Chest
Volume 83, Issue 4, April 1983, Pages 643-646
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Journal Article
Lung Mechanics in Sitting and Horizontal Body Positions

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We measured lung compliance, pulmonary flow-resistance, and expiratory reserve volume (ERV) in ten healthy young adults in sitting, supine, and lateral positions. Average lung compliance was 0.21 in sitting, 0.19 in lateral and 0.16 L.cm H2O–1 in supine positions. The change was significant (p<0.01) between sitting and supine position. Flow-resistance increased from 1.78 in sitting to 2.5 cm H2O·L-l·s (p<0.001) in lateral positions, and did not increase further in the supine posture in spite of a 35 percent decrease in ERV (p<0.001). Since it is known that lower airways resistance increases with decreasing lung volume, the lack of change in flow-resistance when shifting from lateral to supine posture suggests that upper airways flow-resistance (larynx and oropharynx) is greater in the lateral decubitus than in the supine positions. The decrease of lung compliance in horizontal postures probably reflects increased pulmonary blood volume and small airways closure.

Section snippets

MATERIAL AND METHODS

The study was performed on ten healthy male volunteers with a mean age (±SD) of 31.4 ± 3.5 years, mean vital capacity of 5.34 ± 0.38 L (105 ± 9.5 percent predicted), and mean FEV1 of 4.28 ± 0.41 (106 ± 11.4 percent predicted).10 Measurements were made in the sitting, supine, and right and left lateral positions, in a random sequence. A pillow was used when subjects were tested in lateral postures to keep the head horizontal.

Esophageal pressure (Pes) was measured with the esophageal balloon

Lung Volumes

Average values (±SE) of VC and ERV in the ten subjects in four body positions are presented in Table 1. VC decreased by about 5 percent from sitting to lateral positions, the difference being statistically significant (p<0.05). There was no significant difference between right and left lateral or between the sitting and supine positions.

The ERV decreased by about 22 percent when moving from sitting to lateral positions and by 50 percent from sitting to supine. These differences were

DISCUSSION

In agreement with previous studies,13, 14, 15 we found a small reduction of VC in the horizontal postures, which can probably be attributed to increased thoracic blood volume.16 Also in agreement with previous reports,13, 14, 15, 16 the ERV decreased progressively when shifting from sitting to lateral and then to supine position. This reflects mainly gravitational effects, which cause a cephalad displacement of the diaphragm due to increased abdominal pressure in the horizontal postures,

ACKNOWLEDGMENTS:

The authors thank Mr. H. Ghezzo, who performed the statistical analyses of the data, and Mr. S. Filiatrault for technical assistance.

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Supported by Medical Research Council of Canada and NIH grant HL27617.

Manuscript received July 12; revision accepted October 5

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