• Respiratory Measurement
• Lung Physiology

An 82-year-old non-smoker man underwent evaluation for increasing dyspnoea. Clinical examination of the chest was normal but abdominal distension was noted. Pulmonary function test (PFT) revealed a significant increase in thoracic gas volume (TGV). Forced expiratory volume in 1 s (FEV₁) and forced vital capacity (FVC) were reduced (table 1). Asthma was suspected on the basis of hyperinflation and a slightly reduced FEV₁/FVC ratio but the chest X-ray showed significant colonic dilation resulting from a dolichocolon, confirmed by thoracoabdominal CT scan (figure 1). After colonoscopic decompression, without insertion of a decompression tube, dyspnoea improved markedly. Repeat PFT demonstrated near normalisation of FVC and FEV₁ (table 1).

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Figure 1

Frontal image of the thoracoabdominal CT scan. Marked colonic dilation results in an upward shift of both lungs.

TGV remained unaffected. Indeed, plethysmograph tends to count as TGV any air that is within the thoracic cage as it is compressed by the panting manoeuver.1 We usually think that only the air volume being above the diaphragm is counted but in case of diaphragmatic hernia, hiatal hernia2 or major colonic dilation,3 subdiaphragmatic air being forced up into the thoracic cage is also taken into account. In the present case, TGV measured both intrathoracic gases, which increased after colonic exsufflation, and subdiaphragmatic gases, decreased by exsufflation, resulting in a non-significant change in TGV. We can conclude that major accumulation of air within the abdomen can be associated with dyspnea due to decreased lung volumes and may mimic lung hyperinflation on PFT.