Body posture affects lung function. Supine values have been shown to be lower in comparison with sitting or standing (Lalloo et al. 1991; Meysman & Vincken, 1998). Few studies have examined postures between these positions (Manning et al. 1999). The aim of this study is to see the effect of head-up (HU) and head-down (HD) postures on lung function.

Eight healthy Caucasian subjects (7 males, 1 female) participated in a study approved by the local ethics committee and had their lung function measured in six postures: -40 and -20 deg HD, 0 deg supine, and 20, 40 and 60 deg HU). Their mean ± S.D. age was 22.9 ± 3.52 years, height 1.76 ± 0.48 m and weight 76.7 ± 11.15 kg.

A motorized tilt table was used to alter postures and an electronic spirometer (Microlab 3300) was used to record the respiratory indices. The forced expiratory volume in 1 s (FEV₁), forced vital capacity (FVC) and peak expiratory flow (PEF) were measured. Subjects were placed for 10 min at each posture and performed a maximal inspiration followed by maximal expiration three times and the highest values of the indices were used for analysis. Differences in lung function between postures were examined by one-factor repeated measures ANOVA and Bonferroni-corrected paired samples t tests (P < 0.05).

We found an increase in lung function indices from supine (mean ± S.E.M.; FEV₁ = 3.97 ± 0.14 l, FVC = 4.83 ± 0.23 l, PEF = 8.47 ± 0.62 l s^-1) to HU postures (PEF, FVC and FEV₁ increased by 11.9, 7.7 and 6.8 %, respectively). A decrease in lung function was found from supine to HD (PEF, FVC and FEV₁ decreased by 11.6, 4.8 and 6.5 %, respectively). Angle of tilt significantly affected FEV₁, FVC and PEF (P < 0.005). Comparison of supine values with the other five postures showed a significant difference for FEV₁, FVC (except for 20 deg HU) and for PEF (except for 20 and 40 deg HU and 20 deg HD). There was a strong correlation between posture and FVC (individual r range = 0.84Ð0.98, mean 0.96), FEV₁ (individual r range = 0.84Ð0.98, mean 0.98) and PEF (r range = 0.27Ð0.97, mean 0.98).

Our results suggest that changes in lung function are directly proportional to posture (angle of tilt) in degrees and that these changes may be due to changes in intrathoracic blood volume produced by tilting.

All procedures accord with current local guidelines.