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T H Shaffer

Publications and source records attributed to T H Shaffer.

161 records · Page 9Linked to original sources
PubMed1976

Gaseous exchange and acid-base balance in premature lambs during liquid ventilation since birth.

Nine distressed premature lambs were studied before, during, and after ventilation with fluorocarbon liquid (FC-80). It was found that premature lambs, delivered by cesarean section, could be adequately ventilated with oxygenated liquid for period up to 3 hr. Using fluarocarbon liquid in conjunction with the described liquid breathing system, it was possible to maintain remarkably good pulmonary gas exchange and acid-base balance during normothermic conditions. In addition, peak intratracheal pressures measured during recovery from liquid ventilation were significanly reduced (P is less than 0.001) as compared with preliquid ventilation values. This improvement in lung function is in direct contrast to the deterioration in that of the adult animal following liquid ventilation as reported previously.

Acid-Base Equilibrium↗
PubMedDate not supplied

Effect of high-frequency jet ventilation on preterm and rabbit tracheal mechanics.

The effect of high-frequency jet ventilation (HFJV) on both tracheal dimensions and mechanics was evaluated in preterm and term rabbit airways. Seven tracheal segments were studied at 27 days (group I) and 31 days (group II) of gestation, respectively. Tracheal dimensions and segmental pressure-volume relationships were determined before and after 60 minutes of HFJV (peak pressure 20 cm H2O; mean airway pressure 6.7 to 6.8 cm H2O at 10 Hz). Both tracheal lengths and diameters increased significantly (p less than 0.01) in each group and resulted in increased tracheal volumes: 109% in group I (p less than 0.01) and 60% in group II (p less than 0.01). The mean specific tracheal compliance decreased in group I, from 0.036 cm H2O-1 to 0.015 cm H2O-1 (p less than 0.01), and in group II from 0.029 cm H2O-1 to 0.021 cm H2O-1 (p less than 0.01). Furthermore, the collapsing transmural pressure (the pressure required for total collapse of tracheal segments) decreased significantly (p less than 0.01) in both groups. These data demonstrate significant dimensional and mechanical deformation of tracheal segments after HFJV. An increased propensity toward collapsibility is also observed following HFJV. These changes are similar to those with tracheomalacia. The influence of such deformation on tracheal gas flow during HFJV needs to be further investigated.

Animals↗
PubMedDate not supplied

Antenatal triiodothyronine improves neonatal pulmonary function in preterm lambs.

OBJECTIVE: To characterize 1) pulmonary gas exchange, 2) pulmonary function, 3) lung fluid and tissue phospholipid content, and 4) thyroid hormone in the premature lamb (0.85 of term) after intra-amniotic administration of 100 micrograms of triiodothyronine (T3) 2 weeks before delivery. METHODS: Nine fetal lambs were given 100 micrograms of intra-amniotic T3 under ultrasound guidance at 112 +/- 1 days' gestation and delivered at 126 +/- 1 days (term = 149 days). Five saline-injected animals served as controls. Arterial blood gases, pulmonary mechanics, and lung volumes were compared between groups for 1 hour after delivery. At delivery, tracheal fluid and blood was taken for T3, and thyroxine (T4) levels. Tracheal fluid and lung tissues were assayed for total phosphorus and disaturated phosphatidylcholine. RESULTS: Triiodothyronine-treated lambs had significantly higher mean arterial pH and lower PCO2 than controls (P < .05) with a trend toward higher mean PO2. The dynamic lung compliance was increased by 54% with a 40% proportional increase in tidal volume and minute ventilation in the T3-treated group (P < .05). Functional residual capacity increased 69% (P < .05) without a change in specific compliance. The tracheal fluid and pulmonary phospholipids and tracheal fluid and plasma T3 and T4 levels were not different between the two groups. CONCLUSION: A single 100 micrograms dose of antenatal T3 significantly improves neonatal gas exchange and lung compliance. The improvement in lung function was not accompanied by an increase in pulmonary surfactant production. It is inferred that T3 improved lung function via accelerated structural development of the lung with an alternative possible effect on parenchymal connective tissue matrix.

Amniotic Fluid↗
PubMedDate not supplied

Thermal stability and transition studies with a hybrid warming device for neonates.

OBJECTIVE: The use of both warmer beds and incubators is common in neonatal intensive care units (NICU), and transferring between these two warming devices is a routine and necessary event. This study was designed to evaluate the efficacy of a new hybrid-warming device, the Versalet, in transitioning a preterm animal from a warmer bed to an incubator mode and back. STUDY DESIGN: Nine premature lambs were randomized, following delivery, to receive thermal support from a conventional warming bed and an incubator (control group), or from the Versalet (study group) in the warmer bed and incubator modes. Core and various surface temperatures, as well as physiological parameters were measured first during warming in the radiant warmer bed mode, Versalet or Resuscitaire and then during transition to the incubator mode, Versalet or Isolette, and then back to the warmer bed mode. RESULTS: The animals remained stable during all the transitions. Despite careful planning, adverse events occurred in the control group during transfers. There were no significant differences in the temperature or physiologic profiles during any of the transitions in either group. CONCLUSION: Compared with the standard warming technique used in NICUs (separate warmer bed and incubator), the Versalet provides similar thermal and cardiovascular stability without adverse events during transition to different modes of warming. The degree to which this device would contribute to ease of management and improved outcomes in humans needs to be evaluated in a clinical trial.

Animals↗
PubMedDate not supplied

Quantitative structure-activity relationships of perfluorinated hetero-hydrocarbons as potential respiratory media. Application to oxygen solubility, partition coefficient, viscosity, vapor pressure, and density.

It has been extensively reported that liquid-assisted ventilation, using inert perfluorocarbon liquids (PFCs), can reduce interfacial surface tension and allow for improved ventilation at decreased alveolar pressures. PFCs are bioinert, minimally absorbed, and have no deleterious histologic, cellular, or biochemical effects when used as respiratory media. Although several types of PFCs have been characterized, a select few are considered to be compatible with life. Compatibility is often related to the physicochemical profile inherent to the PFC liquids. It is essential that certain physical properties such as respiratory gas solubility, vapor pressure, density, viscosity, and tissue permeability be within a narrow, acceptable range for a PFC to be considered as a possible candidate for respiratory media. The current study sought to characterize the physicochemical profile of commercially available PFCs. This was accomplished by creating a method for accurate, rapid prediction of a host of unknown physical characteristics of PFCs. The physicochemical properties of 16 perfluorinated hetero-hydrocarbons were catalogued from the literature. The input data were categorized into three major groups: empiric properties, geometric indices, and quantum mechanical descriptors, to generate a database. Algorithms were then developed, one for each dependent variable (FUNCTION), including oxygen solubility, partition coefficient (logP), vapor pressure, viscosity, and density, that related the values of these physical properties of potential breathable PFC liquids to the parameters listed in the database. The general form of the algorithm can be written as follows: FUNCTION = sigma (CiPi/magnitude of Pi) + constant; where the FUNCTIONS are oxygen solubility, logP, vapor pressure, viscosity, and density. Ci is a coefficient that weights the relative contribution of each parameter. Each independent parameter, Pi, was normalized by the average value of the parameter used in the analysis, magnitude of Pi. Residual analysis demonstrated validity with all five equations. This method is expected to assist in the prediction of physical properties of PFC liquids with acceptable accuracy, such that PFC production and selection from currently available liquids can be optimized for each liquid ventilation application.

Absorption↗
PubMedDate not supplied

A closed system device for diagnosis and evaluation of neonatal pneumothoraces.

A closed system device with teflon needle, sideholes, and attached stopcock was designed and evaluated for diagnosis and evacuation of neonatal pneumothoraces. Experience with this device has demonstrated specific advantages over existing needles and techniques. Since the system is airtight, diagnosis of pneumothorax can be performed without the risk of introducing air. In addition, the needle sideholes provide more complete and efficient evacuation of air and fluids from the pleural cavity.

Humans↗
PubMedDate not supplied

Liquid ventilation: clinical experiences.

Liquid breathing has been in the medical literature for nearly 80 years and has been proposed as a means of improving gas exchange in patients with acute respiratory failure since the 1970s. There are many potential clinical applications of perfluorochemical (PFC) liquids that span many specialties in medicine. The ability to lower surface tension directed the initial clinical focus on neonatal therapy in the treatment of respiratory distress syndrome. The first clinical trial of PFC ventilation was performed in neonates in 1989. Additional trials using LiquiVent, a medical-grade PFC liquid, were initiated in 1993 in infants, children, and adults with severe respiratory distress. Based on the results of several studies during this time, it was concluded that the technique of liquid ventilation seemed to be safe, improve lung function, and recruit lung volume in patients from these various populations. More than 100 patients from preterm neonates to elderly patients with respiratory distress have been studied. In general, patients experience improvement in lung function and oxygenation, without adverse events. The results of such trials are encouraging and suggest the feasibility of this technique in the neonate with severe respiratory failure requiring respiratory support. Limitations of the technique include a limited understanding of how it works and its effectiveness in different patient populations. It has also become evident that there is a need for additional diagnostic and therapeutic instrumentation to expedite its implementation in the intensive care environment. This article discusses clinical experiences with liquid ventilation and highlights the technical needs to facilitate its implementation in respiratory care management.

Adolescent↗
PubMedDate not supplied

Multifactorial analysis of exchanger efficiency and liquid conservation during perfluorochemical liquid-assisted ventilation.

Liquid-assisted ventilation (LAV) of the lung with perfluorochemical (PFC) requires a method of oxygenating and removing CO2 from the liquid. Current PFC LAV techniques consist of total liquid ventilation, PFC lavage, and partial liquid ventilation. Because PFC liquid is volatile, it may be lost from the lung or ventilator circuit in the expired gas. This study evaluated the efficiencies of two types of exchangers (spray bubbler and membrane oxygenator) with respect to CO2 elimination from the PFC liquid and prevention of the loss of PFC liquid. A multifactorial analysis of exchanger efficiency was performed with respect to liquid conservation and CO2 removal. PFC losses and relative efficiencies of two types of exchangers to eliminate CO2 from expired PFC liquid were evaluated, along with two types of PFC liquids. Gas (100% O2 at 4 and 8 L/min) and PFC liquid were circulated countercurrently through the exchangers (oxygenator and bubbler) through a temperature-controlled (25 degrees or 37 degrees C) open circuit. To evaluate effectiveness of CO2 elimination, an exchanger efficiency index (EEI) for CO2 was calculated applying mass-transfer theory to characterize gas transport down a concentration gradient where EEI equals: [PPFCCO2 out--PPFCCO2 in]/PgasCO2 in--PPFCCO2 in]. Rate of PFC loss from the circuit was calculated from mixed expired gas samples using a thermal detector analyzer. EEI and PFC loss rate were analyzed with respect to gas: PFC liquid flow ratios (analogous to the V/Q ratio). The results showed that 1) PFC loss rate and exchanger efficiency to remove CO2 increased with increasing gas: PFC liquid flow rates independent of the type of exchanger or PFC liquid; 2) PFC loss rate at any gas or liquid flow rate was greater for the bubbler than for the oxygenator; 3) the oxygenator was more efficient than the bubbler with respect to CO2 elimination; 4) although PFC loss rate increased with temperature and vapor pressure, there was little difference in the EEIs for the temperatures studied. These results 1) identify exchanger requirements necessary to maintain effective CO2 elimination up to four times normal CO2 loading conditions during LAV; 2) suggest that using a membrane oxygenator as the gas exchanger, in concert with stringent fluid temperature control, improves PFC liquid conservation and CO2 elimination relative to bubbler exchanger configurations; 3) highlight the importance of matching the exchanger type to the physiocochemical properties of the specific PFC liquid to optimize CO2 elimination while reducing PFC liquid loss by minimizing gas relative to PFC liquid flow rates. Because PFC liquid loss occurs with all current means of oxygenating and removing CO2, this study raises the importance of developing alternative, bulk-gas-flow-independent, means to recondition PFC liquids.

Carbon Dioxide↗
PubMedDate not supplied

Software for real-time control of a tidal liquid ventilator.

The purpose of this project was to develop and test computer software and control algorithms designed to operate a tidal liquid ventilator. The tests were executed on a 90-MHz Pentium PC with 16 MB RAM and a prototype liquid ventilator. The software was designed using Microsoft Visual C++ (Ver. 5.0) and the Microsoft Foundation Classes. It uses a graphic user interface, is multithreaded, runs in real time, and has a built-in simulator that facilitates user education in liquid-ventilation principles. The operator can use the software to specify ventilation parameters such as the frequency of ventilation, the tidal volume, and the inspiratory-expiratory time ratio. Commands are implemented via control of the pump speed and by setting the position of two two-way solenoid-controlled valves. Data for use in monitoring and control are gathered by analog-to-digital conversion. Control strategies are implemented to maintain lung volumes and airway pressures within desired ranges, according to limits set by the operator. Also, the software allows the operator to define the shape of the flow pulse during inspiration and expiration, and to optimize perfluorochemical liquid transfer while minimizing airway pressures and maintaining the desired tidal volume. The operator can stop flow during inspiration and expiration to measure alveolar pressures. At the end of expiration, the software stores all user commands and 30 ventilation parameters into an Excel spreadsheet for later review and analysis. Use of these software and control algorithms affords user-friendly operation of a tidal liquid ventilator while providing precise control of ventilation parameters.

Algorithms↗
PubMedDate not supplied

On-line techniques for perfluorochemical vapor sampling and measurement.

The authors developed a compact gas sampling and perfluorochemical (PFC) measuring system for use in total and partial liquid ventilation systems, based on a precision two-thermistor thermal detector (TD). They describe the sensitivity and linearity of their on-line method for PFC analysis of expired gases and show how it may be used in partial liquid ventilation studies for determining PFC saturation and loss. Gas is sampled for a short time from a breathing circuit through a heated tube at a selectable point in the breathing cycle. Inspiration is sensed by a pressure transducer. The sample of gas is pulled into the heated (48 degrees C) thermistor chamber by suction and held there while the cooling effect of the vapor changes the thermistor temperature. Dry air in another chamber affects a second thermistor, and the difference of these responses is amplified. The raw signal is corrected for the effects of varying O2 levels by a fuel cell. This signal is sampled and held and displayed on a front panel display. Calibration is performed in percentage saturation at 37 degrees C using the PFC in use at that temperature, or another standard such as O2. In-vitro testing showed a linear response in the thermal detector device (R2 = 0.99) over the range of vapor pressures tested (0-14) mmHg) and was reproducible to within 3%. When electronically corrected for changes in O2 concentration, there was less than a 2% change in PFC saturation. The TD responses to CO2 (R2 = 0.99) and water vapor (R2 = 1.0) were linear and approximately equal and opposite over the normal operating ranges of expired gases. In-vivo results in rabbits showed a significant (R2 = 0.73; p < 0.01) correlation between the auto-sampler and manual collection modes for determination of PFC in expired gas.

Animals↗
PubMedDate not supplied

Liquid breathing trials and animal studies with a demand-regulated liquid breathing system.

Experimental results of in vivo animal tests conducted on a demand-regulated liquid breathing system are presented. When a liquid replaces gas as the medium in which oxygen and carbon dioxide are transported, several problems not typical in gas respiration occur. The increased mass and viscosity of a liquid as compared with a gas necessitate some means of mechanical assistance. The lower diffusion rates of gases in liquids as compared with gas rates places several constraints on the design of a mechanically assisted liquid breathing system. The liquid breathing system reported in this study has been designed to be demand-regulated, i.e., the animal has control over cycling the pumps which mechanically assist the circulation of an oxygenated liquid to and from the lungs. This system consists of a gas-operated diaphragm pump, demand controller, liquid regenerator with heater and gas scrubber, and ancillary equipment. A demand controller is described which obtains a control signal from an esophageal balloon catheter in the animal and governs operation of the pneumatically driven diaphragm pump.

Airway Resistance↗
PubMedDate not supplied

A perfluorochemical loss/restoration (L/R) system for tidal liquid ventilation.

Tidal liquid ventilation is the transport of dissolved respiratory gases via volume exchange of perfluorochemical (PFC) liquid to and from the PFC-filled lung. All gas-liquid surface tension is eliminated, increasing compliance and providing lung protection due to lower inflation pressures. Tidal liquid ventilation is achieved by cycling fluid from a reservoir to and from the lung by a ventilator. Current approaches are microprocessor-based with feedback control. During inspiration, warmed oxygenated PFC liquid is pumped from a fluid reservoir/gas exchanger into the lung. PFC fluid is conserved by condensing (60-80% efficiency) vapor in the expired gas. A feedback-control system was developed to automatically replace PFC lost due to condenser inefficiency. This loss/restoration (L/R) system consists of a PFC-vapor thermal detector (+/- 2.5%), pneumatics, amplifiers, a gas flow detector (+/- 1%), a PFC pump (+/- 5%), and a controller. Gravimetric studies of perflubron loss from a flask due to evaporation were compared with experimental L/R results and found to be within +/- 1.4%. In addition, when L/R studies were conducted with a previously reported liquid ventilation system over a four-hour period, the L/R system maintained system perflubron volume to within +/- 1% of prime volume and 11.5% of replacement volume, and the difference between experimental PFC loss and that of the L/R system was 1.8 mL/hr. These studies suggest that the PFC L/R system may have significant economic (appropriate dosing for PFC loss) as well as physiologic (maintenance of PFC inventory in the lungs and liquid ventilator) impact on liquid ventilation procedures.

Calibration↗