Controlled study of respiratory responses during prolonged measurement in patients with chronic hyperventilation

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.

Respiration in psychophysiology: methods and applications

With the use of advanced equipment, respiratory measures can unobtrusively and reliably be assessed in a variety of psychophysiological research settings. New computerized analysis techniques can break down respiration into a number of components that provide valid estimates of variations in respiratory control mechanisms in the brain stem. Thus analysed, respiratory responses may vary in at least two dimensions: (A) with regard to drive and timing aspects, and (B) with regard to the metabolic appropriateness of the respiratory response. Assessment of respiratory responses may be relevant for a broad variety of research areas, including studies of the physiological effects of mental load and stress, investigations of physiological correlates of emotions and affect, and research linking physiological responses to subjective distress and psychosomatic disorders.

Relation of hypocapnic symptoms to rate of fall of end-tidal PCO2 in normal subjects

Hyperventilation is of little clinical relevance unless it causes symptoms. These are often non-specific. Their threshold for onset and relation to steady level of arterial (or its equivalent, end-tidal PCO2; PETCO2) are uncertain, and it has been suggested that they may relate better to the rate of fall of PCO2 than to the absolute level. We investigated this in nine normal subjects, who breathed to and fro through a pneumotachograph into an open circuit in which the concentration of CO2 could be varied. Tidal volume, respiratory frequency and ventilation was measured on-line by a Compaq computer, and PETCO2 at the mouth was measured by capnograph. Subjects overbreathed at a fixed rate and depth until symptoms consisting of dizziness, paraesthesiae and light headedness occurred. Then, without their knowledge and while they continued to overbreathe, inspired CO2 was increased to restore PETCO2 to normal and abolish symptoms, and was then withdrawn again over either approximately 0.1, 2.5 or 5 min until symptoms were again reported. The PETCO2 at this point was noted. The three protocols were performed in each subject in a random order and the same symptoms were reported each time. When averaged across all subjects, symptoms occurred at mean PETCO2 values of 20.3, 19.2 and 18.6 mmHg (2.71, 2.56 and 2.48 kPa), respectively. These were not significantly different, and it can be concluded that there was no influence of rate of fall of PCO2 on threshold for symptoms. Chest pain only occurred in one subject and may have a different mechanism.

Unexplained chest pain and breathlessness

Complaints of chest pain and breathlessness are common in both primary care and medical outpatient settings. A subgroup of these patients who find their way into tertiary care settings and subsequently are found to have no relevant organic pathology are at risk of continuing morbidity. One possible reason for this is that diagnostic strategies often focus on establishing an organic cause of pain and ignore psychosocial factors. In this article I have attempted to describe not only the prevalence but also the clinical characteristics of patients with medically unexplained cardiorespiratory symptoms. A method of establishing a positive diagnosis of noncardiac chest pain has also been outlined. This is based on an interactive and overlapping model that takes into account not only a number of psychological and social factors but also current physical and cardiac risk factors. It is important for nonpsychiatric physicians to diagnose noncardiac pain at an earlier stage in the evolution of the disorder. This would have major beneficial effects for patients, including (1) fewer unnecessary investigations; (2) less distress and functional disability; (3) reduced cost to the hospital; and (4) fewer iatrogenic complications.

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.

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.

Value of measuring end tidal partial pressure of carbon dioxide as an adjunct to treadmill exercise testing

The end tidal partial pressure of carbon dioxide (PCO2) was measured during treadmill exercise in 30 normal controls and 113 patients referred for assessment of chest pain. Among the 92 patients without significant ST depression hypocapnia occurred more often in those reporting "typical" than "atypical" chest pain (17 of 22 patients compared with 29 of 70; p less than 0.01). Hypocapnia was uncommon in patients with significant ST depression whether reporting typical or atypical chest pain (one of 10 patients and two of 11, respectively). Hypocapnia at rest (PCO2 less than 4 kPa) occurred in 16 (14%) patients but in only one control. Hypocapnia occurred during or after exercise in only one control and three of the 21 patients with significant ST depression on exercise (group 1). The remaining 92 patients were divided into those with a history suggestive of hyperventilation (group 2; n = 30) and those without (group 3; n = 62). Hypocapnia developed significantly more often in both these groups (21 and 25 patients respectively) than in controls or patients with significant ST depression. An abnormal response of the PCO2 to exercise provided objective data to support a clinical suspicion of chest pain induced by hyperventilation in 24 cases, suggested a cause for equivocal ST depression other than coronary stenosis in five patients, and led to the diagnosis of previously unsuspected respiratory disease in 14 patients. Measurement of end tidal PCO2 gives additional valuable diagnostic information during the conventional treadmill exercise test in patients with both typical and atypical chest pain.