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Stress fractures of the ribs in amateur golf players.

BACKGROUND: Stress fractures of the ribs are sometimes seen at the Outpatient Department in patients with a history of playing golf enthusiastically. Many are diagnosed as "muscle strain" or "myofascial pain" and patients are simply advised to take some rest or are treated with analgesics and local injection. This case study investigated 11 amateur golfers whose chief complaint was anterior, posterior or lateral chest pain. After X-ray and bone scan evaluation, "stress fracture of the ribs" was diagnosed. A questionnaire presented to them trying to find the possible mechanisms of these stress fractures. Biomechanical analysis showed that the bending force of the ribs was located at posterolateral segments where fractures tend to occur. Overuse, poor technique and inadequate stretch in beginners are postulated as causes for apparent increased susceptibility to these skeletal injuries. METHODS: Questionnaires inquired about (1) warm-up time, (2) number of strikes, (3) fracture sites, (4) pain patterns, (5) combined injuries. RESULTS: All 11 patients were beginners with right side hand dominance who had begun to play golf within the year. Right side ribs fracture occurred in six cases; left side ribs fracture occurred in eight cases including three patients with two fracture sites. Localized pain was reported in six cases and there were five cases with radiating pain along costal margins. All the golfers had spent no more than 10 minutes in warm up them. Seven patients suffered from multiple injuries after they had played. Five were diagnosed by X-ray and six showed positive finding after Tc-99m MDP bone scan. All lesions were located at the posterolateral segments of the ribs. CONCLUSIONS: Stress fractures of the ribs in amateur golfers are certainly not uncommon. Predominant muscle forces are generated by forced coupling of scapular retraction and protraction, acting through the serratus anterior. With early diagnosis and relative rest for four to eight weeks, the pain will improve. Overuse, poor technique and inadequate stretch will probably lead to stress fracture of the rib.

Biomechanical Phenomena↗

Stimulated biosynthesis of flavins in Photobacterium phosphoreum IFO 13896 and the presence of complete rib operons in two species of luminous bacteria.

Photobacterium phosphoreum IFO 13896 emits light strongly when cultured in medium containing 3% NaCl, but only weakly in medium containing 1% NaCl. It is known that dim or dark mutants appear frequently and spontaneously from this parent strain. To confirm that riboflavin biosynthesis is stimulated when the lux operon is active, the amount of light emitted and flavins synthesized under strongly or weakly light emitting conditions was determined. In comparison with the parent strain cultured in 3% NaCl, the same strain cultured in 1% NaCl emitted 1/36 the light and produced 1/4 the flavins, while three dim or dark mutants, M1, M2 and M3 cultured in 3% NaCl, emitted almost no light, 1/58 the light and 1/10 the light and produced 1/8, 1/5 and 1/3 the amount of flavins, respectively. From these results, we deduced that the genes for riboflavin synthesis, rib genes, are organized in an operon in this strain. In P. phosphoreum NCMB 844, it has been reported that a rib gene cluster is present just downstream of the lux operon. However, among rib genes, the gene for pyrimidine deaminase/pyrimidine reductase, ribD, was not found in this cluster. Because a complete rib operon seems to be necessary for efficient regulation at the transcriptional level, we expected ribD to be present downstream of this cluster and sequenced this region, using SUGDAT, Sequencing Using Genomic DNA As a Template. We could not find this gene but found a gene for hybrid-cluster protein (prismane protein). To find ribD in a different region, a partial ribD sequence was amplified and sequenced using a PCR-based method, and subsequently the genomic DNA was sequenced in both directions from this partial sequence using SUGDAT. Because ribC was found just downstream of ribD, we sequenced further downstream of ribC and confirmed that another complete set of rib genes, ribD, ribC, ribBA, and ribE, is present in P. phosphoreum. The presence of a complete rib operon in P. phosphoreum explains why this species can synthesize flavins at enhanced levels to sustain a strong light emission. Furthermore, we sequenced the rib operon in Vibrio fischeri, another representative luminous bacterium, in a manner similar to that described above, and confirmed that a complete operon is present also in this species. The organization of rib genes in an operon in the Proteobacteria gamma-subdivision is discussed.

Amino Acid Sequence↗

The kinetics of tolerance induction by nondepleting anti-CD4 monoclonal antibody (RIB 5/2) plus intravenous donor alloantigen administration.

BACKGROUND: CD4+ T cells play an essential role in allograft rejection. The monoclonal anti-rat CD4 antibody, RIB 5/2, has been shown to modulate the CD4 glycoprotein without eliminating the recipient T cells. We have successfully induced tolerance to rat heart allografts by recipient pretreatment with a single dose of RIB 5/2 plus intravenous administration of donor splenocytes. In this study, we explored whether this potent regimen could induce tolerance to the more resistant kidney and skin allografts. Furthermore, we examined the kinetics and requirements for tolerance to be met by a single dose of RIB 5/2 plus i.v. alloantigen. METHODS: The efficacy of a single i.p. dose of 20 mg/kg RIB 5/2 plus i.v. donor antigen (25x10(6) splenocyte) pretreatment 0, 21, or 40 days before receipt of an MHC-mismatched Lewis (RT1l) to Buffalo (RT1b) rat cardiac, renal, or skin allograft was studied. Another group of Buffalo recipients treated with RIB 5/2 plus an i.v. alloantigen +/-thymectomy received kidney transplants after 40 days. Attempts to prevent tolerance used interleukin-2 or prior sensitization. Mixed lymphocyte cultures, cytotoxic assays, and precursor frequencies of helper and cytotoxic cells, by limiting dilution analysis, serially measured in vitro cell-mediated immunity. RESULTS: RIB 5/2 administration combined with i.v. alloantigen 21 days before induced tolerance to heart and kidney allografts but did not prolong skin graft survival. In contrast, kidney allografts delayed for 40 days after pretreatment were acutely rejected and survival was not affected by the thymectomy. MLC, CTL, and pTH, and pCTL precursor frequencies from recipients of long-term grafts were specifically suppressed to donor, but not third party, alloantigen. CONCLUSION: A single dose of the nondepleting anti-CD4 monoclonal antibody, RIB 5/2, plus i.v. alloantigen is a potent inducer of tolerance to heart and kidney, but not skin, allografts. The RIB 5/2-induced donor unresponsiveness to a delayed kidney or cardiac allograft is time dependent but can be prolonged if specific alloantigen is present. Suppression of cell-mediated allo-immune responsiveness correlates with allograft acceptance.

Adoptive Transfer↗

The RIB element in the goaG-pspF intergenic region of Escherichia coli.

The sequence (2,700 bp) between the aldH and pspF genes of Escherichia coli was determined. The pspF gene encodes a sigma54 transcriptional activator of the phage shock protein (psp) operon (pspA to pspE). Downstream of the pspF transcribed region are two open reading frames (ORFs), ordL and goaG, convergently oriented with respect to pspF. These two ORFs, together with the adjacent aldH gene, may constitute a novel operon (aldH-ordL-goaG). The goaG-pspF intergenic region contains a complex extragenic mosaic element, RIB. The structure of this RIB element, which belongs to the BIME-1 family, is Y(REP1) > 16 < Z1(REP2), where Y and Z1 are palindromic units and the central 16 bases contain an L motif with an ihf consensus sequence. DNA fragments containing the L motif of the psp RIB element effectively bind integration host factor (IHF), while the Y palindromic unit (REP1) of the same RIB element binds DNA gyrase weakly. Computer prediction of the pspF mRNA secondary structure suggested that the transcribed stem-loop structures formed by the 3'-flanking region of the pspF transcript containing the RIB element can stabilize and protect pspF mRNA. Analysis of pspF steady-state mRNA levels showed that transcripts with an intact RIB element are much more abundant than those truncated at the 3' end by deletion of either the entire RIB element or a single Z1 sequence (REP2). Thus, the pspF 3'-flanking region containing the RIB element has an important role in the stabilization of the pspF transcript.

Antigens, Bacterial↗

Action of the inspiratory muscles of the rib cage during breathing in newborns.

To determine whether the rib cage muscles actively contribute to tidal volume change in infancy, we measured tidal volume (VT), using a pneumotachograph, respiratory gastric pressure swings (Pga), using a liquid-filled gastric catheter, and rib cage and abdominal volume, using respiratory inductive plethysmography in 15 newborns, both before and during 2% CO2-induced hyperventilation. Active rib cage expansion produced by phasic contraction of the inspiratory muscles of the rib cage should reduce respiratory abdominal pressure fluctuations by moving the anterior abdominal wall outward and cephalad, thereby having an expanding influence on the abdominal cavity. During quiet sleep (n = 13), CO2-induced hyperventilation was associated with significant increases in VT, Pga, rib cage volume (Vrc), and abdominal volume (Vab). Increments in Pga were small relative to VT, as shown by an increase in the slope of the VT versus Pga respiratory loop (VT/Pga) in all subjects (p less than 0.001, paired t test). CO2 breathing was associated with an increase in the contribution of the rib cage compartment to total volume change (Vrc/Vrc + Vab) in all infants studied (p less than 0.001, paired t test), and the total volume response to hyperventilation was more strongly related to changes in rib cage volume (slope = 0.62, r = 0.90) than to abdominal volume (slope = 0.31, r = 0.60). During REM sleep (n = 6), mean VT/Pga did not change significantly, and the rib cage contribution to tidal breathing decreased in three of six infants.(ABSTRACT TRUNCATED AT 250 WORDS)

Abdomen↗

Characterization of PMHS Ribs: A New Test Methodology.

This paper presents the results of structural tests to investigate, first, the relationships between geometric and constitutive characteristics of ribs and, second, their mechanical behaviour and rupture threshold. A new methodology was developed that included tests on complete isolated ribs. These tests simulated anterior-posterior loading, as seen in frontal impact. The 4(th) to 9(th) ribs were removed from five cadaver rib cages. The costal geometry was obtained from CT scans and was used to build a specific finite-element model for each rib tested. The test set-up was composed of two caps wherein the two rib extremities were potted. One cap was fixed on the frame of the test set-up through a pin joint. The second cap was fixed to a mobile truck through a pin joint. The truck allowed low friction translation along the anterior-posterior axis. Translation was imposed on the cap such that a constant displacement rate was obtained. External forces and moments were recorded by a sensor at the spinal end. The rotational displacements on the sternal and spinal ends and the translational displacement of the truck were recorded. The mineral content of the ribs was also measured. Fracture was found to occur at a mean displacement of 41 mm, at a mean rupture load of 87 N, and at a mean stiffness of 2340 N/m. Three ribs were reconstructed in a finite-element model and the test set-up was simulated. Comparisons between tests and simulations are provided and discussed.

Journal Article↗

Finite element models of rib as an inhomogeneous beam structure under high-speed impacts.

Fracture of ribs commonly occurs during blunt impacts and can lead to serious injuries or even fatality. The finite element (FE) modeling of ribs under impacts, however, is difficult due to the complex geometry, the difficulty in determining material parameters, and the amount of the computational time required. This study develops a method of modeling ribs as inhomogeneous beam structures. The geometries are reconstructed from images acquired with X-ray computed tomography. Bone material properties, orthotropic or isotropic, are determined from the CT pixel values. From the material distribution inside the cross-section, generalized classical beam formulations use to determine the local homogenized stiffness of the nodes along the rib. To compare the accuracy and efficiency of the method, detailed three-dimensional (3D) FE models of ribs are also developed. Simulations of three benchmark problems that represent different loading or impact conditions demonstrate that the beam FE model is very efficient and is at least as accurate as a very finely meshed 3D FE model. Finally, the rib FE model is used to study blunt trauma injury of animal tests under high-speed impacts. The consistency between predictions and experimental results shows that the developed rib model is a great value to study of blunt trauma caused by high-speed impacts.

Acceleration↗

Open rib biopsy guided by radionuclide technique.

When abnormally increased radioactivity is seen in a rib or ribs by bone imaging in a patient with suspected or known malignancy, it frequently is difficult to differentiate fracture from metastatic disease. Histological examination of the lesion is crucial for diagnosis, staging, and planning of therapy. To assess the value of external localization of the site or sites of abnormal uptake in a rib as a guide for open rib biopsy, 10 patients (7 men, 3 women; age range, 34 to 68 years) with known or suspected malignancy were studied. With reference to the oscilloscope image, a cobalt 57 marker was placed on the skin overlying the focus of increased uptake, and the area of increased activity was marked on the skin as a guide to surgical resection. Of ten resected ribs, four showed metastatic disease and five had fractures. (One patient underwent two external marking procedures and two surgical procedures.) Rib biopsy was not performed in 1 patient because prior to the surgical procedure, a small subcutaneous nodule adjacent to the skin marker was excised and confirmed to be carcinoma. Appropriate courses of management (operation, irradiation, chemotherapy) were taken after the biopsies. The surgeon responsible for the biopsy should be present during the skin-marking procedure, and the area beneath the scapula and the region adjacent to the spine should be avoided. Our results indicate that the technique is a very useful aid for approaching open rib biopsies more precisely.

Adenocarcinoma↗

[The echographic assessment of traumatic rib lesions].

INTRODUCTION: Conventional frontal radiography is mandatory in trauma patients and usually sufficient to detect rib fractures, even though the alignment of bone fragments or projection difficulties may sometimes hinder their depiction. Therefore, there exists moderate disagreement between clinically suspected rib fractures and radiographic findings. MATERIALS AND METHODS: We report our personal experience with US in the detection of rib conditions (fractures and bruises), missed at preliminary radiography. Five symptomatic patients with suspected rib fractures underwent radiographic and US studies. All patients were examined with a real time unit (RT 2800, GE Medical Systems, Milwaukee, USA) with a 7.5 MHz linear probe. RESULTS AND CONCLUSION: US demonstrated rib fractures in 4 patients with negative radiographic findings and a parosteal hematoma in one patient. We conclude that US can detect the rib fractures missed at conventional radiography and show rib cartilage conditions, costochondral dislocations and parosteal hematomas. Therefore we suggest the routine use of this technique in all chest trauma patients, as a useful complement to frontal radiographs, for both management and forensic purposes.

Adult↗

Twelfth rib resection. Preferred therapy for subphrenic abscess in selected surgical patients.

OBJECTIVE: To assess the role of 12th rib resection in the treatment of postoperative, subphrenic abscesses. DESIGN: Consecutive case series. SETTING: University hospital, level I trauma center. PATIENTS: Operative logs for a 13-year period were reviewed for all patients undergoing 12th rib resection for drainage of a postoperative subphrenic abscess. Each individual medical record was reviewed for demographic data, primary diagnosis, computed tomographic scan findings, and clinical status (temperature, white blood cell count, and Acute, Physiologic, Age, and Chronic Health Evaluation II score) at the time of rib resection. MAIN OUTCOME MEASURES: Operative results, microbiological data, complications, and outcomes. RESULTS: Twenty-six patients underwent 27 rib resections for a secondary left subphrenic (23) or a right subhepatic (4) abscess. All patients had undergone at least 1 prior laparotomy (average, 1.5; range, 1-4). Sixteen patients had traumatic injuries, and 7 had complicated pancreatitis. Twelve patients had undergone prior failed attempts at percutaneous drainage before rib resection. Fourteen patients underwent operative drainage without attempted percutaneous drainage, mainly for peripancreatic (7) or multiloculated (3) abscesses. There were 3 postoperative complications (3/27 [11%]): a gastrocutaneous fistula, a gastrocolic-cutaneous fistula requiring laparotomy and temporary colostomy, and fasciitis in the resection site. Four (15%) of the 26 patients died: 3 died of progressive multiple system organ failure, and 1 died of an unrelated injury. The remaining 20 (77%) of the patients were discharged from the hospital with healing wounds and no further episodes of intra-abdominal infection. CONCLUSIONS: Twelfth rib resection is an effective alternative therapy for secondary subphrenic abscesses. The nature of the incision allows for open, dependent drainage; avoids subsequent laparotomy; and effectively controls intra-abdominal infections. Twelfth rib resection remains a useful tool in the treatment of subphrenic abscess and may be the preferred approach when other attempts at abscess drainage have failed.

Adult↗

First rib metamorphosis: its possible utility for human age-at-death estimation.

Human first ribs demonstrate predictable, sequential changes in shape, size, and texture with increasing age, and thus, can be used as an indicator of age at death. Metamorphosis of the first rib's head, tubercle, and costal face was documented in a cross-sectional sample of preadult and adult first ribs of known age at death from the Hamann-Todd skeletal collection (Cleveland Museum of Natural History, Cleveland, Ohio). Blind tests of the usefulness of the first rib as an age indicator were conducted, including tabulation of intraobserver and interobserver inaccuracies and biases. First rib age estimates show inaccuracies and biases by decade comparable to those generated by other aging techniques. Indeed, the first rib method is useful as an isolated age indicator. When used in conjunction with other age indicators, the first rib improves the quality of summary age assessments.

Adolescent↗

Rib remodeling dynamics in a skeletal population from Kulubnarti, Nubia.

Bone remodeling variables in the rib were analyzed for a skeletal population of medieval antiquity (ca. A.D. 550-1450) from Kulubnarti, in Sudanese Nubia. The skeletal remains are naturally mummified and in an excellent state of preservation. The study sample consists of thin sections from the ribs of 80 individuals, ranging in age from 15-50+ years. Ribs were examined using a standard microscope and image analysis software. Numbers of intact osteons, fragmentary osteons, forming osteons, and resorption spaces were counted, osteon and Haversian canal areas were measured, and several variables were calculated to assess morphometric and remodeling status in the rib. Variables calculated included mean annual activation frequency, mean bone formation rate, and net osteonal remodeling. Results indicate that age changes are consistent with those observed for other archaeological and modern samples. High numbers of resorption spaces in young males may reflect slower skeletal development in boys compared to girls. Comparisons of rib data with results of a previous study on patterns of femoral bone remodeling in the same population indicate that ribs have more osteons and higher bone formation rates compared to the femur. Also, sexual differences in osteon size observed in the femur were not observed in the rib. Activation frequency and bone formation rate are low in the Kulubnarti population compared to previously published data for a modern sample, a finding consistent with reported results from other archaeological samples. Genetic factors influencing the minimum effective strain setpoint and duration of skeletal maturation, in addition to repetitive high strains at Kulubnarti, may contribute to observed differences.

Age Determination by Skeleton↗

Abnormal skeletogenesis occurs coincident with increased apoptosis in the Splotch (Sp2H) mutant: putative roles for Pax3 and PDGFRalpha in rib patterning.

Although the importance of the transcription factor Pax3 has been identified in many embryological processes including neural crest cell migration, neural tube closure, and limb muscle formation, its role in proper formation of the ribs has not been well characterized. We have used the Splotch mouse which has a mutation in the Pax3 gene to determine what role Pax3 may play in rib morphogenesis. Homozygous Splotch embryos collected from days 13.5 to 16.5 of gestation displayed severe rib abnormalities including fusions at both the proximal and distal regions. Given its expression in the dermomyotome, we sought to determine when Pax3 expression in the Splotch mutant initially becomes abnormal and which rib segment progenitors may be affected. Prior to somite differentiation at 9.5 dpc (days post coitum), Pax3 is normally expressed in the somites; after differentiation, however, Pax3 expression is diminished in Splotch embryos. We also determined that significantly increased levels of apoptosis occur in the thoracic region by 11.0 dpc relative to wild-type littermates. Because Patch mouse mutants which fail to express PDGF alpha-receptor also have rib abnormalities, we sought to determine whether Pax3 may influence the expression of this receptor. By in situ hybridization, we determined that initially the expression of PDGFRalpha is normal in Splotch mutants at 10.0 dpc, but decreases by 12.5 dpc in the thoracic somite region, suggesting that Pax3 may act upstream of PDGFRalpha. Taken together, our results show that Pax3 expression is important for normal rib development and that increased apoptosis occurs in the thoracic muscles. We suggest that Pax3 may influence the expression of PDGFRalpha, and that the reduced and/or deficient thoracic muscles may contribute to the resulting rib abnormalities.

Animals↗

Increased pyrophosphate rib uptake: clinical correlation.

Two hundred and thirty-one patients had 270 bone scans. Increased rib uptake was correlated with radiological findings. Interpretation of results whether due to benign or to metastatic disease depends on other observations. These include whether the uptake is localized or along the rib outline, single or multiple, and associated with other abnormal uptake in the rest of the skeleton. Abnormal rib uptake was encountered in 23% of patients scanned for malignant disease and 10% of patients scanned for benign conditions. In the first group 34% were true positive and of these, rib lesions were multiple in 32% and solitary in 2%. In 20% the rib uptake was due to benign conditions and in 46% it was indefinite because of absent radiological findings. In this last difficult group 17% were due to probably early rib metastases and 29% were due to benign causes. Rib metastases were missed in only two cases, 1.1%. One case was multiple myeloma and the other was direct extension from underlying anaplastic lung carcinoma.

Adolescent↗

Localization of type I and II collagen during development of human first rib cartilage.

The localization of fibrillar type I and II collagen was investigated by immunofluorescence staining with specific antibodies in order to obtain a better understanding of tissue remodelling during the development of first rib cartilage. In childhood and early adolescence type I collagen was found to be restricted to the perichondrium of first rib cartilage, while type II collagen was localized in the matrix of hyaline cartilage. However, in advanced age type I collagen was also found in the territorial matrix of intermediate and central chondrocytes of first rib cartilage. The matrix of subperichondrial chondrocytes was negative for type I collagen. This suggests that some chondrocytes in first rib cartilage undergo a modulation to type I collagen-producing cells. The first bone formation was observed in rib cartilages of 20- to 25-year-old adults. Interestingly, the ossification began peripherally, adjacent to the innermost layer of the perichondrium where areas of fibrocartilage had developed. The newly formed bone matrix showed strong immunostaining for type I collagen. Fibrocartilage bordering peripherally on bone matrix revealed only a faint staining for type I collagen, but strong immunoreactivity to type II collagen. The interterritorial matrix of the central chondrocytes failed to react with the type II collagen antibody, in both men and women, from the end of the second decade. These observations indicate that major matrix changes occur at the same time in male and female first rib cartilages. Thus, our findings indicate that ossification in human first rib cartilage does not follow the same pattern as that observed in endochondral ossification of epiphyseal discs or sternal cartilage.

Adolescent↗

Biomechanical modelling of growth modulation following rib shortening or lengthening in adolescent idiopathic scoliosis.

A biomechanical model was developed to evaluate the long-term correction resulting from rib shortening or lengthening in adolescent idiopathic scoliosis (AIS). A finite element model of the trunk, personalised to the geometry of a scoliotic patient, was used to simulate rib surgery. Stress relaxation of ligaments following surgery was integrated into the model, as well as longitudinal growth of vertebral bodies and ribs and its modulation due to mechanical stresses. Simulations were performed in an iterative fashion over 24 months. A concave side rib shortening, inducing load patterns on the vertebral end-plates that could act against the scoliosis progression, was tested. A fractional factorial experimental design of 16 runs documented the effects of six modelling parameters. Wedging of the apical vertebra in the frontal plane decreased from 5.2 degrees initially to a mean value of 3.8 degrees after 24 months. The wedging decrease in the thoracic apical region was reflected by changes in the spine curvature, with a Cobb angle decrease from 46 degrees to 44 degrees immediately after the surgery and to a mean of 41 degrees after 24 months. However, both rib hump and vertebral axial rotation increased, on average, by 4 degrees at the curve apex. The most significant parameters were the growth sensitivity to stress in ribs and vertebrae and the rate of stress relaxation of intercostal ligaments. The results confirmed the potential of long-term correction of spinal curvature resulting from the rib shortening on the concavity. This modelling approach could be used for further design of less invasive surgery, taking into account residual growth, for scoliosis correction.

Adolescent↗

Morphological study of rib regeneration following costectomy in adolescent idiopathic scoliosis.

This is a prospective observational study comparing cases with retrospective controls. The aim of the study is to compare rib regeneration with a scaffold placed intra-periosteally against no scaffold, after costectomy in adolescent idiopathic scoliosis. A prospective study was conducted at Amrita Institute of Medical Sciences on 16 consecutive patients (51 ribs) with adolescent idiopathic scoliosis who underwent costectomy and application of gel foam in the rib bed as a scaffold. These patients were compared with a retrospective group of 15 patients (33 ribs) who did not have the scaffold. All prospective and retrospective patients were followed up for a minimum period of 6 months and were analyzed radiographically for rib regeneration and morphology. A classification system was devised to include all possible morphologies of regenerate. The resulting data, when analyzed showed that majority of ribs re-grew to normal morphology in 3-6 months in the trial group. In comparison the regeneration in the retrospective controls was slower and poorer in quality. Ribs treated by placement of gel foam scaffold in the bed regenerate to a near normal radiological profile within 6 months of costectomy compared to a slower regeneration in those without gel foam scaffold.

Adolescent↗

Contribution of the parasternal intercostals to inspiratory rib elevation in dogs.

To estimate the contribution of the parasternal intercostals to rib elevation during quiet breathing, parasternal intramuscular pressure, Pim, in the fourth interspace and displacement of the rib just below were measured in eight supine anesthetized dogs during: (1) bilateral stimulation of the parasternals, (2) quiet breathing before, after phrenicotomy, and subsequent vagotomy. During quiet breathing, the parasternal contribution averaged 66 +/- 12% of the rib elevation caused by inspiratory rib cage muscles. This contribution decreased in relative terms after phrenicotomy (37 +/- 14%) and subsequent vagotomy (26 +/- 14%) while it tended to increase in absolute terms (from 1.9 +/- 2.4 to 2.1 +/- 2.5 NS, and 2.4 +/- 2.4 mm P < 0.01, respectively). Rib elevation caused by inspiratory rib cage muscles increased after phrenicotomy (116 +/- 63%, P < 0.001) and subsequent vagotomy (279 +/- 60%, P < 0.001) as did Pim (19 +/- 10% NS and 41 +/- 36% P < 0.01, respectively). Moreover, the mechanical interaction of the parasternals among different interspaces measured in three other dogs, was likely to be limited during quiet breathing. We conclude that after diaphragm paralysis, the parasternals played a progressively smaller role while other rib cage muscles were increasingly recruited.

Animals↗