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J H Bates

Publications and source records attributed to J H Bates.

226 records · Page 13Linked to original sources
PubMedDate not supplied

Influence of the viscoelastic properties of the respiratory system on the energetically optimum breathing frequency.

We hypothesized that the viscoelastic properties of the respiratory system should have significant implications for the energetically optimal frequency of breathing, in view of the fact that these properties cause marked dependencies of overall system resistance and elastance on frequency. To test our hypothesis we simulated two models of canine and human respiratory system mechanics during sinusoidal breathing and calculated the inspiratory work (WI) and pressure-time integral (PTI) per minute under both resting and exercise conditions. The two models were a two-compartment viscoelastic model and a single-compartment model. Requiring minute alveolar ventilation to be fixed, we found that both models predicted almost identical optimum breathing frequencies. The calculated PTI was very insensitive to increases in breathing frequency above the optimal frequencies, while WI was found to increase slowly with frequency above its optimum. In contrast, both WI and PTI increased sharply as frequency decreased below their respective optima. A sensitivity analysis showed that the model predictions were very insensitive to the elastance and resistance values chosen to characterize tissue viscoelasticity. We conclude that the WI criterion for choosing the frequency of breathing is compatible with observations in nature, whereas the optimal frequency predictions of the PTI are rather too high. Both criteria allow for a fairly wide margin of choice in frequency above the optimum values without incurring excessive additional energy expenditure. Furthermore, contrary to our expectations, the viscoelastic properties of the respiratory system tissues do not pose a noticeable problem to the respiratory controller in terms of energy expenditure.

Animals↗
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A model of transient oscillatory pressure-flow relationships of canine airways.

In a previous paper (27) we developed a lumped parameter model of canine pulmonary airway mechanics featuring airway wall elasticity, gas inertance, and laminar and turbulent gas flow. The model accurately accounted for the steady-state pressure-flow data we obtained during sinusoidal cycling of the lung following a period of apnea. In the present paper, we extend the model to account for the transient decrease in the amplitude of the trans-airway pressure swings that we observed immediately following the apnea, which we have shown to be due to a vagally mediated bronchodilatation reflex. The extended model accounts for this transient in terms of a sudden change in airway smooth muscle tone acting on the viscoelastic properties of the airway wall and tissues mechanically coupled to it. Consequently, this model is able to temporarily store a volume of gas in the conducting airway tree as its volume changes cyclically with that of the whole lung. This means that the flow entering the airway tree from the trachea at any instant (V) is not precisely equal to that entering the alveoli (Valv) even when the gas is considered incompressible. We found that assuming V to be equal to Valv can lead to errors in estimating respiratory tissue impedance of as much as 10%. However, tissue hysteresivity remained almost unaffected, suggesting that the hysteretic properties of respiratory system tissues and airway wall are well matched.

Animals↗
PubMedDate not supplied

Characterization of plasmids from strains of Mycobacterium avium-intracellulare.

Strains of Mycobacterium avium-intracellulare were examined for the presence of plasmids. Actively growing cultures were treated with cycloserine and ampicillin to sensitize the cells to lysis by detergent, and cleared lysates were prepared by treatment with sodium dodecyl sulfate and NaCl. Purified plasmid DNA was prepared by equilibrium density centrifugation in CsCl gradients containing ethidium bromide and analyzed by agarose gel electrophoresis. Strain LR25 was found to carry three plasmids, including a large plasmid with a molecular weight of greater than 10(8). Examination of the DNA by electron microscopy confirmed that the bands seen in the agarose gels represented circular DNA molecules. The presence of plasmids was demonstrated in four additional strains. Three plasmids were carried in a strain of serovar 2, and single plasmids were detected in strains of serovars 4, 12, and 18. Plasmids were not detected in three strains of serovars 1, 3, and 5.

DNA, Bacterial↗
PubMedDate not supplied

Current patterns and electrode types for single-source electrical impedance tomography of the thorax.

Electrical impedance tomography (EIT) estimates the spatial distribution of the electrical tissue properties in a cross section of the body. In the present study, we investigated how the quality of static thoracic images obtained from EIT systems with a single current source and sink is affected by the current pattern employed in the presence of measurement noise. The reconstructed images best reproduced our computational phantom when current source and sink were placed at neighboring electrodes. In this case, the mean squared reconstruction error was an order of magnitude smaller than for all other patterns of current injection studied. At a signal-to-noise ratio of 50 dB, 60% of the reconstructions converged successfully with source and sink at neighboring electrodes, while only 10% or less converged for all other configurations. We relate these results to the fact that neighboring currents strengthen the diagonal structure in the Hessian matrix of the iterative reconstruction process that we employed. We also tested the effects on the reconstruction error of the number and type of electrodes. We found that "compound electrodes" that permit voltage measurement at the site of current injection did not yield any practical improvement of the image quality. In contrast, doubling the number of boundary electrodes reduced the reconstruction error by almost two orders of magnitude.

Biomedical Engineering↗
PubMedDate not supplied

Nonparametric block-structured modeling of lung tissue strip mechanics.

Very large amplitude pseudorandom uniaxial perturbations containing frequencies between 0.125 and 12.5 Hz were applied to five dog lung tissue strips. Three different nonlinear block-structured models in nonparametric form were fit to the data. These models consisted of (1) a static nonlinear block followed by a dynamic linear block (Hammerstein model); (2) the same blocks in reverse order (Wiener model); and (3) the blocks in parallel (parallel model). Both the Hammerstein and Wiener models performed well for a given input perturbation, each accounting for greater than 99% of the measured stress signal variance. However, the Wiener and parallel model parameters showed some dependence on the strain amplitude and the mean stress. In contrast, a single Hammerstein model accounted for the data at all strain amplitudes and operating stresses. A Hammerstein model featuring a fifth-order polynomial static nonlinearity and a linear impulse response function of 1 s duration accounted for the most output variance (99.84%+/-0.13%, mean+/-standard deviations for perturbations of 50% strain at 1.5 kPa stress). The static nonlinear behavior of the Hammerstein model also matched the quasistatic stress-strain behavior obtained at the same strain amplitude and operating stress. These results show that the static nonlinear behavior of the dog lung tissue strip is separable from its linear dynamic behavior.

Animals↗
PubMedDate not supplied

A micromechanical model of lung tissue rheology.

The rheological properties of lung tissue are complex and nonlinear and contribute significantly to both the elastic and dissipative mechanical properties of the lung. Nevertheless, there remain large gaps in our understanding of precisely how the bulk rheological behavior of lung tissue is linked to the properties of its constituents and their interactions. In this paper a model is developed that attempts to provide such a link. The model consists of a sheet of randomly aligned fibers whose orientations are constantly changing due to thermal motion. When the sheet is suddenly stretched uniaxially, the fibers align themselves preferentially in the direction of strain. However, as a result of the continual thermal motion of the fibers, there is a net transfer of momentum between the fibers and the rest of the tissue. This produces a restoring force in the tissue sheet. The thermal motion also makes the fibers gradually revert back to a random orientation, so that the strain-generated stress within the tissue decays asymptotically to zero. It is shown that the behavior of this model closely approximates quasilinear viscoelasticity, in which the static stress-strain behavior is separable from the dynamic stress relaxation behavior.

Animals↗
PubMedDate not supplied

An adaptive filter to reduce cardiogenic oscillations on esophageal pressure signals.

Measurements of pressure swings in the esophagus (Pes) can be used to estimate variables of clinical importance, e.g., intrinsic positive end-expiratory pressure (PEEPi). Unfortunately, cardiogenic oscillations frequently corrupt Pes and complicate further analysis. Due to significant band overlap with the respiratory component of Pes, cardiogenic oscillations cannot be suppressed adequately using standard filtering techniques. In this article, we present an adaptive filter that employs the electrocardiogram to identify and suppress the cardiogenic oscillations. This filter was tested using simulated data, where the variance accounted for relative to the simulated respiratory pressure swings increased from as low as 55% for the unfiltered Pes signal to over 95% when the adaptive filter was used. In patient data, the adaptive filter reduced the apparent cardiogenic oscillations without noticeably distorting the sharp deflections in Pes due to respiration. Furthermore, the filter suppressed peaks in the Fourier transform of Pes at integer multiples of the heart rate, while the remaining frequencies remained largely unchanged. During stable breathing, the standard deviation of PEEPi was reduced by between 44% and 71% in these four patients when the filter was used. We conclude that our filter removes a significant fraction of the cardiogenic oscillations that corrupt records of Pes.

Biomedical Engineering↗
PubMedDate not supplied

Lacrimal-duct-probing-induced bacteremia: should children with congenital heart defects receive antibiotic prophylaxis?

PURPOSE: To determine the incidence of bacteremia following lacrimal-duct probing in children, and to evaluate the potential need for antibiotic prophylaxis in children who are at an increased risk of infectious endocarditis (IE). METHODS: In a prospective study beginning in October 1994, 40 consecutive children requiring lacrimal-duct probing performed by a single pediatric ophthalmologist received preoperative lacrimal and blood cultures followed by postoperative probe-induced transient bacteremia that was defined as a negative preoperative blood culture, followed by a positive postoperative blood culture of the same bacteria identified in the positive lacrimal culture. RESULTS: The overall infection rate as described above was 7 of 40 children (17.5%) with a 95% confidence interval of 7.3% to 32.8%. Of these, four children had positive postoperative cultures for Haemophilus influenzae (10.0%) and 3 were positive for Streptococcus pneumoniae (7.5%) One child had a negative preoperative blood and lacrimal culture with a postoperative blood culture positive for Streptococcus viridans. CONCLUSIONS: This study shows a significant incidence of lacrimal-probe-induced bacteremia with organisms that have been documented as etiological agents for IE in children. IE, although less common in children, remains a serious, potentially life threatening infection with high mortality. Although lacrimal-duct probing has never been clearly associated with documented endocarditis, it is the authors' recommendation that it be prudent for patients who are at known high risk for endocarditis to receive SBE prophylaxis considering the low cost/benefit ratio.

Antibiotic Prophylaxis↗
PubMedDate not supplied

Nonparametric block-structured modeling of rat lung mechanics.

The quasistatic and dynamic pressure volume characteristics of the lungs were measured in five anesthetized, paralyzed open-chest rats. Psuedo-random volume perturbations over a frequency range of 0.25 to 25 Hz and having peak-peak amplitudes of 1 to 4 ml were applied after the lungs were allowed to expire against 0.2, 0.4, 0.6, and 0.8 kPa positive end-expiratory pressure (PEEP). The lung mechanics were partitioned in two ways: a linear dynamic block followed by a static nonlinearity (Wiener model) and a static nonlinearity ahead of a linear dynamic block (Hammerstein model). It was found that a Hammerstein model featuring a third-order polynomial static nonlinearity and a linear impulse response function of 1-sec duration accounted for the greatest amount of the output variance (98.8 +/- 0.6%, mean +/- SD from perturbations of 4 ml amplitude and PEEP = 0.8 kPa). The static nonlinear behavior matched the measured quasistatic pressure volume behavior obtained at the same amplitude and at the same level of PEEP, provided that all direct current gain of the model was located within the static nonlinearity. Under these conditions, the linear resistance was inversely dependent on the PEEP, whereas little PEEP or amplitude dependence of the linear compartment elastance was observed. Thus, of the two block-structured models tested, the Hammerstein model accounted better for the large amplitude nonlinear mechanical behavior. However, neither model could account for the dependence of the linear block resistance on PEEP.

Animals↗