Mechanical aspects of chest wall distortion

During passive inflation of the respiratory system, the rib cage (RC) expands because the pressure applied to it [approximately equal to abdominal pressure (Pab)] increases. Similar Pab-tidal volume (VT) relationships between passive and spontaneous inspirations would occur only if 1) Pab acts on RC equally in the two situations (no distortion) or 2) the extradiaphragmatic inspiratory muscles expand RC, compensating for distortion. In anesthetized adult rats and in sleeping human infants the passive relationships between VT and Pab or abdomen motion (AB) were constructed by occluding the airways during expiration. For a given Pab (or AB) in active breathing VT averaged 55% (rats) and 49% (infants) of the passive volume change. With phrenic stimulation in rats VT was only slightly less than during spontaneous breathing, indicating that, in the latter case, the respiratory system was essentially driven only by the diaphragm. In both species occasional breaths with large RC expansion occurred, and VT was then equal to or larger than the passive volume at iso-Pab. We conclude that 1) RC distortion decreases VT to approximately half of the passive value and 2) being on the relaxation curve reflects "compensated" distortion and not absence of it.     

Theoretical analysis of chest wall mechanics

A mathematical model of the chest wall partitioned into rib cage, diaphragmatic and abdominal components is developed consistent with published experimental observations. The model describes not only the orthodox chest wall movements (rib cage and abdomen expand together during inspiration) of the quietly breathing standing adult, but also Mueller maneuvers (inspiration against an occluded airway opening) and the paradoxical breathing patterns (rib cage contracts while abdomen expands during inspiration) observed in quadriplegia and in the newborn. The abdomen is inferred to act as a cylinder reinforced by the abdominal muscles functioning similarly to bands around a barrel. The rib cage and abdominal wall are inferred to act not as though they were directly attached to one another, but as though they were being pressed together by the skeleton. Furthermore, transabdominal pressure is visualized as acting, not across the rib cage isolated from the diaphragm, as has been suggested previously, but instead, across the combined rib cage and diaphragm acting as a deformable unit containing the lungs.     

Gravitational forces on the chest wall

The gravitational work of breathing was determined by measuring the vertical motion of body mass. The subject, seated or lying supine on a force platform, performed breathing maneuvers in which rib cage volume (Vrc) and abdominal volume (Vab) were changed in varying proportions. The increment in the vertical force exerted on the platform and Vrc and Vab were measured over the course of each maneuver. The force signal was integrated twice with respect to time to obtain the change in the product of mass and height of the subject. This was multiplied by the gravitational acceleration to obtain the change in the gravitational potential (Ug). Simultaneous values of Ug, Vrc, and Vab were taken from the data, and the values of the coefficients for which the following equation best fit these values were determined: Ug = a1 Vrc + a2 Vab + (1/2)a11 Vrc2 + a12 Vrc Vab + (1/2)a22 Vab2. The coefficients a1 and a2 can be interpreted as the values of the expiratory gravitational forces on the rib cage and abdomen, respectively. In the seated posture, the force on the rib cage is expiratory and the force on the abdomen is inspiratory; the magnitudes of both are approximately 8 cmH2O. In the supine posture, both are expiratory forces of approximately 9 cmH2O. The coefficients of the quadratic terms in Ug are all positive, and the gravitational work per unit volume of chest wall expansion increases with increasing volume in both postures. The coefficients of the quadratic terms can be interpreted as gravitational contributions to the elastances of the compartments.     

Regional chest wall impedance during nonrespiratory maneuvers

To assess changes in total and regional chest wall properties during nonrespiratory maneuvers, we measured electromyographic activity of various chest wall muscles, esophageal pressure, and rib cage and abdominal surface displacements in six subjects before and during various static tasks. Subjects were seated at functional residual capacity, and quasi-sinusoidal forcing at the mouth (0.4 Hz, 500 ml) was imposed during the maneuver in the absence of active breathing. Magnitude of total chest wall impedance (magnitude of Zw) increased with effort during all maneuvers; changes in phase were small. Maneuvers involving primarily muscles of the neck and rib cage--holding a 10-kg weight, 10 kg of isometric tension between the arms, and isometric neck flexion--roughly doubled the magnitude of rib cage impedance (magnitude of Zrc) and, to a lesser degree, increased magnitude of diaphragm-abdomen impedance (magnitude of Zd-a). Unilateral and bilateral leg lifts, in addition to increasing magnitude of Zd-a, increased magnitude of Zrc. Passive 90 degrees rotation of the torso caused approximately 25% increases in magnitude of Zrc and magnitude of Zd-a; if the rotation was actively maintained by the trunk muscles, both regional impedances increased over 100%. Increases in magnitude of regional impedance were correlated to increases in regional electromyographic activity; changes in phase were small. Passive restriction of rib cage displacement by strapping increased magnitude of Zrc and magnitude of Zw but not magnitude of Zd-a, whereas abdominal strapping increased magnitude of Zd-a but did not affect magnitude of Zrc or magnitude of Zw.(ABSTRACT TRUNCATED AT 250 WORDS)     

Dynamics of chest wall in preterm infants

The chest wall of the preterm infant has visible paradoxical movement during breathing, because of its greater flexibility than those of older children and adults. We studied the dynamics of the chest wall in 10 preterm infants to describe the interaction of the chest wall volume, as partitioned by the inductance plethysmograph, and the transthoracic and abdominal pressures. There was considerable hysteresis between the chest wall volume and the transthoracic pressure, and it had linear pressure-volume behavior during airway occlusion, late inspiration, and early expiration. The slope of this pressure-volume relationship, or the instantaneous chest wall compliance, averaged 0.89 +/- 0.16 and 0.94 +/- 0.18 ml/cmH2O for the respiratory effort during airway occlusion and early expiration, respectively. The dynamic compliance was considerably greater, averaging 7.8 +/- 2.3 ml/cmH2O. This resistive pressure-volume behavior was not related to the absolute value of or the rate of development of the esophageal or abdominal pressures. This additional degree of freedom of motion of the chest wall suggests that its linkage to the diaphragm is flexible, which provides a braking force for expiration and allows free movement of the diaphragm for breathing movements before birth.     

Infraclavicular chest wall tumors in Hodgkin's disease

In six of 91 cases of Hodgkin's disease observed over a three-year period, a tumor mass filling the infraclavicular hollow was noted. It was on the left side in all instances. Although in four cases it was the only superficial manifestation of Hodgkin's disease for a long period, in all cases there were ultimately other areas of involvement. The lesion did not occur in any of 81 cases of lymphosarcoma observed concurrently.     

Surgical management of the radiated chest wall

Fifty consecutive patients with radiation-related problems of the chest wall were treated between 1976 and 1984. There were 40 women and 10 men with an average age of 54 years (range 26 to 78 years). Twenty-three patients had radiation ulcers alone, 20 had recurrent cancer, and 7 had infected median sternotomy wounds. Thirty-six had skeletal resections and 44 had soft-tissue resections. The skeleton was reconstructed with Prolene mesh in 12 patients and with autogenous rib in 3. Sixty-three muscles were transposed in 43 patients. Twelve omental transpositions were performed (8 for primary treatment and 4 for salvage of a failed muscle flap). Hospitalization averaged 20.2 days. There was one operative death (at 29 days). Partial flap necrosis occurred in 10 patients. Mesh was removed in three patients. There were 14 late deaths, most from recurrent tumor. The remaining patients had well-healed wounds and a generally improved quality of life. We conclude that aggressive resection and reliable reconstruction are critical considerations in the surgical management of this perplexing clinical problem.