Use of the Airstretcher with dragging may reduce rescuers' physical burden when transporting patients down stairs.

Transporting patients down stairs by carrying is associated with a particularly high fall risk for patients and the occurrence of back pain among emergency medical technicians. The present study aimed to verify the effectiveness of the Airstretcher device, which was developed to reduce rescuers' physical burden when transporting patients by dragging along the floor and down stairs. Forty-one paramedical students used three devices to transport a 65-kg manikin down stairs from the 3rd to the 1st floor. To verify the physical burden while carrying the stretchers, ratings of perceived exertion were measured using the Borg CR10 scale immediately after the task. Mean Borg CR10 scores (standard deviation) were 3.6 (1.7), 4.1 (1.8), 5.6 (2.4), and 4.2 (1.8) for the Airstretcher with dragging, Airstretcher with lifting, backboard with lifting, and tarpaulin with lifting conditions, respectively (p < 0.01). Multiple comparisons revealed that the Airstretcher with dragging condition was associated with significantly lower Borg CR10 scores compared with the backboard with lifting condition (p < 0.01). When the analysis was divided by handling position, estimated Borg CR10 values (standard error) for head position were 4.4 (1.3), 2.9 (0.9), 3.2 (0.8), and 4.0 (1.1) for the Airstretcher with dragging, Airstretcher with lifting, backboard with lifting, and tarpaulin with lifting conditions, respectively, after adjusting for participant and duration time (F = 1.4, p < 0.25). The estimated Borg CR10 value (standard error) for toe position in the Airstretcher with dragging condition was 2.0 (0.8), and the scores for the side position were 4.9 (0.4), 6.1 (0.3), and 4.7 (0.4) for the Airstretcher with lifting, backboard with lifting, and tarpaulin with lifting conditions, respectively, after adjusting for participant and duration time (F = 3.6, p = 0.02). Transferring a patient down stairs inside a house by dragging using the Airstretcher may reduce the physical burden for rescuers.

Introduction

Emergency medical technicians (EMTs) respond to emergency situations immediately, treat patients in a timely fashion, make decisions about which hospitals to transport patients to, and transfer patients quickly. Some studies reported the frequent occurrence of adverse events during their activities, including back pain among EMTs and fall events for patients [1-4]. An observational study reported that the occurrence of back pain during work was linked to EMTs leaving their jobs or being transferred to a different role [5].

Although powered stretchers with automated loading systems may be effective for preventing musculoskeletal disorders among EMTs and fall events for patients when loading patients into ambulances, the use of manual stretchers is still the most common method of patient transport in Japan [6, 7]. Furthermore, soft stretchers must be used in some situations because corridors and stairs inside houses in Japan are particularly narrow compared with those of other countries.

A variety of transferring instruments are available, including the tarpaulin and rescue sheet (Ferno Japan, Inc., Japan), which are commonly used inside houses. The rigid backboard is a motion restriction device designed for cases of spinal injury and is commonly used in callouts when transferring from the scene to the main stretcher. However, during carrying, transporting patients down stairs is associated with a particularly high fall risk for patients and the occurrence of back pain among EMTs. In a previous study, we identified the occurrence of falls and back pain during on-scene activities as being linked to severe accidents in some cases [3].

The Airstretcher® (Airstretcher, Inc., CA, USA) was recently developed to transport patients by dragging along the floor and stairs. This device has the benefit of reducing the risk of fall events by avoiding the need to lift the patient. We hypothesized that the Airstretcher may decrease the physical burden of EMTs during callouts compared with other methods. The purpose of the present study was to assess the effectiveness of this device for decreasing rescuers’ physical burden when carrying patients down stairs.

Materials and methods

This study was approved by the Niigata University of Health and Welfare Ethics Committee (18452–200717). The study’s objective, significance, methods, and the process of opting out were explained to participants in writing and verbally beforehand. The participants provided written informed consent.

Participants

The participants were 41 third-year paramedical students. Participants had acquired basic paramedical knowledge and had experience with the use of soft stretchers including a tarpaulin and backboards in simulation training.

Before the study, participants attended a 45-minute lecture about how to use soft stretchers, and a 45-minute training session involving the transport of a 65-kg manikin down stairs using an Airstretcher with lifting and with dragging.

Instruments (Fig 1)

We compared the use of three types of instruments for transporting patients down stairs: 1) the Airstretcher, 2) the backboard (Ferno Japan, Inc., Japan) and 3) the tarpaulin stretcher. Each stretcher was loaded with a 65-kg manikin, and groups of three participants were instructed to carry it from the 3rd floor to the 1st floor. Because the students had already been grouped into classes at University, we decided to recruit each group to participate in the study. Participants used the stretchers in the order in which they were accustomed to using them. Therefore, each group carried the manikin using the tarpaulin first, followed by the backboard, the Airstretcher by lifting, and the Airstretcher by dragging. When carrying the manikin, participants selected their own holding position between the head/side/toe sides. When transporting the manikin using the Airstretcher carrying by dragging, two participants carried the instrument, using wide shoulder slings on the head and toe sides of the stretcher. Eleven participants did not carry the manikin when they used the Airstretcher by dragging, because the device does not require more than two operators. Participants decided themselves in each group who would not operate the Airstretcher by dragging. For this reason, we excluded the data of 11 participants from the analysis. Participants were given a sufficient rest period between each carrying session.

Instruments.

The upper left image shows the use of the Airstretcher by lifting. The upper right image shows the use of the Airstretcher by dragging without lifting. The lower left image shows the backboard being carried by lifting. The lower right image shows the tarpaulin being carried by lifting.

Finally, the comparative performance of each instrument was examined using a questionnaire survey.

The Airstretcher (carrying by lifting)

The Airstretcher (www.airstretcher.jp/) has a Cappy original mat produced by Vinal Technology, Inc., and has a length of 192 cm × width of 63 cm × height of 4.5 cm, and a weight of 5.5 kg. The bottom is made of special thermoplastic polyolefin or polyethylene plastic, with a thickness of 2 mm. The head and toe sides of the stretcher have wide slings which can be worn over the shoulder. The instrument has four fixing belts and six gripping points, including the head and toe sides. EMTs generally carry patients by lifting with three or more personnel. The Airstretcher is a registered trademark of Cappy International, Inc., Japan.

The Airstretcher (carrying by dragging, without lifting)

The Airstretcher can be used to transport a patient by dragging by a single operator. In Japan, this stretcher has already used to hospitals, nursing homes, ambulance services, schools, police departments, the Self-Defense Forces, and other institutions. By dragging the Airstretcher, it is relatively easy to transport a patient down narrow stairs with one or two operators. This instrument can be used on any surface, including asphalt, gravel, or iron floor plates. When the EMT opens the air valve on the stretcher, air automatically flows into the mattress.

The backboard (carrying by lifting)

The high-tech backboard (http://www.ferno-jp.com/) is made of acrylonitrile butadiene styrene plastic, which prevents blood and body fluids from absorbing into the interior and allows easy cleaning. The backboard is commonly used for restricting spinal movement of injured persons, mainly in trauma cases. This instrument has length of 183 cm × width of 41 cm × height of 4.5 cm, a weight of 5.9 kg, and a maximum load of 159 kg.

The tarpaulin (carrying by lifting)

This instrument enables transport in narrow stairways, arund tight bends, and in elevators. It is equipped with an anchoring belt to help the patient remain calm. The instrument is constructed from a waterproof tarpaulin fabric and has a length of 180 cm × width of 48 cm × height of 1 cm, and a weight of 1.8 kg. The instrument has two fixing belts and four gripping points, including the head and toe sides.

Evaluation

To verify the physical burden of carrying the stretchers, ratings of perceived exertion were measured using the Borg CR10, a category ratio (CR) scale (Table 1) from 1–10, that was completed immediately after each task. Additionally, pulse rates after the task in all participants were measured [8] using fingertip pulse oximeter. The Borg CR10 scale, pulse rates and the carrying duration were recorded and put it into the database by researchers.

Table 1

The Borg CR10 scale [8].

Score	Level of exertion
0	No exertion at all
0.5	Very, very slight (just noticeable)
1	Very slight
2	Slight
3	Moderate
4	Somewhat severe
5	Severe
6
7	Very severe
8
9	Very, very severe (almost maximal)
10	Maximal

CR: category ratio

Data analysis

In the univariate analyses of continuous variables, one-way analysis of variance was applied. Multiple comparisons were calculated using the Tukey-Kramer test. To examine the comparative performance among the instruments, we used multiple least squares regression analysis. With a significance level of p = 0.05 and a power value of 0.8 at an effect size of 0.1, we estimated that the study needs 27 participants in each group. All data were analyzed using JMP software (version 14.3; SAS Institute, Cary, NC, USA). For each analysis, the null hypothesis was evaluated with a two-sided significance level of p < 0.05.

Results

Thirty-six male and five female students participated in the study. Their mean height (standard deviation [SD]) was 169.8 (6.2) cm, and their mean weight (SD) was 62.9 (8.5) kg.

Borg CR10 scale (Fig 2)

Overall comparisons

Mean (SD) scores on the Borg CR10 scale were 3.6 (1.7), 4.1 (1.8), 5.6 (2.4) and 4.2 (1.8) for the Airstretcher with dragging [AD], Airstretcher with lifting [AL], backboard with lifting [BL] and tarpaulin with lifting [TL] conditions, respectively. The scores were highest when participants carried a manikin using the TL and lowest when they used the AD (p < 0.01). Multiple comparisons revealed that the AD condition was associated with significantly lower Borg CR10 scores compared with the BL condition (p < 0.01). The TL condition was associated with significantly lower Borg CR10 scores compared with the BL condition (p < 0.01).

The Borg CR10 scale.

* p < 0.01, Tukey-Kramer’s HSD test.

Sub-group analysis

Because the multiple least square’s regression analysis revealed that instrument and handling position exhibited a significant interaction (p < 0.01, Table 2), we applied sub-group analysis.

Table 2

Multiple least squares regression analysis.

	p-value
Interaction (instrument and position)	< 0.01
Instruments	< 0.01
Position (head or side/toe)	< 0.01
Participants	0.02
Duration	0.04

Summary of fit: root mean squared error (RMSE) = 1.65, R2 = 0.59.

Interaction between the Borg CR10 scale and other factors. As shown in Fig 3A, estimated values of the Borg CR10 scale (standard error [SE]) were 2.8 (0.6), 4.0 (0.4), 4.9 (0.4) and 4.5 (0.4) for the AD, AL, BL and TL conditions, respectively, after being adjusted for participant, handling position and duration time (F = 3.1, p < 0.01). Multiple comparisons revealed a significant difference between the AD and the BL conditions (p = 0.02).

Fig 3

The Borg CR10 scale after adjustment for other factors.

a: The Airstretcher with dragging, b: The Airstretcher with lifting, c: The Backboard with lifting, d: The Tarpaulin with lifting.

Head position. When the analysis was divided by handling position (Fig 3B), estimated values (SE) of the Borg CR10 scale of head position were 4.4 (1.3), 2.9 (0.9), 3.2 (0.8) and 4.0 (1.1) for the AD, AL, BL and TL conditions, respectively, after adjusting for participant and duration time (F = 1.4, p < 0.25). Multiple comparisons revealed no significant differences among instruments.

Toe and side positions. As shown in Fig 3C, the estimated value on the Borg CR10 scale (SE) of toe position in the AD condition was 2.0 (0.8), and the scores for the side position were 4.9 (0.4), 6.1 (0.3) and 4.7 (0.4) for the AL, BL and TL conditions, respectively, after adjusting for participant and duration time (F = 3.6, p = 0.02). Borg CR10 scores were lower in the AD condition compared with those in the AL condition (p = 0.02) and the BL condition (p < 0.01). Scores were lower in the TL condition compared with those in the BL condition (p = 0.04).

Pulse rates (Fig 4)

Pulse rates after the task were 136.4 bpm, 132.5 bpm, 135.5 bpm and 127.9 bpm for the AD, AL, BL and TL conditions, respectively. However, the univariate analyses did not reveal any significant differences in pulse rates among the four carrying methods (p = 0.36).

Carrying duration (Fig 5)

Mean (SD) carrying durations were 83.7 s (17.1), 51.1 s (6.2), 54.9 s (9.2) and 45.3 s (5.1) in the AD, the AL, the BL and the TL conditions, respectively (p < 0.01). The duration in the AD condition was significantly longer compared with the other conditions (p < 0.01 for each). The duration in the TL condition was significantly shorter than that in the BL condition (p < 0.01).

Duration of carrying.

* Compared with others (p < 0.01). † Compared with the Airstretcher with dragging (p < 0.01) and the Tarpaulin with lifting (p < 0.05). §Compared with the Airstretcher with dragging (p < 0.01) and the Tarpaulin with lifting (p < 0.01).

Questionnaire surveys

Finally, we asked the participants which instruments were the most and least physically demanding to use. Thirty-two (78.0%) reported that the BL was the most physically demanding, and seven (17.1%) reported that the TL was the most physically demanding. In addition, 21 (51.2%) participants reported that the AD was the least physically demanding, and 17 (41.5%) participants reported that the TL was the least physically demanding.

Discussion

The present study demonstrated the superiority of using the Airstretcher by dragging for when rescuers transport a patient from an upper floor to a lower floor via the stairs in terms of physical burden, compared with other methods. More than half of the participants reported that using the Airstretcher by dragging involved the lowest physical burden, even though this was their first experience using the Airstretcher instrument. In addition, ratings of perceived exertion were lowest for the Airstretcher with dragging condition, compared with the other methods. Thus, the Airstretcher may have benefits over other soft stretchers for decreasing physical burden among EMTs, despite the tarpaulin and the backboard being most commonly used for carrying patients inside a house.

The optimal method for carrying patients in pre-hospital settings has not been clarified in previous studies. However, one study reported that lifting techniques with soft stretchers have failed to reduce lifting-related injuries and are unsafe for providers and patients [9]. Our previous study confirmed that fall events among patients often occur during carrying on the scene, by analyzing the database of Fire and Disaster Management Agency in Japan. In Japan, soft stretchers are commonly used, and may be linked to falls among patients. In the current study, we explored the performance of a newly developed patient-carrying instrument designed to decrease the fall risk and physical burden. The current findings suggest that using the Airstretcher with dragging may decrease the physical burden for EMTs.

As an index of physical burden, we compared participants’ ratings of perceived exertion and pulse rate after the completion of each task. The carrying duration when using the Airstretcher with dragging was longer than that in the other conditions. However, estimated values of the Borg CR10 score tended to be lower in the Airstretcher with dragging condition compared with the other conditions. Participants were more familiar with handling the backboard and the tarpaulin compared with the Airstretcher and may have known the optimal amount of hand pressure to use while handling both instruments, but not the Airstretcher. The bottom of the Airstretcher is made of a plastic material, which is a smooth surface that slides easily. Duration of carrying may have increased as they tried to grasp the stretcher firmly to prevent it from sliding down the stairs. Attempting to operate the Airstretcher carefully may have been linked with the longer carrying duration we observed. It should be noted that Borg CR10 scores exhibited a wide range in the Airstretcher with dragging condition. An experimental study revealed that increased muscle oxygenation for experienced subjects is less than that for novice subjects [10-13]. Therefore, muscle oxygenation may differ between trained and untrained individuals. Further training in the handling of the Airstretcher may enable safer and less stressful patient transport.

Limitations

The current study involved several limitations. First, this study sought to identify the most effective instrument for transporting patients down stairs in a pre-hospital setting. However, the operators were students rather than EMTs with work experience. The Airstretcher, which is a newly designed instrument, is not widely used in emergency medical services in Japan. Although we assume that EMTs are likely to have similar preferences to paramedical students, this assumption remains to be verified.

Second, we did not compare the Airstretcher with the Stairchair, which is commonly used internationally. However, use of the Stairchair involves a risk of damaging surfaces inside a house, and stairs inside Japanese houses are typically narrow and constructed from wood. Furthermore, a flat position is typically more suitable in situations where a patient is unconscious. For these reasons, we did not examine this device in the current study.

Finally, the characteristics of the operator, including sex, weight and height may affect the outcome. These effects have been reported in previous studies [14, 15]. The sample size in the current study was larger than that in several other studies of this issue. Therefore, we believe that the present results are meaningful.

Conclusion

Transferring a patient down stairs inside a house by dragging using the Airstretcher may reduce the physical burden for rescuers. Further verification by EMTs is necessary.

10 Jul 2022

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Reviewer #1: Comments

This manuscript reports the assessment of the effectiveness of the Airstretcher® device for decreasing emergency medical technicians’ physical burden when carrying patients downstairs. The Airstretcher was compared to two other instruments for transporting patients downstairs, namely the backboard and the tarpaulin stretcher. Please find below a few comments for your consideration. Line numbers in comments refer to the PDF file generated after manuscript submission.

Major comments

1. Lines 71-79. It is unclear whether all participants tested all 3 instruments (i.e. a repeated-measurement analysis), or if they were assigned to groups (i.e., independent-group analysis). I assume the latter was performed, but even in this case there is no description on how group allocation was performed (e.g. randomization?).

2. Lines 82-84. What was the order of testing the three instruments, fixed or random? What was the rationale for the choice of sequence?

3. Lines 88-89. It is unclear what is meant by ‘Most of the participants carried the manikin three times using the three types of stretcher’. How were these 11 participants selected? How the three repetitions for each instrument were aggregated (e.g. mean, smallest effort)?

4. Lines 130-132. Given the adopted scale (modified Borg scale) and vital sign (hear rate), I suggest using ‘perceived exertion’ rather than ‘physical burden’ across the manuscript.

5. Lines 133-134. How did you record the duration of the task?

6. Lines 136-137. Following comment #1, it is unclear what ANOVA was applied?

Minor comments

1. Abstract. Consider reporting SD alongside the means or the overall effect of the omnibus ad hoc tests (F-test and eta-sq values) rather than mean values with p values alone.

2. Lines 108-110. Why is it important to report the number of sold units in Methods section?

Reviewer #2: The submitted paper from Takei et al. proposes to investigate the potential benefits of using a Airstretcher – a newer device to aid EMT personnel when transporting incapacitated individuals – compared to traditional devices. In the experiment itself, students in EMT training performed the task of transporting a mannikin using either the Airstretcher or one of the more traditional devices. The outcomes measures included Borg’s RPE reporting, heart rate, and questionnaire responses. As reported by the authors, the Airstretcher may reduce the physical burden on EMT personnel compared to more traditional measures, although the current study design does present a few minor limitations.

1. The introduction was well-written and focused on the key aspects of the relevant background information for the study. One point of minor confusion may be lines 56-58, where the authors discuss the potential for falls, and how dropping the patient may lead to severe injuries. I would suggest including a sentence or clarifying here – given that incidence of drops/falls is not part of the present study, how does this relate to the physical burden of traditional devices versus the Airstretcher? Would the Airstretcher likely have a lower drop rate?

2. In the Methods Section (lines 77-79), this portion appears to be a bit repetitive. The specific details provided in this paragraph could likely be combined with the above sentences, to reduce unnecessary repetition.

3. In the Methods Section (line 133), it may be helpful to clarify further how the pulse rate was measured. This may help address questions about variability in the pulse rate measurements, etc.

4. The Results Section was very thorough, and provided detailed information about the outcomes of the study. One minor concern throughout was the readability – while minor, it may help with the ‘flow’ of the results section to simplify the naming of the four conditions with acronyms. In lines 152-153 where the four conditions are listed, parentheses could be included after each condition with an abbreviation or acronym. This would help reduce some of the longer sentences/phrases later in the results section, and clarify the overall section for the reader.

5. Also in the Results Section, it may help to ‘break up’ the Borg RPE section with a few subheadings. This would clarify to the reader what specific aspect of the Borg RPE reporting that the current section is addressing.

6. The Discussion Section was very well done, and easy to follow. One minor point would be the sentence in lines 247-248 dealing with muscle oxygenation. For those familiar with the relationship between muscle oxygenation and physical exertion/workload, this sentence does provide further evidence of the physical demands of transporting patients. However, this sentence may be more clear if the authors expanded upon the interpretation of the findings that muscle oxygenation differs for trained versus untrained individuals, given that the nature of this paper may interest readers who are not as familiar with concepts such as skeletal muscle oxygenation.

7. The Limitations portion of the Discussion Section was well-written, and sets up future directions in a concise but meaningful way. This section was particularly well-handled.

8. One concern in the Figures – Figure 2 presents a box-and-whisker plot for the Borg RPE values. However, this Figure is a bit unclear given the alignment of the dots and variability of their placement. It may help clarify the figure to align the dots over the condition they represent, or choose some other way to represent the individual data.

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Reviewer #1: Yes: Arthur de Sá Ferreira

Reviewer #2: No

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31 Jul 2022

Response to Reviewers

Dear Editors and Reviewers

Thank you very much for reviewing our manuscript and offering valuable advice.

We have addressed your comments with point-by-point responses and revised the manuscript accordingly.

We wish to express our appreciation to the Reviewers for their insightful comments, which have helped us significantly improve the paper.

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3) The data set has been uploaded as the Supporting Information file, and we mentioned it in the cover letter. Please confirm the file.

#0-4. Journal requirements

4. We note that you have stated that you will provide repository information for your data at acceptance. Should your manuscript be accepted for publication, we will hold it until you provide the relevant accession numbers or DOIs necessary to access your data. If you wish to make changes to your Data Availability statement, please describe these changes in your cover letter and we will update your Data Availability statement to reflect the information you provide.

Reply to journal requirements

4) We would like to upload our data set as “Data Availability File” when we resubmit, not to provide repository information. Therefore, we wrote it in the covering letter.

#0-5. Journal requirements

5. Your ethics statement should only appear in the Methods section of your manuscript. If your ethics statement is written in any section besides the Methods, please delete it from any other section.

Reply to journal requirements

5) We confirmed the ethics statement only appeared int the Methods section in the manuscript.

#0-6. Journal requirements

6. We note that Figure 1 includes an image of a participant in the study…

Reply to journal requirements

6) Thank you for pointing it out. We have masked individual faces in the photograph of Fig 1 so that they can not be identified. Please confirm Fig 1.

Reviewer 1 comments

#1-1. Reviewer-1

1. Lines 71-79. It is unclear whether all participants tested all 3 instruments (i.e. a repeated-measurement analysis), or if they were assigned to groups (i.e., independent-group analysis). I assume the latter was performed, but even in this case there is no description on how group allocation was performed (e.g. randomization?).

Reply to Reviewer

1) We wish to express our appreciation to the Reviewer for their insightful comments, which have helped us significantly improve the paper. We have revised the Methods section to establish a clearer method as follow:

- “Because the students had already been grouped into classes at university, we decided to recruit each group to participate in the study. Participants used the stretchers in the order in which they were accustomed to using them. Therefore, each group carried the manikin using the tarpaulin first, followed by the backboard, the Airstretcher by lifting, and the Airstretcher by dragging.”

#1-2. Reviewer-1

2. Lines 82-84. What was the order of testing the three instruments, fixed or random? What was the rationale for the choice of sequence?

Reply to Reviewer

2) Thank you for providing these insights. As mentioned above, because the students had already been grouped into classes at university, we decided to recruit each group to participate in the study. Participants used the stretchers in the order in which they were accustomed to using them. Therefore, each group carried the manikin using the tarpaulin first, followed by the backboard, the Airstretcher by lifting, and the Airstretcher by dragging.”. In addition, we have mentioned in the same section as below:

- “When carrying the manikin, participants selected their own holding position between the head/side/toe sides. When transporting the manikin using the Airstretcher carrying by dragging, two participants carried the instrument, using wide shoulder slings on the head and toe sides of the stretcher. Eleven participants did not carry the manikin when they used the Airstretcher by dragging, because the device does not require more than two operators.”

#1-3. Reviewer-1

3. Lines 88-89. It is unclear what is meant by ‘Most of the participants carried the manikin three times using the three types of stretcher’. How were these 11 participants selected? How the three repetitions for each instrument were aggregated (e.g. mean, smallest effort)?

Reply to Reviewer

3) Thank you for providing these insights. We deleted the sentence “Most of the participants carried the manikin three times using the three types of stretcher”, and added following sentences:

- “Eleven participants did not carry the manikin when they used the Airstretcher by dragging, because the device does not require more than two operators. Participants decided themselves in each group who would not operate the Airstretcher by dragging.”

The question of "how the three repetitions for each instrument were aggregated" has been mentioned the sentences in the Evaluation part. However, we revised the sentences as,

– "...that was completed immediately after each task. Additionally, pulse rates after the task in all participants were measured, and the Borg CR10 scale, pulse rates and the carrying duration were recorded by researchers."

#1-4. Reviewer-1

4. Lines 130-132. Given the adopted scale (modified Borg scale) and vital sign (hear rate), I suggest using ‘perceived exertion’ rather than ‘physical burden’ across the manuscript.

Reply to Reviewer

4) This is a valid assessment of your suggestion; however, in the fields of pre-hospital emergency care as we referenced several articles, same studies using same methods called/defined current evaluation as "physical burden". We would like to standardize a definition as "physical burden". However, if you disagree with this, we could change it from "physical burden" to "perceived exertion".

#1-5. Reviewer-1

5. Lines 133-134. How did you record the duration of the task?

Reply to Reviewer

5) As replied above, we revised/added the sentence “that was completed immediately after each task. Additionally, pulse rates after the task in all participants were measured [8], and the Borg CR10 scale, pulse rates and the carrying duration were recorded and put it into the database by researchers."

#1-6. Reviewer-1

6. Lines 136-137. Following comment #1, it is unclear what ANOVA was applied?

Reply to Reviewer

6) Thank you for providing these insights. We added a word in the sentence as below:

- “In the univariate analyses of continuous variables, one-way analysis of variance was applied.”

#1-7. Reviewer-1, as minor comments

1. Abstract. Consider reporting SD alongside the means or the overall effect of the omnibus ad hoc tests (F-test and eta-sq values) rather than mean values with p values alone.

Reply to Reviewer

7) Thank you for the comment. We have added reporting SDs and F values in the Abstract and Result section. Please confirm it.

#1-8. Reviewer-1, as minor comments

2. Lines 108-110. Why is it important to report the number of sold units in Methods section?

Reply to Reviewer

8) Thank you for pointing it out. We revised the word from “sold” to “used”. Please confirm it.

- “In Japan, this stretcher has already used to hospitals, nursing homes, ambulance services, schools, police departments, the Self-Defense Forces, and other institutions.”

Reviewer 2 comments

#2-1. Reviewer-2

1. The introduction was well-written and focused on the key aspects of the relevant background information for the study. One point of minor confusion may be lines 56-58, where the authors discuss the potential for falls, and how dropping the patient may lead to severe injuries. I would suggest including a sentence or clarifying here – given that incidence of drops/falls is not part of the present study, how does this relate to the physical burden of traditional devices versus the Airstretcher? Would the Airstretcher likely have a lower drop rate?

Reply to Reviewer

1) We wish to express our appreciation to the Reviewer for their insightful comments, which have helped us significantly improve the paper. As the reviewer gave us the suggestion, the incidence of drops/falls is not part of the present study. However, as we mentioned in the introduction, transporting patients down stairs is associated with a particularly high fall risk for patients and the occurrence of back pain among EMTs. We believe the Airstretcher device has not only the benefit of reducing physical burden but also reducing the risk of fall events.

We added the sentence in the introduction as follow:

- “This device has the benefit of reducing the risk of fall events by avoiding the need to lift the patient.”

#2-2. Reviewer-2

2. In the Methods Section (lines 77-79), this portion appears to be a bit repetitive. The specific details provided in this paragraph could likely be combined with the above sentences, to reduce unnecessary repetition.

Reply to Reviewer

2) Thank you for pointing out. We organized these sentences. Please confirm the sentences in the Methods section.

#2-3. Reviewer-2

3. In the Methods Section (line 133), it may be helpful to clarify further how the pulse rate was measured. This may help address questions about variability in the pulse rate measurements, etc.

Reply to Reviewer

3) Thank you for helpful suggestion. We revised the sentence as follow:

- "Additionally, pulse rates after the task in all participants were measured [8] using fingertip pulse oximeter. The Borg CR10 scale, pulse rates and the carrying duration were recorded and put it into the database by researchers.".

#2-4. Reviewer-2

4. The Results Section was very thorough, and provided detailed information about the outcomes of the study. One minor concern throughout was the readability – while minor, it may help with the ‘flow’ of the results section to simplify the naming of the four conditions with acronyms. In lines 152-153 where the four conditions are listed, parentheses could be included after each condition with an abbreviation or acronym. This would help reduce some of the longer sentences/phrases later in the results section, and clarify the overall section for the reader.

Reply to Reviewer

4) Thank you for providing these insights. We expressed the name of four devices as AD (Airstretcher by dragging), AL (Airstretcher by lifting), BL (Backboard by lifting) and TL (Tarpaulin by lifting) in the Result section to reduce some of the longer sentences. However, in other section, we don't express these devices as AD, AL, BL and TL to avoid confusing for readers. Please confirm these sentences in the Result section.

#2-5. Reviewer-2

5. Also in the Results Section, it may help to ‘break up’ the Borg RPE section with a few subheadings. This would clarify to the reader what specific aspect of the Borg RPE reporting that the current section is addressing.

Reply to Reviewer

5) Thank you for your helpful recommendation. We inserted sub-headings in the Borg section as "Overall comparisons", "Sub-group analysis", Interaction between the Borg CR10 scale and other factors", "Head position" and "Toe and side positions". Please confirm these sub-headings in the Borg section.

#2-6. Reviewer-2

6. The Discussion Section was very well done, and easy to follow. One minor point would be the sentence in lines 247-248 dealing with muscle oxygenation. For those familiar with the relationship between muscle oxygenation and physical exertion/workload, this sentence does provide further evidence of the physical demands of transporting patients. However, this sentence may be more clear if the authors expanded upon the interpretation of the findings that muscle oxygenation differs for trained versus untrained individuals, given that the nature of this paper may interest readers who are not as familiar with concepts such as skeletal muscle oxygenation.

Reply to Reviewer

6) Thank you for your kind suggestion. We inserted the sentence of "Therefore, muscle oxygenation may differ between trained and untrained individuals." in the last of Discussion section.

- An experimental study revealed that increased muscle oxygenation for experienced subjects is less than that for novice subjects [10-13]. Therefore, muscle oxygenation may differ between trained and untrained individuals. Further training in the handling of the Airstretcher may enable safer and less stressful patient transport.

#2-7. Reviewer-2

7. The Limitations portion of the Discussion Section was well-written, and sets up future directions in a concise but meaningful way. This section was particularly well-handled.

Reply to Reviewer

7) Thank you for great comments for us.

#2-8. Reviewer-2

8. One concern in the Figures – Figure 2 presents a box-and-whisker plot for the Borg RPE values. However, this Figure is a bit unclear given the alignment of the dots and variability of their placement. It may help clarify the figure to align the dots over the condition they represent, or choose some other way to represent the individual data.

Reply to Reviewer

8) Thank you for your helpful recommendation. We revised Fig 2, 4 and 5.

Lastly, I wish to mention, Thanks to editor and reviewers.

Yours sincerely,

Submitted filename: Response to Reviewers.docx

Click here for additional data file.

1 Sep 2022

Use of the Airstretcher with dragging may reduce rescuers’ physical burden when transporting patients down stairs

PONE-D-21-35282R1

Dear Dr. Takei,

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5 Sep 2022

PONE-D-21-35282R1

Use of the Airstretcher with dragging may reduce rescuers’ physical burden when transporting patients down stairs

Dear Dr. Takei:

I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now with our production department.

If your institution or institutions have a press office, please let them know about your upcoming paper now to help maximize its impact. If they'll be preparing press materials, please inform our press team within the next 48 hours. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information please contact onepress@plos.org.

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