J. Biomedical Science and Engineering, 2011, 4, 130-135
doi: 10.4236/jbise.2011.42019 Published Online February 2011 (http://www.SciRP.org/journal/jbise/
JBiSE
).
Published Online February 2011 in SciRes. http://www.scirp.org/journal/JBiSE
Effects of oxygen enriched tent by a new oxygen concentration
machine on blood oxygen saturation and heart rate in tibet
Guang-Hao Shen1, Kun Wang1, Li-Hua Lu1, Kang-Ning Xie1, Qiao-Lin g Xu1, Xia o-M ing Wu1,
Chi Ta n g1, Er-Ping Luo1
1Department of Military Medical Equipment & Metrology, Academy of Biomedical Engineering, the Fourth Military Medical Uni-
versity, Xi’an, China.
Email: ghlulu@fmmu.edu.cn; wangkun6805@163.com
Received 19 October 2010; revised 4 December 2010; accepted 12 January 2011.
ABSTRACT
Many people who live in the low altitude areas are
often suffered from hypoxia when they entered the
high plateau. This problem may seriously influence
the physical and mental state and work efficacy for
the travelers and workers. Oxygen enrichment of a
small space air at high altitude is considered as a
simple way to provide lowlanders enriched oxygen
for sleeping and resting, improving work efficiency,
so we developed an oxygen concentration machine
based on the technology of oxygen enrichment mem-
brane. This paper tested 8 healthy male lowlanders
(age 21.63±1.77 yr) who have never exposed to pla-
teau performed an incremental exercise on cycle er-
gometer at sea-level in order to be used as sea-level
controls. Two days later, the same subjects were tak-
en to Lhasa (3700 m) by air and exposed to the pla-
teau, performed the same exercise as they did at
sea-level. The next day, all subjects were asked to
enter the experimental tent which was enriched with
oxygen (higher than 24%) by the oxygen concentra-
tion machine and sleep for 10 hours at night, then
exposed to plateau and performed the same exercise
twice at different time (2 hours and 10 hours after
oxygen enrichment). During the tests, subjects must
cycled continuously at 60 rpm beginning with a 3 min
exercise intensity of 0 W followed by incremental in-
creases of 25 W every 3 min until 150 W, pulse oxy-
gen saturation (SpO2) and heart rate (HR) were re-
corded. After sleeping in an oxygen enrichment of
tent air, 2 hours later, the subjects’ load capacity had
no difference compared with control group, but sig-
nificant difference than before (higher SpO2 and
lower HR), which indicated that oxygen concentra-
tion machine is effective in increasing the oxygen
concentration of the air for the tent and sleeping in
the oxygen enrichment tent for l0 h might be effective
in improving exercise performance during high-alti-
tude hypoxia. At the same time, 10 hours later, when
work-load exceeded 125 W, the same effects were also
found. The results indicated the effects of oxygen en-
richment of tent air could last a certain period of
time.
Keywords: Hypoxia; Oxygen Concentration Machine;
Oxygen Enrichment Membrane; High Plateau; Oxygen
Enrichment
1. INTRODUCTION
Qinghai-Tibet Plateau is called “the roof of the world”,
has an average elevation of over 4,500 meters, it is the
highest plateau of the world. There are over 12 million
people in the Qinghai–Tibetan Plateau, of which 6 mil-
lion are lowlanders (Han culture) and migrants [1,2]. In
recent years, with the opening of Qinghai–Tibet railway
in China, more and more people who live in low areas
enter Qinghai-Tibetan high plateau for science investiga-
tion, tour, commercial, or other reasons.
Many of the permanent residents of Qinghai-Tibet
Plateau have been living there for generations and have
probably benefited from evolutionary adaptation [3].
But for many people who live in the low altitude areas,
exposition to plateau often cause them to suffer from
hypoxia, and induce acute high altitude disease
(AHAD), especially for those with some outdoor works,
such as some science investigation and military actions,
scientists and soldiers have to sleep in the tent at high
altitude without well protection [4]. The most common
symptoms of AHAD, including headache, poor appetite,
nausea, fatigue, dizziness and insomnia, usually appear
within the first three days of arrival at high altitude
[5-7]. Moreover, people from low areas may experience
G.-H. Shen et al. / J. Biomedical Science and Engineering 4 (2011) 130-135 131
a decrease in exercise performance on arriving to high
altitude. The higher the altitude is, the more critical the
situation may occur [8,9]. This problem may seriously
influence the physical and mental state and work effi-
cacy for the travelers and workers. The basic physio-
logical problem at high altitude is the low partial pres-
sure of oxygen stemming from the reduced barometric
pressure [10,11]. By raising the concentration of oxy-
gen in the air, the inspired Po2 can be increased and the
deleterious effects of the high altitude can be reduced
[12]. It has been shown that increasing the oxygen
concentration of the air by 1% (e.g. from 21 to 22%)
results in a reduction of equivalent altitude of about
300m [13]. So oxygen enrichment of a small space air
at high altitude is considered as a simple way to pro-
vide lowlanders with enriched oxygen and improving
their performance [14].
The oxygen enrichment membrane is a kind of gas
separation membrane [15], it can be used to enrich oxy-
gen because the oxygen can permeate more than nitro-
gen, and the oxygen concentration of the air can come
up to 40% through this membrane [16]. It has been
widely used in industry, such as steel and chemical, in
order to induce the complete combustion and save en-
ergy, reduce pollution [17].
This paper first demonstrates small oxygen enrich-
ment space built by tent in Lhasa, and the new oxygen
concentration machine based on the technology of oxy-
gen enrichment membrane was used to provide oxy-
gen-enriched gas to the tent. We then report the effects
of 10h sleeping in such an oxygen enrichment tent on
pulse oxygen saturation (SpO2) and heart rates (HR)
during exercises. We showed that such a machine is ef-
fective to provide oxygen-enriched gas and help to build
an oxygen enrichment tent conveniently. Oxygen en-
richment improves the exercise performance during
high-altitude hypoxia, and the effects could last a certain
period of time.
This template
2. MATERIALS AND METHODS
2.1. Subjects
First, Eight young volunteers, all of them are males,
normally live at the sea-level regions, with the average
age of 21.63±1.77 years (aged 1924), all of Han na-
tionality. All of them do not have the habit of smoking
and are healthy without the history of pulmonary, car-
diovascular, hematological, renal or hepatic disease, be-
cause smoking habit and all of the diseases above may
affect the body response to the high altitude. Subjects
were all taken to the altitude of 3700m by air for the first
time. They were familiar with the exercise test on cycle
ergometer.
The study was approved by Medical Ethical Commit-
tee of Fourth Military Medical University. All the sub-
jects had signed informed consent forms. All variables
were measured and groups were separated by the sub-
jects taking exercise at sea-level (control group), before
(A1 group) and after oxygen enrichment for 2 hours (A2
group) and 10 hours (A3 group).
2.2. Oxygen-enriched Tents
Airtight outdoor tents were placed in Lhasa, which were
used as the experimental tents. The tents are all arch
shape about 2.05×1.5×1.05 m3, weighted 1.85 kilo, made
by the material of 210D nylon and have airtight zippers
for people to enter or exit the tents. Each tent is designed
for two persons. For 8 subjects, we used 4 tents for them
to sleep and 4 oxygen concentration machines were used
to provide oxygen-enriched gas to the tents.
2.3. Ventilat ion of Tents
According to the ASHRAE (American Society of Heat-
ing, Refrigerating and Air-Conditioning Engineers)
standards in 1975 [18], the minimum standard of venti-
lation of an office, conference room or dormitory was
8.5 m3 per person per hour, that corresponds to 142
L/min and is calculated to maintain the carbon dioxide
concentration in the room below 0.24%. We use this
standard to control the ventilation of the tent in order to
maintain the air in the tent acceptable.
For each of the tent has the ability to stay 2 people,
the minimum required ventilation is about 300 L/min.
Blowers were used to provide ventilation to the tents
through single opening circular ducts of 10 cm diameter.
Each tent has a blower and the duct was put into the tent
by a hole we cut on a side of the tent before. The joint
was sealed by the rubberized fabric. No exit was pro-
vided because the air can find its way out of the tent
through random leaks [19].
2.4. Carbon Dioxide Concentration in the Tents
Four blood/PH gas analyzers (model 1302, USA) were
used to examine the carbon dioxide concentration and
O2 concentration of the tent air. Each tent has an ana-
lyzer and the output was continuously displayed dur-
ing subjects sleeping in the tent, in order to evaluate
the air and make sure the dioxide concentration is blow
0.24%.
2.5. Oxygen Concentration Machines
We developed a new kind of oxygen concentration ma-
chine based on the technology of oxygen enrichment
membrane. Each machine was about 0.66×0.44×1.2 m3,
only required electrical power to drive, it had an outlet
C
opyright © 2011 SciRes. JBiSE
G.-H. Shen et al. / J. Biomedical Science and Engineering 4 (2011) 130-135
Copyright © 2011 SciRes.
132
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which could provide oxygen-enriched gas, the outlet
could be connected with a circular pipe and the output of
the machine was 35 L/min of 32% oxygen. Inside the
machine had 12 oxygen enrichment membranes con-
nected with a pump by tubes, the pump was used to
pump the air into the tubes at high pressure. The oxygen
enrichment membrane is a kind of gas separation mem-
brane, when air passed through these membranes, the
oxygen concentration of the air is 35% and the tubes are
injected into one tube which connected the outlet of the
machine. The waste air on the other side of the mem-
branes can flow to another tube to the outside environ-
ment because of the high pressure.
2.6. Oxygen Enrichment
Each tent had an oxygen concentration machine placed
outside and the output of the machine was injected into
the 10 cm diameter ventilation duct to the tent. In order
to raise the oxygen concentration of the tent, the outlet
of the machine was connected with a tube which was
injected into the ventilation duct. The blower was first
turned off and the oxygen concentration machine was
turned on for over 1h. Blood/PH gas analyzer (model
1302, USA) was used to examine the O2 concentration
of the tent air, when the concentration was higher than
25%, turn on the blower so the ventilating air was mixed
with the oxygen-enriched gas, which made the O2 con-
centration of the tent air dropped to (24.38±0.25)% and
kept steady.
When the subjects slept in the tent, the same ventila-
tion and oxygen-enriched gas were provided and the O2
concentration of the tent air was continuously monitored,
and the analyzer showed it was always higher than 24%.
2.7. SpO2 and HR Measured
SpO2 and HR were recorded by using a multi-parameter
monitor (model Philips MP20junior203, USA). When all
the subjects arrived in Lhasa, they were asked to have a
rest for 2 hours and prepare for the experiment. Then,
subjects performed an incremental exercise before
sleeping in oxygen enrichment of tent air on cycle er-
gometer (model EMG-II, China), they cycled continu-
ously at 60rpm beginning with a 3min exercise intensity
of 0W followed by incremental increases of 25W every
3min until 150W. SpO2 and HR were recorded at every
2.5 minutes during exercise (A1 group).
The next day, when all the subjects were physical re-
covery, they were asked to enter the tent and sleep in
oxygen enrichment of tent air for 10 hours (10:00pm
08:00am). After leaving the room, the same exercise test
was performed twice at 10:00am (2 hours after oxygen
enrichment, A2 group) and 6:00pm (10 hour after oxy-
gen enrichment, A3 group), respectively. And the SpO2
and HR were also recorded at every 2.5 minutes during
the two exercises. We compared the two variables be-
tween A1 group with A2 group and A3 group, A2 and A3
were also compared with each other.
2.8. Statistical Methods
The results were presented as Mean ± SD and the dif-
ferences were analyzed by the one-way ANOVA. Statis-
tical analysis was carried out with the SPSS for Win-
dows (version 10.0, SPSS, Inc., Chicago, IL). The level
of significance was P<0.05.
3. RESULTS
3.1. Feasibility of Oxygen Enrichment of Tent Air
It was not difficult to set up such an oxygen-enriched
tent at high altitude with the oxygen concentration ma-
chine. Many kinds of tent had the feasibility of airtight
when the zippers were closed. Although pump and the
machine were taken to equipped, but they were not big
and heavy and could be carried in a car easily. The oxy-
gen concentration of the tent air was always higher than
24% all the night and the dioxide concentration was
blow 0.24%. None of the subjects complained uncom-
fortable after leaving the tent.
3.2. Heart Rates (HR) and Blood Oxygen
Saturation (SpO2) during Exercise
Heart rates (HR) of subjects both before and after oxy-
gen enrichment increased with incremental exercise in-
tensity. Significant differences were found between A1
and control group from 100W. (P<0.05, Ta ble 1). But,
they were not significant difference after enrichment (A2
and A3 group) during a similar stage of exercise when
compared with control group. (1) In the A2 group, heart
rates were not significant difference at each level; (2) In
the A3 group, heart rates were not significantly differ-
ence before 150W load level.
As expected, the blood oxygen saturation (SpO2) after
oxygen enrichment was increased significantly. Com-
pared with the control group, average SpO2 was found
significantly difference between A1, A2 and A3 group at
each level (0150 W, P < 0.05). But Compared with the
group before enrichment (A1 group): (1) in the A2 group,
the average SpO2 increased significantly after enrich-
ment at each load level(0150 W, P < 0.05). (2) in the
A3 group, the average SpO2 was significantly higher
since 125 W load level (125150 W, P < 0.05). And in
addition, significant differences were found in SpO2 be-
tween A2 and A3 (0 W, 25 W, 75 W, 100 W, 125 W, 150
W, P < 0.05, Table 2).
G.-H. Shen et al. / J. Biomedical Science and Engineering 4 (2011) 130-135
Copyright © 2011 SciRes.
133
Table 1. Heart rates during exercise before and after oxygen enrichment (
x
s
, n = 8).
Heart rate (beats/min)
Group 0W 25W 50W 75W 100W 125W 150W
Control 88.76±2.10 102.13±4.04 118.22±4.02 130.71±2.30 136.79±2.96 152.18±2.94 163.28±1.99
A1 89.00±2.33 102.63±4.03 119.00±3.66 131.25±2.12 143.88±3.48* 162.13±3.87* 174.25±3.28*
A2 88.88±2.42 102.75±5.42 118.50±4.00 131.38±3.20 137.88±3.76 153.63±3.74 165.38±2.83
A3 89.88±2.31 104.38±5.55 120.25±3.58 133.25±3.45 140.13±5.03 155.00±3.34 167.88±2.23*
Value: Mean ± SD (standard deviation); Level of significance: P < 0.05.*P < 0.05: as compared with control group by one-way ANOVA
Table 2. SpO2 during exercise before and after oxygen enrichment (
x
s
, n = 8).
SpO2 (%)
Group 0W 25W 50W 75W 100W 125W 150W
Control 98.76±1.05 98.22±1.11 97.89±1.91 97.21±1.88 97.10±1.67 96.87±2.32 96.51±2.10
A1 91.38±1.06* 90.25±0.71* 89.00±1.41* 89.00±1.20* 88.25±1.04* 85.75±0.89* 83.25±1.04*
A2 92.88±0.64* 91.88±0.35* 90.63±0.52* 90.13±0.83* 89.38±0.92* 87.88±0.83* 85.75±1.04*
A3 91.13±0.83 90.63±0.52 89.88±1.13 89.21±1.20 87.63±0.92 86.63±0.74 84.75±1.04
Value: Mean ± SD (standard deviation); Level of significance: P < 0.05.*P < 0.05: as compared with control group by one-way ANOVA; P < 0.05 : A2, A3
compared with A1 by one-way ANOVA.
P < 0.05: A3 compared with A2 by one-way ANOVA.
4. DISSCUSSION
4.1. Feasibility and Costs of Oxygen
Concentration Machines
We used the oxygen concentration machines to provide
the oxygen-enriched gas to the tents because they were
convenient, and the costs for these machines were low.
For the machines were based on the technology of oxy-
gen enrichment membranes, the oxygen-enriched gas
could be continuously obtained by the environment air at
high altitude without changing the oxygen enrichment
membranes. Each machine was about 0.66×0.44×1.2 m3
and weighted about 30 kg, which could be easily carried
to outdoors by a car.
JBiSE
Each machine required electrical power to drive; the
car electrical power can perfectly provided the power in
the open plateau. The power consumption of each ma-
chine was just 600 W and that cost about 0.3 an hour.
So it is a very convenient and practical way to build an
oxygen enriched tent with such a machine with very low
costs.
4.2 Feasibility of oxygen enriched tents
We found that oxygen enriched tents were very useful
and convenient to solve the problem of hypoxia for out-
door workers at high altitude, especially in some remote
areas. For now, most of the oxygen enriched ideas were
based on rooms, which meant an airtight room was
needed; the room may cost much and could not be
moved. The oxygen enriched tents could be set up whe-
rever needed and the cost of a tent must be much lower
than a room.
In this paper, we used a blower and a single opening
circular duct of 10 cm diameter for each tent to provide
ventilation, that total costs of these were low too. We
studied 4 arch shape tent, each of them was about
2.05×1.5×1.05 m3 with 2 persons sleeping inside for 10
hours, with an oxygen concentration machine provided
oxygen-enriched gas, the oxygen concentration of the
tent air was always higher than 24% and the carbon di-
oxide concentration was lower than 0.24%, meet the
ASHRAE (American Society of Heating, Refrigerating
and Air-Conditioning Engineers) standards.[20]
4.3. Heart Rates (HR) and Blood Oxygen
Saturation (SpO2) Studies during
Exercises
In this paper, we compared the control group’s heart
rates and blood oxygen saturation (SpO2) with before
(A1 group) and after oxygen enrichment for 2 (A2 group)
and 10 hours (A3 group) during the exercises at each
load. Heart rates reflect the cardiac function of body. If
the heart beats too fast that means the work load will not
be suitable for people to continue and a short time of rest
will be needed. When people work at altitude, the work-
ing heart rates can reflect the ability to work and load
capacity.
Compared with control group, heart rates were found
significantly higher since 100 W load level (100150 W,
P < 0.05) at A1, but no differences were found between
A2 group at each level, which showed oxygen enrich-
ment for 10 hours could significant increase the ability
to work and load capacity at high altitude to the work
and load capacity at sea level. A3 group’s heart rates
were not significantly difference before 150 W load level
compared with control group, which showed that the
increased ability to work and load capacity could last a
certain period of time (Figure 1).
G.-H. Shen et al. / J. Biomedical Science and Engineering 4 (2011) 130-135
134
Figure 1. Heart rates during exercise, at the level of signifi-
cance: P < 0.05.
Figure 2. Blood oxygen saturation (SpO2) during exercise, at
the level of significance: P < 0.05.
SpO2 is an important indicator of oxygen supply for the
body. At high altitude, the low partial pressure of oxygen
stemming from the reduced barometric pressure caused
less oxygen diffuse into the capillaries within the lungs,
finally caused hypoxia and low SpO2 [21].
In this paper, we found control group had significant
higher SpO2 at each load level (0150 W, P < 0.05)
compared with the other groups during the exercise. A2
group had significant higher SpO2 compared between A1
(0150 W, P < 0.05), A3 group had the same effects
since 125 W (125150 W, P < 0.05), that showed oxy-
gen-enriched of tent air raising the concentration of
oxygen in the air, inspired Po2 can be increased by this,
so more oxygen diffuse into the capillaries within the
lungs, and the deleterious effects of the high altitude can
be reduced (Figure 2).
In this paper, we also found significant differences
with SpO2 between A2 and A3 group at some load level
(0 W, 25 W, 75 W, 100 W, 125 W, 150 W, P < 0.05).
Further studies should be needed to analyze the differ-
ences and expound the underlying mechanism.
5. ACKNOWLEDGEMENTS
The authors would like to thank the director of the Department of
Academy of Biomedical Engineering, the Fourth Military Medical
University, for providing necessary support for this study. And the 8
volunteers for their working during the whole study.
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