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Diagnostic Pulmonary Function Tests of a Woman With Hyperventilation FREE TO VIEW

Rui Ya Soh, MMed; Anne Hsu, MMed
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Singapore General Hospital, Singapore, Singapore

Chest. 2014;145(3_MeetingAbstracts):560A. doi:10.1378/chest.1823802
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SESSION TITLE: Miscellaneous Case Report Posters

SESSION TYPE: Case Report Poster

PRESENTED ON: Sunday, March 23, 2014 at 01:15 PM - 02:15 PM

INTRODUCTION: Hyperventilation refers to rapid or deep breathing and is commonly associated with panic and anxiety. Other common causes include somatisation, severe pain, infection, ketoacidosis, asthma, chronic obstructive pulmonary disease, pulmonary embolism and heart failure.

CASE PRESENTATION: A 39-year-old female was referred to the respiratory clinic for recurrent hyperventilation when she felt stressed and during exercise in the fitness centre. She described her attacks of dyspnea with paraesthesia, palpitations, dizziness and occasionally hoarseness. She was twice brought to the emergency unit from the fitness centre but recovered well enough to be discharged. She had a history of panic disorder with agoraphobia. Spirometry was normal with forced expiratory volume in 1 second (FEV1) of 2L (86% predicted), forced vital capacity (FVC) of 2.33L (78.7% predicted) and FEV1/FVC of 85.8%. The patient’s flow-volume (FV) loops showed persistent flattened inspiratory limbs (FEF50%/FIF50%>1), consistent with variable extrathoracic airway obstruction. The FV loops showed sequential decremental size of the loops with each repeated maneuver. Maximal inspiratory pressure (-28.2cmH2O, 33.7% predicted) and maximal expiratory pressure (48.3cmH2O, 50% predicted) were significantly reduced which further decreased to -19.4 cmH2O, 23.2% predicted and 32cmH2O, 33.1% predicted respectively on the second effort. Maximal voluntary ventilation was normal at 81.79L/min (116.8% predicted). Bronchoprovovcation test was normal. This patient was subsequently diagnosed with myasthenia gravis (MG) and started on pyridostigmine with improvement in symptoms.

DISCUSSION: Hyperventilation is an unusual presentation of MG. In our patient, it is possible that the uncomfortable symptom of shortness of breath from MG increased her anxiety and caused hyperventilation, leading to increased fatigue of the respiratory muscles and further vicious cycle of worsening of dyspnea and hyperventilation aborted by fatigue. The reduction in the maximal respiratory pressures (MRP) and decremental responses in the MRP and FV loops with repeated maneuvers are consistent with MG. The flattening of the inspiratory limb of the FV loop is likely due to inspiratory muscles weakness and upper airway obstruction from vocal cord paresis as she also had hoarseness1.

CONCLUSIONS: It is important, even in patients with hyperventilation predisposition, to evaluate hyperventilation for organic causes of dyspnea. Careful examination of all the flow volume loops and maximal respiratory pressures may yield important ventilatory impairment pattern leading to the diagnosis of myasthenia gravis.

Reference #1: Putman MT, Wise RA. Myasthenia gravis and upper airway obstruction. Chest.1996 Feb;109(2):400-4.

DISCLOSURE: The following authors have nothing to disclose: Rui Ya Soh, Anne Hsu

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