2016 Volume 58 Issue 1 Pages 47-55
Objectives: We studied the physical and mental conditions of 8 healthy young female ambulance paramedics working 24-hour shifts during their menstrual cycle, including assessment of cardiac autonomic nervous system activity by heart rate variability power spectral analysis. Methods: The autonomic activity during the awake period of on- and off-duty days in the follicular, late luteal, and menstruation phases was measured. Questionnaires regarding fatigue and menstrual distress were administered and correlated with the autonomic profile. Results: While degrees of fatigue significantly increased after work, the changes in autonomic activity during the awake period on on-duty days were not significantly different from those on off-duty days (LF/HF, p=0.123; HF/(HF+LF), p=0.153). As for the sleeping period, there were no significant differences. Although the Menstrual Distress Questionnaire (MDQ) revealed the presence of mild menstrual discomfort in the late luteal and menstruation phases, no significant difference was observed in the autonomic profile of the three menstrual cycle phases. No significant correlation was observed between the degree of menstrual distress and autonomic profile, though there was a significant correlation in the late luteal phase between degree of menstrual distress and fatigue after work (p<0.01). Conclusion: These results showed that, while subjects experienced menstrual discomfort and fatigue after work, their autonomic profile did not alter in the menstrual cycle. It is suggested that healthy young female ambulance paramedics may tolerate 24-hour shifts, though attention should be paid to subjective menstrual symptoms and fatigue.
(J Occup Health 2016; 58: 47–55)
The work performed by ambulance paramedics is stressful and requires mental and physical tenacity in addition to sufficient ability to perform quick and appropriate emergency primary care1, 2). Ambulance services are also characterized by 24-hour shifts. In recent years, the number of night emergency calls requiring ambulance services has increased in Japan, particularly in urban areas3); hence, frequent night dispatches may be a significant burden for ambulance paramedics who work 24-hour shifts. Takeyama et al. suggested that fatigue and stress levels among male ambulance paramedics were higher than those among firefighters due to more frequent emergency calls at night4).
As in other developed countries, restrictions on working conditions for females have been largely removed in Japan. Revision of the “Regulation on Labour Standards for Women” in 1994, which removed prohibitions against women working night shifts in Japan, enabled female firefighters to serve on “24-hour standby” at fire stations; the first female ambulance paramedics were recruited at the end of 1994. Since then, the number of female ambulance paramedics has been increasing.
Although female workers may tolerate working conditions as well as their male counterparts, some differences in physical and mental characteristics exist between male and female workers. In particular, most females, from menarche to menopause, are affected by hormonal variability during the menstrual cycle, which may affect their daily living activities. The various symptoms that appear during the premenstrual period of the menstrual cycle are classified as “premenstrual syndrome” (PMS). Inukai et al. reported that nurses working night shifts reported increased fatigue and decreased work efficiency in the luteal phase than in the follicular phase5). Female ambulance paramedics working night shifts may also experience similar physical and psychological disturbances; however, to our knowledge, no studies regarding this have been conducted to date.
Shift work has been associated with changes in blood pressure (BP) and heart rate variability (HRV); both are controlled by the autonomic nervous system, and both follow a diurnal rhythm6). In HRV spectral analysis, the high frequency (HF) component of the electrical conduction cycle between two consecutive R waves (the RR interval) is typically around 0.25 Hz and is regarded as reflecting vagal parasympathetic tone involving respiratory reflexes. The low frequency (LF) component, around 0.1 Hz when expressed in normalized units, is considered a marker of the sympathetic nervous system involving the carotid body sensor system7). The power ratios HF/(HF+LF) and LF/HF have been used as indicators of parasympathetic and sympathetic activities, respectively8, 9). During sleep at night, HF/(HF+LF) increases and LF/HF decreases, reflecting increased parasympathetic activity and decreased sympathetic activity, respectively10). These HRV variables have also been useful in objectively evaluating continuous stress levels11, 12).
In females, changes in HRV variables have been associated with the menstrual cycle. Reports have suggested that sympathetic nervous activity in the luteal phase is significantly greater than in the follicular phase, whereas parasympathetic nervous activity is predominant in the luteal phase13). Altered autonomic nervous system functioning in the late follicular phase has been associated with premenstrual distress14).
Mitani et al. reported that among male ambulance paramedicson on duty and off duty 24 hours, the differences in LF/HF and HF/(HF+LF) values during the awake and sleeping periods were insignificant, suggesting a disturbance in the diurnal balance of the autonomic nervous system on on-duty days15). However, no comparative studies of female ambulance paramedics have been performed; hence, it would be interesting to explore whether similar changes in HRV variables between the on- and off-duty days are observed in female ambulance paramedics, and whether the HRV variables are further altered during the menstrual cycle.
In the present study, we observed the values of HRV variables during the awake and sleeping periods on on- and off-duty days of female ambulance paramedics during three phases of the menstrual cycle. We also examined the results of the Menstrual Distress Questionnaires (MDQs) completed by these paramedics regarding fatigue and menstrual distress symptoms, and we correlated these results with data recorded for their HRV variables.
The subjects of this study were 8 healthy female ambulance paramedics (age, 26.3 ± 3.8 yr; height, 160.3 ± 4.6 cm; weight, 53.5 ± 7.9 kg). The group included 7 unmarried and childless women and 1 married mother of a child who was under two years of age. Only women with regular menstrual cycles and biphasic body temperatures were selected for the study. During two months prior to the start of this research, the subjects measured their oral temperature every day to confirm that they had regular menstrual cycle lengths of between 25 and 36 days, as demonstrated by a biphasic body temperature curve. None of the subjects reported a history of PMS treatment or any other gynecological disorders. The participants were not smokers, and they avoided alcohol consumption the day before the experiment. This study was conducted in urban and suburban areas in the vicinity of Tokyo (Japan) from April 4 to November 30, 2012.
The subjects were fully informed about the purpose, methods, and possible risks associated with the study, and they provided written consent before participation. This study was approved by the Kokushikan University Ethics Committee for Research on Human Subjects.
24-h shift schedulesThe regular work schedules of the ambulance paramedics in this study consisted of 7 shift-work days and 1 regular work day over a period of 3 weeks, with an interval of 1 or 2 days between work days. A 24-h shift workday started at 8:30 and ended at 8:40 the next morning. The paramedics could rest for 2 hours during the day and could sleep at night (22:20 to 6:00), unless they were called to provide ambulance services. Daytime work included daily trainings and administrative tasks.
During the study period, none of the subjects were called on duty on any of their off-duty days. In addition, on the day before the experiment, all the subjects had a “day off”.
Menstrual investigation calendarDays in each subject's menstrual cycle were numbered beginning from the onset of menstrual bleeding, which was designated as day 1. Each subject participated in the present study for a total of 6 days, on one 24-hour on-duty day and one 24-hour off-duty day in each of the three phases of the menstrual cycle, as follows: (1) the menstruation phase, one on-duty and one off-duty day between days 2–4; (2) the follicular phase, one on-duty and one off-duty day between days 8–13; and (3) the late luteal phase, one on-duty and one off-duty day between day 21 and the day before day 1 of the next cycle.
Measurements of heart rate, HRV variables, physical activity, and BPSubjects were monitored for 24 hours from the beginning (8:00 am., local time) of each on- and off-duty day, excluding time spent bathing, using an ActiHR4 monitoring system (CamNtech, Cambridge, UK), which simultaneously measured heart beat by ECG and physical activity by accelerometer16). Before the experiment, a skilled technician gave the subjects adequate training on how to attach the ActiHR4. Further, the subjects cleansed their skin with alcohol before connecting the electrodes, and they turned the switch on by themselves. The obtained data were transferred to a personal computer, and frequency analysis of RR intervals was performed using Actiheart Software v.4.0.92 (CamNtech). The HRV LF component values were in the range of 0.04–0.15 Hz, and the HF component values were in the range of 0.15–0.40 Hz; the LF/HF and HF/(HF+LF) ratios were subsequently calculated7–9).
Subjects were asked to report their physical activity during their on- and off-duty days; events reported included the times for ambulance service, training, bathing, and sleeping. The sleeping period was defined as continuous physical inactivity that appeared in the action records for over 30 minutes and was consistent with the self-report. Activation responses to transient arousals were disregarded. The period excluding the sleeping period was defined as the awake period. The average values of the activity, heart rate, and HRV variables during one sleeping time period were considered as the sleeping values; those during one awake period (excluding bathing time) were considered the awake values.
Systolic and diastolic BP was measured with a Hem-7051-HP digital automatic sphygmomanometer (Omron Healthcare, Lake Forest, IL, USA) at the beginning and end of on-duty days.
Questionnaires for fatigue and the MDQModified versions of two subjective rating instruments were used. A questionnaire for recording symptoms of fatigue, developed by the Working Group for Occupational Fatigue of the Japan Society for Occupational Health17), was used to assess work-related fatigue. Subjects rated their subjective levels (ranging from 0 for “none” to 3 for “strong”) of drowsiness, balance, discomfort, physical exhaustion, and impaired cognitive clarity (vagueness). Total scores ranged between 0 and 75. The subjects completed the questionnaire both before starting and after completing their 24-hour shift during each of the three menstrual cycle phases.
The MDQ was used to evaluate menstrual symptoms severity18–20). Subjects rated themselves on 8 factors (pain, impaired concentration, behavior change, autonomic reactions, water retention, negative affect, arousal level, and self-control) associated with 48 physical and psychological symptoms. The subjects filled out the MDQ using a 6-point scale once during each of the three menstrual cycle phases, and the total scores ranged between 0 and 138.
Statistical analysisData are expressed as the mean ± SE. The HRV components during different states of activity (awake vs asleep) and on the basis of subject condition (on duty vs off duty and before duty vs after duty) were compared by using the nonparametric Wilcoxon signed-rank test. Data concerning feelings of fatigue and data from the MDQ for the three menstrual cycle phases were analyzed using Steel-Dwass nonparametric multiple comparisons. The relationships between fatigue feelings scores and sleeping time, HRV components, or MDQ sores were investigated by using the linear regression t-test. Differences were considered significant at p<0.05.
The mean menstrual cycle of the 8 subjects lasted 30.1 ± 6.4 days (mean ± SD), and the mean duration of the menstruation period was 5.7 ± 1.0 days. The mean number of emergency ambulance dispatches the subjects responded to during on-duty days was 5.8 ± 3.2, and the mean total dispatch duration was 567.9 ± 303.7 minutes. The mean total sleeping time was significantly different between on- and off-duty days (188.8 ± 85.1 minutes vs. 355.8 ± 86.9 minutes, p<0.001).
Figure 1 shows typical 24-hour heart rate, physical activity (A), and HRV variable (B) levels during a 24-hour on-duty day. Increases in heart rate and activity were observed during ambulance service time; these measures were low during sleeping periods. As shown in Fig. 1B, high peaks of LF/HF tended to appear during ambulance service time; in contrast, LF/HF markedly decreased during sleeping periods, with HF/(HF+LF) conversely increased.
Typical diurnal changes in physical activity, heart rate (A), LF/HF and HF/(HF+LF) (B) during a working day of a subject. The solid line arrows indicate ambulance service times, and the broken line arrow indicates sleeping time.
Table 1 shows the mean values and statistical significance of physical activity, heart rate, and HRV variables during the awake and sleeping periods on the on- and off-duty days. As predicted, both activity and heart rate were higher during awake periods than during sleeping periods on both on- and off-duty days; activity levels did not differ between on- and off-duty days during either awake or sleeping periods. However, the awake period heart rate was significantly higher when the subjects were on duty than when they were off duty (p<0.01). LF/HF was significantly higher and HF/(HF+LF) was lower during the awake period than during sleeping periods on on- and off-duty days, but there were no significant differences between on- and off-duty days during the awake and sleeping periods.
| p value | ||||||||
|---|---|---|---|---|---|---|---|---|
| On duty | Off duty | On duty | Off duty | Awake | Sleep | |||
| Awake | Asleep | Awake | Asleep | Awake vs. Asleep | Awake vs. Asleep | On duty vs. Off duty | On duty vs. Off duty | |
| Activity (counts) | 242.08 ± 15.16 | 2.65 ± 0.50 | 201.54 ± 28.69 | 4.24 ± 1.49 | <0.001 | <0.001 | 0.600 | 0.549 |
| HR (beats per minute (BPM) | 84.33 ± 1.75 | 59.25 ± 1.49 | 77.50 ± 1.86 | 57.58 ± 1.44 | <0.001 | <0.001 | <0.001 | 0.077 |
| LF/HF | 4.55 ± 0.38 | 1.47 ± 0.20 | 4.23 ± 0.49 | 1.49 ± 0.14 | <0.001 | <0.001 | 0.123 | 0.931 |
| HF/(HF + LF) | 0.29 ± 0.02 | 0.52 ± 0.03 | 0.32 ± 0.02 | 0 .49 ± 0.02 | <0.001 | <0.001 | 0.153 | 0.290 |
All values are means ± SE. n=24 (3 menstrual cycle phases of 8 subjects). P values were obtained using the Wilcoxon signed-rank test.
Table 2 shows the values for LF/HF and HF/(HF+LF) in each of the three menstrual cycle phases during the awake periods on on-duty and off-duty days. Neither LF/HF nor HF/(HF+LF) differed significantly among the three menstrual cycle phases in any combination of awake/sleeping and on-duty/off-duty days.
| p value | ||||||
|---|---|---|---|---|---|---|
| On duty | Off duty | Awake | Asleep | |||
| Awake | Asleep | Awake | Asleep | On duty vs. Off duty | On duty vs. Off duty | |
| LF/HF | ||||||
| Follicular | 4.59 ± 1.45 | 1.18 ± 0.63 | 3.86 ± 0.82 | 1.37 ± 0.43 | 0.124 | 0.401 |
| Late luteal | 4.84 ± 2.38 | 1.69 ± 1.09 | 4.94 ± 3.47 | 1.64 ± 0.80 | 0.779 | 0.889 |
| Menstruation | 4.22 ± 1.75 | 1.55 ± 1.22 | 3.90 ± 2.25 | 1.44 ± 0.87 | 0.327 | 0.575 |
| HF/(HF + LF) | ||||||
| Follicular | 0.29 ± 0.07 | 0.54 ± 0.15 | 0.30 ± 0.05 | 0.50 ± 0.09 | 0.889 | 0.208 |
| Late luteal | 0.28 ± 0.09 | 0.48 ± 0.14 | 0.32 ± 0.09 | 0.48 ± 0.09 | 0.327 | 0.575 |
| Menstruation | 0.30 ± 0.09 | 0.52 ± 0.12 | 0.34 ± 0.08 | 0.51 ± 0.13 | 0.263 | 0.889 |
All values are means ± SE. n=8. P values were obtained using the Wilcoxon signed-rank test for on-duty vs off-duty days. pressure (mmHg)
Table 3 provides a comparison of the systolic and diastolic BP values before duty and after duty among the three menstrual cycle phases. The Steel-Dwass nonparametric multiple comparisons revealed that there were no significant differences in BP values among the three menstrual cycle phases (SBP, p=0.668 before duty and p=0.623 after duty; DBP, p=0.337 before duty and p=0.651 after duty). Only the diastolic BP before duty was significantly higher than after duty, except in the case of the follicular cycle phase (Table 3).
| pressure (mmHg) | Before duty | After duty | p value | ||
|---|---|---|---|---|---|
| Systolic blood | |||||
| Follicular | n=8 | 120.8 ± 4.2 | 116.1 ± 3.7 | 0.124 | |
| Late luteal | n=8 | 120.1 ± 2.5 | 116.1 ± 2.6 | 0.124 | |
| Menstruation | n=8 | 116.9 ± 2.6 | 115.1 ± 1.6 | 0.447 | |
| Average | n=24 | 119.3 ± 1.8 | 115.8 ± 1.5 | 0.086 | |
| Diastolic blood | |||||
| Follicular | n=8 | 74.9 ± 2.9 | 71.5 ± 3.3 | 0.161 | |
| Late luteal | n=8 | 79.5 ± 2.7 | 74.8 ± 2.8 | 0.028 | |
| Menstruation | n=8 | 80.1 ± 2.4 | 72.3 ± 2.6 | 0.025 | |
| Average | n=24 | 78.2 ± 1.6 | 72.8 ± 1.7 | <0.001 | |
All values are means ± SE. P values were obtained using the Wilcoxon signed-rank test for before duty vs after duty.
Total scores for subjective levels of fatigue increased significantly following a 24-hour shift (Table 4). All fatigue factors except for instability increased significantly after shifts. The differences in the total scores before and after the shifts among the three menstrual cycle phases were compared; none were significant.
| Index | Period | Fatigue feeling scores | p value |
|---|---|---|---|
| I: Drowsiness | |||
| Before duty | 3.00 ± 0.87 | 0.007 | |
| After duty | 5.54 ± 0.89 | ||
| II: Instability | |||
| Before duty | 2.13 ± 0.84 | 0.155 | |
| After duty | 1.21 ± 0.49 | ||
| III: Uneasiness | |||
| Before duty | 1.21 ± 0.45 | 0.013 | |
| After duty | 2.38 ± 0.52 | ||
| IV: Pain or dullness | |||
| Before duty | 1.46 ± 0.41 | 0.009 | |
| After duty | 3.04 ± 0.67 | ||
| V: Eyestrain | |||
| Before duty | 1.00 ± 0.27 | <0.001 | |
| After duty | 1.32 ± 0.50 | ||
| Total score | |||
| Before duty | 8.79 ± 2.44 | 0.005 | |
| After duty | 15.00 ± 2.60 | ||
All values are means ± SE. n=24 (3 menstrual cycle phases of 8 subjects). P values were obtained using the Wilcoxon signed-rank test.
As shown in Table 5, the total MDQ scores revealed significant differences between the follicular and late luteal phases and between the follicular and menstruation phases. The scores did not differ significantly between the late follicular and menstruation phases, although they were slightly higher during the menstruation phase. Of the 8 factors assessed, scores for pain, behavior change, and water retention differed significantly between the follicular and late luteal phases, and between the follicular and menstruation phases.
| Index | Menstrual cycle phase | MDQ scores | p value |
|---|---|---|---|
| Pain | |||
| Follicular | 0.50 ± 0.38 | ||
| Late luteal | 3.12 ± 0.61 | 0.009 | |
| Menstruation | 5.88 ± 1.79 | 0.049 | |
| Concentration | |||
| Follicular | 0.00 ± 0.00 | ||
| Late luteal | 2.13 ± 1.11 | 0.154 | |
| Menstruation | 1.88 ± 1.06 | 0.069 | |
| Behavioral change | |||
| Follicular | 0.00 ± 0.00 | ||
| Late luteal | 2.00 ± 0.84 | 0.029 | |
| Menstruation | 2.38 ± 0.94 | 0.029 | |
| Autonomic reactions | |||
| Follicular | 0.00 ± 0.00 | ||
| Late luteal | 0.13 ± 0.12 | 0.577 | |
| Menstruation | 0.38 ± 0.26 | 0.310 | |
| Water retention | |||
| Follicular | 0.25 ± 0.16 | ||
| Late luteal | 3.38 ± 0.75 | 0.008 | |
| Menstruation | 3.13 ± 0.29 | 0.002 | |
| Negative effect | |||
| Follicular | 0.00 ± 0.00 | ||
| Late luteal | 2.75 ± 1.76 | 0.069 | |
| Menstruation | 2.88 ± 1.94 | 0.07 | |
| Arousal | |||
| Follicular | 1.38 ± 0.63 | ||
| Late luteal | 0.13 ± 0.12 | 0.194 | |
| Menstruation | 0.00 ± 0.00 | 0.069 | |
| Control | |||
| Follicular | 0.00 ± 0.00 | ||
| Late luteal | 0.25 ± 0.25 | 0.577 | |
| Menstruation | 0.25 ± 0.25 | 0.577 | |
| Total score | |||
| Follicular | 2.13 ± 0.64 | ||
| Late luteal | 13.88 ± 4.15 | 0.014 | |
| Menstruation | 16.75 ± 4.39 | 0.018 | |
All values are means ± SE. n=8 subjects. Significant differences (p values) were obtained using the Steel-Dwass nonparametric multiple comparisons.
Total post-duty fatigue scores during the on-duty days from the three menstrual cycle phases were combined and correlated with total ambulance service time (Fig. 2A), sleeping time (Fig. 2B), and HF/(HF+LF) during sleeping periods (Fig. 2C). Fatigue positively correlated with amount of time spent on service calls and negatively correlated with amount of time spent sleeping, with slight (p<0.05) and moderate (p<0.01) significance, respectively. Fatigue positively correlated with HF/(HF+LF) (p<0.05) (Fig. 2C) but not with LF/HF (p=0.10) during sleep, whereas fatigue levels did not show significant correlation with HF/(HF+LF) (p=0.55) or LF/HF (p=0.32) during awake periods.
The relationships of the total score of fatigue symptoms after duty and the total ambulance service time (A), sleeping time on on-duty days (B), and HF/(HF+LF) during sleep on the on-duty days (C). n = 24 (3 menstrual cycle phases of 8 subjects). Open circles represent the follicular phase, closed circles represent the late luteal phase, and hatched squares represent the menstruation phase. D: The relationship of the total score of feelings of fatigue after duty during the late luteal phase and the total MDQ score. n = 8 subjects.
The total MDQ score in the late luteal phase showed a relatively strong positive correlation with the total fatigue score during this phase (p<0.01) (Fig. 2D). Regarding this result, the sample size (n=8) might be too small to apply the linear regression t-test without certain assumptions. The p-value recalculated using the Spearman's rank nonparametric method was slightly outside the significance level (p=0.056). The total MDQ score in the late luteal and menstruation phases did not correlate significantly with the HRV variables during the awake or sleeping periods either on on- or off-duty days in the corresponding phase (data not shown).
We found that among Japanese female ambulance paramedics in this study, the natural circadian rhythm of the cardiac sympathetic and parasympathetic nervous systems, i.e., a decreased LF/HF and increased HF/(HF+LF) during sleep and reversed changes during awake periods, was preserved on on-duty days, as well as on off-duty days (Table 1). This result was similar to that of Japanese female nurses working the night shift21) but was in contrast with that of Japanese male ambulance paramedics, who showed a sustained sympathetic tone during sleep on an on-duty day, suggesting that the cardiac autonomic circadian rhythm was disturbed on the on-duty day and recovered on an off-duty day15). One possible reason for this discrepancy is a known cardiac gender difference; that is, females are known to have higher parasympathetic and lower sympathetic HRV levels than males13, 22). Thus, the dominant parasympathetic tone of the female subjects in the present study might have dominated, exerting a suppressive influence on the sympathetic tone. Another possible cause is the age of the subjects. As compared with the study by Mitani et al., whose subjects' mean age was 39.7 years, the subjects in our study were younger, with a mean age of 26.3 years15). Further, the LF/HF power rate has been shown to decrease with age, in both men and women22).
However, the BP data revealed that the female subjects were under moderate levels of strain before duty; their BP was significantly higher before duty than it was after duty (Table 3). On the other hand, the BP values did not differ significantly among the three menstrual cycle phases.
Although the MDQ scores differed significantly between the follicular, late luteal, and menstruation phases (Table 5), the values of LF/HF and HF/(HF+LF) during the three menstrual cycle phases did not differ significantly (Table 2). The fatigue scores of the subjects in our study increased significantly after 24-hour shifts (Table 4), but the differences in total score before and after duty did not differ significantly during the three menstrual cycle phases. Matsumoto et al. reported that the women they studied with histories of PMS had a significantly lower HF component in the late luteal phase than in the follicular phase14); however, the women in the group without histories of PMS showed no such difference, as in our study. Therefore, although the subjects reported increased symptoms of fatigue after work, and the results of the MDQ revealed the presence of mild menstrual discomfort in the late luteal and menstruation phases, the absence of signs of excess stress (measured as HRV associated with menstruation) may indicate that healthy young female ambulance paramedics can well tolerate the current duties of a 24-h shift.
The subjective reports of fatigue-related symptoms after being on duty positively correlated with the ambulance service time, and negatively correlated with the on-duty sleeping time (Figs. 2A and 2B). In addition, the symptoms of fatigue reported during the late luteal phase positively correlated with the MDQ score (Fig. 2D). A positive correlation was also observed between fatigue-related symptoms timing and parasympathetic tone during sleep, as estimated by HF/(HF+LF) on the on-duty days (Fig. 2C). These results may indicate that hard work and insufficient sleep, particularly when the subjects experienced menstrual discomforts, might have induced a compensatory increase in parasympathetic tone and induced deep sleep. Oriyama et al. showed that short naps (about 15 min) helped to reduce body fatigue and sleepiness of night-shift nurses23). Furthermore, Lin et al. suggested that the stress levels of rotating shift workers improved when they had at least 2 days off24). Brief naps and having entire days off should also be useful for improving alertness in 24-hour shifts worked by ambulance paramedics.
Without sufficient recruitment of ambulance paramedics, the recent increase in number of emergency calls may be causing excess stress on workers who staff the responding ambulances. In 2013, the Japanese Ministry of Internal Affairs and Communications launched a program to improve the working conditions of ambulance paramedics, including regularization of office hours, but the Ministry is concerned that it may be inadequate to catch up with the rapid increase in demands for ambulance services.
The present study has several limitations. First, the study included only a small number of subjects. It is necessary to conduct further studies involving a large number of subjects to validate the results. However, this study had difficulties recruiting female ambulance paramedics to participate in 48-h monitoring, including on-duty and off-duty days, three times with a Holter-type ECG recorder. Moreover, the participants in the study were young female paramedics without premenstrual syndrome. Therefore, a wider range of ambulance paramedics including female with premenstrual syndrome and males should be measured in future research. Furthermore, studies are necessary to evaluate the physical and mental stresses faced by ambulance paramedics and to implement effective measures to prevent possible stress-related health conditions, as well as accidents caused by stress-linked human errors. Conversely, since the number of women working in domains once regarded as male-only jobs is increasing, the need for research investigating whether the growth of female workers in such work fields proceeds without any significant disadvantages is increasing.
Acknowledgments: The authors would like to thank Dr. Nakayama, Dr. Tadano, Dr. Yona, and Dr. Muro for their support and all of the paramedics who participated in this study.
Conflict of interest: The authors declare that they have no conflicts of interest.
