Page 142 - Biomedical Engineering and Design Handbook Volume 1, Fundamentals

BIOMECHANICS OF THE RESPIRATORY MUSCLES 119

analogs of all the models described so far have not differentiated between individual groups of respi-
ratory muscles and between the rib cage and the accessory muscles, and thus precluded evaluation
of their contribution to respiration.
Recently, a more realistic model of the chest wall has been developed with the objective to eval-
uate the performance of individual groups of respiratory muscles in terms of the force and the work
generated during breathing maneuvers (Ratnovsky et al., 2005). The two-dimensional model in the
sagittal plane is composed of stationary and mobile bones and the respiratory muscles (Fig. 5.6). The
stationary elements are the bones of the vertebral column, skull, iliac crest, and pelvis, while the rib
cage forms the mobile part of the model. The model incorporates three groups of inspiratory mus-
cles (e.g., diaphragm, external intercostal, and sternomastoid) and four groups of expiratory muscles

A B

Hinge
SM
Skull
γ i
α i
Rib
L T1 EI 1
Sternum
Lung

Central
tendon

CD 1
Vertebral EO 1
CD 4
column
EO 2
EI 23 CD 2
CD 3
EO 3 RD
EI 24
TR RC
Iliac crest EO 4
EO 6 IO Abdominal
EO 8
wall

FIGURE 5.6 Scheme of a two-dimensional model of the human trunk in the sagittal plane. The springs represent the
respiratory muscles while the thick lines represent the vertebral column, sternum, and iliac crest. α represents the rib
i
angles, γ represents the vertebral column curvature angles, and L represents the length of each thorax vertebra. SM,
i Ti
RC, TR, and IO represent the sternomastoid, rectus abdominis, transverse abdominis, and internal oblique muscles,
respectively. EI -EI represent the external intercostal muscle units and their angle with the horizon. EO -EO represent
1 24 1 6
the external oblique muscle units. CD , CD , CD , CD , and RD represent the costal fibers and the crural fibers of the
1 2 3 4
diaphragm muscle, respectively. [From Ratnovsky et al. (2005), with permission.]