Diaphragm muscle shortening modulates kinematics of lower rib cage in dogs

Abstract

We tested the hypothesis that diaphragm muscle shortening modulates volume displacement and kinematics of the lower rib cage in dogs and that posture and mode of ventilation affect such modulation. Radiopaque markers were surgically attached to the lower three ribs of the rib cage and to the midcostal region of the diaphragm in six dogs of ∼8 kg body masses, and the locations of these markers were determined by a biplane fluoroscopy system. Three-dimensional software modeling techniques were used to compute volume displacement and surface area of the midcostal diaphragm and the lower three ribs during quiet spontaneous breathing, mechanical ventilation, and bilateral phrenic nerve stimulation at different lung volumes spanning the vital capacity. Volume displaced by the diaphragm relative to that displaced by the lower ribs is disproportionately greater under mechanical ventilation than during spontaneous breathing in the supine position (P < 0.05). At maximal stimulation, diaphragm volume displacement grows disproportionately larger than rib volume displacement as lung volume increases (P < 0.05). Surface area of both the diaphragm and the lower ribs during maximal stimulation of the diaphragm is reduced compared with that at spontaneous breathing (P < 0.05). In the prone posture, mechanical ventilation results in a smaller change in diaphragm surface area than spontaneous breathing (P < 0.05). Our data demonstrate that during inspiration the lower rib cage moves not only through the pump- and bucket-handle motion, but also rotates around the spine. Taken together, these data support the observation that the kinematics of the lower rib cage and its mechanical interaction with the diaphragm are more complex than previously known.

Diaphragm curvature modulates the relationship between muscle shortening and volume displacement

“…Our data suggest that at higher lung volumes and greater levels of muscle activation, posture continues to be an important determinant of lower rib cage kinematics. In contrast to our diaphragm rib cage VD data, Chu et al (6) showed that the lower ribs displaced greater volume in the prone than the supine posture. However, their VD component is the combination of three different rotations around the spinal axis, and there may be greater cephalic displacement of the lower ribs in the prone posture causing the large diaphragm rib cage VD component shown in our study.…”

“…During higher levels of diaphragm activation, the height of the zone of apposition of the diaphragm decreases markedly so that most of the lower rib cage becomes exposed to the expiratory effect of pleural pressure, rather than the inspiratory effect of abdominal pressure. However, during bilateral maximal phrenic nerve stimulation, this inspiratory effect appears to be absent, and the rib cage moves inward and caudally, consistent with the absent rib cage VD component shown in this study and decreased rib VD found previously (6). This is also consistent with a study by Krayer et al (13), who suggested that diaphragm shortening had no inspiratory effect on the rib cage during maximal stimulation.…”

“…However, at low lung volume ventilation maneuvers (i.e., SB and open FRC), there was a pattern of greater diaphragm abdominal VD, total VD, and less rib cage VD in the prone posture compared with the supine posture. Consistent with these observations, Chu et al (6) reported that posture is an important determinant of VD of the rib cage and diaphragm. However, only SB and maximal stimulation were analyzed in that study.…”

The therian sternum at the lateral somitic frontier: Evolution of a composite structure

“…If so, they shared a mammalian developmental innovation with significant functional correlates. In living mammals, rotation of the ribs at the rib/sternebral junctions and between adjacent sternebrae are important components of expansion of the rib cage during ventilation (Chu et al ., 2010; Gao et al ., 2016, Beyer et al ., 2014). In this way, an evolutionary change in the location of the LSF may be tentatively tied to a structural and functional innovation that facilitates mammalian ventilation.…”

Functional analysis of the human rib cage over the vital capacity range in standing position using biplanar X-ray imaging

“…Several studies have focused on biomechanical modelling of breathing [2][3][4], but the experimental study of breathing presents several challenges. For instance, the changes in rib cage volume and shape during the breathing cycle are often analysed experimentally using only external measurements, in vitro approaches or animal models [5][6][7][8][9][10][11].…”