Một số yếu tố vi khí hậu ảnh hưởng đến tần số tim, huyết áp 24 giờ của cán bộ chiến sĩ công an và giải pháp can thiệp tt tiếng anh

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INTRODUCTION
Global environmental change and climate change have
increasingly impacted onnations in the world. It’s estimated that each
year climate change contrubutes to 150.000 deaths, 5 million sick
people.
Heart rate and blood pressure (hereinafter called BP) regularly
change and are undereffect of various factors including weather, air
pollution, activity state, lifestyle, to name but a few. The impact of
weather is frequently complex with the combination of a series of
meteorological elements in close interaction despite of their different
natures. Meteorological elements have direct impacts and play a role
in involving the effects of outside factors onvariations in BP
depending on human body’s sensitivity to each outside factor.
The complexity in the nexus of the aforementioned factors and
the variation of heart rate and BP undoubtedly increases in tropical
climatic conditions which are characterized by the intensity of
weather changes and the great hygrothermal potential of atmospheric
processes.
The

People’s

Public

Security

Forceworks

in different

environmental conditions. Road Traffic Police isconstantly exposed
to adverse environmental factors. Hence, the research topic of "The
effects of microclimateson 24-hour heart rate, blood pressure of
policemen and Proposed intervention solutions" was carried out
under the State-level Project "Research real situation, developing
forecasting and control modelsofa number of diseases related to
climate change in Viet Nam, ID number DTDL.2012-G/32". The
research deals with the followings:


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1. Description of changes in 24-hour heart rate and BP in
policemen groups in Hanoi City in 2014 - 2015.
2. Analysis of the correlation between selected microclimates
factors and 24-hour heart rate and BP of the research subjects.
3. Evaluation ofimprovementof the microclimate conditions by
equipment set in workplaces of the Road Traffic Police.
Contributions of the thesis
The thesis describes new data on characteristics of variationin
24-hour heart rate and BP of policemen, the correlation between
microclimate factors andtheir heart rate and BP and evaluates the
effectiveness of microclimate improvement by heat-resistant
umbrellas setin workplaces of the Road Traffic Police.
Moreover, this research providesthe Public Security sector with
useful scientific basis in policy making, promulgation ofworking
regulationsand mechanismsin order to help policemen in general and
the Road Traffic Police with minimizing risks to health from their
working environment.
Structure of the thesis
The thesis consists of 115 pages, 14 tables, 4 pictures, 26 figures

and 117 references, including 79 foreign language materials. There
are six main parts with respective lengths as follows: 3 pages of the
Introduction, 35 pages of the Literature Review, 16 pages of
Research Subjects and Methodology, 39 pages of Research Results,
20 pages of Discussion, and 2 pages of Conclusion and
Recommendations.


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Chapter 1
LITERATURE REVIEW
1.1. Microclimates and effects of microclimates on human
health:
1.1.3. Effects of climate change on human health: Climate
change is projected to have an adverse affect on human health. The
main direct effects are on accidents, injuries, mental health, thermal
shock and so forth while the main indirect effects are on
communicable diseases, chronic diseases, malnutrition, maternal and
pediatric health, and occupational health.
1.1.4. Effects of bad microclimateson human health:
1.1.4.1. Detrimental effects of hot microclimates: Diseases
aredoubled inhot microclimate conditionswith common syndromes
of heatstroke and convulsions that lead to dizziness, nausea,
headache and lumbago. In severe cases, human body is stunned with
small vessels, shallow breathing, and convulsions due to water and
electrolyte imbalance.
1.1.4.2. Detrimental effects of cold microclimates: When the
body is cold, voluntary muscles and involuntary muscles shrunk
along with shivering and goosebumps to produce heat. Partial cold
causes vasospasm that leads to numbness, itchyand tingling sensation

in hands and feet that lead to the reduction of motor ability, loss of
sensation, and subsequently result in muscle pain, steroid myopathy,
peripheral neuropathy, and so forth. Additionally, coldness causes
allergy likeasthma, decrease of resistance and immunity, acute
respiratory infections, and rheumatism.
1.1.4.3. Detrimental effects of heat radiation: Infrared
radiationcan cause skin burns and blistery; it goes through the skull,


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heats up the brain organization and meninges which heatstroke is its
direct consequence. Ultraviolet radiation is responsible for eye
diseases such as vision loss, or skin diseases containing skin burnand
skin cancer. Laser beams has beenmostly used in industry and
scientific research, nevertheless, it results in skin burn and retina
burn.
1.2. Cyclic variability of heart rate and blood pressure:
1.2.1. Circadian rhythm: In 1964, F. Halberg first coined the
term "Circadian" with the definitionof“a cycle with a period of about
24 hours that regulates the regular repeats of events roughly at the
same hourin any biological process daily”.
1.2.2. Variation of heart rate and blood pressure by Circadian
rhythm: Frequency of heart rate and BP frequently varies depending
on body’s Circadian rhythm, especially in relation to the sleep-wake
cycle.
- At night: Heart is in a resting state and heart rate, BP is going
to decrease that reaches the lowest value during sleep is
inapproximately between 2:00 AM to 3:00 AM. The highest and
DBP at night decrease by about 20% lower while sleeping than
during daytime, then itraises gradually in the morning.

- During the day: Heart rate, BP reaches the highest valuesat
around 9:00AM to 12:00PM and 17:00PM, and then slightly
decreases.
1.2.3. Variation of heart rate and blood pressure by ages
1.2.4. Variation of heart rate and blood pressure by body’s
posture and movement.
1.3. Effects of microclimates on heart rate and blood
pressure:


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1.3.1. Effects of temperature, humidity, and pressure on heart
rate and blood pressure: Previous studies by domestic and
international

researchers

have

reported

the

effects

of

badmicroclimates on human health. Not only workers’ health
affected by microclimate in polluted working places, but also the
population is suffered from extreme factors such as urban heat

island, wave cold phenomenon, heat and humidity, and so forth in
their daily living environment.
1.3.2. Effects of indoor and outdoor microclimates on heart rate
and blood pressure: Studies of Barnett AG indicatethe association
between systolic BP and indoor and outdoor temperature from the
risk factors surveys from 25 populations in 16 countries. The survey
results show thata 1 degrees C increase in indoor temperature
reduced systolic BPby an average of 0.31 mmHg, and a 1 degrees C
increase in outdoor temperature reduced BPby the smaller average of
0.19 mmHg.
1.3.3. Variation of heart rate and blood pressure by seasons:
Viet Nam is in a tropicalzone. It is characterizedby high humidity
and a strong monsoons and tropical influences. Climate
differentiation in different regions occurs due to the complex
interrelationship between regional atmospheric circulation and
diverse topographies. In each region, weather regimeis diverse and
relatively complicated with different types of weather, accompanied
by sudden changes in weather that lead to increasing the frequencies
and levels of variations in heart rate and BP. Although some research
has been conducted on this issue, there is very little scientific
understanding of the aforementioned nexus.
1.3.4. Effects of working conditions on heart rate and blood
pressure


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1.3.5. Other factors having effects on heart rate and blood
pressure
1.4. Measurement of 24-hour heart rate, blood pressure and
microclimates:

1.4.1. Heat index
The actual temperature that human body is affected and felt is
not the sameas air temperature, whereas it depends on other factors
such as humidity, wind speed, and it is known as Thermesthesia.
Thermesthesia describes more precisely theeffects of environmental
temperature on humans.
1.4.2. Measurement of 24-hour heart rate and blood pressure:
An automatic Holter blood pressure device records the changes in
heart rate and BP over a 24-hour period at regular intervals
throughout the day.
1.4.3. Measurement of 24-hour microclimates: The application
of scientific and technical achievementsin this area is helpful in
developing microclimate measuring devices into a diverse, portable,
convenient fashion which is applicable in different working
conditions and meets dissimilar purposes.
1.5. Control measurement of hot microclimates: Including
measurements such as properworking organization, workshop and
equipmentplanning,
ventilation,
cooling,
equipment
and
technological processes, personal safety, healthy diet.
1.6. Natural characteristics of Hanoi City
Chapter 2
RESEARCH SUBJECTS AND METHODOLOGY
2.1. Time frame and location:
2.1.1. Duration: Six years (from October 2013 to June 2019).
2.1.2. Location: Hanoi City
2.2. Research subjects:

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The research intentionally selected groups of policemen working
in different environmental conditions:
2.2.1. Road traffic police (outdoor working group)
2.2.2. Police officers (indoor working group with air conditioner)
2.2.3. Students of Police Academy (indoor working group
without air conditioner)
2.2.4. Ambient 24-hour microclimate factors:temperature
andhumidity
2.3. Research methodology:
2.3.1. Research design: Research in two stages
2.3.2. Cross-sectional descriptive study (stage 1):
2.3.2.1. Sample size and selection:
The calculation of sample size by R software developed by
Daniel Ludecke is applied with a coefficient of 0.37, statistical
significance of 0.05, power of 0.8, three groups, thus, a minimum
size isa population of 231 people. We eventually have a selection of
244 participants which is sufficient for the research sample. The
sample comprises of 61 police officers, 87 police students, and 96
road traffic policemen.
2.3.2.2. Information areas to be collected:
- 24-hour heart rate and BP of the research subjects.
- Microclimate factors (temperature, humidity) in 24 hours where
subjects are heart rate and BP monitored.
- Confounding factors to control:
+ Demographic information: ages, sexes, localities, occupations.
+ Anthropometric information: height, weight.
+ Information on the working conditions and daily life: indoor,

outdoor, with air-conditioning, without air-conditioning.
+ Behavioral and lifestyle characteristics: Smoking; intake of
alcohol and caffeine, tension, etc.


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+ Medical history: cardiovascular disease, diabetes, metabolic
disorders, psychosomatic, etc.
+ Personal information at each time of 24-hour BP and
microclimate monitoring: activity intensity, clothing, consumption,
environmentand health feeling.
2.3.2.3. Data collection tools:
- 24-hour ambulatory heart rate and BP monitor with the brand
of WatchBP O3 (Holter BP) produced by Microlife Switzerland
- Mobile 24-hour ambulatory microclimate (temperature,
humidity) meter with the brand of RTH20 produced by Extech USA.
- Questionnaire
- 24-hour log
2.3.2.4. Datacollection technique
2.3.3. Intervention research (stage 2):
2.3.3.1. Selection of experimental intervention: Research results
in the Stage 1 indicate that Road Traffic Policemen is the most
impactedgroup by environmental factors than other ones with
noticeable effects of hot microclimate in summer on the variation of
the policemen’s heart rate and BP.
2.3.3.2. Content of experimental intervention: Testing three types
of heat-resistant umbrella (ordinary umbrella, heat-reflective
umbrella, and heat-insulation umbrella) at the intersection of Pham
Van Dong street and Hoang Quoc Viet street, andthe intersection of
Lang Street and Nguyen Chi Thanh Streetduringforecasted hot days

(over 350C) in June and July in 2016. The effectiveness of heatresistant umbrellas is evaluated by measuring temperature and
humidity under thoseumbrellas. At the same time, 36 voluntarily
policemenin the test shallscore the heat level of each umbrella type.
2.4. Data processing and analysis: The research uses STATA 13
and MLwiN 3.1 for data analysis. Moreover, hierarchical multiple


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regressionis applied in order to identify factors related to the
SBP/DBP and heart rate.
2.5. Research errors and solutions: The research errors caused
bypolicemen’s psychological tension while being Holter monitored,
device attachment forgotten, and incomplete 24-hour log will be
resolved.
2.6. Research ethics: The research is a part of the State-level
Project and has been approved by the Ethics Committee in National
Biomedical Research of the Ministry of Health and ensures itsstrict
compliance with regulations of confidentiality and the rights of
research subjects.
Chapter 3
RESEARCH RESULTS
3.1. General information:
The research sample consists of amajority of male (91%), with
fairly young average age (26.7 years old) in which the group of
between 20-29 years old is the most (54.5%). The percentage of
policemen with high blood pressure history is small (1.6%),
however, there are a lot of policemen maintaining harmful habits for
health with high daily smoking rate (77.5%) and 30.3% of the
population having coffee intake every day. In addition, policemen
are affected by other adverse factors such as working pressure

(98%), family issues (99.2%). Notably, 38.1% of those who were
interviewed indicate that they are daily under pressure from work
while 65.6% of those have irregular pressure from family issues.
3.2. Characteristics of 24-hour heart rate and blood pressure
variation of policemen
3.2.1. Heart rate and blood pressure vary according to the
circadian rhythm (day and night rhythm):


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Blood Pressure (mmHg)

The systolic BP (SBP) changes according to circadian rhythm
(day and night rhythm), tends to increase gradually in the early
morning (about 5:00AM to 6:00AM), then slightly fluctuates
throughout the day, gradually decrease in the evening (about
21:00PM to 23:00PM), and drop at night (about 1:00AM to
4:00AM). This trend is observed in both seasons (summer and
winter). BP in summer, SBP value first reaches the peak is earlier
thanit does in winter (9:00AM compared to 12:00PM), and tends to
decrease significantly earlier than that in winter (21:00PM compared
to 22:00PM) with more times that the SBP value are at peak than in
winter (4 times compared to 3 times).
125
123
121
119
117
115

113
111
109
107
105
103
101
99
97
95

Summer

Winter

1 2 3 4 5 6 7 8 9 101112131415161718192021222324
Time (hour)

Figure 3.1: Variation of 24-hour systolic BP of policemen (n=244)

Similarly, the diastolic BP (DBP) varies by the circadian rhythm
(day and night rhythm), tends to increase gradually in the early
morning (about 5:00AM to 6:00AM), then slightly fluctuates
throughout the day and gradually decrease in the evening (about
21:00PM), and sharply drop at night (about 1:00AM to 4:00AM).
This trend is observed in both seasons (summer and winter). The


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DBP value in summer is higher than that in the winter at most of the

time at night and in the morning, nevertheless, the values in the
afternoon and in the evening are not much different. The value of
DBP during daytime (7:00AM to 18:00PM) is higher than that at
night (1:00AM to 6:00AM). In summer, the DBP first reaches its
peak earlier than in the winter (8:00AM compared to 12:00PM), it
tends to decrease significantly at the same time (21:00PM) in both
seasons, the number of peaks in summer is higher than in the winter

Blood Pressure (mmHg)

as well (3 times compared to 2 times).
80
78
76
74
72
70
68
66
64
62
60
58
56
54
52
50

Summer

Winter

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Time (hour)

Figure 3.2: Variation of the 24-hour diastolic BP of policemen (n=244)

The comparison of characteristics of groups suggest some
differences. In summer, the SBP value of the Road Traffic Police is
higher than that of the Police officers and Police students at most of
times during the day (from 8:00AM to 20:00PM). The SBP of the
Police officers and Police students first reaches its peak earlier (at
about 8:00AM) compared to the Road Traffic Police (at about
9:00AM). The SBP of Road Traffic Police and Police officers tends
to decrease at the earlier (21:00PM) than that of the Police students


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(23:00PM). The DBP value of the Road Traffic Police is higher than
that of the Police officers and Police students at most of times during
the day (from 9:00AM to 23:00PM). The DBP of the Police officers
and Police students first reaches its peak earlier (at about 7:00AM)
compared to the Road Traffic Police (at about 11:00AM). The DBP
of the Police officers and Police students tends to decrease at the
earlier (21:00PM) than that of the Road Traffic Police (23:00PM).
The same thing happens in winter when the SBP value of the Road
Traffic Police is higher than that of the Police officers and Police
students at most of times during the afternoon and night (from
13:00PM to 20:00PM). The SBP of Police students first reaches its
peak earlier (7:00AM) compared to the Police officers and Road

Traffic Police (at about 11:00AM). The SBP of Road Traffic Police
tends to decrease at the earliest (21:00PM) while the SBP of Police
officers tends to decrease later (22:00PM), and those of Police
students decrease at the latest (23:00PM).
The DBP value of Road Traffic Police is higher than that of
Police officers and Police students in most of the times in afternoons
and evenings (from 11:00PM to 20:00PM). Further more, the DBP of
the Police officers and Police students reaches the first peakearlier
(7:00AM) compared to that of the Road Traffic Police (at about
11:00AM). The DBP of the Road Traffic Policetens to decrease
earlier (21:00PM) compared to that of the Police officers and Police
students (22:00PM).
The heart rate is in the same way with BP, which tends to vary
according to the circadian rhythm (day and night rhythm), gradually
increases in the early morning (at around 5:00AM to 6:00AM), then
slightly fluctuates throughout the day, it switches to a gradual decline
in the evening (at around 19:00PM to 22:00PM) and reaches the
lowest value at night (at around 1:00AM to 4:00AM). This trend is
observed in both seasons (summer and winter).


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heart rate (time/mint))

90

Summer

Winter

85
80
75
70
65
60
55
50
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Time (hour)

Figure 3.7: Variation of 24-hour heart rate of policemen (n=244)
The heart rate between summer and winter is different but not
significant. In summer, Police students’ heart rate tends to decrease
at the earliest (at around 20:00PM), in the meanwhile, the heart rate
of the Police officers decreases later (at around 21:00PM), and the
Road Traffic Police’s one reduces at the latest (at around 22:00PM).
In winter, those of Police students tend to decrease at the earliest (at
around 19:00PM), followed by the heart rate of the Police officers
and the Road Traffic Police (at around 21:00PM).
3.2.2. Variation of heart rate and blood pressure during sessions
of a day:
Survey of variation of the SBP during 4 sessions in a day
(morning, afternoon, evening, and night), indicates that, daytime
SBP (in morning and afternoon) is higher than at night (evening and
night). At night, the SBP has the sharpest reduction, forming a BP
gap. The comparison of the SBP values among the sessions proves
thatthere is a biggest difference between the SBP pressurevalue in
morning and that in night compared to the other sessions during a

day. These characteristics are found in both summer and winter.


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Blood Pressure (mmHg)

Remarkably, in summer, the night-time SBP does not drop as low as
it in the winter. Correspondingly, the daytime DBP (morning and
afternoon) is higher than that at night (evening and night). Nighttime DBP reaches its trough and creates a BP gap as well.
120
118
116
114
112
110
108
106
104
102
100

Summer

Evening

Night

Winter

Morning

Afternoon

Time (session)

Blood Pressure (mmHg)

Figure 3.10: Average SBP by day sessions of Policemen (n=244)

76
74
72
70
68
66
64
62
60
58
56
54

Summer

Evening

Night
Morning
Time (session)

Winter

Afternoon

Figure 3.11: Average DBP by day sessions of Policemen (n=244)

Additionally, the comparison of the DBP values among sessions
of a day demonstrates similar results with the SBP. The DBP values


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at night and in morning have the largest difference compared to those
values in other sessions during a day. And these characteristics are
found in both summer and winter. In summer, the drop of the DBP at
night is not as low as it is in winter.
Road Traffic Police group, there is the biggest difference of the

heart rate (time/min)

SBP, DBP values between night and morning.
Summer

86
84
82
80
78
76
74

72
70
68
66
64
62
60
58
56
Evening

Night

Morning

Winter

Afternoon

Time (session)

Figure 3.16: Average heart rate by sessions of Policemen (n=244)

The comparison of the heart rate difference between sessions
indicates that the heart rate values at night and in the morning have
the biggest difference compared to other sessions in a day. These
features are found in both summer and winter. Road Traffic Police
group, there is the biggest difference in the heart rate values between
night and morning.
3.3. The correlation between selected microclimates and 24hour heart rate and blood pressure

The correlation between temperature, humidity and heart rate,
BP in all 3 research groups has been found that these natural factors
have a weak effect on heart rate and BP (the SBP and the DBP) of
the Policemen.


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The results of multi-level regression analysis prove that each
increased unit in temperature, humidity, or any changes in humidity
during the day, or shift from winter to summer, or a comparison
between males and females, the SBP shall decrease. Even so, any
changes of temperature during the day, or any random correlation
between temperature and humidity, or any transition of time zones
(sessions in the day) compared to the first time zone(1:00AM to
6:00AM), or any increase in supplemented BMI, or increase in any
risk point, the SBP shall increase accordingly.
Similarly, for the DBP, each increased unit in humidity, or shift
from winter to summer, or comparison between males and females,
the DBP shall decrease. Conversely, any conversion of time zones
(sessions in the day) compared to the first time zone (1:00AM to
6:00AM), or any additional BMI increase, or increase in any risk
point, the DBP shall increase accordingly. There are two factors
without statistical significance in influencingthe SBPbut affecting the
DBP by ages and occupations.
For the heart rate, only the change of humidity during the day,
or the transition of the time zones of the day, or the change of season,
ages, occupationsshall statistically contribute towards the increase of
the heart rate. Interestingly, although the risk points play a significant
role in the increase ofthe SBP and the DBP, they have insignificant
effect on heart rate.

In general, the change in ambient temperature or humidity and
personal characteristics have an important effect on the variation of
Policemen’s heart rate and BP. The change in temperature and
humidity factors over the period of 24 hours contribute the most to
the total change of the SBP and the DBP and heart rate, while
personal characteristics contribute the least to the total change of the
SBP, the DBP and heart rate (26%, 25%, and 23% respectively). In


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other words, the temperature and humidity of the environment
contribute about 74%, 75% and 77% to the change of the SBP, the
DBP and heart rate of the research subjects.
3.4. The improvement of microclimate conditionsby
equipment set in workplace of Road Traffic Police:
Table 3.9: Comparison of heat feeling scoresamong 3 types of
sunscreen umbrella of Policemen
Comparison pairs

Averagescore of heat feeling
(n = 36)
X

SD

7.92
4.97

± 0.937
± 0.941

Ordinary and heat-insulation
umbrellas:

-

Ordinary umbrella
Heat-insulation umbrella

Ordinary and heat-reflection
umbrellas:

-

Ordinary umbrella
Heat-reflection umbrella

Heat-reflection
and
heatinsulation umbrellas
- Heat-insulation umbrella
- Heat-reflection umbrella

p

<0.0001

<0.0001
7.92
3.19

± 0.937
±1.091
<0.0001

4.97
3.19

± 0.941
±1.091

Interview results of 36 voluntary policemen with the content of
cores on heat feeling when standing under three types of umbrellas,
with a scale from 1 (corresponding to a Very pleasant feeling) to 10
(corresponding to a Very uncomfortable feeling) demonstrates that,
with heat-insulation umbrellas, Road Traffic Police feel more
pleasant (4.97 points) than ordinary ones (7.92 points), this
difference is statistically significant (p <0.0001). Similarly, when
comparing the heat feeling scale for ordinary and heat-relative


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umbrellas, it is also shown that, the Road Traffic Police feel more
comfortable (3.19 points) with the heat-relative umbrellas than the
ordinary ones (7.92 points), this difference is statistically significant
(p<0.0001). Comparison results of heat feeling between heatinsulation and Heat-reflection umbrella found that, the Road Traffic
Police feel more comfortable (3.19 points) with the heat-relative
umbrellas than the heat-insulation ones (4.97 points), this difference
is statistically significant (p <0.0001).
Table 3.10: Comparison of temperatures among three types of

sun protection umbrellas
Average temperature (0C)
(n = 6619)
Comparison pairs
X
SD
P
Ordinary and heat-insulation
umbrellas:
- Ordinary umbrella
- Heat-insulation umbrella
Ordinary and Heat-reflection
umbrellas:
- Ordinary umbrella

-

Heat-reflection umbrella
Heat-reflection
and
heatinsulation umbrellas
- Heat-insulation umbrella

-

35.71
34.08

± 5.30
± 4.18

35.71

± 5.30

34.22

± 4.25

<0.0001

<0.0001

<0.0001
34.08

± 4.18

Heat-reflection umbrella
34.22
± 4.25
Comparison of the average temperatures of the sun protection
umbrellas indicates a significant difference, the temperature in the
heat-insulation umbrella (34.080C) is lower than the temperature in
the ordinary umbrella (35.710C) which has statistical significance (p
<0.0001), the temperature in the Heat-reflection umbrella (34.220C)


19
is also lower compared to the temperature in the ordinary umbrella

(35.710C) which gains a statistical significance (p <0.0001) but
higher than the temperature in the heat-insulation umbrella (34.080C)
which is statistically significant (p <0.0001).
CHAPTER 4
DISCUSSIONS
4.1. Characteristics of variation in 24-hour heart rate and
blood pressure of policemen
4.1.1. Policemen’s heart rate and blood pressure varies by 24hour circadian rhythm
The data suggests that there is a common trend in which heart
rate and BP gradually increases in the morning (between 5:00AM
and 6:00AM), reaches the first peak at about 8:00AM to 12:00PM,
then it slightly fluctuates throughout the day and gradually decreases
in the evening (about 21:00PM to 23:00PM), and reaches the trough
at night (about 1:00AM to 4:00AM). This finding is similar to a
number of previous studies describing the BP decrease at night with
the lowest at about 2:00AM to 3:00AM, and increase in the morning,
at about 9:00AM to 12:00PM and 17:00PM when BP increases and
then slightly drops). Nguyen Huu Tram Em et al. pointed out the line
graph regarding two BP peaks during the day from 7:00AM to
9:00AM and from 6:00PM to 8:00PM. In addition to that, in her
study, she identifies a trough in the period of 1:00AM to 3:00AM
and BP start to increase at 5:00AM to 6:00AM.
Although the trends of heart rate and BP are similar, each
policemen group has their respective characteristics as well as the
differences between the highest BP and the lowest BP. The Police
officers’ highest BP reaches their first peak at about 8:00AM to
11:00AM, in the meanwhile, Police students’ one is at about 7:00AM
to 8:00AM, and Road Traffic Police’s first peak is at about 9:00AM
to 11:00AM. The Police Officers’ lowest BP decreases at about
21:00PM to 22:00PM while Police students’ one is at 23:00PM and

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Road Traffic Police is at 21:00PM. The point of time when the
Police Officers’ highest BP goes down is at about 21:00PM to
22:00PM whilst Police Students’ one is at about 23:00PM and Road
Traffic Police’s is at 21:00PM. Correspondingly, for the lowest BP,
it is 22:00PM for Police Officers and Police Students, and at
21:00PM to 23:00PM for Road Traffic Police. It is obviously shown
that the Road traffic police reach their peak at the later time
compared to those oftwo other groups, however, there is insignificant
difference among points of time for BP to decrease. This shall be
explained in the following part.
In this study, data on difference of heart rate and BP points out
that the average difference is biggest between night and morning in
comparison to differences among other sessions during a day. In
other words, when night shifts to morning, heart rate and BP has a
sudden increase (sharp raise) compared to the BP variation in other
sessions by day. It is described by many relevant researches that
hypertension goes up in the morning shall adversely lead to
stroke. BP sharply raises in early morning, including diastolic and
systolic BP, forfirst hours is a change pattern related to a poor
prognosis. The Road Traffic Police in this study have the BP sharp
raise in the morning compared to the rest. It is suggested that this
group is more likely to have cardiovascular events than other groups.
This issue shall be discussed in the part regarding impacts of work
environment on cardiovascular risks.
4.1.2. Variation of 24-hour heart rate and blood pressure by
seasons:
Based on the analysis of heart rate and BP variation by seasons

in this research, it is indicated that the highest BP in summer reaches
its peak earlier than that in winter (except the Police Students with
insignificant difference between 8:00AM and 7:00AM) and BP
values at peak more times than they are in winter. Remarkably, BP in
summer is higher than it is in winter at most of the times during a


21
day. Nevertheless, it is not obviously different when observing heart
rate of Police Students and Road Traffic Police. On the contrary, for
Police Officers’ heart rate in summer is lower than it is in winter
with insignificance. The results obtained from this research are
unlike what J. Goodwin et al. discussed earlier, showing that the 24hour BP in elderly groupsin winter was higher than it is in summer
compared to young people. The explanation for this difference is that
in the UK, where the research of J. Goodwin et al. was carried out,
the weather was pleasant in summer with temperature ranges
between 18 to 200C, while the winter was chilly with temperature
ranges between 6 to 70C. As a result, BP in winter is higher than that
in summer for the elderly.
Conversely, the location of Hanoi where this study was
conducted, is characterized by tropical climate with hot summer
weather when temperature reaches 35 to 400C, even the heatwaves
with temperature of more than 400C. In winter, weather is more
pleasant with temperature ranges between 15 and 200C. Moreover,
research of J. Goodwin et al. was more concerned with the noticeable
effects of winter on the elderly compared to the young. In the
meanwhile, average age of 26.7 of research subjects in this study is
quite young. Thus, the discussed BP in summer is higher than it is in
winter is appropriate. As can be seen that the weather factor
influences heart rate and BP of Road Traffic Police in comparison to

two other groups. It is perceived when Road Traffic Police
frequently work in outdoor conditions where they are directly
exposed to the adverse weather such as heat, humidity, cold ... while
officers and students spend most of their time indoor with less effect
by weather. It is worth mention that summer weather has stronger
effect on heart rate and BP variation of Road Traffic Police than it
has in winter, with higher value than those of the other groups during
the day, when Road Traffic Police’s shifts are under the summer
heat. As discussed above, Road Traffic Police with signs of BP sharp


22
rise in the morning, which have been proposed by many studies,
would be more likely to have cardiovascular occurrences than other
groups. When the features of Road Traffic Police’s heart rate and BP
are separately analyzed in two seasons, it is found that BP in
summer does not deeply decrease than it does winter, and in the
meantime, policemen’s BP in winter have the higher level of sharp
rise in the morning than they do in summer. In this study, Road
Traffic Police have higher heart rate and BP value than those in other
groups in most of the time during a day in summer when they are at
work under strong effect of the hot weather, especially heatwaves.
4.2. Effects of some selected microclimate factors on 24-hour
heart rate and blood pressure of policemen
Previous studies have been developingpredictive models of BP
by patterns of multivariate linear regression when the dependent
variable of BP is frequently measured once or used with average
value. Nonetheless, that method shall not fully describe the
complexity of BP variation. Therefore, this study was designed to
develop a model of heart rate and BP prediction over the period of 24

hours on selected research subjects. Multilevel analysis pattern is
applied in this research. With the advancement of information
technology, multi-layered analysis is likely applied in order to
evaluate complicated correlations and multi-layered pattern more
accurately. By this method, research results may demonstrate the
fluctuations around average heart rate and BP on research
subjects. Additionally, data of this study indicates that weather
changes and personal characteristics contribute towards the variation
of heart rate and BP amongst research populations and how these
factors at different levelshaving effects on BP variation. The
transformation of 24-hour environmental temperature and humidity
(level 1) is repeatedly higher than changes of policemen’s personal
characteristics (level 2) that leads to small intraclass correlation
coefficient (ICC), ranging from 23% to 26%. In other words, level 1


23
(24-hour environmental temperature and humidity) contribute about
74% to 77% to the variation of heart rate and BP of research
subjects. In comparison to a previous study with a sample of 1,831
hypertension patients, it is obvious that weather conditions play more
roles in the variation of policemen’s BP than those with
hypertension.
4.3. Improvement of microclimate conditions by equipment
set in work place of Road Traffic Police:
Sun protection umbrellas have been provided in workplaces of
Road Traffic Police in this study in order to improve hot
microclimate conditions. There are three types of umbrellas for
experiment including ordinary (commonly used by road police for a
long time), heat-insulation, and heat-reflection. Research results

prove that both types of heat-insulation and heat-reflection
umbrellasmake policemen more comfortable than the ordinary, and
this difference is statistically significant (p<0.0001). Furthermore,
the sun protection effects of the two recommend umbrellas are
measured and policeman commented that the heat-reflection is more
helpful than heat-insulation one with statistical significance (p <0,
0001).
CONCLUSION
1. Heart rate and BP of policemen in our surveyvary according
to the circadian rhythm, gradually increase in the morning (5:00AM
to 6:00AM), reach the first peak in the period of 7:00AM to
11:00AM, then slightly fluctuate throughout the day, gradually
decrease in the evening (21:00PM to 23:00PM), reach the trough at
night (1:00AM to 4:00AM). The values of heart rate and BP at night
are lower than they are in the day time with the lowest value in the
period of 1:00AM to 4:00AM. The difference in heart rate and BP
between the night and the morning is the highest. The Road Traffic
Policemen’s heart rate and BP are higher than those of Police


24
officers and Police students at most of the time of the daytime in
summer. Summer heat indices at the workplace of the Road Traffic
Police (92.7 to 100.4) and of Police students (93.2 to 100.2) pose an
extreme warning.
2. A positive correlation between the selected microclimates
with heart rate and BP was foundwith a statistical significance,
nevertheless, the correlation level is small which indicates that the
research subjects’ physical bodies are capable to adapt themselves to
current microclimate changes. The variation level of 24-hour

temperature and humidity in the environmenthas the most (about 2/3)
effect on the total variation of policemen’s heart rate and BP. In the
meanwhile, other aspects of BMI, ages and scores of risk factors gain
a statistical significance for the variation in their heart rate and BP.
3. Heat-insulation and Heat-reflection umbrellas effectively
improve microclimate conditions in their workplaces and help the
Road Traffic Police feel more comfortable.
RECOMMENDATIONS
1. Further studies with more focus on human body’s response
on extreme days while working outdoor and in places without airconditioner are therefore suggested.
2. This is an important issue for future research to have more
large-scale experiment of sun protection umbrellas in order to have
scientific basis for mitigation measurements of hot microclimates to
policemen’s health.
3. The Ministry of Public Security is recommended to conduct
further research and other intervention measurements such as
adjustment of policemen’s working schedules, supply of electrolyzed
reduced water, and campaigns to provide information on health
protection for policemen, especially the Road Traffic Police.