Study Design and Setting:
This prospective cohort study was conducted among long-distance truck drivers traveling on BR 277, one of the main federal highways in the country known for heavy truck traffic transporting agricultural inputs, grain harvests, and fuels. As in a previous study [5], participant sampling and evaluation were carried out at four locations along the BR 277 route, including two-grain processing, storage, and distribution facilities, a fuel storage and distribution company and an agricultural input distributor. Authorization was obtained to conduct the study at these locations, with a specific request for appropriate physical space to ensure participant confidentiality and comfort. The study was approved by the Research Ethics Committee of the Universidade Estadual do Centro-Oeste (approval number 1.593.832/2016) and was conducted from June 2016 to September 2021.
Study Population and Inclusion Criteria:
Truck drivers over the age of 18 were included in the study. Sequential invitations to participate in the research were extended to subjects as they arrived and awaited cargo loading and unloading, from 8 a.m. to 5 p.m., on all days of the week. Inclusion criteria required participants to be able to: 1) provide informed consent by signing a consent form; 2) transport cargo over long distances, exceeding a 160 km radius from their home terminal; 3) be able to return to the exact location for follow-up visits on two future dates and 4) not use non-steroidal anti-inflammatory drugs.
Protocol Sequence
All participants underwent clinical assessments at three distinct timepoints. Subsequently, the truck drivers were monitored via telephone for three consecutive years regarding any health-related incidents to identify cardiovascular outcomes. Furthermore, at the end of the three-year monitoring period, a search was conducted in the national mortality (DATASUS- SIM: Mortality Information System) and hospitalization (SIH-SUS: Hospital Information System) database (Figure 1).
Clinical evaluation
This study conducted a thorough clinical evaluation to assess the cardiovascular risk factors among truck drivers. The assessment involved interviews to gather information on socio-demographic characteristics, occupational factors, chronic disease history, medication use, lifestyle habits, and family history of cardiovascular disease. Additionally, routine and specific exams to detect cardiovascular structure and function (target organ damage) were performed to provide objective data related to cardiovascular health. These variables collectively provide comprehensive information on the demographic, occupational, medical, and physiological aspects of cardiovascular health among truck drivers.
Interview-based variables:
- Socio-demographic characteristics: Age, Education level, Race/color and
Home state
- Truck Driver Profession-related Factors years in the job (years of professional experience as a truck driver); Hours driven per day; Kilometers driven per day
- Medical History and Lifestyle Habits: Prior diagnosis of chronic diseases: Use of medications (including details of drug class and dose); Physically active or sedentary lifestyle; Consumption of alcohol or other stimulants; Smoking habits; Family history of cardiovascular disease (specifically, heart disease, myocardial infarction, bypass surgery, or cardiac catheterization in first-degree relatives under the age of 55 for males and 65 for females)
The definitions and criteria used to ensure precise characterization of crucial factors during cardiovascular risk assessment among truck drivers are presented as supplement 1.
Electrocardiogram (ECG) recordings: The resting 12-lead ECG was obtained using a standardized approach with the Micromed device (Wincardio USB - Version 4.4.a. MICROMED Biotecnology Ltda, Brasília - DF) for all study participants. The acquired ECGs were carefully analyzed to assess the cardiac rhythm and determine the presence of left ventricular hypertrophy (LVH). To evaluate LVH, we employed both the Sokolow-Lyon criteria and the Cornell voltage-duration product criteria.
Heart rate variability – signal acquisition and analyses: Electrocardiogram (ECG) recordings were obtained using a digital electrocardiograph (Micromed, Brazil) at a sampling ratio of 250 Hz. Wincardio (4.4a) software was utilized to automatically generate the R-R interval series from the 12-lead derivations, employing traditional adhesive disposable electrodes. Manual removal of incorrect detections or ectopic beats was performed as necessary. The ECG recordings were obtained to ensure optimal data acquisition while the trucker rested in a supine position in a quiet room, breathing spontaneously. The 15-minute recording was obtained following a 15-minute adaptation period. Before the recording, participants were instructed to refrain from consuming food, caffeine or cigarettes for at least 30 minutes. The stored ECG data were subsequently analyzed to calculate heart rate variability (HRV) values, using CardioSeries software (version 2.4, CardioSeries Software, Universidade de São Paulo, Brazil). All recorded segments were visually inspected, and nonstationary data segments were discarded. A Hanning window was used to minimize artifacts, and the spectrum of each segment was computed using a direct Fast Fourier Transform (FFT). Spectral bands were defined according to established literature references for human HRV evaluation, including low frequency (LF) in the range of 0.04-0.15 Hz, high frequency (HF) in the 0.15-0.4 Hz range, and total power. Spectral components were expressed in absolute values (ms2) and normalized units (nu). Normalized units were calculated by determining the percentage of LF and HF components concerning the total power after subtracting the power of the very-low-frequency component (frequencies <0.04 Hz). Following established methods, the LF/HF ratio of HRV was calculated to assess sympatho-vagal balance. Analysis of the computation of HRV parameters using this well-established technique ensured an accurate assessment of the heart rate variability and sympathetic-vagal balance among the study participants.
The ankle-brachial index (ABI): The ankle-brachial index (ABI) is the systolic blood pressure (SBP) ratio measured at the ankle to that measured at the brachial artery. We used the method indicated by the American Heart Association Statement [22]. Briefly, with the patient resting supine, blood pressure cuffs were placed around the upper arms and ankles to perform the ABI measurement. A Doppler ultrasound device (Medpej - DF-7000-VB, Alphaville, São Paulo, Brazil) was used to detect flow arterial signals of both brachial arteries and of the posterior tibial and dorsalis pedis arteries of both ankles. To calculate the ankle-brachial index, we used the higher ankle systolic blood pressure divided by the higher brachial systolic pressure. An ABI value around 1.0-1.4 indicates normal blood flow, while values below 0.9 suggest the presence of peripheral artery disease.
Follow-up of cardiovascular outcomes monitoring:
After completing the inclusion protocol to monitor cardiovascular outcomes, we conducted telephone interviews with the truck drivers or their family members for three years. These interviews aimed to collect information about their health status, occurrences of health problems and traffic accidents. Additionally, we conducted consultations in the National Mortality System (SIM-SUS) and Hospitalizations (SIH-SUS), which are national databases managed by the Department of Informatics of the Unified Health System (DATASUS).
Statistical analyses
We analyzed the data descriptively and presented absolute and relative frequencies for categorical variables and summary measures (mean, quartiles, minimum, maximum, and standard deviation) for numerical variables. We used the Chi-Square test to verify the existence of associations between two categorical variables. We used Fisher's exact test as an alternative for small samples. We used the standardized adjusted residual to identify local differences for differences in distributions. Cells with absolute values above 1.96 indicate evidence of associations (local) between the categories relative to those cells. We compared two and more than two means using the Student's t-test and Analysis of Variance (ANOVA), respectively. Both tests assume normality in the distribution of data and homoscedasticity, which we verified using the Kolmogorov-Smirnov and Levene's tests, respectively. If data normality was violated, we compared means using the non-parametric Mann-Whitney test (comparison of two means) and the Kruskal-Wallis test. If we detected differences in means in ANOVA and the Kruskal-Wallis test, we would identify groups of distinct means using Duncan's multiple comparisons and Dunn-Bonferroni, respectively, maintaining a global significance level of 5%. We assessed linear associations between numerical variables via Spearman correlation due to the absence of normality in the data distribution. We used univariate and multivariate Poisson regressions to evaluate the effects of general, clinical, and heart rate variability characteristics on CVD incidence rate. This model is used to count data observed over some time. We performed tests of fit adequacy of multivariate models to verify the existence of overdispersion (dispersion of observations higher than expected). In the initial multivariate model, we considered significant variables at 10% in the univariate analysis as predictors due to the number of predictor variables versus the sample size. Then, we excluded non-significant variables at 5%, one by one in order of significance (backward method). For all statistical tests, we used a significance level of 5%. We performed the analyses using SPSS 20.0 and STATA 17 software packages.