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Sex Differences in Thoracic Dimensions and Configuration

Sex Differences in Thoracic Dimensions and Configuration,Francois Bellemare,Alphonse Jeanneret,Jacques Couture

Sex Differences in Thoracic Dimensions and Configuration   (Citations: 6)
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The volume of adult female lungs is typically 10-12% smaller than that of males who have the same height and age. In this study, we investigated how this volume difference is distributed between the rib cage and the diaphragm abdomen compartments. Internal rib cage dimensions, diaphragm position relative to spine, and dia- phragm length were compared in 21 normal male and 19 normal female subjects at three different lung volumes using anterior- posterior and lateral chest radiographs. At all lung volumes exam- ined, females had smaller radial rib cage dimensions in relationship to height than males, a greater inclination of ribs, a comparable diaphragm dome position relative to the spine, and a shorter dia- phragm length. Female subjects exhibited a greater inspiratory rib cage muscle contribution during resting breathing than males, pre- sumably reflecting an improved mechanical advantage conferred to these muscles by the greater inclination of ribs. Because of a greater inclination of ribs, female rib cages could accommodate a greater volume expansion. The results suggest a disproportionate growth of the rib cage in females relative to the lung, which would be well suited to accommodate large abdominal volume displace- ments as in pregnancy. All recommended normal prediction equations for lung vol- umes predict smaller values in females than in males having the same height and age (1). The smaller lung volume of females appears to be established in the first few years of life and is attributable to a lower rate of alveolar multiplication in girls than boys (2). The reason for the lower rate of alveolar multiplication is unknown. Within each sex, there is also a substantial variation in the volume of lungs among subjects having the same age and stature (3). Both findings suggest that lung growth is not very tightly coupled to longitudinal growth. A disproportionate growth of the lower limbs has been suggested as a factor contributing to the difference in lung size between males and females who have the same stature (4). However, the inclusion of sitting height in regres- sion models for lung size (4) or referencing lung volume to thoracic spinal height instead of body height (5) does not abolish the difference between males and females. In a recent study, we have found that the smaller lung volume of females could be entirely accounted for by smaller radial rib cage dimensions, the axial dimension, which is determined by the position of the diaphragm, being if any- thing greater in females than in males of the same height (5). These findings suggested important sex differences not only in the volume of lungs but also in thoracoabdominal
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    • ...Details of the techniques and measurements can be found in recent publications [7, 14, 15]...
    • ...The acute angle formed by the lower border of the sixth rib and the vertical on lateral films and the average height of the two hemidiaphragm domes (Hdi) below the first thoracic vertebra on anterior–posterior films were also measured [15]...
    • ...It has been shown previously that, after adjustment for height, the volume of the rib cage at any given lung volume is smaller in females than in males and that this is explained by a greater inclination of the ribs in females [15]...
    • ...Indeed, both the greater volume capacity of the rib cage relative to the lungs [15] and the longer ribs in relation to height [25] in females than in males have been interpreted as reflecting an evolutionary adaptation for pregnancy that minimises the negative effects of abdominal distension on lung function and abdominal pressure...

    F. Bellemareet al. Sex differences in thoracic adaptation to pulmonary hyperinflation in ...

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