Behavioral inhibition (BI) is a temperament associated with increased vulnerability to stress compared to their non-behaviorally inhibited (NBI) counterparts. Previous studies have demonstrated that BI individuals have a higher stress response than NBI individuals, suggesting that BI individuals have significantly less parasympathetic nervous system output at rest. However, this study only compared room air to 7% carbon dioxide (CO2) concentrations. The difference in the sympathetic nervous system activation between BI and NBI individuals under constant increasing stress is still unknown. Our current study tested the hypothesis that BI individuals will have an increased stress response as the inhaled CO2 concentration increases. In humans, we tested the effect of increasing CO2 concentrations on tidal volume, breathing rate, heart rate, and blood pressure. BI individuals were identified through self-reported questionnaires, such as The Adult Measure of Behavioral Inhibition (AMBI). A 15-minute control period of room air breathing was completed followed by 5 minutes each of 3% and 5% inspired CO2, and 3 minutes of 7% inspired CO2. Preliminary results indicate that BI individuals breathe differently at a physiological level and differ in their stress response. Thank you to Carthage College's Student Travel Grant as well as the Neuroscience and Biology department for supporting this research. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Behaviorally inhibited (BI) temperament is marked by heightened behavioral sensitivity to environmental threats. The degree to which threat sensitivity is reflected in cardiorespiratory responses has been relatively unexplored. Female college students were exposed to modest hypercapnia (7.0% CO2) or ambient air (AA) while engaging in a computerized task with cued reinforcement features. All physiological variables except for blood pressure were processed in 4 min epochs corresponding to pre-exposure, exposure, and post-exposure. Primary respiratory measures were respiratory frequency (fb), tidal volume (VT), and minute ventilation (VE). Electrocardiograms (ECGs) were processed using ARTiiFACT software with resultant heart rate variability (HRV) measures in the frequency domain and time domain. Consistent with the literature, modest hypercapnia increased VT, Fb, and VE. No differences in respiratory parameters were detected between BI and non-behaviorally inhibited individuals (NI). For HRV in the time domain, RMSSD and NN50 values increased during CO2 inhalation which then returned to pre-exposure levels after CO2 cessation. Hypercapnia increased high frequency (HF) power which then recovered. BI exhibited reduced low frequency (LF) power during the pre-exposure period. For NI, LF power reduced over the subsequent phases ameliorating differences between BI and NI. Hypercapnia improved the task performance of BI. This is the largest study of female reactivity to hypercapnia and associated HRV to date. In general, hypercapnia increased time domain HRV and HF power, suggesting a strong vagal influence. Those expressing BI exhibited similar respiratory and HRV reactivity to NI despite inherently reduced LF power. Although 7% CO2 represents a mild challenge to the respiratory and cardiovascular systems, it is nonetheless sufficient to explore inherent difference in stress reactivity in those vulnerable to develop anxiety disorders.

Carbon dioxide (CO2) levels are elevated on the International Space Station, and preliminary reports associate this increased CO2 with headaches, changes in vision, and enhanced emotional experiences, including anxiety. As the duration of space travel extends, improved understanding of the physiologic effects of elevated CO2 exposure is necessary to ensure the capabilities and safety of astronauts. However, studying human breathing has proven difficult at small liberal arts college due to cost and laboratory space constraints. Therefore, the goal of this project is to develop and validate a low budget system that can accurately and dependably mix, store, and deliver enhanced respiratory gases for human research in a liberal arts college setting. Our results provide user-friendly guidelines for building, validating, and maintaining such a system, and broad implementation of this system may increase the quantity and diversity of respiratory research relevant for space travel.

Behavioral inhibition (BI) is a temperament characteristic in which an individual tends to avoid unfamiliar situations or environments. Individuals with high BI are more vulnerable to developing an anxiety disorder, such as Post‐Traumatic Stress Disorder (PTSD), when placed under stressful conditions (Gladstone and Parker, 2005). Behaviorally inhibited organisms learn faster and are slower to extinguish the response to a stimulus (Sheynin et al., 2013; Servatius et al.,, 2008). Our lab over the past several years has been investigating the relationship between a respiratory stress response to CO2 and BI. In this study, participants played a computer game used previously by Sheynin et al., 2013, to evaluate avoidance acquisition and extinction. BI and non‐BI individuals were separated based on Adult Measure of Behavioral Inhibition (AMBI) and Retrospective Measure of Behavioral Inhibition (RMBI). Gas volumes of 4.5% and 7.0% CO2 were applied as different doses of a respiratory stimulant to further the understanding of any physiological differences in breathing between those with BI compared to those without. We hypothesize that individuals with high BI exhibit differences in all parameters of breathing compared to non‐BI individuals during both levels of CO2, and therefore predict that individuals with high BI respond more robustly to CO2. The 4.5% and 7.0% CO2 were obtained by mixing room air with pure CO2 in a Tissot Spirometer and validated using an Oxygraph O2 and CO2 analyzer. The mixed gas was then delivered from a 100 liter gas bag attached to a breathing tube attached to a Hans Rudolph two‐way non‐rebreathing valve. The subjects placed a two‐way valve attached to a mouthpiece into their mouths and then had a nose clip placed over their noses to create a tight seal between the breathing gas bags and themselves. Respiratory data were collected using a BioPac computer data collection system. Our sample sizes are for 4.5% CO2 – Air BI (n=8) and for non‐BI (n=7), and for 7.0% CO2 – Air BI (n=5) and for non‐BI (n=7). When the data were analyzed there were no apparent differences for VT, VI, Fbr between BI and non‐BI individuals exposed to 7.0% CO2, however, in the 4.5% CO2 breathing parameters there was a marked increased both in absolute value and in percent change for Fbr for BI individuals when compared to non‐BI individuals. Given the small sample sizes of the groups, we conclude that increasing the sample sizes is necessary before any more substantive conclusions can be drawn. In addition, our future studies will include measurements of heart rate, blood pressure, salivary cortisol and salivary amylase.Support or Funding InformationNASA Training Grant #NNX15Aj12H, Wisconsin Space Grant Consortium Infrastructure Grant, RIP‐17 #30116‐03This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Behavioral inhibition (BI) is a temperament in which an individual tends to avoid unfamiliar situations or environments. Individuals with high BI are more vulnerable to developing an anxiety disorder, such as Post‐Traumatic Stress Disorder (PTSD), when placed under stressful conditions. Behaviorally inhibited individuals learn faster and are slower to stop the response to a stimulus (Sheynin, 2005; Servatius, 2008). Our lab over the past several years has been investigating the relationship between a respiratory stress response to 4.5% CO2 and BI. BI is characterized by avoidance behavior, which is an active response aimed to reduce fear of a certain stimulus. In this study, a computer game was used as an aversive stimulus to detect BI. 4.5% CO2 was applied as a mild respiratory stimulant to detect any differences in those with BI compared to those without. One indication of PTSD is avoidance behaviors. 4.5% CO2 decreases the pH of the blood, hence causing an increase in frequency of breathing (fbr), tidal volume (VT), and inspired minute ventilation (VI). We hypothesize that individuals with high BI will exhibit greater increases in all parameters of breathing compared to individuals with low BI. The 4.5% CO2 was obtained by mixing room air with pure CO2 in a Tissot Spirometer and was validated using an Oxygraph O2 and CO2 analyzer. The mixed gas was then delivered from a 100 liter gas bag attached to a breathing tube attached to a Hans Rudolph two‐way nonrebreathing valve. The subjects placed the two‐way valve attached to a mouthpiece into their mouths and then had a nose clip placed over their noses to created a tight seal between the breathing gas bags and the participants. BI and non‐BI individuals were separated based on Adult Measure of Behavioral Inhibition (AMBI) and Retrospective Measure of Behavioral Inhibition (RMBI). Heart rate and respiratory data were collected using a BioPac computer data collection system while breathing room air and 4.5% CO2. In BI individuals, we observed a 35.9% (+/−33.3) increase in minute ventilation and a 32.4% (+/−32.1) increase in breathing frequency (n=4). In non‐BI individuals, we observed a −6.4% (+/−18.3) decrease in minute ventilation and a −15.1% (+/−2.9) decrease in breathing frequency (n=2). We observed no difference in tidal volume or heart rate for either group. In conclusion, individuals who scored high on the BI test have a greater response to a respiratory stimuli. Our future studies will include cortisol measurements by analyzing saliva samples taken before and after the test. Support or Funding Information Carthage College Research and Development Grants

Anxiety vulnerable individuals exhibit enhanced acquisition of conditioned eyeblinks as well as enhanced proactive interference from conditioned stimulus (CS) or unconditioned stimulus (US) alone pre-exposures (Holloway et al., 2012). US alone pre-exposures disrupt subsequent conditioned response (CR) acquisition to CS-US paired trials as compared to context pre-exposure controls. While Holloway et al. (2012) reported enhanced acquisition in high trait anxiety individuals in the context condition, anxiety vulnerability effects were not reported for the US alone pre-exposure group. It appears from the published data that there were no differences between high and low anxiety individuals in the US alone condition. In the work reported here, we sought to extend the findings of enhanced proactive interference with US alone pre-exposures to determine if the enhanced conditioning was disrupted by proactive interference procedures. We also were interested in the spontaneous eyeblinks during the pre-exposure phase of training. We categorized individuals as anxiety vulnerability or non-vulnerable individuals based scores on the Adult Measure of Behavioral Inhibition (AMBI). Sixty-six participants received 60 trials consisting of 30 US alone or context alone pre-exposures followed by 30 CS-US trials. US alone pre-exposures not only disrupted CR acquisition overall, but behaviorally inhibited (BI) individuals exhibited enhanced proactive interference as compared to non-inhibited (NI) individuals. In addition, US alone pre-exposures disrupted the enhanced acquisition observed in BI individuals as compared to NI individuals following context alone pre-exposures. Differences were also found in rates of spontaneous eyeblinks between BI and NI individuals during context pre-exposure. Our findings will be discussed in the light of the neural substrates of eyeblink conditioning as well as possible factors such as hypervigilance in the amygdala and hippocampal systems, and possible learned helplessness. Applications of these findings of enhanced proactive interference in BI individuals to pre-exposure therapies to reduce anxiety disorders such as posttraumatic stress disorder (PTSD) will be discussed.