Characteristics of sighing in panic disorder

The psychophysiology of the sigh: II: The sigh from the psychological perspective

A sigh is a distinct respiratory behavior with specific psychophysiological roles. In two accompanying reviews we will discuss the physiological and psychological functions of the sigh. The present review will focus on the psychological functions of the sigh. We discuss the regulatory effects of a sigh, and argue how these effects may become maladaptive when sighs occur excessively. The adaptive role of a sigh is discussed in the context of regulation of psychophysiological states. We propose that sighs facilitate transitions from one psychophysiological state to the next, and this way contribute to psychophysiological flexibility, via a hypothesized resetting mechanism. We discuss how a sigh resets respiration, by controlling mechanical and metabolic properties of respiration associated with respiratory symptoms. Next, we elaborate on a sigh resetting emotional states by facilitating emotional transitions. We attempt to explain the adaptive and maladaptive functions of a sigh in the framework of stochastic resonance, in which we propose occasional, spontaneous sighs to be noise contributing to psychophysiological regulation, while excessive sighs result in psychophysiological dysregulation. In this context, we discuss how sighs can contribute to therapeutic interventions, either by increasing sighs to improve regulation in case of a lack of sighing, or by decreasing sighs to restore regulation in case of excessive sighing. Finally, a research agenda on the psychology of sighs is presented.

Psychological profiles, quality of life, and parental attitudes in children with Sighing dyspnea

BACKGROUND

There are a limited number of studies investigating the relationship of sighing dyspnea (SD) with psychiatric disorders and various mental states.

METHODS

This cross-sectional study enrolled 39 pediatric patients with SD, but free from apparent cardiopulmonary diseases, who presented to a pediatric pulmonology policlinic between June and December 2019 and age-gender matched 34 healthy children were recruited for comparison. Patient characteristics, psychological or physical trauma history, and cigarette smoke exposure were recorded. All the participants completed the "NOSE scale," "Modified Borg Scale," "Children Depression Inventory," "Screen for Child Anxiety Related Disorders," "Pediatric Quality of Life Inventory," "Stress Coping Style Scale," "Family Assessment Device," and "Parents Attitude Scale."

RESULTS

Compared to the control group, there was a statistically significantly higher rate in the SD group of physical or psychological trauma history (35.9% vs. 14.7%, p = .04) and passive cigarette smoking (60.5% vs.27.3%, p = .005). When the groups were compared in respect of depression and anxiety levels, the depression score, total anxiety level, somatic/panic, generalized anxiety and fear of school points were determined to be statistically significantly higher in the SD group. The QoL scores (total, physical, and psychosocial) in the SD group were found to be statistically significantly lower than those of the control group.

CONCLUSION

To the best of our knowledge, this is the first study to have examined the psychological profiles of SD patients and their families in detail, and to have evaluated the effect of SD on quality of life.

The sigh and related behaviors

Breathing is a critical, complex, and highly integrated behavior. Normal rhythmic breathing, also referred to as eupnea, is interspersed with different breathing related behaviors. Sighing is one of such behaviors, essential for maintaining effective gas exchange by preventing the gradual collapse of alveoli in the lungs, known as atelectasis. Critical for the generation of both sighing and eupneic breathing is a region of the medulla known as the preBötzinger Complex (preBötC). Efforts are underway to identify the cellular pathways that link sighing as well as sneezing, yawning, and hiccupping with other brain regions to better understand how they are integrated and regulated in the context of other behaviors including chemosensation, olfaction, and cognition. Unraveling these interactions may provide important insights into the diverse roles of these behaviors in the initiation of arousal, stimulation of vigilance, and the relay of certain behavioral states. This chapter focuses primarily on the function of the sigh, how it is locally generated within the preBötC, and what the functional implications are for a potential link between sighing and cognitive regulation. Furthermore, we discuss recent insights gained into the pathways and mechanisms that control yawning, sneezing, and hiccupping.

Brain Circuit of Claustrophobia-like Behavior in Mice Identified by Upstream Tracing of Sighing

Emotions are distinct patterns of behavioral and physiological responses triggered by stimuli that induce different brain states. Elucidating the circuits is difficult because of challenges in interrogating emotional brain states and their complex outputs. Here, we leverage the recent discovery in mice of a neural circuit for sighing, a simple, quantifiable output of various emotions. We show that mouse confinement triggers sighing, and this "claustrophobic" sighing, but not accompanying tachypnea, requires the same medullary neuromedin B (Nmb)-expressing neurons as physiological sighing. Retrograde tracing from the Nmb neurons identified 12 forebrain centers providing presynaptic input, including hypocretin (Hcrt)-expressing lateral hypothalamic neurons. Confinement activates Hcrt neurons, and optogenetic activation induces sighing and tachypnea whereas pharmacologic inhibition suppresses both responses. The effect on sighing is mediated by HCRT directly on Nmbneurons. We propose that this HCRT-NMB neuropeptide relay circuit mediates claustrophobic sighing and that activated Hcrt neurons are a claustrophobia brain state that directly controls claustrophobic outputs.

Habituation or Normalization? Experiential and Respiratory Recovery From Voluntary Hyperventilation in Treated Versus Untreated Patients With Panic Disorder

Psychophysiological theories postulate respiratory dysregulation as a mechanism contributing to panic disorder (PD). Additionally, symptomatic and respiratory recovery from voluntary hyperventilation (HVT-recovery) have been shown to lag in PD and it is unclear if HVT-recovery normalizes with treatment. Thirty-seven panic disorder patients were randomized to hypoventilation therapy (TX, n = 20) or waitlist control (WL, n = 17) (Meuret et al., 2008). In a secondary analysis, their HVT-recovery was analyzed at pre- and post-TX/WL, compared to 29 healthy controls (HC). HVT included three phases: 5-min baseline, 3-min hyperventilation, and 8-min recovery. HVT-elicited symptom severity and anxiety were rated following each phase, and end-tidal PCO₂ and respiratory rate (RR) were recorded throughout. Treatment, compared to WL, was highly effective in reducing PD pathology (d=2.21, Meuret et al., 2008). At pre-TX/WL, PD demonstrated delayed HVT-recovery PCO₂ and higher RR. Treated patients demonstrated normalization of HVT-recovery for PCO₂ and RR; however, improvements of HVT-recovery for symptom severity and anxiety did not differ between TX and WL. Results replicate pretreatment HVT respiratory recovery abnormalities in PD and further demonstrate normalization, comparable to HC, following successful treatment. The results provide support for respiratory dysregulation as a feature of PD and demonstrate the utility of HVT respiratory recovery as treatment outcome measure for respiration-based PD therapy.

Role of deep breaths in ultrasonic vocal production of Sprague-Dawley rats

Deep breaths are one of three breathing patterns in rodents characterized by an increased tidal volume. While humans incorporate deep breaths into vocal behavior, it was unknown whether nonhuman mammals use deep breaths for vocal production. We have utilized subglottal pressure recordings in awake, spontaneously behaving male Sprague-Dawley rats in five contexts: sleep, rest, noxious stimulation, exposure to a female in estrus, and exposure to an unknown male. Deep breaths were produced at rates ranging between 17.5 and 90.3 deep breaths per hour. While overall breathing and vocal rates were higher in social and noxious contexts, the rate of deep breaths was only increased during the male's interaction with a female. Results also inform our understanding of vocal-respiratory integration in rats. The rate of deep breaths that were associated with a vocalization during the exhalation phase increased with vocal activity. The proportion of deep breaths that were associated with a vocalization (on average 22%) was similar to the proportion of sniffing or eupnea breaths that contain a vocalization. Therefore, vocal motor patterns appear to be entrained to the prevailing breathing rhythm, i.e., vocalization uses the available breathing pattern rather than recruiting a specific breathing pattern. Furthermore, the pattern of a deep breath was different when it was associated with a vocalization, suggesting that motor planning occurs. Finally, deep breaths are a source for acoustic variation; for example, call duration and fundamental frequency modulation were both larger in 22-kHz calls produced following a deep inhalation.NEW & NOTEWORTHY The emission of a long, deep, audible breath can express various emotions. The investigation of deep breaths, also known as sighing, in a nonhuman mammal demonstrated the occasional use of deep breaths for vocal production. Similar to the human equivalent, acoustic features of a deep breath vocalization are characteristic.

Restoring Ventilatory Control Using an Adaptive Bioelectronic System

Ventilatory pacing by electrical stimulation of the phrenic nerve or of the diaphragm has been shown to enhance quality of life compared to mechanical ventilation. However, commercially available ventilatory pacing devices require initial manual specification of stimulation parameters and frequent adjustment to achieve and maintain suitable ventilation over long periods of time. Here, we have developed an adaptive, closed-loop, neuromorphic, pattern-shaping controller capable of automatically determining a suitable stimulation pattern and adapting it to maintain a desired breath-volume profile on a breath-by-breath basis. The system adapts the pattern of stimulation parameters based on the error between the measured volume sampled every 40 ms and a desired breath volume profile. In vivo studies in anesthetized male Sprague-Dawley rats without and with spinal cord injury by spinal hemisection at C2 indicated that the controller was capable of automatically adapting stimulation parameters to attain a desired volume profile. Despite diaphragm hemiparesis, the controller was able to achieve a desired volume in the injured animals that did not differ from the tidal volume observed before injury (p = 0.39). Closed-loop adaptive pacing partially mitigated hypoventilation as indicated by reduction of end-tidal CO₂ values during pacing. The closed-loop controller was developed and parametrized in a computational testbed before in vivo assessment. This bioelectronic technology could serve as an individualized and autonomous respiratory pacing approach for support or recovery from ventilatory deficiency.

Habituation of the electrodermal response - A biological correlate of resilience?

Current approaches to quantifying resilience make extensive use of self-reported data. Problematically, this type of scales is plagued by response distortions–both deliberate and unintentional, particularly in occupational populations. The aim of the current study was to develop an objective index of resilience. The study was conducted in 30 young healthy adults. Following completion of the Connor-Davidson Resilience Scale (CD-RISC) and Depression/Anxiety/Stress Scale (DASS), they were subjected to a series of 15 acoustic startle stimuli (95 dB, 50 ms) presented at random intervals, with respiration, skin conductance and ECG recorded. As expected, resilience (CD-RISC) significantly and negatively correlated with all three DASS subscales–Depression (r = -0.66, p<0.0001), Anxiety (r = -0.50, p<0.005) and Stress (r = -0.48, p<0.005). Acoustic stimuli consistently provoked transient skin conductance (SC) responses, with SC slopes indexing response habituation. This slope significantly and positively correlated with DASS-Depression (r = 0.59, p<0.005), DASS-Anxiety (r = 0.35, p<0.05) and DASS-Total (r = 0.50, p<0.005) scores, and negatively with resilience score (r = -0.47; p = 0.006), indicating that high-resilience individuals are characterized by steeper habituation slopes compared to low-resilience individuals. Our key finding of the connection between habituation of the skin conductance responses to repeated acoustic startle stimulus and resilience-related psychometric constructs suggests that response habituation paradigm has the potential to characterize important attributes of cognitive fitness and well-being–such as depression, anxiety and resilience. With steep negative slopes reflecting faster habituation, lower depression/anxiety and higher resilience, and slower or no habituation characterizing less resilient individuals, this protocol may offer a distortion-free method for objective assessment and monitoring of psychological resilience.

Automated analysis of breathing waveforms using BreathMetrics: a respiratory signal processing toolbox

Nasal inhalation is the basis of olfactory perception and drives neural activity in olfactory and limbic brain regions. Therefore, our ability to investigate the neural underpinnings of olfaction and respiration can only be as good as our ability to characterize features of respiratory behavior. However, recordings of natural breathing are inherently nonstationary, nonsinusoidal, and idiosyncratic making feature extraction difficult to automate. The absence of a freely available computational tool for characterizing respiratory behavior is a hindrance to many facets of olfactory and respiratory neuroscience. To solve this problem, we developed BreathMetrics, an open-source tool that automatically extracts the full set of features embedded in human nasal airflow recordings. Here, we rigorously validate BreathMetrics' feature estimation accuracy on multiple nasal airflow datasets, intracranial electrophysiological recordings of human olfactory cortex, and computational simulations of breathing signals. We hope this tool will allow researchers to ask new questions about how respiration relates to body, brain, and behavior.

A Multisite Benchmarking Trial of Capnometry Guided Respiratory Intervention for Panic Disorder in Naturalistic Treatment Settings

Panic disorder (PD) is associated with hyperventilation. The efficacy of a brief respiratory feedback program for PD has been established. The aim of the present study was to expand these results by testing a similar program with more clinically representative patients and settings. Sixty-nine adults with PD received 4 weeks of Capnometry Guided Respiratory Intervention (CGRI) using Freespira, which provides feedback of end-tidal CO₂ (P_ETCO₂) and respiration rate (RR), in four non-academic clinical settings. This intervention is delivered via home use following initial training by a clinician and provides remote monitoring of client adherence and progress by the clinician. Outcomes were assessed post-treatment and at 2- and 12-month follow-up. CGRI was associated with an intent-to-treat response rate of 83% and a remission rate of 54%, and large decreases in panic severity. Similar decreases were found in functional impairment and in global illness severity. Gains were largely sustained at follow-up. P_ETCO₂ moved from the slightly hypocapnic range to the normocapnic range. Benchmarking analyses against a previously-published controlled trial showed very similar outcomes, despite substantial differences in sample composition and treatment settings. The present study confirms prior clinical results and lends further support to the viability of CGRI in the treatment of PD.

A sigh of relief or a sigh of expected relief: Sigh rate in response to dyspnea relief

Research has suggested that sighs may serve a regulatory function during stress and emotions by facilitating relief. Evidence supports the hypotheses that sighs both express and induce relief from stress. To explore the potential role of sighs in the regulation of symptoms, the present study aimed to investigate the relationship between sighs and relief of symptoms, and relief of dyspnea, specifically. Healthy volunteers participated in two studies (N = 44, N = 47) in which dyspnea was induced by mild (10 cmH₂ O/l/s) or high (20 cmH₂ 0/l/s) inspiratory resistances. Dyspnea relief was induced by the offset of the inspiratory resistances (transitions from high and mild inspiratory resistance to no resistance). Control comparisons included dyspnea increases (transitions from no or mild inspiratory resistance to high inspiratory resistance) and dyspnea continuations (continuations of either no resistance or a high resistance). In Experiment 1, dyspnea levels were cued. In Experiment 2, no cues were provided. Sigh rate during dyspnea relief was significantly higher compared to control conditions, and sigh rate increased as self-reported dyspnea decreased. Additionally, sigh rate was higher during cued dyspnea relief compared to noncued dyspnea relief. These results suggest that sighs are important markers of dyspnea relief. Moreover, sighs may importantly express dyspnea relief, as they are related to experiential dyspnea decreases and occur more frequently during expected dyspnea relief. These findings suggest that sighs may not only be important in the regulation of stress and emotions, but also may be functional in the regulation of dyspnea.

Sigh rate during emotional transitions: More evidence for a sigh of relief

Evidence suggests that sighs regulate stress and emotions, e.g. by facilitating relief. This study aimed to investigate sigh rates during relief. In addition, links between sighs, anxiety sensitivity and HPA-axis activity were explored. Healthy volunteers (N=29) were presented cues predicting the valence of subsequent stimuli. By sequencing cues that predicted pleasant or unpleasant stimuli with or without certainty, transitions to certain pleasantness (relief) or to certain unpleasantness (control) were created and compared to no transitions. Salivary cortisol, anxiety sensitivity and respiration were measured. Sigh frequency was significantly higher during relief than during control transitions and no transition states, and higher during control transitions than during no transition states. Sigh frequency increased with steeper cortisol declines for high anxiety sensitive persons. Results confirm a relationship between sighs and relief. In addition, results suggest that sigh frequency is importantly related to HPA-axis activity, particularly in high anxiety sensitive persons.

Metabolic decoupling in daily life in patients with panic disorder and agoraphobia

Various studies have assessed autonomic and respiratory underpinnings of panic attacks, yet the psychophysiological functioning of panic disorder (PD) patients has rarely been examined under naturalistic conditions at times when acute attacks were not reported. We hypothesized that emotional activation in daily life causes physiologically demonstrable deviations from efficient metabolic regulation in PD patients. Metabolic coupling was estimated as within-individual correlations between heart rate (HR) and indices of metabolic activity, i.e., physical activity (measured by 3-axial accelerometry, Acc), and minute ventilation (Vm, measured by calibrated inductive plethysmography, as proxy for oxygen consumption). A total of 565 daytime hours were recorded in 19 PD patients and 20 healthy controls (HC). Pairwise cross-correlations of minute-by-minute averages of these metabolic indices were calculated for each participant and then correlated with several indices of self-reported anxiety. Ambulatory HR was elevated in PD (p = .05, d = 0.67). Patients showed reduced HR-Acc (p < .006, d = 0.97) and HR-Vm coupling (p < .009, d = 0.91). Combining Vm and Acc to predict HR showed the strongest group separation (p < .002, d = 1.07). Discriminant analyses, based on the combination of Vm and Acc to predict HR, classified 77% of all participants correctly. In PD, HR-Acc coupling was inversely related to trait anxiety sensitivity, as well as tonic and phasic daytime anxiety. The novel method that was used demonstrates that anxiety in PD may reduce efficient long-term metabolic coupling. Metabolic decoupling may serve as physiological characteristic of PD and might aid diagnostics for PD and other anxiety disorders. This measure deserves further study in research on health consequences of anxiety and psychosocial stress.

Are respiratory abnormalities specific for panic disorder? A meta-analysis

OBJECTIVES

There is evidence of baseline respiratory abnormalities in panic disorder (PD), but whether they are specific to PD remains unclear. To investigate this issue, we meta-analyzed results from studies comparing baseline respiratory and hematic variables between subjects with PD and subjects with other anxiety disorders.

METHODS

A literature search in bibliographic databases was performed. Fixed-effects models were applied. Several moderator analyses and publication bias diagnostics were performed.

RESULTS

We found: (1) significantly lower mean end-tidal partial pressure of CO(2) (et-pCO(2)) in subjects with PD than in those with social phobia (SP) or generalized anxiety disorder (GAD), and (2) higher mean respiratory rate, lower venous et-pCO(2) and HCO(3)(-) concentration in subjects with PD than in those with SP. No publication bias was found.

CONCLUSIONS

Subjects with PD show a condition of baseline hyperventilation when compared to subjects with SP or GAD. Hematic variables suggest that the hyperventilation may be chronic. These results support the idea that baseline respiratory abnormalities are specific to PD pathophysiology. Further studies are needed to clarify whether these abnormalities are related to a malfunction of the respiratory system or to specific cognitive/emotional/behavioral factors in this population.

The effects of sighing on the cardiovascular system

Elicitation of high-amplitude oscillations in the cardiovascular system may serve to dampen psychophysiological reactivity to emotional and cognitive loading. Prior work has used paced breathing to impose clinically valuable high-amplitude ∼ 0.1 Hz oscillations. In this study, we investigated whether rhythmical sighing could likewise produce high-amplitude cardiovascular oscillations in the very low frequency range (0.003-0.05 Hz). ECG, respiration, skin conductance, and beat-to-beat blood pressure were collected in 24 healthy participants during baseline, 0.1 Hz paced breathing, and 0.02 Hz paced sighing (1 sigh every 50s, with normal breathing interspersed). Results showed that each sigh elicited a strong, well-defined reaction in the cardiovascular system. This reaction did not habituate when participants repeatedly sighed for 8.5 min. The result was a high-amplitude 0.02 Hz oscillation in multiple cardiovascular parameters. Thus, paced sighing is a reliable method for imposing very low frequency oscillations in the cardiovascular system, which has research and clinical implications that warrant further study.

Respiratory patterns reflect different levels of aggressiveness and emotionality in Wild-type Groningen rats

Respiratory patterns represent a promising physiological index for assessing emotional states in preclinical studies. Since disturbed emotional regulation may lead to forms of excessive aggressiveness, in this study we investigated the hypothesis that rats that differ largely in their level of aggressive behavior display matching alterations in respiration. Respiration was recorded in male high-aggressive (HA, n = 8) and non-aggressive (NA, n = 8) Wild-type Groningen rats using whole-body plethysmography. Subsequently, anxiety-related behaviors were evaluated in the elevated plus maze and social avoidance-approach tests. During respiratory testing, HA rats showed elevated basal respiratory rate, reduced sniffing, exaggerated tachypnoeic response to an acoustic stimulus and a larger incidence of sighs. In addition, HA rats spent less time in the open arms of the plus maze and displayed higher levels of social avoidance behavior compared to NA rats. These findings indicate that HA rats are characterized by alterations in respiratory functioning and behavior that are overall indicative of an anxiety-like phenotype.

Coordination of breathing with nonrespiratory activities

Many articles in this section of Comprehensive Physiology are concerned with the development and function of a central pattern generator (CPG) for the control of breathing in vertebrate animals. The action of the respiratory CPG is extensively modified by cortical and other descending influences as well as by feedback from peripheral sensory systems. The central nervous system also incorporates other CPGs, which orchestrate a wide variety of discrete and repetitive, voluntary and involuntary movements. The coordination of breathing with these other activities requires interaction and coordination between the respiratory CPG and those governing the nonrespiratory activities. Most of these interactions are complex and poorly understood. They seem to involve both conventional synaptic crosstalk between groups of neurons and fluid identity of neurons as belonging to one CPG or another: neurons that normally participate in breathing may be temporarily borrowed or hijacked by a competing or interrupting activity. This review explores the control of breathing as it is influenced by many activities that are generally considered to be nonrespiratory. The mechanistic detail varies greatly among topics, reflecting the wide variety of pertinent experiments.

Responses to voluntary hyperventilation in children with separation anxiety disorder: implications for the link to panic disorder

BACKGROUND

Biological theories on respiratory regulation have linked separation anxiety disorder (SAD) to panic disorder (PD). We tested if SAD children show similarly increased anxious and psychophysiological responding to voluntary hyperventilation and compromised recovery thereafter as has been observed in PD patients.

METHODS

Participants were 49 children (5-14 years old) with SAD, 21 clinical controls with other anxiety disorders, and 39 healthy controls. We assessed cardiac sympathetic and parasympathetic, respiratory (including pCO2), electrodermal, electromyographic, and self-report variables during baseline, paced hyperventilation, and recovery.

RESULTS

SAD children did not react with increased anxiety or panic symptoms and did not show signs of slowed recovery. However, during hyperventilation they exhibited elevated reactivity in respiratory variability, heart rate, and musculus corrugator supercilii activity indicating difficulty with respiratory regulation.

CONCLUSIONS

Reactions to hyperventilation are much less pronounced in children with SAD than in PD patients. SAD children showed voluntary breathing regulation deficits.

Different patterns of respiration in rat lines selectively bred for high or low anxiety

In humans, there is unequivocal evidence of an association between anxiety states and altered respiratory function. Despite this, the link between anxiety and respiration has been poorly evaluated in experimental animals. The primary objective of the present study was to investigate the hypothesis that genetic lines of rats that differ largely in their anxiety level would display matching alterations in respiration. To reach this goal, respiration was recorded in high-anxiety behavior (HAB, n = 10) and low-anxiety behavior (LAB, n = 10) male rats using whole-body plethysmography. In resting state, respiratory rate was higher in HABs (85 ± 2 cycles per minute, cpm) than LABs (67 ± 2 cpm, p<0.05). During initial testing into the plethysmograph and during a restraint test, HAB rats spent less time at high-frequency sniffing compared to LAB rats. In addition, HAB rats did not habituate in terms of respiratory response to repetitive acoustic stressful stimuli. Finally, HAB rats exhibited a larger incidence of sighs during free exploration of the plethysmograph and under stress conditions. We conclude that: i) HAB rats showed respiratory changes (elevated resting respiratory rate, reduced sniffing in novel environment, increased incidence of sighs, and no habituation of the respiratory response to repetitive stimuli) that resemble those observed in anxious and panic patients, and ii) respiratory patterns may represent a promising way for assessing anxiety states in preclinical studies.

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.

Imposing respiratory variability patterns

To ensure respiratory stability and flexibility, healthy breathing shows balanced variability consisting of considerable correlated variability (parameters of each breath are correlated to parameters of adjoining breaths) and some random variability. Sighing resets this balance when respiration lacks variability or becomes excessively irregular. The present study aimed to investigate the effect of imposed patterns of breathing variability on sighing and self-reported (dis)comfort. Spontaneous breathing was compared to imposed non-variable, correlated and random breathing. Results show that executing imposed breathing is difficult, demanding, and induces tension. Sigh occurrence following spontaneous and imposed breathing patterns could be predicted by self-reported discomfort and increased random variability. However, including non-variable, correlated and random breathing patterns only, the effects of self-reported discomfort on sigh occurrence override the effects of altered breathing variability.

Respiratory variability and sighing: a psychophysiological reset model

Whereas respiratory psychophysiological research has mainly studied respiratory time and volume, variability in these parameters has been largely disregarded, even though it may provide important information about respiratory regulation. The present paper reviews the literature on respiratory variability and elaborates on the importance of assessing various components of respiratory variability when studying the interrelationships between emotions and breathing. A model is proposed that predicts specific action tendencies related to emotions to disturb the balance between various respiratory variability components depending on valence by arousal and control dimensions. The central focus of the paper is sighing. The causes and consequences of sighing are reviewed and integrated in the proposed model in which sighing is hypothesized to function as a resetter in the regulation of both breathing and emotions, because it restores a balance in respiratory variability fractions and causes relief.

A sigh following sustained attention and mental stress: effects on respiratory variability

Normal breathing consists of considerable correlated variability (parameters of subsequent breaths are correlated) and some random variability. Emotional and attentive states alter normal breathing variability, which can be restored by a sigh. The present study aimed to investigate the effects of mental arithmetic and sustained attention on respiratory variability. In addition, the effect of a spontaneous sigh following both conditions was examined, compared to an instructed sigh and a control maneuver. Mental arithmetic and sustained attention were characterized by decreased correlated and total breathing variability, respectively. A spontaneous sigh restored correlated variability. An instructed sigh restored correlated variability following mental arithmetic, and increased total variability following sustained attention. These results suggest that a spontaneous sigh and an instructed sigh, when physiologically appropriate, restore respiratory variability influenced by stress or attention.

The "other" respiratory effect of opioids: suppression of spontaneous augmented ("sigh") breaths

The purpose of this study was to examine the effects of a clinically relevant opioid on the production of augmented breaths (ABs) in unanesthetized animals breathing normal room air, using a dosage which does not depress breathing. To do this we monitored breathing noninvasively, in unrestrained animals before and after subcutaneous injection of either morphine, or a saline control. The effect of ketamine/xylazine was also studied to determine the potential effect of an alternative sedative agent. Last, the effect of naloxone was studied to determine the potential influence of endogenous opioids in regulating the normal incidence of ABs. Morphine (5 mg/kg) had no depressive effect on breathing, but completely eliminated ABs in all animals in room air (P = 0.027). However, when animals breathed hypoxic air (10% O(2)), animals did express ABs, although their incidence was still reduced by morphine (P < 0.001). This was not a result of sedation per se, as ABs continued at their normal rate in room air during sedation with ketamine. Naloxone had no effect on breathing or AB production, and so endogenous opioids are not likely involved in regulating their rate of production under normal conditions. Our results show that in unanesthetized animals breathing normal room air, a clinically relevant opioid eliminates ABs, even at a dose that does not cause respiratory depression. Despite this, hypoxia-induced stimulation of breathing can facilitate the production of ABs even with the systemic opioid present, indicating that peripheral chemoreceptor stimulation provides a potential means of overcoming the opioid-induced suppression of these respiratory events.

Stress-induced respiratory pattern changes in asthma

OBJECTIVES

To build upon prior research on stress-related breathing pattern changes in asthma. Previous research has considered a limited set of respiratory parameters and has remained equivocal. Emotions and stress are known to change the respiratory pattern. In asthma, certain breathing patterns have adverse effects on the airways and lead to symptom exacerbation.

METHODS

We studied respiration during resting conditions and an acute psychosocial stressor (a free speech and mental arithmetic task) in participants with asthma (n = 20) and healthy controls (n = 19). The respiratory pattern was recorded with respiratory inductance plethysmography. Partial pressure of end-tidal carbon dioxide (PCO(2)) was measured with capnometry before and after stress.

RESULTS

The overall minute ventilation was higher in asthma (mean [standard deviation] = 9.0 [4.0] L versus 6.8 [4.1] L, p < .05), but levels of the PCO(2) were comparable (34.6 [3.5] mm Hg versus 35.0 [3.7] mm Hg, p = .667) to healthy controls during prestress and poststress phases. Participants with asthma also showed a significant lengthening of inspiration, expiration, and the total respiratory cycle during stress compared with healthy controls (p < .05). During stress tasks, all participants showed marked increases in tidal volume, inspiratory flow, minute ventilation, tidal volume instability, ribcage contribution to tidal volume, and ribcage-abdominal asynchrony. A significant increase in tidal volume instability and a tendency toward lengthening of expiration and the total respiratory cycle were observed in quiet-sitting periods at prestress to poststress in asthma.

CONCLUSIONS

Expiratory lengthening and variable tidal volumes are characteristic for individuals with asthma during psychosocial stress. The function and possible association of these changes with symptom exacerbations require further study.

Naturalistically observed sighing and depression in rheumatoid arthritis patients: a preliminary study

OBJECTIVE

This study tested the degree to which naturalistically observed sighing in daily life is a behavioral indicator of depression and reported physical symptoms (i.e., experienced pain and flare days) in rheumatoid arthritis (RA) patients.

DESIGN

Thirteen RA patients wore the Electronically Activated Recorder (EAR), an observational ambulatory assessment tool, for two weekends (Friday through Sunday) approximately one month apart. The EAR periodically recorded snippets of ambient sounds from participants' momentary environments (50 s every 18 min). Sighs were coded from the sampled ambient sounds.

MAIN OUTCOME MEASURES

Depression was assessed with the Center for Epidemiological Studies Depression Scale and the Beck Depression Inventory. Pain during the past month was assessed with a 10-cm visual-analog scale, and number of flare days during the prior 6 months was reported.

RESULTS

Sighing was significantly and strongly related to patients' levels of depression and nonsignificantly and less strongly related to their reported pain and number of flare days.

CONCLUSION

The findings suggest that sighing can serve as an observable marker of depression in RA patients. Because the sample size was small, the findings should be considered preliminary.

Airway response to emotion- and disease-specific films in asthma, blood phobia, and health

Earlier research found autonomic and airway reactivity in asthma patients when they were exposed to blood-injection-injury (BII) stimuli. We studied oscillatory resistance (R(os)) in asthma and BII phobia during emotional and disease-relevant films and examined whether muscle tension counteracts emotion-induced airway constriction. Fifteen asthma patients, 12 BII phobia patients, and 14 healthy controls viewed one set of negative, positive, neutral, BII-related, and asthma-related films with leg muscle tension and a second set without. R(os), ventilation, cardiovascular activity, and skin conductance were measured continuously. R(os) was higher during emotional compared to neutral films, particularly during BII material, and responses increased from healthy over asthmatic to BII phobia participants. Leg muscle tension did not abolish R(os) increases. Thus, the airways are particularly responsive to BII-relevant stimuli, which could become risk factors for asthma patients.

Temporal stability and coherence of anxiety, dyspnea, and physiological variables in panic disorder

Twenty-five panic disorder (PD) patients, 19 social phobics (SP), and 20 healthy controls (HC) sat quietly for 15 min, rating their anxiety and dyspnea every 30s while respiratory, cardiovascular, and electrodermal responses were recorded. No panic attacks were reported. For self-reported anxiety and dyspnea, within-subject variability over time was higher in PD than in SP or HC. In PD within-subject correlations across 30-s epochs were significant for (a) self-reported anxiety versus dyspnea, end-tidal pCO2, minute volume, duty cycle, skin conductance level, and interbeat interval, and for (b) dyspnea versus end-tidal pCO2, minute volume, tidal volume, and inspiratory flow rate. Several positive or negative correlations were greater in PD than in other groups. Thus in PD, experienced anxiety and dyspnea are temporally unstable but are correlated with each other and with fluctuations in respiratory and autonomic variables, even in the absence of panic attacks.

Hyperventilation in panic disorder and asthma: empirical evidence and clinical strategies

Sustained or spontaneous hyperventilation has been associated with a variety of physical symptoms and has been linked to a number of organic illnesses and mental disorders. Theories of panic disorder hold that hyperventilation either produces feared symptoms of hypocapnia or protects against feared suffocation symptoms of hypercapnia. Although the evidence for both theories is inconclusive, findings from observational, experimental, and therapeutic studies suggest an important role of low carbon dioxide (CO2) levels in this disorder. Similarly, hypocapnia and associated hyperpnia are linked to bronchoconstriction, symptom exacerbation, and lower quality of life in patients with asthma. Raising CO2 levels by means of therapeutic capnometry has proven beneficial effects in both disorders, and the reversing of hyperventilation has emerged as a potent mediator for reductions in panic symptom severity and treatment success.

Take a deep breath: the relief effect of spontaneous and instructed sighs

Spontaneous sighing is related to subjective relief of negative emotional states. Whether this also applies to instructed sighing is not known. The present study aimed to investigate sEMG and respiratory variability (1) during recovery from mental stress with and without an instructed sigh; (2) before and after spontaneous sighs throughout the experiment. A spontaneous sigh was preceded by increasing sEMG and increasing random respiratory variability, and followed by decreasing sEMG and increased structured correlated respiratory variability. Following an instructed sigh, a smaller reduction in sEMG and an increase in random respiratory variability during recovery from mental stress were observed. Thus, a spontaneous sigh seemed to induce relief. An instructed sigh appeared to inhibit recovery from mental stress.

Diversity of effective treatments of panic attacks: what do they have in common?

By comparing efficacious psychological therapies of different kinds, inferences about common effective treatment mechanisms can be made. We selected six therapies for review on the basis of the diversity of their theoretical rationales and evidence for superior efficacy: psychoanalytic psychotherapy, hypercapnic breathing training, hypocapnic breathing training, reprocessing with and without eye-movement desensitization, muscle relaxation, and cognitive behavior therapy. The likely common element of all these therapies is that they reduce the immediate expectancy of a panic attack, disrupting the vicious circle of fearing fear. Modifying expectation is usually regarded as a placebo mechanism in psychotherapy, but may be a specific treatment mechanism for panic. The fact that this is seldom the rationale communicated to the patient creates a moral dilemma: Is it ethical for therapists to mislead patients to help them? Pragmatic justification of a successful practice is a way out of this dilemma. Therapies should be evaluated that deal with expectations directly by promoting positive thinking or by fostering non-expectancy.

HPA axis, respiration and the airways in stress--a review in search of intersections

Given clear connections between respiratory distress and subjective anxiety, it is not surprising that respiratory psychophysiologists have been interested in the psychobiology of anxiety. Given parallel links between anxiety and stress, it is not surprising that the hypothalamic-pituitary adrenal (HPA) stress system has also been a focus in anxiety research. However, despite extensive work in respiratory psychophysiology and stress neuroendocrinology--and evidence that these systems are jointly dysregulated in anxiety disorders--direct studies of their interactions are rare. This paper reviews evidence for scientific intersections, providing an overview of the HPA axis, its psychobiology, and shared neural substrates for HPA and respiratory control. We examine HPA hormone effects on respiration, immune/inflammatory mediators, and lung maturation. We also examine respiratory/dyspnea effects on HPA axis. There are clear points of intersection in the neuroscience of respiration and stress. Given the importance of both systems to an organism's ability to survive and adapt in challenging and changing environments, further study of their interactions is needed.

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 pathophysiology of panic disorder: an ambulatory monitoring study

OBJECTIVE

To assess the external validity of laboratory baselines in panic disorder (PD), frequently associated with respiratory pattern abnormalities like increased respiratory variability and sighing, implying a stable pathophysiologic trait characteristic.

METHODS

Physical activity and a variety of breath-by-breath volumetric, timing, and variability measures of respiration were recorded in the daily life of 26 patients with PD and 26 healthy controls (HC), using a novel ambulatory monitoring system optimized for reliable assessment of respiratory pattern. Data were stratified for physical activity to eliminate its confounding effects.

RESULTS

Groups showed strong and consistent diurnal patterns in almost all respiratory variables. However, patients with PD did not differ from HC regarding any of the respiratory timing, volumetric and variability measures, with negligible group effect sizes for all measures. Patients with fewer self-reported respiratory symptoms of anxiety exhibited more pronounced rapid shallow breathing as well as diminished total breath time and its variability.

CONCLUSIONS

Despite state-of-the-art ambulatory assessment and sufficient statistical power to detect respiratory alterations previously observed in the laboratory, we found no evidence for such alterations in PD patients' daily life. Neither the total PD group nor patients with particularly pronounced respiratory symptomatology displayed increased respiratory variability. These results caution against interpreting results from laboratory baselines in PD as reflecting a stable trait characteristic. Rather, they likely represent a state-trait interaction due to enhanced reactivity of PD patients to novel environments. These results challenge aspects of respiratory theories of PD that were based on laboratory findings.

Respiratory variability preceding and following sighs: a resetter hypothesis

Respiratory behavior is characterized by complex variability with structured and random components. Assuming that both a lack of variability and too much randomness represent suboptimal breathing regulation, we hypothesized that sighing acts as a resetter inducing structured variability. Spontaneous breathing was measured in healthy persons (N=42) during a 20min period of quiet sitting using the LifeShirt(®) System. Four blocks of 10 breaths with a 50% window overlap were determined before and after spontaneous sighs. Total respiratory variability of minute ventilation was measured using the coefficient of variation and structured (correlated) variability was quantified using autocorrelation. Towards a sigh, total variability gradually increased without concomittant changes in correlated variability, suggesting that randomness increased. After a sigh, correlated variability increased. No changes in variability were found in comparable epochs without intermediate sighs. We conclude that a sigh resets structured respiratory variability, enhancing information processing in the respiratory system.

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.

Do blood phobia patients hyperventilate during exposure by breathing faster, deeper, or both?

BACKGROUND

Recently we found that patients with blood-injection-injury (BII) phobia tend to hyperventilate when exposed to feared stimuli. Hyperventilation results from increases in minute ventilation above levels required by metabolic demand and can result from increases in either frequency or depth of breathing, or a combination of both.

METHOD

In order to determine which of these factors contributed most to hyperventilation in BII phobia we analyzed breathing patterns of BII phobia patients (N=12) and non-anxious controls (N=14), recorded with respiratory inductance plethysmography. Participants viewed ten film clips of either an emotionally positive, negative, or neutral quality, as well as surgery and asthma-relevant clips. During five film clips (one from each category) they also tensed their leg muscles.

RESULTS

Minute ventilation was markedly increased in blood phobia patients compared to other groups during surgery films. Also, tidal volume and irregularity of tidal volume showed strong increases, while respiration rate was not affected. Leg muscle tension increased ventilation in general but far below the extent brought about by hyperventilation in BII phobia. Patients who were breathing deeper during exposure reported stronger symptoms of dizziness, light-headedness and faintness. In general, patients showed a higher rate of spontaneous sighs throughout all film presentations, but not at baseline.

CONCLUSION

Thus, hyperventilation in blood phobia is produced by excessively deep and irregular breathing and may contribute to fainting responses. Behavioral interventions for BII phobia could benefit from attention to this aspect of dysfunctional breathing.

Fear-conditioned respiration and its association to cardiac reactivity

This study aimed to investigate ventilatory correlates of conditioned fear responses. Respiratory, end-tidal carbon dioxide pressure (PetCO(2)) and heart rate changes were studied in a differential fear-conditioning paradigm. Forty-two participants viewed pictures of faces. One picture (CS+) was followed by a human scream (US) during the acquisition phase, but not in a subsequent extinction phase. Conditioning of PetCO(2) (decrease), respiratory cycle time (decrease) and inspiratory duty time (increase) was established and subsequently extinguished. When participants were clustered according to their conditioned PetCO(2) responses during acquisition, only a group showing a conditioned decrease in PetCO(2) showed also a differential cardiac acceleration, a decrease in expiratory duration and an increase in inspiratory duty time in response to the CS+. These results suggest that preparation for defensive action is characterized by a tendency towards hyperventilation and cardiac acceleration.