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PubMed1976

Pulmonary elasticity in children and adolescents.

Static (Cst(L)), dynamic (Cdyn(L)), and "specific lung compliance (CL/TLC, CL/FRC) and the elastic recoil pressure of the lungs (Pst/(L)) were measured in 131 healthy children and the adolescents (age 6 to 17 years) from simultaneous recordings of esophageal pressure and lung volume. Esophageal elastance and vertical esophageal pressure gradients were also studied. Pst(L), measured at different lung volumes (fractional) from the expiratory quasi-static pressure-volume (PV) curves of the lungs, increased significantly with increasing body height, age, and body surface. Cst(L), determined from the midportion of PV curves, and Cdyn(L) measured during normal breathing at frequencies around 20/min also increased significantly with somatic growth. "Specific" Cst(L) decreased with increasing body height, age, and body surface. "Specific" Cdyn(L), esophageal elastance, and the vertical esophageal pressure gradient were independent of body height, age, and body surface, Cdyn(L) was less than Cst(L) mainly in smaller and younger children, and was not considered a valid index of pulmonary elasticity. Values of Pst(L), "specific" Cst(L), and the change of slope of the midportion of PV curves in children and adolescents suggested developmental changes of pulmonary elasticity in man over the age range studied.

Adolescent↗
PubMed1987

Longitudinal elastic wave propagation in pulmonary parenchyma.

Consideration of the lung as an elastic continuum led us to investigate the possible propagation of elastic waves. Here the relevant stiffness and density are given by the Lamé constants and density of the parenchyma. To test this hypothesis, we measured propagation velocities (c) in dog lobes by recording transit times of a velocity impulse on one side of the lobe and the subsequent arrival on the other side. We compared our measured values of c with elastic longitudinal wave velocities (c long) predicted by values of elastic moduli given by Lai-Fook et al. (J. Appl. Physiol. 40: 508-513, 1976) as a function of translobar pressure (PL) and our measured densities. Good agreement was found between c and c long. Typical values of c ranged from 250-1,500 cm/s as PL ranged from 2-20 cmH2O. No systematic difference in the c-c long relation was found between inflation and deflation, suggesting that the elastic moduli of lungs are essentially a function of pressure. No significant effect was observed by changing the physical properties of the gas within the lobe [air vs. He vs. sulfur hexafluoride (SF6)], suggesting that indeed we were observing waves associated with the coupling of parenchymal density to parenchymal stiffness.

Animals↗
PubMed1990

Elastic energy storage in tendons: mechanical differences related to function and age.

We investigated the possibility that tendons that normally experience relatively high stresses and function as springs during locomotion, such as digital flexors, might develop different mechanical properties from those that experience only relatively low stresses, such as digital extensors. At birth the digital flexor and extensor tendons of pigs have identical mechanical properties, exhibiting higher extensibility and mechanical hysteresis and lower elastic modulus, tensile strength, and elastic energy storage capability than adult tendons. With growth and aging these tendons become much stronger, stiffer, less extensible, and more resilient than at birth. Furthermore, these alterations in elastic properties occur to a significantly greater degree in the high-load-bearing flexors than in the low-stress extensors. At maturity the pig digital flexor tendons have twice the tensile strength and elastic modulus but only half the strain energy dissipation of the corresponding extensor tendons. A morphometric analysis of the digital muscles provides an estimate of maximal in vivo tendon stresses and suggests that the muscle-tendon unit of the digital flexor is designed to function as an elastic energy storage element whereas that of the digital extensor is not. Thus the differences in material properties between mature flexor and extensor tendons are correlated with their physiological functions, i.e., the flexor is much better suited to act as an effective biological spring than is the extensor.

Age Factors↗
PubMed1990

Effects of elastic loading on porcine trachealis muscle mechanics.

To shorten in vivo, airway smooth muscle must overcome an elastic load provided by cartilage and lung parenchyma. We examined the effects of linear elastic loads (0.2-80 g/cm) on the active changes in porcine trachealis muscle length and tension in response to electrical field stimulation in vitro. Increasing elastic loads produced an exponential decrease in the shortening and velocity of shortening while causing an increase in tension generation of muscle strips stimulated by electrical field stimulation. Shortening was decreased by 50% at a load of 8 g/cm. At small elastic loads (less than or equal to 1 g/cm) contractile responses approximated isotonic responses (shortening approximately 60% of starting length), whereas at large loads (20 g/cm) responses approximated isometric responses with minimal shortening (20%). We conclude that elastic loading significantly alters the mechanical properties of airway smooth muscle in vitro, effects that are likely relevant to the loads against which the smooth muscle must contract in vivo.

Animals↗
PubMed2004

Role of rib cage elastance in the coupling between the abdominal muscles and the lung.

The abdominal muscles expand the rib cage when they contract alone. This expansion opposes the deflation of the lung and may be viewed as pressure dissipation. The hypothesis was raised, therefore, that alterations in rib cage elastance should affect the lung deflating action of these muscles. To test this hypothesis and evaluate the quantitative importance of this effect, we measured the changes in airway opening pressure (Pao), abdominal pressure (Pab), and rib cage transverse diameter during isolated stimulation of the transversus abdominis muscle in anesthetized dogs, first with the rib cage intact and then after rib cage elastance was increased by clamping the ribs and the sternum. Stimulation produced increases in Pao, Pab, and rib cage diameter in both conditions. With the ribs and sternum clamped, however, the change in Pab was unchanged but the change in Pao was increased by 77% (P < 0.001). In a second experiment, the transversus abdominis was stimulated before and after rib cage elastance was reduced by removing the bony ribs 3-8. Although the change in Pab after removal of the the ribs was still unchanged, the change in Pao was reduced by 62% (P < 0.001). These observations, supported by a model analysis, indicate that rib cage elastance is a major determinant of the mechanical coupling between the abdominal muscles and the lung. In fact, in the dog, the effects of rib cage elastance and Pab on the lung-deflating action of the abdominal muscles are of the same order of magnitude.

Abdominal Muscles↗
PubMed1984

Distribution of elastic system fibers in hyaline and fibrous cartilages of the rat.

Rat hyaline and fibrous cartilages whose glycosaminoglycans had been removed by hyaluronidase digestion were studied by comparing the ultrastructural features with the observation of sections stained by selective methods for elastic system fibers under the light microscope. Except for the fibrous layer in the perichondrium of tracheal hyaline cartilage, where elastic fibers were found, no elastic fibers could be detected in the cartilages studied. However, cartilaginous tissues contained oxytalan and elaunin fibers. A distinct pattern of distribution of the above-mentioned elastic-related fibers could be observed in both kinds of cartilages. Hyaline cartilages possess oxytalan fibers in the extracellular matrix that surrounds the chondrocytes, whereas elastic fibers were localized in the fibrous layer of the perichondrium that encloses the cartilage. Elaunin fibers could be detected in the transition (chondrogenic) layer adjacent to the perichondrium. The methods used disclosed the presence of oxytalan and elaunin fibers running along the periphery of the collagen bundles in fibrocartilage.

Animals↗
PubMed1997

Is elastic energy storage of quantitative relevance for the functional morphology of the human locomotor apparatus?

Elastic storage of energy in the vertebrate locomotor apparatus is supposed to be an important functional factor in cyclic and acyclic movements. In terms of physics, for humans a proof for the occurrence and quantitative relevance of this phenomenon in vivo and under physiological conditions has been missing until now. In addition to the large amount of plausible, but inconclusive information about elasticity in humans and animals, we describe a simple experiment to prove the existence of quantitatively relevant elastic energy storage in the human locomotor apparatus. Ten volunteers (5 female, 5 male) each assumed a relaxed, upright posture on a steel platform. After the release of a support, the volunteers and the platform fell for a defined distance of 33 mm. Loaded with the volunteers, the platform fell significantly (p < 0.001) faster than predicted by the laws of stiff body mechanics (50 vs. 82 ms). For a minimum time of 50 ms, the human locomotor apparatus is able to support an average external power output of more than 400 W by means of an energy transfer of more than 20 J. During the fall, no EMG activities of the ankle flexors could be recorded. We conclude that the acceleration of the platform fall is induced by elastic elements serving as energy sources. Elastic energy storage is of quantitative relevance for the functional morphology and biomechanics of the human locomotor apparatus.

Adult↗
PubMed1976

Measurement of the elasticity of the male urethral meatus by urinary drop spectrometry.

The urinary stream breaks up into drops shortly after leaving the external meatus. For normal males the frequency of the drops is related in a characteristic way to the flow rate. From this relation the elastic properties of an elastic constriction near the external meatus are calculated, using a theory of flow through distensible tubes. The elastic constriction behaves as if rigid at low flow rates, but distends elastically at flow rates above a critical value. This theoretical result is verified by observations of the stream emerging from a mechanical model, constructed with similar elastic properties. Functional meatal stenosis is associated with a lack of distensibility at the higher flow rates, which is reflected clinically in a changed relation between drop frequency and flow rate. Measurement of the relation, by the urinary drop spectrometer, offers a quick, non-invasive way of diagnosing this type of urethral obstruction.

Elasticity↗
PubMed2000

Assessment of aortic line of elasticity using polynomial regression analysis.

BACKGROUND: The aim of this study was to assess the sigmoid line of elasticity in the human aorta. METHODS AND RESULTS: The pressure-diameter relation was measured in the descending aorta in 120 subjects. In an additional group of 6 subjects, transient vena caval occlusion produced 5 sets of pressure-diameter data. We found that the best fit curve of the pooled pressure-diameter data was a third-order polynomial. A polynomial equation was used to calculate the sigmoid line of elasticity in the entire population and after the administration of diltiazem (15 patients) or enalaprilat (10 patients). The sigmoid line of elasticity was significantly different with respect to age (P<0.001), history of hypertension (P<0.004), and hypercholesterolemia (P<0.02). The difference between the transition point and the peak systolic pressure was increased in normal subjects compared with patients (P<0.0001). The sigmoid line shifted leftward and upward with diltiazem, but it remained unchanged with enalaprilat. During an average of 3 years of follow-up, 19 of 88 patients developed stroke (n=4), unstable angina (n=8), acute myocardial infarction (n=4), or acute pulmonary edema (n=3). CONCLUSIONS: This approach provides a quantitative evaluation of the aortic line of elasticity, which can differentiate the intrinsic from the extrinsic aortic elastic properties. Furthermore, it is a powerful and independent risk factor for cardiovascular events.

Aorta↗
PubMed1990

Is standardization of left ventricular chamber elastance necessary?

Because of the relation between left ventricular (LV) chamber elastance and heart size, it has been hypothesized that maximum time-varying elastance (Emax) must be standardized to differentiate between preserved and depressed LV systolic performance. To test this hypothesis, we studied 66 patients, of whom 25 had a normal LV, 20 had aortic regurgitation, 14 had mitral regurgitation, and seven had cardiomyopathy, with micromanometer-determined LV pressures and radionuclide angiograms during multiple LV loading conditions. Multiple regression analysis established that Emax was independently related to LV end-diastolic volume (r = -0.69). When the Emax and LV end-diastolic volume (EDV) data from all patients were plotted, a curvilinear relation was evident. Data transformation to the base e identified two distinct linear relations, one in the normal patients of lnEmax = -0.60 (lnEDV) +4.34 (r = -0.67, p less than 0.001); and one in the patients with cardiac pathology of lnEmax = -1.06 (lnEDV) +6.12 (r = -0.73, p less than 0.001), which differed from each other (p less than 0.01). When a mathematical standardization was applied to these data to eliminate the independent contribution of heart size to the reduction in lnEmax, the normal patients had a standardized lnEmax versus lnEDV slope of 0, whereas that in the patients with cardiac pathology remained negative and continued to differ from that in the normal patients (p less than 0.001). Dichotomization of patients with cardiac pathology into those with preserved and depressed LV chamber elastance by lnEmax or standardized lnEmax provided highly concordant data (k = 0.73, p less than 0.001). Moreover, the estimated contribution of LVEDV to the reduction in Emax in patients with cardiac pathology averaged only 14 +/- 7%. We conclude from these data that LV chamber elastance calculated with radionuclide angiography has an independent relation with LVEDV, that a mathematical standardization of Emax for heart size does not significantly alter the dichotomization of patients with cardiac pathology into those with preserved and depressed LV systolic performance, and that heart size makes a relatively small contribution to the reduction in this index of LV systolic performance. Thus, standardization for heart size may not be necessary to identify whether preserved or depressed LV chamber elastance exists in an individual adult patient with cardiac pathology compared with normal adult patients.

Adult↗
PubMed1994

Measurement of regional elastic properties of the human aorta. A new application of transesophageal echocardiography with automated border detection and calibrated subclavian pulse tracings.

BACKGROUND: Evaluation of regional aortic elastic properties in humans has been hampered by the need for invasive techniques to access instantaneous aortic pressure, wall thickness, and cross-sectional area or diameter. In this study, a new noninvasive method is presented for quantification of regional aortic elastic properties. METHODS AND RESULTS: Twenty-five patients were studied during transesophageal echocardiographic procedures. Measurements of instantaneous aortic cross-sectional area were obtained with an automated border detection algorithm applied to short-axis transesophageal two-dimensional echocardiographic images of the proximal descending thoracic aorta. Instantaneous aortic wall thickness was derived from combined two-dimensional targeted M-mode end-diastolic wall thickness and instantaneous aortic area measurements. Instantaneous aortic pressures were estimated from calibrated subclavian pulse tracings recorded simultaneously. Data were digitized to generate aortic area-pressure loops. Regional aortic mechanical properties were quantified in terms of compliance per unit length (C is the slope of the area-pressure regression), aortic midwall radius (Rm), and incremental elastic modulus of the aortic wall (Einc). To assess the independent effect of age, Rm and Einc values were compared at a common level of aortic midwall stress (0.666 x 10(6) dynes/cm2). Mean values (+/- SD) for C, Rm, and Einc were 0.01 +/- 0.004 cm2/mm Hg, 1.14 +/- 0.17 cm, and 7.059 +/- 4.091 x 10(6) dynes/cm2, respectively. An inverse linear correlation was found between aortic compliance per unit length and age (r = -.68, P < .0007). Incremental elastic modulus was related to age (r = +.80, P < .00003) in a nonlinear fashion such that it increased sharply after the age of 60 years. Finally, midwall radius was less tightly correlated with age (r = +.45, P < .05). Values for C, Rm, and Einc as well as the age dependency of these properties are similar to those reported previously when invasive techniques were used. CONCLUSIONS: This methodology constitutes a new tool to improve the clinical evaluation of regional aortic elastic properties in multiple disease states.

Adult↗
PubMed1997

Unfavorable effect of smoking on the elastic properties of the human aorta.

BACKGROUND: Smoking is a major risk factor for cardiovascular morbidity and mortality. Because previous studies have shown that smoking affects vasomotor response, we hypothesized that smoking may also acutely alter aortic elastic properties. METHODS AND RESULTS: We studied 40 male current and long-term smokers who underwent diagnostic cardiac catheterization for chest-pain evaluation. Twenty subjects (age, 48 +/- 2 years, mean +/- SEM) were randomly assigned to smoking and 20 (age, 47 +/- 2 years) to sham smoking studies. Aortic elastic properties were studied with the determination of the aortic pressure-diameter relation before smoking, every minute for the first 5 minutes after the initiation of smoking or sham smoking, and every 5 minutes for the following 15 minutes. Instantaneous diameter of the thoracic aorta was measured with a special ultrasonic dimension catheter developed in our laboratory and previously validated. Instantaneous aortic pressure was measured at the same site as was diameter with a Millar micromanometer. Smoking was associated with significant changes in the aortic pressure-diameter relation that denote deterioration of the elastic properties and were maintained during the whole study period: the slope of the pressure-diameter loop became steeper (baseline, 35.43 +/- 1.38; minute 1, 45.26 +/- 1.65; peak at minute 10, 46.36 +/- 1.69 mm Hg/mm; P < .001) and aortic distensibility decreased (baseline, 2.08 +/- 0.12; minute 1, 1.60 +/- 0.08; nadir at minute 5, 1.54 +/- 0.07 x 10(-6) cm2.dyne-1; P < .001). In contrast, no changes in aortic elasticity indexes were observed with sham smoking. CONCLUSIONS: Smoking is associated with an acute deterioration of aortic elastic properties. This effect of smoking may contribute to the unfavorable consequences of smoking on the cardiovascular system.

Aorta, Thoracic↗
PubMed1995

Direct effects of smooth muscle relaxation and contraction on in vivo human brachial artery elastic properties.

The direct effect of smooth muscle relaxation on arterial elastic properties is controversial. Studies in animals show both a decrease and an increase in elastic modulus. In human subjects, the contribution of smooth muscle to arterial elastic mechanics has been limited by difficulty in separating the direct effects of a vasodilator drug on the arterial wall from the indirect effects due to reduced blood pressure. The purpose of the present study was to assess the direct contribution of vascular smooth muscle to brachial artery elastic mechanics in normal human subjects in vivo. We measured brachial artery compliance and incremental elastic modulus (Einc) in eight normal subjects (age, 22 to 51 years) by using intravascular ultrasound. A 3.5F 30-MHz intravascular ultrasound catheter was placed through a sheath into the brachial artery, and intraarterial pressure, cross-sectional area, and wall thickness were measured simultaneously under baseline conditions and after the administration of intra-arterial nitroglycerin (100 micrograms) and norepinephrine (1.2 micrograms). A pressurized cuff surrounding the brachial artery was inflated to reduce transmural brachial artery pressure. Using this technique, we were able to measure the following arterial characteristics for the first time in human subjects in vivo: (1) the effective unstressed arterial radius and (2) the pressure-area, stress-strain, and pressure-Einc relations over a wide pressure range (0 to 100 mm Hg). Intra-arterial nitroglycerin increased brachial artery area by 22% and intraarterial norepinephrine decreased brachial artery area by 17% at 100 mm Hg transmural pressure (P < .001 versus baseline).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

Involvement of internal elastic lamina in development of induced cerebral aneurysms in rats.

To elucidate the role of the internal elastic lamina in the development of cerebral aneurysm, the bifurcation of the anterior cerebral artery and olfactory artery was histologically studied in control and experimental rats treated with unilateral carotid ligation and renal hypertension. Various stages of aneurysm formation were compared, and it was found that early aneurysmal changes were always present just distal to the apical intimal pad on the anterior cerebral artery side. The internal elastic lamina was thinned and fragmented just distal to the pad even in the very early stage of aneurysm formation when the medial layer was still present. In control rats, the internal elastic lamina had a tendency to thin and fragment at the site where aneurysms would develop in experimental rats. Our study shows that changes of the internal elastic lamina were present just distal to the pad even in control rats, which never develop cerebral aneurysms. Under hemodynamic stress augmented by experimental treatments, further degenerative changes of the internal elastic lamina and involvement of the medial layer are considered to occur and result in aneurysm formation there.

Animals↗
PubMed2005

Risk factors identified in childhood and decreased carotid artery elasticity in adulthood: the Cardiovascular Risk in Young Finns Study.

BACKGROUND: Exposure to risk factors in childhood may have long-term influences on vascular function. We examined the relationship between risk factors identified in childhood and arterial elasticity assessed in adulthood. METHODS AND RESULTS: Carotid artery compliance (CAC), Young's elastic modulus (YEM), and stiffness index (SI), 3 measures of large-artery elasticity, were assessed with noninvasive ultrasound in 2255 healthy white adults aged 24 to 39 years participating in a population-based cohort study and who had risk factor data available since childhood. In multivariate models, childhood obesity (skinfold thickness) predicted decreased CAC (P<0.001), increased YEM (P<0.01), and increased SI (P<0.01) in adulthood. Childhood blood pressure was inversely associated with CAC (P<0.001) and directly associated with YEM (P<0.001). The number of risk factors identified in childhood, which included high LDL cholesterol (at or above 80th percentile), elevated blood pressure, skinfold thickness, low HDL cholesterol (at or below 20th percentile), and smoking, was related inversely with CAC (P<0.001) and directly with YEM (P<0.001). These associations remained highly significant after adjustment for the number of risk factors identified in adulthood (P=0.005 for CAC and P<0.001 for YEM). CONCLUSIONS: Cardiovascular risk factors identified in childhood and adolescence predict decreased carotid artery elasticity in adulthood. These data suggest that risk factors operating in early life may have sustained deleterious effects on arterial elasticity.

Adolescent↗
PubMed2002

Retrovirally mediated overexpression of versican v3 by arterial smooth muscle cells induces tropoelastin synthesis and elastic fiber formation in vitro and in neointima after vascular injury.

Versican is an extracellular matrix (ECM) proteoglycan that is synthesized as multiple splice variants. In a recent study, we demonstrated that retroviral-mediated overexpression of the variant V3, which lacks chondroitin sulfate (CS) chains, altered arterial smooth muscle cell (ASMC) phenotype in short-term cell culture. We now report that V3-overexpressing ASMCs exhibit significantly increased expression of tropoelastin and increased formation of elastic fibers in long-term cell cultures. In addition, V3-overexpressing ASMCs seeded into ballooned rat carotid arteries continued to overexpress V3 and, at 4 weeks after seeding, produced a highly structured neointima significantly enriched in elastic fiber lamellae. In contrast to the hydrated, myxoid neointima produced by rounded or stellate vector-alone--transduced cells, V3-expressing cells produced a compact and highly ordered neointima, which contained elongated ASMCs that were arranged in parallel arrays and separated by densely packed collagen bundles and elastic fibers. These results indicate that a variant of versican is involved in elastic fiber assembly and may represent a novel therapeutic approach to facilitate the formation of elastic fibers.

Animals↗
PubMed1996

Bronchial elastic fibers in normal subjects and asthmatic patients.

Elastic fibers required to maintain bronchial patency during ventilation may be damaged in asthma as a result of repair following inflammation or stretching during exacerbations. Fifteen normal subjects and 40 asthmatics of variable severity were studied. Bronchial biopsies were obtained from a subsegmental bronchus using a flexible bronchoscope. The elastic fibers were examined using orceine-eosine sustaining and/or immunohistochemistry with two monoclonal antibodies against elastin or transmission electron microscopy (six asthmatics and four control subjects). Orceine-eosine staining revealed that most normal subjects had normal fibers throughout the submucosa whereas of the 21 asthmatics analyzed only three had a normal superficial elastin network. In five patients, elastin had virtually disappeared. In the remaining patients, fibers appeared fragmented. The deeper layer of elastic fibers was abnormal in 17 asthmatics, fibers being patchy, tangled, and thickened. The fragmentation of the superficial network of elastic fibers shown in asthmatics was confirmed by immunohistochemistry. Electron microscopy studies suggested that the elastinolytic process and fragmentation of elastic fibers occurred in asthmatics. Elastinolysis occurs in the airways of asthmatics possibly as a result of repair elicited by chronic inflammation. Mechanical stretch induced by breathing and edema may lead to the fragmentation of fibers in asthmatic airways.

Adult↗
PubMed1979

Age-related changes in elastic fibers and elastin of lung.

The effect of age on the lung elastic tissue of inbred BALB/c mice were studied. Static compliance of excised lungs increased with age. Morphometrically determined total elastic fiber length increased with lung expansion in age- and sex-matched mice (r = 0.83, P smaller than 0.001), indicating an axial extension of elastic fibers. However, total elastic fiber length of aging lungs fixed at a distending pressure of 15 cm H2O showed no significant change despite an age-related increase in lung volume (male, r = 0.96, P smaller than 0.001; female, r = 0.95 P smaller than 0.001). The correlative finding of decreased elastin content (r = -0.87, P smaller than 0.001) indicates that there is a loss of elastic fibers in the aging lung. It is suggested that the absence of pseudoelastin fibers, as demonstrated by histochemical techniques, accounts for the observed differences in elastin content of aging human and mouse lungs.

Aging↗