The effect of calcification on the structural mechanics of the costal cartilage

The costal cartilage often undergoes progressive calcification with age. This study sought to investigate the effects of calcification on the structural mechanics of whole costal cartilage segments. Models were developed for five costal cartilage specimens, including representations of the cartilage, the perichondrium, calcification, and segments of the rib and sternum. The material properties of the cartilage were determined through indentation testing; the properties of the perichondrium were determined through optimisation against structural experiments. The calcified regions were then expanded or shrunk to develop five different sensitivity analysis models for each. Increasing the relative volume of calcification from 0% to 24% of the cartilage volume increased the stiffness of the costal cartilage segments by a factor of 2.3–3.8. These results suggest that calcification may have a substantial effect on the stiffness of the costal cartilage which should be considered when modelling the chest, especially if age is a factor.     

Relationships between abdominal and diaphragmatic volume displacements

We investigated the relationship between the volumes displaced by the diaphragm and the abdominal wall during spontaneous breathing in supine anesthetized dogs. Diaphragmatic volume displacement (Vdi) was calculated from measurements taken from anteroposterior fluoroscopic images employing a previously described geometric model. The volume displacement of the abdominal wall (Vabd) was measured with a calibrated Respitrace. Shortening of single diaphragm muscle bundles in costal and crural regions was measured as the distance between radiopaque beads sutured to the peritoneal surface of the muscle. We found that Vdi always exceeded Vabd, but Vabd/Vdi was larger in animals in which the abdominal wall was more compliant. In this preparation, Vdi is better correlated with costal than with crural shortening. Vabd did not correlate with either costal or crural shortening. We infer that the difference between Vdi and Vabd reflects the volume displacement of the lower rib cage caused by diaphragm contraction. This volume difference was tightly correlated with costal shortening. We conclude from these data that coupling between Vdi and Vabd is influenced by the relative compliances of the chest wall and abdomen. Shortening of regions of the diaphragm may have variable relationships to the measured volume displacement, but costal shortening is intimately related to expansion of the lower rib cage.     

A model approach to assess diaphragmatic volume displacement

Diaphragmatic volume displacement (Vdi) is calculated from two models using measurements obtained from anteroposterior fluoroscopic images of supine anesthetized dogs. In model 1, diaphragmatic descent was treated as if it were a "piston in a cylinder." In contrast, model 2 incorporated thoracic configuration as well as inspiratory changes in rib cage diameter and diaphragm shape. In one dog, a computerized tomography reconstruction of Vdi was compared with Vdi calculated using the models. Vdi calculated from model 2 lay within 11% of the computerized tomographic value, whereas Vdi based on model 1 was 30% larger. In seven animals, radiopaque markers were sewn to the right costal diaphragm. Digitized fluoroscopic images were used to measure intermarker distance, an index of muscle shortening. For four tidal breaths per dog, in model 2 Vdi averaged 49 +/- 18% of tidal volume and was weakly correlated with costal diaphragm muscle shortening (R = 0.74). It is concluded that Vdi can be estimated from linear dimensions in the coronal plane, provided that inspiratory changes in rib cage diameter and diaphragmatic shape change are taken into account.     

Vagal modulation of respiratory muscle activity in awake dogs during exercise and hypercapnia.

Using chronically instrumented awake tracheotomized dogs, we examined the contributions of vagal feedback to respiratory muscle activities, both electrical and mechanical, during normoxic hypercapnia (inspired CO2 fraction = 0.03, 0.04, 0.05, and 0.06) and during mild treadmill exercise (3, 4.3, and 6.4 km/h). Cooling exteriorized vagal loops eliminated both phasic and tonic mechanoreceptor input during either of these hyperpneas. At a given chemical or locomotor stimulus, vagal cooling caused a further increase in costal, crural, parasternal, and rib cage expiratory (triangularis sterni) muscles. No further change in abdominal expiratory muscle activity occurred secondary to vagal cooling during these hyperpneas. However, removal of mechanoreceptor input during hypercapnia was not associated with consistent changes in end-expiratory lung volume, as measured by the He-N2 rebreathe technique. We conclude that during these hyperpneas 1) vagal input is not essential for augmentation of expiratory muscle activity and 2) decrements in abdominal expiratory muscle activity may be offset by increments in rib cage expiratory muscle activity and contribute to the regulation of end-expiratory lung volume.     

Dependence of diaphragmatic length on lung volume and thoracoabdominal configuration

Changes in lung volume can be partitioned into volume displacements of the rib cage and abdomen. Abdominal displacements are often used as estimates of diaphragmatic displacements and changes in lengthening of diaphragmatic muscle. We used X-rays, ultrasound, and linear measurements of thoracic and abdominal diameters to estimate relationships among lung volume, thoracoabdominal configuration and diaphragmatic length, and we found that diaphragmatic length was strongly dependent on rib cage as well as abdominal displacement. In three subjects, the diaphragm shortened 57-85% as much during a breath made without abdominal displacement as during a normal breath in which the abdominal wall moved outward with the rib cage. We conclude that changes in diaphragmatic length can be estimated from surface measurements without radiation and that the length of the diaphragm cannot be estimated from displacements of the abdominal wall alone.     

Regional deformation of the canine diaphragm.

To follow regional deformation of the diaphragm in dogs, radiopaque markers were implanted under surgical anesthesia into different anatomic regions of the muscle in triangular arrays (approximately 1 cm to a side). After recovery from surgery, changes in area and shape of the triangles were followed with biplane cinefluorography during quiet breathing and during inspiratory efforts against an occluded airway (Mueller maneuvers). From changes in shape of the triangles during contraction, area changes were decomposed into a major direction and magnitude of shortening (Eg1) and a minor length change (Eg2) perpendicular to Eg1, both expressed as a fraction of initial length at end expiration. With the use of these techniques, systematic differences in regional area change were observed in different parts of the diaphragm during inspiratory efforts at different lung volumes. Regional area always decreased during contraction in the crural and midcostal zones of apposition to the rib cage. Area decreased less and often increased during inspiratory efforts in the costal dome near the central tendon and in the costal region near its rib cage insertion. Differences in regional area change were not due to differences in the Eg1 in different parts of the diaphragm but were a consequence of differences in widening of the muscle along Eg2 perpendicular to the direction of Eg1. As lung volume was passively increased above functional residual capacity, regional area decreased in all parts of the diaphragm except in the costal regions near rib cage insertion, where area increased.     

Effect of intestinal afferent stimulation on pattern of respiratory muscle activation

The purpose of the present study was to examine the reflex effects of mechanical stimulation of intestinal visceral afferents on the pattern of respiratory muscle activation. In 14 dogs anesthetized with pentobarbital sodium, electromyographic activity of the costal and crural diaphragm, parasternal intercostal, and upper airway respiratory muscles was measured during distension of the small intestine. Rib cage and abdominal motion and tidal volume were also recorded. Distension produced an immediate apnea (11.16 +/- 0.80 s). During the first postapneic breath, costal (43 +/- 7% control) and crural (64 +/- 6% control) activity were reduced (P less than 0.001). In contrast, intercostal (137 +/- 11%) and upper airway muscle activity, including alae nasi (157 +/- 16%), genioglossus (170 +/- 15%), and posterior cricoarytenoid muscles (142 +/- 7%) all increased (P less than 0.005). There was greater outward rib cage motion although the abdomen moved paradoxically inward during inspiration, resulting in a reduction in tidal volume (82 +/- 6% control) (P less than 0.005). Postvagotomy distension produced a similar apnea and subsequent reduction in costal and crural activity. However, enhancement of intercostal and upper airway muscle activation was abolished and there was a greater fall in tidal volume (65 +/- 14%). In conclusion, mechanical stimulation of intestinal afferents affects the various inspiratory muscles differently; nonvagal afferents produce an initial apnea and subsequent depression of diaphragm activity whereas vagal pathways mediate selective enhancement of intercostal and upper airway muscle activation.     

Mechanical coupling of upper and lower canine rib cages and its functional significance

We studied rib cage distortability and reexamined the mechanical action of the diaphragm and the rib cage muscles in six supine anesthetized dogs by measuring changes in upper rib cage cross-sectional area (Aurc) and changes in lower rib cage cross-sectional area (Alrc) and the respective pressures acting on them. During quiet breathing in the intact animal the rib cage behaved as a unit (Aurc: 14.6 +/- 7.9 vs. Alrc: 15.1 +/- 9.6%), whereas considerable distortions of the rib cage occurred during breathing after bilateral phrenicotomy (Aurc: 21.0 +/- 5.1 vs. Alrc: 7.0 +/- 4.8%). These distortions were even more pronounced during phrenic nerve stimulation and separate stimulation of the costal and crural parts of the diaphragm (e.g., phrenic nerve stimulation; Aurc: -7.1 +/- 5.1 vs. Alrc: 6.9 +/- 3.5%). During the latter maneuvers the upper rib cage deflated along the relationship between upper rib cage dimensions and pleural pressure obtained during passive deflation, whereas the lower rib cage inflated close to the relationship between lower rib cage dimensions and abdominal pressure obtained during passive inflation. The latter relationship is expected to differ between costal and crural stimulation, since costal action has both an appositional and insertional component and crural action only has an appositional component. The difference between costal and crural stimulation, however, was relatively small, and the slopes were only slightly steeper for the costal than for the crural stimulation (2.9 +/- 1.2 vs. 2.2 +/- 1.0%.(ABSTRACT TRUNCATED AT 250 WORDS)     

Costal cartilages--a clue for determination of sex

Mineralization and ossification in the human costal cartilages were studied radiologically. The aim of our study was to evaluate differences between males and females with respect to patterns of costal cartilage calcification and also with respect to ageing. Material for this study consists of 1044 chest and abdominal radiograms of the Czech population from the Department of Radiology (537 males and 507 females). Further radiograms of 18 chest plates were obtained at routine necropsy of cadavers. The radiograms were examined for pattern of ossification of the costal cartilage. The first rib cartilages were not considered because there are no sex differences. The lower ribs exhibit sexual dimorphism. Mineralization and ossification changes appear at the end of puberty and their occurrence increases with age. The sexual difference in pattern of human costal cartilages is statistically significant and thus highly predictive of sex determination.     

Effect of position on the mechanical interaction between the rib cage and abdomen in preterm infants.

To determine the influence of body position on chest wall and pulmonary function, we studied the ventilatory, pulmonary mechanics, and thoracoabdominal motion profiles in 20 preterm infants recovering from respiratory disease who were positioned in both the supine and prone position. Thoracoabdominal motion was assessed from measurements of relative rib cage and abdominal movement and the calculated phase angle (an index of thoracoabdominal synchrony) of the rib and abdomen Lissajous figures. The ventilatory and pulmonary function profiles were assessed from simultaneous measurements of transpulmonary pressure, airflow, and tidal volume. The infants were studied in quiet sleep, and the order of positioning was randomized across patients. The results demonstrated no significant difference in ventilatory and pulmonary function measurements as a function of position. In contrast, there was a significant reduction (-49%) in the phase angle of the Lissajous figures and an increase (+66%) in rib cage motion in prone compared with the supine position. In addition, the degree of improvement in phase angle in the prone position was correlated to the severity of asynchrony in the supine position. We speculate that the improvement in thoracoabdominal synchrony in the prone position is related to alterations of chest wall mechanics and respiratory muscle tone mediated by a posturally related shift in the area of apposition of the diaphragm to the anterior inner rib cage wall and increase in passive tension of the muscles of the rib cage. This study suggests that the mechanical advantage associated with prone positioning may confer a useful alternative breathing pattern to the preterm infant in whom elevated respiratory work loads and respiratory musculoskeletal immaturity may predispose to respiratory failure.     

Dynamic behavior of excised dog rib cage: dependence on muscle

To assess the contribution of the rib cage to chest wall elastance and hysteresis, we measured force-displacement behavior of the isolated canine rib cage during sinusoidal forcing of the sternum in the midsagittal plane at low frequencies (0.02-2.0 Hz). Elastance of the rib cage was nearly invariant with frequency of forcing from 0.02 to 1.0 Hz and decreased with increasing amplitude. Hysteresis, the width of the force-displacement loop at middisplacement (zero displacement), was nearly constant with frequency below 1.0 Hz and increased with increasing amplitude of forcing. Removal of muscle reduced elastance and hysteresis of the rib cage substantially. The data suggest that the excised dog rib cage shows dynamic behavior similar to that of the intact human rib cage and chest wall and that respiratory muscle is responsible for a major part of the behavior of the passive chest wall. We also calculated the major and minor stiffnesses in the sagittal plane, which differed by a factor of 3-11, and their directions lay close to the dorsoventral and cephalocaudal axes, respectively. Removal of muscle reduced the stiffnesses but did not change their directions. Thus, although respiratory muscles impede motion in the sagittal plane, they do not alter its pattern.     

Relative strengths of the chest wall muscles

We hypothesized that during maximal respiratory efforts involving the simultaneous activation of two or more chest wall muscles (or muscle groups), differences in muscle strength require that the activity of the stronger muscle be submaximal to prevent changes in thoracoabdominal configuration. Furthermore we predicted that maximal respiratory pressures are limited by the strength of the weaker muscle involved. To test these hypotheses, we measured the pleural pressure, abdominal pressure (Pab), and transdiaphragmatic pressure (Pdi) generated during maximal inspiratory, open-glottis and closed-glottis expulsive, and combined inspiratory and expulsive maneuvers in four adults. We then determined the activation of the diaphragm and abdominal muscles during selected maximal respiratory maneuvers, using electromyography and phrenic nerve stimulation. In all subjects, the Pdi generated during maximal inspiratory efforts was significantly lower than the Pdi generated during open-glottis expulsive or combined efforts, suggesting that rib cage, not diaphragm, strength limits maximal inspiratory pressure. Similarly, at high lung volumes, the Pab generated during closed-glottis expulsive efforts was significantly greater than that generated during open-glottis efforts, suggesting that the latter pressure is limited by diaphragm, not abdominal muscle, strength. As predicted, diaphragm activation was submaximal during maximal inspiratory efforts, and abdominal muscle activation was submaximal during open-glottis expulsive efforts at midlung volume. Additionally, assisting the inspiratory muscles of the rib cage with negative body-surface pressure significantly increased maximal inspiratory pressure, whereas loading the rib cage muscles with rib cage compression decreased maximal inspiratory pressure. We conclude that activation of the chest wall muscles during static respiratory efforts is determined by the relative strengths and mechanical advantage of the muscles involved.     

Determinants of transdiaphragmatic pressure in dogs

We measured the transdiaphragmatic pressure (Pdi) during bilateral phrenic nerve stimulation and evaluated the determinants of its change with lung volume, chest wall geometry, and respiratory system impedance in supine dogs. Four rows of radiopaque markers were sewn onto muscle bundles of the costal and crural diaphragm between their origin on the central tendon and their insertion on the rib cage and spine. The length of the diaphragm (L) was determined from the projection images of marker rows using biplane fluoroscopy. Measurements were made at lung volumes between total lung capacity and functional residual capacity before and after the infusion of Ringer lactate solution into the abdominal cavity. In contrast to relaxation, during tetanic stimulation the active lengths of the muscle bundles were similar at all volumes, but the diaphragm assumed different shapes. Although the small differences in active muscle length with volume and liquid loads are consistent with only small changes in muscle force output, Pdi varied by a factor of greater than or equal to 5. There was no single L/Pdi curve that fitted all data during 50-Hz stimulations. We conclude that under these experimental conditions Pdi is not a unique measure of the force produced by the diaphragm and that lung volume, chest wall geometry, and respiratory system impedance are important determinants of the mechanical efficiency of the diaphragm as a pressure generator.     

Effect of mechanical loading on displacements of chest wall during breathing in humans

Using a respiratory inductive plethysmograph (Respitrace) we studied thoracoabdominal movements in eight normal subjects during inspiratory resistive (Res) and elastic (El) loading. The magnitude of loads was chosen so as to produce a fall in inspiratory mouth pressure of 20 cmH2O. The contribution of rib cage (RC) to tidal volume (VT) increased significantly from 68% during quiet breathing (QB) to 74% during El and 78% during Res. VT and breathing frequency did not change significantly. During loading a phase lag was present on inspiration so that the abdomen led the rib cage. However, outward movement of the abdomen ceased in the latter part of inspiration, and the RC became the sole contributor to VT. These observations suggest greater recruitment of the inspiratory musculature of the RC than the diaphragm during loading, although changes in the mechanical properties of the chest wall may also have contributed. Indeed, an increase in abdominal end-expiratory and end-inspiratory pressures was observed in five out of six subjects, indicating abdominal muscle recruitment which may account for part of the reduction in abdominal excursion. Both Res and El increased the rate of emptying of the respiratory system during the ensuing unloaded expiration as a result of a reduction in rib cage expiratory-braking mechanisms. The time course of abdominal displacements during expiration was unaffected by loading.     

Chest wall motion of infants during spinal anesthesia

To test the extent to which diaphragmatic contraction moves the rib cage in awake supine infants during quiet breathing, we studied chest wall motion in seven prematurely born infants before and during spinal anesthesia for inguinal hernia repair. Infants were studied at or around term (postconceptional age 43 +/- 8 wk). Spinal anesthesia produced a sensory block at the T2-T4 level, with concomitant motor block at a slightly lower level. This resulted in the loss of most intercostal muscle activity, whereas diaphragmatic function was preserved. Rib cage and abdominal displacements were measured with respiratory inductance plethysmography before and during spinal anesthesia. During the anesthetic, outward inspiratory rib cage motion decreased in six infants (P less than 0.02, paired t test); four of these developed paradoxical inward movement of the rib cage during inspiration. One infant, the most immature in the group, had inward movement of the rib cage both before and during the anesthetic. Abdominal displacements increased during spinal anesthesia in six of seven infants (P less than 0.05), suggesting an increase in diaphragmatic motion. We conclude that, in the group of infants studied, outward rib cage movement during awake tidal breathing requires active, coordinated intercostal muscle activity that is suppressed by spinal anesthesia.     

Chest wall motion during spontaneous breathing and mechanical ventilation in dogs

We measured the volume change of the thoracic cavity (delta Vth) and the volumes displaced by the diaphragm (delta Vdi) and rib cage (delta Vrc) in six pentobarbital-anesthetized dogs lying supine. A high-speed X-ray scanner (dynamic spatial reconstructor) provided three-dimensional images of the thorax during spontaneous breathing and during mechanical ventilation with paralysis. Tidal volume (VT) was measured by integrating gas flow. Changes in thoracic liquid volume (delta Vliq, presumably caused by changes in thoracic blood volume) were calculated as delta Vth - VT. Absolute volume displaced by the rib cage was not significantly different during the two modes of ventilation. During spontaneous breathing, thoracic blood volume increased during inspiration; delta Vliq was 12.3 +/- 4.1% of delta Vth. During mechanical ventilation, delta Vliq was nearly zero. Configuration of the relaxed chest wall was similar during muscular relaxation induced by either pharmacological paralysis or hyperventilation. Expiratory muscle activity produced 50 +/- 11% of the delta Vth during spontaneous breathing. We conclude that at constant VT the volume displaced by the rib cage is remarkably similar during the transition from spontaneous breathing to mechanical ventilation, while both diaphragmatic volume displacement and changes in intrathoracic blood volume decrease by a similar amount.     

A cadaveric analysis of the ideal costal cartilage graft for Asian rhinoplasty

Augmentation rhinoplasty of the Asian nose may be effectively accomplished with alloplastic materials. However, certain circumstances mandate the use of autologous grafts (e.g., dorsal augmentation that exceeds 8 mm and patient intolerance of alloplastic implants). Septal and auricular cartilages are inadequate for dorsal augmentation of the Asian nose. The use of costal cartilage for autologous augmentation in select Asian patients has proven to be a reliable method in more than 500 operative cases during a 10-year period. This study was designed to evaluate the ideal costal cartilage graft for augmentation rhinoplasty. Forty-two preserved cadavers were studied for the relationship of the individual rib cartilages to the surrounding tissue and for the length and caliber of each costal cartilage. The seventh rib was found to be the ideal rib graft by virtue of its safe location and overall size for grafting. The seventh rib is situated over the abdominal cavity, so the risk of pneumothorax is insignificant. The internal thoracic artery and vein descend in close apposition behind the first to sixth ribs but begin a course medial to the ribs inferior to this point, and therefore vascular injury during seventh-rib harvesting is unknown. The seventh rib also provides the greatest overall available length (90.7 mm, right; 89.6 mm, left) and thickness (17.6 mm, right; 17.5 mm, left). Despite the more conspicuous location of the incision required to harvest the seventh rib, the limited 3-cm incision that is used has healed favorably in almost all cases. The other major drawback for seventh-rib harvesting is the dissection required through the overlying rectus abdominis muscle, but little technical difficulty or postoperative morbidity is added with muscle dissection. The seventh rib is advocated as the ideal choice for augmentation rhinoplasty and potentially other recipient sites.     

Thixotropy of rib cage respiratory muscles in normal subjects.

In this study, we searched for signs of thixotropic behavior in human rib cage respiratory muscles. If rib cage respiratory muscles possess thixotropic properties similar to those seen in other skeletal muscles in animals and humans, we expect resting rib cage circumference would be temporarily changed after deep rib cage inflations or deflations and that these aftereffects would be particularly pronounced in trials that combine conditioning deep inflations or deflations with forceful isometric contractions of the respiratory muscles. We used induction plethysmography to obtain a continuous relative measure of rib cage circumference changes during quiet breathing in 12 healthy subjects. Rib cage position at the end of the expiratory phase (EEP) was used as an index of resting rib cage circumference. Comparisons were made between EEP values of five spontaneous breaths immediately before and after six types of conditioning maneuvers: deep inspiration (DI); deep expiration (DE); DI combined with forceful effort to inspire (FII) or expire (FEI); and DE combined with forceful effort to inspire (FIE) or expire (FEE), both with temporary airway occlusion. The aftereffects of the conditioning maneuvers on EEP values were consistent with the supposition that human respiratory muscles possess thixotropic properties. EEP values were significantly enhanced after all conditioning maneuvers involving DI, and the aftereffects were particularly pronounced in the FII and FEI trials. In contrast, EEP values were reduced after DE maneuvers. The aftereffects were statistically significant for the FEE and FIE, but not DE, trials. It is suggested that respiratory muscle thixotropy may contribute to the pulmonary hyperinflation seen in patients with chronic obstructive pulmonary disease.     

A model for studying the initiation of normal calcification in vivo

1. Rat costal cartilage was found to begin to calcify normally when the rats weigh 35-45g. 2. The cartilage is suggested as a model for the study in vivo of mechanisms concerned with normal calcification. 3. The model was tested by studying the incorporation of fluoride into the mineral deposited in the tissue. 4. The percentage of inorganic material in cartilage rose from approx. 3% of the dry weight in the uncalcified tissue to 62% in the tissue from rats weighing 300g. 5. Mineral deposited had a calcium/phosphorus molar ratio of 1.65. 6. After the oral administration of sodium fluoride to rats, fluoride was incorporated into cartilage mineral. 7. The concentration of fluoride in cartilage ash increased rapidly with calcification and the mineral became more highly fluoridated than the corresponding rib bone. 8. Fluoridated mineral showed a marked decrease in citrate concentration.