Assessment of heart rate
variability and reaction time in traffic policemen
Kuppusamy S.1, Niraimathi
D 2, John N.A.3
1Dr Saranya Kuppusamy, Assistant Professor, 2Dr Dhanapal Niraimathi,
Associate Professor, 3Dr Nitin Ashok John,
Professor Head; all authors are affiliated with Department of
Physiology, Indira Gandhi Medical College Research Institute,
Puducherry, India
Address for
Correspondence: Dr. Saranya K., Assistant Professor,
Department of Physiology, IGMC RI, Kathirkamam, Puducherry-9.
Email id: ktsaran28@gmail.com
Abstract
Introduction:
Air Pollution can have a deleterious effect on cardiovascular function
and cognition. Heart rate variability (HRV), which is a non-invasive
and objective measure of cardiac autonomic function, is a
cardiovascular risk predictor. Reaction time is a simple method of
assessing the perceptual-cognitive processing capability of the central
nervous system. Hence, the aim of the study was to assess the heart
rate variability and reaction time in traffic police officers of
Puducherry. Methods:
Fifty-five age and BMI matched traffic police and healthy controls were
recruited. Basal cardiovascular parameters; basal heart rate, systolic
and diastolic blood pressure (BHR, SBP, DBP) were assessed. Short term
HRV analysis was done. Time and frequency domain indices were computed.
Simple and Choice Auditory and Visual reaction time (SART, CART, SVRT,
CVRT) were measured. Results:
BHR and DBP were significantly increased in traffic police. Time domain
indices (Mean RR, SDNN, RMSSD, pNN50) were significantly reduced in
traffic police. In frequency domain, Total Power was significantly
reduced. LF-HF ratio was increased, though not significant. SVRT was
significantly delayed in traffic police. CVRT, SART and CART were
delayed in traffic police though not significant. Conclusion: Traffic
police have decreased HRV with increased sympathetic and decreased
vagal tone, and delayed reaction time.
Key words:
Traffic Police, Autonomic function, Heart rate variability, Cognition,
Reaction time
Manuscript received:
27th September 2016,
Reviewed: 10th October 2016
Author Corrected:
25th October 2016,
Accepted for Publication: 12th November 2016
Introduction
Air pollution is a form of environmental degradation which has become
rampant in recent times [1]. In 2010, as per the Global Burden of
Disease study, around 3.1 million deaths of overall 52.8 million deaths
had been attributed to air pollution [2]. Such is the burden
and impact of air pollution on human health.
Vehicular emissions are the prime cause of air quality crisis in
cities. Owing to the expanding economic base, use of motor vehicles
increased with a subsequent increase in air pollution.
Automobile exhaust causing health hazard are mainly oxides of nitrogen,
sulfur and particulate matter (PM), with contribution from carbon
monoxide and benzene [2,3].
Along with environmental pollution, occupation is also a major
determinant of health. In this aspect, traffic police
officers are at a risk, since they are continuously exposed to
emissions from vehicles. The relationship between air pollution and
respiratory diseases, such as chronic obstructive pulmonary disease and
asthma, is well established [3,4]. In fact, a study conducted in
Puducherry has demonstrated obstruction and narrowing of airways in
traffic police officers [5].
But recent studies also reveal the relationship between air pollution
and cardiovascular (CV) morbidity [6,7]. Short-term particulate matter
exposures, lead to acute CV events including myocardial infarction,
cardiac arrhythmia while long-term exposure has been linked to
increased development of atherosclerosis. Various postulated mechanisms
include pulmonary and systemic inflammatory response, myocardial
ischemic response, endothelial dysfunction, atherosclerosis and
thrombosis [6,7]. Though the exact underlying link between PM exposure
and CV outcomes is not yet clear, alterations in cardiac autonomic
function have been suggested to be one of the pathophysiologic pathways
[6,7].
Heart rate variability (HRV) is a non-invasive, independent and
quantitative marker of cardiac autonomic control [8]. HRV is an
indicator of autonomic control of the heart rate, and an alteration in
HRV is associated with increased risk for cardiac events [8].
Air pollution can also have a deleterious effect on the central nervous
system. Animal studies have shown that exposure to fine or ultrafine PM
is associated with CNS inflammation and lipid peroxidation, neuronal
degeneration, impairments in spatial learning and memory and
behavioural changes with depressive-like responses [9,10]. To further
potentiate, the CV effects of air pollution may lead to CNS dysfunction
via the vascular brain pathology [9]. A possible manifestation of CNS
dysfunction is cognitive decline. Studies have evidenced ambient
traffic-related air pollution was associated with decreased cognitive
function in middle-aged and older adults [11]. Reaction time
(RT) is the time taken to respond to a sensory stimulus, which includes
stimulus recognition, cognitive processing, and the motor response to
the stimulus [12].
Since vehicular emissions are associated with increased cardiovascular
risk and cognitive decline, understanding the underlying mechanisms for
this association has significant public health relevance. With the
paucity of literature on the heart rate variability (HRV) and reaction
time in traffic police officers of Pondicherry, in this study, we plan
to assess short-term heart rate variability in Traffic police officers
in Puducherry.
Aim
and Objectives
To assess the heart rate variability and reaction time in traffic
police officers of Puducherry
Materials
& Methods
It was an analytical cross-sectional study, conducted in Department of
Physiology, IGMC & RI, Puducherry. Before commencement of the
study, the approval from the Institute Research Committee and Human
Ethics committee was obtained. After explaining the study to
the participants, their written informed consent was obtained.
Participants:
The study involved two groups with 55 participants in each group.
Inclusion criteria
Group 1: Traffic police officers (males) employed in Puducherry, aged
between 25 to 45 years, employed for at least five years.
Group 2: Age, Gender, and BMI-matched healthy men.
Exclusion criteria
For both the groups: Participants who are smokers, chronic alcoholics,
taking hormonal/drug therapy, diabetes mellitus, hormonal disorders,
known hypertension, cardiovascular & pulmonary disease.
Methodology
The participants fulfilling the inclusion criteria were recruited. All
the participants were asked to report at 9.00 a.m., two h after a light
breakfast, and after emptying their bladder. Participants were asked to
avoid any caffeinated beverage on the day of the trial. The recording
was done in a quiet room with the ambient temperature maintained at
25°C (±2°C). The procedure was duly
explained to them.
Parameters assessed
Anthropometric measurements- BMI was calculated by Quetelet’s
index. The Asian criterion for BMI was followed for grouping the
subjects based on the level of BMI [13].
Basal Parameter- Basal
heart rate (BHR), systolic blood pressure (SBP), and diastolic blood
pressure (DBP) were measured after 10 minutes of supine rest, by the
oscillometric method using an Omron MX3 automated blood pressure
monitor (Omron Healthcare, Kyoto, Japan).
Heart Rate variability analysis: Short-term HRV analysis
Recording of HRV-Lead II electrocardiogram (ECG) was recorded,
following the standard procedure as per the recommendation of Task
Force. The data acquisition was performed using
INCO-NIVIQUIRE digital acquisition system, version 52.0, INCO systems,
Ambala, India. The sampling rate was kept at 500 samples/s per channel.
Raw ECG was filtered using a band pass filter (2–40 Hz). The
RR tachogram obtained from the filtered ECG was then analyzed for time
domain and frequency domain measures (power spectral analysis using
fast Fourier transformation) using the software from the Biomedical
Signal Analysis Group ver. 2.1 (Kuopio, Finland).
HRV indices &
their implications: The frequency domain indices included
low frequency (LF; 0.04–0.15 Hz), high frequency (HF;
0.15–0.4 Hz), total power (TP), LF in normalized units
(LFnu), HF in normalized units (HFnu) and the ratio of LF to HF (LF-HF
ratio). The LF and LFnu represent sympathetic tone. The HF and HFnu,
represent the cardiac parasympathetic drive (vagal tone). The LF-HF
ratio depicts the sympathovagal balance [8].
The time domain measures included mean RR (mean of RR interval),
standard deviation of RR interval (SDNN), the square root of the mean
of the sum of the squares of the differences between adjacent NN
intervals (RMSSD), the number of pairs of adjacent NN intervals
differing by more than 50 msec in the entire recording (NN50) and the
percentage of NN50 counts, given by NN50 count divided by total number
of all NN intervals (PNN50). The SDNN, RMSSD, NN50 and PNN50 of HRV
indices represent the cardiac parasympathetic drive (vagal tone) [8].
Reaction time assessmen- Reaction
time is a simple and inexpensive method for indirectly measuring the
perceptual-cognitive processing capability of the central nervous
system.
The RT was recorded using RT apparatus supplied by Anand Agencies
(Pune, India). The RT apparatus consists of an automated chronoscope
with a four-digit display that can record the response time with an
accuracy of 1ms. It is capable of providing an auditory input signal of
two different tones namely beep and click, and likewise, visual input
signals of two colors namely red and green.
Evaluation of RT to auditory and visual signals was done. The
participants were instructed to use their self-reported dominant hand
to record their response to the presented stimulus. Participants were
instructed to release the response key as soon as they perceived the
stimulus and the time interval between the stimulus and the response
was recorded. The apparatus was in front of the participant to avoid
lateralization of the stimuli to one side. Before recording the RT,
three practice sessions were given to all the study participants to
familiarize them to the RT apparatus as RT. Both simple and choice
auditory and visual reaction times were assessed.
Simple Reaction time: Only
one stimulus was presented, to which the participant was asked to
respond. Simple Auditory Reaction Time (SART): The subjects were asked
to respond to beep sound. Simple Visual Reaction Time (SVRT):
The subjects were asked to respond to red light.
Choice Reaction time: Among
the two stimuli (beep & click auditory stimuli / red &
green color of visual stimuli), one will act as the
“memory” stimulus for which the participant is
instructed to respond by releasing the response switch, while the other
will act as a “distractor” stimulus for which the
participant is instructed not to respond.
Choice Auditory Reaction
Time (CART): The subjects were asked to
selectively respond to beep sound when intervened with the click sound.
Choice Visual Reaction
Time (CVRT): The subjects were asked to respond
to red light when intervened with the green light.
Sample Size Calculation
and Statistical analysis: The sample size was calculated
using the formula 4pq/L2. Considering proportion of people
with decreased heart rate variability as 50% and taking allowable error
as 30 % of p, with p = 50 and q = 100-p = 50, at 5% significant level
with 95% confidence interval, sample size is calculated as follows:
4*p*q / (L)2 = 4*50*50/15*15 = 10000/225 = 44. Considering the drop out
of 10% and no response of 10% total sample size has been calculated as
55 in each group.
Continuous data were tested for normality and expressed as mean
± SD or median with range. For intergroup comparison of
continuous data, unpaired student’s t-test for parametric and
Mann-Whitney-U test for non-parametric data was used. Statistical
analysis was done at two-tailed significance and p-value of
<0.05 was considered as significant.
Results
Age, anthropometric, basal cardiovascular parameters: Both the cases
and control subjects were of comparable age (P=0.290) and BMI (P=0.236)
(Table1). Among the cardiovascular baseline parameters, BHR and DBP
were significantly high (P=0.034, P=0.007 respectively) in traffic
police compared to that of controls. The SBP was found to be high in
traffic police, though not significant.
Table-1: Comparison of
anthropometric & basal cardiovascular parameters between
Controls & Traffic Police
|
Parameters
|
Controls
(n=55)
|
Traffic Police
(n=55)
|
P value
|
|
Age
|
30.76 ± 5.08
|
31.98 ± 6.81
|
0.290
|
|
BMI
|
23.60 ± 3.94
|
24.29 ± 1.75
|
0.236
|
|
BHR
|
70.24 ± 8.32
|
74.16 ± 10.70
|
0.034
|
|
SBP
|
113.69 ± 10.60
|
116.64 ± 10.37
|
0.144
|
|
DBP
|
67.76 ± 7.46
|
72.35 ± 9.92
|
0.007
|
Analysis done by Unpaired Student’s t Test, Data
expressed as Mean with SD. BMI, body mass index; BHR, basal heart rate;
SBP, systolic blood pressure; DBP, diastolic blood pressure.
Short-term HRV analysis: Time domain indices: All the time domain
indices; mean-RR (P=0.004), SDNN (P=0.001), RMSSD, NN50 and pNN50 (for
all P<0.001) were significantly decreased in traffic police
compared to that of controls (Table 2).
Frequency domain indices: Among the frequency domain indices, total
power (TP) was significantly reduced among the traffic police (P=0.001]
(Table 2). When the absolute powers were expressed in normalized units,
increased LFnu (P=0.177) and decreased HFnu (P=0.187) were observed in
traffic police, though not significant. The LF/HF ratio was increased
in traffic police (P=0.214) compared to the controls, but not
significantly.
Table-2: Comparison of
HRV indices between Controls and Traffic Police
|
Time Domain Indices
|
|
Parameters
|
Controls (n=55)
|
Traffic Police (n=55)
|
P value
|
|
Median
|
IQR
|
Median
|
IQR
|
|
Mean RR (ms)
|
865.50
|
154.40
|
777.29
|
234.67
|
0.004
|
|
SDNN (ms)
|
48.00
|
20.80
|
37.80
|
13.51
|
0.001
|
|
RMSSD (ms)
|
36.30
|
29.10
|
29.40
|
13.88
|
< 0.001
|
|
NN50
|
49.00
|
113.00
|
27.00
|
46.00
|
< 0.001
|
|
pNN50
|
15.60
|
36.40
|
7.71
|
13.62
|
< 0.001
|
|
Frequency Domain Indices
|
|
Parameters
|
Controls (n=55)
|
Traffic Police (n=55)
|
P value
|
|
Median
|
IQR
|
Median
|
IQR
|
|
TP (ms2)
|
1742.00
|
1216.00
|
1108.40
|
862.80
|
0.001
|
|
LF(nu)
|
52.80
|
19.90
|
56.14
|
22.11
|
0.177
|
|
HF(nu)
|
47.00
|
19.40
|
43.65
|
21.85
|
0.187
|
|
LF:HF
|
1.12
|
1.02
|
1.29
|
1.43
|
0.214
|
Analysis done by Mann Whitney – U test, Data
expressed as Median with IQR. SDNN, standard deviation of NN
intervals;. RMSSD, square root of the mean squared differences of
successive NN intervals; NN50, number of pairs of adjacent NN intervals
differing by more than 50 msec; pNN50, percentage of NN50; TP: total
power; HF: high frequency; LF: low frequency; nu, normalized units.
Reaction time assessment:
Simple Reaction time: The SART was increased in traffic
police, though not significant (P=0.059). The SVRT is significantly
increased in traffic police (P=0.014). Choice Reaction time: The CART
and CVRT were increased in traffic police, though not significant
(P=0.222, P=0.057) (Table 3).
Table-3: Comparison of
Reaction time between Controls and Traffic Police
|
Parameters
|
Controls
(n=55)
|
Traffic Police (n=55)
|
P value
|
|
SART (ms)
|
163.8 ±
23.1
|
173.1 ±
27.6
|
0.059
|
|
SVRT (ms)
|
215.9 ±
31.3
|
229.2 ±
24.0
|
0.014
|
|
CART (ms)
|
235.7 ±
43.7
|
245.3 ±
37.8
|
0.222
|
|
CVRT (ms)
|
325.8 ±
43.0
|
340.6 ±
37.3
|
0.057
|
Analysis done by Unpaired Student’s t Test, Data
expressed as Mean with SD. SART: Simple auditory reaction time; SVRT:
Simple visual reaction time; CART: Choice auditory reaction time; CVRT:
Choice visual reaction time.
Discussion
In our study TP, the index of overall heart rate variability was
significantly reduced in traffic police, indicating a decreased HRV.
Decreased HRV depicts decreased cardiovagal modulation and is a potent
risk for cardiovascular health [8].
Also the increased LFnu (P=0.0001) and lowered HFnu (P=0.0001) seen
among the traffic policemen reflected the increased adrenergic drive
and attenuated vagal activity. Subsequently, the LF-HF ratio, which is
the marker of sympathovagal balance was elevated among them, though not
significant (P=0.0016). This depicts the deviation of sympathovagal
balance more towards the adrenergic system [8].
The time domain indices depict the high-frequency variations in
short-term recording of HRV, which are due to vagal activity [8]. The
time domain indices also revealed a significant reduction in traffic
police. The reduction in these parameters reveals a decreased vagal
modulation of cardiac functions consistent with the findings in
frequency domain analysis.
Also, we found that the baseline cardiovascular parameters (BHR and
DBP) were significantly higher in traffic policemen when compared to
the controls (P<0.0001). The SBP was also higher in traffic
police though not significant. Since HR is mainly under vagal
modulation, an increased BHR in these patients could be attributed to
the decrease in vagal activity [14]. The raised DBP observed in traffic
police could be considered due to exaggerated adrenergic drive as
maintenance of BP is mainly under sympathetic modulation [14].
Our findings corroborate with the findings of a previous study
conducted in Brazil, depicting decreased HRV in traffic police,
attributed to air pollution [15].
There are many theories postulated to explain the effects of air
pollution on cardiovascular diseases. Among them are the increased
levels of inflammatory markers, the ischemic response of myocardium to
pollutants and endothelial injury. All of these can have a cause and
effect relationship with autonomic dysfunction [16].
The cardiovascular system and HR are under the influence of the
sympathetic and parasympathetic nervous systems. HRV reflects the
autonomic modulation of the heart rate and has been used as a risk
marker for arrhythmia and sudden death. Decrease in HRV reflects the
decreased capacity of the autonomic nervous system to adapt to a myriad
of stimuli that we encounter in our daily life [8].
Hence, we hypothesize that cardiac autonomic dysfunction with decreased
HRV could be the plausible mechanistic pathway in the causal of
cardiovascular disease in traffic police.
The RT assessment revealed increased simple and choice reaction time in
traffic police, indicating a delayed response. RT is the duration
between application of a stimulus to the onset of response. It is the
process by which human use their cognition to respond towards the
sensory input; visual or auditory. RT acts as a reliable indicator of
attention, rate of processing of sensory stimuli and its motor response
by the nervous system [17].
RT is categorized according to the number of diverse stimuli in a task
that need to be responded with a specific motor reaction viz; simple
and choice reaction time. When the number of stimuli is equal to one,
this kind of reaction time task is called simple RT task; if higher
than one, it is defined as choice reaction time task. In simple
reaction time task, there is only one particular stimulus and the same
response is always required. In choice RT task, there are several
different stimuli and response for a particular stimulus amidst
different stimuli is required [18].
RT can get affected by many physiological and pathological parameters.
Air pollution is a potential pathological factor that can have long
term and considerable effects on cognition. Brains of individuals
living in a highly polluted environment have higher inflammatory
mediators, β-amyloid deposition, oxidative damage to DNA, as
well as blood–brain barrier disruption, than those from a
city with low levels. Further, it has been evidenced from
animal studies that long-term exposure to PM at levels typical of
cities in parts of the developing country such as India, would induce
neuroinflammation and adjustments in neuronal morphology and behaviour
and decreased cognitive abilities [9,10]. It is evident that chronic
exposure to air pollution accelerates cognitive decline. In our study,
though insignificant, we observed that the traffic police had delayed
response time reaction time in comparison to controls. This suggests
that the traffic police, due to constant exposure to PM, are at risk
for cognitive derangement in the long term.
Conclusion
The traffic police have decreased HRV, with increased sympathetic and
decreased vagal tone. Also, they are at risk of cognitive derangement.
Based on the proposition that air pollution exposure may induce
cardiovascular changes mediated by the autonomic nervous system and
cognitive decline, the present study reinforces the effects of air
pollution on heart rate variability, blood pressure and cognition in
healthy traffic police in the city of Puducherry. Also, it stresses
upon the need for appropriate precautionary measures at an early stage,
to prevent cardiovascular and cognitive morbidity.
Limitations &
future perspectives: The limitation of our study is that
we did not control for occupational stress. Psychological stress can
affect autonomic function. So the effects of both pollution
and stress on autonomic function could not be delineated. But, since we
took traffic police officers with a work experience of more than five
years, we expect adaptation to work environment, which could have
mitigated the work stress.
In future, we recommend a complete battery of autonomic function tests
to be performed, which would enable to arrive at a more certain
proposition regarding the autonomic status. Also, the association with
the inflammatory markers can be established.
Funding:
Nil, Conflict of
interest: None initiated.
Permission from IRB:
Yes
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How to cite this article?
Kuppusamy S, Niraimathi D, John N.A. Assessment of heart rate
variability and reaction time in traffic policemen. Int J Med Res Rev
2016;4(11):1958-1964.doi:10.17511/ijmrr. 2016.i11.09.