Ch. Guger, W. Domej, G. Schwaberger, G. Edlinger

Christoph Guger, Wolfgang Domej, Günther Schwaberger, Günter Edlinger

Changes of ECG, oxygen saturation, Lake Louis Score and concentration performance on Kilimanjaro

Veränderung von EKG, Sauerstoffsättigung, Lake Louise Score und Konzentrationsfähigkeit am Kilimanjaro

SUMMARY

ECG parameters such as heart rate (HR) and heart rate variability (HRV), oxygen saturation (SaO2) and the Lake Louise Score (LLS) are common tools to describe the effects of high altitudes on the human body. Besides these parameters, we also tested mental processing performance at high altitudes. In this study, 8 subjects climbed Mt. Meru and Mt. Kilimanjaro within 9 days. The Mt. Meru (4,566 m) climb was undertaken shortly before the ascent of Mt. Kilimanjaro (5,896 m) to adapt to the altitude. The HR, the LLS, the SaO2 and d2 test score were determined at three points: (i) at 3,500 m on the way up Mt. Meru, (ii) at 4,633 m on the way to Uhuru Peak, and (iii) at sea level in Mombassa. The results show that heart rate and LLS reached their maxima, and the concentration performance its minimum at 3,500 m and not at 4,633m. Only the SaO2 values were slightly lower at 4,633 m than at 3,500 m. The study showed that the acclimatization hike up Mt. Meru and the acclimatization days before reaching 4,633 m had a positive effect on heart rate, LLS and concentration performance. The d2 test proved to be a very effective and easy tool that can be used by anyone to study the high altitude effect.

Keywords: high altitude medicine, Lake Louise Score, d2 test, heartrate

ZUSAMMENFASSUNG

EKG-Parameter wie die Herzfrequenz (HR) und Herzratenvariabilität (HRV), die Sauerstoffsättigung (SaO2) und der Lake Louise Score (LLS) werden häufig zur Beschreibung der Höhensymptomatik verwendet. Neben diesen Parametern

untersuchten wir auch die Konzentrationsleistungsfähigkeit in der Höhe. Im Rahmen der Studie wurden von 8 Personen der Mt. Meru und der Mt. Kilimanjaro in 9 Tagen bestiegen. Dabei wurde der Mt. Meru (4,566 m) vor dem Mt. Kilimanjaro (5,896 m) bestiegen, um eine bessere Akklimatisation zu gewährleisten. Die HR, der LLS, SaO2 und der d2-Test wurden auf 3 verschiedenen Höhen eruiert: (i) auf 3,500 m am Weg zum Mt. Meru, (ii) auf 4,633 m auf dem Weg zum Uhuru Peak und (iii) auf Meereshöhe in Mombassa. Die HR und der LLS erreichten das Maximum und die Konzentrationsleistungsfähigkeit ihr Minimum auf 3,500 m und nicht auf 4,633 m. Nur die SaO2 Werte waren geringfügig auf 4,633 m niedriger im Vergleich zu 3,500 m. Im Rahmen dieser Studie konnte die positive Auswirkung der Akklimatisationstour auf den Mt. Meru und der zusätzlichen Akklimatisationstage am Mt. Kilimanjaro auf Herzrate, LLS und Konzentrationsleistungsfähigkeit gezeigt werden. Der d2-Test ist ein sehr effektiver und einfach zu verwendender Test, um die Auswirkung der Höhe zu beschreiben, und kann leicht von jedem verwendet werden.

Schlüsselwörter: Höhenmedizin, Lake Louise Score, d2 Test, Herzrate

INTRODUCTION

ECG parameters such as heart rate (HR) and heart rate variability (HRV), the Lake Louise Score (LLS) or oxygen saturation are common tools to investigate the effects of high altitude on the human body. It was shown that even with little subjective awareness of the reduced amount of oxygen at an altitude of 2,700 m, the cardiovascular and central nervous systems are already affected (1). A study of 10 subjects on the Dachstein showed that the heart rate (HR) increased from an altitude of 990 m to 2,700 m (1) and heart rate variability (HRV) parameters decreased significantly. With the increase in altitude, the sympathetic system becomes more active than the parasympathetic system. These effects were also shown in a study in a hypobaric chamber at 4,000 and 5,000 m altitude (2, 3), in studies of long-term exposure to altitudes above 4,000 m (4, 5, 6), and in mountaineers at 2,700 m and 3,700 m (7). The Lake Louise Score (LLS) was created in Canada and is a simplified and standardized scoring system that allows diagnosis and quantification of acute mountain sickness (AMS) in altitude research (9). Currently, it is widely used by mountaineers and trekkers because it is short, has a simple format and is easy to complete. The LLS is sensitive enough to detect AMS, but the very specific scoring system also avoids over-diagnosis.

Due to reduced atmospheric pressures at high altitude, alveolar oxygen pressure and therefore arterial oxygen saturation (SaO2) are reduced. The resulting lack of oxygen seen at tissue level is regarded as a crucial trigger mechanism in the development of high altitude illness in hitherto healthy persons (4). It can easily be measured non-invasively by pulse oximetry and serves as an objective indicator of oxygen delivery to the tissue. Some studies have shown that SaO2 at rest correlates with high altitude symptomatology even at higher altitude and with high altitude performance [9, 10]. Next to these parameters, mental processing performance at altitude was also of interest. The present study introduces the d2 test as instrument to quantify the effect of altitude. It is a standard instrument for quantifying concentration, speed and attention in clinical and other settings (11). The test was originally developed to investigate aptitude for driving a motor vehicle. The subject’s task is to differentiate similar visual symbols as quickly and accurately as possible. The number of correctly processed items is a marker for individual attention and concentration performance. The test lasts approximately 5 minutes and can also be performed simultaneously by groups. We also looked at the effect of acclimatization on HR, LLS, SaO2 tration performance. and concen-

EXPERIMENTS AND METHODS

In July 2006, eight healthy subjects (3 female, 5 male, 31-36 years) participated in the Kilimanjaro study. Seven subjects were first-time participants. One subject had taken part in the same experiment 2 years earlier in the Alps. Seven subjects were right handed, one was left handed. After an ascent of Mt. Meru for acclimatization, Mt. Kilimanjaro was climbed via the Machame route (Fig. 1). The height profile of the Kilimanjaro climb is shown in Figure 2.

Fig.1.

Mt. Kilimanjaro, 5.895 m

The measurements for the experimental studies were performed 3 times: (i) at 3,570 m at Saddle Hut on the way to Mt. Meru; (ii) at 4,633 m in the Barafu Camp on the way to the summit of Mt. Kilimanjaro; and (iii) at sea level in Mombassa. The measurements always took approximately 1.5 hours.

Fig.2. Height profile of the Mt. Meru and Mt. Kilimanjaro climb. The numbers on the x-axis indicate the day; B – breakfast, L – lunch, D – dinner. The climb started at 1,380 m in Arusha. The first measurement point (MP) was at 3,570 m in the Saddle Hut on the way to Mt. Meru. The second measurement point was at 4,633 m in the Barafu Camp. This is the last camp before reaching the Uhuru Peak (highest summit of Mt. Kilimanjaro). The third measurement was per. formed at sea level in Mombassa 7 days after the climb.

First, ECG data to assess autonomous and central nervous system function were acquired with the g.MOBIlab+ pocket PC-based ECG recording system (g.tec medical engineering GmbH, Graz, Austria). The ECG was recorded as Einthoven I lead with 256 Hz and 16-bit resolution. The oxygen saturation (SaO2) was measured with a portable device (SPO 5500 P, Graseby Medical Ltd, UK) fixed on the index finger. The Lake Louise Score questionnaire was then filled out. The questionnaire contains 8 items covering headache, gastrointestinal symptoms, fatigue/weakness, dizziness, difficulty sleeping, mental status, ataxia and peripheral edema. AMS