Effect of natural panting frequency and cheek support on the plethysmographic determination of thoracic gas volume in patients with chronic obstructive pulmonary disease]

The authors studied the effects of natural panting frequency (NF) and the cheek support on the plethysmographic measurement of thoracic gas volume (TGV) in 8 normal subjects (non-smokers) and 46 patients with chronic obstructive pulmonary disease (COPD). The patients were divided into 2 groups according to the degree of airway obstruction (group I; specific airway conductance (SGaw) greater than 0.1 (n = 18), group II; SGaw less than 0.1 (n = 28)). TGV was measured with a pressure-type body plethysmograph (BP). NF was 2.00 +/- 0.43 Hz (mean +/- SD) in control subjects, 1.92 +/- 0.78 Hz in group I, and 1.39 +/- 0.59 Hz in group II, respectively, indicating lower NF in the patients with severe airway obstruction. In control subjects and group I, the differences between TGV at NF and at 0.5-1.0 Hz (TGVNF-TGV1.0) were -0.01 +/- 0.07L, and -0.06 +/- 0.16L, respectively, and cheek support did not alter the difference. On the other hand, in group II, the difference was slightly larger than other groups in spite of the lower NF, and this overestimation was abolished by cheek support (0.13 +/- 0.25L-----0.06 +/- 0.27L, p less than 0.05). These results suggest that, in patients with severe airway obstruction, TGVNF may be overestimated even if NF is relatively low. This overestimation may be mainly due to the extrathoracic airway compliance including the cheek.