Agoraphobia and the hyperventilation syndrome

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.

Respiratory manifestations of panic disorder: causes, consequences and therapeutic implications

Multiple respiratory abnormalities can be found in anxiety disorders, especially in panic disorder (PD). Individuals with PD experience unexpected panic attacks, characterized by anxiety and fear, resulting in a number of autonomic and respiratory symptoms. Respiratory stimulation is a common event during panic attacks. The respiratory abnormality most often reported in PD patients is increased CO2 sensitivity, which has given rise to the hypothesis of fundamental abnormalities in the physiological mechanisms that control breathing in PD. There is evidence that PD patients with dominant respiratory symptoms are more sensitive to respiratory tests than are those who do not manifest such symptoms, and that the former group constitutes a distinct subtype. Patients with PD tend to hyperventilate and to panic in response to respiratory stimulants such as CO2, triggering the activation of a hypersensitive fear network. Although respiratory physiology seems to remain normal in these subjects, recent evidence supports the idea that they present subclinical abnormalities in respiration and in other functions related to body homeostasis. The fear network, composed of the hippocampus, the medial prefrontal cortex, the amygdala and its brain stem projections, might be oversensitive in PD patients. This theory might explain why medication and cognitive-behavioral therapy are both clearly effective. Our aim was to review the relationship between respiration and PD, addressing the respiratory subtype of PD and the hyperventilation syndrome, with a focus on respiratory challenge tests, as well as on the current mechanistic concepts and the pharmacological implications of this relationship.

Organic and Hyperventilatory Causes of Anxiety-type Symptoms

In treating anxiety and phobic disorders it is helpful to be aware of physical illnesses that can present with anxiety-type features. This paper discusses a number of organic conditions whose presenting features could be mistaken for an anxiety state, viz. hyperthyroidism, Cushing's syndrome, hypoparathyroidism, phaeochromocytoma, hypoglycaemia, mitral valve prolapse, paroxysmal tachycardia, temporal lobe epilepsy, caffeinism, and food and chemical allergy. Hyperventilation is also discussed since it is an important but frequently neglected mechanism in many cases of anxiety and phobia.

Clinical Aspects and Treatment of the Hyperventilation Syndrome

The Hyperventilation Syndrome is a common disorder and clinical psychologists will be regularly confronted with it, because the syndrome is closely interwoven with psychological problems. The literature is reviewed with respect to pathophysiology of the complaints, aetiology of the syndrome and treatment. A new developmental model is presented and directions for future research are proposed.

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.

Depersonalization and derealization during panic and hypnosis in low and highly hypnotizable agoraphobics

The primary aim of the present study was to investigate the association between spontaneous experiences of depersonalization or derealization (D-D) during panic states and hypnosis in low and highly hypnotizable phobic individuals. Secondarily, the association among level of hypnotizability, capacity for imaginative involvement, and severity of phobic complaints was also assessed. Sixty-four patients with panic disorder with agoraphobia according to the DSM-III-R (American Psychiatric Association, 1987) criteria participated in the study. Proneness to experience D-D during hypnosis was positively related to hypnotizability, but only for agoraphobic patients who had already experienced these perceptual distortions during panic episodes. Correlations of level of hypnotizability and capacity for imaginative involvement with severity of agoraphobic complaints were not significant. These findings suggest that hypnotizability may be a mediating variable between two different, although phenotypically similar, perceptual distortions experienced during panic states and hypnosis. Implications for both theory and clinical practice are discussed.

Learning to have psychosomatic complaints: conditioning of respiratory behavior and somatic complaints in psychosomatic patients

OBJECTIVE

Assuming a subjective similarity between the experience of a hyperventilation episode and inhaling CO2-enriched air, we tested whether a respiratory challenge in association with a particular stimulus could result in altered respiratory behavior and associated somatic complaints upon presenting the stimulus only.

METHOD

Psychosomatic patients (N = 28) reporting hyperventilation complaints participated in a differential conditioning paradigm using odors with a positive or negative valence as conditioned stimuli (CS+ or CS-) and 7.4% CO2-enriched air as the unconditioned stimulus (US). Three CS+ and three CS-acquisition trials were run. During the test phase, two CS(+)- and two CS(-)-only trials were run, followed by two new test odors (with a positive or negative valence). Respiratory frequency, tidal volume, end-tidal fractional concentration of CO2, and heart rate were measured throughout the experiment. Somatic complaints were registered after each trial.

RESULTS

We observed a) increased respiratory frequency and an elevated level of somatic complaints upon presenting the CS+ only; b) a selective association effect: conditioning was only apparent with the negatively valenced CS+ odor; (c) no generalization of respiratory responses and complaints to the new odors; (d) no conditioning effect on dummy complaints that are usually not reported when inhaling CO2; (e) in exploratory comparisons with normal subjects, stronger conditioning effects on typical hyperventilation complaints in patients, and, in female subjects, on respiratory frequency.

CONCLUSION

Respiratory responses and psychosomatic complaints can be elicited by conditioned stimuli in a highly specific way. The findings are relevant for disorders in which respiratory abnormalities and/or psychosomatic complaints may play a role and for multiple chemical sensitivity.

Double-blind placebo-controlled study of the hyperventilation provocation test and the validity of the hyperventilation syndrome

BACKGROUND

Hyperventilation syndrome (HVS) describes a set of somatic and psychological symptoms thought to result from episodic or chronic hyperventilation. Recognition of symptoms during the hyperventilation provocation test (HVPT) is the most widely used criterion for diagnosis of HVS. We have investigated the validity of the HVPT and of the concept of HVS.

METHODS

In a randomised, double-blind, crossover design, the ability of 115 patients with suspected HVS to recognise symptoms during the HVPT was compared with the ability to recognise symptoms during a placebo test (isocapnic overbreathing, with carbon dioxide levels maintained by manual titration). 30 patients who had positive results on the HVPT underwent ambulatory transcutaneous monitoring of pCO2 to ascertain whether they hyperventilated during spontaneous symptom attacks.

FINDINGS

Of the 115 patients who underwent the HVPT and the placebo test, 85 (74%) reported symptom recognition during the HVPT (positive diagnosis HVS). Of that subset, 56 were also positive on the placebo test (false-positive), and 29 were negative on the placebo test (true-positive). False-positive and true-positive patients did not differ in symptom profile or in physiological variables. During ambulatory monitoring (15 true-positive, 15 false-positive) 22 attacks were registered. Transcutaneous end-tidal, pCO2 decreased during only seven. The decreases were slight and apparently followed the onset of the attack, which suggests that hyperventilation is a consequence rather than a cause of the attack. There were no apparent differences between false-positive and true-positive patients.

INTERPRETATION

The HVPT is invalid as a diagnostic test for HVS. Hyperventilation seems a negligible factor in the experience of spontaneous symptoms. The term HVS should be avoided.

Effects of high and low anxiety provoking instructions on the responses to the hyperventilation provocation test

This study examined the effect of high and low anxiety provoking instructions in subjects submitted to a Hyperventilation Provocation Test (HVPT). Subjects were 43 out-patients referred to our clinic for a diagnostic examination of Hyperventilation Syndrome (HVS). Results showed that anxiety levels were affected by the instruction manipulation, but the magnitude of this effect was less than expected and the instruction manipulation had no effect on intensity arid type of reproduced symptoms, nor on symptom recognition. Subjects who met Diagnostic and Statistical manual of Mental Disorders (3rd ed., rev,; American Psychiatric Association, 1987) criteria for Panic Disorder (PD) were not more responsive to the instruction manipulation than non-PD patients. It is argued that the small effect of the manipulation is probably not due to the solidity of the HVPT but to the pervasiveness of pretest cognitions and expectations. In line with this, the report of HVS symptoms appeared highly related to psychological trait measures like anxiety, fear of bodily sensations, and a general tendency to report somatic symptoms.

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Discordance between symptom and physiological criteria for the hyperventilation syndrome

Hyperventilation is assumed to produce a set of somatic and psychological symptoms, the so-called Hyperventilation Syndrome (HVS). Recognition of symptoms during the hyperventilation provocation test (HVPT) is the most widely used criterion for diagnosing HVS, but additional physiological and symptom criteria have been proposed. The concordance of various diagnostic criteria for HVS is investigated in the present study. Forty-eight psychiatric patients with panic disorder and 90 somatic patients with symptoms suspective of HVS performed a HVPT. There was a strong interrelationship between the various symptom criteria as well as the physiological criteria. However, almost no association between symptom and physiological HVS criteria were found. Symptom recognition was significantly related to trait anxiety, agoraphobia and depression. These data do not only question the validity of the HVPT, but also of the concept of HVS. The results are more consistent with a cognitive approach to anxiety in which the HVPT is seen as an aspecific stressor during which more anxious patients anticipate an anxiety attack.

The hyperventilation provocation test in panic disorder

Forty-eight patients with DSM-III-R Panic Disorder underwent a hyperventilation provocation Test (HVPT). Twenty-four patients rated the symptoms induced during the HVPT as similar to those occurring during panic attacks in daily life. Contrary to the classical hyperventilation model of panic, no differences were found in respiratory physiology between recognizers and non-recognizers before and during voluntary hyperventilation. Moreover, recognizers and non-recognizers reported comparable levels of panic and hyperventilation symptoms and state anxiety during panic attacks in daily life. Ten of the recognizers also had a panic attack during the HVPT, independent of any differential CO2 alterations. Compared to non-panickers, panickers obtained higher scores for agoraphobia and depression. On the basis of these results, it is concluded that recognizers or panickers do not show a tendency towards hyperventilation, but that reports of severe panic and hyperventilation symptoms are more closely related to the level of anxiety. These results are more consistent with the cognitive model of panic, which emphasizes the patient's tendency to interpret somatic symptoms catastrophically.

Psychophysiological investigations of patients with unilateral symptoms in the hyperventilation syndrome

Anxiety states sometimes lead to hyperventilation (HV) which may, in turn, give rise to a variety of physical symptoms. One way in which HV may present is with unilateral somatosensory symptoms, often left-sided. We report nine such cases. The mechanisms of lateralisation was examined using EEG and bilateral somatosensory evoked potentials which were carried out before and after HV. No difference in conduction velocity was found between affected and unaffected arms, but non-specific abnormalities were frequently noted in the EEGs. The results support the role of a central rather than a peripheral mechanism in the production of unilateral symptoms in HV.

Specific respiratory patterns distinguish among human basic emotions

Prototypical respiratory-facial-postural actions ('emotional effector patterns') related to six basic emotions had been extracted from an ensemble of physiological reactions present in subjects reliving intense emotional situations (Bloch & Santibañez, 1972). Subjects reproducing these actions could evoke the corresponding subjective experience, which suggested their use as an experimental model for generating controlled emotional states. The aim of the present study was to quantify the respiratory parameters which characterize the emotions of joy-laughter, sadness-crying, fear-anxiety, anger, erotic love and tenderness. Respiratory movements and facial/postural expressions were recorded from 36 young actors who had learned in previous workshops to express these emotions by reproducing the corresponding prototypical actions. A qualitative analysis of the recordings showed that as the emotional reproduction went along, both breathing and expression evolved from an initial 'robot-like' phase to a more natural stage in which spontaneous vocalizations and gestures appeared. This suggested a partial activation of the emotional network. The quantitative analysis of the respiratory movements for the fundamental cycles showed that for anger, erotic love and tenderness significant changes in amplitude, rate and duration of the 'expiratory pause' were the major elements of differentiation, while for sadness, joy and fear inspiratory over expiratory time ratios were the elements of differentiation. These last three emotions were further characterized by small amplitude/high rate saccadic respiratory movements superposed to different phases of the fundamental cycles. It is concluded that quantitatively well differentiated sets of respiratory changes characterize each of six basic emotions. The bottom-up experimental model for generating such emotions based on the joint activation of the respiratory-facial-postural systems and its relation to corresponding 'real-life' emotions is discussed.

Hyperventilation-induced panic attacks in panic disorder with agoraphobia

Eight minutes of hyperventilation to an end-tidal PCO2 of less than 20 mmHg led to a panic attack in 7 of 12 patients with panic disorder with agoraphobia and only 1 of 12 normal controls. Patients experienced greater increases in panic symptoms than controls during hyperventilation. Patients who reported more distress from somatic symptoms of hyperventilation during the preceding week were more likely to panic during hyperventilation. Patients who panicked during hyperventilation exhibited a delayed recovery of normocapnia following hyperventilation. Hyperventilation by this protocol is an effective means of inducing panic attacks in the laboratory. A hyperventilation challenge may identify a subgroup of patients for whom hyperventilation symptoms are frequently associated with panic.

Hyperventilation provocation in patients with chest pain and a negative treadmill exercise test

Seventeen (39%) of 44 patients with chest pain but without significant ST depression on treadmill exercise had their usual chest pain reproduced during or after 3 min of voluntary hyperventilation (VHV) at rest. These patients with hyperventilation positive tests had not only significantly more hyperventilation-related symptoms and respiratory complaints but also shorter breath-holding times, lower mean resting end-tidal pCO2 and higher mean respiratory rates than those with negative tests and normal controls. Of the psychological variables, only phobic avoidance scores for agoraphobia were higher in patients with positive tests. These findings suggest that in two fifths of patients with exercise tests negative for ischaemia, chest pain is associated with HV, but abnormalities of breath control and relative hypocapnia are present even in the absence of chest pain. It is possible that a chronic abnormality of respiratory control may interact with attitudinal factors in the experience of non-cardiac chest pain.

Treatment of panic attacks using cognitive therapy without exposure or breathing retraining

Cognitive treatment of panic attacks is based on the hypothesis that panic results from the catastrophic misinterpretation of bodily sensations, and that changing such misinterpretations will block the occurrence of panic. The treatment normally involves an integrated set of cognitive and behavioural techniques. In a consecutive series of panic patients, a multiple baseline across subjects design was used to investigate whether a modified form of treatment involving only cognitive procedures could reduce panic attack frequency. The results provide preliminary evidence that cognitive procedures directed at changing misinterpretations of bodily sensations can reduce panic attack frequency, and also that cognitive procedures which do not target misinterpretations may not reduce panic.

Hyperventilation and panic attacks

The role of hyperventilation in the aetiology of panic attacks is still unclear. This paper briefly reviews the role of hyperventilation and abnormal respiration to panic attacks and examines the experimental evidence. Evidence has been found that physiological variables such as paCO2 and pH are involved in the aetiology of panic attacks and panic disorder but the extent and the nature of the involvement of cognitive variables is undetermined. Based on current evidence, there is a need to integrate cognitive variables with the physiological framework proposed by the hyperventilation theory. Until clear experimental evidence is produced about the relationships between cognitive and physiological factors, the applicability of hyperventilation in the aetiology and treatment of panic attacks remains in question.

Elevated serum lactate following hyperventilation during glucose infusion in panic disorder

Early investigators reported that patients with anxiety syndromes associated with panic attacks produced more lactate during exercise than control subjects. These studies suggested a metabolic difference between patients and controls. However, the possibility that patients were simply less fit than controls could not be excluded. In this study, serum lactate was measured in panic disorder patients in response to a metabolic challenge not involving exercise. Voluntary hyperventilation during iatrogenic hyperglycemia led to an increase in serum lactate. The increase in serum lactate was significantly greater in panic disorder patients than in controls. Hyperventilation provoked panic attacks in 4 of 8 patients and none in 6 controls. There was no evidence of a relationship between the increase in lactate or the associated decrease in phosphate and the level of anxiety produced by this procedure.

Affective responses to hyperventilation: a test of the cognitive model of panic

A cognitive explanation of the association between acute hyperventilation and panic attacks has been proposed: the extent to which sensations produced by hyperventilation are interpreted in a negative and catastrophic way is said to be a major determinant of panic. Non-clinical subjects were provided with a negative or a positive interpretation of the sensations produced by equivalent amounts of voluntary hyperventilation. As predicted, there was a significant difference between positive and negative interpretation conditions on ratings of positive and negative affect. Subjects in the positive interpretation condition experienced hyperventilation as pleasant, and subjects in the negative interpretation condition experienced hyperventilation as unpleasant, even though both groups experienced similar bodily sensations and did not differ in their prior expectations of the affective consequences of hyperventilation. When the subjects were given a positive interpretation, the number of their sensations correlated with positive affect; when a negative interpretation was given, the number of bodily sensations correlated with negative affect. The results provide support for a cognitive model of panic and are inconsistent with the view that panic is simply a symptom of hyperventilation syndrome.

Waning of panic sensations during prolonged hyperventilation

Recent theories about panic emphasize that a hyperventilatory positive feedback loop is involved in panic: catastrophic misinterpretation of bodily sensations may trigger anxiety, anxiety may stimulate hyperventilation, hyperventilation may promote the salience of feared sensations etc. Such models leave unexplained how and when panics come to an end. It was hypothesised that panic with hyperventilation may end because pronounced hyperventilation becomes, in the course of time, less powerful in generating perceivable bodily sensations. Twenty healthy subjects hyperventilated forcefully and experienced clear panic symptoms as defined by DSM IIIR. When pCO2 was kept 55% below base line for 90 min, panic symptoms waned. The mean intensity of the symptoms declined as did the number of symptoms occurring. No panic symptoms were observed in the control group (n = 20) who ventilated normally. In so far as hyperventilation is involved in the positive feedback loops that characterize panic, panic attacks may be time-limited because sensations induced by hyperventilation become less salient even if massive hyperventilation continues. As to the explanation of the reported phenomenon, it is suggested that, apart from habituation, local physiological changes due to prolonged hyperventilation may produce a decrease in interoceptive input.

The pharmacology of human anxiety

The human pharmacology of anxiety disorders, including panic disorder, is detailed. The major theories center around the role of benzodiazepine receptor, noradrenergic and serotonergic dysfunction. The contribution that challenge tests with lactate, hyper- and hypocapnia, beta- and alpha-2-adrenoceptor agonists, peptides, pentylenetetrazol, and caffeine make to our understanding of the biological basis of anxiety and these major theories are described and discussed.

Symptom reporting during voluntary hyperventilation and mental load: implications for diagnosing hyperventilation syndrome

Hyperventilation is considered an important factor in the production of a variety of somatic symptoms. This complex of symptoms is called the Hyperventilation Syndrome (HVS). Recognition of symptoms during the hyperventilation provocation test (HVPT) is a widely used criterion for diagnosing HVS. The validity of this criterion is tested in the present study. Twenty-three patients suspected of HVS performed a HVPT (hyperventilation during 3 min) and a mental load task (Stroop Color Word Test; CWT). It appeared that about the same number of patients (61%) recognized symptoms during the HVPT as during the CWT (52%), despite severe hypocapnia in the first test and normocapnia in the second. Reporting of symptoms was significantly related to psychological state and trait measures (SCL-90 and STAI scores) and unrelated to the degree of hypocapnia. These data have far reaching consequences, as they not only undermine the validity of the HVPT, but also question the tenability of the concept of HVS.

Hyperventilation: is it a cause of panic attacks?

During transcutaneous PCO2 (PtcCO2) monitoring of 15 freely ambulant patients suffering from panic attacks, all the patients experienced a typical attack. Seven were identified as hyperventilators, as PtcCO2 fell to abnormally low levels during the attack. This group could not be distinguished on the basis of either their usual symptoms of panic or the hyperventilation provocation test. There was no apparent association between absolute levels of PCO2 and the nature of symptoms. The anxiety ratings of hyperventilators were lower than those of non-hyperventilators. These data do not support the hypothesis that hyperventilation causes panic attacks or contributes to their severity. Hyperventilation may be better understood as a consequence of panic.

Fear talk versus voluntary hyperventilation in agoraphobics and normals: a controlled study

Twenty-three drug-free patients with agoraphobia and panic disorder (DSM-III criteria) had, at rest, lower mean end-tidal PCO2 (32 v. 36 mmHg) and higher mean heart rate (92 v. 83 bpm) than did 18 controls. During 5 min of listening to fear talk, only eight (35%) patients and three (16%) controls panicked, but panic was associated with marked physiological changes in only two patients and one control. Patients said that breathlessness began slightly more often before than after panic. In 59% of patients the symptoms from voluntary hyperventilation (VHV) were very similar or identical to those of their usual panics. Compared with the remainder, these patients felt more unpleasant during hyperventilation (HV); in such patients HV may aggravate somatic symptoms. Agoraphobics with panic differed from controls in having higher baseline arousal, but were not more reactive than controls to HV or fear talk.

Respiratory control: its contribution to the treatment of panic attacks. A controlled study

Patients who experienced panic attacks, with or without avoidance, were treated for two weeks with either training in controlled breathing or a placebo treatment. Subsequently, both groups received a limited period of conventional anxiety treatments, most commonly in vivo exposure. Patients were subdivided into 'hyperventilators' and 'non-hyperventilators' on the basis of the conventional provocation test. Observer ratings of anxiety showed a greater improvement for the group that received breathing training, but there was no evidence that 'hyperventilators' benefited more from respiratory training than 'non-hyperventilators'. Self-report measures of anxiety, avoidance, and depression/dysphoria showed no difference between treatments. These findings suggest that training in controlled breathing is not of specific benefit for those identified as 'hyperventilators' by the provocation test, but that it may have a non-specific effect in the treatment of patients with panic attacks.

The effect of hypocapnia on extinction of conditioned fear responses

Conditioning models have been very helpful in the understanding of the etiology and maintenance of anxiety. Such laboratory models, however, leave unexplained why in many cases of naturally occurring anxiety, as in the case of agoraphobia, the fear responses do not extinguish. Literature on experimental anxiety provocation suggests that a systemic alkalosis might play a role in the maintenance of phobic fear. It was hypothesized that a subject in a state of respiratory alkalosis would show delayed extinction to classical conditioned anxiety. In a differential classical conditioning paradigm, consisting of a habituation-, an acquisition-, and an extinction-phase, slides and electric shocks were used as conditioned stimuli (CS) and unconditioned stimuli (US) respectively. The skin conductance response was taken as (U)CR. Subjects were randomly assigned to two groups: hyperventilation or control. It was shown that the extinction was not delayed when subjects were hypocapnic during the extinction. These data support the view that a respiratory alkalosis per se is not a sufficient condition for the maintenance of neurotic fears. The data of the present study are discussed in the context of existing literature on a psychological interpretation of the maintenance of anxiety.

The hyperventilation syndrome in panic disorder, agoraphobia and generalized anxiety disorder

The symptom complex of panic disorder and generalized anxiety disorder suggests an etiological role for hyperventilation. The present study investigates the overlap between DSM-III-R panic disorder, panic disorder with agoraphobia and generalized anxiety disorder with hyperventilation syndrome (HVS). The anxiety disorder diagnoses were based on a structured interview, and HVS syndrome (HVS). The anxiety disorder diagnoses were based on a structured interview, and HVS determined by the so-called hyperventilation provocation test (a brief period of voluntary hyperventilation with recognition of symptoms). The overlap rates with HVS were: 48% for panic disorder, 83% for panic disorder with agoraphobia and 82% for generalized anxiety disorder. However, a pilot study on transcutaneous monitoring of carbon dioxide tension leads us to question the validity of the voluntary hyperventilation method that we used to determine HVS-status. It is unclear whether hyperventilation plays an important role in panic and general anxiety, as our overlap findings suggest. For patients who recognize the symptoms induced by voluntary hyperventilation, the hyperventilation provocation procedure provides a therapeutic means of exposure to feared bodily sensations.

Breathing retraining, exposure and a combination of both, in the treatment of panic disorder with agoraphobia

The present study investigates the differential effectiveness of three treatment packages for agoraphobia. Patients suffering from panic disorder with agoraphobia (DSM-III-R) received one of three treatments: Breathing Retraining with Cognitive Restructuring (BRCR), graded self-exposure in vivo (EXP), or a combination of BRCR and EXP. Treatments consisted of 8 sessions. Assessment consisted of self-report measures for panic, phobic anxiety and avoidance, depression, general anxiety, somatic complaints and fear of body sensations, and of two respiratory measures (respiratory rate and alveolar pCO2). The treatments resulted in a reduction in symptomatology on all self-report measures, except panic frequency, and in a decrease in respiratory rate. There was no evidence for a differential efficacy for any of the treatments on any of the variables. Contrary to expectation, and at odds with findings from earlier studies, BRCR had no significant effect on panic frequency. A detailed comparison of sample characteristics of patients in our study and previous studies, did not yield insight into possible causes for the failure to replicate earlier results. The limited effectiveness of breathing retraining in reducing panic, as observed in the present study, leads us to conclude that the role of hyperventilation in panic is less important than previously thought.

Hyperventilation and anxiety in panic disorder, social phobia, GAD and normal controls

Patients with DSM-III Agoraphobia, Panic Disorder, GAD, Social Phobia and normal controls underwent a series of experimental procedures and measures to determine whether panic attack patients show a greater tendency towards hyperventilation that is independent from their anxiety levels. Contrary to expectations, the Agoraphobia and Panic Disorder patients did not show significantly lower levels of expired pCO2 at rest than the other anxious or non-anxious groups. However, the panic attack patients did show significantly higher levels of anxiety and hyperventilatory symptoms during a hyperventilation test and during breathing 5% CO2 in air. A strong relationship was found between hyperventilatory symptoms and anxiety in all groups of patients and in the controls. On the basis of these results it was concluded that Agoraphobia and Panic Disorder patients do not show a unique tendency toward hyperventilation, but rather that their hyperventilatory symptoms and perhaps intermittent overbreathing episodes are a function of the high levels of anxiety they experience.

Effects of low pulmonary CO2 on panic anxiety

In order to investigate the possible role of hyperventilation in the pathogenesis of panic, 11 panic patients and eight normal controls underwent a hyperventilation provocation test. The word "hyperventilation" itself was not used; the subjects were told the test was meant to measure the amount of carbon dioxide in their expired air. End tidal pCO2 was reduced to less than half of its initial value, resulting in a significant increase in physical symptoms, both in patients and controls. However, there proved to be no significant increase in subjective anxiety. It is suggested, that hypocarbia alone is not sufficient to provoke anxiety in panic disorder patients.

Rebreathing to cope with hyperventilation: experimental tests of the paper bag method

To explore if and how the common rebreathing (paper bag) approach to hyperventilation works, two experiments were carried out. In the first experiment, 12 normal volunteers, aware of the common physiological rebreathing rationale, were twice asked to overbreath intensely and then either to rebreath or to restart normal ventilation. Alveolar CO2 increased more quickly and physical symptoms disappeared earlier in the rebreathing condition. The second experiment had a similar design; however, this time the subjects were led to believe that, after both hyperventilation provocation tests, they were rebreathing in a semiclosed tube system. On one of the occasions, the tube system was, in fact, open. The CO2 restoration again differed in the two conditions. In this second experiment, the moment of symptom disappearance was not significantly earlier in the rebreathing condition. The combined results of the studies suggest that expectation and suggestion play a role in the effects of rebreathing approaches on hyperventilation.

Panic disorder and agoraphobia: fear of fear or fear of the symptoms produced by hyperventilation?

Two versions of the fear-of-fear hypothesis of panic disorder are discussed. The fear-of-the-somatic-effects-of-fear version, which is distinguished from the classical conditioning version, is compared with the hyperventilation theory of panic disorder and agoraphobia. The fear-of-the-somatic-effects-of-fear hypothesis is criticized on the basis of its inability to explain adequately (a) the initiation of panic attacks, (b) the growth in intensity of panic attacks, and (c) the termination of panic attacks. The tenability of the hyperventilation theory is supported by evidence from programs of treatment derived from the basic assumptions of the theory.

Hyperventilation and panic disorder

Hyperventilation syndrome and panic disorder are both common, serious, and easily treatable disorders. The similarity of their symptoms and physiology, the demonstration of hyperventilation during spontaneous and laboratory-induced panic episodes, provocation of panic-like symptoms in some patients with panic disorder using hyperventilation, the importance of psychologic factors in producing hyperventilation, and successful treatment of panic disorder with breathing retraining all indicate a strong association between these two conditions. About 50 percent of patients in each group show evidence of both disorders. It is suggested that many patients in each group show evidence of both disorders. It is suggested that many patients with either diagnosis have the same disorder and share a biologically and often genetically determined hypersensitivity of a central "alarm" system. Panic and hyperventilation provoked by inappropriate activation of this system are postulated to reinforce each other by a positive feedback loop. Treatments directed at any part of this loop are likely to be successful. Clinical implications of the link between these conditions are discussed.

Pulmonary carbon dioxide and panic-arousing sensations after 35% carbon dioxide inhalation: hypercapnia/hyperoxia versus hypercapnia/normoxia

Experimental research has demonstrated that CO2 inhalation provides a valid laboratory model for acute panic. Earlier studies employed CO2/O2 mixtures that were not only hypercapnic but also hyperoxic, raising the question of the relative contribution of the hyperoxidity. A comparison between a hypercapnic/hyperoxic mixture (35% CO2/65% O2) and a hypercapnic/normoxic mixture (35% CO2/20% O2/45% N2) revealed no differences on self-reported panic symptoms or end tidal pCO2. It is concluded that findings from previous CO2/O2 inhalation studies should be attributed to the hypercapnic, rather than to the hyperoxic, nature of the mixtures.

Effects of induced hyperventilation on electrodermal response habituation to agoraphobia-relevant stimuli

The role of hyperventilation in the aetiology of anxiety disorders was investigated in an analogue study. It was hypothesised that induced hyperventilation would alter subsequent subjective and physiological responses to visually presented agoraphobic material. Three groups (N = 16) of students were used and each was divided into two sub-groups which were presented with slides of either potentially agoraphobic or neutral content. During the first phase of the experiment, subjects were exposed to 10 slides whilst their breathing rate was manipulated. Group FB was instructed to hyperventilate by asking the subjects to breathe fast and deeply, Group SB was instructed to breathe at a slow rate and Group NB breathed normally. After a recovery phase, subjects were re-exposed to the same visual stimuli as used in the first phase of the experiment. Measures of skin conductance response amplitude were obtained for each stimulus in the series. In addition, heart rate and respiration were monitored, and subjective measures of somatic and affective states were obtained. Subjects also rated the pleasantness of the stimuli. The hyperventilation instructions resulted in delayed electrodermal habituation relative to the other groups. This finding could not be accounted for in terms of group differences in either physiological or subjective 'arousal'.

Respiratory control in the treatment of panic attacks: replication and extension with concurrent measurement of behaviour and pCO2

A case series is reported in which nine patients who experienced phobic and/or nonphobic panic attacks were given a cognitive-behavioural treatment based on the supposition that catastrophic interpretations of sensations produced by hyperventilation played an important role in their attacks. Large and rapid reductions in panic attack frequency and questionnaire report of fear were observed. Patients' resting pCO2 was significantly lower than controls and rose to normal levels during treatment.

Respiratory distress during panic attacks associated with agoraphobia

59 patients with agoraphobia and panic attacks completed check lists of physical and cognitive panic-related symptoms to estimate the extent to which respiratory distress is associated with panic. Over half of the patients reported experiencing difficulty breathing during most or all panic attacks, but respiratory difficulty was not consistently associated with panic. Further research is needed using alternative methods of assessment, but these findings suggest that biologically oriented explanations of panic which ascribe a precipitative role to respiratory dysfunction cannot account for many of the panic attacks experienced by agoraphobics.