Chest
ReviewsThe Pathophysiology of Hyperventilation Disorders
Section snippets
PHYSIOLOGY
Hyperventilation is an abnormality of respiratory control and is defined as breathing in excess of metabolic requirements, ie, CO2 production. In subjects with normal lungs, PaCO2 is very close to alveolar PCO2 (PACO2), which in turn can be approximated by end-tidal PCO2 (PETCO2). Alveolar ventilation ( ), CO2 production ( ), and PACO2 are linked through an equation with the general form of (barometric pressure-H2O vapor pressure), the graphic
SYMPTOMS
Hyperventilation is unlikely to be a problem to a patient unless it results in symptoms, and the way in which these symptoms are induced may hold the key to understanding why hyperventilation becomes a major problem for some patients. Painful tingling in the hands and feet, numbness and sweating of the hands, and cerebral symptoms following voluntary hyperventilation were first described by Haldane and Poulton.67 The first cases of spontaneous hyperventilation with dizziness and tingling
SIGNS
Signs are often unhelpful in detection of hyperventilation. While increase in chest wall movement and rate may be obvious in acute hyperventilation, in chronic hyperventilation this may not be so and resting PETCO2 can be halved with only about a 10% increase in minute ventilation as shown in Figure 1 for patients with chronic hyperventilation.31 Patients with hyperventilation often sigh repeatedly (see below), but even in acute hyperventilation as discussed above, dramatic sighing or panting
Measurement of PCO2
The gold standard for diagnosis of hyperventilation and respiratory alkalosis is measurement of arterial PCO2 and blood gas parameters. However, arterial puncture is invasive, may itself induce anxiety and hyperventilation, and will fail to diagnose patients with variable or transient hyperventilation. Alternative measures are less satisfactory.
End-Tidal PCO2: PETCO2127, 128 can be measured by capnograph or mass spectrometer from a small sample extracted continuously from a manifold through
ETIOLOGY
Factors that can induce hyperventilation will be discussed individually, although such a division is artificial and a number of factors often combine to induce symptomatic hypocapnia. These factors are shown in Figure 3 and can be classified as psychogenic, organic, and physiologic. It is useful to distinguish those that can initiate hyperventilation from those that sustain it.
HYPERVENTILATION-CLINICAL PRESENTATIONS
The clinical finding of a low arterial or PETCO2 will provide a diagnosis of hyperventilation, but this may not be associated with symptoms of hypocapnia, or such symptoms may be of minor importance compared with the symptoms of the disorder causing the hyperventilation. In these cases, a diagnosis of hyperventilation is of little clinical relevance. In other situations, the symptoms of hyperventilation are pivotal to the patient's clinical presentation. In our view, it is not clinically useful
CLINICAL MANAGEMENT
A positive clinical strategy with a stepwise approach to assessment is required. It is helpful to categorize patients according to the groupings described above, and simplistic labeling of patients as having hyperventilation syndrome should be avoided. These patients are very time consuming, and a detailed initial history and assessment with multiple follow-ups are usually required. In our experience, joint management by a chest physician and a liaison psychiatrist in a chest clinic offers the
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revision accepted August 19.