A numerical single path model of respiratory gas exchange with distributed alveolar gas sources was used to estimate the anatomical changes in small peripheral airways such as occur in chronic obstructive pulmonary diseases (COPD). A previous sensitivity analysis of the single path model showed that decreasing total acinar airway cross-sectional area by an area reduction factor, R, results in computed gas expirograms with Phase III steepening similar to that observed in COPD patients. From experimental steady state CO2 washout data recorded from six healthy subjects and six COPD patients, optimized area reduction factors for the single path model were found that characterize peripheral airway anatomy for each subject. Area reduction factors were then combined with measured functional residual capacity data to calculate the normalized peripheral airspace diameters in a given subject, relative to the airspace diameters in the generations of an idealized standard lung. Mean area reduction factors for the patient subgroup were 63% of those for the healthy subgroup, which is related to the gas transport limitation observed in disease. Mean airspace sizes for the patient subgroup were 235% of the healthy subgroup, which characterizes the increase in size and reduction in number of peripheral airspaces due to tissue erosion in emphysema. From these results, the air-phase diffusive conductance in COPD patients was calculated to be 32% of the mean value in the healthy subjects. These findings correlated well with standard pulmonary function test data for the patients and yield the recovery of acinar airway information from gas washout by combining the single path model with experimental measurements.

Adult↗

PubMedDate not supplied

Countercurrent extraction of sparingly soluble gases for membrane introduction mass spectrometry.

Membrane introduction mass spectrometry has been applied to inert gas measurements in blood and tissue, but gases with low blood solubility are associated with reduced sensitivity. Countercurrent extraction of inert gases from a blood sample into a water carrier phase has the potential to extract most of the gas sample while avoiding dependence of signal on blood solubility. We present the design of a membrane countercurrent exchange (CCE) device coupled with a conventional direct insertion membrane probe to measure partial pressure of low solubility inert gases in aqueous samples. A mathematical model of steady-state membrane CCB predicts that countercurrent extraction with appropriate selection of carrier and sample flow rates can provide a mass spectrometer signal nearly independent of variations in solubility over a specified range, while retaining a linear response to changes in gas partial pressure over several orders of magnitude. Experimental data are presented for sulfur hexafluoride and krypton in water samples. Optimal performance is dependent on adequate equilibration between the sample and carrier streams, and the large resistance to diffusion in the aqueous phase for insoluble gases presents a substantial challenge to the application of this principle.

Animals↗

PubMedDate not supplied

Effects of Fenwal 4C2423 transfusion microfilter on microaggregates and other constituents of stored blood.

The effects of a new micropore transfusion filter (Fenwal 4C2423) on stored whole blood have been examined. Five filters were preloaded by passage of two units of outdated type specific bank blood, and the effects of filtration on a third unit, consisting of 21-day-old blood, flowing under 150 mmHg pressure, were measured. Filtration did not significantly alter red blood cell count, total hemoglobin, red blood cell fragility, plasma sodium, potassium, albumin, or globulin. Some platelets and white blood cells were removed and a small amount of hemolygis of erythrocytes (less than 0.1%) was observed. Removal of microaggregates, assessed by Coulter counting, screen filtration pressure, total screen porteins, wet and dry weights of material retained, and scanning electron microscopy, was shown to be excellent over the entire range of particle size. Comparison of the Bentley PFS-127, Fenwal 4C2417, Johnson & Johnson Intersept, Pall Ultipore, and Swank IL200 filters led to the conclusion that the Fenwal 4C2423 was both a significant improvement over the previous Fenwal design and comparable to the most efficient of these filters for both the removal of microaggregates during massive blood transfusion and for the blood flow rates obtained.

Blood Flow Velocity↗

PubMedDate not supplied

Evaluation of the Swank IL-201 transfusion filter.

The effects of a new transfusion filter (Swank IL-20U) on stored, whole blood have been examined. Six filters were preloaded by passage of two units of outdated, type-specific bank blood, and the effects of filtration on a third unit of 21-day-old blood flowing under 150 mm Hg pressure were measured. Filtration did not significantly alter erythrocyte or leukocyte count, total or plasma hemoglobin, red-cell fragility, and plasma sodium, potassium, albumin, or globulin. Platelet counts were reduced by 33%. Removal of microaggregates, assessed by Coulter counting, screen filtration pressure, total screen protein, wet and dry weight of material retained, and scanning electron microscopy, was shown to be effective over the entire range of particle size. In comparison with other transfusion filters previously examined in this laboratory, the Swank IL-201 filter combines the features of efficient microaggregate removal with moderate blood-flow rate. Compared to its predecessor, the Swank IL-200, this new filter design has improved flow characteristics without loss of microaggregate removal efficiency. In view of the similarity of performance demonstrated for several of the available filters, it seems likely that relative cost will constitute an important determinant of filter selection.

Blood Transfusion↗

PubMedDate not supplied

Electrical impedance properties of the body and the problem of alternate-site burns during electrosurgery.

The radiofrequency (RF) impedance at 500 kHz was measured between multiple contact points on the bodies of six healthy volunteers by a tetrapolar measurement technique. The impedance between various contact points was predictable and could increase by a factor of two, depending on the sites selected for electrode application. These results were related to a simple resistive model of RF current distribution through the body. Based on the model and on data from human subjects, a hierarchy of optimal locations was developed to minimize the impedance between a surgical site and a dispersive electrode site and to reduce the potential for alternate-site burns from electrosurgery.

Adolescent↗

PubMedDate not supplied

The role of high frequency ventilation in clinical medicine.

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Humans↗