Head Regional Differences in Thermal Comfort: Evaluating a Novel Surgical Helmet Cooling Method with Phase Change Material

: Thermal comfort is a signiﬁcant factor in maintaining a satisfactory perception of the body temperature and inﬂuences behavioral thermoregulation. This pilot study aimed to investigate regional differences in thermal comfort in the head and neck areas by applying a surgical helmet equipped with cooling pads containing octadecane (CAS 593-45-3) as a phase change material (PCM) in healthy volunteers. Forty-three surgeons and nurses were enrolled. Octadecane is an odorless alkane hydrocarbon with an appearance of white crystal and a melting point of 28 ◦ C. The PCM pads, each with a diameter of 5 cm and containing 7 g of octadecane, were placed between the helmet and the wearer’s head directly in contact with the skin. To identify the areas of the head and neck investigated, the surface was sampled and numbered, with the identiﬁcation of a total of 38 different locations. A climate chamber maintained at 23–26 ◦ C was used for the experiment. Thermal comfort of the stimulated area was reported by the subjects in an evaluation questionnaire at the end of the local stimulation conducted for 1 h. The sensations were reported as 1 (maximum uncomfortable) to 7 (maximum cold comfort), with 4 indicating a neutral sensation. The duration of the thermal comfort effect was also recorded. The highest mean value reported was 6 in ﬁve areas. The frontal region, the frontotemporal region, and the neck region were the areas sensitive to thermal comfort. A neutral sensation was reported in 13 areas. No uncomfortable sensation was reported in any area. This pilot study provides preliminary evidence of the feasibility and potential beneﬁts of integrating PCM cooling pads into surgical helmets to enhance thermal comfort.


Introduction
A sterile surgical helmet system (SSHS) is commonly used in orthopedic surgery to protect both the surgeon and the patient, to reduce microorganism spread to the surgical site, and to protect the surgeon from contamination by blood splashes [1].The International Consensus Group advocated for the use of SSHSs in joint arthroplasty surgery [2].Recently, Rahardja et al. analyzed data recorded by the New Zealand Joint Registry and Surgical Site Infection Improvement Programme and reported that the use of SSHS was associated with a lower rate of periprosthetic joint infection after primary total knee arthroplasty than convention surgical gowning [3].It was also recently demonstrated that SSHSs with high-efficiency particulate air filtration equal to or better than that of the recommended N-95 masks could be protective against coronaviruses such as COVID-19 [4].However, an SSHS can become uncomfortable while performing surgery because increasing heat transfer to the body of the surgeon and the use of these systems have been associated with a variety of symptoms, including fatigue, diaphoresis, nausea, headache, and irritability.Indeed, thermal comfort plays a crucial role in behavioral thermoregulation, as it motivates individuals to seek out optimal thermal conditions to maintain their body temperature within a normal range [5].In fact, the sensation of thermal comfort is shaped by both the thermal state of the skin and the body's core.Furthermore, it represents an emotional experience that can differ in sensitivity and the way it is subjectively perceived across various regions of the body's surface [6,7].Usually, in the context of operating rooms (ORs), a condition of thermal discomfort can be experienced by healthcare professionals and patients.This is highly influenced by physical activity and clothing, as well as by environmental parameters, such as the air temperature and the air-conditioning system's performance, which can impact the thermal comfort of everyone present and also increase the risk of microbial contamination within the room [8].
In a study by Nakamura and colleagues [6], they examined the variations in thermal comfort experienced in different body areas.Their results showed that, during hot conditions, people typically prefer a cooler sensation on their head, whereas in cold conditions, they favor retaining warmth in the abdominal region.The study also highlighted that the head area is more sensitive to cooling compared to other parts of the body, mainly due to increased sudomotor thermosensitivity [9].Thus, cooling the face results in a two-tofive times more powerful suppression of sweating and thermal discomfort than cooling a comparable area [10].Usually, selective head cooling (SHC), also known as therapeutic hypothermia, is a medical procedure that aims to protect the brain in case of cardiac arrest or other brain injury [11,12].The process involves cooling the head, which can reduce the brain's oxygen demand and limit damage to brain cells [13,14].However, it has been shown that SHC can have significant benefits in various circumstances in sports and medicine [15].Indeed, in addition to invasive or demanding methods, such as intravenous infusion of cold solution or a cooling helmet with circulating cold water, SHC can be induced by noninvasive methods such as surface cooling with ice packs [16] and forced cold air cooling [17], contributing to the expansion of its application in healthy subjects and other scenarios.In this context, hyperthermia during physical exercise negatively affects performance, especially in endurance athletes [18].Noninvasive SHC techniques have been reported [19] to reduce local skin temperature in the areas where cooling is applied, resulting in improved local sensation, and they are recommended in athletes to facilitate heat loss and optimize performance [18].Also, sleep quality is affected by the core body temperature, and studies reported that SHC improves subjective sleep quality, thus confirming its effectiveness in inducing a state of well-being [20].The effectiveness of the SHC also depends on the area to which the cooling strategy is applied, as body tissues do not have the same perfusion and thermoregulatory capacity [19].
Consequently, the heat stress induced by the surgical team's use of helmets and impermeable surgical gowns could potentially elicit stress reactions and hinder cognitive functions while performing surgery.Limited research suggests that heat can negatively affect memory, reaction time, and complex motor skills in various settings, but more studies are needed to examine the relationship between heat, occupational stress, thermal comfort, and cognitive and motor performance in surgical teams.Understanding these associations is critical for improving procedures and ensuring the well-being and performance of healthcare professionals in the surgical setting [8,21].
A phase change material (PCM) is a passive two-phase thermal storage technology that utilizes the latent heat of fusion to absorb thermal energy, and it acts as a transient thermal barrier that regulates heat flow and provides cooling.
In light of current knowledge on the clinical usefulness and application of cooling measures that help surgeons increase well-being in the operating room with the possibility of improving their performance, the objective of this pilot study was to test the properties of a new surgical cooling helmet that uses a lightweight, odorless PCM, without consuming energy.In detail, the aim of this study was to examine regional differences in thermal comfort in the head and neck areas by applying a helmet equipped with cooling pads with octadecane as a PCM in healthy volunteer healthcare professionals during their normal work activities.
The starting hypothesis is that heat and thermal discomfort greatly reduce the wellbeing of surgical operators in the operating room, thus also greatly influencing their performance.Individual cooling tools can help greatly but require strong scientific evidence and the identification of appropriate tools and areas of the head to act on.The tool tested in this work could facilitate this step and facilitate further research in this area.

Participants
Forty-three consecutive orthopedic surgeons and nurses were invited to participate in this study between October 2022 and February 2023.The study protocol was approved by the local Ethics Committee, and the research was conducted in compliance with the Declaration of Helsinki.Informed consent was obtained from all individual participants included in the study.Participants satisfying the inclusion criteria were (1) aged greater than 18 years old, (2) healthy individuals, and (3) resident or consultant orthopedic surgeon and surgical nurses.Subjects were instructed to avoid alcohol from the evening of the day before the experiment, caffeinated drinks, hot food, and physical training on the experiment day and not to eat for at least 1 h before participating in the experiment.

Test Procedure
Subjects arrived at the laboratory, changed into a surgical uniform, and entered a climatic chamber with a temperature between 23 and 26 • C and a relative humidity of 50%.A surgical helmet equipped with cooling pads containing octadecane (CAS 593-45-3, THI, Total Healthcare Innovation, GmbH, Feistritz im Rosental, Austria) as the PCM was used for the cooling effect.The PCM is in the solid phase at the beginning of the application; the heat coming from the user's head makes it change into the liquid phase.During the time interval in which the phase change takes place, the temperature of the material remains constant and thus acts as a heat accumulator that can absorb heat without increasing its temperature.How long it takes for the phase change from solid to liquid to be completed depends on the type and amount of material and the amount of heat exchanged, which, in turn, is related to the temperature difference between the material itself and the surface it is in contact with.The temperature of PCM should be lower than the temperature of the skin so that heat can be transferred by conduction from the surface of the user's head to the PCM.No external energy source is required to operate this system.In detail, octadecane is an odorless alkane hydrocarbon with an appearance of white crystal in solid state, a melting point of 28 • C, a density of 0.7786 g/cm at 28 • C, and a standard enthalpy of formation (∆H • f ) of −505.40 ± 2.70 kJ/mol.In the current study, the PCM was packaged in soft round pads, each containing 7 g of octadecane, with a diameter of 5 cm and a maximum height of the central part of 1 cm, and placed between the helmet and the wearer's head, directly in contact with the skin and creating minimal pressure.The outer casing of these pads is made up of two different materials: the part in contact with the head surface is made of polyether polyurethane (aromatic polyether polyurethane) (THI, Total Healthcare Innovation, GmbH, Feistritz im Rosental, Austria), while the part in contact with the helmet is made of Veltex fabric (THI, Total Healthcare Innovation, GmbH, Feistritz im Rosental, Austria) that can be attached to the helmet using Velcro ® (THI, Total Healthcare Innovation, GmbH, Feistritz im Rosental, Austria).The helmet used is made of polypropylene (THI, Total Healthcare Innovation, GmbH, Feistritz im Rosental, Austria), and the neck extension is made of polyurethane foam (THI, Total Healthcare Innovation, GmbH, Feistritz im Rosental, Austria), for a total weight of 124 g.
To identify the areas of the head and neck investigated, the surface was sampled and numbered, excluding the occipital-parietal area with the greatest hair density, with the identification of a total of 38 different locations (Figure 1).
To identify the areas of the head and neck investigated, the surface was sampled and numbered, excluding the occipital-parietal area with the greatest hair density, with the identification of a total of 38 different locations (Figure 1).The geometry and arrangement of the PCM pads are soft at the points of contact points between the helmet and the head of the user (Figure 2).The helmet was worn without the hood and sterile gowns, and the subjects had to carry out his or her normal work activities.The geometry and arrangement of the PCM pads are soft at the points of contact points between the helmet and the head of the user (Figure 2).The helmet was worn without the hood and sterile gowns, and the subjects had to carry out his or her normal work activities.Thermal comfort of the stimulated area was reported by the subjects in an evaluation questionnaire at the end of the local stimulation conducted for 1 h.The sensations were reported as 1 (maximum uncomfortable) to 7 (maximum cold comfort), with 4 indicating neutral sensation.The duration of the thermal comfort effect was also recorded.Thermal comfort of the stimulated area was reported by the subjects in an evaluation questionnaire at the end of the local stimulation conducted for 1 h.The sensations were reported as 1 (maximum uncomfortable) to 7 (maximum cold comfort), with 4 indicating neutral sensation.The duration of the thermal comfort effect was also recorded.

Statistical Analysis
All data were reported to one-decimal accuracy.The mean, standard deviation, and range were noted for continuous variables; counts were recorded for the categorical variables.An area was considered sensitive to cooling thermal comfort in the case of the following: (1) mean value ≥5, (2) standard deviation ≤1 as evidence of the agreement of the result between the observations, and (3) mean duration of thermal comfort >45 min.IBM SPSS Statistics software (version 26, IBM Corp., Armonk, NY, USA) and G*Power (version 3.1.9.2, Institut für Experimentelle Psychologie, Heinrich Heine Universität, Düsseldorf, Germany) were used for database construction and statistical analysis.

Results
The demographics of the included participants are reported in Table 1.Table 2 and Figure 3 show the results for each area investigated in terms of sensation and duration of thermal comfort.The highest mean value reported was 6 in five areas.A neutral sensation with a mean value of 4 was reported in 13 areas.No uncomfortable sensation was reported in any area.Areas 4,13,14,15,16,21,22,27,28,31,32,33,34,35,36,37,and 38 were considered to be sensitive to cooling thermal comfort.Relating to the areas 15, 16, 21, and 22, 90% of the participants reported a value of at least 6, with a mean duration of thermal comfort of 60 min.In relation to areas 33, 34, 35, 36, 37, and 38, 75% of the participants reported a value of at least 5, with a mean duration of thermal comfort of 45 min.

Discussion
The effectiveness of SHC in critical scenarios, such as traumatic brain injury, cardiac arrest, and physical activity, and the luteal phase of the menstrual cycle is supported by previous research [20,22,23].This study demonstrated that the integration of PCM cool pads into surgical helmets as a form of SHC can provide improved thermal comfort.The frontal region, the frontotemporal region, and the neck region are the areas sensitive to thermal comfort.In recent years, there has been some evidence regarding the possible use of refrigeration and individual comfort systems also in the surgical environment, with the aim of improving the work experience for operators in the ORs [8].In a recent review of the literature, the authors examined thermal comfort in hospitals, health centers, and elderly care facilities.They concluded that ensuring a comfortable thermal environment for healthcare professionals and patients is essential, and underexplored areas include the impact of thermal comfort on productivity in hospital settings [24].
Indeed, it is well known that, during surgical procedures, surgeons often experience discomfort due to limited heat dissipation caused by insulating surgical gowns [25], and this discomfort can potentially affect their cognitive performance [26].A recent study aimed to assess the thermal comfort, cognitive performance, core and mean skin temperatures, perceptions of sweaty clothing, fatigue, and exertion among surgeons when using a cooling vest, with a small orthopedic surgeons sample, similar to our study [27].According to these findings, and in line with the application of our study, wearing a cooling vest during surgery may help lower core and skin temperatures, enhance thermal comfort, and reduce perceptions of sweatiness and fatigue [27].This result increases the belief that preliminary data obtained from pilot studies on new equipment should be tested on larger and more varied populations.

Discussion
The effectiveness of SHC in critical scenarios, such as traumatic brain injury, cardiac arrest, and physical activity, and the luteal phase of the menstrual cycle is supported by previous research [20,22,23].This study demonstrated that the integration of PCM cool pads into surgical helmets as a form of SHC can provide improved thermal comfort.The frontal region, the frontotemporal region, and the neck region are the areas sensitive to thermal comfort.In recent years, there has been some evidence regarding the possible use of refrigeration and individual comfort systems also in the surgical environment, with the aim of improving the work experience for operators in the ORs [8].In a recent review of the literature, the authors examined thermal comfort in hospitals, health centers, and elderly care facilities.They concluded that ensuring a comfortable thermal environment for healthcare professionals and patients is essential, and underexplored areas include the impact of thermal comfort on productivity in hospital settings [24].
Indeed, it is well known that, during surgical procedures, surgeons often experience discomfort due to limited heat dissipation caused by insulating surgical gowns [25], and this discomfort can potentially affect their cognitive performance [26].A recent study aimed to assess the thermal comfort, cognitive performance, core and mean skin temperatures, perceptions of sweaty clothing, fatigue, and exertion among surgeons when using a cooling vest, with a small orthopedic surgeons sample, similar to our study [27].According to these findings, and in line with the application of our study, wearing a cooling vest during surgery may help lower core and skin temperatures, enhance thermal comfort, and reduce perceptions of sweatiness and fatigue [27].This result increases the belief that preliminary data obtained from pilot studies on new equipment should be tested on larger and more varied populations.
Van Gaever et al. reported that current technical standards on heating, ventilation, and air conditioning (HVAC) fail to provide a comfortable thermal environment for all members of surgical staff in the OR [28].Moreover, it should be considered that there is a need to look for better wearable personal cooling systems to improve local body cooling while working in indoor environments, as reported by Yang et al., who investigated personal thermal management systems (PTMSs) [29].However, despite the assumption that thermal comfort also plays a decisive role in the therapeutic outcome and in the surgical performance of the operators, there is still a lack of data in this regard.
The use of SHC in the surgical field is not widespread, as it is primarily associated with critical scenarios [30,31].The devices used in the surgical field, in fact, are equipped with a ventilation system for the circulation of air inside the environment that houses the garment, and if, on the one hand, they prevent perspiration from depositing on the scalp, causing discomfort, and help to keep the surgeon refrigerated and oxygenated, on the other hand, this benefit is limited after a certain period of time since the humidity inside the helmet reaches high levels due to exhalation and perspiration, those negatively influencing thermal comfort [32,33], as well as causing fogging of the visor.
Still, satisfaction with the thermal environment in healthcare facilities is influenced by various factors and is subjectively experienced.In ORs, striking a balance between the diverse needs of occupants poses a significant challenge.The patient, who is under anesthesia and minimally clothed, requires a relatively high temperature and humidity to prevent chilling and tissue dehydration.Conversely, the surgical team prefers a cooler, well-ventilated, and drier environment to maintain optimal performance during extended periods.Additionally, individual physiological attributes and the nature of tasks performed can impact the thermal comfort levels [34,35].The occurrence of all of these events can affect the efficiency and performance of the surgical team.Indeed, perioperative personnel can be impacted by heat stress, which occurs when heat becomes trapped beneath their impermeable surgical gowns.This can elevate their body temperature and disrupt their thermal comfort [21].The reaction of the body to heat stress encompasses intricate physiological and psychological mechanisms that have the potential to impact cognitive abilities.In a recent review of eight articles, one study focused on the effects of heat on task performance in male surgical residents within a simulated OR environment [21].The study found no significant differences in task performance between the heat intervention and control conditions.However, participants reported an increase in perceived distractions when exposed to heat.In simulated environments such as climatic chambers, some participants exhibited a reduced cognitive performance in heated conditions, as evidenced by decreased memory, accuracy, and reaction time.Similar decreases in reaction time were observed among foundry workers in warm conditions.Limited research exists exploring the potential connections among heat stress, thermal comfort, and cognitive performance.However, further research is necessary to gain a comprehensive understanding of how occupational heat stress may impact surgical team members.
A recent review of the literature that was conducted on 180 articles investigated the topic of thermal comfort in hospital buildings, offering insights into future research trends.The article is based on the assumption that hospital buildings are obligated to provide various indoor environments that cater to the specific needs of patients and staff [36].One crucial aspect of indoor environmental quality is thermal comfort, which significantly influences both patients' healing processes and the well-being of medical staff.Due to the patients' medical conditions and compromised immune systems, their thermal comfort takes precedence.Thus, authors conducted a scientometric analysis to identify key research themes, including influencing factors, field surveys, improvement measures, and energysaving strategies related to thermal comfort.The primary finding suggested that ventilation systems play a vital role in maintaining acceptable and thermally comfortable conditions for patients and medical teams.Furthermore, it is worth noting that the perception of acceptable thermal comfort is highly individual, with substantial variations depending on the patient's health status and the nature and intensity of activities undertaken by the staff.The review also addressed current strategies to reduce energy consumption.Notable concerns, such as the limitations of the predicted mean vote as a measure of thermal comfort and the influence of factors like gender and age, were also emphasized.However, it is striking that the possibility of using a surgical helmet equipped with cooling pads containing PCM is included neither in data already present nor in future prospects, therefore representing a new and promising frontier of clinical development and research.
To determine thermal comfort, it would be possible to use cooling systems with a very low temperature material (e.g., a 4-10 • C gel extracted from refrigerator).However, this solution is not effective because the low temperature causes the vapor to condense with the formation of drops of water on the head and face of the helmet user.For this reason, the idea was to provide a temporary reduction in head temperature using a PCM, which can be integrated into the helmets used in surgery to improve the comfort of the surgeon and scrubbed nurse and, thereby, their performance, reducing fatigue and allowing for a supply of oxygen.Indeed, this method avoids the occurrence of condensation, as the material used to achieve the cooling effect has a temperature similar to room temperature (18-26 • C) but, in any case, considerably lower than that of the body (37 • C).The PCM used in the current study is octadecane; we used it due to its melting point at 28 • C, which is well suited when considering the average surface temperature of the human body.We also conducted preliminary evaluations with other PCMs, such as hexadecane and heptadecane, but excluded them due to their lower melting points at 18 and 22 • C, respectively.To evaluate their effectiveness, these cooling pads have begun to be tested on healthy subjects during the performance of their work, medical, nursing, or care activities in environments with ambient temperatures ranging between 23 and 26 • C, therefore making them above the maximum temperature limit allowed inside the ORs.What has been found is a subjective benefit provided by these cool pads, mostly from those placed in positions 13, 14, 15, and 16, occupying the frontal region; in positions 21, 22, 27, and 28, occupying the frontotemporal region; and in positions 31, 32, 33, 34, 35, 36, 37, and 38, occupying the neck region.The reason for this is that the most important blood vessels are located in the frontal, temporal, and occipital regions, and they are therefore exposed to greater temperature fluctuations, especially during heat stress.
Cooling the neck may be advantageous because of the neck's proximity to large blood vessels [37], and cooling the neck is strongly recommended during exercise because the neck is readily accessible compared to other body areas, is in close proximity to the thermoregulatory center, and is an area of high alliesthesial thermosensitivity [38].
There is some evidence that hyperthermia of the head plays a key role in impairing cognitive performance in highly specialized and precise activities [10,21,39], just as there are results of studies demonstrating that lowering the head temperature in conditions of stress and high ambient temperature can have positive effects on individual performance [40].This is also true in surgical settings, as heat stress can affect the surgical team due to the accumulation of heat beneath their impervious protective surgical gowns, leading to elevated body temperature and affecting their thermal comfort.The body's response to heat stress involves intricate physiological and psychological processes that can influence an individual's cognitive performance.Simulated environments, such as climatic chambers, demonstrated that participants exposed to heat exhibited reduced cognitive performance, including decreased memory, accuracy, and reaction time [21].
Another important aspect of discussion with respect to the results obtained is to evaluate whether certain specific areas do have more influence than others on the thermal comfort of subjects, with consequent practical implications on the surgical performance of the operators.Indeed, there appear to be more factors regarding devices used that influence this point, including heat distribution/transfer, sweat management, individual sensitivity to cooling, helmet design/features, environmental conditions, and operators' health and physiology [8,[41][42][43].However, there are currently no supporting works in the literature that address a single application standard; therefore, exploratory studies such as ours could help identify variables that can be used for future applications.
Therefore, when considering activities performed in the operating room (OR), maintaining personnel's thermal comfort is crucial.Indeed, negative thermal sensations can cause discomfort that hampers the performance of the surgical team.Thus, it is essential to manage thermal comfort characteristics regularly to ensure air quality and serve as indicators of potential issues.Deviations in temperature conditions may lead to operator discomfort and, consequentially, impact the surgical performance and outcome.
Moreover, it should also be considered that ensuring thermal comfort is essential for creating a conducive and effective working environment.In the context of ORs, achieving thermal comfort for the surgical team can be influenced by several factors, including the environment cooling system and the working conditions specific to ORs, as well as the mandatory surgical clothing.Additionally, factors such as the type of procedure, patient requirements, individual physiological characteristics, and activity levels can impact thermal comfort.
On this note, a recent study that was conducted to investigate the factors affecting the thermal comfort of surgeons revealed that the ventilation and temperature perceived in the OR, as well as the impact of their clothing, had a detrimental effect on thermal comfort.Indeed, this study, based on surgeons' feedback, revealed that only 33.8% of participants expressed satisfaction with the thermal conditions experienced in the OR [44].In particular, women, personnel wearing additional clothing, and those who voiced complaints about ventilation or temperature were more likely to experience thermal discomfort.Consequently, participants who perceived inadequate thermal comfort had a detrimental impact on their health and work performance [44].
The limitations of this pilot study include the small sample size, which may limit the generalizability of the findings.With a limited number of participants, the study may not capture the full range of responses or possible variations in efficacy and tolerability of the novel helmet cooling method with PCM.Therefore, the findings may not be representative of the broader population or individuals with specific medical conditions or characteristics.Moreover, in consideration of the exploratory nature of this pilot study, a small population of healthcare providers in orthopedics was taken into consideration in order to evaluate the feasibility and success of the study.In the future, studies with a larger and more varied series of surgeons, nurses, and operators, including those belonging to other surgical disciplines, will need to be involved.
Additionally, as a pilot study, the primary focus was on feasibility and initial evaluation of the new cooling method.The study may lack statistical power to detect subtle effects or establish definitive conclusions about the efficacy or safety of the intervention.Further studies with larger sample sizes and rigorous study designs are necessary to confirm and validate the results observed in this preliminary investigation.Furthermore, the study focused solely on healthy volunteers, and the outcomes may not reflect the responses and experiences of individuals with medical conditions or specific vulnerabilities.Despite the growing interest in the subject, there is a limited amount of research addressing the potential relationships between thermal comfort and cognitive and surgical performance.The PCM technology, with proper positioning of pads along the head and neck areas to obtain the optimal thermal regulation, can be applied in future SSHS's design to enhance comfort during surgical procedures.Further research is needed to gain a comprehensive understanding of how improved thermal comfort can impact surgical team members.

Conclusions
In this cross-sectional pilot study, we aimed to investigate regional differences in thermal comfort in the head and neck areas by using a surgical helmet equipped with cooling pads containing PCM. Forty-three surgeons and nurses participated in the study, with PCM pads placed between the helmet and the wearer's head.Subjects reported their thermal comfort in the stimulated area through a questionnaire, and the duration of the thermal comfort effect was recorded.The frontal region, frontotemporal region, and neck region were found to be sensitive to thermal comfort, and no discomfort was reported in any area.Thus, our findings suggest that integrating PCM cooling pads into surgical helmets could enhance thermal comfort, although further research is needed.Informed Consent Statement: All participants signed informed consent before any procedure took place.Written informed consent for the publication of the photo was collected from the person who appears in Figure 2.

Figure 1 .
Figure 1.Anatomical location of the head and neck areas investigated was sampled and numbered.

Figure 1 .
Figure 1.Anatomical location of the head and neck areas investigated was sampled and numbered.

Figure 2 .
Figure 2. The helmet equipped with cooling pads with phase change material in frontal (A) and right oblique (B) views.

Figure 2 .
Figure 2. The helmet equipped with cooling pads with phase change material in frontal (A) and right oblique (B) views.

Figure 3 .
Figure 3. Radar chart showing the sensation of thermal comfort for each area investigated.All around are the 38 head and neck areas investigated.The vertical numbers from 0 to 6 represent the mean value (blue) and the standard deviation (orange) calculated for each area.An area was considered sensitive to cooling thermal comfort in the case of (1) a mean value ≥5 and (2) a standard deviation ≤1.

Figure 3 .
Figure 3. Radar chart showing the sensation of thermal comfort for each area investigated.All around are the 38 head and neck areas investigated.The vertical numbers from 0 to 6 represent the mean value (blue) and the standard deviation (orange) calculated for each area.An area was considered sensitive to cooling thermal comfort in the case of (1) a mean value ≥5 and (2) a standard deviation ≤1.

Figure 4 .
Figure 4. Sensitive areas to thermal comfort in blue among all areas sampled and numbered.

Figure 4 .
Figure 4. Sensitive areas to thermal comfort in blue among all areas sampled and numbered.

Author
Contributions: Conceptualization M.M., G.G. and O.G.; methodology, R.d.F., M.M. and O.G.; formal analysis, M.M. and R.d.F.; data curation, M.M.; writing-original draft preparation, M.M., R.d.F. and O.G.; writing-review and editing, R.d.F., M.M., G.G., F.F. and O.G.; supervision, G.G. and O.G.All authors have read and agreed to the published version of the manuscript.Funding: This research received no external funding.Institutional Review Board Statement: The study was conducted in accordance with the Declaration of Helsinki and approved by the Institutional Review Board of Magna Graecia University of Catanzaro (protocol code 08/22, 12 September 2022).

Table 1 .
Baseline characteristics of included participants.
SD, standard deviation; n, number of cases.

Table 2 .
Results for each area investigated in terms of sensation and duration of thermal comfort.
SD, standard deviation; na, non-applicable.The areas that satisfied all the criteria to be considered as sensitive to thermal comfort are shown in bold.Surgeries 2023, 4, FOR PEER REVIEW 7