Dachstein, the subjects needed only 6 min by cable car to ascend from 990 m to 2,700 m. In Königsbrück, the ascent from 134 m to 4,000 m was completed within 11 hours. This means that the time was longer but the altitude was also higher. On Kilimanjaro, the altitude was 4,640 m but acclimatization extended over 8 days. In Pakistan, the acclimatization period was 16 days. What is remarkable is that all these studies nonetheless have a very similar HR and LF/HF response. This shows that a fast ascent to lower altitudes leads to the same values as a slow ascent to higher altitudes and shows the acclimatization effect.

HR HR LF/HF LF/HF Altitude Ascent- GroupLow High Low High time size [bpm] ,] [1] [1] [m] Dachstein 69.1 80.4 2.1 4.4 2,700 6 min 10 Königsbrück68.9 81.6 2.5 3.9 4,000 11 h 10 Kilimanjaro 71.6 79.3 2.4 3.2 4,640 8 days 8 Pakistan 66.1 80.2 2.8 3.2 4,480 16 days 4

All differences are significant p< 0.01

Table 3: Comparison of HR, LF/HF parameters

Summarizing, we can recommend using the d2 test as an additional parameter to detect symptoms of high altitude sickness. It is simply a sheet of paper with a task that takes only about 5 minutes to perform and can be done simultaneously by the whole group to save time.

ACKNOWLEDGEMENT

We are grateful to Eva Hornbachner, Elisabeth Pranzl, Nicole Guger-Ulrich, Mike Gruber, Hannes Stiebitzhofer, Robert Leeb, and Herbert Ramoser for their participation in the Kilimanjaro study. The project was partially funded by the European Union PRESENCCIA Project and the FFG in Austria. We are also grateful to the Austrian Society for Alpine and High Altitude Medicine (_GAHM) for the Scientific Award and funding for this study. We are indebted to Eugenia Lamont (native speaker), B.A., and former Senior Technical Editor, Library of Congress, Washington, DC, for linguistic proofreading of the manuscript.

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