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Biomedical subjects

L A Engel

Publications and source records attributed to L A Engel.

At least 109 records · Page 6Linked to original sources
PubMed1977

Influence of pericardial fluid on cardiogenic gas mixing in the lung.

Respirat. Environ. Exercise Physiol. 42(1): 5-12, 1977. -In eight open-chested dogs we measured the end-inspiratory N2 concentration within 12 airways, 2.5-8.3 mm in diameter during constant flow inflations with 0.5 liter of O2 before and after the introduction of saline into the pericardial sac. The critical flow rate necessary to achieve a given end-inspiratory FN2, as well as the maximal amplitude of cardiogenic N2 fluctuations, became smaller in the presence of pericardial fluid (PF). In the presence of only 25-50 ml of saline in the pericardium the effective diffusion coefficient, incorporating cardiogenic gas mixing, decreased by as much as 50-66%, respectively. Studies in two dogs with the chest intact showed that PF caused a qualitatively similar impairment of gas mixing during breath holding. Multiple-breath N2 washouts did not reflect the decreases in gas mixing produced by PF. We believe that PF decreases cardiogenic gas mixing mainly by protecting the lung from the rotational thrust of the heart during myocardial contraction.

Animals↗
PubMed1977

Diaphragmatic contraction and the gradient of alveolar expansion in the lateral posture.

Using 133Xe we measured the vertical distribution of regional volume in four subjects in the lateral decubitus posture at 20, 40, 60, and 80% of vital capacity (VC). To study the influence of diaphragmatic tone, all measurements were performed either when transdiaphragmatic pressure (Pdi) was low, i.e., diaphragm was "relaxed" (RD) or during voluntary diaphragmatic contraction (VDC). The latter was achieved by tensing the abdominal muscles while keeping the glottis open. Under both conditions the gradient of alveolar expansion tended to be curvilinear, with a discontinuity at the level of the mediastinum. At all lung volumes the difference in regional volume between dependent and nondependent lung regions was less during VDC than during RD. At 70% total lung capacity (TLC) this difference, expressed as percent of regional TLC (%TLCr), decreased from 19.7 +/- 1.7 (mean +/- 1 SE) %TLCr during RD to 3.9 +/- 1.5% TLCr during VDC. It is likely that diaphragmatic tension influences the pleural pressure gradient and regional volume distribution 1) by modifying the transmission of the abdominal hydrostatic pressure gradient to the thorax, and 2) by an upward displacement of the mediastinum.

Diaphragm↗
PubMed1976

Convection, diffusion and cardiogenic mixing of inspired gas in the lung; an experimental approach.

In 8 open-chested dogs, we measured the FN2 within 26 airways, 2.5-8.6 mm in diameter, during constant flow inflations with 0.5 liter of O2. At low flows the FN2 did not fall to zero but reached a plateau, at a value that was inversely related to inspiratory flow. When inspiratory flow is constant, the measured FN2 represents one point on a stationary front separating inspired and alveolar gas. At all points on the front the convective and diffusive transport of N2 is equal and opposite in direction. We quantitated cardiogenic gas mixing by comparing in vivo and post mortem the flow which resulted in a given stable FN2 value within the same airway. In vivo, this flow and therefore the calculated effective diffusion coefficient (D') was more than 5 times greater than that post mortem. Our results confiem some of the predictions made from model analyses of gas transport in the lung. However, calculations based on molecular diffusion as the sole mixing mechanism necessarily overestimate diffusion times and the magnitude of stratification.

Animals↗
PubMed1976

Influence of diaphragmatic contraction and expiratory flow on the pattern of lung emptying.

Transdiaphragmatic pressure (Pdi) and expiratory flow (V) were monitored during vital capacity single breath N2 washouts in 7 seated subjects. Transient increases in V were produced (1) actively, by subjects increasing mouth pressure while expiring through a constant resistance of (2) passively, by the operator transiently decreasing the resistance. Voluntary contraction of the diaphragm (increased Pdi) was achieved when abdominal muscles were tensed while maintaining V constant. In 5 subjects a transient increase in Pdi of 25-150 cm H2O consistently produced a transient increase in expired N2 concentration of 1.80 +/- 0.06% (Mean +/- 1 SE); in 1 subject N2 concentration decreased by 0.8% to 2.7% N2, and in one subject the alveolar plateau was uninfluenced by changes in Pdi. Passive increases in V up to 21/sec had no effect on FEN2 in any of the subjects. Active increase in V changed FEN2 only when associated with increases in Pdi. Qualitatively similar results were obtained during helium (He) bolus washouts. However, whereas diaphragmatic contraction, maintained throughout expiration, had no measurable influence on the N2 washout, it changed the slope of the He alveolar plateau in 6 out of 7 subjects. We conclude that in normal subjects the alveolar N2 plateau is relatively insensitive to flow variations up to 21/sec. The fluctuations in FEN2 observed when the expiratory flow is varied are due to concomittant changes in Pdi. We propose that diaphragmatic contraction changes the pattern of lung emptying by altering the vertical gradient of pleural pressure.

Diaphragm↗
PubMed1976

Influence of bronchomotor tone on regional ventilation distribution at residual volume.

We studied the topographical distribution of 133Xe boluses inhaled slowly from RV, as well as the distribution of regional volumes at RV (RVr) in seven seated normal subjects before and after aerosolized isoprenaline (ISO) and after aerosolized methacholine hydrochloride (Mech). After Mech the ratio of inhaled 133Xe in the upper lung regions to that in lower lung regions (U/L) decreased from 3.21 +/- .33 (mean +/- 1 SE) to 1.27 +/- 0.12 (P less than 0.001) and returned to 3.89 +/- 0.55 after Iso. Iso alone increased U/L from 3.23 +/- 0.47 to 5.49 +/- 0.85 (P less than 0.025). The height of phase IV in expired 133Xe vs. volume plots correlated with U/L, being greater after Iso and smaller after Mech in each subject. The difference in RVr between upper and lower lung regions decreased after Mech in four out of five subjects from 0.22 TLC to 0.11 TLC. Iso alone did not change the gradient of RVr. The results are consistent with the concept that increased bronchomotor tone widens the range of critical opening and closing pressures with a more patchy and extensive distribution of airway closure.

Adult↗
PubMed1976

Influence of diaphragmatic contraction on ventilation distribution in horizontal man.

The washout of a bolus of helium (inhaled from residual volume) during relaxed expiration (RE) through a resistance was compared with that during expiration with voluntary diaphragmatic contraction (VDCE) achieved by tensing the abdominal muscles while maintaining constant expiratory flow (less than 0.4 l/s). In six subjects in the lateral decubitus position, phase IV during RE started at 58 +/- 1.6% vital capacity (VC) (mean +/- 1 SE). During VDCE, when the transdiaphragmatic pressure (Pdi) exceeded 30 cmH2O, phase IV commenced at 8.2 +/- 0.8% VC. The expired He concentration (FEHe) at lung volumes greater than 70% VC was 1.3 +/- 0.05 times that during RE. In supine subjects VDCE flattened the slope of the alveolar plateau and decreased closing volume by 3.7 +/- 0.4% VC. Our results suggest that when the diaphragm is relaxed in the horizontal subject, the hydrostatic gradient of pressure within the abdomen enhances early emptying of dependent lung zones. Diaphragmatic contraction results in more homogeneous emptying. We conclude that diaphragmatic tone influences the vertical gradient of regional volume, and hence of pleural pressure. The latter is not constant, being less during inspiration than during expiration. Therefore, differences in the changes of applied pressure between dependent and nondependent lung regions influence ventilation distribution in subjects in the horizontal posture.

Diaphragm↗
PubMed1976

Effect of gas physical properties and flow on lower pulmonary resistance.

We measured lower pulmonary resistance (Rlp) in eight dogs and three men breathing gas mixtures having different densities (p) and similar viscosities (mu). Rlp increased with gas density and with flow rate (V). In the dogs, these effects were not observed in lung segments subtended from 4-mm-ID bronchi; in more central airways, resistance varied approximately as (mup V)0.5. These results are compatible with Poiseuille flow in peripheral airways, and, in central airways, with flow resistance described by the equation of boundary layer growth. Rather than two discrete flow regimes, it is likely that flow patterns undergo a continual metamorphosis as Reynolds' numbers (Re) decrease between trachea and alveoli. Accordingly, the airways pressure-flow relationship is not described by any single fluid dynamics equation, but may be explained by the general equation, P = Kmu2-apa-1Va, where a reflects the proportion of inertial to viscous pressure losses and varies between 1 and 2 according to Re. Rohrer's equation described the observed pressure-flow relationships and predicted the change in Rlp with gas physical properties, suggesting a physical basis underlying this adequate mathematical description.

Airway Resistance↗
PubMed1976

Influence of posture on flow dependence of distribution of inhaled 133Xe boli.

The second 100 ml of gas inspired at constant flow rates (V) from 0.1 to 2.5 l/s was tagged with 133Xe to determine the apicobasal bolus distribution ratio (VAlvA/VAlvB) for seven normal subjects in both the upright and supine postures. Gas was preferentially distributed to the base at low V. As V increased, redistribution to the apex occurred but was greater in the supine posture. As apicobasal time constant differences should be minimal in the supine posture, the greater flow dependence of bolus distribution suggests that the pressure swing was greater over apical zones than basal zones. Model studies indicate that the pressure differences (deltaPd) necessary to predict the measured VAlvA/VAlvB at all flow rates are less than 1.0 cmH2O. Such sensitivity of gas distribution to deltaPd at both low and high flow rates makes it appear relatively insensitive to regional compliance and resistance.

Adult↗
PubMed1975

Demonstration of airway closure in man.

After partial equilibration of the lung with a N2O gas mixture absorption of N2O by the pulmonary circulation results in a flow of gas into the lungs during breath holding. A bolus of 133Xe introduced at the mouth at the beginning of the breath hold is carried in by the gas flow and distributed according to regional perfusion. In three subjects, breath holding at FRC, apex-to-base distribution of a 133Xe bolud delivered by N2O absorption (Xecar) was similar to that of a bolus injected intravenously (Xeiv). Near RV however, much less of Xecar penetrated into dependent zones than expected from the distribution of Xeiv. In fact, distribution of Xecar did not differ from that of a slowly inhaled bolus. Correction for Compton scatter in the chest wall, measured in one subject, accounted only in part for the radioactivity recorded over dependent lung regions. The findings indicate that near RV some but not all of the dependent airways must be closed. Furthermore, the distribution of airway closure completely accounts for the distribution of a bolus inhaled from RV.

Adult↗