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Biomedical subjects

I D Frantz

Publications and source records attributed to I D Frantz.

At least 37 records · Page 2Linked to original sources
PubMed1989

Preferential axial flow during high-frequency oscillations: effects of gas density.

Allen et al. (J. Clin. Invest. 76: 620-629, 1985) reported that regional phasic lung distension during high-frequency oscillations (HFO) is substantially and systemically heterogeneous when both frequency (f) and tidal volume (VT) are large. They hypothesized that this phenomenon was attributable to central airway geometry and preferential axial flow induced therein by the momentum flux of the inspiratory gas stream. According to that hypothesis, the observed distribution of phasic lung distension would depend on the ratio VT/VD* (where VD* is an index of anatomic dead space), independent of gas density (rho), when f is scaled in proportion to lung resonant frequency, fo. To test this hypothesis, we used the methods of Allen et al. (ibid.) to study six excised dog lungs during HFO (f = 2-32 Hz; VT = 5-80 ml) using gases of different densities. Alveolar pressure excursions (PA) were measured as rho spanned a 12-fold range using He, air, and SF6. The apex-to-base and right-to-left ratios of PA were used as indexes of regional heterogeneity of phasic lung distension. For each gas at low f, distension of the lung base was favored slightly independent of VT, but at higher f distension of the lung apex was favored when VT was small, whereas distension of the lung base was favored when VT was large. In addition, we observed substantial right-to-left differences in apical lobes during oscillation at high f not seen before.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Gas exchange in healthy rabbits during high-frequency oscillatory ventilation.

We examined the effects of oscillatory frequency (f), tidal volume (VT), and mean airway pressure (Paw) on respiratory gas exchange during high-frequency oscillatory ventilation of healthy anesthetized rabbits. Frequencies from 3 to 30 Hz, VT from 0.4 to 2.0 ml/kg body wt (approximately 20-100% of dead space volume), and Paw from 5 to 20 cmH2O were studied. As expected, both arterial partial pressure of O2 and CO2 (PaO2 and PaCO2, respectively) were found to be related to f and VT. Changing Paw had little effect on blood gas tensions. Similar values of PaO2 and PaCO2 were obtained at many different combinations of f and VT. These relationships collapsed onto a single curve when blood gas tensions were plotted as functions of f multiplied by the square of VT (f. VT2). Simultaneous tracheal and alveolar gas samples showed that the gradient for PO2 and PCO2 increased as f. VT2 decreased, indicating alveolar hypoventilation. However, venous admixture also increased as f. VT2 decreased, suggesting that ventilation-perfusion inequality must also have increased.

Animals↗
PubMed1989

Mixed and obstructive apneas are related to ventilatory oscillations in premature infants.

In our previous study of 14 premature infants, apnea occurred at the minimum phase of ventilatory oscillations. The apneas corresponded to cessation of airflow at the nose and mouth and were not distinguished as central, mixed, or obstructive. Changes in heart rate associated with the apneas were not identified. To determine whether ventilatory pattern characteristics might predict either the type of apnea or heart rate changes during the apnea, we analyzed measurements of chest wall movement and heart rate that were made during the earlier studies. Chest wall movement measured by magnetometers was compared with airflow measured with a face mask and pneumotachograph. Tidal volume, breath duration, and ventilation were calculated on a breath-by-breath basis, converted to time-axis data strings, and filtered with a comb of zero phase shift digital band-pass filters to detect breathing patterns. Of 182 apneas greater than or equal to 3 s duration, 55% were central, 31% were mixed, and 14% were obstructive. All three types of apnea were related to ventilatory oscillations. Multiple linear and logistic regressions showed that an apnea was more likely to be obstructive when it was long and when the underlying ventilatory oscillation was due primarily to an oscillation in breath duration. Multiple linear and logistic regressions showed that decreases in heart rate were related primarily to the duration of apnea and secondarily to the characteristics of the underlying breathing patterns.

Airway Obstruction↗
PubMed1989

Rib cage vs. abdominal displacement in dogs during forced oscillation to 32 Hz.

Allen et al. (J. Clin. Invest. 76: 620-629, 1985) reported that during oscillatory forcing the base of isolated canine lungs distends preferentially relative to the apex as frequency and tidal volume increase. The tendency toward such nonuniform phasic lung distension might influence phasic displacement of the rib cage (RC) relative to the abdomen (ABD). To test this hypothesis we measured RC and ABD displacement in four anesthetized dogs during forced oscillation. Sinusoidal volume changes were delivered through a tracheostomy at 1-32 Hz and measured by body plethysmography. RC and ABD displacements were measured by inductive plethysmography. During oscillation with air at fixed tidal volumes (10-80 ml) RC, normalized to unity at 1 Hz, increased to 2.06-2.22 at 8 Hz (P less than 0.001) and then decreased to 1.06-1.35 (P less than 0.0025) at 32 Hz. ABD, normalized to unity at 1 Hz, was 1.12-1.16 at 4 Hz (P less than 0.001) and decreased to 0.12-0.14 at 32 Hz (P less than 0.001). Displacement of ABD relative to RC did not increase systematically with increasing tidal volume during sinusoidal forcing at any frequency. Thus we found no discernible influence of nonuniform phasic lung distension on chest wall behavior. We infer that in the dog the nonuniform mechanical behavior of the chest wall dominates the nonuniform (but opposing) mechanical tendency of the lung.

Abdomen↗
PubMed1988

Cardiovascular risk factor change--1973-74 to 1980-82: the Minnesota Heart Survey.

Reductions in population risk factor levels, including blood pressure, blood cholesterol, and cigarette smoking may be associated with the observed decline in cardiovascular disease (CVD) mortality rates. However, few recent population-based comparisons of risk trends are available. To evaluate changes in these risk characteristics in the recent period, data were compared from two surveys performed in the same metropolitan area using similar methods. The Lipid Research Clinic (LRC) Prevalence Study surveyed a population sample of 4185 adults aged 25-59 in 1973-74. The Minnesota Heart Survey (MHS) surveyed a population sample of 2914 adults of the same age in the same metropolitan area in 1980-82. The average systolic and diastolic blood pressures were significantly lower in the 1980-82 survey averaging 1.5/3.8 mmHg for men and 1.6/2.8 mmHg for women. The use of anti-hypertensive medications increased significantly over the period while the prevalence of hypertension was similar. Significant declines in mean serum cholesterol were also observed in 1980-82, averaging 3.3 mg/dl for men and 5.5 mg/dl women. The prevalence of regular cigarette smoking in men was also lower in 1980-82, 36.3 vs 42.1% in 1973-74. Women had a lower prevalence of smoking (38.8-35.6%) but the average woman smoker increased consumption of cigarettes while the average man did not. These observations suggest that population risk defined by these characteristics is declining which may explain part of recent Minnesota trends in CVD mortality and could have a favorable effect on future disease patterns.

Adult↗
PubMed1987

Heterogeneity of mean alveolar pressure during high-frequency oscillations.

Mean alveolar pressure may exceed mean airway pressure during high-frequency oscillations (HFO). To assess the magnitude of this effect and its regional heterogeneity, we studied six excised dog lungs during HFO [frequency (f) 2-32 Hz; tidal volume (VT) 5-80 ml] at transpulmonary pressures (PL) of 6, 10, and 25 cmH2O. We measured mean pressure at the airway opening (Pao), trachea (Ptr), and four alveolar locations (PA) using alveolar capsules. Pao was measured at the oscillator pump, wherein the peak dynamic head was less than 0.2 cmH2O. Since the dynamic head was negligible here, and since these were excised lungs, Pao thus represented true applied transpulmonary pressure. Ptr increasingly underestimated Pao as f and VT increased, with Pao - Ptr approaching 8 cmH2O. PA (averaged over all locations) and Pao were nearly equal at all PL's, f's, and VT's, except at PL of 6, f 32 Hz, and VT 80 ml, where (PA - Pao) was 3 cmH2O. Remarkably, mean pressure in the base exceeded that in the apex increasingly as f and VT increased, the difference approaching 3 cmH2O at high f and VT. We conclude that, although global alveolar overdistension assessed by PA - Pao is small during HFO under these conditions, larger regional heterogeneity in PA's exists that may be a consequence of airway branching angle asymmetry and/or regional flow distribution.

Animals↗
PubMed1987

Regulation of end-expiratory lung volume during sleep in premature infants.

To investigate the regulation of end-expiratory lung volume (EEV) in premature infants, we recorded airflow, tidal volume, diaphragm electromyogram (EMG), and chest wall displacement during sleep. In quiet sleep, EEV during breathing was 10.8 +/- 3.6 (SD) ml greater than the minimum volume reached during unobstructed apneas. In active sleep, no decrease in EEV was observed during 28 of 35 unobstructed apneas. Breaths during quiet sleep had a variable extent of expiratory airflow retardation (braking), and inspiratory interruption occurred at substantial expiratory flow rates. During active sleep, the expiratory flow-volume curve was nearly linear, proceeding nearly to the volume axis at zero flow, and diaphragm EMG activity terminated near the peak of mechanical inspiration. Expiratory duration (TE) and inspiratory duration (TI) were significantly shortened in quiet sleep vs. active sleep although tidal volume was not significantly different. In quiet sleep, diaphragmatic braking activity and shortened TE combined to maintain EEV during breathing substantially above relaxation volume. In active sleep, reduced expiratory braking and prolongation of TE resulted in an EEV that was close to relaxation volume. We conclude that breathing strategy to regulate EEV in premature infants appears to be strongly influenced by sleep state.

Diaphragm↗
PubMed1987

Factors influencing mechanical performance of neonatal high-frequency ventilators.

Factors influencing the mechanical performance of neonatal high-frequency ventilators of diverse design were assessed under controlled conditions. Each of eight ventilators was coupled to in vitro models of the neonatal respiratory system simulating disease of varying severity. The principal performance characteristics examined were frequency dependence and load dependence of tidal volume delivered, peak inspiratory flow rate, and waveforms of pressure at either end of the endotracheal tube. Despite wide diversity of ventilator designs, including jets, flow interrupters, and oscillators, common features emerged. In almost all devices tidal volume increased with endotracheal tube size, was invariant with respiratory system compliance, and decreased with frequency of oscillation. Peak inspiratory flow rates for a given tidal volume and frequency were smallest in the group of oscillators compared with jets and flow interrupters. Proximal pressure was a poor indicator of distal pressure. These findings suggest that delivered tidal volume may be sensitive to endotracheal tube size and airway patency but relatively insensitive to changes in lung tissue or chest wall mechanical properties. In these regards high-frequency ventilation differs from pressure-limited conventional mechanical ventilation. Comparison of data obtained at different clinical centers using high-frequency ventilators of varying design may be possible by taking these factors into account.

Humans↗
PubMed1987

Rib cage versus abdominal displacement in rabbits during forced oscillations to 30 Hz.

We measured relative displacement of the rib cage (RC) and abdomen (ABD) in 12 anesthetized rabbits during forced oscillations. Sinusoidal volume changes were delivered through a tracheostomy at frequencies from 0.5 to 30 Hz and measured by body plethysmography. Displacements of the RC and ABD were measured by inductive plethysmography. During oscillation at fixed tidal volume (VT = 1.3 ml/kg) the ratio ABD/RC, normalized to unity at 0.5 Hz, was 0.88 +/- 0.06 at 2 Hz and increased to 1.28 +/- 0.13 at 6 Hz (P less than 0.01). As frequency increased further ABD/RC fell sharply but between 20 and 30 Hz reached a plateau of 0.17 +/- 0.02 (P less than 0.001). Displacements of RC and ABD were nearly synchronous from 0.5 to 2 Hz, but as frequency increased ABD lagged RC progressively, reaching a phase difference of 90 degrees between 6 and 8 Hz and 180 degrees between 16 and 20 Hz. In six additional rabbits we measured chest wall displacements while varying VT from 0.5 to 3.7 ml/kg. ABD/RC was independent of VT at low frequencies (less than or equal to 6 Hz) but fell sharply with increasing VT at the higher frequencies. We interpreted these findings using a chest wall model having an RC compartment whose displacements are governed primarily by a nonlinear compliance, in parallel with an ABD compartment whose displacements are governed by a series resistance, inertance, and in addition a nonlinear compliance. The experimental findings are in large measure accounted for by such a model if the degree of nonlinearity of ABD and RC compliances are comparable.(ABSTRACT TRUNCATED AT 250 WORDS)

Abdomen↗
PubMed1986

Respiratory distress syndrome.

Increasing knowledge of the pathophysiology of respiratory distress syndrome has led to improvements in clinical management. Future advances in prevention and therapy, including administration of agents to prevent prematurity or to accelerate lung maturation, provision of surfactant replacement, and new techniques of mechanical ventilation, will further decrease mortality and morbidity.

Animals↗
PubMed1986

Interlaboratory testing of the transferability of a candidate reference method for total cholesterol in serum.

In 1975 the Centers for Disease Control, in cooperation with the American Association for Clinical Chemistry Cholesterol Reference Method Study Group, began an investigation to develop a reference method for total cholesterol. Five potential reference methods were compared with the definitive method developed by the National Bureau of Standards before the chemical method of Abell et al. (J Biol Chem 1952;195:357-66) was selected as the recommended reference method. Because acceptance of a proposed reference method depends so greatly on the method's capability for transfer to other laboratories by written specifications and instructions, a transferability testing study was designed and conducted with 14 laboratories. The study consisted of preliminary testing of readiness of equipment, reagents, and personnel followed by transferability testing with eight runs on 10 serum pools. Laboratoires that did not meet readiness specifications had higher CVs in the transferability testing. The study demonstrated that the proposed method permits laboratories to attain a CV of less than 1.5% for one laboratory and of less than 3.0% among laboratories. The mean percent bias value was less than 1.0% for six of the 14 laboratories, less than 1.5% for 12, and less than 3.0% for all 14 laboratories.

Calibration↗
PubMed1986

Patterns of dyslipoproteinemia in selected North American populations. The Lipid Research Clinics Program Prevalence Study.

This article describes the assignment of dyslipoproteinemia (DLP) in several free-living North American populations and presents mean lipid and lipoprotein levels for each type. Dyslipoproteinemic phenotypes were assigned by a modified version of the National Institutes of Health (Fredrickson) phenotyping system. Criteria for assigning phenotypes included age- and sex-specific 5th and 95th percentiles for low-density lipoprotein and high-density lipoprotein cholesterol and total triglyceride, as well as other qualitative and quantitative criteria. Phenotypes IIb, III, I, and V were uncommon, confirming clinical impressions of their frequency. Lipid and lipoprotein levels in specific phenotypes were generally as expected. In the type III phenotype, however, mean cholesterol and triglyceride levels were surprisingly low. Gonadal hormone use, in the form of both oral contraceptives and postmenopausal estrogens, was reported in approximately 30% of women in these populations and was associated with dramatic differences in the frequency of DLP when compared with women not taking hormones. In general, these differences reflected the previously described effects of estrogen and progestins on lipoprotein levels. These data gathered in free-living populations: confirm clinical impressions of the rarity of some phenotypes, focus attention on those phenotypes in which diminished rather than elevated lipoproteins are found, and provide further evidence of the effect of hormones on lipid and lipoprotein levels.

Adolescent↗
PubMed1985

Effect of clofibrate and colestipol singly and in combination on plasma lipids and lipoproteins in type III hyperlipoproteinemia.

The effects of colestipol, clofibrate, and a combination of these two drugs on plasma lipid and lipoprotein values were evaluated in seven subjects with type III hyperlipoproteinemia. When compared to baseline, colestipol administration resulted in a significant decrease in LDL-cholesterol (146 v 99, P less than 0.01) and a significant increase in VLDL-triglycerides (260 v 399, P less than 0.05). The increases in total triglycerides (346 v 462, P = 0.09) and VLDL-C (117 v 155, P = 0.17) noted with colestipol were not statistically significant. Clofibrate administration increased HDL-C (37 v 46, P less than 0.05), and lowered VLDL-C (117 v 56, P less than 0.05), VLDL-triglycerides (260 v 144, P less than 0.05) and total triglycerides (346 v 218, P less than 0.01). The combined regimen was more effective than clofibrate in lowering total and LDL-cholesterol, and no other significant differences were noted.

Adult↗
PubMed1985

Elevated lung volume and alveolar pressure during jet ventilation of rabbits.

We measured lung volume, tidal volume, and pressures at the airway opening, trachea, and alveoli during jet ventilation of rabbits at frequencies from 2 to 15 Hz when inspiratory time was varied from 10 to 50% of the ventilator cycle. Lung volume was determined dynamically and was dependent on tidal volume, expiratory duration, and the expiratory time constant of the respiratory system. Tidal volume decreased with increasing frequency and lung volume, and was greater than estimated dead-space volume over most of the frequency range studied. Pressure at the airway opening was not a good estimate of either mean pressure or pressure swings in the alveoli. Tracheal pressure corresponded fairly well to alveolar pressure. Alveolar pressure swings diminished with increasing frequency and decreasing inspiratory duration. In the clinical setting these results mean that measurement of pressures at the airway opening is not an adequate way to monitor patients during jet ventilation. In addition, the clinician must be aware that substantial increases in functional residual capacity may occur during jet ventilation, thereby placing the patient at risk of pneumothorax.

Animals↗
PubMed1985

Alveolar pressure magnitude and asynchrony during high-frequency oscillations of excised rabbit lungs.

One possible advantage of high-frequency ventilation (HFV) over conventional mechanical ventilation is that adequate pulmonary ventilation may be established with lower pressure swings. Pressure swings measured at the airway opening may not accurately reflect pressure swings in the alveoli, however. Furthermore, little is known about the synchrony of alveolar filling during HFV. We have assessed the magnitude of alveolar pressure swings (PA) relative to those at the airway opening (Pao) and investigated asynchrony of alveolar filling during small tidal volume (less than 1.0 ml), high-frequency (1 to 60 Hz) oscillations (HFO) in 8 excised rabbit lungs. The PA was measured in several capsules glued to the pleural surface and communicating with alveolar gas via pleural punctures. The peak value of the ratio [PA/Pao] occurred near the resonant frequency and was 1.90, 1.45, and 1.0 at distending pressures of 25, 10, and 5 cm H2O, respectively. Temporal asynchrony of PA between sampled lung regions was quantified by measuring the interregional standard deviation of alveolar pressure phase angles, delta phi. The delta phi increased with increasing frequency and decreasing transpulmonary pressure. The maximal observed delta phi was 30 degrees. These results, when compared with earlier results on excised canine lungs, show that the amplification of PA during HFO is lung-size dependent. The observed degree of phase differences in pressure swings between peripheral alveolar locations implies substantial asynchrony of alveolar filling. This in turn suggests interregional gas transport as an important contributor to gas mixing during HFV.

Airway Resistance↗
PubMed1985

Regional alveolar pressure during periodic flow. Dual manifestations of gas inertia.

We measured pressure excursions at the airway opening and at the alveoli (PA) as well as measured the regional distribution of PA during forced oscillations of six excised dog lungs while frequency (f[2-32 Hz]), tidal volume (VT [5-80 ml]), and mean transpulmonary pressure (PL [25, 10, and 6 cm H2O]) were varied. PA's were measured in four alveolar capsules glued to the pleura of different lobes. The apex-to-base ratio of PA's was used as an index of the distribution of dynamic lung distension. At low f, there was slight preferential distension of the lung base which was independent of VT, but at higher f, preferential distension of the lung apex was found when VT's were small, whereas preferential distension of the lung base was found when VT's approached or exceeded dead space. These VT-related changes in distribution at high frequencies seem to depend upon the branching geometry of the central airways and the relative importance of convective momentum flux vs. unsteady inertia of gas residing therein, which, in this study, we showed to be proportional to the ratio VT/VD*, where VD* is an index of dead space. Furthermore, they imply substantial alteration in the distribution of ventilation during high frequency ventilation as f, VT, and PL vary. The data also indicate that alveolar and airway opening pressure costs per unit flow delivered at the airway opening exhibit weakly nonlinear behavior and that resonant amplification of PA's, which has been described previously for the case of very small VT's, persists but is damped as VT's approach dead space values.

Airway Resistance↗