Search PubMed⌕ Search

Biomedical subjects

J H Bates

Publications and source records attributed to J H Bates.

At least 217 records · Page 12Linked to original sources
PubMed1970

Amphotericin B serum concentrations during therapy.

Therapeutic outcome of patients being treated for systemic mycoses with amphotericin B is possibly related to the serum concentrations of this drug that are produced in these patients. Because current data are conflicting, the magnitude of these concentrations was restudied by using a bioassay which gave precise and accurate results. The highest of 155 serum concentrations was 2.01 mug/ml. Mean concentrations were 1.21, 0.62, and 0.32 mug/ml, at 1, 18, and 42 hr, respectively, after intravenous infusion of amphotericin B. This drug was detected in serum 7 weeks after completion of treatment, but it could not be detected 13 weeks after treatment. Drug levels did not appreciably decrease in serum stored for 8 to 9 months at - 10 C. Unequal serum content in assay tubes and measurement of assay turbidity by visual inspection may explain previously reported amphotericin B levels of 3.0 to 12.5 mug/ml.

Amphotericin B↗
PubMedDate not supplied

Measurement of respiratory mechanics using the Siemens Servo Ventilator 900C.

The interrupter technique involves measuring the pressure changes at the airway opening during sudden cessation of flow and has been advocated for monitoring respiratory mechanics in artificially ventilated patients. The Siemens Servo Ventilator 900C has the ability to make airway occlusions without interrupting the patient's respiratory support. This study was performed to determine the suitability of the end-inspiratory occlusion facility of the ventilator for interrupter measurements of respiratory resistance and compliance. Measurements were made in a physical model of the respiratory system consisting of two parallel compartments, whose individual resistances and elastances were independently determined. The accuracy of the resistance measurements made using the ventilator were found to be dependent on the inspiratory flow. With an inspiratory flow of 100 ml/s, the resistance of the system could be measured to within 18% of the true value, and the static compliance could be measured to within 26% of the true value. Much of the error in these determinations was due to the finite closure time of the valve in the ventilator, and to the compliance of the gas in the tubing connecting the ventilator with the model. We conclude that the Siemens Servo Ventilator 900C can be used to conveniently obtain estimates of resistance and compliance in ventilated patients.

Airway Resistance↗
PubMedDate not supplied

Noninvasive determination of respiratory mechanics during mechanical ventilation of neonates: a review of current and future techniques.

Study of the mechanical properties of the respiratory system is needed to help provide a better understanding of the pathogenesis of diseases causing respiratory failure. The nature of neonatal intensive care requires that any technique for monitoring respiratory mechanics be simple, noninvasive, and allow continued free access to the neonate. The peak airway pressure developed during volume cycled ventilation reflects the mechanical properties of the respiratory system but cannot distinguish between changes in the flow-resistive or elastic properties. Similarly, dynamic compliance combines both the flow-resistive and elastic components of the respiratory system in a single number and flow-volume loops also reflect both elements. Extracting a single time-constant from the expiratory limb of the latter assumes a single-compartment model for the respiratory system and, as such, does not provide sufficient information to describe frequency dependence of resistance and compliance. Furthermore, flow-volume loops are markedly distorted by the presence of an endotracheal tube, which must be corrected for, before calculating values of resistance and compliance. To provide the information to understand better the physiologic processes and adaptive mechanisms in diseased states causing acute respiratory failure, it is necessary to use a method that is based on a more detailed and realistic model of the respiratory system. Two such techniques that appear to warrant further investigation in ventilated infants are the interrupter technique and the forced-oscillation technique.

Biomechanical Phenomena↗
PubMedDate not supplied

Lung tissue rheology and 1/f noise.

The mechanical properties of lung tissue are important contributors to both the elastic and dissipative properties of the entire organ at normal breathing frequencies. A number of detailed studies have shown that the stress adaptation in the tissue of the lung following a step change in volume is very accurately described by the function t-k, for some small positive constant k. We applied step increases in length to lung parenchymal strips and found the ensuing stress recovery to be extremely accurately described by t-k over almost 3 decades of time, despite the quasi-static stress-length characteristics of the strips being highly nonlinear. The corresponding complex impedance of lung tissue was found to have a magnitude that varied inversely with frequency. We note that this is highly reminiscent of a phenomenon known as 1/f noise, which has been shown to occur ubiquitously throughout the natural world. 1/f noise has been postulated to be a reflection of the complexity of the system that produces it, something like a central limit theorem for dynamic systems. We have therefore developed the hypothesis that the t-k nature of lung tissue stress adaptation follows from the fact that lung tissue itself is composed of innumerable components that interact in an extremely rich and varied manner. Thus, although the constant k is no doubt determined by the particular constituents of the tissue, we postulate that the actual functional form of the stress adaptation is not.

Animals↗