The Science Journal of the American Association for Respiratory Care

2008 OPEN FORUM Abstracts

ARE PLETHYSMOGRAPHIC LUNG VOLUMES MEASUREMENT AFFECTED BY THE SEQUENCE OF FRC-SVC OR SVC-FRC MANEUVERS?

Marshall Krashin1Luis Torre-Bouscoulet1, Felipe Cortopassi1, Russell Sabbag1, Nelson Gomez1, Sohail Qadir1, Sadamu Ishikawa1, Bartolome R. Celli1, Victor M. Pinto-Plata1



Background: According to the ATS/ERS standardization for plethysmographic lung volumes measurement (Eur Respir J 2005; 26: 511-522), functional residual capacity (FRC) must be obtained before a slow vital capacity (SVC) maneuver. However, the panting maneuver (for FRC acquisition) might induce acute hyperinflation modifying the reported values of lung volumes. Therefore, the aim of this study was to analyze the agreement between 2 sequences to measure lung volumes (FRC-SVC vs. SVC-FRC) in patients with obstructive or non-obstructive spirometry.

Methods:
Consecutive patients referred to a single pulmonary physiology center to complete spirometry and plethysmographic lung volumes. They were classified according to post bronchodilator values in two groups; obstructive (FEV1/FCV <0.7) or non-obstructive. Every patient underwent two randomized sequences consecutively (FRC-SVC and SVC-FRC). Agreement analysis was performed for the following variables: TLC, FRC, RV and IC/TLC.

Results:
We included 20 obstructive and 50 non-obstructive patients. The obstructive group had 8 female and 12 male, the mean age was 65±10 years, FEV1 72±23%, FEV1/FVC 54±11 %. The non-obstructive group included 27 female and 23 male with mean age of 48±17 years, FEV1 92±14% and FVC 93±15%. In the obstructive group; for TLC the intra-class correlation coefficient (ICC) was 0.92 (95%CI 0.85-0.98), with an average difference (figures from FRC-SVC sequence minus SVC-FRC sequence) of -0.3 L; for FRC the ICC was 0.88 (0.79-0.97) with a difference of -0.3 L; for RV the ICC was 0.77 (0.62-0.93) with a difference of -0.4 L and for IC/TLC the ICC was 0.93 (0.87-0.99) with a difference of 1.1%. In non-obstructive group; for TLC the ICC was 0.90 (0.85-0.95) with a difference of -0.2 L; for FRC the ICC was 0.88 (0.83-0.94) with a difference of -0.2 L; for RV the ICC was 0.72 (0.60-0.85) with a difference of -0.2 L and for IC/TLC the ICC was 0.90 (0.85-0.95) with a difference of 1.8%.

Conclusion:
Although good agreement was observed between the FRC-SVC vs. SVC-FRC sequences for most of the tested variables, the SVC-FRC sequence was associated with higher lung volume values, in both obstructive and non-obstructive patients. Our results suggest that the acquisition of FRC after SVC (without the patient coming off the mouthpiece) might be a better method to measure plethysmographic lung volumes.