Analysis of the method for ventilation heterogeneity assessment using the Otis model and forced oscillations.

Increased heterogeneity of the lung disturbs pulmonary gas exchange. During bronchoconstriction, inflammation of lung parenchyma or acute respiratory distress syndrome, inhomogeneous lung ventilation can become bimodal and increase the risk of ventilator-induced lung injury during mechanical ventilation. A simple index sensitive to ventilation heterogeneity would be very useful in clinical practice. In the case of bimodal ventilation, the index (H) can be defined as the ratio between the longer and shorter time constant characterising regions of contrary mechanical properties. These time constants can be derived from the Otis model fitted to input impedance (Zin) measured using forced oscillations. In this paper we systematically investigated properties of the aforementioned approach. The research included both numerical simulations and real experiments with a dual-lung simulator. Firstly, a computational model mimicking the physical simulator was derived and then used as a forward model to generate synthetic flow and pressure signals. These data were used to calculate the input impedance and then the Otis inverse model was fitted to Zin by means of the Levenberg-Marquardt (LM) algorithm. Finally, the obtained estimates of model parameters were used to compute H. The analysis of the above procedure was performed in the frame of Monte Carlo simulations. For each selected value of H, forward simulations with randomly chosen lung parameters were repeated 1000 times. Resulting signals were superimposed by additive Gaussian noise. The estimated values of H properly indicated the increasing level of simulated inhomogeneity, however with underestimation and variation increasing with H. The main factor responsible for the growing estimation bias was the fixed starting vector required by the LM algorithm. Introduction of a correction formula perfectly reduced this systematic error. The experimental results with the dual-lung simulator confirmed potential of the proposed procedure to properly deduce the lung heterogeneity level. We conclude that the heterogeneity index H can be used to assess bimodal ventilation imbalances in cases when this phenomenon dominates lung properties, however future analyses, including the impact of lung tissue viscoelasticity and distributed airway or tissue inhomogeneity on H estimates, as well as studies in the time domain, are advisable.

A new endotracheal tube for infants--laboratory and clinical assessment: a preliminary study.

BACKGROUND: Conventional endotracheal pediatric tubes offer high resistance due to their small diameters and relatively high flow during ventilation. Any increase of the diameter of the tube lumen decreases the airway resistance and subsequently, the work of breathing (WOB). We compared ventilation mechanics using a new, cone-shaped endotracheal tube of our design to the Cole and standard tubes. METHODS: The study has been divided into three parts: (i) preliminary laboratory tests, (ii) in vitro study with infant lung model, and (iii) clinical study in infants. Flow resistance and WOB were compared, using standard, Cole (in experimental phase only) and cone tubes. RESULTS: We proved that inspiratory (Ri ) and expiratory (Re ) resistance, and WOB, were significantly lower in patients ventilated via a cone tube. Mean Ri decreased by 37%, compared with the baseline values, Re - by 35%, and total WOB - by 12%. CONCLUSION: The cone tube offers lower resistance to gas flow than the standard, used nowadays in clinical practice. It can be especially beneficial to spontaneously breathing patients reducing WOB and improving gas exchange.

[Mycolic acids analysis from various species mycobacterium by high pressure liquid chromatography (HPLC)]. / Analiza kwasów mikolowych róznych gatunków z rodzaju Mycobacterium metoda wysokocisnieniowej chromatografii cieczowej (HPLC).

HPLC is the most useful method to analyze various species of mycobacteria by using mycolic acids. The purpose was to prepare a library containing chromatographic patterns of mycolic acids derived from reference species Mycobacterium, which had been cultivated in standard conditions. 28 reference strains (27 ones from American Type Culture Collection and one cultivated from the vaccine M. bovis BCG) were used. The analysis of mycolic acids involved chromatographic separation of their bromophenacyl derivatives according to Centers for Disease Control recommendation. Mycolic acids profiles formed by HLPC were reproducible for all reference species in this study. Standard deviation of relative retention time of every peak did not exceed 2.5%. The species included into M. tuberculosis complex beyond M. bovis BCG shared the same mycolic acids pattern. HPLC is the only mean to distinguish M. tuberculosis from M. bovis BCG. The other studied stains had species specific patterns which differed from M. tuberculosis complex and M. bovis BCG. The prepared library comprising 28 reference elution profiles of mycolic acids from known mycobacteria species can be applied in diagnostic procedure of tuberculosis and mycobacteriosis.

[Use of mycolic acids analysis in diagnosis of tuberculosis and mycobacteriosis--three-year experience]. / Zastosowanie analizy kwasów mikolowych w diagnostyce gruzlicy i mikobakterioz--3 lata doswiadczen.

The aim of the study was to estimate the utility of the HPLC-based method of mycolic acids analysis to classify Mycobacterium species in routine diagnostic procedure on the basis of own three-year experience. 2142 patients' specimens were examined. 141 AFB were cultured. 36.2% strains were classified as M. tuberculosis complex by HPLC. The identification was confirmed by AMPLICOR MTB (Roche diagnostic, USA). M. xenopi (17.0%), M. kansasii (14.2%) and M. gordonae (14.2%) were the most frequent identified out of nontuberculous mycobacteria. Four mycobacteriosis cases were suspected because of repeated identification of the isolated strains. 136 strains on L-J slant shipped from other centres were identified. We confirm that the HPLC method is highly effective and specific for Mycobacterium species classification, which can be performed in no more than a couple of hours. In our opinion it is a very helpful tool, hard to replace in diagnostic procedure of tuberculosis and mycobacteriosis.