Biomedical subjects

L A Engel

Publications and source records attributed to L A Engel.

At least 37 records · Page 2Linked to original sources

PubMed1991

Influence of posterior cricoarytenoid muscle activity on pressure-flow relationship of the larynx.

We examined the effect of posterior cricoarytenoid (PCA) muscle activity on the pressure-flow (PV) relationship of the larynx in five anesthetized tracheostomized dogs. The PCA activity was recorded using bipolar fine-wire electrodes, expressed as a percentage of the quiet breathing level and altered by mechanical ventilation, changes in lung volume, and chest wall compression. Subglottic pressure was recorded while a constant flow of air was passed through the upper airway. In the absence of PCA activity the PV relationship was alinear and could be described by a power function (P = K0Va, where K0 and a are constants). The slope of the log P-log V plots in the absence of PCA and thyroarytenoid activity was 1.83 +/- 0.02 (SD), whereas with increasing PCA activity it was 1.88 +/- 0.11. An effective hydraulic diameter (DH) was calculated for 20% increments of PCA activity, and in two dogs glottic diameter (Dg) was calculated from glottic area measurements obtained by fiber-optic laryngoscopy. Both DH and Dg increased linearly with increasing PCA activity. Denervation of the cricothyroid muscle had no systematic effect on laryngeal resistance. The results indicate that the PV relationship of the larynx may be described by a power function with a single exponent, the magnitude of which is independent of glottic dilator muscle activity and consistent with orifice flow. However, laryngeal diameter increases linearly with PCA activity in the range studied.

Airway Resistance↗

PubMed1991

Blood flow distribution within the rib cage muscles.

We used 15-microns radiolabeled microspheres to study the regional distribution of blood flow (Q) among parasternal (PS), transversus thoracis, and external (EI) and internal intercostal muscles (II) in nine anesthetized supine mongrel dogs. We measured Q (ml.min-1.100 g-1) in each intercostal space (ICS) during spontaneous breathing, inspiratory resistive loading, and mechanical ventilation following paralysis. At necropsy the EI, II, and PS were excised and sampled separately for each ICS. During paralysis there was no consistent gradient in Q among the PS, II, and EI muscles. During spontaneous breathing, Q to PS increased linearly by 125% between the first and fourth to sixth ICS, Q to EI decreased progressively from the first/second ICS to the fifth/sixth ICS, whereas Q to the II was uniform. During inspiratory resistive loading, in which mouth pressures of -16 +/- 4 cmH2O were generated, the PS gradient was similar to that during spontaneous breathing. Also, Q to the EI increased in the cranial interspaces (P less than 0.02), whereas Q to the II of the seventh/eighth ICS was greater than that of the first/second ICS (P less than 0.001). Furthermore, with loading, ventrodorsal gradients in Q appeared within both EI and II interspaces. There was no consistent gradient in Q within the transversus thoracis muscle during any of the interventions. Our results demonstrate nonuniform Q within PS, EI, and II during both spontaneous and inspiratory resistive loaded breathing. On the assumption that changes in Q reflect changes in activation, our results suggest systematic topographical patterns of recruitment of rib cage respiratory muscles.

Animals↗

PubMed1991

Relationship between alae nasi activation and breathing route during exercise in humans.

We studied the relationship between alae nasi muscle (AN) activation and breathing route in normal subjects during exercise. Nasal and oral airflow were measured simultaneously using a partitioned face mask and were recorded with the AN electromyogram. Subjects breathed via 1) the nose and mouth (NM) 2) the nose only (N), or 3) the mouth only (M). As ventilation (VE) rose progressively, the peak phasic inspiratory AN activity (IAAN) increased for all breathing routes. IAAN during N [11.8 +/- 2.0 arbitrary units (AU)] was greater than during NM (3.3 +/- 1.3 AU) and M (2.4 +/- 1.0 AU; P less than 0.01) measured at the highest common VE (over a 10-l/min range). At the highest 20% of IAAN recorded during NM, the total VE during N (24 +/- 5 l/min). However, for the same IAAN, nasal VE during NM (27 +/- 3 l/min) was similar to that during N. Thus, as ventilation increases during exercise, AN activity and nasal ventilation are tightly correlated, independently of flow through the mouth. This suggests either reflex modulation of AN activity by nasal flow or coordination of AN activation with the flow-partitioning mechanism of the upper airway.

Adult↗

PubMed1991

Oronasal partitioning of ventilation during exercise in humans.

The partitioning of oronasal breathing was studied in five normal subjects during progressive exercise. Subjects performed three to five identical runs, each consisting of four 1-min work periods at increments of 50 W. Nasal and oral airflow were measured simultaneously using a partitioned face mask both during and for 4 min after exercise. Total mean flows were the sum of nasal and oral flows. At a total mean inspiratory flow of 2 l/s, the nasal fraction of total flow was 0.36 +/- 0.04 (SE) and decreased by 6 +/- 3% between total flows of 1.5 and 2.5 l/s. Throughout exercise, the nasal fraction of total mean inspiratory flow did not differ from that of total expiratory flow and was similar to that of total mean inspiratory flow during the postexercise period at a corresponding total mean flow (both P greater than 0.02). The results show that oronasal flow partitioning is not directly due to the exercise itself but is related to the level of ventilation and is uninfluenced by the direction of upper airway flow (i.e., inspiratory vs. expiratory). These findings suggest tightly controlled modulation of the relative resistances of the oral and/or nasal pathways.

Adult↗

PubMed1991

Regional distribution of blood flow within the diaphragm.

We investigated the regional distribution of blood flow (Q) within the costal and crural portions of the diaphragm in a total of eight anesthetized supine mongrel dogs. Q was measured with 15-microns microspheres, radiolabeled with three different isotopes, injected into the left ventricle during spontaneous breathing (SB), inspiratory resistive loading (IR), and mechanical ventilation after paralysis (P). At necropsy, the costal and crural portions of each hemidiaphragm were arbitrarily subdivided along a sagittal plane into five to seven and three sections, respectively. During P, there was a dorsoventral Q gradient within the costal part of the diaphragm. During SB there was a fourfold increase in the gradient of Q. Furthermore, during IR, in which mouth pressures of -16 +/- 4 cmH2O were generated, there was a further increase in the gradient of Q. During both SB and IR, Q to the most ventral portion of the costal diaphragm was 26 +/- 6% less than the peak value. In two dogs, studied prone and supine, there was no difference in the Q gradients between the two postures. Over the dorsal 80% of the costal diaphragm there was also a dorsoventral gradient of muscle thickness, such that the most dorsal part was 54 +/- 2% (n = 5) that of the ventral portion. In contrast, there was no consistent gradient of Q or muscle thickness within the crural diaphragm. Our results demonstrate a topographical gravity-independent distribution of Q in the costal, but not the crural, diaphragm.(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthesia↗

PubMed1991

Posterior cricoarytenoid activity and glottic size during hyperpnea in humans.

We measured the electromyographic activity of the posterior cricoarytenoid (PCA) muscle simultaneously with glottic width (dg) in five normal human subjects during hyperpnea induced by hypoxia (7% CO2 in N2) or hypercapnia (9% CO2 in 50% O2). The glottic aperture was measured during inspiration at the time corresponding to peak inspiratory PCA activity and during expiration at the time corresponding to the minimum tonic activity. During hyperpnea, peak and tonic PCA activity increased simultaneously with widening of the vocal cords in both phases of the respiratory cycle. The PCA activity during both inspiration and expiration showed a single curvilinear relationship with dg of the form dg = A - Be-k.PCA (where A, B, and k are constants) in three of the five subjects. At 50% of maximum PCA activity, dg already reached 95% of its maximum value, which was less than that recorded during a voluntary forced expiratory maneuver. The single curvilinear relationship between PCA activity and dg could be due to the length-tension relationship of the PCA muscle and/or changes in its mechanical coupling, as well as simultaneous agonist and antagonist laryngeal muscle activity during progressive chemical stimulation. Also, further widening of the glottis during forced expiration suggests recruitment of additional muscles, e.g., the arytenoideus.

Adult↗

PubMed1991

Lung and chest wall mechanics in microgravity.

We studied the effect of 15-20 s of weightlessness on lung, chest wall, and abdominal mechanics in five normal subjects inside an aircraft flying repeated parabolic trajectories. We measured flow at the mouth, thoracoabdominal and compartmental volume changes, and gastric pressure (Pga). In two subjects, esophageal pressures were measured as well, allowing for estimates of transdiaphragmatic pressure (Pdi). In all subjects functional residual capacity at 0 Gz decreased by 244 +/- 31 ml as a result of the inward displacement of the abdomen. End-expiratory Pga decreased from 6.8 +/- 0.8 cmH2O at 1 Gz to 2.5 +/- 0.3 cmH2O at Gz (P less than 0.005). Abdominal contribution to tidal volume increased from 0.33 +/- 0.05 to 0.51 +/- 0.04 at 0 Gz (P less than 0.001) but delta Pga showed no consistent change. Hence abdominal compliance increased from 43 +/- 9 to 70 +/- 10 ml/cmH2O (P less than 0.05). There was no consistent effect of Gz on tidal swings of Pdi, on pulmonary resistance and dynamic compliance, or on any of the timing parameters determining the temporal pattern of breathing. The results indicate that at 0 G respiratory mechanics are intermediate between those in the upright and supine postures at 1 G. In addition, analysis of end-expiratory pressures suggests that during weightlessness intra-abdominal pressure is zero, the diaphragm is passively tensed, and a residual small pleural pressure gradient may be present.

Abdomen↗

PubMed1991

Influence of nasal airflow temperature and pressure on alae nasi electrical activity.

The influence of nasal airflow, temperature, and pressure on upper airway muscle electromyogram (EMG) was studied during steady-state exercise in five normal subjects. Alae nasi (AN) and genioglossus EMG activity was recorded together with nasal and oral airflows and pressures measured simultaneously by use of a partitioned face mask. At constant ventilations between 30 and 50 l/min, peak inspiratory AN activity during nasal breathing (7.2 +/- 1.4 arbitrary units) was greater than that during oral breathing (1.0 +/- 0.3 arbitrary units; P less than 0.005). In addition, the onset of AN EMG activity preceded inspiratory flow by 0.38 +/- 0.03 s during nasal breathing but by only 0.17 +/- 0.04 s during oral breathing (P less than 0.04). When the subject changed from nasal to oral breathing, both these differences were apparent on the first breath. However, peak AN activity during nasal breathing was uninfluenced by inspiration of hot saturated air (greater than 40 degrees C), by external inspiratory nasal resistance, or by changes in the expiratory route. The genioglossus activity did not differ between nasal and oral breathing (n = 2). Our findings do not support reflex control of AN activity sensitive to nasal flow, temperature, or surface pressure. We propose a centrally controlled feedforward modulation of phasic inspiratory AN activity linked with the tonic drive to the muscles determining upper airway breathing route.

Adult↗

PubMed1991

Nasal and oral airway pressure-flow relationships.

We examined the inspiratory and expiratory pressure-flow relationships of both the oral and nasal airways before and after exercise in normal upright subjects. With the use of a partitioned facemask, nasal resistance was measured using posterior rhinomanometry, and oral resistance was measured by recording transoral pressure during oral breathing. Both the nasal and oral pressure-flow relationships for inspiration and expiration were curvilinear and were well described by a power function of the form delta P = aVb (where P is pressure, V is flow, a and b are constants) (r2 = 0.96 +/- 0.01). The exponent b describes the curvilinearity of the pressure-flow curve and can be used to infer the flow regimen. At rest, the inspiratory nasal and oral curves suggested a similar degree of turbulence (b = 1.77 +/- 0.06 and 1.83 +/- 0.04, respectively). However, inspiratory flow regimens were inferred to be more turbulent than those during expiration both before and after exercise. After exercise, decreases in inspiratory nasal resistance at low flows were associated with a change in flow regimen from fully turbulent to orifice flow over the entire flow range. Thus the application of a power function to nasal and oral pressure-flow data permits representation of the whole relationship and allows insight into the nature of the flow regimens.

Adult↗

PubMed1990

Relationship between thyroarytenoid activity and laryngeal resistance.

We examined the relationship between subglottic pressure (P), flow (V), and thyroarytenoid (TA) muscle activity in six anesthetized tracheostomized dogs while a constant flow (0.05-1.2 l/s) of warmed humidified air was passed through the upper airway in an expiratory direction. The TA activity was recorded by fine bipolar wire electrodes and was reflexly altered by changes in lung volume and chest wall compression. The integrated muscle activity was expressed as a percentage of a maximal peak integrated TA activity (%max). In the absence of TA activity the pressure-flow relationship was alinear and could be described by a power function. Log-log P-V plots at varying levels of TA activity were linear, with a slope a of 1.84 +/- 0.07 (SD). When TA activity increased, laryngeal resistance increased exponentially. An effective hydraulic diameter was calculated for increments in %max TA and decreased linearly with %max TA. In three dogs the glottic diameter was computed from glottic area measured by fiber-optic laryngoscopy, and it also decreased linearly as TA increased. Sectioning of the external motor branch of the superior laryngeal nerve to the cricothyroid muscle demonstrated no consistent effect on laryngeal resistance over a range of TA activity. The results indicate that laryngeal dimensions decrease linearly with TA activity. However, the P-V relationship of the larynx may be described by a power function, with a single exponent consistent with an orifice flow regimen. Spontaneous activity of the cricothyroid muscle does not measurably influence this relationship.

Airway Resistance↗

PubMed1990

Distribution of inhaled 99mtechnetium labelled ultrafine carbon particle aerosol (Technegas) in human lungs.

Using a gamma camera, we quantified the topographical intrapulmonary distribution of inhaled 100 ml boluses of Technegas (TG), an ultrafine dispersion of carbon aggregates labelled with 99mTc, and 133Xenon (Xe) in six seated, normal subjects, inhaling from residual volume (RV) and from within a 1 l volume range above functional residual capacity (FRC) at a flow less than 0.5 l.s-1. Following inspiration of air to total lung capacity (TLC) counts were recorded during a 20 s breathhold. Twenty min after administration of the final TG bolus (TGF) counts were again recorded (TG20). Upper (U), middle (M) and lower (L) zones, as well as central (C) and peripheral (P) regions were identified in each lung. The relative fractional concentration (Fr) of TG and Xe was calculated for all zones after RV and FRC boluses, using counts obtained during Xe equilibration. The U/M or U/L ratios for XeFr did not differ significantly from those for TGFr (paired t-test; p greater than 0.1). The P/C count ratio constitutes a penetration index, which for TG was 1.07 +/- 0.13 (mean +/- SD) that of Xe. After correction for radioactive decay, TG20 counts were no different from TGF counts. The results suggest that the intrapulmonary distribution and penetration of TG in normal lungs is no different from Xe and that stable deposition in the lung periphery makes TG suitable for multiple-view imaging of ventilation distribution.

Adult↗

PubMed1990

Intrapulmonary distribution of 99mtechnetium labelled ultrafine carbon aerosol (Technegas) in severe airflow obstruction.

Technegas (TG), an ultrafine dispersion of carbon aggregates labelled with 99mTechnetium (99mTc), has been recently introduced for clinical imaging of lung ventilation. In 12 selected subjects with severe chronic airflow limitation (FEV1 = 0.89 +/- 0.22; mean +/- SD, l) we have studied the regional intrapulmonary distribution of TG and compared it quantitatively with that of 133Xenon (133Xe). A 133Xe equilibration image was acquired for 10-15 s during a breathhold at total lung capacity (TLC). Six subjects (Group 1) inspired 100 ml boli of TG or 133Xe from functional residual capacity (FRC) and another 6 subjects (Group 2) inspired 1.0 l of labelled gas from FRC followed by air to TLC at a constant flow rate less than 0.5 l.s-1. Lung images were then acquired with the chest position rigorously controlled. From the equilibration image, upper, middle, lower, central and peripheral regions were defined. Relative regional fractional concentrations (RFC) were then calculated using the equilibration image to correct for ventilated lung volume. In addition, in four of the Group 2 subjects, each lung image was divided into multiple regions (12-17 per lung). The RFC were then calculated as above (RFCM). The highest and lowest RFC were not significantly different between 133Xe and TG in either Group 1 or Group 2 subjects. Similarly the RFCM analysis showed no systematic difference between 133Xe and TG. The ratio of peripheral to central RFC constitutes a penetration index which for TG was 0.99 +/- 0.23 that of 133Xe. Our results indicate that even in the presence of severe airflow limitation the radiolabelled tracer TG mimics the regional distribution of a real gas.

Aged↗

PubMed1990

The effect of hyperinflation on respiratory muscle work in acute induced asthma.

To examine the relationship between end-expiratory lung volume and respiratory muscle work during acute bronchoconstriction, we measured the work of breathing in nine asthmatic subjects, in whom bronchoconstriction was induced with histamine aerosol. When the forced expiratory volume in one second (FEV1) fell below 60% of the control value, work was measured at the spontaneously hyperinflated lung volume (VLS), at a volume equivalent to the control functional residual capacity (FRC) and at a volume 30% of vital capacity (VC) above the control FRC. Hyperinflation to VLS caused a 39% decrease in the total positive work per breath from 2.8 +/- 0.4 to 1.7 +/- 0.1 J, entirely due to a decrease in expiratory work per breath from 1.6 +/- 0.4 to 0.10 +/- 0.05 J. Inspiratory work did not change at any lung volume, because the increase in inspiratory elastic work due to hyperinflation was offset by the decrease in flow resistive work. Breathing above VLS did not alter the total positive muscle work, but did increase the negative work of the inspiratory muscles from 0.4 +/- 0.1 to 0.8 +/- 0.1 J.breath. We conclude that during induced asthma spontaneous hyperinflation minimizes the total respiratory muscle work and may constitute a mechanism for minimizing energy expenditure.

Adult↗

PubMed1989

Postural changes in spontaneous and evoked regional diaphragmatic activity in dogs.

We addressed the question whether gravity-dependent differences in passive tension and length of the diaphragm are associated with differences in its regional activation. By using intramuscular electrodes, we measured the electromyographic activity of different parts of the diaphragm (Edi) during quiet breathing in several postures in 13 anesthetized mongrel dogs. The Edi of the left and right costal hemi-diaphragm was compared between the left and right lateral decubitus postures, whereas that from the substernal and crural regions was compared between the supine and prone positions. On changing posture, the Edi of the dependent part of the diaphragm decreased in both cases, whereas that of the non-dependent part increased. The results were consistent with reflex modulation of regional diaphragm activation in response to postural changes in local resting length. However, these changes in Edi persisted after bilateral vagotomy, cordotomy (C7-T1) and dorsal rhizotomy of the C5-C7 roots. Compound muscle action potentials, recorded in different regions of the diaphragm and evoked by supramaximal stimulation of the phrenic nerves, were altered with changes in posture in the same direction as Edi. Because the stimuli were supramaximal, these changes reflected systematic changes in the recording conditions with posture, possibly because of a combination of 1) changes in the electrical environment surrounding the intramuscular electrodes and 2) passive changes in muscle length. Our results demonstrate systematic, reproducible, posture-dependent changes in regional Edi that may not be due to different neural drive.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗

PubMed1989

Effect of lung volume on ventilation distribution.

To examine the effect of preinspiratory lung volume (PILV) on ventilation distribution, we performed multiple-breath N2 washouts (MBNW) in seven normal subjects breathing 1-liter tidal volumes over a wide range of PILV above closing capacity. We measured the following two independent indexes of ventilation distribution from the MBNW: 1) the normalized phase III slope of the final breaths of the washout (Snf) and 2) the alveolar mixing efficiency during that portion of the washout where 80-90% of the lung N2 had been cleared. Three of the subjects also performed single-breath N2 washouts (SBNW) by inspiring 1-liter breaths and expiring to residual volume at PILV = functional residual capacity (FRC), FRC + 1.0, and FRC - 0.5, respectively. From the SBNW we measured the phase III slope over the expired volume ranges of 0.75-1.0, 1.0-1.6, and 1.6-2.2 liters (S0.75, S1.0, and S1.6, respectively). Between a PILV of 0.92 +/- 0.09 (SE) liter above FRC and a PILV of 1.17 +/- 0.43 liter below FRC, Snf decreased by 61% (P less than 0.001) and alveolar mixing efficiency increased from 80 to 85% (P = 0.05). In addition, Snf and alveolar mixing efficiency were negatively correlated (r = 0.74). In contrast, over a similar volume range, S1.0 and S1.6 were greater at lower PILV. We conclude that, during tidal breathing in normal subjects, ventilation distribution becomes progressively more inhomogeneous at higher lung volumes over a range of volumes above closing capacity.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1989

Effect of airway closure on ventilation distribution.

We examined the effect of airway closure on ventilation distribution during tidal breathing in six normal subjects. Each subject performed multiple-breath N2 washouts (MBNW) at tidal volumes of 1 liter over a range of preinspiratory lung volumes (PILV) from functional residual capacity (FRC) to just above residual volume. All subjects performed washouts at PILV below their measured closing capacity. In addition five of the subjects performed MBNW at PILV below closing capacity with end-inspiratory breath holds of 2 or 5 s. We measured the following two independent indexes of ventilation maldistribution: 1) the normalized phase III slope of the final breaths of the washout (Snf) and 2) the alveolar mixing efficiency of those breaths of the washout where 80-90% of the initial N2 had been cleared. Between a mean PILV of 0.28 liter above closing capacity and that 0.31 liter below closing capacity, mean Snf increased by 132% (P less than 0.005). Over the same volume range, mean alveolar mixing efficiency decreased by 3.3% (P less than 0.05). Breath holding at PILV below closing capacity resulted in marked and consistent decreases in Snf and increases in alveolar mixing efficiency. Whereas inhomogeneity of ventilation decreases with lung volume when all airways are patent (J. Appl. Physiol. 66: 2502-2510, 1989), airway closure increases ventilation inequality, and this is substantially reduced by short end-inspiratory breath holds. These findings suggest that the predominant determinant of ventilation distribution below closing capacity is the inhomogeneous closure of airways subtending regions in the lung periphery that are close together.

Adult↗

PubMed1989

Lung volumes, chest wall configuration, and pattern of breathing in microgravity.

We studied the changes in functional residual capacity (FRC), thoracoabdominal volume (Vw), and chest wall configuration in five normal subjects seated in an aircraft flying parabolic trajectories resulting in 20-s periods of microgravity. We measured vital capacity (VC), inspiratory capacity, and tidal volume by integrating airflow at the mouth and changes in rib cage and abdominal volume (delta Vrc and delta Vab, respectively, where delta Vrc + delta Vab = delta Vw) using induction plethysmography. During microgravity (0 Gz) FRC decreased by 413 +/- 70 (SE) ml and VC by 0.37 liter. The decrease in Vw did not differ from that in FRC and was entirely the result of reduction of Vab, the Vrc showing no significant change. During tidal breathing the abdominal contribution (delta Vab/delta Vw) increased from 0.39 +/- 0.08 at 1 Gz to 0.57 +/- 0.08 at 0 Gz. During brief periods of hypergravity (approximately 1.8 Gz) all changes were opposite in sign and relatively smaller. Limited data during "roller coaster" flight patterns suggested that, in contrast to configurational changes, the temporal pattern of breathing was uninfluenced by changes in Gz. We conclude that at the onset of weightlessness there are substantial changes in lung volume and thoracoabdominal configuration. Abdominal contribution to tidal excursions increases but the temporal pattern of breathing is unchanged.

Abdomen↗

PubMed1989

Reversibility of induced bronchoconstriction by deep inspiration in asthmatic and normal subjects.

Five normal and five asthmatic subjects underwent a progressive methacholine provocation study. At each concentration inspiratory pulmonary resistance (RL) was measured, as well as isovolumic maximal flow and residual volume from both partial and complete forced expirations. Results were compared over the RL range of 6-11 cmH2O.1-1.S-1. The reversibility of bronchoconstriction by deep inspiration was quantified as the ratio of the flow increase to potential maximal increase; the reversibility of gas trapping was the ratio of decrease in residual volume to potential maximal decrease. The reversibility of bronchoconstriction did not differ between the groups. In contrast, the reversibility of gas trapping was smaller in asthmatic subjects (21 +/- 17%) than in normals (84 +/- 6%). As gas trapping reflects airway closure, our findings suggest that during induced bronchoconstriction airway closure is more resistant to the effects of deep inspiration in asthmatic than in normal subjects but the reversibility of bronchoconstriction by deep inspiration is not different.

Adult↗