Nature, correlates, and consequences of stress-related biological reactivity and regulation in Army nurses during combat casualty simulation

Summary

This study examined the nature, concomitants, and consequences of stress-related biological reactivity and regulation among Army nurses. Saliva was collected, heart rate (HR) and blood pressure (BP) recorded from 38 Army nurses (74% female; mean age 28.5 years [SD = 6.5]) before, during, and after participation in the Combat Casualty Stress Scenario (CCSS). Saliva was assayed for cortisol and alpha-amylase (sAA). The CCSS simulates emergency combat rescue, employing two simulated combat casualties, aversive body odors, recorded battlefield sounds, and smoke in a low light environment. Participants locate and conduct preliminary assessments of the simulated patients, triage based on injury severity, initiate treatment, and coordinate medical evacuation by radio. Results revealed large magnitude increases in cortisol, sAA, HR, systolic BP and diastolic BP in response to the CCSS, followed by recovery to baseline levels 30 min after the task for all physiological parameters except cortisol. Age, gender, perceived difficulty of the CCSS, and previous nursing experience were associated with individual differences in the magnitude of the physiological responses. Lower levels of performance related to triage and treatment were associated with higher levels of reactivity and slower recovery for some of the physiological measures. The findings raise important questions regarding the utility of integrating measures of the psychobiology of the stress response into training programs designed to prepare first responders to handle highly complex and chaotic rescue situations.

Introduction

Research examining individual differences in health and behavior emphasizes the role that biological sensitivity to context plays in translating adverse experience into later risk or resilience (e.g., Boyce and Ellis, 2005, Ellis et al., 2011). Theoretical models suggest that the vast majority of environmental threats or challenges are accommodated at the “behavioral surface” by changing our actions and thoughts (e.g., Gottlieb, 1992). The probability of activating rapid responding physiological systems, such as the hypothalamic–pituitary–adrenal (HPA) axis and autonomic nervous system (ANS), increases when one or both of the following circumstances are present: (a) behavioral or cognitive response options are undeveloped, inaccessible or inadequate, and (b) the environmental challenge is novel, intense, and unpredictable. In theory, activation of these physiological systems enables or reallocates resources to facilitate adaptive change in cognition, behavior, or performance (Weiner, 1992). The threshold and set-points of reactivity and regulation for these fast-acting components of the psychobiology of the stress response are thought to help organisms adapt to change in the environment, but are also capable of inducing pathology with over or under utilization, failure to habituate, or ineffective regulation (McEwen, 1998, McEwen, 2008). A “U-shaped” relationship between physiologic processes and pathology exists: high, chronic, or intermediate activity may lead to deleterious outcomes characterized by reduced hippocampal volume and function, decreased neurogenesis, and impaired cognitive (memory) function (Sorrells and Sapolsky, 2007). By contrast, atypically low levels of HPA activation may allow physiological mechanisms with destructive potential (e.g., inflammation, autoimmunity) to go unchecked. Both high and low levels of stress-related physiological activity are associated with atypical cognitive function, memory, emotion, and behavior (Fries et al., 2005). Not surprisingly, there is increased interest in translating the basic science of the psychobiology of stress into clinical and applied settings in an effort to prevent and ameliorate the potential negative effects of exposure to unpredictable, highly challenging, chaotic, and complex environments (Yehuda, 2001). This is paramount in high risk and high stress populations, including police officers, emergency responders, medical professionals, and military personnel.

The psychobiology of the stress response has at least two principal components: activation of the HPA axis with subsequent secretion of glucocorticoids (e.g., cortisol) and activation of the ANS and associated release of catecholamines (e.g., norepinephrine) (Chrousos and Gold, 1992). The sympathetic (SNS) branch of the ANS is responsible for a host of effects commonly referred to as the “fight or flight” response, including increased cardiovascular tone, respiratory rate, blood glucose, and muscle blood flow (Cannon, 1914). While the HPA axis and the ANS are related at several biological points (Young et al., 2005), functional differences between the systems exist. In addition to differing rates of habituation (Schommer et al., 2003), evidence suggests that the HPA axis is activated by negative affect associated with stress, including fear and frustration, whereas the ANS is valence non-specific (Lovallo and Thomas, 2000).

Individual differences in the activity of the HPA axis and ANS can be measured non-invasively in saliva. Measurement of the activity of the HPA axis via salivary cortisol is well established (e.g., Hellhammer et al., 2009). SNS activity can be measured non-invasively by pre-ejection period (PEP) and skin conductance (SCL), but more recently, researchers have explored measuring ANS activity via salivary alpha-amylase (sAA; Granger et al., 2007a), an enzyme produced locally in the oral mucosa and a surrogate marker of the ANS component of the stress response (e.g., Chatterton et al., 1997, Skosnik et al., 2000; for reviews see Granger et al., 2007a, Nater and Rohleder, 2009). Salivary alpha-amylase can be affected by both chemical and environmental manipulation. Stress-related increases in sAA are inhibited by the adrenergic blocker propranolol (van Stegeren et al., 2006). Researchers consistently report increased sAA in response to laboratory stress procedures (for a review, see Nater and Rohleder, 2009).

Technical advances afford the opportunity to create realistic environments with challenging simulations that can be standardized and used for both training and evaluative purposes. These advances raise the possibility that with integration of salivary analytes into simulated environments, training programs may be designed to teach individuals self-regulation strategies and manage their biological and behavioral sensitivities. Development and mastery of skills that enhance self regulation, followed by application to contexts extending beyond the scope of the original training may translate into significant downstream positive consequences for programming effectiveness, behavioral adjustment, and maximizing individual performance.

In the present study, we take a step toward addressing this possibility by examining individual differences in biobehavioral reactivity and regulation of Army nurses in response to a medically relevant combat training scenario. A simulated battlefield condition served as the backdrop for the Combat Casualty Stress Scenario (CCSS) and employed two patient simulators with combat trauma. Participants were under time pressure and entered the CCSS with specific performance objectives: locate and conduct preliminary assessments of the simulated patients, triage patients based on injury severity, initiate treatment, and coordinate aeromedical evacuation using a two-way radio to an unsympathetic seasoned combat veteran. Thus, this study integrates new measurement and training technology to explore stress response patterns in Army nurses to a simulation of a highly chaotic and complex environment: a standardized combat rescue scenario.

Although nurses do not engage in combat patrols, being first responders to combat casualties is plausible: nurses may be assigned to US Special Operations units, live on bases subjected routinely to indirect fire, or travel extensively within the theater of operations. Rote knowledge of “Common Soldier Tasks” (e.g., basic medical care, map reading, requesting medical evacuation of casualties) is essential, but equally important is the ability to respond immediately and process information from multiple sources in an unpredictable environment. Effective individual engagement and decisive action leading to successful completion of tasks has the best chance for optimal outcomes on the battlefield. In this process, elevated levels of ANS and HPA activity during these high stress conditions may interfere with nurses’ performance. In his review of the biological stress response, Henry (1992) suggested that in the early phases of a challenge, there may be an optimal level of arousal facilitating performance. However, as the stressful situation continues and the demands exceed the individual's ability to respond effectively to the situation, performance will drop off, accompanied by increased activation of the HPA axis and feelings of loss of control. Taylor et al. (2007) indeed found that the association between endocrine activity (assessed with dehydroepiandrosterone [DHEA], DHEA-sulfate, and cortisol) and performance during military training depended on the intensity of the challenge, with increased endocrine reactivity associated with less optimal performance only for the high-intensity challenge. Ineffective physiological regulation of the stress elicited by these complex and chaotic environments may in the long term also affect individuals’ overall health and adjustment. For example, subjective work stress in nurses is directly associated with increased levels of cortisol and other markers of the biological stress and immune systems (e.g., Fujimaru et al., 2012, Fukuda et al., 2008, Metzenthin et al., 2009). In fact, Wingenfeld et al. (2009) found that alterations in the diurnal rhythm of cortisol in nurses were associated with burnout symptoms.

There are 308 military registered nurses (RNs) in the target population, with approximately 48 new Army nurses trained annually. Our aim was to recruit Army nurses to validate the CCSS as a realistic, stressful simulation environment that (a) reliably activates the HPA and ANS subcomponents of the psychobiology of the stress response, and (b) elicits individual differences in physiological reactivity and regulation that map onto nurses’ perception of the CCSS and their actual performance for each of the patient simulators. Given that the CCSS was designed as a highly intense, chaotic and complex environment, and that the sample consisted primarily of nurses with little experience, we hypothesize that the CCSS elicits a clear increase in activity of the HPA and ANS components of the biological stress response, and that higher levels of reactivity and slower recovery would be associated with less optimal performance.