Sex differences in thoracic dimensions and configuration.

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 diaphragm 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 examined, 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 diaphragm length. Female subjects exhibited a greater inspiratory rib cage muscle contribution during resting breathing than males, presumably 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 displacements as in pregnancy.

Effects of emphysema and lung volume reduction surgery on transdiaphragmatic pressure and diaphragm length.

STUDY OBJECTIVES: To determine the effect of emphysema and lung volume reduction surgery (LVRS) on diaphragm length (Ldi) and its capacity to generate transdiaphragmatic pressure (Pdi). DESIGN: Prospective clinical trial with a parallel group design. SETTING: Laboratory investigations in normal volunteers recruited by advertisement and in emphysema outpatients being evaluated for elective LVRS. STUDY POPULATION: Thirteen normal subjects and 13 emphysema patients matched for age and sex. Six emphysema patients underwent LVRS. MEASUREMENTS: Ldi and maximal Pdi during static inspiratory efforts (PdiMax) were measured at three different lung volumes (LVs). Pdi during maximal bilateral phrenic nerve twitch stimulation (PdiTw) was measured at functional residual capacity (FRC). All measurements were repeated at 3, 6, and 12 months postoperatively. RESULTS: Ldi, PdiMax, and PdiTw were lower in emphysema patients than in normal subjects at their respective LVs. PdiMax and PdiTw at FRC returned within the normal range after LVRS in emphysema patients. The relationships between PdiMax and LV or Ldi were shifted respectively to higher LV and shorter Ldi in emphysema patients relative to normal subjects, both before and after LVRS. LVRS effected craniad displacement of the diaphragm but no change in rib cage dimensions. Improvements in dyspnea and quality of life after LVRS correlated with changes in LV and Ldi but not with changes in airway caliber. CONCLUSION: Adaptive mechanisms, consistent with sarcomere deletion, tend to restore diaphragm strength in emphysema patients at FRC, which are fully expressed after LVRS. Lung remodeling by LVRS may alter pleural surface pressure distribution, causing a sustained change in chest wall shape.