The effect of cooling vest along with hospital full-body protection equipment on physiological and cognitive indicators among hospital nurses: an interventional study

Abstract

Background

Nurses experience physiological and cognitive challenges in high-temperature hospitals while wearing full-body Personal Protective Equipment (PPE). Identifying solutions is crucial for their well-being and performance. The aim of this study was to assess the effects of integrating cooling vests into full-body PPE on physiological and cognitive markers among hospital nurses in Iran.

Methods

Forty nurses from Shiraz, Iran, participated, with 20 participants in the control group and 20 participants in the intervention group. The control group wore standard PPE, while the intervention group used cooling vests with their PPE. Objective evaluations included physiological measurements and cognitive function tests, while subjective evaluations assessed fatigue, thermal sensation, thirst, and moisture.

Results

Physiological measurements, including heart rate maximum, and energy expenditure, showed no notable differences between the two groups. The effect of the cooling vest in the Continuous Performance Test (CPT) in comparison between the two groups decreased the response time (p < 0.001). The N-Back test, no response (p = 0.189), and response time (p = 0.871) between the two groups showed no significant difference. Subjective parameters were considerable reduced in the intervention group (p < 0.001).

Conclusion

Integrating cooling vests into PPE may alleviate physiological and cognitive challenges nurses experience in high-temperature environments, emphasizing the importance of providing appropriate PPE and cooling solutions for healthcare professionals working in hot conditions.

Clinical trial number

Not applicable.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12913-025-13671-z.

Background

Healthcare professionals are essential assets for nations worldwide [1]. Nurses are the largest group of health professionals in all countries [2]. They were essential in the pandemic response because they spent the most time with patients [3]. Maintaining employee health and safety is critical for providing safe patient care and managing outbreaks [4]. However, healthcare professionals provide care for individuals affected by Severe Acute Respiratory Syndrome and Middle East Respiratory Syndrome during outbreaks [5]. Issues resulting from occupational exposures have garnered widespread attention from healthcare professionals worldwide, particularly nurses, who are often the primary healthcare providers [6].

One of the most notable and prevalent working issues in many industries is heat stress. The employees of many jobs are directly or indirectly exposed to this harmful factor and the problems and diseases caused by it [7]. Depending on the activity, the human body generates heat at rest in the range of 100 W or more and while working in the range of 500 W or more [8]. Physical heat-related indicators (which include thirst, fatigue, increased sweating, and uncomfortable temperature) and their impact on work performance (such as lower work performance and less accurate task execution) are categorized as heat strain [9]. Heat strain is induced by the body’s physiological reactions to heat stress, which include raised core and skin temperature, sweat, and an increased heart rate [10, 11]. Additionally, numerous studies have observed a decrease in cognitive performance under hot conditions. This phenomenon could contribute to human errors due to decreased attention and also elevate the probability of engaging in risky behaviour [12]. According to Stubblefield et al.‘s assessment of the impact of hyperthermia on cognitive function during the Heat Stress Test (HST), working memory performance was gradually decreased the hyperthermic (mean correct = 7.155 + 1.478) compared to the normothermic (mean correct = 8.151 + 1.60) condition [13]. In order to maintain homeostasis and prevent heat-related illnesses and injuries, the body must dissipate most of this heat into the environment through processes such as sweat evaporation, convection, and conduction [14]. To avoid cross-contamination with COVID-19 patients, healthcare staff employ substantial personal protection equipment, which includes isolation gowns, gloves, face masks, eye protection, and hair caps [9]. Using these devices can create severe physical and psychological stress, especially for Healthcare Workers (HCW) who have to wear them for long periods [15, 16]. In the ongoing pandemic, numerous healthcare workers are using personal protective equipment for four hours or longer [17]. The impermeable, encapsulating aspect of some Personal Protective Equipment (PPE) reduces heat loss, which can lead to heat stress and consequently cause thermal strain, resulting in elevated skin and core temperatures (38.86 ± 0.42 °C) in the control condition among healthcare workers [18]. Using a cooling system may lead to enhanced productivity and comfort, as well as safer working conditions [19]. In challenging environmental conditions, cooling therapies, such as ingesting ice slurries, using face water sprays, and wearing cooling vests, can provide instant relief from heat stress [20]. Cooling vests have been shown to be the most effective cooling intervention (+ 0.73) in the majority of occupational settings in highly stressful environments [21]. Cooling vests can be divided into Air Cooling Vest (ACV), Liquid Cooling Vest (LCV), Phase Change Vest (PCV), Evaporative Cooling Vest (ECV), and Hybrid Cooling Vest (HCV) [22]. One method to reduce heat and achieve a comfortable temperature is by using individual cooling vests equipped with PCM. These cooling vests enhance thermal comfort by absorbing excess heat through phase change materials. PCMs can absorb or release widespread amounts of energy as latent heat by transitioning between their solid and liquid states [23]. PCM can be added to the cooling vest in the form of packets that are inserted into the vest’s pockets [24, 25]. Since PCM must solidify after usage, it must be kept in a freezer or cold environment [26]. Among PCMs, water is the best-known one. Ice cooling vests provide several advantages, including high latent heat, widespread availability, and inexpensive cost. However, prolonged contact with ice can induce tissue irritation, which limits its usefulness [27]. The purpose of this study was to investigate the effect of a cooling vest along with hospital full-body protection equipment on physiological and cognitive indicators among Iranian nurses.

Methods

Location and date of the study

This field trial was conducted in one of the major hospitals in Shiraz, Iran, during the summer of 2021.

Sample size

An a priori sample size estimation was conducted based on heart rate, which was identified as the primary physiological outcome [28]. Using the standard formula for comparing two group independent means, with a significance level of α = 0.05 (Z₁₋α/2 = 1.96) and a statistical power of 80% (Z₁₋β = 0.84)​, the required sample size was estimated to be 18 participants per group. To account for potential dropouts, 40 nurses were recruited for the study (20 per group).

Inclusion and exclusion criteria

Inclusion criteria were: (a) employment as a hospital nurse for at least one year, (b) adequate sleep the night before the test, and (c) no prior history of cardiovascular, respiratory, thyroid, metabolic, or psychiatric disorders. Exclusion criteria included (a) regular use of medications affecting metabolism or thermoregulation, (b) participation in professional sports or special diets, and (c) for female participants, being in the menstrual cycle phase during data collection.

Randomization procedure

Participants were randomly allocated into two groups (control and intervention) using a block randomization method with blocks of four to ensure balanced group sizes throughout the study. Initially, 40 eligible nurses (20 men and 20 women) were selected through systematic random sampling from different hospital departments. The 40 participants were divided into 10 blocks of four. Within each block, a computerized random sequence determined which two participants were assigned to the control group (PPE only) and which two to the intervention group (PPE + Cooling Vest). The allocation sequence was prepared by a researcher independent of data collection and kept confidential. Each participant’s assignment was placed inside a sealed opaque envelope, which was opened only at the time of the experiment. This procedure maintained allocation concealment, minimized selection bias, and ensured balanced group sizes.

Blinding

Due to the nature of the intervention (wearing a cooling vest), blinding of participants was not feasible. However, outcome assessors and data analysts were blinded to group allocation.

Ethics and safety

It should be mentioned that the participants provided their informed consent forms, and participation in the study was entirely voluntary. Furthermore, in order to comply with health protocols and prevent virus infection, personal protective equipment was provided to each participant separately in the hospital. Also, the cooling vest was washed and disinfected after the end of the test.

Data gathering tools

A combination of experimental assessment and standardized questionnaires was used to collect the necessary data. Physiological parameters such as heart rate and core body temperature were measured using validated monitoring devices, while cognitive performance was assessed through computerized tests focusing on attention and working memory. In addition, questionnaires gathered demographic information, health status, and participants’ subjective experiences, such as those related to thermal comfort and fatigue.

Questionnaires

• Questionnaire on demographics and health status: The questionnaire includes inquiries about age, sex, height, weight, Body Mass Index (BMI), work history, ensuring adequate sleep (seven to nine hours) the night before the exam, past respiratory, thyroid, cardiovascular, and metabolic conditions, mental health history, use of particular drugs, adherence to a specific diet, and performing specific sports exercises (Supplementary file 1).

• Subjective fatigue rating scale: A ten-point Visual Analogue Scale (VAS) was employed to subjectively evaluate fatigue, where zero and ten denoted the minimum and maximum fatigue levels, respectively [29].

• Thermal sensation subjective evaluation scale: A seven-point rating system was utilized to assess thermal sensation. The scale includes the following numbers in sequence: -3 (cold), -2 (cool), -1 (slightly cool), 0 (neutral), 1 (slightly warm), 2 (warm), and 3 (hot) [30].

• Subjective thirst Scale of assessment: Using this 7-point rating system, evaluate people’s subjective feeling of thirst, from 1 (I am not thirsty at all) to 7 (I am very very thirsty) [31].

• The scales of Nielsen et al.: Skin and clothing moisture levels were subjectively assessed using the following scales. The numbers on the skin wetness assessment scale signify: [32]

1 = Less dry than usual.

2 = Typically dry.

3 = Certain body parts are damp.

4 = Larger body parts are damp.

5 = Certain body parts are soaked.

6 = Larger body parts are soaked.

7 = Perspiration drips in some areas.

8 = Perspiration drips in many areas.

On the clothing moisture assessment scale, 1 = dry, 2 = somewhat moist, 3 = moist, and 4 = wet.

Experimental tools

• Personal protective equipment: Full-body personal protective equipment includes an impervious full-body coverall, an N95 mask, latex gloves, shoe covers, a face shield, and commercial cooling vest.

• Cooling vest: The maker of the ice gel cooling vest is one of Iran companies (Hifit Cool Company). This cooling vest is made of 70% linen and 30% polyester and has 10 pockets in the front and back, for a total weight of 2.3 kg.

• Polar RS400: A Polar RS400 device, which consists of a wristband worn on the wrist and a chest strap across the chest, was used to measure heart rate and energy expenditure.

• Tympanic thermometer infrared Ri-thermo N: Using a Ri-thermo N tympanic infrared thermometer (Riester), the temperature of the body’s core was determined from the tympanic temperature.

• USB temperature and humidity data logger: A wireless USB temperature and humidity data logger (MIC-98583) was used to record the temperature and humidity of the clothing microclimate, which were placed inside the clothing. The software device allows for measurement within the time intervals set.

• N-Back test: The N-Back test is frequently used in neuroimaging studies to stimulate subjects’ brain functions and is utilized for assessing cognitive function associated with executive function. In 1958, Kirchner introduced this task for the first time, laying the groundwork for its widespread use as a fundamental tool in cognitive research [33]. The participants in the general method are shown a series of visual stimuli, and their task is to determine whether the current stimulus is similar to the previous n-stimuli. “N” can be 1, 2, or 3 in this software, and increasing the value of n makes the task harder. The latest stimulus shown is compared to the immediately preceding one in the 1-Back condition (N = 1), whereas in the 3-back condition (N = 3), the most recent stimulus is compared to the three preceding stimuli. Participants are required to answer with a “?” if the stimulus that is being presented is the same as the previous n steps in the sequence. If not, they need to use the keyboard’s “Z” key [34]. Higher values of n (N = 2, 3), however, result in higher reliability coefficients but further raise the quantity of mistakes and response time. In this present study, we used the 2-Back test according to the real environment conditions and work complexity. Previous research has established the validity and reliability of the N-Back test’s Persian version [35].

• Continuous Performance Test: Developed in 1956, the Continuous Performance Test (CPT) has been widely used in psychological and neuroscientific research, making widespread contributions to the understanding of cognitive functions [36] and quickly gained widespread acceptance. This test aims to evaluate sustained attention, vigilance, and focused attention. There are many forms of CPT testing that have been created for therapeutic or research objectives. In all versions of this test, the individual is required to focus on a relatively straightforward series of visual or auditory stimuli and react by pressing a key when the target stimulus is presented. In this test, 150 stimuli were shown, with 20% being target stimuli (to which individuals were required to react). Every stimulus was shown for 200 ms, with a one-second interval between each [34]. The Visual CPT was utilized to assess sustained attention and cognitive functions in the study. The Persian CPT version was validated, confirming its reliability for cognitive assessments [37].

Experimental procedure

The participants were randomly chosen continuously in one working day and in 2 groups with a sample size of 20 people in each group. In the control group (only PPE) participants wore impermeable full-body coveralls, surgical masks or FFP2 respirators, goggles, face shields, long-sleeved clothing, and gloves, but in the second group, the intervention group included (PPE + Cooling Vest).

First, the nurses were instructed to sit comfortably in a chair for five minutes until their heart rate and breathing rate returned to normal levels. Following that, objective and subjective evaluations were completed. Objective evaluations included assessments of physiological and cognitive function. Physiological performance was evaluated by measuring HR, energy expenditure, core body temperature, clothing microclimate temperature, and humidity. The N-Back and CPT tests were used to evaluate cognitive function. The order of cognitive tests for each participant was chosen at random. Subjective evaluations included a rating of fatigue and thermal sensation. Nielsen et al.‘s scales were also used to assess skin and clothing moisture levels.

Following that, nurses in the first group wore personal protective equipment and performed daily activities in the hospital for one hour; also, in the second group, nurses wore cooling vests under PPE but over their standard medical scrubs (Fig. 1) and worked for an hour. After the activity, all the above tests were repeated. The flowchart of the study process is shown in (Fig. 2). All tests were performed in the hottest season of the year in one of the hospitals in Shiraz, from 9 am to 3 pm. The dry-bulb temperature ranged from 24 to 28 °C, and the Wet-Bulb Globe Temperature (WBGT) index was maintained between 17 and 19 °C, providing a controlled and consistent environment for all tests.

Fig. 1.

Presentation of how the phase change material (PCM) cooling vest was worn over the standard medical scrub (A) and underneath the personal protective equipment (B)

Fig. 2.

Flowchart of the study process *Objective assessments: a physiological performance assessments including heart rate, energy expenditure, core body temperature, clothing microclimate temperature, and clothing microclimate humidity; b cognitive performance assessments including N-back test and continuous performance test. Subjective assessments: fatigue, thirst, thermal sensation, skin wetness, and clothing moisture.Figure 2Alt Text A flowchart showing different stages of the experiment in order. The boxes in the flowchart with arrows from top to bottom show the order of the different stages of the experiment

Statistical analysis

To make intra-group comparisons, we used paired T-test if normal; otherwise, we employed the Wilcoxon test; in between-group comparisons, we used independent T-test, if normal; Otherwise, the test of Mann-Whitney was employed. Analyses were done in SPSS, version 21. Also, less than 0.05 was the regarded significance level for the tests. To complement statistical significance testing, effect sizes were calculated to assess the practical relevance of the intervention. For each outcome variable, the mean change score (i.e., post-test minus pre-test) was calculated within both the intervention and control groups. These change scores were then compared between groups to evaluate the magnitude of the intervention’s effect. For normally distributed data, Cohen’s d was used as the measure of effect size. Interpretation of Cohen’s d followed standard guidelines: values less than 0.2 were considered small, between 0.2 and 0.5 as medium, between 0.5 and 0.8 as large, and values greater than 0.8 as very large. All statistical analyses, including effect size calculations, were performed using SPSS software, version 27.

Results

Demographic/occupational characteristics

Table 1 presents the demographic and occupational characteristics of the participants. For the Quantitative variable (age, height, weight, BMI, and work experience), the mean and standard deviation are reported, while for the qualitative variable (sex and education level), percentages are provided.

Table 1.

Demographic characteristics of the participants (n = 40)

Quantitative variable	Mean ± SD
Age (year)	31 ± 4.7
Height (cm)	170 ± 7.68
Weight (kg)	66.7 ± 9.72
BMI (kg/m 2 ) *	23 ± 2.74
Work experience (year)	5.7 ± 4.38
Qualitative variable	No. (%)
Sex  Male  Female	20 (50%) 20 (50%)
Education level  Bachelor’s degree  Associate degree	38 (95%) 2 (5%)

* Body Mass Index

Objective assessment

Physiological performance assessment

The cooling vest affected all physiological parameters evaluated, including heart rate, energy expenditure, core body temperature, clothing microclimate temperature, and clothing microclimate humidity. In Table 2, the median and interquartile ranges were used for non-normally distributed variables. In the intergroup comparison, heart rate maximum (p = 0.499, IF = 0.012) and energy expenditure (p = 0.091, IF = 0.361) were not significant. In contrast, the other variables showed significant differences: heart rate (p = 0.048, IF = 0.099), core body temperature (p < 0.001, IF = 0.018), clothing microclimate temperature (p < 0.001, IF = 0.338), and clothing microclimate humidity (p = 0.002, IF = 0.230). Based on the interpretation of the effect sizes, the intervention had a small impact on heart rate and core body temperature, a medium effect on clothing microclimate humidity, and a medium impact on clothing microclimate temperature.

Table 2.

Evaluation of the effects of the cooling vest along with personal protective equipment on physiological performance in the two non-intervention and intervention groups (n = 40)

Physiological variable		Non-intervention** M ± SD or Mdn (IQR)*	Intervention** M ± SD or Mdn (IQR) *	p-value•	Effect size
Heart rate (beat per minute)	Before	84 ± 6.69	82 ± 7.07
	After	91 ± 5.97	92 ± 5.4
	Difference ••	7 ± 3.59	10 ± 4.27	0.048	0.099
Heart rate-max (beat per minute)	Before	99 ± 9.55	98 ± 8.29
	After	114 ± 8.39	116 ± 7.25
	Difference ••	15 ± 8.4	18 ± 12.12	0.499	0.012
Energy expenditure (Kcal.min− 1)	Before	0.9(0.60)	1 (0.31)
	After	3.5(1.58)	4.6 (0.7)
	Difference ••	2.6 ± 0.61	3.7 ± 0.83	< 0.091	0.361
Core body temperature (°C)	Before	36(1)	36.4(1)
	After	36.5(1)	36 (1)
	Difference ••	0.5(0.45)	−0.4(0.3)	< 0.001	0.018
Clothing microclimate temperature (°C)	Before	29.7 ± 1.31	30.4 ± 1.4
	After	30.9 ± 2.02	29 ± 1.83
	Difference ••	1.2 ± 2.04	−1.4 ± 1.68	< 0.001	0.338
Clothing microclimate humidity (%)	Before	39.5(5)	41.5(3)
	After	40.1 (4)	38.5(2)
	Difference ••	−0.6(5.6)	−3 (3.47)	0.002	0.230

^* M: Mean, SD: Standard Deviation, Mdn: Median, IQR: Interquartile Range

^** Non-intervention: group 1 (only PPE). Intervention: group2 (PPE + Cooling vest)

^• Between-group comparisons: independent T-test, if normal, otherwise, the Mann-Whitney test

^•• The mean difference between pre-test and post-test

Cognitive performance assessment

Based on the result, the cooling vest affects all the assessment cognitive parameters, including CPT and N-Back tests. In the CPT, response time differed between groups (p < 0.001, IF = 0.345) (Table 3). In the N-back test (Table 4), correct responses (p = 0.015, IF = 0.020), incorrect responses (p = 0.012, IF = 0.191), and the percentage of correct responses (p = 0.003, IF = 0.054) showed statistically detectable differences between groups. However, no response (p = 0.189, IF = 0.000) and response time (p = 0.871, IF = 0.014) did not differ between groups. Based on the interpretation of the effect sizes, the intervention had a small impact on response time in the CPT. In the N-back test, the intervention had a small effect on correct responses, a small effect on incorrect responses, and a small effect on the percentage of correct responses.

Table 3.

Evaluation of the effects of a cooling vest with personal protective equipment on cognitive function (CPT) in the two non-intervention and intervention groups (n = 40)

CPT test		Non-intervention** M ± SD or Mdn (IQR) *	Intervention** M ± SD or Mdn (IQR) *	p-value•	Effect size
Response time (ms)	Before After	462 (36) 512 (119.8) 45 ± 50.165	524.5 (127.5) 468.5 (39.5) − 41.4 ± 105.75
	Difference ••			< 0.001	0.345

^* M: Mean, SD: Standard Deviation, Mdn: Median, IQR: Interquartile Range

^** Non-intervention: group 1 (only PPE). Intervention: group 2 (PPE + Cooling vest)

^• Between-group comparisons: independent T-test, if normal, otherwise, the Mann-Whitney test

^•• The mean difference between pre-test and post-test

Table 4.

Evaluation of the effects of a cooling vest with personal protective equipment on cognitive function (N-Back) in the two non-intervention and intervention groups (n = 40)

N-Back test		Non-intervention** M ± SD or Mdn (IQR)*	Intervention** M ± SD or Mdn (IQR) *	p-value•	Effect size
Correct response	Before	52.60 ± 16.86	55.45 ± 10.42
	After	50.90 ± 14.17	57.4 ± 11.11
	Difference ••	−7.5 (11.75)	3.5 (8.5)	0.015	0.020
No response	Before	59.5 (20.8)	58 (6.5)
	After	60 (24)	58 (9.3)
	Difference ••	1.5 (13.5)	0 (8.25)	0.189	0.000
Incorrect response	Before	9 (5.5)	8 (5.8)
	After	10 (12.8)	6.5 (5)
	Difference ••	1 (10.25)	−1.5 (5)	0.012	0.191
Number of correct responses (%)	Before	43.5 (13.5)	45 (5)
	After	41.5 (14.5)	48 (8.3)
	Difference ••	−2 (10.75)	3 (7.5)	0.003	0.054
Response time(ms)	Before	724.05 ± 175.01	634.85 ± 111.03
	After	720.25 ± 138.11	604.05 ± 148.88
	Difference ••	−42.5 (192)	−33 (75.5)	0.871	0.014

^* M: Mean, SD: Standard Deviation, Mdn: Median, IQR: Interquartile Range

^** Non-intervention: group 1(only PPE).Intervention: group 2 (PPE + Cooling vest)

^• Between-group comparisons: independent T-test, if normal, otherwise, the Mann-Whitney test

^•• The mean difference between pre-test and post-test

Subjective assessments

In the subjective assessment scales (Table 5), participants in the intervention group reported a significant reduction in fatigue (p < 0.001, IF = 0.615), as well as a lower thermal sensation (p < 0.001, IF = 0.295). The intervention also led to a decrease in skin moisture perception (p < 0.001, IF = 0.810) and clothing moisture sensation (p < 0.001, IF = 0.682). Additionally, thirst levels were notably lower in the intervention group (p < 0.001, IF = 0.569) compared to the control group. Based on the interpretation of the effect sizes, the intervention had a large impact on fatigue reduction, a medium effect on thermal sensation, a very large effect on skin moisture perception, a large effect on clothing moisture sensation, and a large effect on thirst reduction.

Table 5.

Evaluation of the effects of the cooling vest along with personal protective equipment on subjective evaluations in the two non-intervention and intervention groups (n = 40)

Subjective scale		Non-intervention** M ± SD or Mdn (IQR) *		Intervention** M ± SD or Mdn (IQR) *	p-value•	Effect size
Fatigue assessment scale	Before	4.6 ± 2.01	4.5 ± 2.13
	After	7.4 ± 1.30	4 ± 1.61
	Difference ••	2.8 ± 1.23	-0.5 ± 1.46		< 0.001	0.615
Thermal sensation scale	Before	0 (1.8)	2 (1)
	After	2 (0)	-1.5 (1)
	Difference ••	2 (1.75)	-3 (1)		< 0.001	0.295
Skin moisture scale	Before	2 (1.8)	2.5 (1)
	After	4 (2)	1 (1)
	Difference ••	2 (1)	-1.5 (0.75)		< 0.001	0.810
Clothing moisture scale	Before	1 (0.8)	2 (0.8)
	After	2 (1)	1 (0)
	Difference ••	1 (0)	-1 (1)		< 0.001	0.682
Thirst assessment scale	Before	4 (2)	5 (1)
	After	5 (1)	4 (2)
	Difference ••	1 (1)	-1 (1)		< 0.001	0.569

^* M: Mean, SD: Standard Deviation, Mdn: Median, IQR: Interquartile Range

^** Non-intervention: group 1(only PPE).Intervention: group 2 (PPE + Cooling vest)

^• Between-group comparisons: independent T-test, if normal, otherwise, the Mann-Whitney test

^•• The mean difference between pre-test and post-test

Discussion

Based on the current research, wearing a cooling vest underneath the personal protective equipment increases the heart rate and energy expenditure and decreases the core body temperature and Clothing microclimate temperature and humidity. The cooling vest reduced incorrect responses and response time in our cognitive tests, which improved nurses’ performance. Moreover, subjective evaluations such as fatigue, heat sensation, skin moisture, clothing moisture, and thirst reduced after using cooling vest.

Physiological assessments

Heart rate

The average heart rate was substantial higher after the test compared to before the test in each group separately. After the test, the heart rate increased in both groups; however, the rise was greater in the intervention group. The average increase in heart rate was 9.8 bpm for the cooling vest group and 7.25 bpm for the control group, showing approximately 35% higher rise in the intervention group (p = 0.048). This suggests a measurable cardiovascular response associated with the use of the cooling vest. This finding was not in the same line with those of some previous studies. For instance, in de Korte et al.‘s study in which the cooling vest reduced the heat stress in nurses in the hospital environment, no difference in maximum HR was observed, while the average HR was slightly lower in the cooling vest condition [38]. In the study of Yousefi, et al., which evaluated the phase change cooling vest in a hot and humid environment, the maximum heart rate for the group without the cooling vest was higher than that those with it, and increases the average heart rate in the participants with the cooling vest compared to those without the cooling vest [23]. In the study of Barr et al. on the cooling strategy for physiological reduction on firefighters, the heart rate in the control group increased compared to the intervention group [39]. Furthermore, the investigation conducted by Zare et al. examined the impact of paraffin and optimum ice-cooling vests on physiological and cognitive strain. The findings showed that the average heart rate was lower in participants wearing the cooling vest (100.55 bpm) compared to those without a vest (113.33 bpm), indicating a reduction of approximately 11% in heart rate due to the vest. The findings of a study by Zare et al. showed that the movement on the treadmill induced the airflow resulting from the movements of the cooling vest, which enhanced the transfer of heat. These mechanisms lead to a reduction in both skin and core temperature. Additionally, the heart rate is influenced due to its association with body temperature [27].

On contrary, wearing a cooling vest under PPE can lead to an increase in the heart rate due to several possible reasons. Heat is absorbed from the body by cooling vests and dissipating it, which can induce a cooling effect. However, the body may interpret this cooling as a drop in body temperature, triggering a thermoregulatory response. This cooling effect can cause blood vessels near the skin to dilate, allowing for enhanced heat dissipation. The body responds to this vasodilation ensure sufficient blood circulation to the extremities and meet the metabolic demands of the body [40]. The results of a systematic review on precooling and its effects on athletic performance demonstrated that a certain method of precooling resulted in a notable constriction of the blood vessels in the skin. This was evident from the substantial and lasting decrease in the skin temperature (up to 11.5 degrees Celsius) and muscle temperature (0.8 degrees Celsius), accompanied by an increase in the heart rate (approximately 10–20 beats per minute) [41]. Overally, it seems that the effect of wearing a cooling vest on the heart rate can vary between studies due to several factors, including the specific experimental conditions, participant characteristics, and cooling vest design. It is essential to take into account that each individual responses to cooling can differ, and conflicting findings may arise from the complex interplay of various physiological factors.

Energy expenditure

The average energy expenditure among the cooling vest group is widespread higher compared to the one without it. The amount of energy expenditure in each group widespread increased after the implementation of the intervention, compared to the energy expenditure levels observed prior to the intervention. The present study shows that the cooling vest has no effect on the energy expenditure and it depends on the intensity of the work.

According to Jahangiri et al.‘s study, workload intensity greatly impacts energy expenditure. Consequently, energy expenditure was notably higher in PPE-wearing conditions across all workload levels, aligning with the findings of the current study [34]. Additionally, according to Smolander et al.‘s study, at both work levels, the average energy expenditure in the tests with and without the ice vest was relatively similar [42]. One of the possible reasons for the increase in energy expenditure after using cooling vests is that these vests allow the nurses to feel more comfortable in hot environments [38], which may result in increased physical activity. If nurses are more active while wearing cooling vests, they may burn more energy, leading to increased energy expenditure.

Carrying additional weight, even if it’s relatively light, can require additional muscular effort. The extra effort exerted by the body to support and move with the added weight of the cooling vest can result in increased energy expenditure. Ghiyasi et al. assessed the impact of PPE on firefighters’ heat stress, finding that the weight of the PPE directly elevated heart rate and indirectly boosted metabolism [43]. In the study of Wen et al., it was found that there was a positive relationship between the weight of clothing and oxygen consumption [44]. Specifically, the metabolic rate was observed to increase by 2.7% for each kilogram of additional clothing weight [45].

Core body temperature

Compared to the control group, the intervention group exhibited a lower average core temperature. Following the test, both groups showed a reduction in core temperature; however, the decrease was more pronounced in the control group (Median (Mdn) = 0.5 °C, Interquartile Range (IQR) = 0.45) than in the intervention group (Mdn = − 0.3 °C, IQR = 0.3). This unexpected pattern in the control group may reflect the nurses’ physiological adaptation to PPE over time.

In the study of Yuan et al., it was about the liquid cooling vest that caused a decrease in the core body temperature compared to the state without it, which was in accordance with our study [46]. In NI et al.‘s study, a new personal cooling vest equipped with phase change materials and fans was found to reduce core body temperature compared to the control group [47]. Also, in Kenny et al.‘s study, the ice cooling vest reduced the increase in core temperature [48].

Clothing microclimate temperature and humidity

In the present study, notable differences were observed in the clothing microclimate temperature and humidity between the groups. The intervention group experienced a decrease in microclimate temperature, while the control group showed an increase, resulting in a total temperature difference of approximately 3.6 °C between the two groups. This indicates the cooling effect of the vest. Regarding humidity, the intervention group showed a greater reduction in humidity (approximately 2.5% more) compared to the control group, highlighting the more effective moisture regulation of the cooling vest. This is consistent with the results of a study which aimed at improving firefighter uniforms by developing a comfortable and thermally balanced design, with a specific focus on incorporating a cooling vest. The study showed that the cooling vest was comfortable and flexible, and had a positive impact on the wearer’s microclimate [49]. In the study conducted by Totong et al., adding cooling garments and devices to the PPE ensemble lowered the microclimate temperature and humidity compared to not using any cooling methods [50].

Cognitive assessments

The two cognitive assessments in this study serve distinct purposes in evaluating mental performance. The N-Back test primarily measures working memory, requiring participants to continuously monitor and update stimuli presented in a sequence, which reflects their ability to temporarily store and manipulate information. This task is cognitively demanding and sensitive to fluctuations in mental workload, stress, and thermal comfort. In contrast, the CPT evaluates sustained attention and impulse control through the detection of target stimuli over an extended period.

These findings can be better understood through the lens of the Yerkes-Dodson law (1908), which proposes an inverse-U relationship between arousal and performance—suggesting that moderate levels of arousal can enhance cognitive function, while both low and high arousal may impair it [51]. Elevated thermal load, like other physiological stressors, can increase arousal beyond optimal levels, potentially reducing performance on complex cognitive tasks. Diamond (2005) further emphasized that the effects of stress and arousal on cognitive functioning depend on the complexity of the task, with more demanding tasks—such as the N-Back—being more vulnerable to performance decrements under excessive stress [52].

In the present study, the use of a cooling vest appeared to mitigate thermal stress and maintain participants within a more optimal arousal range. This was reflected in a statistically significant improvement in performance on the CPT, with a widespread reduction in response time in the intervention group compared to the control group—an average improvement of approximately 86 milliseconds (p < 0.001). These results suggest that cooling interventions may enhance sustained attention and cognitive efficiency by buffering the effects of heat-induced cognitive strain.

In the study of Bonel et al. regarding the effect of personal cooling on the performance, comfort, and heat stress of healthcare workers in PPE in the laboratory, no effect on cognitive performance was observed. This may be due to the special conditions of the laboratory compared to the real hospital environment Also, the sample size, and the average age of the nurses in the study, has the effect of confounding the results [17].

Moreover, in the study by Jaipurkar et al., the response time was reduced with a cooling vest compared to without it, and therefore, it can be inferred that the behavioral alertness of the person was better with CV than without CV, which was in agreement with our study [53]. In another study by Simmons et al., increases in both skin and core temperature were associated with decreased perception of heat-induced fatigue and elevated cardiovascular strain, which ultimately resulted in cognitive performance impairments. These impairments were characterized by faster response times, likely due to increased urgency or stress, but accompanied by a significant loss of accuracy [54].

In the study of Hemmatjo et al., the cooling vest was effective in reducing cognitive performance during the firefighting activity, and the cooling vest reduced the number of errors in the CPT test [55]. Also, Jason Lee and colleagues observed an increase in the participants’ mental performance by using body cooling techniques while wearing clothes [56].

In the N-Back task, no statistically significant difference was found in response time between the groups. However, the intervention group showed slightly faster and more consistent performance, with a median response time of − 33 milliseconds (IQR = 75.5) compared to − 42.5 milliseconds (IQR = 192) in the control group, suggesting improved temporal stability under cooling conditions.

Regarding correct responses, participants wearing the cooling vest achieved approximately four more correct answers than those in the control group, a relative improvement of over 50%, highlighting the potential of thermal regulation in enhancing working memory performance.

Furthermore, the number of incorrect responses in the intervention group was reduced by about three points compared to the control group, indicating a notable decrease in cognitive errors under cooler conditions. This pattern suggests that improved thermal comfort may reduce the cognitive strain often associated with heat exposure, thereby optimizing decision-making accuracy during working memory tasks.

The relationship between physiological stress such as heat exposure and cognitive performance has long been described by the inverse U-shaped curve, a concept first proposed by Yerkes and Dodson (1908). According to this model, moderate arousal levels enhance performance, while very low or excessively high arousal impairs it. Later, Diamond (2005) emphasized that task complexity plays a crucial role in this pattern: simple tasks may tolerate higher stress, whereas complex tasks especially those requiring executive function are more sensitive to overload.

Patterson et al. found that depending on how simple or complex the task was, workers’ response time varied when they were under heat stress. As the temperature raise from 21 to 35 degrees Celsius, the response time increased [57]. In addition, According to Gaoua et al., after the core temperature hit 38.7 °C, the early gains in attentional cognitive performance stopped [58]. As a result, it is well known that there is an inverse U-shaped relationship between elevated body temperature and improved cognitive function. This association shows that heat improves both simple and sophisticated cognitive activities when the core temperature is less than 38.5 °C [59]. In this study core temperature remained below the threshold in both groups.

Subjective assessments

In the present study, the average fatigue score in the control group was 2.80 ± 1.23, which was considerably higher than that of the intervention group (–0.55 ± 1.46). This significant difference (< 0.001) indicates that the use of the cooling vest effectively reduced perceived fatigue during the task. However, in the control group, fatigue was higher after the test compared to before the test, and this increase was significant. The weight of the vest and the intensity of the work might have contributed to this effect. Numerous research studies have also shown the fatigue that comes with wearing protective equipment for healthcare personnel [8, 60–63].

In the Tokizawa et al. study, the researchers examined how well a liquid cooling vest reduced thermal stress when worn in conjunction with protective apparel. According to the findings, using the cooling vest did not increase the participants’ perception of fatigue compared to the control condition [64]. However, it is important to note that the burden of wearing the cooling vest may still contribute to fatigue.

In the present study, the median thermal sensation score in the intervention group was (–3.0 (IQR = 1)), which was substantially lower than that of the control group (2.0 (IQR = 1.75)). This notable difference reflects the effectiveness of the cooling vest in reducing the subjective feeling of heat, but in the intra-group comparison, it caused an increase in the feeling of heat in the control group and a decrease in the intervention group, which shows the effect of the cooling vest. These findings were made with the study conducted by De Court and colleagues, in which participants in the intervention group had a 59% difference in feeling (slightly) hot compared to the control group [38], as well as several previous studies that confirm the positive impact of cooling vests on reducing heat stress [17, 18, 23].

The average perceived skin moisture and perceived clothing moisture in the intervention group were substantial lower than the control group (p < 0.001), indicating the effectiveness of the cooling vest. However, the increase in sweat on clothing and skin was stabilized and eventually stopped after a while, probably due to adaptation to the environment and the clothing material.

The cooling vest in the intervention group resulted in a notable reduction in perceived thirst compared to the control group. The median thirst score in the intervention group was (–1 (IQR = 1)), while it was (1 (IQR = 1)) in the control group, and this difference was statistically significant (p < 0.001). Furthermore, in each group separately, thirst increased in the control group and decreased in the intervention group both before and after the study. These outcomes align with those of the study conducted by Cleary et al., in which the thirst response in the cooling condition was lower (4.5 ± 0.3 points) than in the control condition (5.3 ± 0.4 points), supporting our findings that the cooling vest group experienced reduced levels of thirst compared to the control group [65].

Strengths and limitations

As far as current research indicates, our work is the first to examine how hospital whole-body protection equipment in conjunction with a cooling vest affects physiological and cognitive markers in an actual hospital in Shiraz. Conducting the research in an actual clinical environment considerable enhances the ecological validity of the findings, as the physical demands, mental stress, environmental temperature, and workflow dynamics in a hospital cannot be accurately replicated in laboratory simulations. Moreover, the simultaneous assessment of cognitive and physiological indicators provides a comprehensive evaluation of the cooling vest’s effectiveness.

Another innovative aspect of this study is the use of a practical, reusable, and low-cost ice-based cooling vest, which could serve as an accessible thermal management solution for healthcare workers, especially during high-risk, high-stress scenarios. Given the increasing ageing of populations worldwide, the rising burden of chronic diseases, and the potential for future epidemics and pandemics that necessitate prolonged use of PPE, these findings have global relevance and application.

However, this study has certain limitations. Due to the high workload and clinical obligations of nurses, the sample size was relatively small. The intervention duration was also limited to one hour, primarily because of the cooling capacity of the ice packs and the unpredictable nature of hospital emergencies. Additionally, the research was conducted only in hospitals located in Shiraz, which may limit the generalizability of the results to other regions and healthcare systems.

Future studies are encouraged to include larger sample sizes, longer intervention durations, and a broader range of hospital settings, including technologically advanced urban hospitals with air-conditioning systems, under-resourced rural hospitals, and healthcare facilities in conflict zones.

In parallel, advancements in cooling vest technology are essential. It is recommended that future designs focus on reducing the weight of the vest and improving ergonomic compatibility with PPE to minimize movement restriction and reduce fatigue.

Conclusion

The study showed that the use of a cooling vest along with hospital body protection equipment could reduce heat stress in nurses working in infectious departments (such as Covid-19 and Ebola) and laboratories. The intervention group was compared to the control group. The nurses’ activity increased the heart rate and energy expenditure and decreased the core body temperature and clothing microclimate temperature and humidity. Subjective assessments in the intervention group compared to the control group were in accordance with our hypotheses and the cooling vest decreased the feeling of heat and also decreased the perceived skin and clothing moisture. Also, the cooling vest reduced fatigue and thirst, and its indirect effects led to increased cognitive performance (more attention and alertness and faster response time) compared to the control group. Cognitive errors among nurses are widely recognized as one of the most preventable yet impactful contributors to patient morbidity and mortality in clinical settings. Improved mental functioning, facilitated by thermal comfort, may help reduce decision-making delays, attentional lapses, and procedural mistakes—especially under high-stress conditions involving prolonged PPE use. Consequently, the integration of effective cooling strategies into PPE protocols could not only improve the physical well-being of healthcare workers but also play a critical role in promoting patient safety by minimizing cognitive load and reducing the risk of error.

Supplementary Information

Below is the link to the electronic supplementary material.

Abbreviations

ACV

Air Cooling Vest

CPT

Continuous Performance Test

ECV

Evaporative Cooling Vest

HCV

Hybrid Cooling Vest

HCW

Healthcare Workers

HST

Heat Stress Test

LCV

Liquid Cooling Vest

PCV

Phase Change Vest

PPE

Personal Protective Equipment

Author contributions

ZZ, HD, NG, FV, MZ and HJ were involved in the study design, analysis and interpretation of the data, drafting of the manuscript. HJ was involved in the study design, data collection, and drafting of the manuscript. All authors have read and approved the final manuscript.

Funding

This work was supported by the Shiraz University of Medical Sciences under Grant 25803.

Data availability

We are unable to share data publicly because of ethical and legal restrictions. The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Declarations

Ethics approval and consent to participate

The study was approved by the ethics committee of Shiraz University of Medical Sciences (Ethics Code: IR.SUMS.SCHEANUT.REC.1401.072). In addition, this study was conducted according to the Helsinki Declaration and its later amendments. In the study, the written informed consent principle was used. Both oral and written information about the study was provided to potential volunteers. The details included plans for publication as well as the purpose and methodology of the investigation. The confidentiality promise, guidelines for volunteer participation, and contact details for the study’s sponsoring organization and researcher were also included in the material. A form for seeking written informed consent was also included in the written information. Before beginning, written informed consent form completed and returned by each participant.

Consent for publication

‘Not applicable’ for that section.

Competing interests

The authors declare no competing interests.