Journal of Behavioral and Brain Science, 2013, 3, 13-25
http://dx.doi.org/10.4236/jbbs.2013.31003 Published Online February 2013 (http://www.scirp.org/journal/jbbs)
Blood Chemistry, Acid-Base, Electrolyte, Blood Lactate
Metabolism and Sleep at 3480 m in
Mountain Marathon Runners
Ivana Gritti1*, Clara Mauri1, Stefano Defendi1, Daniele Cesana2, Federica Consonni2,
Alberto Dolci3, Sabrina Luoni1
1Department of Biomedical and Clinical Science Luigi Sacco, University of Milan,
Milan, Italy
2Roche Diagnostic SpA, Viale Stucchi 110, Milan, Italy
3Hospital Luigi Sacco, University of Milan, Milan, Italy
Received December 20, 2012; revised December 27, 2012; accepted February 19, 2013
ABSTRACT
Altered blood chemistry, acid-base and electrolyte are suggested determinants of sleep disturbance, with frequent arou-
sal at high altitude even in well and long-trained altitude marathon runners. In this sample of experienced altitude
marathon runners with maximal aerobic power at sea level of 61.4 ± 2.7 ml/kg−1·min−1 we found that pO2 and percent of
oxygen saturation (%SO2) were lower at 2050 m and 3480 m than at sea level; pO2 was higher after 38 - 41 hours than
after 30 - 31 hours of acclimatization at 3480 m (P < 0.05). After ascentto 3480 m %SO2 decreased (P < 0.003). Com-
pared to sea level values, pH increased at high altitude (P < 0.05) consistent with changes in pCO2 and (P <
0.05). Nocturnal %SpaO2 at a sleeping altitude of 3480 m was lower (P < 0.05) than at sea level. At high altitude, the
percent of wake (W) time and delay falling asleep (DFA) increased, whereas non-rapid eye movement sleep (N-REM),
REM sleep and total sleep time (TST) decreased (P < 0.05). Simple regression analysis disclosed a significant correla-
tion between the changes in TST and the percent of REM sleep and the changes in %SpaO2 recorded during sleep (P <
0.05). Simple regression analysis showed a positive correlation between the changes in pO2 at higher altitude and the
percent of W and of TST (P < 0.05). The changes in pO2, tCO2 and
3
HCO−


3
HCO−




3
HCO−
correlated negatively and significantly
with the percent of REM sleep changes at high altitude (P < 0.05). The TST changes at high altitude correlated posi-
tively with the changes in pO2 and pH and correlated negatively with the changes in %SO2, pCO2, tCO2, and




3
HCO−


(P < 0.05). The changes in the percent of W at high altitude correlated significantly and positively with the changes in
bases excess [BE] at high altitude (P < 0.05). The changes in the percent of REM sleep correlated significantly and
positively with the changes in [iCa++] and [BE] and negatively with the changes in buffered bases [BB] and [BEeffec-
tive] (P < 0.05). The change in the percent of NREM + REM sleep at high altitude correlated significantly and posi-
tively with the changes in [BE] and [BB] concentration (P < 0.05). The increase in DFA at high altitude correlated sig-
nificantly and negatively with the changes in pCO2 and significantly and negatively with the changes in [K+] (P < 0.05).
Simple regression analysis demonstrated that the changes in pH at high altitude correlated positively and significantly
with the percent of W and the DFA and negatively with the percent of changes in NREM sleep, REM sleep, NREM +
REM sleep (P < 0.05). The decrease in the TST at high altitude correlated significantly and negatively with the changes
in pCO2, tCO2, and
[K+] (P < 0.05). Our data demonstrate that the arterialized ear lobe techniques we used
for evaluating most of the changes in blood chemistry, acid-base, electrolyte and blood lactate metabolism aresuitable
for clinical and laboratory assessment and are important predictors of the quality and quantity of acclimatization and
sleep at high altitude.
Keywords: Clinical Investigation at High Altitude; Laboratory Investigation at High Altitude; Hematochemistry;
Acid-Base Metabolism; Electrolyte Metabolism; Blood Lactate Metabolism; Hydration Status; Sleep
Quality Indicators; EEG; Mountain Marathon Runners
*Corresponding author.
C
opyright © 2013 SciRes. JBBS

I. GRITTI ET AL. 14
1. Introduction
Clinical and laboratory investigations can help us to un-
derstand how the body adjusts its biochemical and phy-
siological cellular needs to counter health risks associ-
ated with exposure and activities in hypobaric-hypoxia
conditions. Research into these mechanisms is funda-
mental for studying the appropriate time course of accli-
matization and the quality and quantity of sleep at high
altitude [1-5].
Increasingly popular as a recreational sport, endurance
and marathon race events at high altitude (2500 - 5500 m)
became part of the Olympic games in 1968. Mountain
running competitions are generally long-distance races
similar to the classic marathon race, over rough terrain at
high altitude, under relatively hypoxic conditions, with
different gradients between the start and the end of the
race.
Usually referred to as mountain marathon sky runners,
some athletes possess the anthropometric characteristics
typical of marathoners [6]. Experimental studies on the
exercise physiology of mountain marathon runners dem-
onstrated that marathon performance at high altitude is
safe, demands strenuous effort, and induces transient, psy-
chological, hematological and hormonal variations that
fully resolve within 24 hours [6-16].
Studies of hypobaric-hypoxic high-altitude conditions
have reported different degrees of high-altitude-induced
altered states of consciousness [16,17]: insomnia, dizzi-
ness, sleep-wake disturbances [18], paroxysm [19] in nor-
mal subjects and mountain climbers and cognitive chan-
ges in mountain marathon runners [16].
Fundamental for attaining maximal performance in
mountain marathon running at high altitude is the degree
of acclimatization and training [7-16]. Current debate
centers on the use of specific metabolic markers [3-5]
and sleep quality and quantity as indices of general and
central nervous system health status [2], as well as the
tempo of acclimatization to high altitude conditions in
mountain marathon runners preparing for performance at
high altitude.
We studied healthy mountain marathoners native to
sea level, matched for aerobic power, anthropometrical
characteristics and level of athletic performance at high
altitude under a controlled standard method/protocol for
physical and psychological stressors. For clinical and la-
boratory investigation we took repeated measurement of
metabolic variations in acid-base, electrolyte and blood
lactate. The nocturnal percent of peripheral arterial oxy-
gen saturation was measured every 30 seconds, and poly-
somnographic activity during sleep was recorded by
means of electroencephalogram (EEG), electro-oculo-
gram (EOG) and electromyogram (EMG) and by admini-
stration of questionnaires investigating sleep quality. The
aim of the study was to collect data on the degree and
tempo of acclimatization after ascent to 3480 m, which
might be, together with nutrition, energetics [20], and
exercise level [6], a crucial step in acclimatization when
mountain marathon runners need to perfect their physical
work capacity and performance during races at altitudes
between 2000 m and 5000 m.
2. Materials and Methods
2.1. Subjects
Six healthy male mountain marathon runners (age range
37 - 44 years) were recruited for the study. The subjects
were part of a group of experienced high-altitude runners
that had been clinically tested since 1994. The mean
body mass was 65.8 ± 4 kg; the height was 1.76 ± 0.37
cm; the mean maximal aerobic power at sea level was
61.4 ± 2.7 ml/kg−1·min−1. Maximal aerobic power was
measured by using open circuit spirometry during a step-
incremental treadmill run to volitional exhaustion.
Diet was controlled for food and water intake at low
and at high altitudes during the study period; no neuro-
depresssive or neuroactive beverages were allowed. The
subjects were also asked to avoid aerobic and anaerobic
exercise about 12 hours before the sea level testing ses-
sion and during the long testing sessions at high altitude.
All experiments were carried out in accordance with the
Helsinki Declaration (1975/1983) and the 86/609/EEC
directive for experimental human care and designed to
reduce stress and suffering to a minimal level, number of
subjects used, and number of tests performed. Impor-
tantly, informed consent was obtained from each subject
before each experiment, in accordance with the rules of
the International Federation of Sport at Altitude (FSA).
Local time and barometric pressure (PB) at an altitude
of 122 m (Department of Clinical Science, Luigi Sacco
Hospital, University of Milan, Milan, Italy), at 2050 m
(Cervinia, Aosta, Valle d’Aosta, Italy) and at 3480 m
(Plateau Rosà, Cervinia, Aosta, Valle d’Aosta, Italy)
were measured using a chronometer and barometer sen-
sors mounted on a mobile hemogasanalyzer kindly pro-
vided by OptiCCA®, Roche Diagnostics (Monza, Italy).
The mountain marathon runners ascended from 122 m
at 11:00 h, reaching 2050 m at 13:00 - 14:00 h by car and
3480 m at about 15:00 - 16:00 h by cable car. Metabolic
measurements were taken with the subjects in a behav-
ioral wakeful state, preferably supine, otherwise in a sit-
ting position, after at least 3 hours of rest, and before,
during and after sleep in a wooden room.
2.2. Hematochemical, Acid-Base and Electrolyte
Metabolism
In five mountain marathon runners, hematochemical pa-

I. GRITTI ET AL. 15
rameters were measured in capillary blood drawn from
the earlobesand in venous blood drawn from the brachial
vein using heparinized capillaries and syringes. In the
preanalytical phase, care was always taken to avoid as far
as possible physical or chemical alteration of blood com-
position during sampling and while injecting the samples
into the analyzer almost immediately after sampling. All
analyses were performed on a portable hemogasanalyzer
with throwaway cartridges (kindly provided by OptiCCA®,
Roche Diagnostics, Monza, Italy). During the final data
evaluation, not all the cartridge cells were found to be
perfect for correct detection of chemicals due to mistakes
in transporting the kit at the correct temperature for
working at high altitude.
Sea level. Sampling was done with the subjects in a
wakeful behavioral state at 122 m (11:19 ± 0.08 h; PB
742 ± 7.7 mm Hg). Capillary arterialized blood samples
from the earlobe were collected to measure partial oxy-
gen pressure (pO2; mm Hg), hemoglobin saturation (SO2
[%]), partial carbon dioxide pressure (pCO2; mm Hg),
carbon dioxide content (tCO2; mmol/L), hemoglobin con-
tent (tHb; g/dL), pH, bicarbonate concentration (3 HCO−



;
mmol/L),the electrolytic pattern concentrations of so-
dium ([Na+]; mmol/L), potassium ([K+]; mmol/L), ion-
ized calcium ([iCa++]; mmol/L) and bases excess ([BE];
mmol/L), buffered bases ([BB]; mmol/L), bases excess
active ([BE act]; mmol/L) and bases excess effective
([BEeffect]; mmol/L).
High altitude. Capillary blood samples were collected
with the subjects awake on reaching an altitude of 2050
m (13:02 ± 1.09 h; PB 587.6 ± 0.22 mm Hg), after 6
hours of acclimatization at 3480 m (21:42 ± 0.13 h; PB
491 ± 7.9 mm Hg), following 30 - 32 hours of acclimati-
zation at 3480 m (22:30 ± 0.9 h; PB 495.7 ± 3.7 mm Hg),
then at a sleeping altitude of 3480 m after a night’s sleep
and 38 - 41 hours of exposure (9:06 ± 1.06 h; PB 495.4 ±
3.19 mm Hg). Capillary blood samples at the final alti-
tude were taken from the earlobes to measure pO2, SO2
[%], pCO2, tCO2, tHb, pH, 3
HCO−



, the electrolytic
pattern concentrations of [Na+], [K+], [iCa++ ], the [BE],
[BB], [BE act] and [BE effect].
Venous blood samples at high altitude were collected
with the subjects in the supine position in a wakeful state
after about 3 hours of rest, 30 - 32 hours of acclimatiza-
tion, before going to sleep, after a night’s sleep, and 40 -
41 hoursafter reaching an altitude of 3480 m. The sam-
ples were taken to measure pO2, SO2[%], pCO2, tCO2,
tHB, pH, , [Na+], [K+] and [iCa++].
3
HCO−


2.4. Blood Lactate Metabolism
In five mountain marathon runners blood lactate ([La−];
mmol/L) was measured in capillary blood drawn from
the earlobes, with the subjects in the supine or sitting
position, in a wakeful state, after 3 hours of rest at 122 m,
then just after reaching 2050 m, after (after 3 hours of
rest) 6, 30 - 31, and 38 - 41 hours of acclimatization at an
altitude of 3480 m. The lactate concentrations were mea-
sured on a portable analyzer (YSI 1500 Sport, L-Lactate
Analyzer®, Yellow Springs, OH, USA).
2.5. Polysomnographic Recordings
Polysomnographic signals were recorded at low altitude
at the Department of Clinical Science, Luigi Sacco Hos-
pital, University of Milan, Milan, Italy, and between 30 -
31/38 - 41 hours of acclimatization at an altitude of 3480
m (V High Mountain Alpinist High-House, Plateau Rosà,
Cervinia, Aosta, Valle d’Aosta, Italy). Electroencephalo-
graphic (EEGs, µV/cm) activities were recorded by means
of Ag/AgCl EEG scalp electrodes placed on the scalp of
both hemispheres of the frontal, parietal and occipital
cortices according to the international 10 - 20 system.
The Ag/AgCl electrodes were covered with gauze, filled
with conductive Grass EEG betonies paste and fixed with
collodion 5%.The resistance between the electrodes was
5 - 32 kΩ for each pair of electrodes. Electro-oculograms
(EOGL and R, µV/cm) were performed using small throw-
away electrodes placed to the right and left sides of each
eye in the right up-orbital and the left down-orbital re-
gions. Submental electromyograms (EMG-Sub, µV/cm)
were recorded by means of two cupping Ag/AgCl elec-
trodes fixed at a maximum distance of 1 cm. Amplified
EEGs signals were acquired from F3-F4; F3-P3; P3-A2;
O1-O2, EOGL and R and EMG-derivations at a frequency
of 512 Hz sent to a computer equipped with software
applications for on-line digitalization, recording and dis-
play of signals (Extensa 355, Texas Instruments; Daq-
Book-100, IO-Tec, Milan, Italy) and for subsequent off-
line signal analysis (LabView, National Instruments®,
Milan, Italy). In the six mountain marathon runners the
percent of nocturnal peripheral arterial oxygen saturation
(%SpaO2) was recorded every 30 seconds by means of a
8500 Nonin finger pulse oxymeter (Nonin Med. Inc. MN,
USA) during sleep at 122 m and between 30 - 31 and 38 -
41 hours of acclimatization at an altitude of 3480 m and
at an approximate PB of 495 mm Hg.
2.6. Subjective Perception of Sleep Quality
After polysomnographic recording at sea level and at
high altitude, the subjects completed a questionnaire in-
vestigating perceived sleep quality according to the fol-
lowing indicators: 1) sleep latency (minutes of delay in
falling asleep); 2) total number of hours slept; 3) awaking
time before expected; 4) number of arousals; 5) whether
or not rested on waking; 6) 10-point visual analogue
scale (VAS) scored from poor (1) to excellent (10).

I. GRITTI ET AL. 16
2.7. Statistical Analysis 0.05 were considered statistically significant.
Data are presented as the mean ± standard deviation (SD).
Measurements were submitted to statistical analysis em-
ploying one way analysis of variance (ANOVA) fol-
lowed by post-hoc multiple comparison of the means by
applying Fisher’s Protected Least Significant Difference
(PLSD), Scheffé and Dunnet. Differences between paired
and unpaired single or repeated measurements were also
analyzed using Student’s t-test. Linear simple regression
analysis was also performed. Probability levels of P <
3. Results
3.1. Hematochemical and Acid-Base Metabolism
The results of capillary and venous blood analysis showed
changes in respiratory alkalosis and metabolic compen-
sation during 6, 30 - 31, 40 - 41 hours of acclimatization
at 3480 m. Changes in hemoglobin values were observed
within the normal range for this type of athletes (Tables
1-3).
Table 1. Hematochemical, acid base, electrolyte, and blood lactate values at 122 m, during acclimatisation at 2050 m and after
6, 30 - 31, 38 - 41 hours of acclimatisation at an altitude of 3480 m. Data from capillary earlobe samples (1,2,3,4).
Parameters 122 m 2050 m 3480 m (6 h)
vs 122 m vs 122 mvs 2050 m
No. (5) MeanSD No. (5)Mean SDP t-test No. (5)Mean SD P t-test P t-test
PB mmHg 4 742.17.7 5 587.6 0.20.0001 5 491.3 7.89 0.0001 0.0001
pO2 mmHg 4 71.46 5 58.18 20.02 5 39.89 4.5 0.0002 0.00025
pCO2 mmHg 4 41.213.38 5 34.74 3.30.03 5 33.65 0.85 0.01811
tCO2 mmol/L 4 29.871.44 5 27.22 1.80.04 5 27.16 1.37 0.02698
SO2% 4 93.92.19 5 91.321 1.5 5 77.7 6.3 0.0028 0.00712
tHb g/L 4 15.721.45 5 16.62 1.1 5 15.64 1.95
pH 4 7.460.02 5 7.4954 00.03 5 7.5074 0.022 0.00791
3
−


HCO
3
−


HCO
mmol/L 4 28.631.39 5 26.14 1.80.05 5 26.12 1.331 0.03183
[Na+] mmol/L 1 139 5 138.96 1.6 2 141.5 0.771
[K+] mmol/L 1 4.7 5 5.06 0.9 2 4.25 0.007
[iCa++] mmol/L 1 1.17 5 1.19 0 2 1.19 0.014
[BE] mmol/L 4 4.350.77 5 3.3 1.3 5 3.54 1.6
[BB] mmol/L n.r. n.r.n.r. 5 52.02 1.6 n.r. n.r. n.r.
[BEact] mmol/L n.r. n.r.n.r. 5 3.82 1.3 n.r. n.r. n.r.
[BEeffect] mmol/L n.r. n.r.n.r. 5 3.7 2.7 n.r. n.r. n.r.
[La−] mmol/L 3 0.770.1 5 0.96 0.2 5 0.88 0.2419
Parameters 3480 m (30 - 31 h) 3480 m (38 - 41 h)
vs
122 m
vs
2050 m
vs 3480 m
(6 h)
vs
122 m
vs
2050 m
vs 3480 m
(6 h)
vs 3480 m
(30 - 31 h)
No. (5) MeanSD P t-test P t-testP t-test No. (5)MeanSD P t-test P t-test P t-test P t-test
PB mmHg 10 495.73.4 0.0001 0.0001 10 495.43.180.0001 0.0001
pO2 mmHg 10 45.324.22 0.00105 0.0001 0.0565 10 49.494.030.0022 0.0001 0.0045 0.0366
pCO2 mmHg 10 29.332.61 0.0021 0.01670.0004 10 28.032.330.0016 0.0066 0.0001
tCO2 mmol/L 10 83.554.82 0.00015 0.0005 10 86.453.510.0009 0.0025 0.0322
SO2% 10 24.251.81 0.00049 0.0172 0.0057 10 22.771.750.0001 0.002
tHb g/L 10 15.901.5 10 16.411.29 0.0003
pH 10 7.520.02 0.00075 10 7.5110.030.0001
mmol/L 10 23.361.73 0.00058 0.01960.0063 10 21.921.7 0.0001 0.0002 0.00036
[Na+] mmol/L 7 141.31.49 0.0337 7 139.61.36 0.0445
[K+] mmol/L 7 5.230.63 0.0057 7 5.230.67 0.0079
[iCa++] mmol/L 7 1.210.04 7 1.2040.06
[BE] mmol/L 10 1.681.42 0.00104 0.058 10 0.411.57 0.0041 0.00412
[BB] mmol/L 5 50.541.49 4 49.332.32
[BEact] mmol/L 5 2.181.4 4 1.6251.13 0.0299
[BEeffect] mmol/L 5 1.341.15 4 1.9251.44
[La−] mmol/L 5 0.920.36 5 0.6010.25 0.0498
(1) Abbreviations of haematochemical parameter and units are detailed in the method sections. (2) Measurements were submitted to statistical analyses, em-
ploying one-way analyses of variance ANOVA followed by post-hoc multiple comparisons of the meansby applying Fisher’s and Scheffe’s Protected Least
Significance Difference (PLSD) and Student t-test. The significant level was set at P < 0.05. (3) Measurements submitted to statistical Dunnet analysis were
found not significantly different. (4) Only the detailed values regarding the Student t-test are reported. (5) No = Number of measurements performed in the five
mountain runners at different altitudes.

I. GRITTI ET AL. 17
Table 2. Delta of hematochemical, acid base, electrolyte, and blood lactate values at 122 m, during acclimatisation at 2050 m,
and after 6, 30 - 31, and 38 - 41 hours at an altitude of 3480 m. Data from capillary earlobe samples.
Parameters 122 m
vs 2050 m vs 3480 m (6 h) vs 3480 m (30 - 31 h) vs 3480 m (38 - 41 h)
PB mmHg −154.5 −250.8 −264.4 −246.7
pO2 mmHg −13.22 −31.51 −26.08 −21.91
pCO2 mmHg −6.47 −7.56 −11.88 −13.18
tCO2 mmol/L −2.65 −2.71 −5.62 −7.1
SO2% −2.58 −23.2 −8.35 −7.45
tHb g/L 0.9 −0.08 0.18 0.69
pH 0.0359 0.0479 0.069 0.0516
3
−


HCO
3
−


HCO
3
−


HCO
3
−


HCO
mmol/L −2.485 −2.505 −5.265 −7.335
[BE] mmol/L −1.05 −0.81 −2.67 −3.94
[La−] mmol/L 0.26 0.18 0.22 0.099
Parameters 2050 m
vs 3480 m (6 h) vs 3480 m (30 - 31 h) vs 3480 m (38 - 41 h)
PB mmHg −96.3 −91.9 −92.2
pO2 mmHg −18.29 −12.86 8.69
pCO2 mmHg −1.09 −5.41 −6.715
tCO2 mmol/L −0.06 −2.97 −4.45
SO2% −20.62 −5.77 −4.78
tHb g/L −0.98 −0.72 −0.21
pH 0.012 0.025 0.0157
mmol/L −0.02 −2.78 −4.85
[Na+] mmol/L 2.54 2.33 0.61
[K+] mmol/L −0.81 0.17 0.17
[iCa++] mmol/L 0 0.02 0.0142
[BE] mmol/L 0.24 −1.62 −2.89
[BB] mmol/L −2.38 −3.6875
[BEact] mmol/L −1.64 −2.195
[BEeffect] mmol/L −2.36 −1.775
[La−] mmol/L −0.08 −0.04 −0.359
Parameters vs 3480 m (6 h)
vs 3480 m (30 - 31 h) vs 3480 m (38 - 41 h)
PB mmHg 4.4 4.1
pO2 mmHg 5.43 9.6
pCO2 mmHg −4.32 −5.62
tCO2 mmol/L −2.91 −4.39
SO2% 14.85 15.75
tHb g/L 0.26 0.77
pH 0.013 0.0037
mmol/L −2.76 −4.83
[BE] mmol/L −1.85 −3.13
[La−] mmol/L 0.04 −0.279
Parameters 3480 m (30 - 31 h)
vs 3480 m (38 - 41 h)
PB mmHg −0.3
pO2 mmHg 4.17
pCO2 mmHg −1.305
tCO2 mmol/L −1.48
SO2% 0.9
tHb g/L 0.51
pH −0.0093
mmol/L −2.07
[Na+] mmol/L −1.72
[K+] mmol/L 0
[iCa++] mmol/L −0.00058
[BE] mmol/L −1.27
[BB] mmol/L −1.3075
[BEact] mmol/L −0.555
[BEeffect] mmol/L 0.585
[La−] mmol/L −0.319

I. GRITTI ET AL. 18
Table 3. (a) Differences in hematochemical, acid-base and electrolyte values observed after 30 - 31 and 38 - 41 hours of accli-
matisation at an altitude of 3480 m. All data from venous blood samples; (b) Delta between the hematochemical, acid base
and electrolytic capillary earlobe values (Table 1) observed after 30 - 31 and 38 - 41 hours of acclimatisation at an altitude of
3480 m versus those observed in venous blood samples (Table 3(a)); (c) Results of one-way ANOVA of capillary earlobe val-
ues (Table 1) and venous blood values (Table 3(a)) observed after 30 - 31 hours of acclimatisation at an altitude of 3480 m; (d)
Results of one-way ANOVA of capillary earlobe values (Table 1) and venous blood values (Table 3(a)) observed after 38 - 41
hours of acclimatisation at an altitude of 3480 m.
(a)
Venous Blood Samples
Parameters 3480 m (30 - 31 h) 3480 m (38 - 41 h)
No subjects Mean SD No subjects Mean SD Delta P t-test
PB mmHg 6 496 6.32 5 498 5.77 2.4 0.53
pO2 mmHg 5 40.4 9.78 5 44.12 12.87 3.75 0.42
pCO2 mmHg 6 39.9 5.21 5 37.32 4.74 −2.58 0.42
tCO2 mmol/L 6 77.5 13.69 5 78.86 16.25 1.36 0.89
SO2% 6 26.58 2.56 5 25.87 1.99 −0.71 0.58
tHb g/L 6 14.2 2.49 5 15.78 1.53 1.58 0.26
pH 6 7.4167 0.02 5 7.434 0.05 0.01730.42
3
−


HCO mmol/L 6 25.33 2.39 5 24.68 1.89 −0.65 0.6
[Na+] mmol/L 6 144.2 4.9 5 141.5 2.31 −2.7 0.29
[K+] mmol/L 6 4.49 0.32 5 4.46 0.1 −0.03 0.85
[iCa++] mmol/L 6 1.27 0.1 5 1.22 0.05 −0.05 0.4
(b)
Parameters Delta 30 - 31 h Delta 38 - 41 h
pO2 mmHg −4.92 −5.37
pCO2 mmHg 10.57 9.295
tCO2 mmol/L 2.33 3.1
SO2% −8.05 −7.59
tHb g/L −1.7 −0.63
pH −0.1037 −0.0771
3
−


HCO mmol/L 1.97 3.39
[Na+] mmol/L 2.91 1.93
[K+] mmol/L −0.74 −0.77
[iCa++] mmol/L 0.06 0.0158
(c)
Parameters DF F P Fisher PLSDSheffe’Dunnet
pCO2 mmHg 1,15 29.8 0.00014.158 29.8 5.456
SO2% 1,12 25.2 0.003 6.208 25.2 5.019
tCO2 mmol/L 1,15 4.6 0.05 2.334 4.6 2.145
pH 1,15 95.5 0.00010.023 95.53 9.771
(d)
Parameters DF F P Fisher PLSDSheffe’Dunnet
pCO2 mmHg 1,14 27.003 0.00023.856 27.0035.196
tCO2 mmol/L 1,12 10.741 0.007410.825 10.7413.277
SO2% 1,14 9.044 0.01012.162 9.044 3.007
pH 1,14 18.002 0.001 0.039 18.0024.243
3
−


HCO mmol/L 1,14 7.838 0.015 2.084 7.838 2.8

I. GRITTI ET AL. 19
There was a statistically significant decrease between
pO
23
2 (mm Hg) values measured at 3480 m and at a PB of
approximately 495 mm Hg and those observed at 122 m
and at PB of approximately 742 mm Hg (Tables 1-3).
pO2 values measured after 30 - 31 hours and after 38 - 41
hours of acclimatization and at a PB of approximately
495 mm Hg were both significantly higher than those
after 6 hours at an altitude of 3480 m and at a PB of ap-
proximately 491 mm Hg; pO2 values increased between
30 - 31 hours and 38 - 41 hours of acclimatization at
3480 m and at a PB of approximately 495 mm Hg (Ta-
bles 1-3).
Both pCO (mm Hg) and HCO−




ltitudes (
n those
fter 38 -
ere determined by mea-
3.3. Blood Lactate Metabolism
ing
- 41 hours of accli-
nographic Recordings
ncreased wake-
t < 0.01) and a parallel signifi-
rial Oxygen
leep-
t-test 001)
65% of subjects took longer than their
p [DFA];
SpaO2 Changes
va-
lues, tREM, REM, NREM + REM
of
the %SpaO2
SimplREM,
REM of TST disclosed a sig-
(mmol/L) signifi-
cantly decreased at higher aTables 1-3); pCO2
and 3 HCO−


values were significantly higher at 2050
m thaat 30/31 - 40/41 hours after reaching 3480
m. A decrease was also noted between measurements
taken at 30 - 31 and 38 - 41 hours at 3480 m versus those
after 6 h at 3480 m (Tables 1-3). The 3
HCO−


concen-
tration after 38 - 41 hours of acclimatization at 3480 m
was lower than that measured after 30 - 31 hours at 3480
m (Tables 1-3).
There was a statistically relevant increase in pH at
high altitude compared to that measured at 122 m (Ta-
bles 1-3). Comparison of the pH values at 2050 m with
those recorded at 3480 m still showed an increase be-
tween measurements taken after 6 and 30 hours of high-
altitude exposure. Although other changes were not sta-
tistically significant, pH values tended to decrease after
38 - 41 hours of high-altitude exposure (Tables 1 and 2).
There was a significant linear decrease in all types of
bases [BE], [BB], [BE active], [BE effective] (mmol/L)
at high altitude (Tables 1 and 2).
No significant changes were noted in the average he-
matochemical values of venous blood samples collected
from the brachial vein between 30 - 31 and 38 - 41 hours
of acclimatization at 3480 m (Table 3).
Nevertheless, there were statistical differences between
SO2[%], pCO2, tCO2 (mmol/L) and pH levels in capillary
and venous blood samples collected after 30 - 31 hours
of acclimatization at 3480 m (Table 3). There were also
statistically significant differences between the SO2[%],
pCO2, tCO2, pH and 3
HCO−


in capillary and venous
blood samples taken a 41 hours of acclimatiza-
tion at 3480 m (Table 3).
3.2. Electrolyte Metabolism
Changes in electrolyte balance w
suring the concentration of sodium [Na+] (mmol/L), po-
tassium [K+] (mmol/L) and ionized calcium [iCa++]
(mmol/L). The normal average electrolyte values barely
changed at high altitude (Tables 1-3); the [Na+] and [K+]
varied significantly at high altitude (Tables 1 and 2).
During the waking state at low altitude, after reach
2050 m, and after 6, 30 - 31 and 38
matization at an altitude of 3480 m, the capillaryblood lac-
tate values were consistently less than 2 mmol/L. None-
theless, after 38 - 41 hours of acclimatization and two
nights of sleep at 3480 m, the lactate values were signifi-
cantly lower than those measured at 2050 m (Tables 1
and 2).
3.4. Polysom
3.4.1. EEG Recordings
Sleep at 3480 m was characterized by i
fulness ([W] 38.8%; Pt-tes
cant decrease of 28% in non-REM sleep (NREM) (Pt-test
< 0.0311) and of 11% in rapid eye movement (REM)
sleep (Pt-test < 0,008). The total sleep time ([TST]; Pt-test <
0.01) decreased by 38.5% (Table 4).
3.4.2. Percentage of Peripheral Arte
Saturation during Sleep
The average %SpaO2 was significantly lower at a s
ing altitude of 3480 m than at sea level (P < 0.
(Table 4).
3.4.3. Subjective Perception of Sleep Quality
We found that
normal time to fall asleep (delay in falling aslee
Table 4); 30% woke up 2 hours before the expected time
and 60% woke up more than once. Sleep quality was per-
ceived as significantly poorer at 3480 m than at 122 m
(5.58 ± 1.8 vs 7.84 ± 1.47; P < 0.05); sleep duration was
shorter and 60% of subjects felt poorly restored on wak-
ing up.
3.4.4. ANOVA of Quantity and Quality Sleep and
%
ANOVA revealed significant differences in %SpaO2
he percent of W, N
sleep, and in TST between measurements taken at 122 m
and those at an altitude at 3480 m (Table 4(b)).
3.5. Other Statistical Analyses
3.5.1. Simple Regression Analysis
Polysomnographic Data and
Recorded during Sleep
e regression analysis of the percent of W, N
, NREM + REM sleep and
nificant correlation between the changes in TST and the
percent of REM sleep and the %SpaO2 changes recorded
during sleep (Table 4(c)).

I. GRITTI ET AL. 20
Table 4. (a) Changes in the percent of nocturnal peripheral arl oxygen saturation (%SpaO2), Wake (W)ter, Non-Rapid Eye
Movement (%NREM) sleep, Rapid Eye Movement (%REM), Total Sleep time (TST, h) and Delay in Falling Asleep (DFA, s)
(a)
122 m 3480 m
ia
observed during sleep at 122 m and between 30 - 31 and 38 - 41 hours of acclimatization at an altitude of 3480 m. (b) Noctur-
nal %SpaO2, %W, %NREM, %REM, %NREM + REM, TST (h) and DFA (s) recorded at 122 m and at 3480 m resulted
significantly different at one way ANOVA for each measurement. (c) Simple regression analysis between the nocturnal
%SpaO2, %REM sleep, and TST (h) resulted significant.
Parameters Mean SD Mean SD
%Spa O2 95.6 0.85 80 3.64
%W 19.5 10.4 58.3 29.9
%NREM
%NM 1
7 0 4 1:53:15
(b)
63 8 34.7 26.5
%REM 17.5 5 7.2 5.8
REM + RE80.5 0.6 41.8 30
TST (h) :31:50:43:57 :53:15
DFA (s) 349.5 383.5 693.7 616.1
Parameters DF F P Fisher PLSD Sheffe’ Dunnet
%Spa O2 1,10 10.1 05.5 0003.4 105.5 10.25
%W 1,11 9.03 0.0132 28.8 9.03 3
%NREM 2.
%NM
3.
0 6
1,12 6.28 0.0311 25.2 6.28 51
%REM 1,13 10.88 0.008 6.98 10.88 3.3
REM + RE1,14 9.03 0.0132 28.68 9.03 3
TST (h) 1,15 12.11 0.05 1.7 12.11 48
DFA (s) 1,16 1.35 .272360.171.35 1.16
(c)
Parameters Observations DF R-sqaefficient F P t red Co
%Spa O2
%REM 12 1, 0. −38. 0.0174 2.
2
11 459.07 0984
TST (h) 12 1,11 0.74 −10.74 8.3930.0003 5.329
.5.2. Simple Regression Analysis of Changes in
Simpl ation
at high altitude (Table 6). The changes in the percent of
ents and Sleep
gnifi-
3
Metabolic Components of Capillary Blood
Analysis and Sleep
e regression analysis showed a positive correl
between the changes in pO2 at higher altitude and the
percent of W and of TST (Table 5). The changes in pO2,
tCO2 and 3 HCO−


correlated negatively and signifi-
cantly with the percent of REM sleep changes at high
altitude (Table 5). The TST changes at high altitude cor-
related positively with the changes in pO2 and pH and
correlated negatively with the changes in SO2[%], pCO2,
tCO2, and 3 HCO−


(Table 5).
The changes in the percent of W at high altitude cor-
related significantly and positively with the [BE] changes
REM sleep correlated significantly and positively with
the changes in [iCa++] and [BE] and negatively with the
changes in [BB] and [BEeffective] (Table 6). The change
in the percent of NREM+REM sleep at high altitude cor-
related significantly and positively with the changes in
[BE] and [BB] concentration (Table 6).
3.5.3. Simple Regression Analysis of Changes in
Venous Blood Metabolic Compon
The increase in DFA at high altitude correlated si
cantly and negatively with the changes in pCO2 and sig-
+
nificantly and negatively with the changes in [K] in ve-
nous blood (Table 7). Simple regression analysis demon-

I. GRITTI ET AL. 21
Table 5. Results of simple regression analysis between pO2, %2, pCO2, tCO2, pH and [3 HCO −] values in earlobe capillary SO
ation and
P t
blood samples taken after 30 - 31 and 38 - 41 hours of acclimatiz%Wake (W), Rapid Eye Movement (REM) sleep
and Total Sleep Time (TST, h) recorded between 30 - 31 and 38 - 41 hours of acclimatization at 3480 m.
Parameters Observations DF R−squared Coefficent F
pO2 mmHg
%W 10 1.125.3 6. 0.02 2.
0. −13. 0.0225 2.
pCO Hg
0. −0.7 100.08 3.
tCO
0. −29.0.0287 2.
0. 23.9 6.0.0322 2.


HCO mol/L
%R 0. −31.0.0273 2.
9 0.441 963236513
TST 10 1.9 0.479 0.719 7.35 0.0266 2.711
%SO2
TST 10 1.9 449 745 7.959 821
2 mm
TST 10 1,9 5658.19 12192
2 mmol/L
%REM 10 1.9 47938 7.083 661
TST 10 1.9 0.619 −4.912 12.976 0.007 3.602
pH
TST 10 1.9 5663 704 589
3
− m
EM 10 1.9 476 226 7.255 694
TST 10 1.9 0.615 −5.139 12.786 0.0072 3.576
], [BE],Table 6. Rof simple regressionalysis bet [iCa++ [BB] anive] varome capy
blood samples taked during 30 - 31 and 38 - 41 hours of acclimatization and the percent of Wake (%W), Rapid Eye Move-
Observations DF R-squared Coefficient F P t
esults anweend [BEeffectlues f earlobillar
ment (%REM) sleep, and NREM + REM (%NREM + REM) as measured by EEG between 30 - 31 and 38 - 41hours of ac-
climatisation at 3480 m.
Parameters
[iCa++] mmol/L
%REM 7 10.182.3 12.5 0.0176 3.5
ol/L
10 1, 0.81.7 5.0.0406 2.4
+ REM 1
1 0.−22 2 0.0077 11.26
+ REM
10. −0.4 200.0463 4.7
,6 708 191448
[BE] mm
%W 9427 51954 4
%REM 10 1,9 0.557 0.01 10.056 0.0132 3.171
%NREM 10 1,9 0.428 8.6335.977 0.0403 2.445
[BB] mmol/L
%REM 4 ,3 985 8.309 128.273
%NREM 4 1,3 0.916 694.503 21.857 0.0428 4.675
[BEeffect] mmol/L
%REM 4 ,3 9162.13 48

I. GRITTI ET AL. 22
Tesults of simple regressionalysis ben pC, pH, [H−nd [K+s in vlood samples
nd the percent
leep T
Coefficient F P t
able 7. Rn atweeO22, tCO3
CO] a] valueenous b
collected. after 30 - 31 and after 38 - 41 hours of acclimatization at 3480 m aof Wake (%W), Non-Rapid Eye
Movement (%NREM sleep), Rapid Eye Movement sleep (%REM), Total Sime (TST, h), Delay in Falling Asleep (DFA,
s) recorded between 30 - 31 and 38 - 41 hours of acclimatisation at 3480 m.
Parameters Observations DF R-squared
pCO2 mmHg
DFA 10 1, 0.−3.0.0178 2.
ol/L
10 1, 0.−10.1 0.0012 4.
10 1, 0.6.8.0.0185 2.
REM
3
−] mmol/L
10 1, 0.−10.1 0.5.
mol/L
1 0.−6.5 111 0.08 3.
9525 28 8.842 973
TST 10 1,9 0.415 −4.883 5.665 0.0445 2.38
tCO2 mm
TST 9751 402 24.10909
pH
%W 9521 084 695 949
%REM 10 1,9 0.429 −4.406 6.009 0.0399 2.451
%NREM 10 1,9 0.534 −1.528 9.179 0.0163 3.03
%NREM +10 1,9 0.517 −5.934 8.569 0.0191 2.927
DFA 10 1,9 0.563 11.224 10.29 0.0125 3.208
[HCO
TST 9758 331 25.06001 006
[K+] m
DFA 7 ,6 689 28.0720327
TST 7 1,6 0.819 −19.784 22.579 0.0051 4.752
hat the changes in pH at high altitude correlated
cussion
onsiderations
ption values recor-
been shr the deination oO2
ntain marathon runners in our study, the he-
matochemical alterations at high altitude resembled and
strated t
positively and significantly with the percent of W and the
DFA and negatively with the changes in the percent of
NREM sleep, REM sleep, NREM + REM sleep (Table
7). The decrease in the TST at high altitude correlated
significantly and negatively with the changes in pCO2,
tCO2, 3 HCO−


and [K+] in venous blood.
4. Dis
4.1. Technical C
The metabolic aerobic power consum
ded in our subjects were averaged and found to be simi-
lar to those reported by Muller et al. [17]. Questions re-
main about the validity of blood gas values measured in
arterialized earlobe blood instead of peripheral arterial
blood samples for clinical and laboratory investigation.
Recently, arterialized earlobe blood sampling has been
demonstrated a simple and safe method suitable for cli-
nical, laboratory molecular evaluation. The earlobe blood
sampling technique has been reported to be less painful
than the more correct arterial sampling and is advocated
as a reliable method for arterial blood gas determination
and as standard practice for acid-basic balance analysis
[21]. The validity of arterialized earlobe blood samples
Arterialized earlobe blood is said to be more suitable for
clinical assessment of arterial pO2 only for values < 60
mm Hg and less suitable for higher values due to under-
estimation of the real value [21]. Overall, our study seems
to confirm that the techniques we used for evaluating
most of the changes in blood chemistry, acid-base equili-
brium [21], electrolyte and blood lactate are suitable for
clinical assessment and for metabolic research at high
altitude.
4.2. Hematochemical and Acid-Base Equilibrium
In the mou
has own fotermf pC levels.
followed the classic physiological time course of re-
sponses to the hypobaric-hypoxemia and hypocapnic
state [3-5,20]. The physiological responses became no-
ticeable after 30 - 31 hours to 40 - 41 hours at 3480 m. At
low altitude the average pH was approximately 7.4595 ±
0.0139, slightly higher than that reported by Samaja et al.
[5]. The average pH in the mountain marathon runners at
an altitude of 3460 m after 6 - 41 hours of acclimatiza-
tion was slightly higher than that reported in Caucasian
control subjects exposed to approximately the same alti-

I. GRITTI ET AL. 23
tude [3-5].
In the mountain marathon runners, the average pCO2
at sea level was similar to that reported in by Samaja et
al. [4]; after 41 hours of acclimatization and sleep at
3480 m, it was similar to that recorded in the Sherpas [4].
Th
urs of acclimatization at 3480 m, a
va
nity and subsequently the blood
pO
a were reported in a
st
he average excess
of
is study demonstrates that: 1) at 122 m the average
pO2 was similar to that previously reported in Table 1 by
Samaja et al. [3-5]; 2) the average pO2 level observed in
the mountain marathon runners after 6 hours at 3480 m
was similar to that observed in the Caucasian subjects at
6450 m, and lower than that observed at 5050 m; 3) the
average pO2 in the mountain marathon runners after 41
hours of acclimatization was nearly similar to that ob-
served in the Caucasians and Sherpas at 3400 m after
acclimatization [4].
The average %SpaO2 in the mountain marathoners af-
ter 6 hours of acclimatization at 3480 m was similar to
that observed at 6450 m by Samaja et al. and reached
83% after 30 - 31 ho
lue similar to what Samaja et al. [3,4] reported after 5
weeks of acclimatization at 5050 m. It rose to 86% after
41 hours of acclimatization at 3480 m, which was very
near the average values (88%) that Samaja et al. recorded
in Caucasian subjects at 5050 m after several days of
acclimatization [3,4].
In agreement with Samaja et al. [3-5], we suggest that
(as in their Caucasian subjects) the metabolic response to
respiratory alkalosis may have slightly but significantly
improved blood O2 affi
2 level in our subjects (Table 1).
The continuous decrease in pH, pCO2 and bicarbonate
values collected after a night’s sleep and 41 hours of stay
at 3480 m showed that compensation of respiratory alka-
losis had been activated. Similar dat
udy conducted many years ago [22].
In line with data reported by Weil [18], the %SpaO2
measured in our subjects during sleep, and between 30 -
31 and 38 - 41 hours of acclimatization at 3480 m, fluc-
tuated between 65% and 84% [23]. T
bases [BE] recorded after 40 - 41 hours of acclimati-
zation to high altitude was 0.41 mmol/L and was higher
than that considered necessary for reaching a physiologi-
cal pH value. Of the bases excess, the average 3 HCO−




closely followed the same trend as [BE], decreasing
fairly consistently during acclimatization. In brief, in this
study, a correct activation of compensation of respiratory
alkalosis and acclimatization at 3480 m was de-
ted by the linear decrease in the bases excess. The de-
crease in [BE] was not sufficient to normalize the pH,
even after 41 hours of acclimatization at 3480 m; none-
theless, it was probably the best value that could be
reached at that altitude at a PB of 490 mm Hg [3-5] and
with the chosen exercise and dietary regimen [20].
4.3. Electrolyte Metabolism
While alterations were noted in acid-base metabolism,
the concentration of [Na+], [K+] and [iCa++] ions re-
mained within the normal range. We found that, u
monstra
nder
creased after 6 hours of
urned to the values ob-
as aerobic through-
o 3480 m. The de-
d at sea level significantly
e
t
of noO2 taken every 30 seconds can be used
oreceptor activation of
th
controlled conditions, the [Na+] in
exposure to high altitude but ret
served at 122 m within 41 hours of exposure at 3480 m.
4.4. Blood Lactate Metabolism
On average, blood lactate levels after a night’s sleep and
41 hours of acclimatization at 3480 m were lower than
those observed during the wakeful state. Our data show
that the peripheral metabolic pathway w
out acclimatization from 2050 m t
crease in blood lactate values observed after 41 hours of
acclimatization and a sleeping altitude of 3480 m sug-
gests that the aerobic power of mountain marathon run-
ners at rest improves [20,24].
4.5. Subjective Perception of Sleep Quality and
Quantity
The decrease in the nocturnal %SpaO2 values at high
altitude versus those measure
correlated with the significant decrease in total sleep tim
(TST) and %REM sleep, indicating that the measuremen
cturnal %Spa
as an index of sleep quantity and quality. It is also very
important for evaluating the degree of acclimatization to
high altitude and for indicating the risk of altered states
of consciousness, as described by Finnegan et al. [19].
Importantly, unlike these authors, we found no paroxys-
mal figures on the EEG tracings.
In this study, one of the factors underlying the de-
crease in NREM and REM sleep was significantly corre-
lated with the decrease in nocturnal %SpaO2. Altitude-
induced low arterial oxygen pressure might have elicited
cortical arousal via afferent chem
e ascending reticular activating system located in the
brain stem reticular formation. This mechanism may ex-
plain the decrease in NREM and REM sleep in the
mountain marathon runners. In other words, at a baro-
metric pressure of 495 mm Hg in the hypoxic-hypobaric
conditions of this study, the nocturnal pO2/pCO2 ratio
most likely may have played, cyclically, a critical role in
activating directly and/or indirectly the bulbo-pontine and
hypothalamic reticular activating system involved in the
behavioral and metabolic integration of autonomic, car-
diovascular and respiratory functions and in cortical
arousal.
5. Conclusion
Overall, our results suggest that monitoring the time

I. GRITTI ET AL. 24
course of changes in blood chemistry, acid-base balance,
electrolyte and blood lactate metabolism during the w
ful state and the nocturnal %SpaO2 during sleep may help
or assessing how well mountain mara-
NCES
doi:10.2165/00007256-199520030-00003
ake-
to set new criteria f
thon runners acclimatize to high-altitude exposure and
for predicting the quality of their refreshed sleep. Study-
ing the time course of acclimatization to high altitude is a
fundamental part of the correct physiological approach to
exercise training at high altitude and essential for pre-
paring athletes to live and exercise at high altitude.
6. Acknowledgements
We are indebted to the Federation of Sports at Altitude
(Biella, Italy) for funding since 1994. We are indebted to
the Roche Diagnostics S.p.A, Monza, Italy
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