The study was approved by the Interuniversity Ethics Committee, Protocol No. 05–18, dated May 24, 2018. All methods were performed in accordance with the relevant guidelines and regulations. 183 male train crew members (106 train drivers, 77 train driver assistants) of an average age 37.7 ± 9.4 years were examined. The results of the last medical examination were written out from the medical records and analyzed. The selection of members of train crews was carried out in a randomized manner so that the number of those who underwent and did not undergo the medical exam was in a ratio of 6 : 4 (usually the number of those who did not have health examination does not exceed 10%) (The reasons for the suspension were: pulse more than 90 beats / min or less than 60 beats per minute − 60%, arterial blood pressure more than 140 mmHg. − 53%, blood pressure more than 90 mmHg.- 20% (the total amount is not equal to 100%, since one employee could have several reasons for suspension from work).
The study did not include individuals suspended from duties due to fever and / or alcohol consumption. All included in the study gave their voluntary informed consent. The study was carried out at the pre-trip examination center at the Rostov-Main Station of the North-Caucasian Railway and included only those members of train crews who were permanently assigned to the depot. This made it possible to gain access to the employee's medical records, where the earlier diagnoses were copied from.
A complex of hardware-software measurements as well as analysis of pulse parameters, blood pressure and bioelectric potentials of the heart, pre-working examination of operators of complex technical devices and systems KAPD-02-ST according to Technical Specifications (TS) U 9441-002-45520949-2005, manufacturer: JSC "Scientific and Production Enterprise "System Technologies.” were used. Also, the ECG apparatus - electrocardiograph EK 12T-01- "R-D" in accordance with TS 9441-005-24149103-2003, manufactured by Scientific and Production Enterprise "Monitor", pulse oximeter - optoelectric sensor DASM.012.554.1 in accordance with TS 9441 -001-30857241-12, manufactured by OJSC "Axioma", blood pressure measuring device for measuring blood pressure LD-60 in accordance with GOST standard R519.1-2002, manufactured by Little Doctor Electronics (Nantong). All devices produced the measurement results in digital form with an interval of 1 ms. The results were recorded on a computer for the further analysis.
The pre - trip medical examination was carried out by a medical assistant who had underwent additional special training in electrocardiography. Blood pressure measurements were taken according to Korotkoff in a seated position. The frequency of heart contractions, systolic and diastolic blood pressure (BPs, BPd), as well as pulse pressure were measured.
The body temperature was taken with a digital thermometer OMRON, manufactured by OMRON HELSKEA Co., Ltd., Japan, while alcometry was carried out with an analyzer of ethanol vapors in exhaled air, Alkotektor Jupiter in accordance with TS 26.60.12-001-82139963-2011, manufactured by Alkotektor LLC. The increase in body temperature up to 37 ° C and above, as well as the presence of alcohol vapors in the exhaled air, served as a contraindication for the inclusion of a train crew member in the study.
The pulsogram and electrocardiogram (second standard lead) were recorded simultaneously in the supine position. 100 RR intervals (approximately 3 minutes of recording) were analyzed. The R 'points were determined as the maximum points for the pulsogram. Based on the measurement of RR intervals for ECG and R'R 'intervals for pulse, the following parameters were calculated:
1. SDNN - standard deviation of NN intervals
where NNi is the value of the i- interval, NNavg is the average over NNi of the entire record, N is the number of intervals.
2. pNN50 (%) is the percentage of NN50 of the total number of consecutive pairs of intervals
where N is the number of intervals.
where NNi is the value of the i- interval, N is the number of intervals. NN50, the number of pairs of consecutive NN intervals, which differed by more than 50 milliseconds, was obtained over the entire recording period
3. TI - Tension Index
where Mo is the mode of RR intervals, AMo is the amplitude of the mode, the number of cardiointervals corresponding to the value of the mode in% to the sample volume, X is the variation range of the RR or R'R 'interval
4. RMSSD - root-mean-square difference between the duration of adjacent RR intervals, expressed in ms. It is calculated as the square root of the sum of the squares of the difference between the values of consecutive pairs of NN intervals (normal RR intervals); an indicator of the activity of the parasympathetic link of autonomic regulation.
For every member of the train crew, a one-time comparison of the variability parameters calculated on the basis of ECG and pulsogram was carried out, regardless of the results of the pre-trip health examination.
Statistics
The results were calculated using Excel. Statistical processing was performed using the Statistica software package. The mean and its standard deviation were calculated. The correspondence of the studied parameters to the normal distribution law was checked on the basis of the Kolmogorov criterion. The correspondence of studied parameters with a normal distribution law was not found. Therefore, the comparison of the mean values was carried out by the U-test. Kendall rank correlation coefficients were calculated. Factorial and discriminant analyzes were also used. In the tables, data are presented as mean ± standard deviation and median [interquartile range].
Research results
According to the conclusions of the medical commission, 54% of the individuals included in the study were healthy (Fig. 1). 14% had hypertension, 10% had atherosclerosis, 8% had cardiac arrhythmias and gastrointestinal diseases. According to the medical documentation, 40% of those surveyed were recommended to take medications on a regular basis, but only 33% of the train crew members indicated that they used self-administered therapy (Fig. 2)
All 100% of those who did not pass the pre-trip medical examination had previously been diagnosed with chronic non-infectious diseases. The average readings of BPd, BP and pulse pressure were significantly lower in the group of individuals allowed to work (Table 1).
Table 1
Heart rate frequency and blood pressure readings among members of train crews
parameter
|
those allowed to work
|
those who didn’t pass pre-trip medical health examination
|
р
|
heart rate
|
77.1 ± 7.6
80[72;83]
|
with bradycardia:
62.1 ± 5.5
64 [57;68]
|
< 0.01
|
with tachycardia:
101 ± 10.2
98[92;106]
|
< 0.01
|
Arterial blood pressure
mm HG
|
117.2 ± 7.7
116[112;122]
|
135.2 ± 9.3
125[120;155]
|
< 0.01
|
arterial blood pressure
mm hg
|
75.9 ± 5.0
75[73;80]
|
81.9 ± 5.9
80[75;86]
|
< 0.05
|
pulse pressure
mm hg
|
41.4 ± 5.7
38[36;44]
|
53.3 ± 5.5
39[40;66]
|
< 0.05
|
Here and further in Table 1: top line - mean and its standard deviation, bottom line - median and interquartile range |
A high degree of correlation between the parameters of heart rate variability calculated on the basis of ECG and pulsogram was found (Table 2). It should be noted that the greatest deviations from the apromaximum line are observed for large SDNN values (Fig. 3). Thus, if we consider SDNN values which don’t exceed 50, then the correlation coefficient of the parameter calculated from ECG and pulse wave becomes 0.98.
Table 2
Comparison of heart rate variability parameters calculated on the basis of ECG and pulsogram
|
Correlation coefficient
|
Tension Index
|
0.89
|
PNN50
|
0.86
|
SDNN
|
0.95
|
RMSDD
|
0.91
|
It should be noted that the revealed significant differences in the parameters of heart rate variability both recorded by ECG and by pulsogram (Table 3) between the members of train crews who underwent and did not undergo the pre-trip examination,. The indices of those who did not undergo the PTME are characterized by lower values of the studied parameters, in particular, SDNN ', which corresponds to more stringent characteristics of heart rate variability. The number of individuals with severe heart rate variability parameters was: SDNN ’<40 ms - n = 71 (39%), PN50’ <10 - n = 83 (45%), RMSSD ’<25 - n = 46 (25%)
Table 3
Values of variability calculated on the basis of ECG and pulsogram among members of train crews
Parameter
|
those allowed to work
|
those who didn’t pass medical examination
|
Р (between who passed/didnot pass medical exam)
|
Pulsogram
|
ECG
|
Pulsogram
|
ECG
|
Tension Index
|
61.7 ± 24.5
44[42;75]
|
60.2 ± 23.4
43[41;72]
|
67.0 ± 33.2
61[43;80]
|
68.1 ± 23.1
62[44;76]
|
< 0.1
|
PN50
|
24.9 ± 12.5
11.1[7.1;34.2]
|
24.3 ± 10,1
10.9[6.9;32.4]
|
14.1 ± 12.3
4.0[1.0;34.4]
|
13.5 ± 9.8
3.9[0.9;26.9]
|
< 0.01
|
SDNN
|
98.5 ± 10.1
85.3[57.7;139.3]
|
102.3 ± 9.8
89.4[61.1;135.1]
|
47,7 ± 19,9
37.6[28.1;57.5]
|
49.1 ± 10.9
36.1[25.2;52.7]
|
< 0.01
|
RMSSD
|
39.5 ± 10.7
35.7[21.5;53.1]
|
40.7 ± 10.2
36.6[22.4;52.9]
|
31.2 ± 12.2
29.3[15.5;40.5]
|
29.3 ± 8,8
27[12;39.3]
|
< 0.05
|
Factorial and discriminant analysis (Table 4) shows that the differences between the groups allowed and suspended from work are significant (F (9.174) = 11.471, p < 0,000). Significant variables for classification are: heart rate, tension index ', SDNN'.
Table 4
Results of discriminant analysis (significant ones with p < 0.05 are highlighted in color)
Parameter
|
Wilks lambda
|
Private lambda
|
F
|
p
|
Tolerance
|
R2
|
Age
|
0.628843
|
0.998051
|
0.33978
|
0.560710
|
0.843181
|
0.156819
|
Heart rate
|
0.668361
|
0.939039
|
11.29582
|
0.000955
|
0.742587
|
0.257413
|
САД Systolic BP
|
0.627651
|
0.999947
|
0.00931
|
0.923230
|
0.014225
|
0.985775
|
ДАД Diastolic BP
|
0.628747
|
0.998204
|
0.31309
|
0.576512
|
0.052878
|
0.947122
|
Pulse pressure
|
0.629057
|
0.997711
|
0.39925
|
0.528306
|
0.026339
|
0.973661
|
Tension Index
|
0.646145
|
0.971326
|
5.13665
|
0.024657
|
0.574703
|
0.425297
|
PNN50
|
0.633537
|
0.990656
|
1.64126
|
0.201857
|
0.355515
|
0.644485
|
SDNN’
|
0.658740
|
0.952754
|
8.62853
|
0.003758
|
0.435531
|
0.564470
|
RMSSD
|
0.627871
|
0.999597
|
0.07023
|
0.791310
|
0.574949
|
0.425052
|