Autonomic reactivity of panic patients during a CO2 inhalation procedure

Amygdala-driven apnea and the chemoreceptive origin of anxiety

Although the amygdala plays an important part in the pathogenesis of anxiety and generation of exteroceptive fear, recent discoveries have challenged the directionality of this brain-behavior relationship with respect to interoceptive fear. Here we highlight several paradoxical findings including: (1) amygdala lesion patients who experience excessive fear and panic following inhalation of carbon dioxide (CO₂), (2) clinically anxious patients who have significantly smaller (rather than larger) amygdalae and a pronounced hypersensitivity toward CO₂, and (3) epilepsy patients who exhibit apnea immediately following stimulation of their amygdala yet have no awareness that their breathing has stopped. The above findings elucidate an entirely novel role for the amygdala in the induction of apnea and inhibition of CO₂-induced fear. Such a role is plausible given the strong inhibitory connections linking the central nucleus of the amygdala with respiratory and chemoreceptive centers in the brainstem. Based on this anatomical arrangement, we propose a model of Apnea-induced Anxiety (AiA) which predicts that recurring episodes of apnea are being unconsciously elicited by amygdala activation, resulting in transient spikes in CO₂ that provoke fear and anxiety, and lead to characteristic patterns of escape and avoidance behavior in patients spanning the spectrum of anxiety. If this new conception of AiA proves to be true, and activation of the amygdala can repeatedly trigger states of apnea outside of one's awareness, then it remains possible that the chronicity of anxiety disorders is being interoceptively driven by a chemoreceptive system struggling to maintain homeostasis in the midst of these breathless states.

Stress and Loss of Ovarian Function: Novel Insights into the Origins of Sex-Based Differences in the Manifestations of Respiratory Control Disorders During Sleep

The respiratory system of women and men develops and functions in distinct neuroendocrine milieus. Despite differences in anatomy and neural control, homeostasis of arterial blood gases is ensured in healthy individuals regardless of sex. This convergence in function differs from the sex-based differences observed in many respiratory diseases. Sleep-disordered breathing (SDB) results mainly from episodes of upper airway closure. This complex and multifactorial respiratory disorder shows significant sexual dimorphism in its clinical manifestations and comorbidities. Guided by recent progress from basic research, this review discusses the hypothesis that stress is necessary to reveal the sexual dimorphism of SDB.

Sex-Specific Effects of Stress on Respiratory Control: Plasticity, Adaptation, and Dysfunction

As our understanding of respiratory control evolves, we appreciate how the basic neurobiological principles of plasticity discovered in other systems shape the development and function of the respiratory control system. While breathing is a robust homeostatic function, there is growing evidence that stress disrupts respiratory control in ways that predispose to disease. Neonatal stress (in the form of maternal separation) affects "classical" respiratory control structures such as the peripheral O₂ sensors (carotid bodies) and the medulla (e.g., nucleus of the solitary tract). Furthermore, early life stress disrupts the paraventricular nucleus of the hypothalamus (PVH), a structure that has emerged as a primary determinant of the intensity of the ventilatory response to hypoxia. Although underestimated, the PVH's influence on respiratory function is a logical extension of the hypothalamic control of metabolic demand and supply. In this article, we review the functional and anatomical links between the stress neuroendocrine axis and the medullary network regulating breathing. We then present the persistent and sex-specific effects of neonatal stress on respiratory control in adult rats. The similarities between the respiratory phenotype of stressed rats and clinical manifestations of respiratory control disorders such as sleep-disordered breathing and panic attacks are remarkable. These observations are in line with the scientific consensus that the origins of adult disease are often found among developmental and biological disruptions occurring during early life. These observations bring a different perspective on the structural hierarchy of respiratory homeostasis and point to new directions in our understanding of the etiology of respiratory control disorders. © 2021 American Physiological Society. Compr Physiol 11:1-38, 2021.

Cardiorespiratory Response to Moderate Hypercapnia in Female College Students Expressing Behaviorally Inhibited Temperament

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 (f_b), tidal volume (V_T), and minute ventilation (V_E). 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 V_T, F_b, and V_E. 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.

Panic attack provocation in panic disorder patients with a computer simulation

BACKGROUND

Computer simulations (CS) and virtual reality exposure are promising techniques for research and treatment of panic disorder with agoraphobia (PDA). The objective of this study was to ascertain whether a given CS was a stimulus capable of producing panic attacks (PAs), anxiety and psychophysiological changes in patients with PDA.

METHODS

Thirty PDA patients and 30 healthy subjects were recruited for this study. Subjects were exposed to a 3-min CS of a situation relevant to agoraphobic patients. Anxiety, panic symptoms, PAs, heart rate, skin conductance and respiration were recorded before, during and after the CS exposure.

RESULTS

The CS effectively induced anxiety, hyperventilation and electrodermal responses in PDA patients but not in healthy subjects. Forty percent of PDA patients had a PA while none of the control subjects had a PA. A subgroup of patients who were less sensitive to the CS than the other subgroup of PDA patients and did not present full-blown PAs still had more panic symptoms, higher anxiety levels and more respiratory irregularities than the controls.

LIMITATIONS

Low immersion and low sense of presence, lack of interaction with the environment.

CONCLUSIONS

Exposure to the CS produced effects similar to in vivo exposure, respiratory and caffeine challenges. Subsequent studies should: make direct comparisons between CS and other challenges for PDA; investigate if CS can be a tool for predicting effects of medication; determine the potential of CS as a desensitization technique for situational PAs.

The relationship between dlPFC activity during unpredictable threat and CO2-induced panic symptoms

Panic disorder is characterized by sudden, repeated, and unexpected attacks of intense fear and overwhelming anxiety about when another attack may strike. Patients with panic disorder and healthy individuals with a history of panic attacks show a hypersensitivity to unpredictable threats, suggesting a possible link between panic and sustained anxiety. The purpose of this study was to determine the degree to which induced symptoms of panic relate to fear and anxiety, as well as activity in the neural systems that mediate and regulate these affective states. Psychological and physiological symptoms of panic were assessed during an 8-min 7.5% CO₂ challenge task. Psychological, physiological, and neural symptoms of fear and anxiety were measured during two sessions (one psychophysiology and one functional magnetic resonance imaging where subjects experienced several blocks of no threat (N), predictable shock (P), and unpredictable shock (U; NPU threat task). We used a principle component analysis to characterize panic susceptibility (PS), and found that PS significantly predicted dorsolateral prefrontal cortex (dlPFC) activity to the unpredictable cue during the NPU threat task. When examining the weighted beta coefficients from this analysis, we observed that self-reported fear/anxiety during the CO₂ challenge negatively loaded onto dlPFC activity during the NPU task. Consistent with this observation, dlPFC activity during the unpredictable cue was also negatively correlated with anxiety during the NPU sessions. Together, these results suggest that panic symptoms and anxiety are regulated by the same prefrontal cognitive control system.

P wave dispersion in obsessive-compulsive disorder

BACKGROUND

P wave dispersion (Pd) is defined as the difference between the maximum and the minimum P wave duration. It has recently been associated with increased anxiety levels, thereby predisposing affected individuals to fatal heart disease. Despite of evidence of this autonomous nervous system (ANS) relationship, there are no electrocardiography (ECG) studies in the patients with obsessive-compulsive disorder (OCD). Thus, in this study, we aimed to evaluate the Pd in OCD patients.

MATERIALS AND METHODS

The study consisted of a total of 25 patients with OCD and same number of physically and mentally healthy age- and gender-matched controls. For psychological testing, Yale-Brown Obsession and Compulsion (Y-BOCS) was administered.

RESULTS

Pmax was found to be significantly higher in the patients compared to controls. Pmin did not differ between groups. Left atrium sizes were not different between groups. As for the main parameter investigated in the present study, it was found that Pd was significantly increased in the OCD patients than the controls. Y-BOCS scores for the patient group was positively correlated with Pd (r = 0.73, P < 0.01).

CONCLUSIONS

In conclusion, our results suggest that Pd may be associated with OCD though our sample is too small to allow us to obtain a clear conclusion. Future studies with larger sample evaluating the effects of treatment are required.

Respiratory manifestations of panic disorder in animals and humans: a unique opportunity to understand how supramedullary structures regulate breathing

The control of breathing is commonly viewed as being a "brainstem affair". As the topic of this special issue of Respiratory Physiology and Neurobiology indicates, we should consider broadening this notion since the act of breathing is also tightly linked to many functions other than close regulation of arterial blood gases. Accordingly, "non-brainstem" structures can exert a powerful influence on the core elements of the respiratory control network and as it is often the case, the importance of these structures is revealed when their dysfunction leads to disease. There is a clear link between respiration and anxiety and key theories of the psychopathology of anxiety (including panic disorders; PD) focus on respiratory control and related CO2 monitoring system. With that in mind, we briefly present the respiratory manifestations of panic disorder and discuss the role of the dorso-medial/perifornical hypothalamus, the amygdalar complex, and the periaqueductal gray in respiratory control. We then present recent advances in basic research indicating how adult rodent previously subjected to neonatal stress may provide a very good model to investigate the pathophysiology of PD.

QT wave dispersion in patients with panic disorder

OBJECTIVE

QT dispersion (QTd), defined as the maximal inter-lead difference in QT intervals on 12 leads of the surface electrocardiogram (ECG), reflects the regional heterogeneity of ventricular repolarization and has been suggested as an important marker for risk of arrhythmia in addition to the QT interval. Some investigators proposed that it might be a predisposing factor for arrhythmic events and sudden death. Thus, we aimed to investigate whether QTd differs in patients with panic disorder from that in healthy controls.

METHODS

In 40 panic disorder patients and 40 healthy controls, Q(max), Q(min), and QTd values were measured. In addition, the Hamilton depression rating scale and the panic agoraphobia scale were scored for both patients and healthy volunteers.

RESULTS

Q(max) and Q(min) values in the panic disorder patients were significantly higher than those in healthy controls. The mean corrected QTd was significantly greater in the patients than in the controls. One-way analysis of covariance (ANCOVA; using left atrial size, age and heart rate as covariates) also corrected the significant difference. In addition, ANCOVA revealed a significant main effect for the diagnosis, indicating a significantly higher QTd for patients compared with controls.

CONCLUSION

QTd might be associated with panic disorder. Future studies in larger samples evaluating the effects of treatment are required.

The benefits of being mindful: trait mindfulness predicts less stress reactivity to suppression

BACKGROUND AND OBJECTIVES

There has been a recent proliferation of research evaluating the efficacy of mindfulness as a clinical intervention. However, there is still little known about trait mindfulness, or how trait mindfulness interacts with maladaptive emotion regulation strategies. The current study further explores the effect of trait mindfulness on emotion regulation, as well as whether specific factors of trait mindfulness are uniquely associated with subjective and autonomic reactivity to stress.

METHODS

Forty-eight healthy male participants were trained in the use of the suppression strategy and then instructed to suppress their responses to the inhalation of a 15% CO2-enriched air mixture for 90 s while their subjective distress and heart rate were recorded.

RESULTS

After controlling for anxiety-related variables, the ability to provide descriptions of observed experiences predicted less heart rate reactivity to CO2 inhalation, while skillfulness at restricting attention to the present moment was uniquely predictive of less subjective distress. The tendency to attend to bodily or sensory stimuli predicted greater distress during CO2 inhalation.

LIMITATIONS

The inclusion of only healthy males limits the generalizability of study findings. Also, the sample size was relatively small.

CONCLUSIONS

These findings suggest that factors associated with trait mindfulness predict less stress reactivity and distress while engaging in suppression above and beyond other variables that have been shown to predict anxious responding. The implications for emotion and clinical research are discussed.

Neuronal control of breathing: sex and stress hormones

There is a growing public awareness that hormones can have a significant impact on most biological systems, including the control of breathing. This review will focus on the actions of two broad classes of hormones on the neuronal control of breathing: sex hormones and stress hormones. The majority of these hormones are steroids; a striking feature is that both groups are derived from cholesterol. Stress hormones also include many peptides which are produced primarily within the paraventricular nucleus of the hypothalamus (PVN) and secreted into the brain or into the circulatory system. In this article we will first review and discuss the role of sex hormones in respiratory control throughout life, emphasizing how natural fluctuations in hormones are reflected in ventilatory metrics and how disruption of their endogenous cycle can predispose to respiratory disease. These effects may be mediated directly by sex hormone receptors or indirectly by neurotransmitter systems. Next, we will discuss the origins of hypothalamic stress hormones and their relationship with the respiratory control system. This relationship is 2-fold: (i) via direct anatomical connections to brainstem respiratory control centers, and (ii) via steroid hormones released from the adrenal gland in response to signals from the pituitary gland. Finally, the impact of stress on the development of neural circuits involved in breathing is evaluated in animal models, and the consequences of early stress on respiratory health and disease is discussed.

Baseline respiratory parameters in panic disorder: a meta-analysis

BACKGROUND

The presence of abnormalities in baseline respiratory function of subjects with panic disorder (PD) is expected according to PD respiratory theories. We aimed to meta-analyze results from studies comparing baseline respiratory and hematic parameters related to respiration between subjects with PD and controls.

METHODS

A literature research in bibliographic databases was performed. Fixed-effects models were applied for all parameters while random-effects models only when suitable (at least 10 independent studies). Several moderator analyses and publication bias diagnostics were performed.

RESULTS

We found significantly higher mean minute ventilation and lower et-pCO(2) in subjects with PD than controls. Moreover we also found evidences of reduced HCO(3)(-) and PO(4)(-) hematic concentrations, higher indexes of respiratory variability/irregularity and higher rate of sighs and apneas. Evidence of heterogeneity was partly explained by moderator analyses. No relevant publication bias was found.

LIMITATIONS

Several shortcomings affected the included studies, such as over-inclusive recruitment criteria, samples unbalanced for socio-demographic characteristics, lack of statistical details and small number of studies available for several parameters.

DISCUSSION

Our results support the idea of abnormalities in respiratory function of subjects with PD. Compared to controls, they showed baseline hyperventilation; the results from hematic parameters suggest that hyperventilation may be chronic and not simply caused by their high anxiety levels during respiratory assessment. Evidences of higher variability and irregularity in respiratory patterns of subjects with PD were also found. It is unclear to what extent the higher rate of sighs and apneas may explain the other baseline respiratory abnormalities found in PD.

Panic disorder and the respiratory system: clinical subtype and challenge tests

INTRODUCTION

Respiratory changes are associated with anxiety disorders, particularly panic disorder (PD). The stimulation of respiration in PD patients during panic attacks is well documented in the literature, and a number of abnormalities in respiration, such as enhanced CO2 sensitivity, have been detected in PD patients. Investigators hypothesized that there is a fundamental abnormality in the physiological mechanisms that control breathing in PD.

METHODS

The authors searched for articles regarding the connection between the respiratory system and PD, more specifically papers on respiratory challenges, respiratory subtype, and current mechanistic concepts.

CONCLUSIONS

Recent evidences support the presence of subclinical changes in respiration and other functions related to body homeostasis in PD patients. The fear network, comprising the hippocampus, medial prefrontal cortex, amygdala and its brainstem projections, may be abnormally sensitive in PD patients, and respiratory stimulants like CO2 may trigger panic attacks. Studies indicate that PD patients with dominant respiratory symptoms are particularly sensitive to respiratory tests compared to those who do not manifest dominant respiratory symptoms, representing a distinct subtype. The evidence of changes in several neurochemical systems might be the expression of the complex interaction among brain circuits.

Elucidation of neurobiology of anxiety disorders in children through pharmacological challenge tests and cortisol measurements: a systematic review

Anxiety disorders are common both in adults and children. While there have been major advances in understanding the neurobiology of anxiety disorders in adults, progress has been more limited in the elucidation of the mechanisms underlying these disorders in childhood. There is a need to delineate childhood biological models, since anxiety represents a significant clinical problem in children and is a risk factor for the subsequent development of anxiety and depression in adulthood. We conducted a review of the literature regarding pharmacological challenge tests and direct hypothalamic-pituitary-adrenal axis measurement in children with anxiety disorders, with emphasis on panic disorder and social anxiety disorder. Studies identified were contrasted with those in adult panic disorder and social anxiety disorder. Despite this broad approach few studies emerged in children, with only 22 studies meeting inclusion criteria. When contrasted with adult neurobiological models of panic disorder and social anxiety disorder, children studied showed some abnormalities which mirrored those reported in adults, such as altered baseline respiration, altered responses to CO(2) challenge tests and blunted growth hormone response to yohimbine. However, results differed from adults with panic disorder and social anxiety in some aspects of noradrenergic and serotonergic function. For endpoints studied in panic disorder children, unlike adults, displayed a lack of baseline end-tidal CO(2) abnormalities and a different hypothalamic-pituitary-adrenal pattern response under low-dose CO(2). The biology of these anxiety disorders in children may only partially mirror that of adult anxiety disorders. However, caution is required as the evidence is limited, and many studies combined patients with panic disorder and social anxiety disorder with other disorders or non-specific anxiety. Further research is required to fully understand the biology and progression of childhood anxiety disorders.

Anxiogenic properties of a computer simulation for panic disorder with agoraphobia

BACKGROUND

There are several useful methods to induce anxiety in patients with panic disorder with agoraphobia (PDA). Our aim was to ascertain if a computer simulation (CS) could induce anxiety and physiologic alterations in PDA patients.

METHODS

10 healthy controls (HC) and 10 patients who fulfilled DSM-IV criteria for PDA were recruited for this study. The anxiety level was measured with the Subjective Units of Distress Scale (SUDS) and the Diagnostic Symptom Questionnaire (DSQ) was used to ascertain panic attack (PA) symptoms. The heart rate, skin conductance and respiration were monitored during exposure to the CS. The CS was a 3D computer animation of a short bus trip, from a first person perspective.

RESULTS

In PDA patients CS exposure increased anxiety levels, they also had higher scores in the DSQ and two of them had PA. Compared to the HC, the PDA patients had higher skin conductance level, electrodermal response magnitude, respiratory rate, tidal volume, and respiratory rate irregularities. The heart rate means were higher for PDA patients who had PA, followed by HC and PDA patients who did not have PA. There were no significant differences between the two groups regarding the sense of presence.

LIMITATIONS

The main limitations were the small sample size, and some PDA patients under medications.

CONCLUSIONS

This study indicated that CS exposure may induce anxiety, electrodermal and respiratory alterations in patients with PDA. CS exposure may be a useful tool in the research and treatment of PD patients.

Heart rate and blood pressure changes during autonomic nervous system challenge in panic disorder patients

OBJECTIVE

To test the hypothesis that panic disorder (PD) patients have a heightened or deregulated autonomic nervous system at rest and during autonomic challenge compared with healthy controls (HC); and to test a second hypothesis that severity of illness differentiates patients'; sympathovagal balance both at rest and during orthostatic challenge.

METHODS

Spectral analysis of heart rate (HR) and blood pressure was performed on 30 PD and 10 HC participants during an orthostatic challenge (head-up tilt).

RESULTS

PD patients presented higher HR (p < .001), lower heart rate variability (HRV) (p < .015), higher mean diastolic blood pressure (p < .006), higher low-frequency component of HR (p < .001), and a higher ratio of low-frequency to high-frequency component of HR (LF/HF) (p < .022) than HC at baseline. During tilt, PD patients responded with higher HR (p < .039), lower HRV (p < .043), increased mean diastolic blood pressure (p < .028), and a mild increase in LF/HF, whereas controls responded with a five-fold increase in LF/HF (p < .022). Patients with higher illness severity ratings (Clinical Global Impression Scale) showed higher HR (p < .002), lower HRV (p < .026), and a lower total power of systolic blood pressure (p < .02) compared with less ill patients.

CONCLUSION

These findings demonstrate a consistently higher or deregulated autonomic arousal in PD patients at rest and during orthostatic challenge compared with HC. These data also reveal a possible association between the level of anxiety illness severity and sympathovagal balance, which may imply greater cardiac risk.

Challenging anxiety: a focus on the specificity of respiratory symptoms

Physiological symptoms are characteristic features of anxiety states. Presumably, specific psychophysiological profiles differentiate between anxiety disorders, which would offer potential for diagnostic purposes. Abundant evidence points to a causal relationship between panic disorder and instability of respiratory regulation. However, the specificity of most measures that indicate aberrant functioning of the respiratory system in PD can be questioned. Possibly, the traditional measures of respiratory functioning are too restricted. The underlying respiratory vulnerability in PD seems to constitute a subtle, unstable trait, which calls for more sensitive and sophisticated measures of respiratory variability and chaos. To increase the probability of finding parameters with diagnostic specificity, the application of disorder specific challenge paradigms is recommended.

Respiratory patterns in panic disorder reviewed: a focus on biological challenge tests

OBJECTIVE

To provide a systematic review of studies investigating respiration in PD and comments on relative inconsistencies.

METHOD

A Medline search of controlled studies focusing on pCO(2), respiratory rate, tidal volume, and minute volume in PD patients was conducted for baseline/resting condition, challenge, and recovery phase. Respiratory variability and comparisons between panickers and non-panickers were also examined.

RESULTS

Lower pCO(2) levels in PD subjects are a consistent finding during the baseline/resting condition, the challenge, and recovery phases. Tidal volume and minute volume are increased in PD subjects relative to controls during the baseline/resting condition. However, the most robust finding is a higher than normal respiratory variability, which appears to be a promising factor for the identification of respiratory etiopathological pathways in PD.

CONCLUSION

Respiratory variability might be a candidate for a biological marker of PD: an abnormal breathing pattern as found in panic disorder (PD) patients compared with controls might indicate instability of the respiratory homeostasis.

Caffeine challenge in patients with panic disorder: baseline differences between those who panic and those who do not

A proportion of patients with panic disorder (PD) display an increased sensitivity to the anxiogenic/panicogenic properties of caffeine. The aim of this study is to identify probable baseline differences between PD patients who panic and those who do not, after caffeine administration. In a randomized, double-blind, cross-over experiment performed in two occasions 3-7 days apart, 200 and 400 mg of caffeine, respectively, were administered in a coffee form to 23 patients with PD with or without Agoraphobia. Evaluations included the State-Trait Anxiety Inventory, the DSM-IV 'panic attack' symptoms (visual analogue scale form), the Symptom Checklist-90-Revised (SCL-90-R), as well as breath-holding (BH) duration, heartbeat perception accuracy and heart rate. Only those patients who did not present a panic attack after both challenges ('no panic group', N=14, 66.7%), and those who presented a panic attack after at least one challenge ('panic group', n=7, 33.3%) were included in the analysis. The panickers, compared to the non-panickers, presented at baseline: significantly higher total score of the SCL-90-R; significantly higher scores on all the SCL-90-R clusters of symptoms, except that of 'paranoid ideation'; significantly lower BH duration. The present preliminary findings indicate that PD patients who panic after a 200 mg or a 400 mg caffeine challenge, compared to the PD patients who do not panic after both of these challenges, may present at baseline significantly higher non-specific general psychopathology--as reflected in the SCL-90-R--and significantly shorter BH duration.

Objective and subjective measures in recovery from a 35% carbon dioxide challenge

OBJECTIVES

Because hyperventilation, dyspnea, and a feeling of choking are often core features of a panic attack, respiration has been one of the most widely studied physiological parameters in panic disorder (PD) patients. A respiratory subgroup of PD, with distinct etiological pathways, has also been suggested. Investigation of the recovery phase following a respiratory challenge may be a reliable way to establish respiratory impairment in PD patients. The objective of the present study was to investigate the recovery phase from a 35% carbon dioxide challenge in PD patients and in healthy controls, and to test the hypothesis of a different respiratory pattern in patients, compared to control subjects.

METHODS

Eleven nonmedicated PD patients with or without agoraphobia, 11 medicated PD patients, and 11 control subjects took part in a 35% carbon dioxide and 65% oxygen inhalation challenge. Respiratory rate, partial pressure of carbon dioxide, heart rate, and blood pressure were recorded during the baseline phase (10 minutes) and the recovery phase (10 minutes). Visual Analogue Scale of Anxiety and Panic Symptom List scores were collected pre- and post-challenge.

RESULTS

Nonmedicated patients had increased variability in respiratory rate and partial pressure of carbon dioxide during recovery, compared with control subjects and medicated PD patients. Also, PD patients tended to have higher heart rates and to need more time to recover from the challenge than control subjects.

CONCLUSIONS

Results suggest that PD patients have less effective homeostatic control after their physiological equilibrium has been disrupted by a respiratory stressor.

Medically unexplained symptoms and between-group differences in 24-h ambulatory recording of stress physiology

People with medically unexplained symptoms (MUS) often have a comorbid history of stress and negative affect. Although the verbal-cognitive and (peripheral) physiological stress systems have shown a great degree of independence, at the same time it is claimed that chronic stress and negative affect can result in a disregulated physiological stress system, which may lead to MUS. Previous studies could not demonstrate a straightforward between subject relationship between MUS and stress physiology, supporting the view of independence. The aim of the current study was to further explore this relationship using an improved methodology based on ecologically valid 24-h real-life ambulatory recordings. Seventy-four participants (19 male; 55 female) with heterogeneous MUS were compared with 71 healthy controls (26 male; 45 females). Momentary experienced somatic complaints and mood, heart rate, cardiac autonomic activity, respiration and saliva cortisol were monitored using electronic diary and ambulatory registration devices. Participants with MUS reported much more momentary complaints and negative affect as compared to controls. Although MUS seemed to be associated with elevated heart rate and reduced low and very-low frequency heart period variability, these effects disappeared after controlling for differences in sports behaviour. No group differences were found for cardiac autonomic activity, respiration, end-tidal CO(2) and saliva cortisol. Our 24-h real-life ambulatory study did not support the existence of a connection between MUS and disregulated peripheral stress physiology. Future studies may instead focus on central measures to reveal potential abnormalities such as deviant central processing of visceral signals in MUS patients.

Human fear-related motor neurocircuitry

Using functional magnetic resonance imaging and an experimental paradigm of instructed fear, we observed a striking pattern of decreased activity in primary motor cortex with increased activity in dorsal basal ganglia during anticipation of aversive electrodermal stimulation in 42 healthy participants. We interpret this pattern of activity in motor neurocircuitry in response to cognitively-induced fear in relation to evolutionarily-conserved responses to threat that may be relevant to understanding normal and pathological fear in humans.

P-wave dispersion in panic disorder

BACKGROUND

P-wave dispersion (PWD) is defined as the difference between the maximum and the minimum P-wave (Pmax and Pmin, respectively) duration. Significant variation in cardiac atrial PWD has been correlated with changes in systemic autonomic tone such as during periods of anxiety. It is also known that the degree of PWD seen on 12-lead electrocardiogram (ECG) may be a predictor of susceptibility of the atrial myocardium to future atrial fibrillation (AF). Therefore, we firstly aimed to show an association between PWD and panic disorder, a state of high sympathetic tone.

METHODS

PWD was measured in 40 outpatients with panic disorder and in 40 physically and mentally healthy age- and gender-matched controls. In addition, the Panic Agoraphobia Scale (PAS) and the Hamilton Depression Rating Scale (HDRS) were scored concomitantly.

RESULTS

Both Pmax and Pmin were significantly higher than those of healthy controls. PWD was significantly greater in the panic disorder group than in the controls. As expected, the mean score on PAS was significantly higher for the panic disorder group than for the controls and correlated significantly with PWD. Heart rate (measured as RR intervals in milliseconds on electrocardiogram) did not differ significantly between the groups.

CONCLUSIONS

The findings of the present study suggest that the disorder may be associated with an increase in PWD. This association may result from prolonged anxiety and increase in sympathetic modulation, which are main characteristics of panic disorder.

Characterization of a 7% carbon dioxide (CO2) inhalation paradigm to evoke anxiety symptoms in healthy subjects

The present study is aimed at characterizing the carbon dioxide (CO2) procedure in healthy subjects to achieve reliable provocation of anxiety symptoms. Thirty healthy subjects inhaled in single-blind both compressed air and 7% CO2 mixture. Panic Symptom List (PSLIII-R), Visual Analogue Scale-Anxiety (VAS-A), State Anxiety Inventory (STAI-Y/1), respiratory parameters and skin conductance were measured. 'Responders' were classified depending on PSLIII-R scores after CO2. Twelve out of the 21 'responders' performed a second test to assess test-retest repeatability. In 21 subjects Delta%VAS-A (45.4 +/- 32.1) and PSLIII-R (pre-test 2.3 +/-2.1, post-test 17.5 +/- 8.2) but not STAI-Y/1, significantly increased during CO2 inhalation. Respiratory Rate, Minute Volume, end-Tidal CO2 and skin conductance rose in 'responders'. Repeatability was studied with Bland-Altman plots, revealing mean difference between tests close to 0 for both Delta%VAS-A and PSLIII-R. Among physiologic parameters, end-Tidal CO2 and Respiratory Rate showed good repeatability, with a within-subject CV of 9.2% and 6%, respectively. The challenge produced measurable response in healthy subjects. Good test-retest repeatability was observed in 'responders'. These data indicate that the test can be suitable for testing putative anti-panic or anxiolytic drugs in clinical studies using a within subject, crossover design.

Sleep panic attacks: a micro-movement analysis

Earlier work by our group and others has pointed to a role for movement during sleep in sleep-panic attacks. Specifically, our group has reported that panic disorder patients, as a group, appear to move more during sleep than age-matched controls, whereas the subgroup of panic disorder who "panic" during sleep move less on the nights they experience sleep-panic attacks than they do on nights without sleep-panic attacks. We studied the movement of sleep-panic patients in a more detailed fashion with more than one sleep movement index. Fourteen patients with sleep-panic attacks were compared with 14 waking panic patients, 13 social phobic patients, and 14 normal controls. Subjects from the other groups were age matched to the sleep-panic group. Their comparison study night corresponded to the night number of the sleep-panic attack. Sleep-panic patients did move less on panic nights than did the normal controls on the corresponding sleep-panic night according to two separate sleep movement indices. Although not statistically significant, sleep-panic patients also moved less on their panic night than did either of the other anxious groups on corresponding nights. Rechtshaffen and Kales' Movement Time (MT) measure appears to overestimate actual min of movement during sleep in all subjects. The movement noted in sleep-panic patients may have some role in the pathophysiology of sleep-panic attacks. A possible mechanism is explained.

Panic disorder: from respiration to the homeostatic brain

There is some experimental evidence to support the existence of a connection between panic and respiration. However, only recent studies investigating the complexity of respiratory physiology have revealed consistent irregularities in respiratory pattern, suggesting that these abnormalities might be a vulnerability factor to panic attacks. The source of the high irregularity observed, together with unpleasant respiratory sensations in patients with panic disorder (PD), is still unclear and different underlying mechanisms might be hypothesized. It could be the result of compensatory responses to abnormal respiratory inputs or an intrinsic deranged activity in the brainstem network shaping the respiratory rhythm. Moreover, since basic physiological functions in the organism are strictly interrelated, with reciprocal modulations and abnormalities in cardiac and balance system function having been described in PD, the respiratory findings might arise from perturbations of these other basic systems or a more general dysfunction of the homeostatic brain. Phylogenetically ancient brain circuits process physiological perceptions/sensations linked to homeostatic functions, such as respiration, and the parabrachial nucleus might filter and integrate interoceptive information from the basic homeostatic functions. These physiological processes take place continuously and subconsciously and only occasionally do they pervade the conscious awareness as 'primal emotions'. Panic attacks could be the expression of primal emotion arising from an abnormal modulation of the respiratory/homeostatic functions.

Exaggerated perception of normal physiological responses to stress and hypercapnia in young women with numerous functional somatic symptoms

OBJECTIVE

This study tested whether functional somatic symptoms are associated with exaggerated increases in self-reported anxiety and somatic complaints in response to stress and CO(2)-enriched air breathing, and whether this association exists in parallel to or in the absence of exaggerated physiological responses.

METHODS

Out of 499 young somatically healthy undergraduate women, 18 participants high in functional somatic symptoms (HSS group) and 18 participants low in symptoms (LSS) were selected. They were submitted to mental stress, mild physical exercise and relaxation during conditions of normal breathing, breathing compressed normal air, and breathing compressed 5% CO(2)-enriched air. In all conditions, self-reported anxiety and somatic symptoms and respiratory and autonomic responses were assessed.

RESULTS

HSS participants reported, as compared to LSS, more tenseness, anxiety, and somatic symptoms at baseline and increased responses to mental stress and during 5% CO(2) breathing, but not in response to exercise. However, no evidence was found for a corresponding exaggerated respiratory or autonomic response.

CONCLUSIONS

A young, female, and nonclinical population with numerous functional somatic symptoms and high levels of anxiety is characterized by an exaggerated perception of a normal physiological response.

Heart rate variability as predictor of nonresponse to mirtazapine in panic disorder: a preliminary study

Using spectral analysis of heart rate, several studies have shown that panic disorder patients are characterized by a reduced heart rate variability (HRV), indicative of abnormalities in autonomous nervous system (ANS) function. We recently reported that patients with panic disorder, who did not respond to pharmacotherapy, were characterized at baseline by a higher heart rate. In this study, ANS functioning is investigated as a possible predictor of nonresponse to pharmacotherapy. Twenty-eight medication-free panic disorder patients entered a 12-week open-label treatment study with mirtazapine. Five-minute HRV recordings were obtained before treatment and were analysed using spectral analysis. The data of 17 patients could be used. The total spectrum and low frequency power of responders to mirtazapine were significantly higher than those of nonresponders. Our findings suggest that nonresponders to short-term mirtazapine treatment are characterized at baseline by a lowered output of the ANS. The results are preliminary in view of the small sample studied.

Functional MRI changes during panic anticipation and imagery exposure

While undergoing fMRI, six patients with DSM IV diagnosis of panic disorder and six normal controls performed directed imagery of neutral, moderate and high anxiety situations based on an individually determined behavioral hierarchy. Brain activity was compared during high vs neutral anxiety blocks for each group of subjects using SPM99b. Panic patients showed increased activity in inferior frontal cortex, hippocampus and throughout the cingulate both anterior and posterior, extending into the orbitofrontal cortex and encompassing both hemispheres. These areas may constitute the important circuit in the psychopathology of panic disorder. We propose that this pattern of activity may enhance the encoding and retrieval of strong emotional events, facilitating the recapitulation of traumatic experiences and leading to panic disorder in vulnerable individuals.

Respiratory dysregulation in anxiety, functional cardiac, and pain disorders. Assessment, phenomenology, and treatment

Respiration is a complex physiological system affecting a variety of physical processes that can act as a critical link between mind and body. This review discusses the evidence for dysregulated breathing playing a role in three clinical syndromes: panic disorder, functional cardiac disorder, and chronic pain. Recent technological advances allowing the ambulatory assessment of endtidal partial pressure of CO2 (PCO2) and respiratory patterns have opened up new avenues for investigation and treatment of these disorders. The latest evidence from laboratories indicates that subtle disturbances of breathing, such as tidal volume instability and sighing, contribute to the chronic hypocapnia often found in panic patients. Hypocapnia is also common in functional cardiac and chronic pain disorders, and studies indicate that it mediates some of their symptomatology. Consistent with the role of respiratory dysregulation in these disorders, initial evidence indicates efficacy of respiration-focused treatment.

The somatic symptom paradox in DSM-IV anxiety disorders: suggestions for a clinical focus in psychophysiology

Although DSM-IV criteria for anxiety disorders include physiological symptoms, these symptoms are evaluated exclusively by verbal report. The current review explores the background for this paradox and tries to demonstrate on theoretical and empirical grounds how it could be resolved, providing new insights about the role of psychophysiological measures in the clinic. The three-systems approach to evaluating anxiety argues that somatic measures as well as verbal and behavioral ones are indispensable. However, the low concordance between these domains of measurement impugns their reliability and validity. We argue that concordance can be improved by examining the relationship of variables less global than anxiety and by restriction to specific anxiety disorders. For example, recent evidence from our and other laboratories indicate a prominent role of self-reported and physiologically measured breathing irregularities in panic disorder. Nonetheless, even within a diagnosis, anxiety patients vary radically in which somatic variables are deviant. Thus, in clinical practice, individual profiles of psychological and physiological anxiety responses may be essential to indicate distinct therapeutic approaches and ways of tracking improvement. Laboratory provocations specific to certain anxiety disorders and advances in ambulatory monitoring vastly expand the scope of self-report and physiological measurement and will likely contribute to a refined assessment of anxiety disorders.