APG(Acceleration Plethysmography) Correlate with Moods in Nursing Workers with Fatigue after Work


 Fatigue or stress in the workplace is a serious problem. The profession of nursing, in particular, is physically and mentally stressful, which often leads to job retrenchment, and shortage of workers. Solving this problem requires a deeper understanding of the fatigue and stress caused by work, and there is a need to consider countermeasures. Purpose: The purpose of this study is to assess the correlation between the psychological and physiological fatigue of healthy nurses during normal work, and to measure nursing stress and fatigue more conveniently. Method: We examined healthy nurses’ physiology (Acceleration Plethysmography: APG and Blood Pressure: BP) and psychology (Visual Analogue Scale: VAS and Mood Inventory Scale: MIS) before and after a normal workday. Results: We observed that after a normal days’ work, the nurses’ autonomic activity, high-frequency component power (HF), low-frequency component power/high-component power ratio (LF/HF ratio), and total power (LF་HF) increased significantly. Psychologically, VAS increased significantly, while the MIS Refreshing Mood decreased remarkably. The HF value correlated significantly with VAS and the MIS Refreshing Mood. The MIS Refreshing Mood correlates significantly with increased sympathetic and autonomic nervous function. Thus, an MIS test may alternative for physiological tests to detect fatigue more quickly and easily. Conclusion: These findings may help nurses and other workers reduce fatigue, cope with stress, and prevent illness. We hope this study will contribute towards addressing the issues related to workers’ mental health in the workplace.


Introduction
Workplace fatigue impacts workers' physical and mental health (Holmes & Raha 1976). Large-scale sociological investigations reveal that more than 50% adults suffer from fatigue .
Fatigue not only impairs concentration and work e ciency, but, in worst cases, it can lead to sickness and death (Chaudhuri & Behan 2004). Japan's aged society faces a chronic shortage of nurses and other care-staff members. Many nurses were physically and mentally tired. Long working hours and interpersonal challenges increase this fatigue, causing many to leave the work force. Therefore, understanding nursing fatigue is important to improve the nurses' mental and physical health, and to reduce job attrition.
Many people think that feeling of gure expressed as "tired" can be overcome by "spirit", and it is di cult to make an accurate evaluation. The phenomenon of fatigue is recognized by everyone, and it is an unquestionable fact that it has a quantitative nature. Fatigue can be classi ed as physical and mental.
Physical fatigue, also known as peripheral fatigue, results from repeated muscle actions. By contrast, mental fatigue represents a failure to complete mental tasks that require self-motivation and internal cues in the absence of demonstrable cognitive failure or motor weakness (Chaudhuri & Behan 2000). And fatigue can have various effects on autonomous functions such as cardiac function and hemodynamics Mizuno et al. 2011). Thus, mental fatigue decreases the sufferers' work e ciency in daily life. Previous studies have consistently demonstrated the decrease in sympathetic nervous activity due to mental stress (Mezzacappa, Kindlon, Saul & Earls 1998;Johnson et al. 2006). Mental fatigue not only increases sympathetic nervous activity but it also decreases parasympathetic nervous agility (Blitz, Hoogstraten & Mulder 1970;Hyndman & Gregory 1975;Pagani et al. 1986;Pagani et al. 1989;Lucini et al. 1997). In general, it is a question of whether fatigue is evaluated as a subjective sensation by recognizing reaction, and time delay, increased false reaction, and multiple attention di culties. The di culty in measuring and evaluating fatigue as a medical subject may be due to its delay as another medical research area. Questionnaires typically used to evaluate subjective fatigue (Chalder et al. 1993;Amagasa & Nakayama 2012;Amagasa & Nakayama 2013) fail to achieve objectivity, while physiological studies of fatigue fall short of capturing its subjective feeling.
Pulse waves contain a lot of information about hemodynamics from the heart to peripheral blood vessels. In the volume pulse wave, the pulsation generated at the origin of the aorta propagates to the peripheral artery site, and the volume change of the peripheral artery is recorded accordingly (Otuka et al., 2006). Digital plethysmogram (DPG) is a measurement of blood ow uctuations from changes in the absorbance of hemoglobin at the ngertips. Accelertion pletymogram (APG) is an improvement of the DPG waveform to a second derivative waveform for quantitative analysis of pulse waves. It is mainly used as a test that re ects peripheral vascular hemodynamics and autonomic nervous function. The APG waveform is composed of the ve components, a,b,c,d, and e. the a-a interval of APG has the same physiological signi cance as the autonomic nerve analysis by the R-R interval of the electrocardiogram (Akselrod et al.1985). It has become possible to evaluate autonomic nervous function more easily.
Autonomic nerve fatigue may cause chronic fatigue syndrome (CFS) (Stewart 2000;Freeman 2002;Winkler et al. 2004;Wyller, Saul, Amlie & Thaulow 2007;Burton et al. 2010), multiple sclerosis (MS) (Keselbrener et al. 2000;Merkelbach et al. 2001;Flacheneckr et al. 2003), and primary biliary cirrhosis (Newton et al. 2007). These reports suggest that changes in autonomic nervous activity are related to the mechanisms underlying fatigue. However, this relationship has between demonstrated only in patients with speci c diseases, but not in healthy subjects.
Fatigue is not only a symptom common to such speci c diseases, but it is also observed in healthy individuals (Chen 1986;Pawliknowska et al. 1994). Recent research using 30 minutes of fatigue-inducing mental tasks has shown decreased parasympathetic activity and increased sympathetic activity even in healthy volunteers (Nozaki et al. 2009). Similarly, a comparison of autonomic activity and mental fatigue after eight hours of fatigue-inducing mental tasks (corresponding to a normal workday for healthy adults) has indicated decreased parasympathetic activity (HF) and increased autonomic function (LF/HF ratio). However, that study examined subjective fatigue only with a visual analogue scale (VAS), and did not address nurses in particular ).
Our study aims to advance current research by (1) speci cally targeting nurses, and (2) comparing psychological mood tests with physiological fatigue trials after eight hours of work.

Method Ethics committee and ethical consideration
This study examined the nurses' physiology and moods, with the approval of the Medical College Ethical Review Board. Both orally and in writing, we explained the study contents, privacy policy, and right to withdraw, to receive participants' consent.

Subject recruitment
We enrolled 33 nurses (23 women, 10 men, aged 20-65; mean 44.87±12.6 years) working in an elderly care institution. We con rmed their health through medical checkups and preliminary interviews, excluding candidates with suspicion of physical or mental instability.

Research design
We measured the nurses' physical and mental conditions before (7:45-9:30 a.m.) and after (17:00-19:00 p.m.) their working day. We gauged their autonomic nervous system at rest in sitting position using acceleration plethysmography (APG) (Arttet, Umedica, Osaka), and then their systolic and diastolic blood pressure, and heart rate using a sphygmomanometer (HEM-6300, Omron Health Care, Kyoto) on their upper arm. We measured APG and BP twice in three minutes both before working and after working. We adopted the stable recorded data that showed the least deviation from the baseline (Heart rate variability 1996; Piccirillo et al. 2009). After each physiological examination, we administered VAS and MIS questionnaires.

Questionnaires
Like , we asked subjects to record their fatigue on a visual analogue scale (VAS) based on Japanese Fatigue Society guidelines, rating their fatigue from 0 (no fatigue) to 100 (complete exhaustion) (Lee, Hicks & Nino-murcia 1991). Going beyond Mizuno, we used the Sakano's Mood Inventory scale, with con rmed reliability and validity in its Japanese version (1994). The Sakano's Mood Inventory comprises ve groups (Tension and Excitement, Feeling Refreshed, Fatigue, Depressive Mood, and Anxiety) with eight questions in each, totaling 40 items, using a 4-point Likert scale. The total score for each factor ranges from 8 to 32, with higher scores indicating greater conformity.

Accelerated Plethysmography (APG)
Photoplethysmography was used to measure changes in the absorption of light by hemoglobin, related to blood ow volume. We used accelerated plethysmography (APG) (Yamaguchi 2007;Tajima et al. 2008;Mizuno et al. 2010; Takada, Ebara & Kamijima 2010) to evaluate autonomic function, using a pulsimeter (Artett, U-Medica, Osaka) with a sensor positioned on the tip of the ventral side of the index nger. The pulsimeter automatically analyzed the APG wave form consisting of four waves in systole (a-d) and one in diastole (e). The output of the pulsimeter sensor was preprocessed by an analogue lter (2 nd order, low pass lter with 23 Hz of cutoff frequency). The data were recorded using an analogue-to-digital converter (3.3 volt to 10 bit) with a real time sampling rate of 1,000 samples per second. These digital data were processed with a 67 th order nite impulse response lter using the Hanning window, interpolated to submillisecond order. Frequency analyses for pulse-interval variation were diagnosed with fast Fourier transformation.
Resolution ability for power spectrum was 0.001 Hz. For the frequency analyses, the total power was calculated as the power within a frequency range of 0-0.4 Hz. We classi ed frequency range of 0.04-0.15 Hz as low frequency component power (LF), and high frequency (HF) as the frequency range of 0.15-0.4 Hz. The HF is vagally mediated (Akselrod et al. 1981;Pomeranz et al. 1985;Malliani, Pagani, Lombardi & Cerutti 1991), whereas the LF originates from a variety of sympathetic and vagal mechanisms (Akselrod et al. 1981;Appel et al. 1989). The low-frequency component power/high-frequency component power ratio (LF/HF) re ects autonomic function ).

Statistical analysis
The pulse rate and the VAS value for fatigue are shown as the mean±SD. We evaluated the difference between before work and after work with a paired t-test and used Spearman's correlation analysis to compare (VAS value, Mood Scale) with fatigue and LF/HF ratio. All p values were 2-tailed, and p values less than 0.05 were considered statistically signi cant. Statistical analysis was performed using Stata IC 15 (Light Stone Inc.). Table 1 shows blood pressure and autonomic activities measured by accelerated plethysmography (APG) before and after working. Pulse rate (bpm) increased, but not signi cantly. Total Power (HF LF) (ms 2 ) gained signi cant momentum in comparison with before working (p<0.05). LF increased signi cantly after work (p<0.01), while the HF did not differ signi cantly. LF/HF rate increased signi cantly from the baseline after working (p<0.01). Results not listed on the table (Systolic and diastolic blood pressure (SBP and DBP) did not signi cantly differ. Table 2 shows questionnaire evaluation before (baseline) and after work. The visual analogue scale (VAS) value for fatigue increased signi cantly after work (p<0.01). In the Mood Inventory, the only statistically signi cant change after work (p<0.05) was that of Feeling Refreshed. The component of Tension and Excitement of the Mood Inventory increased, but not signi cantly. The other constituents such as Fatigue, Depression, and Anxiety did not signi cantly differ. Figures 1 and 2 show the correlation between physiology and questionnaire. The HF correlated negatively with VAS values for fatigue (r=-0.31, p<0.01) (Figure 1). The HF correlated positively with the component of Feeling Refreshed in the Mood Inventory (r=0.21, p<0.05) (Figure 2).

Discussion
Our study showed that, after 8 hours of work, autonomic activity, the LF, and LF/HF ratio changed signi cantly. In other words, fatigue increased objectively. It must be mentioned, but after 8 hours of work, it cannot be denied that there is also the in uence of the circadian rhythm. However, nursing labor requires considerable physical and mental additions. However, nursing labor requires considerable physical and mental additions. Therefore, the effects of inducing fatigue and affecting autonomic nervous function are fully expected. The present nding that mental fatigue affects the sympathetic nervous system (increased LF/HF ratio) is consistent with previously reported results (Toichi & Kamio 2003), in which fatigue-inducing mental tasks increased sympathetic activity and decreased parasympathetic activity Mizuno et al. 2011).
Our nding that HF negatively associated with the visual analogue scale (VAS) replicates previous studies. More interestingly, the positive association of the LF/HF with the Feeling Refreshed item of Sakano's Mood Inventory, is a new nding of the present study. This nding suggests that subjective evaluation by questionnaire might be a valid index of evaluation of autonomic activity. Stressful mental fatigue affects not only mental but physical bodily functions as well. Increased sympathetic activity and decreased parasympathetic activity suggest autonomic hypervigilance. The prefrontal cortex (PFC) and anterior cingulate cortex (ACC) play an important role in the regulation of autonomic nervous activities . The PFC normally inhibits sympathy-excitatory subcortical circuits (Tang et al. 2009;Thayer 2006;Thayer & Sternberg 2006), while the ACC regulates parasympathetic activity (Amat et al. 2005;Kubota et al. 2001). Several studies have reported that prolonged mental tasks lasting an hour or longer gradually reduced brain activity related to mental task processing (Takahashi & Arito 1996;Tanaka et al. 2006). Our study suggests that nursing work entails continuous activation of the PFC, and that acute mental tasks might temporarily cause the PFC and ACC to dysfunction, increasing sympathetic and decreasing parasympathetic activities (Caseras et al. 2008;Danckert et al. 2000;Weissman et al. 2003;Schreppel et al. 2008;Morishima et al. 2009). Neuroimaging studies may be required to con rm this hypothesis.

Conclusion
Our results provide evidence that nurses' fatigue increases sympathetic activity and autonomic function and is also related to mood. The nurses' subjective psychological state after work affects their autonomous function, so physiological indicators may provide an objective assessment of nursing fatigue. Our new nding is that the eight questions in Sakano's Feeling Refreshed category correlate with physiological indicators; hence, Sakano's Questionnaire may be an alternative to physiological test when assessing nursing fatigue and can be tested more quickly and concisely. These ndings may lead to stress coping and prevention not only for nurses but also for workers with fatigue. We hope this study will contribute towards addressing the issues related to workers' mental health in the workplace.

Limitations
The present study has several limitations. First, we should be noted that fatigue is not only physiological and psychological, but also under the in uence of human circadian rhythms. Second, our study included only a small number of participants, limited to nursing care facilities in Fukushima. Third, our study's cross-sectional correlations cannot clarify cause-and-effect relationships. To generalize our results, studies involving a larger number of participants with better cause-and-effect analyses are essential.

Declarations
We delate that manuscript is original, has not been published before and is not currently being considered for publication elsewhere. We know of no con icts of interest associated with this publication, and there has been no signi cant nancial support for this work that could have in uenced its outcome. We have con rmed the availability to the "minimal dataset "required for reproduction and development. As corresponding author, I con rm that the manuscript has been read and approved for submission by all the named authors.

Funding
In carrying out this work, no subsidies have been received.

Con ict of interest
All authors declare that they have no con icts of interest.

Ethics approval
This study was conducted with the approval of the Fukushima Medical University Ethics Committee according to guidelines.

Consent to participate
Both orally and in writing, we explained the study contents, privacy policy, and right to withdraw, to receive participants' consent.

Consent for publication
All authors contributed to and have approved the nal manuscript.

Availability of date and material
We have con rmed the availability to the "minimal dataset "required for reproduction and development.
Author's contributions Miki Ishizuka, Shin-ichiro Katsuda, and Akihiro Hazama designed the study and wrote the protocol. Miki Ishizuka managed the literature searches and wrote the rst draft of the manuscript. Miki Ishizuka performed statistical analyses under technical supervision by Shin-ichiro Katsuda, and Akihiro Hazama. Shin-ichiro Katsuda, and Akihiro Hazama helped with interpretation of data.