Week 6 Sunday Assignement PICOT

Review Article Effect of Stress on Autonomic and Cardiovascular Systems in Military Population: A Systematic Review

Álvaro Bustamante-Sánchez,1 José Francisco Tornero-Aguilera,1,2

Valentı́n E. Fernández-Elı́as,1 Alberto J. Hormeño-Holgado,1,2 Athanasios A. Dalamitros,3

and Vicente Javier Clemente-Suárez 1,2,4

1Universidad Europea de Madrid, Faculty of Sport Sciences, Madrid, Spain 2Studies Centre in Applied Combat (CESCA), Toledo, Spain 3Laboratory of Evaluation of Human Biological Performance, School of Physical Education and Sport Sciences, Aristotle University of )essaloniki, )essaloniki, Greece 4Grupo de Investigación en Cultura, Educación y Sociedad, Universidad de la Costa, Barranquilla, Colombia

Correspondence should be addressed to Vicente Javier Clemente-Suárez; vctxente@yahoo.es

Received 14 December 2019; Accepted 24 July 2020; Published 11 August 2020

Academic Editor: Anne Knowlton

Copyright © 2020 Álvaro Bustamante-Sánchez et al. -is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Stress is regulated by the autonomous nervous system, increasing the sympathetic modulation when a threat is perceived. A multifactorial response usually leads to significant behavioural modifications and alterations on homeostasis and physical and psychological status. Moreover, stress is an emotional response that can lead to psychosocial and psychophysiological adversity. Regarding military population, military operations and combat exposure are important stressors that influence acute and chronic stress response in soldiers, affecting their performance and health. A bibliographic search was carried out between April and May 2019, focusing on recent studies (2013–2019) that analysed psychophysiological response, stress, stress regulation, heart rate, heart rate variability, and posttraumatic stress disorder in military population. Autonomic and cardiovascular chronic stress seems to be modulated by experience and previous specific training of each military unit. Physical exercise, music embedded with binaural beat technology, bidirectional sensory motor rhythm training, heart rate variability biofeedback, and transcutaneous vagal nerve stimulation are the main techniques applied to balance stress and to recover body homeostasis. Since military population are usually exposed to multiple stressors, knowing previous training and experience, together with developing techniques to balance stress, is the main practical application in this field of study to balance autonomic and cardiovascular systems.

1. Introduction

Stress is a multifactorial response that leads to significant behavioural modifications and alterations on homeostasis and physical and psychological status. -e stress response is regulated by the autonomous nervous system, increasing the sympathetic modulation when a threat is perceived and causing increases in the physiological response (heart rate, blood pressure, breathing frequency, glucose levels, etc.). When stressors disappear, the parasympathetic modulation increases, returning the organism to the homeostasis state [1]. Stress has become a challenge for humans because of its

negative physiological and psychological implications [2], which are normally related to cardiovascular diseases [3]. A chronic activation of the autonomous sympathetic nervous system could trigger acute heart diseases and hypertension [4].

In this line, posttraumatic stress disorder (PTSD) is one of the most common postdeployment chronic stress diseases [5] and usually happens after a war deployment and the highly stressful events that military personnel have to cope with. PTSD reduces the quality of life by a hyperarousal state that influences autonomic modulation. In fact, PTSD was prospectively associated with heart disease mortality among

Hindawi Cardiology Research and Practice Volume 2020, Article ID 7986249, 9 pages https://doi.org/10.1155/2020/7986249

veterans free of heart disease at baseline [6]. Stress should be trained and monitored during military rehearsal: heart rate (HR) is one of the most used indexes to measure stress response, although heart rate variability (HRV) (variability of the time between R waves of the electrocardiogram or RR intervals) is more sensitive to cardiac autonomic modulation changes [7].

While there have been systematic reviews on PTSD among military and ex-military personnel, there are no systematic reviews in the acute and chronic stress response of military population and its effect on the cardiovascular and autonomic nervous system. -en, we proposed the present research with the aim to analyse the effect of acute, chronic, and regulation stress methods of soldiers in their cardiovascular and autonomic nervous system.

2. Materials and Methods

2.1. Search Strategy. -e bibliographic search was carried out between April and May 2019. -e electronic databases such as Web of Science, EBSCOHost, SCOPUS, and PubMed identified studies published between January 2013 and May 2019. -e keywords used were as follows: “heart rate,” “heart rate variability,” “autonomic modulation,” “stress,” “military,” “combat,” “soldier,” “PTSD,” and “Armed forces.” -e reference lists of included studies were checked for further relevant papers.

2.2. Inclusion Criteria. Inclusion criteria for the systematic review were as follows: (1) studies measuring psychophys- iology response, stress, stress regulation, heart rate, heart rate variability, and PTSD; (2) studies focusing on military samples exposed to stressful situations; (3) studies published between 2013 and 2019; (4) studies published in English; and (5) the design of the studies met the level 2 (prospective cohort study and retrospective study), according to the guidance of -e Journal of Bone and Joint Surgery level of evidence grading tool [8].

2.3. Selection Criteria. A total of 959 papers were retrieved from the above bibliographic searches, and 433 papers were removed after publishing period inclusion criteria. Eighty- one papers were removed as duplicates, and 422 were rejected after reviewing paper titles and abstracts. -e final 23 papers were read to be considered relevant to the search criteria and appropriate for assessing our research objective (Figure 1). Reviews were used for the introduction section.

2.4.ExclusionCriteria. Exclusion criteria were as follows: (1) reviews, PhD dissertations, conference proceedings, ab- stracts, unpublished studies and books, study cases, and papers not in English.

3. Results and Discussion

-e general definition of “stress” focuses on acute intense situations as in the fight-or-flight response presented in military population during combat and combat simulation.

However, the brain, as the central organ managing stress, since it perceives what is threatening, as well as the behavioural and physiological responses to the stressor, leads to adaptations (i.e., “allostasis”) but also contributes to pathophysiology (“allostatic load/overload”) when overused and dysregulated [9]. -us, when the stressor keeps affecting the psychophysiological response over time, the stress re- sponse becomes chronic.

3.1. Stress Response in the Military Population. Regarding military population, military operations and combat training simulation exposure are important stressors that influence chronic stress response in soldiers, affecting their perfor- mance and physical integrity and health.

Paratroopers are a military corps that suffers the stress of parachute jumping and combat. Regarding the parachute jump, two studies have analysed the effects of chronic stress response comparing experienced and novice paratrooper. In the first study, the psychophysiological response and specific motor skills of 17 novel and 23 expert warfighters before and

959 papers initially identified

433 papers were removed after

publishing period inclusion criteria

526 possible relevant articles

81 papers removed as duplicates

445 possibly relevant articles

remained

422 rejected after reviewing

abstracts due to inclusion criteria

23 studies included in the present review

Figure 1: Flowchart of study search.

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after a tactical combat parachute jump were analysed [10]. -ey found a 1.7% greater increase in HR, 38.7% in salivary cortisol, 52.5% in creatine kinase, and 188.9% in lactate in novel paratrooper compared to expert ones. However, in any case, fine motor skills and muscle performance were affected. In the second study, conducted by the same research group, the psychophysiological response of 11 sports parachute jumps, 8 manual tactical parachute jumps, and 4 tandem pilot and 4 tandem passengers parachute jumps was com- pared. In this case, only the 4 tandem passengers were novice with the rest of the paratroopers having more than 30 jumps experience. It was found that novice parachute jumpers presented a higher psychophysiological stress response be- fore and after the parachute jumps than the experienced jumpers. Also, they presented a large anticipatory anxiety response before the jump, but it was decreased afterwards [11]. In the case of parachute jumps, it seems that experience modulates chronic stress response, reducing the psycho- physiological and cardiovascular anticipatory and during the task responses, although it does not seem to affect specific performance.

Infantry units and other ground forces usually use simulated combat as training for real combat situations. Within these methods, new operation theatres, such as close- quarter combat, underground operations, or urban combat, examples of asymmetrical combat, are defined as highly stressful combat situations in which there are a large number of uncontrolled threats (urban areas, the presence of civil- ians in the battlefield, and unstructured and undefined battlefield [12]). Chronical exposure to this kind of stressors can drive soldiers to PTSD or other diseases. -e effect of chronic stress on soldier’s performance has been studied compared with nonelite soldier with less or no previous exposure to different combat situations. -e effect of combat stress on psychophysiological responses and performance of elite and nonelite infantry soldiers was analysed during a tactical combat developed in urban area [13]. -ey found the elite soldiers presented a significantly higher lactate con- centration after combat than nonelite soldiers (3.8±1.5 vs. 6.6±1.3 mmol/L). Nonelite soldiers had a higher heart rate before and after the simulation than elite soldiers (82.9±12.3 vs. 64.4±11 bpm, pre nonelite and elite, re- spectively; 93.0±12.8 vs. 88±13.8 bpm post nonelite and elite, respectively). Also, elite soldiers presented higher muscular strength than nonelite before and after the combat simulation. Nonetheless, cortical arousal was not signifi- cantly modified in any group. In a subsequent study, the effect of combat stress on psychophysiological response attention and memory of experienced and novel infantry soldiers during urban combat was analysed [14]. -ey found a significant increase in the low-frequency domain and a significant decrease in the high-frequency domain of the heart rate variability of experienced and highly trained soldiers. Also, they found that experienced had significantly higher values in blood lactate, blood glucose, blood oxygen saturation, rated perceived exertion, heart rate, and cognitive and somatic anxiety. However, the postmission question- naire showed that experienced soldiers presented a higher negative effect on memory probably due to the highest

psychophysiological activation, which seems to be related to chronic stress exposure.

-is higher sympathetic activation before and during the combat was also found during urban combat simulation when comparing light infantry soldiers [15], more experi- enced in asymmetrical combat, with heavy infantry soldiers, less accustomed to close-quarter combat. Moreover, light infantry showed lower metabolic, cardiovascular, and anx- iogenic responses before and after the combat simulation than heavy infantry. Nevertheless, fine motor skill measured by time of ammunition of a pistol magazine was similar in both groups before (39.25±7.62 and 35.38±8.19 s for light and heavy infantry, respectively) and after combat (31.58±5.12 and 28.79±4.77 s for light and heavy infantry, respectively). However, when comparing elite vs. nonelite soldiers during close-quarter combat [15], these same re- searchers found that the higher metabolic, cardiovascular, and anxiogenic responses viewed in elite soldiers supposed a significant loss in the fine motor skill after the combat manoeuvre (−8.34% vs. −11.23% of change in gun reloading time of elite group and novel group (p<0.05)). -ese dif- ferences between studies may lean on the greater training and experiences of heavy infantry compared to nonelite soldiers despite the differences in the task specificity. Finally, a study comparing experienced soldiers and civilians psy- chophysiological and memory responses during an under- ground combat simulation, with interference of night-vision systems use or not, and previous fire situation or not, showed that, before the simulation, soldiers’ sympathetic modulation was greater than civilians and that all groups increased their psychophysiological response and deterio- rated their memory and time consciousness after simulation [16]. However, the civilian control group presented the highest number of incorrect answers on the postmission memory recall questionnaire (73% vs. 47.5, 65 and 57.8% for the soldiers’ groups). -us, it seems that experience disposes soldiers towards better self-confidence and readiness despite the effect on chronic stress that increased the anticipatory higher metabolic, cardiovascular, and anxiogenic response previous to combat. -is activation seems to lead to a better fine motor skill. Nevertheless, this higher level of self- confidence and readiness does not translate into better physical performance when compared with nonelite soldiers or civilians.

Several studies have analysed stress response, mainly through questionnaires, heart rate (HR), or heart rate var- iability (HRV) in military population. In all cases, HR and/or HRV measures were included to evaluate stress. Mostly, male population was used, although in three cases [14, 16, 17] female soldiers were also examined. Only one study included a control group in the experimental design [14]. Standard methods using specific software for HRV analysis were implemented in almost all studies. In the majority of the selected studies, stress responses were in- vestigated during ground operations, except one study that focused on air force soldiers in which HR and perceived stress augmented after a combat jet manoeuvre in profes- sional pilots [18] and four studies in which participants were engaged in parachute jumps [10, 11, 19, 20].

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Generally, researchers were interested in analysing acute stress responses in terms of different levels of expertise [10, 11, 13, 16]. In one of these studies, HR augmented after a parachute jump in both novice and experienced warfighters, although the psychophysiological response was higher in the less experienced group, which had less self-confidence, and more somatic anxiety with higher blood lactate levels [10]. -ere were no differences when examining parachute jump modalities, among sport parachute jump, manual tactical parachute jump, tandem pilots, and tandem passengers, but they were when considering the experience of the jumpers. -e less experienced jumpers had a higher psychophysio- logical response and higher values of anxiety before the jump [11]. Underground operations also produced a stress re- sponse (blood lactate, blood oxygen saturation, rated per- ceived exertion, heart rate, cognitive and somatic anxiety, and sympathetic modulation) in soldiers with different experimental conditions of fire night vision, with no dif- ferences between the groups with different equipment, but a negative effect on memory modulated by previous experi- ence [16]. Combat stress was also addressed in elite and nonelite soldiers, with higher values of heart rate for nonelite in pre- and postmeasures, but similar cortical arousal values [13].

Researchers also focused on studying units with different training backgrounds [14, 15, 21]. In one of these studies, hypoxia induced different cognitive performances for dif- ferent tasks, according to the job profile (transport pilots, fighter pilots, helicopter pilots, and transport aircrew). Al- though HR increases due to a lower blood oxygen saturation, hypoxia did not affect HR and HRV differently when the groups were compared [21]. Light infantry and heavy in- fantry units have been assessed in combat simulation: light infantry training background involved a different stress response with less anxiety and lower metabolic and car- diovascular stress, both before and after the combat ma- noeuvre [15]. Highly trained soldiers (5.9±0.8 years) had a higher stress response than lower trained soldiers (3.9±3 years), with more cognitive and memory impairment and a higher physiological activation [14].

In the cases where a single task was analysed [10, 11, 13, 15, 16, 19, 20, 22, 23], data collection was performed during 2 occasions of the selected task, i.e., before and during/after. One of the studies monitored stress during four consecutive days, finding higher stress after a simulated air accident manoeuvre, with questionnaire and HRV analysis [17]. Regarding the acute stress responses in the parameters measured, a reduction in high-frequency HRV with a concurrent increase in low-frequency HRV was identified [14, 15, 19, 20, 22, 23]. Moreover, experienced soldiers presented lower HR values during a stressful situ- ation [10, 13, 16] compared to their less experienced counterparts, or no significant changes after a parachute jump [11]. In contrast, the single study that included a control group noted a significant decrease in all the variables evaluated during HRV analysis [14].

Table 1 shows a summary of the articles related to stress response in the military population that met the level 2 (prospective cohort study and retrospective study),

according to the guidance of -e Journal of Bone and Joint Surgery level of evidence grading tool [8]:

3.2. Regulation of Stress Methods. Stress as an emotional response with adaptive function can lead to psychosocial and psychophysiological adversity. It is directly linked with a dysregulation of the autonomic nervous system, which leads to a disruption of body homeostasis and may lead to pathological conditions and syndromes due to either acute or chronic psychophysiological changes. Since no one is stranger to stress and its effects, recently, authors have tried to identify new mechanisms and intervention programs in order to improve stress management.

Physical exercise, when correctly periodized and regu- larly practiced, can modify the cardiac autonomic balance by increasing the parasympathetic activity and decreasing the sympathetic activity, promoting the autonomic nervous system function to meet the demands of the cardiovascular system, thus, HRV. Authors found just after 12 weeks sig- nificant increases in the vagal tone, thus increases in the parasympathetic activity, consequence of high-intensity exercise programs intervention, and however, greater sig- nificant increases and peak vagal tone was obtained at 20- week intervention program [24]. In comparison with other modalities of physical exercise, those in which the workload is interval and intense are those which have greater benefit in the autonomic nervous system and vagal tone as in sport modalities like Judo [25].

Despite physical exercise, the use of technology for stress treatment and management is largely extended. -e use of music embedded with binaural beat technology (BBT) with a focus on the theta brainwave frequency was studied, as an effective, noninvasive tool with great potential on stress reduction and management. Subjects, under the interven- tion program (PTSD diagnosed soldiers), presented in- creased parasympathetic activation and decreased sympathetic response, showing greater self-reported relax- ation, after using this technology [26]. In another research study, a noninvasive acoustic stimulation in PTSD patients showed improvements in SDNN, HF, LF, and systolic and diastolic blood pressure and reduction in C-reactive protein (CRP), angiotensin II to angiotensin 1–7 ratio, and inter- leukin-10. It was based on real-time translation of dominant brain frequencies into audible tones of variable pitch and timing to support the autocalibration of neural oscillations. PTSD symptomatology, insomnia, depressive mood, and anxiety were reduced after 6-month intervention program [27]. -e increasing and growing interest in the application of psychophysiological signals and biofeedback is clear.

Bidirectional sensory motor rhythm training (SMR) and heart rate variability biofeedback were used, which allowed subjects after 21 training sessions, to control their SMR frequency bidirectionally, showing significant improve- ments in stress management [28]. However, no significant effects were seen in sleep quality improvement, possibly explained since bidirectional training does not result in the same neuroplastic changes seen with unidirectional training, due to the constant changing contingencies (i.e., up vs. down

4 Cardiology Research and Practice

Table 1: Summary of articles about stress response in military population.

Authors and year

Study title Participants Aim of study/assessment Main outcomes

Clemente- Suárez et al. (2016) [10]

Experience modulates the psychophysiological response of airborne

warfighters during a tactical combat parachute jump

40 male warfighters divided in two groups: novels (n � 17) and experts

(n � 23)

To analyse the effect of experience in the

psychophysiological response and fine motor skills of novel and expert

parachute warfighters during a combat

Experience influences the psychophysiological

response. Novel paratroopers were more affected than

experts

Clemente- Suárez et al. (2017) [11]

Psychophysiological response in parachute jumps, the effect of experience and

type of jump

27 male airborne brigade in parachute jump (n: 11; 41.0±9.7 years), manual tactical parachute jump (n: 8; 33.1±5.3 years), tandem pilots (n: 4; 35.5±3.0 years), and tandem passengers

(n: 4; 28.5±5.4 years)

To analyse the effect of experience and jump on the

psychophysiological response

Novice parachute jumpers had higher values of stress

than the experienced jumpers, and a large

anticipatory anxiety response before the jump

Clemente- Suárez and Robles-Pérez (2013) [12]

Mechanical, physical, and physiological analysis of

symmetrical and asymmetrical combat

20 soldiers from the Spanish Army and Spanish

Forces and Security Corps (34.5±4.2 years;

176.4±8.4 cm; 74.6±8.7 kg; 63.3±8.0 kg

muscular mass; 7.6±3.2 kg fat mass)

To analyse physical, mechanical, and

physiological parameters during symmetrical and asymmetrical combat

simulations

Asymmetrical combat showed higher maximum speed, number of sprints, sprint distance, and average

heart rate. Symmetric combat presented a higher number of impacts and

training load

Tornero- Aguilera et al. (2017) [13]

Effect of combat stress in the psychophysiological

response of elite and non- elite soldiers

40 warfighters divided in two groups: elite

(n: 20; 28.5±6.38 years) and nonelite

(n:20; 31.94±6.24 years)

To analyse the effect of combat stress in the psychophysiological responses of elite and

nonelite soldiers

Elite soldiers had higher muscular strength than

nonelite in all tests (before and after the combat

simulation), while cortical arousal was not modified significantly in both groups

Tornero- Aguilera et al. (2018) [14]

Use of psychophysiological portable devices to analyse stress response in different

experienced soldiers

49 soldiers of Spanish Army (19 men and 1 woman; 34.5±4.2

years; 176.4±8.4 cm; 74.6±8.7 kg; 63.3±8.0 kg

muscular mass; 7.6±3.2 kg fat mass)

To analyse the effect of experience and training in

psychophysiological response and attention and

memory of soldiers in combat

-e most experienced soldiers presented higher physiological activation as

well as cognitive and memory impairment than lower experienced soldiers, and memory function was modulated by the type of

external stimulus

Sánchez- Molina et al. (2018) [15]

Assessment of psychophysiological

response and specific fine motor skills in combat units

31 male soldiers of the Spanish Army, 19

nonexperienced soldiers (30.2±5.25 years, 9.95±5.17 years of experience) and 12 experienced soldiers (34.5±4.85 years,

14.58±4.87 years of experience)

To analyse the psychophysiological

response and specific motor skills in an urban combat

simulation with two infantry units with different previous training and experience

A combat simulation changed the

psychophysiological basal state and unbalanced the

sympathetic-vagal interaction, but motor skills were not affected after the

combat

Tornero- Aguilera and Clemente- Suárez (2018) [16]

Effect of experience, equipment and fire actions in

psychophysiological response and memory of

soldiers in actual underground operations

Fifty-four professional soldiers of the Spanish

Army (mean age 30.60±4.6 years; 8.85±4.1 years of experience) and 16 were civilians (mean age

26±3 years)

To analyse the effect of underground operations on the psychophysiological and memory response of soldiers depending on the previous experience and the use of nocturne vision systems

-e underground operation produced a significant

increase in blood lactate, blood oxygen saturation, rated perceived exertion, heart rate, cognitive and somatic anxiety, and

sympathetic modulation in all groups

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Table 1: Continued.

Authors and year

Study title Participants Aim of study/assessment Main outcomes

Hormeño- Holgado et al. (2019) [17]

Psychophysiological response of air mobile

protection teams in an air accident manoeuvre

12 male and 1 female soldiers from an air

security force unit of the Spanish Air Force

(32.4±8.0 years; 7.2±4.8 years of experience)

To study the psychophysiological

response of an air security force in a simulated air

accident in a hostile area and its subterfuge to a safe area

An air accident manoeuvre of three nights and four days caused a higher sympathetic nervous system modulation and increased stress, muscle strength, and dehydration

Hormeño- Holgado and Clemente- Suárez (2019) [18]

Effect of different combat jet manoeuvres in the psychophysiological

response of professional pilots

29 fighter pilots of the Spanish Air Forces (28.3±7.4 years)

To analyse the effect of air combat manoeuvres (defence

and attack) on the psychophysiological

response of air combat fighter pilots

-e defensive manoeuvre produced a significant decrease in forced vital

capacity and an increase in heart rate, stress, and

exertion in both manoeuvres

Clemente- Suárez et al. (2017) [19]

Psychophysiological response and fine motor skills in high-altitude parachute jumps

16 veteran male soldiers of the Spanish Army with more than 200 parachute

jumps experience 8 high-altitude low-

opening (32.6±7.7 years) and 8 high-altitude high- opening (30.3±5.6 years)

To analyse the psychophysiological

response and specific fine motor skill of an experienced jumper in high-altitude low- opening and high-altitude high-opening parachute

jumps

High-altitude low-opening and high-altitude high-

opening jumps produced a significant increase in CK, lactate, and RPE and a

decrease in glucose. High- altitude high-opening

decreased cortical arousal and presented a higher

sympathetic modulation and a higher HR during the jump

than high-altitude low- opening

Clemente- Suárez et al. (2016) [20]

Psychophysiological response in an automatic

parachute jump

We analysed 38 male sport active soldiers of Spanish Army (25.6±5.9 years;

172.3±4.7 cm; 70.3±4.9 kg;

23.8±0.5 BMI) with an average of 44.7±82.1 civil and military parachute

jumps

To analyse modifications in blood oxygen saturation,

heart rate, cortisol, glucose, lactate, creatine kinase, muscle strength, cortical

arousal, autonomic modulation, and anxiety

before and after an automatic open parachute jump

An automatic parachute jump increased physiological and cortical response and

decreased somatic anxiety of participants

Bustamante- Sánchez et al. (2019) [21]

Psychophysiological response of different aircrew

in normobaric hypoxia training

22 male pilots (10 helicopter pilots, 7 transport aircrew, 3

transport pilots, and 3 fighter pilots) from the Spanish Air Forces

To study the effect of hypoxia training in cortical arousal, autonomic modulation, muscle strength, and cognitive function

Hypoxia produced an increase in perceived stress and effort, a higher heart rate, and a decreased function of breathing muscles. Working

memory and pattern recognition were impaired after hypoxia exposition. Aircrew groups performed differently in cognitive tests, suggesting differences in their previous training

Delgado- Morerno et al. (2017) [22]

Combat stress decreases memory of warfighters in

action

Twenty male soldiers from the Spanish Army (35.4±6.2 years; 179.9±7.0 cm;

82.3.8±10.5 kg; BMI: 25.7±2.6; 14.6±6.4 years

of experience)

To analyse the effect of combat stress in the psychophysiological

response and attention and memory of warfighters in a simulated combat situation

Combat stress increased the psychophysiological

response and caused a selective decrease of

memory, depending on the dangerous or harmless nature of the stimulus

Gamble et al. (2018) [23]

Different profiles of decision making and physiology

under varying levels of stress in trained military personnel

26 male active duty US Army Infantrymen

(age � 30.73±7.71 years)

To examine the relationship between decision making and physiology under

varying levels of stress in trained military personnel

Participants performed worse in the high-stress condition, and heart rate variability measurements could help to measure the adaptive response when danger is imminent

6 Cardiology Research and Practice

Table 2: Summary of articles about stress regulation.

Authors and year

Study title Sex/participants/age Aim of study/assessment Main outcomes

Grant et al. (2018) [24]

-e difference between exercise-induced autonomic

and Fitness changes measured after 12 and 20 weeks of medium-to-high intensity military training

154 healthy recruits (male � 89, female � 65,

age � 20.91±1.29 with a body mass index of 22.85±2.78 kg/

m2)

To compare the physical fitness, based on VO2max and exercise-induced cardiac

autonomic changes, measured by heart rate

variability of 12 weeks with 20 weeks of training in the South African National

Defence Force

Cardiorespiratory fitness (VO2max) did not increase during the 12- to 20-week

period although heart rate and sympathetic cardiac control decreased with a simultaneous

increase in vagal cardiac control

Campos et al. (2018) [25]

Influence of autonomic control on the specific

intermittent performance of judo athletes

Sixteen judo athletes of both sexes (12 men and 4 women, age of 19.6±2.9 years, body

mass of 67.9±12.1 kg)

To verify the correlation between heart rate variability at rest with performance in the special judo fitness test

-e rates of vagal tone in the time domain of resting heart rate variability correlated

positively with the performance of judo athletes

(number of throws)

Gantt et al. (2017) [26]

-e effect of binaural beat technology on the

cardiovascular stress response in military service members with postdeployment stress

74 military service members with a complaint of continued stress following a deployment

To assess the efficacy of embedded theta brainwave frequency in music using binaural beat technology

compared to music alone on the cardiovascular stress

response in military service members with

postdeployment stress

Participants who used music with embedded binaural beat

technology displayed a decrease in sympathetic

responses and an increase in parasympathetic responses, while participants who used music alone had the opposite

effect

Tegeler et al. (2017) [27]

Successful use of closed-loop allostatic neurotechnology for

post-traumatic stress symptoms in military

personnel: self-reported and autonomic improvements

Eighteen service members or recent veterans (15 active duty and 3 veterans, most from special operations, 1 female, age � 40.9±6.9 years) and symptoms of posttraumatic stress disorder from 1 to 25

years

To document changes in self- reported symptoms,

autonomic, and functional measures after use of a closed-loop acoustic

stimulation neurotechnology

-ere were significant improvements in multiple measures of heart rate

variability in both time and frequency domains

Binsch et al. (2017) [28]

No effects of successful bidirectional SMR feedback training on objective and subjective sleep in healthy

subjects

62 participants, all military working at the Dutch Ministry of Defence

To analyse to what extent participants could gain

voluntary control over sleep- related parameters and

secondarily to assess possible influences of this training on

sleep metrics

After the training, the heart rate variability values

improved, but no effects were found on sleep spindles,

actigraphy, sleep diaries, and self-reported sleep quality

Wahbeh et al. (2016) [30]

Mechanistic pathways of mindfulness meditation in

combat veterans with posttraumatic stress disorder

102 combat vetera