Prenatal diagnosis of transposition of the great arteries over a 20-year period: improved but imperfect.

OBJECTIVE: To evaluate temporal trends in the prenatal diagnosis of transposition of the great arteries with intact ventricular septum (TGA/IVS) and its impact on neonatal morbidity and mortality. METHODS: We included in this study cohort newborns with TGA/IVS who were referred for surgical management to our center over a 20-year period (1992-2011). The study period was divided into five 4-year periods and the primary outcome was rate of prenatal diagnosis. Secondary outcomes included neonatal preoperative status and perioperative survival. RESULTS: Of the 340 patients with TGA/IVS, 81 (23.8%) had a prenatal diagnosis. The rate of prenatal diagnosis increased over the study period, from 6% in 1992-1995 to 41% in 2008-2011 (P < 0.001). Compared to patients with a postnatal diagnosis, balloon atrial septostomy (BAS) was performed earlier in patients with a prenatal diagnosis (0 days after delivery vs 1 day after delivery, respectively; P < 0.001) and fewer prenatally diagnosed neonates required mechanical ventilation (55.6% vs 68.0%; P = 0.03). Between patients with a prenatal or postnatal diagnosis of TGA/IVS, there were no statistically significant differences in the incidence of preoperative acidosis (16.0% vs 25.5%; P = 0.1), need for preoperative extracorporeal membrane oxygenation (2.5% vs 2.7%; P = 1.0) or mortality (one preoperative and no postoperative deaths among prenatally diagnosed patients compared with four preoperative and six postoperative deaths among postnatally diagnosed patients). CONCLUSIONS: The prenatal detection rate of TGA/IVS has improved but still remains below 50%, suggesting the need for strategies to increase detection rates. The mortality rate was not statistically significantly different between prenatally and postnatally diagnosed patients, however, there were significant preoperative differences with regard to earlier BAS and fewer neonates that required mechanical ventilation. Ongoing work is required to ascertain whether prenatal diagnosis confers long-term benefits.

Chiari type I malformation in children and adolescents with cystic fibrosis.

Chiari type I malformation is characterized by herniation of the cerebellar tonsils through the foramen magnum. An association between Chiari type I malformation and cystic fibrosis (CF) has not previously been established. We report on five children and adolescents with CF in whom Chiari type I malformations were diagnosed. Three patients were 17-18 years old at time of diagnosis, one was 3 years old, and one was 10 months of age. All patients were followed at the Cystic Fibrosis Center at St. Christopher's Hospital for Children and were diagnosed with the malformations between June 1988 and June 1997. Over this same period, 400 CF patients 18 years or younger were followed routinely. All patients had the diagnosis of Chiari type I confirmed by brain-stem MRI. Neurologic findings included swallowing dysfunction, syncopal episodes, numbness of extremities, recurrent vomiting, and headaches. No two patients had the same presenting neurologic findings. Our data suggest that Chiari type I malformation is more common in CF than in the general population. The possibility of Chiari type I malformation should be included in the differential diagnosis of unexplained neurologic complaints in patients with CF.

Risk factors for emergence of Stenotrophomonas maltophilia in cystic fibrosis.

The number of patients with cystic fibrosis (CF) whose sputum culture has yielded Stenotrophomonas maltophilia has increased in the last 5 years at St. Christopher's Hospital for Children. We conducted a case-control study to determine risk factors for recovery of S. maltophilia in respiratory secretions from patients with CF. We reviewed the outpatient and inpatient records of patients colonized with S. maltophilia between 1993 and 1997, and of age-matched (at time of initial recovery of S. maltophilia) control patients with CF who had never had a positive sputum culture for S. maltophilia. Variables included age at time of CF diagnosis, gender, severity of CF (based on Shwachman-Kulczycki (S-K) scores and spirometry), frequency of hospitalizations, use of oral, intravenous, or inhaled antibiotics, and use of oral or inhaled corticosteroids in the 2 years prior to the first isolation of S. maltophilia from respiratory secretions. Statistical methods included stepwise logistic regression to determine risk factors for acquisition of S. maltophilia. During the study period, 58 patients with CF had a positive sputum or deep throat culture for S. maltophilia. The distribution of S. maltophilia acquisition by year increased from 7 patients in 1993 (incidence, 2.8%) to 16 in 1997 (incidence, 6.2%). Patients positive for S. maltophilia were found to have significantly worse growth parameters, S-K score, and spirometric values than S. maltophilia-negative CF controls (P < 0.05). Stepwise logistic regression demonstrated that treatment with long-term antibiotics (P = 0.0016) and number of days of intravenous antibiotic therapy (P = 0.035) were significant risk factors for S. maltophilia colonization in our group of CF patients. We conclude that patients with CF whose respiratory secretions yield S. maltophilia have an overall worse clinical status at the time of initial S. maltophilia isolation than noncolonized patients, and that preceding treatment with antibiotics may have predisposed them to the acquisition of this bacterium in their respiratory secretions.

Primary ciliary dyskinesia: a genome-wide linkage analysis reveals extensive locus heterogeneity.

Primary ciliary dyskinesia (PCD), or immotile cilia syndrome (ICS), is an autosomal recessive disorder affecting ciliary movement with an incidence of 1 in 20000-30000. Dysmotility to complete immotility of cilia results in a multisystem disease of variable severity with recurrent respiratory tract infections leading to bronchiectasis and male subfertility. Ultrastructural defects are present in ciliated mucosa and spermatozoa. Situs inversus (SI) is found in about half of the patients (Kartagener syndrome). We have collected samples from 61 European and North American families with PCD. A genome-wide linkage search was performed in 31 multiplex families (169 individuals including 70 affecteds) using 188 evenly spaced (19cM average interval) polymorphic markers. Both parametric (recessive model) and non-parametric (identity by descent allele sharing) linkage analyses were used. No major locus for the majority of the families was identified, although the sample was powerful enough to detect linkage if 40% of the families were linked to one locus. These results strongly suggest extensive locus heterogeneity. Potential genomic regions harbouring PCD loci were localised on chromosomes 3p, 4q, 5p, 7p, 8q, 10p, 11q, 13q, 15q, 16p, 17q and 19q. Linkage analysis using PCD families with a dynein arm deficiency provided 'suggestive' evidence for linkage to chromosomal regions 8q, 16pter, while analyses using only PCD families with situs inversus resulted in 'suggestive' scores for chromosomes 8q, and 19q.

Newer therapies for cystic fibrosis.

Cystic fibrosis (CF) is a chronic, progressive, genetic disease caused by flawed ion transport across epithelial membranes due to a genetic mutation. Most therapeutic efforts are centred on the main clinical manifestations of the disease: progressive destructive airway disease and pancreatic insufficiency. Most individuals with CF succumb to lung disease. The present-day therapeutic armamentarium includes agents that have been used for many decades, some of which have experienced transformations in their formulation or mode of administration thanks to the introduction of new manufacturing technologies. The development of new therapies involves new conceptual approaches, based on recent understanding of the disease. These therapies await proof of concept or clinical experimentation before being accepted as useful means to arrest the progression of the disease. In this article we will review therapeutic agents introduced into the clinical arsenal in the last 20 years, as well as experimental therapies under active investigation.

Epidemiologic study of cystic fibrosis: design and implementation of a prospective, multicenter, observational study of patients with cystic fibrosis in the U.S. and Canada.

Cystic fibrosis (CF) is a complex illness characterized by chronic lung infection leading to deterioration in function and respiratory failure in over 85% of patients. An understanding of the risk factors for that progression and the interaction of these factors with current therapeutic strategies should materially improve the prevention of this progressive lung disease. The Epidemiologic Study of Cystic Fibrosis (ESCF) was therefore designed as a multicenter, longitudinal, observational study to prospectively collect detailed clinical, therapeutic, microbiologic, and lung function data from a large number of CF treatment sites in the U.S. and Canada. The ESCF also serves an important role as a phase-IV study of dornase alfa. To be eligible for enrollment, subjects must have the diagnosis of CF and receive the majority of their care at an ESCF site. In this paper, the authors present the ESCF study design in detail. Further, enrollment data collected at 194 study sites in 18,411 subjects enrolled from December 1, 1993 to December 31, 1995 are presented in summary form. This comprehensive study is unique in the detail of clinical data collected regarding patient monitoring and therapeutic practices in CF care. Two companion articles present data regarding practice patterns in cystic fibrosis care, including data on resource utilization and prescribing practices.

Patterns of medical practice in cystic fibrosis: part I. Evaluation and monitoring of health status of patients. Investigators and Coordinators of the Epidemiologic Study of Cystic Fibrosis.

This report characterizes patterns of evaluation and monitoring of the health status of patients with cystic fibrosis (CF) as observed in the Epidemiologic Study of Cystic Fibrosis (ESCF), and compares these practices to published guidelines. All patients (18,411) who enrolled in ESCF at 194 study sites in the United States and Canada from December 1, 1993 to December 31, 1995 were considered for study. Patients enrolled before January 1, 1995 with >/=1 healthcare encounters during 1995 (12,631) were included in the analysis. Patients enrolled after January 1, 1995 (5,266), or who died (354), withdrew from the study (128), or were lost to follow-up (21) were excluded. Frequency of encounters (outpatient and hospital), spirometry, respiratory tract cultures, and chest radiographs were recorded during a 1-year period (1995) and analyzed by gender, age, severity of lung disease, and presence of any Pseudomonas species in the respiratory tract. The 12,631 patients had 53,024 outpatient visits. In 57.5% of patients, the recommended criteria of >/=4 total visits per year were met. Only 27.4% of all patients had >/=4 routine visits; 3.1% had only sick visits, and 59.0% had no sick visits. One third (34.6%) were hospitalized at least once, for a total of 8,561 hospitalizations. Older patients with lower pulmonary function and Pseudomonas in their respiratory tract had fewer routine visits and more sick visits, and were hospitalized more than were younger patients. In three fourths (75.8%) of patients the recommended criterion of two spirometry assessments per year was met, whereas in 79.3% the criterion of one culture was met, and in 68.3% the criterion of one radiograph/year was met. We conclude that in the majority of CF patients, the recommended criteria for routine evaluation and monitoring were met. However, in a rather substantial number they were not. An increase in the utilization of healthcare resources was observed in patients with more severe disease. This information will help to establish benchmarks for future quality assessment programs.

Patterns of medical practice in cystic fibrosis: part II. Use of therapies. Investigators and Coordinators of the Epidemiologic Study of Cystic Fibrosis.

This report describes the prescribing pattern of therapeutic interventions in the management of patients with cystic fibrosis (CF), as observed in the Epidemiologic Study of Cystic Fibrosis (ESCF). Use of 20 therapies by 12,622 patients was recorded from each health care encounter (53,024 outpatient visits and 8,561 hospitalizations) during a 1-year period (1995), and analyzed by gender, age, severity of lung disease, and presence of any Pseudomonas species in the respiratory tract. The percentage of patients using the following pulmonary therapies was observed (in descending order): airway clearance techniques (88.2%); inhaled bronchodilators (82.2%); oral antibiotics (excluding quinolones) (68. 2%); dornase alfa (52.9%); intravenous antibiotics (34.4%); oral quinolones (34.4%); inhaled antibiotics (34.3%); mast cell stabilizers (29.5%); inhaled corticosteroids (25.9%); oral corticosteroids (17.1%); oral bronchodilators (16.2%); oxygen (8. 1%); inhaled mucolytic agent acetyl cysteine (6.5%); and diuretics (1.4%). The percentage of patients using nutritional therapies was: pancreatic enzymes (96%); oral nutritional supplements (31.1%); enteral nutrition (7.3%); and parenteral nutrition (0.7%). The percentage of patients using other therapies was: nonsteroidal anti-inflammatory drugs (7.9%); and insulin or oral hypoglycemic agents (6.1%). The general trend was for therapies to be used more by older patients, those with lower pulmonary function, and by those with Pseudomonas in their respiratory tract. Exceptions to this trend occurred for airway clearance, oral antibiotics, mast cell stabilizers, and pancreatic enzymes. Four therapies (oral nutritional supplements, parenteral nutrition, diuretics, and pancreatic enzymes) were used more by males than females. However, there was no gender difference for this group of therapies on pulmonary or nutritional status.

Pulmonary function in hospitalized infants and toddlers with cystic fibrosis.

UNLABELLED: In older children with cystic fibrosis (CF), well-documented improvements in lung function occur during hospitalization for treatment of pulmonary exacerbations. OBJECTIVES: (1) To test the hypothesis that improvement in lung function occurs in infants and toddlers hospitalized because of CF pulmonary exacerbations. (2) To compare changes in lung function measured during forced expiratory flow and tidal breathing. STUDY DESIGN: Seventeen infants and toddlers with CF were evaluated at the beginning and end of hospitalization by the rapid thoracic compression technique to yield maximal flow at forced residual capacity. Tidal mechanics were measured by the esophageal balloon technique to yield lung conductance and compliance. RESULTS: Lung function improved during the course of hospitalization. The greatest change was observed in measurements of maximal flow at functional residual capacity (.VmaxFRC), increasing from 38.5% +/- 6% predicted (mean +/- SEM) to 59.8% +/- 6% at the end (p < 0.005). Lung conductance (GL) increased from 60% +/- 6% to 78% +/- 8% (p < 0.02); lung compliance (CL) increased from 66% +/- 5% to 75% +/- 5% (p < 0.03). The degree of improvement of .VmaxFRC, GL, and CL was related to baseline measurements; those with poorer pulmonary function at baseline had the greatest degree of improvement during hospitalization. CONCLUSION: Assessments of airflow obstruction from measurements of .VmaxFRC and GL do not necessarily demonstrate similar findings in a given infant with CF, perhaps because these two techniques measure different physiologic properties. Changes in .VmaxFRC may best reflect the predominant pathophysiology of lung disease in infants and toddlers with CF.

Self-management of cystic fibrosis: short-term outcomes of the Cystic Fibrosis Family Education Program.

This study tested the efficacy of the Cystic Fibrosis Family Education Program, a cystic fibrosis self-management program, on improving participants' knowledge, self-efficacy, self-management behavior, health, and quality of life. A quasi-experimental pretest-posttest nonequivalent comparison group design was employed. Participants made up 104 patient-primary caregiver dyads from the intervention site cystic fibrosis center and 95 from the usual care comparison center. The intervention, a self-paced print curriculum based on social cognitive theory, targeted behavioral capability, self-efficacy, and outcome expectations and was implemented as an integral part of medical care. Parents, early childhood, middle childhood, and adolescents received separate materials on respiratory, nutrition and malabsorption, communication, and coping issues. Significant intervention effects were found on the knowledge scores for caregivers, adolescents, and children; caregiver and adolescent total self-management scores; Child Behavior Checklist total score; one parent coping scale score; the modified NIH score; NIH pulmonary factor 1; and the Brasfield total score. Significant interaction effects were evident in the self-efficacy scores for caregivers and children.

Safety of repeated intermittent courses of aerosolized recombinant human deoxyribonuclease in patients with cystic fibrosis.

OBJECTIVES: To determine the effect of repeated doses of aerosolized recombinant human deoxyribonuclease (rhDNase) on the development of anti-rhDNase antibodies, acute allergic reactions, and pulmonary function in patients with cystic fibrosis. DESIGN: A multicenter, open-label study in which 184 patients received 10 mg aerosolized rhDNase twice a day for 14 days followed by a 14-day washout period for a total of 6 treatment cycles. Serial determinations of anti-rhDNase antibodies and pulmonary functions were performed. RESULTS: Detectable anti-rhDNase antibodies developed in 16 (8.7%) patients. These patients had no changes in their symptoms from the time they entered the trial. Antibodies detected were all of the IgG isotype. Increases in both forced expired volume in 1 second and forced vital capacity were noted from the beginning to the end of each cycle of treatment returning to baseline during the off-treatment period of each cycle. Seropositivity to rhDNase was not associated with allergic reactions and had no relationship on improvement in pulmonary function. CONCLUSIONS: Development of anti-rhDNase antibodies occurred in a small number of patients and was not associated with side effects. Intermittent administration of rhDNase for 24 weeks to patients with cystic fibrosis was well tolerated and was not associated with anaphylaxis in any patient. Pulmonary function improved significantly during the 14-day cycles while rhDNase was administered and returned to baseline when rhDNase was discontinued.

Fibrosing colonopathy in children with cystic fibrosis.

PURPOSE: Fibrosing colonopathy is a newly described entity seen in children with cystic fibrosis. The radiological hallmarks are foreshortening of the right colon with varying degrees of stricture formation. High-dose enzyme therapy has been implicated as the cause of this process. The purpose of this study is to review the author's experience with evaluation and treatment of these patients. METHODS: There are currently 380 patients being treated at our CF center. Fifty-five of these patients have been treated with high-dose enzyme therapy (> 5,000 units of lipase/kg). The medical records of these patients, who are at risk for developing fibrosing colonopathy, were reviewed for the presence of recurrent abdominal complaints, and the work-up and treatment of these symptoms. RESULTS: Chronic complaints of abdominal pain, distension, change in bowel habits, or failure to thrive were present in 24 of the 55 patients treated with high-dose enzymes. So far, 18 of these 24 patients have been evaluated by contrast enema. Thirteen of eighteen have been found to have fibrosing colonopathy characterized by foreshortening and strictures of the colon. Additional findings included focal strictures of the right colon (7 of 13), long segment strictures (5 of 13), and total colonic involvement (1 of 13). Nine patients with the most severe symptoms have undergone colon resection, including five segmental right colectomies, three extended colectomies (ileo-sigmoid anastomosis), and one subtotal colectomy with end-ileostomy. Pathological evaluation has shown submucosal fibrosis, destruction of the muscularis mucosa, and eosinophilia. No postoperative complications or deaths occurred. All nine postoperative patients have noted marked symptomatic improvement. Contrast enema follow-up results are available for six patients, and have documented no recurrent strictures to date. Three of four nonoperative patients have less severe symptoms and are currently being treated conservatively. The other family has refused surgery and the patient is being treated symptomatically. CONCLUSION: High-dose lipase replacement has been implicated as the etiology for FC and was present in all of our patients. Our cystic fibrosis center now routinely limits lipase to 2,500 U/kg per dose. We recommend the use of the contrast enemas to evaluate at-risk patients who have chronic abdominal complaints or who present with recurrent bowel obstruction. Colon resection should be performed in those with clinically and radiographically significant strictures with the expectation of a good outcome.

A multicenter study of alternate-day prednisone therapy in patients with cystic fibrosis. Cystic Fibrosis Foundation Prednisone Trial Group.

The purpose of this study was to evaluate the efficacy and safety of alternate-day prednisone therapy in treating patients with mild-to-moderate cystic fibrosis during a 4-year period. In 15 North American cystic fibrosis centers, we screened 320 patients and enrolled 285 patients from April 1986 to December 1987. Patients were randomly assigned to take prednisone, 1 mg/kg per dose or 2 mg/kg per dose, or a matching placebo given on alternate days. Lung function, clinical status, hospitalizations, growth, and steroid side effects were monitored. During the first 24 months the percentage of the predicted forced vital capacity was greater in the 1 mg/kg group (p < 0.0001) and the 2 mg/kg group (p < 0.01) when each was compared with placebo. Patients in the 1 mg/kg group had a higher percentage of predicted forced vital capacity than placebo patients during the entire 48 months (p < 0.0025), but only in the group of patients who were colonized with Pseudomonas aeruginosa at baseline. For 48 months, the 1 mg/kg group had a higher percentage of predicted forced expiratory volume in 1 second than patients given placebo (p < 0.02). The prednisone-treated groups had a reduction in serum IgG concentrations (1 mg/kg vs placebo, p < 0.007; 2 mg/kg vs placebo, p < 0.003). From 6 months onward, height z scores fell in the 2 mg/kg group compared with those given placebo (p < 0.001). For the 1 mg/kg group, height z scores were lower from 24 months. An excess of abnormalities in glucose metabolism was seen in the 2 mg/kg group compared with the placebo group (p < 0.005). Our findings suggest a role for alternate-day prednisone therapy at a dose of 1 mg/kg in patients with mild to moderate cystic fibrosis. The benefit of improved lung function appears to outweigh the potential for adverse effects when the treatment period is less than 24 months.

Interstitial lung diseases in children: a review.

Interstitial lung diseases (ILD) are disorders of the lower respiratory tract, characterized by chronic inflammation of the lung parenchyma, varying degree of fibrosis, derangement of the alveolar walls and loss of the functional alveolar capillary units. ILD are relatively uncommon in children. Most of the interstitial lung diseases have no known etiology. In children, common diseases associated with ILD include viral respiratory tract infections (RSV, parainfluenza, etc.), gastroesophageal reflux, idiopathic pulmonary fibrosis, pulmonary hemosiderosis, eosinophilic pneumonia, pneumonitis associated with AIDS, etc. Chronic inflammation of the alveoli (alveolitis), the initial injury in ILD, and several mediators released from inflammatory cells (eosinophils, neutrophils and macrophages) can cause fibrosis and derangement of alveolar walls. Dyspnea and a non-productive cough are the cardinal symptoms of ILD. Other findings include chest pain, hemoptysis and weight loss. Clubbing of fingers occur in approximately 50 per cent of cases. Diagnosis is based on a combination of history, clinical findings, radiographic findings, pulmonary function tests and histologic findings. Open lung biopsy has been very helpful in providing information regarding the extent and nature of the damage, prognosis and response to therapy. There are 3 main aspects in the treatment of ILD. The most important step is to identify and eliminate the cause. The second is suppression of the inflammation. The third is supportive and symptomatic treatment. Corticosteroids are the drugs commonly used for suppression of inflammation. Immunosuppressive drugs (azathioprine, cyclophosphamide) have also been tried. Lung transplantation and heart transplantation have been successfully achieved in selected patients. The results of therapy should be regularly monitored by clinical symptoms, chest radiographs and serial pulmonary function studies.

Primary ciliary dyskinesia (the immotile cilia syndrome).

OBJECTIVE: The purpose of this review is to familiarize the reader with the genetic aspects, clinical manifestations, diagnostic techniques and management of the primary ciliary dyskinesia syndrome. Further, this article illustrates some unusual features of this syndrome and discusses some speculative hypotheses concerning its pathogenesis and clinical presentation. DATA SOURCES: The bibliography includes references in English as well as some references of historical interest in German. Both human and veterinary literature are quoted. Sources included computerized bibliographic searches of recent literature and reviews of literature. STUDY SELECTION: Selection of papers was made based on their historic importance in the definition and characterization of the disease, and on reviews of large bodies of novel or interesting information. Some review papers were not included to avoid repetition. RESULTS: Although the incidence of primary ciliary dyskinesia is low, the inclusion of this condition in the differential diagnosis of chronic and recurrent sinobronchial disease in children and older individuals is very common. Primary ciliary dyskinesia should be suspected in individuals who present chronic respiratory symptoms already in the neonatal period, develop profuse, chronic mucopurulent rhinorrhea, and chronic otitis media and sinusitis. Chronic cough, obstructive lung disease, and bronchorrhea associated with the aforementioned manifestations should also make clinicians suspect this syndrome. Male sterility is almost universally present and situs inversus is present in 50% of affected persons. The diagnosis of primary ciliary dyskinesia is clinical and is confirmed by studies of ciliary motility and ultrastructure of the respiratory mucosa. Management is directed to microbial suppression by frequent antibiotic administration, and to clearing of retained secretions. CONCLUSIONS: The diagnosis of primary ciliary dyskinesia requires familiarity with the clinical picture and the specific techniques of identification. Although the basic mechanism of disease is known, the molecular genetics of primary ciliary dyskinesia and the causes for the phenotypic variability remain to be explained. Future research should be directed to the identification of the gene(s) responsible for the manifestations of the disease and to effective methods of activation, in vivo, of dysfunctional cilia.

Effects of CPAP on lung mechanics in infants with acquired tracheobronchomalacia.

Continuous positive airway pressure (CPAP) has been used in the treatment of infants with tracheobronchomalacia (TBM). However, the effects of CPAP on lung mechanics in these infants are unknown. We hypothesized that CPAP prevents airway collapse and improves forced exhalation. We studied respiratory mechanics of nine infants (age 15 +/- 3 mo, SEM) with acquired TBM documented by bronchoscopy, during quiet respiration and forced exhalation, using the esophageal balloon and rapid thoracic compression techniques, respectively. Measurements were made when infants received no CPAP and repeated when 5 and 8 cm H2O CPAP were applied to the airway opening via a modified Mapleson anesthesia circuit. Expiratory resistance (RL), midexpiratory tidal flow (VE50), and maximal flow at functional residual capacity (Vmax FRC) were compared at each level of CPAP. Vmax FRC increased threefold from baseline to 8 cm H2O CPAP (p < 0.005). In contrast, there was no difference in expiratory RL or in VE50 at any level of CPAP. These data suggest that in infants with acquired TBM, assessments of forced expiratory flow reflect the amount of CPAP necessary to prevent airway collapse during forced exhalation better than can measurements of tidal mechanics.