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Biomedical subjects

A C Jackson

Publications and source records attributed to A C Jackson.

At least 109 records · Page 6Linked to original sources
PubMed1985

CO2 elimination as predicted by augmented dispersion and convection in an asymmetrical dog airway model.

We have developed a computer model of the dog lung based upon an asymmetrically branching network of tubes to describe gas exchange during high-frequency oscillations. Impedances to oscillatory flows were calculated for each airway segment and used to determine flow distributions in all airway generations. Gas exchange was assumed to occur by convective and augmented dispersive mechanisms. Also included in the model were features commonly found in animal studies including the effects of bias flow of fresh gas at the airway opening and equipment dead-space volume. The magnitude of CO2 elimination predicted by the model closely resembled actual experimental data. Specifically, it predicted that CO2 elimination is proportional to frequency to the 0.82 power and tidal volume to the 1.25 power. It also indicated that the bias flow rate and equipment dead-space volume influence gas exchange characteristics and thus these variables should be considered when comparing data from different studies.

Airway Resistance↗
PubMed1985

The encephalopathy of sepsis.

Twelve fatal cases of encephalopathy associated with sepsis were examined in a ten-year retrospective study. The sources of infection and organisms isolated were variable. Six of the patients had focal neurologic signs; five had seizures. The level of consciousness varied from drowsiness to deep coma, and electroencephalograms revealed diffuse or multifocal abnormalities. Computed tomographic head scans and cerebrospinal fluid examinations were usually unremarkable. Eight patients had disseminated microabscesses in the brain at autopsy. Four patients had proliferation of astrocytes and microglia in the cerebral cortex, a feature associated with metabolic encephalopathies. Additional findings included cerebral infarcts, brain purpura, multiple small white matter hemorrhages, and central pontine myelinolysis. Although sepsis may cause encephalopathy by producing disturbances in cerebral synaptic transmission and cerebral energy production through a toxic mechanism, bacterial invasion of the brain with the formation of disseminated microabscesses is also an important cause.

Adult↗
PubMed1985

Frequency dependence of CO2 elimination and respiratory resistance in monkeys.

In dogs, respiratory system resistance (Rrs) is frequency independent, and during high-frequency oscillatory ventilation (HFO) the relationship between CO2 elimination (VCO2) and frequency is linear. In contrast, we found in rabbits a large frequency-dependent decrease in Rrs with increasing frequency along with a nonlinear relationship between frequency and VCO2 (J. Appl. Physiol. 57: 354-359, 1984). We proposed that frequency dependent mechanical properties of the lung account for inter-species differences in the frequency dependence of gas exchange during HFO. In the current study we tested this hypothesis further by measuring VCO2 and Rrs as a function of frequency in a species of monkey (Macaca radiata). In these monkeys, Rrs decreased minimally between 4 and 8 Hz and in general increased at higher frequencies, whereas VCO2 was linearly related to frequency. This is further evidence supporting the hypothesis that nonlinear frequency-VCO2 behavior during HFO is related to frequency-dependent behavior in Rrs.

Airway Resistance↗
PubMed1984

Dynamic respiratory mechanics in monkeys measured by forced oscillations.

We measured impedances of the lungs (ZL) and respiratory system (Zrs) by discrete frequency (f) forced oscillations in adult bonnet monkeys at two lung volumes, FRC and at transrespiratory system pressure (Prs) of -5 cm H2O. Measurements were made from 2 to 32 Hz to study f dependence of effective resistances (Reff) and reactances, and from 1 to 8 Hz to study f dependence of effective pulmonary compliance (Ceff,L). Estimates of resistances (R), inertances (I) and compliances (C) of the lungs (L), chest wall (W) and respiratory system (rs) were obtained by fitting the 2-32 Hz data to a series RIC network model. Reff,L, Reff,W and Reff,rs were found to be f dependent. The magnitude of ZL was small relative to that of Zrs at all f with RL only 30% of Rrs and CL six times Crs. Decreasing lung volume from FRC to Prs = -5 cm H2O increased RL, RW and Rrs, slightly decreased CL, CW and Crs, slightly increased resonance frequencies, and increased the f dependent behavior of Ceff,L. Our results indicate both similarities and differences between the respiratory system of these primates and man.

Airway Resistance↗
PubMed1984

CO2 elimination and airway opening pressure during high frequency oscillation in dogs.

CO2 elimination (VCO2) and pressure at the airway opening (Pao) were measured over a wide range of frequencies (f) (5-40 Hz) and tidal volumes (VT) (1-45 ml) during high frequency oscillatory ventilation (HFO) in 11 anesthetized, paralyzed dogs. CO2 elimination was found to depend primarily on the product off and VT which is consistent with theoretical predictions of gas exchange by augmented dispersion. Airway opening pressures during HFO were frequency dependent. At frequencies near 5 Hz Pao was lower, while at frequencies above 5 Hz Pao was higher than Pao during conventional mechanical ventilation (12 cm H2O). The minimum Pao (5 cm H2O) achieved while maintaining VCO2 equivalent to normal metabolic CO2 production occurred when VT was near that of the dead space volume and frequency was near 5 Hz. At lower VT, higher frequencies were required to maintain VCO2 and this increased frequency resulted in an increase in Pao amplitude (10-15 cm H2O).

Animals↗
PubMed1984

Oscillatory mechanics of the respiratory system in ozone-exposed rats.

The respiratory system impedance of tracheostomized cardiorespiratory disease-free Sprague-Dawley rats was measured from 20 to 90 Hz at constant flow amplitudes in 10 rats exposed to 0.64 ppm (UV) ozone for 7 days, and eight rats exposed to the same level of ozone for 20 days. This data was compared with respiratory system impedence spectra of 24 normal rats obtained in the same manner. When compared with control, the real part (effective resistance) was significantly different at several frequencies in the 7-day group (P less than 0.05), and group means were higher at all frequencies. The 20-day group showed no significant differences in effective resistance. The imaginary part (effective reactance) was significantly lower at higher frequencies (f greater than 36) in both exposure groups (P less than 0.05). When the impedance curves for each individual were fit to a lumped six-parameter model, and the parameters were compared, only the peripheral resistance parameter of the 7-day group was significantly different from control (P less than 0.05). We conclude that ozone exposure at this level causes changes in respiratory system impedance, that these changes consist primarily of decreased reactances at higher frequencies, and that at 7 days these changes can be modeled by an increase in peripheral resistance.

Airway Resistance↗
PubMed1984

Respiratory system, lung, and chest wall impedances in anesthetized dogs.

We measured impedances of the respiratory system (Zrs) and lung (ZL) in anesthetized and paralyzed dogs at frequencies between 4 and 64 Hz. Zrs was measured at functional residual capacity (FRC) and with mean transpulmonary pressures (Ptp) of 12 and 30 cmH2O; ZL was measured with the chest wall open at FRC and Ptp = 12 cmH2O. From these data we derived chest wall impedances at FRC and 12 cmH2O. Effective resistances of the respiratory system, lung, and chest wall were all frequency dependent. At frequencies below 22 Hz frequency dependence of respiratory system resistance was due to the frequency dependence of the chest wall, whereas at higher frequencies it was due to frequency dependence of the lung. Analysis of the impedance data between 4 and 32 Hz provided estimates of resistance, inertance, and compliance of the lung, chest wall, and respiratory system. At FRC, 41% of the respiratory system resistance was due to the lung and 59% was associated with the chest wall. Nearly all of the respiratory inertance (98%) was due to the lung. Lung compliance was approximately twice that of the chest wall, the former accounting for approximately one-third of respiratory elasticity. As lung volume was increased, respiratory resistance and compliance decreased; inertance also decreased, although this change was not significant.

Airway Resistance↗
PubMed1984

Tracheal cross-sectional areas from acoustic reflections in dogs.

The cross-sectional area of airways can be estimated from their response to an acoustic pressure pulse introduced at the airway opening. Errors in these area estimates are expected if the airways do not behave rigidly at these frequencies. In eight dogs we tested the accuracy of this technique to estimate tracheal cross-sectional areas by comparing them with area estimates made from radiographic bronchograms. Tracheal areas using this technique were not statistically different from areas determined radiographically. The results indicate that the dog trachea does behave rigidly enough so that this method can be used to measure its cross-sectional area.

Acoustics↗
PubMed1984

CO2 elimination as a function of frequency and tidal volume in rabbits during HFO.

CO2 elimination (VCO2) was monitored during high-frequency oscillation (HFO) over a frequency (f) range of 2-30 Hz in anesthetized and paralyzed rabbits to determine whether effective gas exchange could be achieved in this species, to determine the f and tidal volume (VT) dependence of gas exchange in this species, and to compare these results with those from dog and human studies. We were able to produce VCO2 levels during HFO that exceeded normal steady-state levels of CO2 production with VT's less than the total dead space volume. VCO2 was related to f in a curvilinear fashion, whereas in some rabbits VCO2 became independent of f at higher frequencies. This curvilinear relationship between f and VCO2 is similar to data from humans but contrasts with the linear relationship found in dogs. Evidence is presented indicating frequency-dependent behavior of gas exchange is correlated with a frequency-dependent decrease in respiratory system resistance. We propose that the frequency-dependent mechanical properties of the rabbit lung may also account for the species differences in HFO gas exchange.

Animals↗
PubMed1984

Airway pressures in an asymmetrically branched airway model of the dog respiratory system.

A computer model of the mechanical properties of the dog respiratory system based on the asymmetrically branching airway model of Horsfield et al. (11) is described. The peripheral ends of this airway model were terminated by a lumped-parameter impedance representing gas compression in the alveoli, and lung and chest wall tissue properties were derived from measurements made in this laboratory. Using this model we predicted the respiratory system impedance and the distribution of pressures along the airways in the dog lung. Predicted total respiratory system impedances for frequencies between 4 and 64 Hz at three lung volumes were found to compare quite closely to measured impedances in dogs. Serial pressure distributions were found to be frequency-dependent and to result in higher pressures in the lung periphery than at the airway opening at some frequencies. The implications of this finding for high-frequency ventilation are discussed.

Airway Resistance↗
PubMed1984

Mitral valve prolapse and cerebral ischemic events in young patients.

We evaluated 32 young patients with mitral valve prolapse (MVP) as the only recognized cause of cerebral ischemia. The mean follow-up from the time of the first ischemic event was 8 years. At the time of the follow-up evaluation, 24 patients (75%) had a normal cardiac examination, and 4 had midsystolic clicks; only 1 had the characteristic click-murmur. In 75%, the first ischemic event was stroke. When MVP-associated ischemia was recognized, 44% had recurrent ischemic events. In the mean 4-year period between diagnosis of MVP-associated ischemia and follow-up, 16% had recurrent ischemic events, but none had a new persistent deficit from these events. At the time of follow-up, 63% of patients were taking platelet antiaggregants or anticoagulants. These data suggest a good prognosis for recurrent ischemic events after diagnosis of MVP-associated ischemia.

Adolescent↗
PubMed1983

Protein deficiency: effects on lung mechanics and the accumulation of collagen and elastin in rat lung.

Groups of weanling (approximately 50 g) or young adult (approximately 300 g) rats were fed ad libitum casein-based diets varying in protein content from 4 to 16%. A group was also fed the 16% protein diet in an amount on a daily basis restricted to that consumed by the protein-deficient group (4% protein). The rats were fed the diets for either 4 weeks (weanling) or 6 weeks (adults). Protein-deficient or "food-restricted" rats (whether weanling or adults) were smaller and had smaller lungs than rats fed ad libitum the diets containing 16% protein. The lung elastin content was more resistant to dietary manipulation than was the lung collagen content. Lung collagen was significantly decreased in both weanling and adult rats fed the 4% protein diet. In weanling rats, pressure-volume relationships derived from saline-filled lungs (analyzed by exponential curve-fitting methods) suggested that lungs from food-restricted rats may be less compliant than lungs from rats fed the control diet ad libitum. When expressed in absolute terms, lungs from protein-deficient rats also appeared to be less compliant than normal rats; however, on a relative basis (percentage of volume at a given recoil pressure or the expression of volume on a weight basis) differences in compliance were less apparent. It is proposed that in weanling rats the differences in lung composition and compliance are the result of retarded lung growth and perhaps development.

Age Factors↗
PubMed1983

Association of mitral valve prolapse and intracranial aneurysms.

This paper describes five patients with mitral valve prolapse (MVP) and intracranial aneurysms. Patients with MVP frequently have evidence of a more generalized disorder of connective tissue. An association of intracranial aneurysms and MVP could be related to mesodermal disturbances involving collagen and elastic tissue in the vasculature. Further study is needed to confirm this association and to elucidate the nature of any underlying connective tissue defect.

Adult↗
PubMed1983

Technique for making hollow central airway casts.

We have developed a method for producing rigid hollow casts of the central airways. Woods metal (melting point 70 degrees C) was poured into the airways at the trachea of an excised canine lung air-dried at a transpulmonary pressure of 30 cmH2O. The tissue was dissolved and removed, and the resulting negative cast was carefully trimmed leaving only airways with a diameter of 2 mm or greater. The cast was then electroplated with copper that provided a rigid jacket encasing the Woods metal. Heating this structure to 100 degrees C liquefied the Woods metal allowing the majority of it to flow out. Residual amounts were readily removed by a high-pressure steam hose attached to the trachea. Comparisons were made between airway diameters from in vivo radiographic bronchograms (DB) and direct measurements of the resulting trimmed Woods metal cast (DC). Linear regression analysis of these data indicated a high degree of correlation (DC = 0.98 DB + 0.03, r = 0.99). We concluded that this technique produces positive casts which provide a good representative model of the central airways.

Animals↗
PubMed1982

Oscillatory mechanics of the respiratory system in normal rats.

Respiratory system impedances were measured by a modified forced oscillatory technique in 30 normal male CRD-free Sprague-Dawley rats at frequencies between 20 and 90 Hz. A resonance frequency was found (mean = 39 Hz) below which reactances were negative and above which reactances were positive. Resistances were generally found to be frequency dependent, increasing with increasing frequencies. Frequency dependent behavior in resistance has been ascribed to inhomogeneities in parallel airway pathways and to the effects of airway wall compliance. optimization techniques were used to estimate the values of parameters in a variety of lumped-parameter mechanical networks incorporating parallel pathways and/or airway wall compliance. The model whose response compared the best with the data and that resulted in the most consistent parameter values was found to be one where the airways are separated into central and peripheral components by a shunt pathway containing an airway wall compliance. The mean values for each of the parameters within the model were central airway resistance (54 cm H2O/L/sec), peripheral airway resistance (53 cm H2O/L/sec), central airway inertance (0.058 cm H2O/L/sec2), peripheral airway inertance (0.116 cm H2O/L/sec2)(, airway wall compliance (0.182 X 10(-4) L/cm H2O), and respiratory system compliance (1.267 X 10(-4) L/cm H2O).

Airway Resistance↗
PubMed1982

Interaction of oscillatory and unidirectional flows in straight tubes and an airway cast.

Because oscillatory resistance of the respiratory system is often measured during tidal breathing, we studied the interaction between simultaneous oscillatory and unidirectional flows in three straight tubes (radius ranging from 0.3025 to 0.679 cm and length either 30.7 or 173 cm) and a central airway cast (tracheal radius 0.685 cm). Oscillatory flow was generated by a loudspeaker, airway pressure was measured with a transducer, and flow was calculated from pressure changes in an airtight enclosure mounted behind the flow source (loudspeaker plethysmograph). Oscillatory resistance, i.e., the real part of impedance, was determined from 2 to 64 Hz. In the absence of unidirectional flow, frequency dependence of resistance was observed for the two 30.7-cm-long tubes to match previously published theory. Frequency dependence of resistance for the airway cast was similar to that of the tube of comparable inlet radius. In the presence of unidirectional flow, oscillatory resistance at low frequency was independent of frequency and determined by the magnitude of the unidirectional flow. Oscillatory resistance at high frequency was frequency dependent but still influenced by the magnitude of the unidirectional flow. Our results indicate that the presence of unidirectional flow alters the oscillatory resistance of tubes and the cast at any given frequency, presumably by changing the shape of the boundary layer.

Airway Resistance↗
PubMed1981

Fast integrated flow plethysmograph for small mammals.

The accurate measurement of a forced vital capacity (FVC) maneuver in a small mammal requires that the plethysmograph in use have good response characteristics at high frequencies. We develop, on a theoretical basis, the behavior of zeroth-order (pressure type), first-order (flow type without inertance), and second-order (flow type with inertance) plethysmogrphs. The actual frequency response of a mouse-sized plethysmograph is then presented, and a technique for improving its response characteristics is described. A flat amplitude response (within 3% of a reference flow taken as truth) was obtained for sinusoidal inputs below 240 Hz. A phase lag with respect to the reference flow equivalent to a simple time delay of 1.4 ms was observed up to 150 Hz. A typical FVC curve for a mouse is shown, and criteria are provided for designing similar plethysmographs suitable for use with larger animals.

Animals↗