Lung Mechanics: A Review of Solid Mechanical Elasticity in Lung Parenchyma.

The lung is the main organ of the respiratory system. Its purpose is to facilitate gas exchange (breathing). Mechanically, breathing may be described as the cyclic application of stresses acting upon the lung surface. These forces are offset by prominent stress-bearing components of lung tissue. These components result from the mechanical elastic properties of lung parenchyma. Various studies have been dedicated to understanding the macroscopic behaviour of parenchyma. This has been achieved through pressure-volume analysis, numerical methods, the development of constitutive equations or strain-energy functions, finite element methods, image processing and elastography. Constitutive equations can describe the elastic behaviour exhibited by lung parenchyma through the relationship between the macroscopic stress and strain. The research conducted within lung mechanics around the elastic and resistive properties of the lung has allowed scientists to develop new methods and equipment for evaluating and treating pulmonary pathogens. This paper establishes a review of mathematical studies conducted within lung mechanics, centering on the development and implementation of solid mechanics to the understanding of the mechanical properties of the lung. Under the classical theory of elasticity, the lung is said to behave as an isotropic elastic continuum undergoing small deformations. However, the lung has also been known to display heterogeneous anisotropic behaviour associated with large deformations. Therefore, focus is placed on the assumptions and development of the various models, their mechanical influence on lung physiology, and the development of constitutive equations through the classical and non-classical theory of elasticity. Lastly, we also look at lung blast mechanics. No explicit emphasis is placed on lung pathology.

Disseminated strongyloidiasis in a diabetic patient.

A case of disseminated strongyloidiasis in an Indian diabetic patient who was not receiving any immunosuppressive therapy, is reported. Strongyloides stercoralis was detected in peritoneal fluid, stools and blood. To our knowledge this represents the first such case to be reported in the English literature. The need for both clinicians and microbiology laboratories to be on the alert for this parasite in patients who are compromised either because of underlying disease or therapy with immunosuppressive drugs, is emphasised.

Multiresistant Klebsiella pneumoniae in a neonatal nursery: the importance of maintenance of infection control policies and procedures in the prevention of outbreaks.

During a 3-week period, nine babies in the neonatal unit of a large teaching hospital in Durban were infected or colonized with Klebsiella pneumoniae resistant to a range of antimicrobial agents including amikacin and cefotaxime. Resistance to cefotaxime was reduced by clavulanic acid in vitro suggesting production of extended-spectrum beta-lactamase activity. All the isolates had the same antibiotic resistance profile, belonged to the same serotype (K17), were non-typable with bacteriophages, and had identical plasmid profiles indicating that they belonged to the same strain. During a 1-day microbiological survey of the ward, the outbreak strain was isolated from the nose and hands of a doctor based in the nursery and from the hands of a nurse and the mother of an infected baby. The strain was also isolated from nine of 67 environmental samples. Investigation revealed that infection control practices which had been instituted following a previous outbreak in the nursery with multi-resistant methicillin-resistant Staphylococcus aureus (MRSA) were not being adhered to. The re-introduction and strict enforcement of these procedures under the supervision of an Infection Control Nurse resulted in the abrupt end of the outbreak.

Neonatal group B streptococcal infections in Indian (Asian) babies in South Africa.

In this, the first report of group B streptococcal (GBS) infections in Asian neonates in South Africa, the incidence was 2.65/1000 live births over a period of 3.5 years. Early onset disease (EOD), defined as arising less than or equal to 5 days after birth, was present in 79% cases; in most of these, the onset was before the age of 24 h. One baby presented with two episodes of late onset GBS infection. The incidence of culture-proven neonatal septicaemia during the same period was 12.3/1000 live births, GBS being commonest organism isolated. It was also the most frequent cause of bacterial meningitis in the newborn, accounting for 89% cases. Although neurological signs were present in 40% patients with EOD, only 13.3% had CSF-culture-positive meningitis. Radiographic features of hyaline membrane disease were found in half of the babies with EOD and for whom a chest radiograph was performed, while one had a pneumothorax. The overall mortality was 13.2% which is much lower than that reported in other series.

Typhoid fever in the adult and paediatric Indian population of Durban.

The features of typhoid fever in Indian South Africans are described. In children the illness was usually uncomplicated. However, anaemia, thrombocytopenia and hypo-albuminaemia were found in both adults and children. The initial symptoms on presentation of diarrhoea and vomiting frequently led to a misdiagnosis of gastro-enteritis. The previous administration of antibiotics also resulted in failure to isolate Salmonella typhi in 41% of patients studied. Typhoid acquired in the microbiology laboratory and that seen in visitors returning from India and the Far East is emphasised. The S. typhi isolates were uniformly sensitive to all antibiotics tested. The disproportionately high number of Indians of south Indian ancestry presenting to the R. K. Khan Hospital needs to be investigated.

A laboratory-confirmed outbreak of rifampicin-methicillin resistant Staphylococcus aureus (RMRSA) in a newborn nursery.

The routine laboratory monitoring of methicillin-resistant strains of Staphylococcus aureus (MRSA) at a large teaching hospital led to the detection of a new, multiply-resistant strain of MRSA, which was resistant not only to penicillin, oxacillin, methicillin, cephamandole, erythromycin, tetracycline, kanamycin and gentamicin but also to rifampicin and sulphamethoxazole-trimethoprim. The rifampicin-methicillin resistant strain of S. aureus (RMRSA) was first detected in blood cultures of babies from the newborn nursery. A bacteriological investigation of the nursery revealed the source to be a paediatric medical officer who was colonised with the resistant strain, and who at the time was receiving rifampicin for pulmonary tuberculosis. The rifampicin resistance was presumably acquired during rifampicin therapy. The outbreak in the nursery was brought to an abrupt end by treatment of the colonised medical officer with mupirocin, applied nasally twice a day for a week, and by the introduction of standard infection-control measures. Reference laboratory assistance was needed to confirm the initial assumption that the outbreak was caused by a single strain.

Comparison of passive haemagglutination test with Widal agglutination test for serological diagnosis of typhoid fever in an endemic area.

A passive haemagglutination test, using sheep red blood cells sensitised with Salmonella typhi lipopolysaccharide, was compared with the Widal test for the serological diagnosis of typhoid fever in an endemic area. The results obtained on sera from 152 patients with bacteriologically confirmed typhoid and 183 patients who did not have typhoid were analysed in terms of sensitivity, specificity, simplicity, and rapidity of the respective tests. The passive haemagglutination test was found to be more sensitive (80%) than the S typhi O antigen (71%) but marginally less sensitive than the H antigen (82%) of the Widal test. The false positive rate on control sera was 1.2% and 6.6%, respectively, for the Widal O and H antigens, and 1.6% for the passive haemagglutination test. Our findings indicate that the passive haemagglutination test is comparable with the Widal test for the serological diagnosis of typhoid fever in endemic areas, but is more simple, rapid, and economic. The passive haemagglutination test may be a useful alternative to the Widal test for the serological diagnosis of typhoid fever in busy microbiology laboratories in areas in which the disease is endemic.