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

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.

Temporal variations in the pattern of breathing: techniques, sources, and applications to translational sciences

The breathing process possesses a complex variability caused in part by the respiratory central pattern generator in the brainstem; however, it also arises from chemical and mechanical feedback control loops, network reorganization and network sharing with nonrespiratory motor acts, as well as inputs from cortical and subcortical systems. The notion that respiratory fluctuations contain hidden information has prompted scientists to decipher respiratory signals to better understand the fundamental mechanisms of respiratory pattern generation, interactions with emotion, influences on the cortical neuronal networks associated with cognition, and changes in variability in healthy and disease-carrying individuals. Respiration can be used to express and control emotion. Furthermore, respiration appears to organize brain-wide network oscillations via cross-frequency coupling, optimizing cognitive performance. With the aid of information theory-based techniques and machine learning, the hidden information can be translated into a form usable in clinical practice for diagnosis, emotion recognition, and mental conditioning.

Reading on a smartphone affects sigh generation, brain activity, and comprehension

Electronic devices have become an indispensable part of our daily lives, while their negative aspects have been reported. One disadvantage is that reading comprehension is reduced when reading from an electronic device; the cause of this deficit in performance is unclear. In this study, we investigated the cause for comprehension decline when reading on a smartphone by simultaneously measuring respiration and brain activity during reading in 34 healthy individuals. We found that, compared to reading on a paper medium, reading on a smartphone elicits fewer sighs, promotes brain overactivity in the prefrontal cortex, and results in reduced comprehension. Furthermore, reading on a smartphone affected sigh frequency but not normal breathing, suggesting that normal breathing and sigh generation are mediated by pathways differentially influenced by the visual environment. A path analysis suggests that the interactive relationship between sigh inhibition and overactivity in the prefrontal cortex causes comprehension decline. These findings provide new insight into the respiration-mediated mechanisms of cognitive function.

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.

Respiratory Variability, Sighing, Anxiety, and Breathing Symptoms in Low- and High-Anxious Music Students Before and After Performing

Music performance anxiety (MPA) is a major problem for music students. It is largely unknown whether music students who experience high or low anxiety differ in their respiratory responses to performance situations and whether these co-vary with self-reported anxiety, tension, and breathing symptoms. Affective processes influence dynamic respiratory regulation in ways that are reflected in measures of respiratory variability and sighing. This study had two goals. First, we determined how measures of respiratory variability, sighing, self-reported anxiety, tension, and breathing symptoms vary as a function of the performance situation (practice vs. public performance), performance phase (pre-performance vs. post-performance), and the general MPA level of music students. Second, we analyzed to what extent self-reported anxiety, tension, and breathing symptoms co-vary with the respiratory responses. The participants were 65 university music students. We assessed their anxiety, tension, and breathing symptoms with Likert scales and recorded their respiration with the LifeShirt system during a practice performance and a public performance. For the 10-min periods before and after each performance, we computed number of sighs, coefficients of variation (CVs, a measure of total variability), autocorrelations at one breath lag (ARs(1), a measure of non-random variability) and means of minute ventilation (V’_E), tidal volume (V_T), inspiration time (T_I), and expiration time (T_E). CVs and sighing were greater whereas AR(1) of V’_E was lower in the public session than in the practice session. The effect of the performance situation on CVs and sighing was larger for high-MPA than for low-MPA participants. Higher MPA levels were associated with lower CVs. At the within-individual level, anxiety, tension, and breathing symptoms were associated with deeper and slower breathing, greater CVs, lower AR(1) of V’_E, and more sighing. We conclude that respiratory variability and sighing are sensitive to the performance situation and to musicians’ general MPA level. Moreover, anxiety, tension, breathing symptoms, and respiratory responses co-vary significantly in the context of music performance situations. Respiratory monitoring can add an important dimension to the understanding of music performance situations and MPA and to the diagnostic and intervention outcome assessments of MPA.

Relationships Between Smoking Status and Psychological Distress, Optimism, and Health Environment Perceptions at Time of Diagnosis of Actual or Suspected Lung Cancer

BACKGROUND

While much research and practice resources have addressed smoking cessation among cancer patients, less emphasis has been placed on personal psychological and environment factors associated with smoking at the time of diagnosis.

OBJECTIVE

The aim of this study was to examine differences in psychological distress, optimism, and perceptions of the health environment/illness experience based on smoking status in patients with current, former, and no smoking history with newly diagnosed suspected or actual lung cancer.

METHODS

Data were derived from a descriptive study of 52 patients (34 men and 18 women aged 37-83 years) undergoing diagnostic evaluation for actual or suspected lung cancer. Descriptive statistics were used to characterize data. Analysis of variance, χ, and Spearman correlation tests were used to determine relationships among main study variables (smoking status, anxiety, worry, perceived cognitive functioning, optimistic outlook, health environment/illness experience perceptions).

RESULTS

Current smoking status was associated with higher psychological distress (anxiety and worry) among patients facing a new suspected or actual cancer diagnosis.

CONCLUSIONS

The study was able to provide important information relative to smoking status and psychological distress at the time of diagnosis of suspected or actual lung cancer. Findings demonstrate needs for assessment and targeted interventions to reduce psychological distress and to promote long-term adaptation in patients smoking at time of diagnosis.

IMPLICATIONS FOR PRACTICE

Nurses are positioned to provide support and resources for cancer patients. It is critical that smoking cessation interventions also address nicotine craving, emotion regulation, and adaptive coping skills.

Post-sigh sleep apneas in mice: Systematic review and data-driven definition

Sleep apneas can be categorized as post-sigh (prevailing in non-rapid eye movement sleep) or spontaneous (prevailing in rapid eye movement sleep) according to whether or not they are preceded by an augmented breath (sigh). Notably, the occurrence of these apnea subtypes changes differently in hypoxic/hypercapnic environments and in some genetic diseases, highlighting the importance of an objective discrimination. We aim to: (a) systematically review the literature comparing the criteria used in categorizing mouse sleep apneas; and (b) provide data-driven criteria for this categorization, with the final goal of reducing experimental variability in future studies. Twenty-two wild-type mice, instrumented with electroencephalographic/electromyographic electrodes, were placed inside a whole-body plethysmographic chamber to quantify sleep apneas and sighs. Wake-sleep states were scored on 4-s epochs based on electroencephalographic/electromyographic signals. Literature revision showed that highly different criteria were used for post-sigh apnea definition, the intervals for apnea occurrence after sigh ranging from 1 breath up to 20 s. In our data, the apnea occurrence rate during non-rapid eye movement sleep was significantly higher than that calculated before the sigh only in the 1st and 2nd 4-s epochs following a sigh. These data suggest that, in mice, apneas should be categorized as post-sigh only if they start within 8 s from a sigh; the choice of shorter or longer time windows might underestimate or slightly overestimate their occurrence rate, respectively.

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.

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.

Increased ventilatory variability and complexity in patients with hyperventilation disorder

It has been hypothesized that hyperventilation disorders could be characterized by an abnormal ventilatory control leading to enhanced variability of resting ventilation. The variability of tidal volume (VT) often depicts a nonnormal distribution that can be described by the negative slope characterizing augmented breaths formed by the relationship between the probability density distribution of VT and VT on a log-log scale. The objectives of this study were to describe the variability of resting ventilation [coefficient of variation (CV) of VT and slope], the stability in respiratory control (loop, controller and plant gains characterizing ventilatory-chemoresponsiveness interactions) and the chaotic-like dynamics (embedding dimension, Kappa values characterizing complexity) of resting ventilation in patients with a well-defined dysfunctional breathing pattern characterized by air hunger and constantly decreased PaCO2 during a cardiopulmonary exercise test. Compared with 14 healthy subjects with similar anthropometrics, 23 patients with hyperventilation were characterized by increased variability of resting tidal ventilation (CV of VT median [interquartile]: 26% [19-35] vs. 36% [28–48], P = 0.020; slope: −6.63 [−7.65; −5.36] vs. −3.88 [−5.91; −2.66], P = 0.004) that was not related to increased chemical drive (loop gain: 0.051 [0.039–0.221] vs. 0.044 [0.012–0.087], P = 0.149) but that was related to an increased ventilatory complexity (Kappa values, P < 0.05). Plant gain was decreased in patients and correlated with complexity (with Kappa 5 − degree 5: Rho = −0.48, P = 0.006). In conclusion, well-defined patients suffering from hyperventilation disorder are characterized by increased variability of their resting ventilation due to increased ventilatory complexity with stable ventilatory-chemoresponsiveness interactions.

Detecting paralinguistic events in audio stream using context in features and probabilistic decisions

Non-verbal communication involves encoding, transmission and decoding of non-lexical cues and is realized using vocal (e.g. prosody) or visual (e.g. gaze, body language) channels during conversation. These cues perform the function of maintaining conversational flow, expressing emotions, and marking personality and interpersonal attitude. In particular, non-verbal cues in speech such as paralanguage and non-verbal vocal events (e.g. laughters, sighs, cries) are used to nuance meaning and convey emotions, mood and attitude. For instance, laughters are associated with affective expressions while fillers (e.g. um, ah, um) are used to hold floor during a conversation. In this paper we present an automatic non-verbal vocal events detection system focusing on the detect of laughter and fillers. We extend our system presented during Interspeech 2013 Social Signals Sub-challenge (that was the winning entry in the challenge) for frame-wise event detection and test several schemes for incorporating local context during detection. Specifically, we incorporate context at two separate levels in our system: (i) the raw frame-wise features and, (ii) the output decisions. Furthermore, our system processes the output probabilities based on a few heuristic rules in order to reduce erroneous frame-based predictions. Our overall system achieves an Area Under the Receiver Operating Characteristics curve of 95.3% for detecting laughters and 90.4% for fillers on the test set drawn from the data specifications of the Interspeech 2013 Social Signals Sub-challenge. We perform further analysis to understand the interrelation between the features and obtained results. Specifically, we conduct a feature sensitivity analysis and correlate it with each feature's stand alone performance. The observations suggest that the trained system is more sensitive to a feature carrying higher discriminability with implications towards a better system design.

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.

The nuclear progesterone receptor reduces post-sigh apneas during sleep and increases the ventilatory response to hypercapnia in adult female mice

We tested the hypothesis that the nuclear progesterone receptor (nPR) is involved in respiratory control and mediates the respiratory stimulant effect of progesterone. Adult female mice carrying a mutation in the nPR gene (PRKO mice) and wild-type controls (WT) were implanted with an osmotic pump delivering vehicle or progesterone (4 mg/kg/day). The mice were instrumented with EEG and neck EMG electrodes connected to a telemetry transmitter. The animals were placed in a whole body plethysmograph 7 days after surgery to record ventilation, metabolic rate, EEG and neck EMGs for 4 consecutive hours. The animals were exposed to hypercapnia (5% CO₂), hypoxia (12% O₂) and hypoxic-hypercapnia (5% CO₂+12% O₂–5 min each) to assess chemoreflex responses. EEG and EMG signals were used to characterize vigilance states (e.g., wake, non-REM, and REM sleep). PRKO mice exhibited similar levels of minute ventilation during non-REM and REM sleep, and higher frequencies of sighs and post-sigh apneas during non-REM sleep compared to WT. Progesterone treatment increased minute ventilation and metabolic rate in WT and PRKO mice during non-REM sleep. In WT mice, but not in PRKO mice, the ventilation under hypercapnia and hypoxic hypercapnia was enhanced after progesterone treatment. We conclude that the nPR reduces apnea frequency during non-REM sleep and enhances chemoreflex responses to hypercapnia after progesterone treatment. These results also suggest that mechanisms other than nPR activation increase metabolic rate in response to progesterone treatment in adult female mice.

The integrative role of the sigh in psychology, physiology, pathology, and neurobiology

"Sighs, tears, grief, distress" expresses Johann Sebastian Bach in a musical example for the relationship between sighs and deep emotions. This review explores the neurobiological basis of the sigh and its relationship with psychology, physiology, and pathology. Sighs monitor changes in brain states, induce arousal, and reset breathing variability. These behavioral roles homeostatically regulate breathing stability under physiological and pathological conditions. Sighs evoked in hypoxia evoke arousal and thereby become critical for survival. Hypoarousal and failure to sigh have been associated with sudden infant death syndrome. Increased breathing irregularity may provoke excessive sighing and hyperarousal, a behavioral sequence that may play a role in panic disorders. Essential for generating sighs and breathing is the pre-Bötzinger complex. Modulatory and synaptic interactions within this local network and between networks located in the brainstem, cerebellum, cortex, hypothalamus, amygdala, and the periaqueductal gray may govern the relationships between physiology, psychology, and pathology. Unraveling these circuits will lead to a better understanding of how we balance emotions and how emotions become pathological.

Revisão sistemática sobre tratamentos psicológicos para problemas relacionados ao crack

OBJETIVO: O objetivo deste artigo é apresentar uma revisão sistemática da literatura sobre tratamentos psicológicos oferecidos para usuários de crack. MÉTODOS: Foi realizada uma revisão sistemática por meio de uma busca na literatura internacional e nacional, indexada nas bases de dados Medline, SciELO, Lilacs e Web of Science. Os descritores utilizados foram: crack or crack cocaine or cocaine smokers (crack) and psychosocial treatment or psycotherapy or psychosocial treatment (tratamento psicológico) e a busca incluiu artigos publicados no período de 2001 a 2011. RESULTADOS: No total foram encontrados 155 artigos por meio dos descritores utilizados. Os artigos foram agrupados em três dimensões: tratamentos psicossociais na internação e cuidados continuados, relaxamento respiratório e outras técnicas comportamentais e abordagens fundamentadas na Entrevista Motivacional, Cognitivo-Comportamental e Modelo Transteórico de Mudança. CONCLUSÃO: Com base nos estudos examinados, pode ser formulado um elenco de algumas intervenções que estão sendo estudadas para o tratamento de usuários de crack e algumas apresentam resultados satisfatórios. Os poucos esforços de comparação entre técnicas resultaram em evidências de pouca ou nenhuma diferença, ainda que se registre o benefício para os usuários na aplicação de qualquer delas. Não existe consenso acerca da efetividade no tratamento de usuários de crack. Parece oportuno e necessário o aprofundamento dos estudos nesse campo.

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.

Sigh rate and respiratory variability during normal breathing and the role of negative affectivity

Spontaneous breathing was measured in healthy persons scoring either high (N=45) or low (N=30) on trait negative affectivity (NA), during a 10 min period of quiet sitting using the LifeShirt System®. Sighing and respiratory variability before and after sighs were assessed. Total respiratory variability of minute ventilation was indexed by the coefficient of variation and structured (correlated) variability was quantified by the autocorrelation. Total variability was higher before a sigh than before a non-sigh, without concomitant differences in structured variability, suggesting more random variability before a sigh. After a sigh, correlated variability increased whereas it remained the same after a non-sigh. Thus sighing acted as a resetter of the respiratory system. However, when comparing the low and the high NA group, this pattern was specific for high NA individuals. We conclude that it is important to take into account individual difference variables when studying the psychophysiological functions of sighing.

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.

Sigh rate and respiratory variability during mental load and sustained attention

Spontaneous breathing consists of substantial correlated variability: Parameters characterizing a breath are correlated with parameters characterizing previous and future breaths. On the basis of dynamic system theory, negative emotion states are predicted to reduce correlated variability whereas sustained attention is expected to reduce total respiratory variability. Both are predicted to evoke sighing. To test this, respiratory variability and sighing were assessed during a baseline, stressful mental arithmetic task, nonstressful sustained attention task, and recovery in between tasks. For respiration rate (excluding sighs), reduced total variability was found during the attention task, whereas correlated variation was reduced during mental load. Sigh rate increased during mental load and during recovery from the attention task. It is concluded that mental load and task-related attention show specific patterns in respiratory variability and sigh rate.