Behavioural and Physiological Factors Affecting Breathing Pattern and Ventilatory Control in Patients with Idiopathic Hyperventilation

Summary

Idiopathic Hyperventilation may be defined as breathing in excess of metabolic requirements, resulting in hypocapnia and concomitant respiratory alkalosis which is not associated with other cardiorespiratory disease. It is characterised both by an inappropriate level of ventilation and by a disorganised breathing pattern. Common symptoms reported by patients include shortness of breath, dizziness, chest tightness and parasthesia. High levels of anxiety have also been observed. The aetiology of this condition is unknown but is likely to be a combination of multiple factors, both psychological and physiological. Mechanical, chemical and behavioural elements are likely to be involved in the symptomatology. In this chapter, we discuss the history of idiopathic hyperventilation and explain how the diagnosis can be made. We demonstrate the variability of breathing pattern and suggest the mechanisms that may be involved in its maintenance. We also describe an index which may be useful in assessing and assigning a numerical value to this disorganised breathing pattern, which may prove to be useful for diagnostic purposes, for assessing progression or the effects of therapy. In addition we describe respiratory physiological changes observed in our laboratory in these subjects including an exaggerated ventilatory response both to low levels of exercise and to CO₂ when replaced to normocapnic levels. We demonstrate that these patients have a lower control point for CO₂ compared to normals and discuss how this altered chemoresponsiveness may partially explain the poor exercise tolerance and symptomatology in these individuals. We provide evidence that control point may be altered by behaviour which suggests that psychological factors may alter physiology in these individuals.