Hyperventilation in patients with recurrent functional symptoms.

In view of the similarity between the reported effects of hyperventilation and recurrent functional symptom presented in primary care, a study was undertaken to establish whether such symptoms are attributable to hyperventilation. Twenty patients with two or more recurrent functional symptoms which their doctors found difficult to diagnose or treat, and 30 controls, were studied using symptom questionnaires and a series of hyperventilation provocation tests during which the partial pressure of carbon dioxide (PCO2) and symptoms were recorded. Sixteen cases (80%) had unexplained breathlessness compared with two of the controls (7%). All of the cases recognized familiar functional symptoms during provoked hyperventilation, and in 16 (80%), these included primary physical symptoms; only 23% of the controls recognized any previously experienced symptom. Considerable overlap of PCO2 values between groups meant that absolute values of PCO2 were not useful in differentiating between groups, but cases were more likely than controls to have a PCO2 of less than 4 kPa at rest, three minutes after hyperventilation, or during mental stress (75% of cases fulfilled one or more of these criteria versus 40% of controls). This is the first study in primary care to examine the effect of hyperventilation in a group of patients with multiple somatic symptoms. The findings have implications for the recognition and management of such patients.