Novel Approach to Simulate Sleep Apnea Patients for Evaluating Positive Pressure Therapy Devices

Bench testing is a useful method to characterize the response of different automatic positive airway pressure (APAP) devices under well-controlled conditions. However, previous models did not consider the diversity of obstructive sleep apnea (OSA) patients’ characteristics and phenotypes. The objective of this proof-of-concept study was to design a new bench test for realistically simulating an OSA patient’s night, and to implement a one-night example of a typical female phenotype for comparing responses to several currently-available APAP devices. We developed a novel approach aimed at replicating a typical night of sleep which includes different disturbed breathing events, disease severities, sleep/wake phases, body postures and respiratory artefacts. The simulated female OSA patient example that we implemented included periods of wake, light sleep and deep sleep with positional changes and was connected to ten different APAP devices. Flow and pressure readings were recorded; each device was tested twice. The new approach for simulating female OSA patients effectively combined a wide variety of disturbed breathing patterns to mimic the response of a predefined patient type. There were marked differences in response between devices; only three were able to overcome flow limitation to normalize breathing, and only five devices were associated with a residual apnea-hypopnea index of <5/h. In conclusion, bench tests can be designed to simulate specific patient characteristics, and typical stages of sleep, body position, and wake. Each APAP device behaved differently when exposed to this controlled model of a female OSA patient, and should lead to further understanding of OSA treatment.     

On the anatomical definition of arterial networks in blood flow simulations: comparison of detailed and simplified models

Biomechanics and Modeling in Mechanobiology - The goal of this work is to assess the impact of vascular anatomy definition degree in the predictions of blood flow models of the arterial network. To...     

Techniques for the detection of pathogenic Cryptococcus species in wood decay substrata and the evaluation of viability in stored samples

In this study, we evaluated several techniques for the detection of the yeast form of Cryptococcus in decaying wood and measured the viability of these fungi in environmental samples stored in the laboratory. Samples were collected from a tree known to be positive for Cryptococcus and were each inoculated on 10 Niger seed agar (NSA) plates. The conventional technique (CT) yielded a greater number of positive samples and indicated a higher fungal density [in colony forming units per gram of wood (CFU.g^-1) ] compared to the humid swab technique (ST). However, the difference in positive and false negative results between the CT-ST was not significant. The threshold of detection for the CT was 0.05.10³ CFU.g^-1, while the threshold for the ST was greater than 0.1.10³ CFU^-1. No colonies were recovered using the dry swab technique. We also determined the viability of Cryptococcus in wood samples stored for 45 days at 25ºC using the CT and ST and found that samples not only continued to yield a positive response, but also exhibited an increase in CFU.g^-1, suggesting that Cryptococcus is able to grow in stored environmental samples. The ST.1, in which samples collected with swabs were immediately plated on NSA medium, was more efficient and less laborious than either the CT or ST and required approximately 10 min to perform; however, additional studies are needed to validate this technique.     

Absence of regional differences in the size and oxidative capacity of diaphragm muscle fibers

The oxidative capacity and cross-sectional area of muscle fibers were compared between the costal and crural regions of the cat diaphragm and across the abdominal-thoracic extent of the muscle. Succinate dehydrogenase (SDH) activity of individual fibers was quantified using a microphotometric procedure implemented on an image-processing system. In both costal and crural regions, population distributions of SDH activities were unimodal for both type I and II fibers. The continuous distribution of SDH activities for type II fibers indicated that no clear threshold exists for the subclassification of fibers based on differences in oxidative capacity (e.g., the classification of fast-twitch glycolytic and fast-twitch oxidative glycolytic fiber types). No differences in either SDH activity or cross-sectional area were noted between fiber populations of the costal and crural regions. Differences in SDH activity and cross-sectional area were noted, however, between fiber populations located on the abdominal and thoracic sides of the costal region. Both type I and II fibers on the abdominal side of the costal diaphragm were larger and more oxidative than comparable fibers on the thoracic side.     

Structural and functional relationships between prokaryotic and eukaryotic DNA polymerases.

The Bacillus subtilis phage luminal diameter 29 DNA polymerase, involved in protein-primed viral DNA replication, was inhibited by phosphonoacetic acid (PAA), a known inhibitor of alpha-like DNA polymerases, by decreasing the rate of elongation. Three highly conserved regions of amino acid homology, found in several viral alpha-like DNA polymerases and in the luminal diameter 29 DNA polymerase, one of them proposed to be the PAA binding site, were also found in the T4 DNA polymerase. This prokaryotic enzyme was highly sensitive to the drugs aphidicolin and the nucleotide analogues butylanilino dATP (BuAdATP) and butylphenyl dGTP (BuPdGTP), known to be specific inhibitors of eukaryotic alpha-like DNA polymerases. Two potential DNA polymerases from the linear plasmid pGKL1 from yeast and the S1 mitochondrial DNA from maize have been identified, based on the fact that they contain the three conserved regions of amino acid homology. Comparison of DNA polymerases from prokaryotic and eukaryotic origin showed extensive amino acid homology in addition to highly conserved domains. These findings reflect evolutionary relationships between hypothetically unrelated DNA polymerases.     

Production of enterotoxin A by supposedly nonenterotoxigenic Staphylococcus aureus strains

The production of staphylococcal enterotoxins A (SEA) and B (SEB) was studied by inoculating six well-defined staphylococcal collection strains into cow's, goat's, or sheep's milk (individually or as a 50% mixture of cow's + goat's or cow's + sheep's), into brain heart infusion, and into a medium generally used to enhance the synthesis of enterotoxins (3+3 medium). Four of the strains used are considered to be SEB producers, another is considered an SEA producer, and the remaining strain is nonenterotoxigenic but produces large quantities of staphylococcal protein A. Staphylococcal protein A masked the results in most cases. Only one strain secreted exclusively SEB, while the other three SEB producers synthesized SEA in different amounts. We conclude that enterotoxin production depends on the natural substrate and may differ from the results obtained when the strain is grown on cellophane over agar to determine its toxigenicity.     

Production of enterotoxin A by supposedly nonenterotoxigenic Staphylococcus aureus strains.

The production of staphylococcal enterotoxins A (SEA) and B (SEB) was studied by inoculating six well-defined staphylococcal collection strains into cow's, goat's, or sheep's milk (individually or as a 50% mixture of cow's + goat's or cow's + sheep's), into brain heart infusion, and into a medium generally used to enhance the synthesis of enterotoxins (3+3 medium). Four of the strains used are considered to be SEB producers, another is considered an SEA producer, and the remaining strain is nonenterotoxigenic but produces large quantities of staphylococcal protein A. Staphylococcal protein A masked the results in most cases. Only one strain secreted exclusively SEB, while the other three SEB producers synthesized SEA in different amounts. We conclude that enterotoxin production depends on the natural substrate and may differ from the results obtained when the strain is grown on cellophane over agar to determine its toxigenicity.