PURPOSE: One of us (LMV) has observed that some patients with mild asthma show wheezes in the supine position that disappear while sitting. The hypothesis that this finding is due to increased airway resistance in recumbent position finds support in reports of higher airflow resistance (Raw) in normal subjects and in patients with left ventricular failure when body position is changed to supine position (1,2).
METHODS: Patients that were scheduled to pulmonary function tests with the sole indication of asthma and presented FEV1 => 60% and FEF25-75 <80% of predicted values performed spirometry in sitting and supine positions before bronchodilator testing. Group I included patients with FEF1=>80% and Group II patients with FEV1 60-79% of predicted values. A control group consisted of laboratory staff and medical students with normal spirometry.
RESULTS: : Using paired t-test to analyze data obtained, in Control Group (n=21) we observed significantly lower FEF75 in supine position (sitting: 2,14±0,184 (mean±SE); supine: 1,77±0,155; p<0,001). All other flow values were also lower in the supine position, but the difference did not achieve statistical significance. In Group I (n=19), all the spirometric data were significantly lower in supine position: FEV1: 2,52±0,190 × 2,2±0,177 (p<0,001); FVC:3,16±0,229 x2,96±0,219 (p=0,003); peak flow: 384,05±33,61 × 332,33±32,864 (p<0,001); FEV1/FVC: 78,2±1,038 × 74,53±1,336 (p=0,001); FEF25-75: 2,22±0,249 × 1,72±0,172 (p=0,001); FEF50: 2,62±0,238 × 2,14±0,215 (p=0,001) and FEF75: 0,912±0,986 × 0,695±0,0796 (p<0,001). In Group 2 (n=10) only peak flow (267,6±21,04 × 241,2±17,85; p=0,004) and FEF25-75 (0,45±0,086 × 0,426±0,074; p=0,046) did achieve statistical significance, although here a similar pattern was also observed.
CONCLUSION: Although both normal controls and asthma patients revealed a fall in spirometric values from sitting to recumbent position, only in patients with milder airflow obstruction (FEV1=> 80% and FEF25-75<80%) the difference achieved statistical significance for all spirometric data.
CLINICAL IMPLICATIONS: Because it is not clear why asthma patients with milder airflow obstruction increase their airway resistance in supine position further studies are necessary.
DISCLOSURE: Laercio Valenca, None.