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Hyperventilation is excessive ventilation of the lungs, beyond what is required to achieve normal arterial blood gases.
Hyperventilation syndrome is where hyperventilation occurs chronically or in recurrent episodes and is associated with somatic (respiratory, neurological, intestinal) or psychological (anxiety) symptoms.
Some prefer to describe it as 'psychogenic dyspnoea' or 'behavioural breathlessness', emphasising hyperventilation as the consequence rather than cause of the perceived breathlessness. There is a strong overlap with panic disorder - most patients showing characteristics of both disorders - but generally lacking the positive finding of any underlying organic disease.
About 5-10% of general medical outpatients are thought to suffer from this syndrome and, because of the range of somatic symptoms, the risk of misdiagnosis is high.
Hyperventilation has little effect on arterial pO2 and almost no effect on oxygen saturation which is nearly 100% under normal circumstances. Its main effect is to lower pCO2 and produce a respiratory alkalosis. A secondary hypocalcaemia also occurs as calcium dissociation is shifted towards the unionised, bound form.
There are many factors that influence the respiratory drive, including the elasticity of the lungs and the resistance in the airways but the most important factors are:
- Arterial pH
Of these, pCO2 is most important, although some people with chronic obstructive pulmonary disease (COPD) can depend on the hypoxic drive.
- It is quite common but precise prevalence is unknown. A postal survey indicated that 8% of adults without asthma suffer from functional breathing problems (of which symptomatic hyperventilation is the most common).
- It can occur at any age after infancy but the onset is usually between the ages of 15-55 years with a female preponderance of around 7:1.
- It is more common in asthmatic patients, occurring in 29% in one survey.
The most common reason for increasing respiratory rate and depth is exercise, the extent depending upon the level of exercise. However, as this is a normal physiological response, it is inappropriate to call it hyperventilation.
Other causes include:
- Metabolic acidosis, which will cause compensatory hyperventilation. This may occur with diabetic ketoacidosis or with renal failure. Carbon dioxide is a very weak acid but the volume exchanged in a day makes it the most important contributor to acid base balance.
- Problems of respiratory exchange may exist, including V/Q imbalance due to, for example, pulmonary embolism or poor gas exchange with pulmonary oedema.
- Hypoxia, which can be the result of altitude, especially when ascent has been too rapid and acclimatisation has not occurred. Hyperventilation can cause mountain sickness with cerebral oedema. Rapid descent is imperative as the condition can be fatal.
- Fever, toxins and drugs - these can all increase the respiratory rate, possibly by a central action on the brain.
- Aspirin overdose, which leads first to a primary hyperventilation and respiratory alkalosis by central stimulation and then to a secondary hyperventilation for the metabolic acidosis caused by the acidic nature of the drug.
- Iatrogenic hyperventilation by over-ventilating patients with head injuries, which was once a common technique but has fallen from favour, as it has been shown to produce a worse outcome.
- Hyperventilation in response to anxiety, which is common. It is more common in women and may be associated with panic disorder.
- Hyperventilation which may also occur as part of dysfunctional breathing in asthma sufferers.
The remainder of this article will concentrate on hyperventilation as it may present in the community.
- The complaint is usually of a paroxysmal rather than a continuous nature, although chronic hyperventilation can occur.
- The patient may complain of shortness of breath when an attack occurs.
- Pain or discomfort in the chest is common.
- Paraesthesiae usually affects both arms. The complaint is often of numbness or tingling in the fingers and sometimes toes.
- Other symptoms include:
There are unlikely to be any signs unless the patient is seen during an acute attack when:
- The patient will look very anxious and be struggling to breathe.
- Speech is difficult and the accessory muscles of ventilation are used.
Note the ratio of the inspiratory duration to the expiratory duration:
- In quiet breathing, this is about 1:2.
- In asthma, the expiratory phase is prolonged, especially if severe, and the patient may expire through pursed lips.
- In hyperventilation, the inspiratory phase may be more energetic and the expiratory phase is not prolonged.
- Trousseau's sign (also called 'main d'accoucheur' or carpopedal spasm) is muscle spasm in the hands, with the tips of the fingers and thumb apposed and the fingers straight. It results from hypocalcaemia.
- Chvostek's sign is also due to hypocalcaemia. Flick behind the ear, just in front of the mastoid bone where the facial nerve emerges. The hypersensitive facial nerve makes the muscles of the face twitch.
Chronic hyperventilation may be rather more difficult to diagnose. The patient rarely hyperventilates in a clinically apparent manner and may have been through multiple investigations already.
- There may be a persistently low arterial pCO2 with a high renal excretion of bicarbonate so that pH is normal.
- Occasional deep, sighing breaths may be noted. These keep the pCO2 depressed.
- They may hyperventilate more obviously when stressed and readily produce symptoms under these conditions.
The diagnosis may be obvious from the history.
- Occurring at rest while reading or watching TV.
- Associated with lightheadedness and paraesthesiae.
- Poorly related to severity of exertion.
- Associated with fear of dying during attacks.
- Panic attack or agoraphobia
- Asthma (mild asymptomatic asthma is not associated with clinically significant hyperventilation but is associated with a significant reduction in both arterial and end tidal pCO2 relating to airway hyperresponsiveness).
- Other causes of respiratory distress, eg recurrent pulmonary emboli or pneumothorax.
- Chest pain (hyperventilation can precipitate angina).
- Cervical spondylosis and nerve compression (where sensory symptoms are unilateral).
- Migrainous vertigo (especially in adolescents with dizziness and headache).
Chronic hyperventilation may mimic many serious organic disorders, but features are often atypical. Patients with exercise-induced hyperventilation are more likely to have a psychiatric than a cardiac disorder. Early detection and treatment of these patients may reduce the potential morbidity associated with unnecessary invasive investigations.
The diagnosis is essentially clinical one but it may be necessary to perform various tests to exclude other conditions:
- Arterial blood gases in an attack may be helpful but pCO2 can also be measured in end expiratory air. The latter test is more often used, as it is less invasive, less painful and so less likely to induce hyperventilation.
- ECG may exclude ischaemic heart disease or arrhythmia and D-dimer testing and CXR may be required in case of pulmonary embolism or pneumothorax. It may also reveal a prolonged QT interval due to hypocalcaemia during an acute attack.
- Toxicology screen.
- Hyperventilation provocation tests have poor specificity and are of dubious value.
- Anxiety can cause hyperventilation, producing symptoms that are interpreted as indicating serious physical illness. This causes more hyperventilation, worse symptoms and a vicious circle.
- Careful explanation of the nature of the condition is needed. Patients may find it difficult to accept the aetiology. Reproducing symptoms with voluntary hyperventilation may be useful.
- Rebreathing into a paper bag can be used to help build up the pCO2 but this should only be used where the diagnosis is certain, as it may be dangerous if there is physical disease.
- Relaxation techniques and breathing exercises may be helpful. Patients who hyperventilate are often thoracic rather than diaphragmatic breathers and teaching diaphragmatic breathing can help to overcome chronic hyperventilation.
- Treating asthmatics with dysfunctional breathing, using a brief physiotherapy intervention (teaching breathing retraining exercises), improves quality of life but this is only maintained in a quarter of patients six months on.
The basis of treatment should be behavioural therapy rather than medication but there may be a place for drugs.
- Benzodiazepines can be used in the acute situation if severe. Use only occasionally, as there is the potential for sedation and dependence.
- Propranolol may be of value if asthma has been excluded.
- Tricyclic antidepressants and selective serotonin reuptake inhibitors (SSRIs) may also be of value.
Treat any associated contributory conditions:
- Approximately 50% of patients with panic disorder and 60% of patients with agoraphobia hyperventilate as part of their disorder but only 25% of patients with hyperventilation syndrome also have panic disorder.
- Other psychiatric disorders, eg obsessive-compulsive disorders; however, not all patients have demonstrable psychological pathology.
- Mortality attributable to hyperventilation syndrome is vanishingly rare.
- There is significant psychiatric morbidity associated with the syndrome.
- Individuals are at risk of iatrogenic complications from investigation or treatment of wrong diagnosis.
- It tends to be a long-term and recurrent condition, especially if it started at an early age.
- Management of associated disorders (such as agoraphobia) will alter the course of the hyperventilation.
- Patients treated with breathing retraining, stress reduction interventions and certain drug treatment (eg SSRIs) appear to experience significant reductions in the frequency and the severity of exacerbations.
Further reading & references
- Malmberg LP, Tamminen K, Sovijarvi AR; Orthostatic increase of respiratory gas exchange in hyperventilation syndrome. Thorax. 2000 Apr;55(4):295-301.
- Howell JB; The hyperventilation syndrome: a syndrome under threat? Thorax. 1997 Aug;52 Suppl 3:S30-4.
- Thomas M, McKinley RK, Freeman E, et al; The prevalence of dysfunctional breathing in adults in the community with and without asthma. Prim Care Respir J. 2005 Apr;14(2):78-82.
- Thomas M, McKinley RK, Freeman E, et al; Prevalence of dysfunctional breathing in patients treated for asthma in primary care: cross sectional survey. BMJ. 2001 May 5;322(7294):1098-100.
- Stocchetti N, Maas AI, Chieregato A, et al; Hyperventilation in head injury: a review. Chest. 2005 May;127(5):1812-27.
- Perkin GD, Joseph R; Neurological manifestations of the hyperventilation syndrome. J R Soc Med. 1986 Aug;79(8):448-50.
- Osborne CA, O'Connor BJ, Lewis A, et al; Hyperventilation and asymptomatic chronic asthma. Thorax. 2000 Dec;55(12):1016-22.
- Weisleder P, Fife TD; Dizziness and headache: a common association in children and adolescents. J Child Neurol. 2001 Oct;16(10):727-30.
- Bass C, Chambers JB, Kiff P, et al; Panic anxiety and hyperventilation in patients with chest pain: a controlled study. Q J Med. 1988 Dec;69(260):949-59.
- Hornsveld HK, Garssen B, Dop MJ, et al; Double-blind placebo-controlled study of the hyperventilation provocation test and the validity of the hyperventilation syndrome. Lancet. 1996 Jul 20;348(9021):154-8.
- Callaham M; Hypoxic hazards of traditional paper bag rebreathing in hyperventilating patients. Ann Emerg Med. 1989 Jun;18(6):622-8.
- DeGuire S, Gevirtz R, Hawkinson D, et al; Breathing retraining: a three-year follow-up study of treatment for hyperventilation syndrome and associated functional cardiac symptoms. Biofeedback Self Regul. 1996 Jun;21(2):191-8.
- Thomas M, McKinley RK, Freeman E, et al; Breathing retraining for dysfunctional breathing in asthma: a randomised controlled trial. Thorax. 2003 Feb;58(2):110-5.
- Bass C, Gardner WN; Respiratory and psychiatric abnormalities in chronic symptomatic hyperventilation. Br Med J (Clin Res Ed). 1985 May 11;290(6479):1387-90.
- Kern B et al; Hyperventilation Syndrome, Medscape, Dec 2010
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Dr Chloe Borton
Dr Hayley Willacy
Dr Colin Tidy