Resumo

NIGRO, Carlos A. et al. Overestimation of thoracic gas volume during the airway resistance maneuver: A potencial error in the diagnosis of air trapping. Medicina (B. Aires) [online]. 2005, vol.65, n.1, pp.31-35. ISSN 0025-7680.

There are no data published about the agreement between the measurement of thoracic gas volume (TGV) during the airway resistance (TGV-Raw) and the conventional technique described by Dubois. The aim of this study was to establish the agreement between both methods to measure TGV. We studied eighty consecutive subjects. Only sixty-six performed acceptable plethysmography maneuvers. The patients were measured with a constant volume plethysmograph (Medical Graphics 1085 DL). TGV was performed in the same patient with two techniques: 1) during the airway resistance (Raw) measurement (TGV-Raw) and 2) during quiet breathing at the end of expiration (TGV). The panting frequency was 1 to 2 Hz with both maneuvers. The differences between both techniques were expressed in percentage (D TGV %) and absolute values (D TGV). The TGV-Raw of the whole group was higher than TGV (3.69 ± 1.08l vs 3.28 ± 1.05l, p < 0.001). Similarly, the subgroups of patients had a greater TGV-Raw than TGV (Normal: 3.44 ± 0.77l vs 2.98 ± 0.72l, p < 0.001; Obstructive: 4.08 ± 1.19l vs 3.71 ± 1.15l, p < 0.001; Restrictive: 2.62 ± 0.49l vs 2.25 ± 0.51l, p < 0.01). There was a considerable lack of agreement between the TGV-Raw and TGV, with discrepancies of up to +0.95l or +34%. The D TGV % was similar between the patients' subgroups and between the subjects with different degree of airflow obstruction (Normal: 16.5 ± 10%, Obstructive: 10.8 ± 9.4%, Restrictive: 18 ± 14.3%, p NS; mild obstruction: 10.7 ± 11%, moderate obstruction: 12.3 ± 5.7, severe obstruction: 10.1± 6.6, p NS). In conclusion, TGV-Raw was larger than TGV. This was because the patients generally panted at a volume above FRC when performing the TGV-Raw maneuver. TGV-Raw should not be used to estimate FRC because FRC would be overestimated and the diagnosis of air trapping may be erroneous.

Palavras-chave : Static lung volume; Thoracic gas volume; Body plethysmography.

        · resumo em Espanhol     · texto em Inglês     · Inglês ( pdf )