Regional lung volume differences between the side-lying and semi-prone positions

Factors Affecting Lung Function: A Review of the Literature

Lung function reference values are traditionally based on anthropometric factors, such as weight, height, sex, and age. FVC and FEV₁ decline with age, while volumes and capacities, such as RV and FRC, increase. TLC, VC, RV, FVC and FEV₁ are affected by height, since they are proportional to body size. This means that a tall individual will experience greater decrease in lung volumes as they get older. Some variables, such as FRC and ERV, decline exponentially with an increase in weight, to the extent that tidal volume in morbidly obese patients can be close to that of RV. Men have longer airways than women, causing greater specific resistance in the respiratory tract. The increased work of breathing to increase ventilation among women means that their consumption of oxygen is higher than men under similar conditions of physical intensity. Lung volumes are higher when the subject is standing than in other positions. DLCO is significantly higher in supine positions than in sitting or standing positions, but the difference between sitting and standing positions is not significant. Anthropometric characteristics are insufficient to explain differences in lung function between different ethnic groups, underlining the importance of considering other factors in addition to the conventional anthropometric measurements.

Compression of the lungs by the heart in supine, side-lying, semi-prone positions

[Purpose] Clarification of the differences in the compression volume of the lungs by the heart (CVLH) between postures may facilitate the selection of optimal postures in respiratory care. Determining CVLH in the supine, semi-prone (Sim’s position), and side-lying positions was the aim of this study. [Subjects and Methods] Eight healthy volunteers (six males, two females; mean age, 29.0 ± 9.2 years) were enrolled in the study. Measurements were performed in the supine, right and left semi-prone, and right and left side-lying positions. semi-prone position was inclined 45° ventrally from the side-lying position. A 1.5-T system with a fast advanced spin-echo sequence in the coronal plane was used for magnetic resonance imaging. [Results] CVLH and heart compression ratio were significantly lower in the semi-prone position on both sides than the other positions. The heart was displaced ventrally when semi-prone and a larger area of the heart leaned on the ventral chest wall, localizing compression to part of the ventral region of the dependent lung. [Conclusion] The region of lungs compressed by the heart is reduced in the semi-prone position due to ventral displacement of the heart. These results suggest that maintaining expansion of the dependent lung is easier in the semi-prone position.