|Year : 2021 | Volume
| Issue : 2 | Page : 183-190
Changes in the psychophysiological and cognitive parameters of the sailors wearing cooling vest while working in high ambient temperature condition of the engine room onboard a naval ship: An experimental study
Raksha Jaipurkar1, SS Mohapatra2, Chitra Banerjee3, Saurabh Bobde4, Santosh Karade5
1 Department of Physiology, AFMC, Pune, Maharashtra, India
2 MI Room, INS Shikra, Mumbai, Maharashtra, India
3 Administrative Wing, Command Hospital Central Command, Lucknow, Uttar Pradesh, India
4 Department of Preventive and Social Medicine, AFMC, Pune, Maharashtra; Administrative Wing, Command Hospital Central Command, Lucknow, Uttar Pradesh, India
5 Department of Microbiology, Command Hospital (Southern Command), Pune, Maharashtra, India
|Date of Submission||13-Nov-2020|
|Date of Decision||10-Apr-2021|
|Date of Acceptance||13-Apr-2021|
|Date of Web Publication||21-Sep-2021|
Surg Capt (Prof) S S Mohapatra
INS Shikra, Colaba (Near) Fire Station, Mumbai - 400 005, Maharashtra
Source of Support: None, Conflict of Interest: None
Background: Cooling vests are supportive garments used to overcome heat stress among individuals working in hot and humid environment. These vests were used extensively by fire-fighters and coal mine workers in past. In this study we have evaluated the effectiveness of cooling vest on psychophysiological and cognitive parameters of the sailors working in the engine room of a Naval ship. Aims and Objectives: Aim of out is to evaluate effectiveness of cooling vests in alleviating heat strain and maintain physiological parameters and behavioural alertness of sailors working in the hot and humid climate of engine room. Materials and Methods: The Physiological Strain Index (PSI), the level of Anxiety and the Psychomotor Vigilance testing was determined from 50 healthy male sailors while on 4 hrs of watch in the engine room in two different occasions i.e. once wearing the cooling vest and once more without wearing it. Subjective perception of acceptability of cooling vest was assessed by a self-made questionnaire. Results: The mean body temperature (Aural), pulse rate, respiration rate along with the Physiological Strain Index (PSI) was significantly lower both during mid watch as well as at the end watch among the engine room sailors while performing the watch wearing the cooling vest (Watch-2) in comparison to the watch without wearing it (Watch-1). The mean change in reaction time in the Psychomotor Vigilance Testing (PVT) was lesser while performing the watch with cooling vest (Watch-2) than the watch without it (Watch-1). Similarly, a higher proportion of participants had shown to have no increase in their anxiety level (Hamilton Anxiety Score) at the end of the watch when performing it with cooling vest. Also, the positive acceptance for the cooling vest was also observed among larger portion of participants. Conclusion: The study indicated lesser heat strain, lesser deterioration of Psychomotor vigilance function, lesser proportion of participants showing anxiety among the sailors wearing cooling vest while working in the hot and humid condition of engine room of a naval ship. A positive acceptance for cooling vest was also observed among higher number of these participants.
Keywords: Cooling vest, engine room, heat stress
|How to cite this article:|
Jaipurkar R, Mohapatra S S, Banerjee C, Bobde S, Karade S. Changes in the psychophysiological and cognitive parameters of the sailors wearing cooling vest while working in high ambient temperature condition of the engine room onboard a naval ship: An experimental study. J Mar Med Soc 2021;23:183-90
|How to cite this URL:|
Jaipurkar R, Mohapatra S S, Banerjee C, Bobde S, Karade S. Changes in the psychophysiological and cognitive parameters of the sailors wearing cooling vest while working in high ambient temperature condition of the engine room onboard a naval ship: An experimental study. J Mar Med Soc [serial online] 2021 [cited 2021 Dec 3];23:183-90. Available from: https://www.marinemedicalsociety.in/text.asp?2021/23/2/183/326273
| Introduction|| |
The engine rooms (ERs) of the Naval ships are considered the hottest working environments. The ambient temperature in these areas especially in the ships driven by steam engines touches 50° C. There is an inherent risk of exertional heat illnesses when a healthy individual is physically active in hot and humid environments., Heat-stress is an occupational hazard commonly faced by miners, firefighters, bakery workers, people working in factories with furnaces, sportsmen, and Armed Forces personnel. The military personnel at risk includes infantry soldiers deployed in deserts, armored vehicle crew, fighter pilots, and personnel working in the ER of a ship. Engine crew on board naval ships are subjected to continuous heat strain due to hot and humid conditions during long-distance sailing.
Physical and psychological fatigue and anxiety have been reported in individuals performing ER duties. Fatigued individuals play a direct or indirect role in safety mishaps, collisions, and near misses afloat.,, Prolonged thermal stress faced by ER workers may impair cognitive function thereby affecting vigilance, crucial decision-making tasks such as time or distance estimation, tracking and monitoring of gadgets contributing to accidents and injuries.
Psychomotor vigilance is a form of alertness performance that can be conveniently measured using the reaction time (RT) to a visual task on a programmed digital assistance (PDA)-based psychomotor vigilance test (PVT) device.,,, Thermal stress and mental fatigue may further increase the anxiety levels in workers. Hamilton anxiety score (HAM-A) is commonly used as a sensitive measure to document anxiety levels in subjects.,,
Over the past decade, novel methods have been developed to keep core body temperature within normal range while working in hot and humid environment. Some of these cooling methods include water spray, cool-air spray, face fanning, whole-body liquid cooling garments, ice towels, head-cooling units, and cooling vests (CVs).,, Phase change material (PCM)-based CV is one such economical solution that can provide controlled microclimate cooling. The PCM in this vest melts at warmer temperatures and has been used in an attempt to enhance cooling by avoiding vasoconstriction, which supposedly occurs with ice CVs. Previous studies have shown that such controlled microclimate cooling devices markedly reduced heat strain.,,, So far, no study has been conducted on the role of these CVs in alleviating the effects of heat stress among ER workers of a battleship in tropical condition. Therefore, the research question addressed was, “Do CVs alleviate heat strain and maintain physiological parameters and behavioural alertness of sailors working in the hot and humid climate of ER?”
In this study, the ER sailors were assessed for their physiological, psychological, and cognitive parameters during their “ER watch duties.” The changes in these parameters during the watch wearing the CV were determined and analyzed to assess the effectiveness of CV objectively. The subjective assessment on the suitability of the CV by participants was also obtained by conducting a questionnaire survey.
| Materials and Methods|| |
The study was conducted in the ER of an Indian Naval ship. A total of 50 ER sailors were randomly selected for the study. After explaining to them the study protocol, written “Informed Consent” was obtained. The study was approved by the ethics committee of the Institute of Naval Medicine, Mumbai.
The study was conducted under “Pre-Experimental Research Design (One-Group Pretest-Posttest type),” where repeated measures method with each “case” serving as his/her own “control” was used. The CV was used as an interventional measure for the randomly selected ER sailors.
Demographic and lifestyle information from the participants was collected before the sailing. The ambient temperature and the relative humidity of the ER were recorded before each watch. The participants were involved in the ER watch duties (4 h) as per the duty roster promulgated by the ship administrative authority. After a week of sailing when all participants have got a sufficient number of exposures toward the heat acclimatization, two watches per participant were logged for the study. In one of these two watches, the participants wore the CV entire 4 h of watch period.
The physiological parameters in the form of aural body temperature, blood pressure (BP), pulse rate, respiratory rate (RR), were recorded at the beginning of the watch as baseline parameters. Subsequently, all these parameters were repeated in the middle of watch (end of 2 h) and at the end of watch (end of 4 h).
Ambient temperature was measured with dry bulb thermometer and aural body temperature was recorded by infrared digital thermometer. The aural body temperature of the participants was measured instead of rectal temperature to compute Physiological Strain Index (PSI) as indicator of heat strain taking into consideration the operational and logistic constrains of the onboard conditions. A PSI based on rectal temperature (Tre) and heart rate (HR), capable of indicating heat strain. The index rates the physiological strain on a universal scale of 0–10. PSI can be computed by using the formula 5(Tret − Tre0) ⋅ (39.5 − Tre0) −1 + 5 (HRt − HR0) ⋅ (180 − HR0) −1, where Tret and HRt are simultaneous measurements taken at any time during the exposure and Tre0 and HR0 are the initial measurements. The BP and pulse were measured in the right arm of the subject at sitting position by digital BP apparatus (OMRON HEM-7112, Accuracy + 3 mm of Hg).
The other outcome measures recorded were as RT and the anxiety level. Cognitive performance was assessed by measuring RT using a PDA-based PVT device (PVT-192, Ambulatory Monitoring Inc., Ardsley, NY, USA). The anxiety level of the participants was measured using a paper-pencil test called “HAM-A.”
Participants used CV having PCM (Techkewl™, TECHNICH International) while working in the ship's ER. The microclimate cooling garment weighed 0.45 kg. Following the manufacturer's instructions, the CV was charged by placing it in a standard household freezer at its lowest setting for 5–6 h. After it was charged, the CV was snugly fitted over sailor's uniform with self-adhesive straps.
To start with, each participant recruited for the study was administered with 3–5 practice sessions on Psychomotor Vigilance Test (PVT) before the commencement of the study. Thereafter, each of them was evaluated twice during his watch duties in the ER, once without wearing the CV (named as Watch-1) and once wearing it (named as Watch-2). HAM-A rating scale was administered 15 min before commencing their watch. The baseline pre-exposure physiological parameters in form of aural body temperature, BP, pulse rate, and RR were recorded. After this recording, each participant was tested for the RT in PVT and underwent a paper-pencil test for HAM-A for recording the level of anxiety. Then the participant could work in the ER (as in routine watch) without a CV for a period of 4 h. The same physiological parameters along with RT were measured twice during this period firstly, at the middle of the watch (after 2 h) and secondly, at the end of watch (after 4 h). A post exposure questionnaire and HAM-A rating scale were repeated at the end of watch. The entire procedure was repeated later with the same participants doing duties wearing CV (Watch-2).
The PSI was computed using the HR and core body temperature (aural body temperature). The PSI at 2 h and 4 h in each watch were tabulated for analysis. Similarly, the change in RT (from PVT) at 2 h and 4 h from its baseline values in each watch were calculated and tabulated for statistical analysis.
The baseline parameters of Watch-1 and Watch-2 were compared for any statistical difference using Student's t-test after confirming the normality of the data. The mean PSI and the mean RT changes at the end of 2 h and 4 h of Watch-2 were compared with those of Watch-1 by employing One-Way ANOVA after checking for normality with Shapiro-Wilk and Homogeneity using Levene's test. Further, a post hoc analysis for pair-wise comparison was carried out using Tukey Honestly significant difference. Similarly, HAM-A (anxiety) score at the end of each watch was compared with its baseline level to compute the number of participants showing increase against the numbers showing decrease or no change. This proportion for each watch was compared to determine the percentage of participants showing no increase in their anxiety level when using CV. The results of self-made questionnaire were also analyzed to find out the number of participants responding positively toward acceptance of the CV. All analyses were carried out using Statistical Package for Social Sciences (SPSS: Version 13.0) (SPSS Inc, Chicago, IL, USA).
| Results|| |
A total of 50 ER sailors had completed the study. The demographic details of these participants are shown in [Table 1]. The mean and Standard deviation (SD) for age, weight, and height of the participants were 28 ± 4.4 years, 69 ± 6.05 kg, and 172 ± 4.7 cm respectively. The average ER temperature was 109°F ± 5°F dry bulb temperature with 70% relative humidity for Watch-1 and 108°F ± 4.5°F dry bulb temperature with 73% relative humidity for Watch-2 and are not statistically different (P = 0.98). The means and SDs of various physiological parameters recorded as baseline, at the end of 2 h (mid watch) and 4 h of watch (end watch) along with the means (SD) of the respective differences from the baseline values are displayed in [Table 2]. the mean baseline parameters for aural body temperature, systolic BP (SBP), diastolic BP (DBP), pulse rate, RR recorded at the beginning of watch-1 and Watch-2 were not significantly different [Table 3]. The results of One-Way ANOVA carried out to ascertain any significant changes for these parameters at the end of 2 and 4 h is indicative of significant changes in all parameters except SBP AND DBP [Table 3]. The changes in the aural temperature at mid-watch and end watch are 2°F and 1.5°F respectively for Watch-1 and 1.2°F and 1.3°F respectively for Watch-2. The changes in the pulse rate at mid-watch and end watch are 16/min and 17/min respectively for Watch-1 and 8/min and 13/min for Watch-2. Similarly, the changes in the RR at mid watch and end watch are 2/min and 2/min respectively for Watch-1 and 2/min and 1/min for Watch-2. These differences were also compared employing One-Way ANOVA. The results of One-Way ANOVA and the post hoc analysis for pair-wise comparison for the pairs showing significant differences are displayed in [Table 4]. It is evident that there is a mid-watch increase of body temperature in the Watch-1, which is significantly more than the mid watch increase of body temperature of the Watch-2 (2°F vs. 1.2 °F, P = 0.00001 with large effect size = 0.74). Similarly, the end watch increase of body temperature in the Watch-1 is significantly more than the end watch increase of body temperature of Watch-2 (1.5°F vs. 1.3 °F, P = 0.00001). The effect size for these changes is also large (0.74). The mid watch increase of pulse rate in the Watch-1 is significantly more than the mid watch increase of pulse rate of Watch-2 (16/min vs. 8/min, P = 0.00001). Similarly, the end watch increase of pulse rate in the Watch-1 is significantly more than the end watch increase of pulse rate of Watch-2 (17/min vs. 13/min, P = 0.00001). The effect size for these changes are also large (0.79). It is also evident that the mid watch increase of RR in the Watch-1 is not significantly different than the mid watch increase of RR of Watch-2 (2/min vs. 2/min, P = 0.97). However, the end watch increase of RR in the Watch-1 is significantly more than the end watch increase of RR of Watch-2 (2/min vs. 1/min, P = 0.002). The effect size for these changes is also large (0.56).
|Table 1: Demographic details of participants showing age, weight and height (n=50)|
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|Table 2: Baseline, “mid watch” and “end watch” data (means and standard deviations) for physiological, psychological and cognitive parameters during Watch-1 and Watch-2|
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|Table 3: Comparisons of baseline differences for physiological, psychological and cognitive parameters during Watch-1 and Watch-2 using student’s t-test|
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|Table 4: Comparisons of baseline, mid watch and end watch means for physiological parameters during Watch-1 and Watch-2 using one-way ANOVA|
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Physiological strain index
In both the watches, mid watch and end watch PSI were computed by considering the respective values for aural body temperature and pulse rate. The mid watch PSI in the Watch-1 is significantly more than the mid watch PSI of Watch-2 (3.20 vs. 2.03, P = 0.00001). Similarly, the end watch PSI in the Watch-1 is significantly more than the end watch PSI of Watch-2 (3.40 vs. 2.67, P = 0.009). The effect size for these changes are large (0.42).
Reaction time in PVT
The mean baseline RT in PVT for the participants in Watch-1 and Watch-2 showed no significant difference (P = 0.87) [Table 3]. However, there was a mid watch as well as an end watch increase in mean RT for both Watch-1 and Watch-2. It is evident that the mid watch increase of RT in the Watch-1 is significantly more than the mid watch increase of RT in Watch-2 (0.128 s vs. 0.003 sec, P = 0.00001). Similarly, the end watch increase of RT in the Watch-1 is significantly more than the end watch increase of RT in Watch-2 (0.247 s vs. 0.019 sec, P = 0.00001). The effect size for these changes is large (0.72).
Hamilton Anxiety Score–A
The average anxiety score before the commencement of watch of the participants as calculated from the HAM-A, for Watch-1 and Watch-2 were 12 and 11, respectively [Table 3] and these scores are not significantly different (P = 0.99). However, the end watch the score for Watch-1 is 23 showing a significant increase (P = 0.002). But the end watch anxiety for Watch-2 is 12, thus showing no significant increase (P = 0.93). On further analysis, it was evident that only 20 of 50 participants in Watch-2 showed an increase in their level of anxiety in comparison to 48 of 50 participants in Watch-1. Many participants in Watch-2 (60%) had the anxiety score unchanged or less in comparison to the baseline [Table 5] and [Table 6].
|Table 5: Comparisons of “mid watch” and “end watch” differences for physiological, psychological and cognitive variables during Watch-1 and Watch-2 using one-way ANOVA|
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|Table 6: The number of participants (and percentage) showing increase and decrease/no change in their anxiety score at the end of Watch-1 and Watch-2|
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The results of the questionnaire survey showed that 82% of participants felt CV was comfortable. When asked whether CV is too cold or too wet, 76% of individuals replied as negative. 74% participants felt that CV did not interfere with work, while 86% felt that it improved their work efficiency.
| Discussion|| |
The primary objective of this study was to ascertain the effectiveness of PCM-based CV on physiological parameters and behavioral alertness of individuals working in hot and humid environment of the ER in naval ships. The study showed that in comparison to the baseline, there is an increase in body temperature, pulse rate, and the RT of PVT among the participants during Watch-1 as well as during Watch-2. However, the magnitude of increase both at mid watch (after 2 h) and end watch (after 4 h) is more when the sailors are performing the watch without the CV (Watch-1) than the watch with CV. The increase in the HR can be explained by increase in body temperature reflecting additional efforts to maintain homeostasis and performance while doing Watch-1 in hot and humid environment of ER. The PSI, which is one of the most reliable heat strain indices was computed from the body temperature and HR. It was evident the heat stress exerted on the participants during the ER watch was less severe when CV was worn [Figure 1].
|Figure 1: The mean Physiological Strain Index recorded at 2 and 4 h during Watch-1 (without Cooling Vest) and Watch-2 (with Cooling Vest)|
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There was no difference in the systolic and DBP while performing watch with and without CV. Since high ambient temperature causes reflex vasodilation in the skin, BP is maintained by a combination of the peripheral vasodilation and increased cardiac output. Increased pulse rate in Watch-1 combined with unaltered BP, is therefore, indicative of the homeostatic response to the increase in body temperature. This may also be attributed to excellent homeostatic functions maintained by the participants. The participants who are the ER sailors have already conditioned to the hot and humid conditions of ER due to regular exposures. These results are corroborated with results from previous studies. Nishihara et al. have also taken into consideration the design of the CV for the thermal comfort. Cooling garments primarily reduce skin temperature by increasing thermal gradient between core and skin. The use of CVs found to decrease the thermoregulatory and cardiovascular strain on the wearer during watch hours in a hot and humid environment. A study on the utility of CV has shown beneficial effects among US army soldiers who worked in chemical protective clothing. A study by House JR on Royal Navy nuclear, biological and chemical cleansing stations' teams reviewed potential solutions to heat stress and suggested that hand immersion in cold water (50°F) would be the most effective cooling method, providing that personnel were able to take regular rest periods to immerse hands and CVs are the most effective method for the workers working continuously to maintain body temperature.
In the ER of a sailing ship, the heat stress could be a significant problem that may impair physical and mental performance. Studies in the past have elucidated the physiological effect of working at high temperatures and humidity however their respective effect on cognitive functions required further exploration. Our study showed that the increase in the RT in the PVT is less when the test was performed by the participants wearing the CV [Figure 2]. Therefore, it can be inferred that the behavioral alertness of the person was better with CV than without CV. These findings coincide with a current trend in the literature., A study by Raymann and Van Someren showed the relationship between the body temperature and vigilance function by demonstrating a decrease in vigilance performance by experimental inducing subtle increase in skin temperature. Our results showed that there is increase in aural body temperature and impaired vigilance in the form of increase RT among the participants when working in ER without CV.
|Figure 2: The mean Reaction time in psychomotor vigilance task recorded at 2 h and 4 h during Watch-1 (without Cooling Vest) and Watch-2 (with Cooling Vest)|
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A study by Radakovic et al. has shown that despite the relatively high degree of heat strain, the acclimatized soldiers did not show any substantial deficit of attention performance. Furthermore, improved RTs have also been previously observed in hot environments. This may be due to increased nerve conduction velocity in hot environment. However, prolonged heat stress has been shown to have detrimental effects on RT. When core body temperature increases to 101.6°F the beneficial effect of heat exposure on RT disappears.
In addition to physiological parameters, our study also assessed the psychological aspects. The assessment of HAM-A scores showed that the baseline anxiety levels were comparable before the Watch-1 and Watch-2. However, there was a significant increase in the HAM-A score for the participants performing the watch without CV. It was also evident that only 20 of 50 participants in Watch-2 showed an increase in their level of anxiety in comparison to 48 of 50 participants in Watch-1. A large number of participants in Watch-2 (60%) had the anxiety score unchanged or less in comparison to the baseline [Figure 3].
|Figure 3: The number of participants (and %) showing increase and decrease/no change in their anxiety score at the end of Watch-1 (without Cooling Vest) and Watch-2 (with Cooling Vest)|
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The questionnaire survey which had enquired whether the participants were comfortable working with the CV. High percentage of individuals felt that CVs are comfortable, did not interfere in work-related regular activities, and increased their work efficiency while performing the watch duties inside the ER [Figure 4] and [Figure 5].
|Figure 4: Results of Employability survey on use of Cooling Vest by the participants (n = 50)|
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|Figure 5: Employability matrix on use of cooling vest by the participants (n = 50)|
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Chronic heat stress may impair cognitive functions and cause accidents or near-miss events. Hence it is essential to adopt suitable measures in demanding work environments to ensure the optimal performance of an individual. Using PCM-based CVs clothes during physical activity in hot and humid conditions reduces sweating and alleviates heat stress manifested by increased skin temperatures and HR values. These effects directly improve heat tolerance and decrease the risk of heat illness.
Limitations of the study
There were some limitations of our study which need to be acknowledged. First, we have recorded aural body temperature and not rectal temperature to quantify heat stress (PSI) which might have introduced some error though few investigators have used the aural temperature to calculate the PSI with acceptable results. In addition, the duration between the two work exposures (without CV and with CVs) was variable. This aspect was beyond the control of the investigating team due to the fact that the platform where the study was conducted was an operational ship and the ER sailors were available for the study as per the ship's routine. The heat acclimatization of participants was variable and not taken into consideration.
| Conclusion|| |
Accumulated evidence has proven that heat stress affects the performance of person at workplace. Our study shows that wearing CV while working in the hot and humid condition of ER is beneficial in maintaining physiological parameters, behavioral alertness, and stability of mood which likely improve work efficiency. Thus, CV is an appropriate countermeasure that can be implemented to reduce the effects of heat strain during work performed in arduous ER conditions.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]