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Biomedical subjects

D R Boughner

Publications and source records attributed to D R Boughner.

At least 19 recordsLinked to original sources
PubMed2000

Evaluation of 3-D colour Doppler ultrasound for the measurement of proximal isovelocity surface area.

Three-dimensional (3-D) colour Doppler ultrasound (US) enables flow rate estimation across a diseased valve without the need for a priori geometric assumptions. This study quantitatively evaluates the accuracy of 3-D colour Doppler US for measuring the flow rate (8. 3-75 mL/s) through a valve using the proximal flow convergence field. Flow rate measurements by this 3-D technique underestimate flow through finite circular orifices due to two major sources of error: 1. surface area slicing technique (18.3% +/- 3.8%) and 2. Doppler angle effect (41.0% +/- 1.5%). Combined total underestimation is 51% +/- 3.3%. To utilize 3-D US, the development of an improved proximal isovelocity surface area (PISA) measurement technique and a correction factor for the Doppler angle effect is required.

Blood Flow Velocity↗
PubMed2000

Three-dimensional echocardiography: assessment of inter- and intra-operator variability and accuracy in the measurement of left ventricular cavity volume and myocardial mass.

Accurate left ventricular (LV) volume and mass estimation is a strong predictor of cardiovascular morbidity and mortality. We propose that our technique of 3D echocardiography provides an accurate quantification of LV volume and mass by the reconstruction of 2D images into 3D volumes, thus avoiding the need for geometric assumptions. We compared the accuracy and variability in LV volume and mass measurement using 3D echocardiography with 2D echocardiography, using in vitro studies. Six operators measured the LV volume and mass of seven porcine hearts, using both 3D and 2D techniques. Regression analysis was used to test the accuracy of results and an ANOVA test was used to compute variability in measurement. LV volume measurement accuracy was 9.8% (3D) and 18.4% (2D); LV mass measurement accuracy was 5% (3D) and 9.2% (2D). Variability in LV volume quantification with 3D echocardiography was %SEMinter = 13.5%, %SEMintra = 11.4%, and for 2D echocardiography was %SEMinter = 21.5%, %SEMintra = 19.1%. We derived an equation to predict uncertainty in measurement of LV volume and mass using 3D echocardiography, the results of which agreed with our experimental results to within 13%. 3D echocardiography provided twice the accuracy for LV volume and mass measurement and half the variability for LV volume measurement as compared with 2D echocardiography.

Analysis of Variance↗
PubMed2000

The radiographic quantitation of aortic valve calcification: implications for assessing bioprosthetic valve calcification in vitro.

Calcification of natural aortic and bioprosthetic heart valves is a poorly understood phenomenon that results in valvular obstruction and tissue failure. We describe a non-destructive quantitative computed microtomographic (QCT) technique for determining both calcium content and local calcium distribution within explanted valves. As a reference standard, a dual-energy x-ray absorptiometry (DEXA) system with an accuracy demonstrated to be within 1% of the true calcium mass of test material was used to obtain the total calcium content of 24 human aortic valve cusps recovered at autopsy from patients aged 51-80 years. These cusps were then scanned using our unique volume QCT scanner, with multiple x-ray projections acquired by rotating the explanted tissue through a single axis of rotation. A three-dimensional cross-sectional map was reconstructed for each cusp. Voxel size was 0.003 mm3 and a calibration phantom was used to calculate calcium content. The minimum detection limit for calcium mass was 1 mg within the whole cusp. The DEXA and QCT scans were compared with respect to total calcium content, which ranged from 0 to 15 mg. An excellent correlation between the two independent techniques was demonstrated with an r2 value of 0.94 (p < 0.001). Non-destructive microtomographic CT scanning provided excellent volumetric density measurements, with quantitative 3D images permitting an assessment of any individual area of the cusp for calcium content and spatial distribution. This new approach to valve tissue analysis allows for subsequent histologic assessment.

Absorptiometry, Photon↗
PubMed2000

The aortic valve blood supply.

BACKGROUND AND AIM OF THE STUDY: Normal valves are known to be metabolically active, yet the route of oxygen delivery is unclear. Although diffusion from the valve surface is the presumed source, the presence, distribution and importance of the aortic valve's vascular bed is unclear. METHODS: Seventeen porcine hearts (51 cusps) were obtained at slaughter. The coronary circulation was pressure-rinsed with a heparin solution and filled with an Aquablack solution at physiological pressure. The cusps were subsequently dissected and fixed for viewing with an inverted microscope. The anterior leaflet of the mitral valve was evaluated as a control for the vessel filling protocol. Using Adobe Photoshop and captured images, whole cusps were reconstructed, a grid was overlaid and vascular distribution evaluated. RESULTS: Of the 15 porcine aortic valves that filled, 32/45 (71%) of the cusps contained vessels. Nine valves had vasculature in all three cusps and two valves were completely avascular. Vessels were found predominantly in the basal third of the cusps and extended in from the commissures almost to the level of the free edge. There was a statistically significant difference (p<0.001) between the appearance of vessels in the basal region and in the mid and free edge regions of the valve. No difference in vascularization pattern was noted between the left, right or non-coronary cusps. CONCLUSIONS: The presence of a vasculature suggests that the metabolic activity of the cusp is greater than can be supported by diffusion from the cusp surface alone. The absence of functioning vessels might explain the failure associated with cryopreserved implants and may play a role in the durability problems faced by bioprosthetic valves. It will also be important to consider the role of this intrinsic circulation with the advent of tissue-engineered valves.

Animals↗
PubMed2000

Intracoronary ultrasound imaging: methods and clinical applications.

OBJECTIVE: To review the development of intracoronary ultrasound, its current utility and the impetus for its continued development as a coronary imaging modality. DATA SOURCES: English-language literature (1966 to 1999) was searched in the MEDLINE database with the key words 'ultra- sound', 'intravascular' and 'intracoronary', and limited to human studies. In addition, an online public access catalogue was searched using the subject headings 'cardiovascular diseases - therapy', 'heart diseases' and 'vascular diseases'. STUDY SELECTION AND DATA EXTRACTION: Articles relating to the history of intravascular or intracoronary ultrasound, methods and materials employed, advantages and disadvantages, safety issues and future directions of research in the area of intracoronary ultrasound were selected. DATA SYNTHESIS: Intracoronary ultrasound has been shown to improve upon demonstrated weaknesses of coronary angiography. This imaging technique, while invasive, has not been associated with significant, acute adverse effects and has proved to be useful in guiding interventions, and evaluating the mechanism and extent of their success. Technological limitations with respect to the equipment employed, and the acquisition, processing and display of images are the subject of intense research focus because they hinder more widespread clinical use of intracoronary ultrasound. CONCLUSIONS: Intracoronary ultrasound has emerged as a safe and useful tool in the visualization of the coronary vasculature. Technological limitations and questions about long term safety are a concern. Its ability to overcome the inherent limitations of coronary angiography, and to guide and evaluate coronary interventions supports the notion that this technique will continue to assume an ever-expanding role in interventional cardiology.

Coronary Disease↗
PubMed2000

The pericardial bioprosthesis: altered tissue shear properties following glutaraldehyde fixation.

BACKGROUND AND AIM OF THE STUDY: Glutaraldehyde-fixed bovine pericardial tissue used in the construction of valvular bioprostheses undergoes repeated bending stress during the cardiac cycle. To bend smoothly, internal tissue shearing is required. The effect of glutaraldehyde fixation on internal shear properties of this material was examined. METHODS: Pericardium from each of 12 bovine hearts was cut into two pieces; one piece was retained as fresh tissue, the other was glutaraldehyde-fixed. Circular samples were then mounted and installed in a shear testing apparatus. For each sample, the shear stress versus shear strain characteristics were measured in circumferential and radial directions at strain rates of 1.0, 0.1 and 0.02 s(-1) while immersed in a 20 degrees C bath; similar measurements were made on six fresh and six fixed samples at 37 degrees C. In addition, the stress relaxation properties were measured by holding the tissue at maximum shear for 100 s after each of the three shear deformations, and recording force generated with time. RESULTS: The shear stress-strain test on fresh tissue (n = 12) showed non-linear behavior at the three shear rates. The shear modulus for fresh tissue increased from <1.0 kPa to 5 kPa at a shear strain approaching 1.0, and results were identical in radial or circumferential directions. For glutaraldehyde-fixed pericardium (n = 12), shear modulus increased promptly to 15-20 kPa at a strain of 0.2, and did not vary with strain rate. Shear relaxation was similar in fresh and fixed tissue. CONCLUSION: Fresh pericardium sheared easily at low shear stresses, with minimal resistance developing until the shear strain exceeded 0.5, while glutaraldehyde-fixed tissue displayed a marked resistance to shearing, with an immediate rise in shear stress at low strain. No differences were detected in shear properties between radial and circumferential directions. Such marked tissue stiffening may be a factor in collagen fiber disruption, leading to bioprosthetic heart valve failure.

Biomechanical Phenomena↗
PubMed1999

Quasi-Linear Viscoelastic theory applied to internal shearing of porcine aortic valve leaflets.

The elements of Quasi-Linear Viscoelastic (QLV) theory have been applied to model the internal shear mechanics of fresh and glutaraldehyde-fixed porcine aortic valve leaflets. A novel function estimation method was used to extract the material functions from experimental shear data obtained at one strain rate, and the model was used to predict the material response at different strain rates. In general, experiments and predictions were in good agreement, the larger discrepancies being in the prediction of peak stresses and hysteresis in cyclic shear. In shear, fixed tissues are stiffer (mean initial shear modulus, 13 kPa versus 427 Pa), take longer to relax to steady state (mean tau 2 4,736 s versus 1,764 s) with a slower initial relaxation rate (mean magnitude of G(0), 1 s-1 versus 5 s-1), and relax to a lesser extent than fresh tissues (mean percentage stress remaining after relaxation, 60 versus 45 percent). All differences were significant at p = 0.04 or less, except for the initial relaxation slope. We conclude that shear experiments can complement traditional tensile and biaxial experiments toward providing a complete mechanical description of soft biomaterials, particularly when evaluating alternative chemical fixation techniques.

Animals↗
PubMed1999

Laser-induced fluorescence (LIF) recognition of the structural composition of porcine heart valves.

Reconstruction and replacement of heart valves with grafts fro pig tissue is a common procedure. However, bioprosthetic valves wear out in a shorter time span than mechanical valves. Bioprosthetic valve structure may contribute to degenerative changes that lead to valve failure. There is, at present, no method to examine the structure of a tissue valve prior to implant. Laser-induced fluorescence (LIF) of natural fluorophores is an elegant method developed for the detection of tumors, dermal lesions and atherosclerosis. We have studied LIF as a potential diagnostic technique for analysis of valvular tissue. Using excimer laser excitation, we examined natural fluorescence recorded from porcine aortic, mitral and pulmonary valves. All three valve outflow surface tissue layers are less fluorescent at 390-450 nm than the inflow layers. Immunohistochemical analysis of collagen I and elastin content in inflow and outflow surface layers of all three valves correlated well with LIF intensities and dI/d lambda values at selected wavelengths. In conclusion, the differences observed in emitted LIF from valve surface layers are found to correlate well with diversity in the structural protein content. The LIF spectroscopic measurements may provide an appropriate tool for examination of tissue valve structure prior to use for implantation.

Animals↗
PubMed1998

Spongy left ventricular myocardium in an adult.

"Spongy left ventricular myocardium," or noncompaction of left ventricular myocardium, is a rare disorder of endomyocardial morphogenesis. It is usually seen in the pediatric population and is often associated with other congenital cardiac malformations. We describe an adult with noncompaction of left ventricular myocardium without associated congenital cardiac anomalies.

Adolescent↗
PubMed1997

Contrasting structure of the saphenous vein and internal mammary artery used as coronary bypass vessels.

OBJECTIVES: To report quantitatively on the three-dimensional layered organization of the collagen and smooth muscle component of the two most successful vessels for coronary bypass-the internal mammary artery (IMA) and the long saphenous vein (SV). Our aim was to provide an explanation for the differential structural stiffness of these two vessels (both functioning at arterial pressures in their new environment), and how they might be susceptible to endothelial thickening. METHODS: Eleven human saphenous veins and 23 internal mammary arteries were fixed at arterial distending pressure of 110 mmHg, and were sectioned in cross-section at 7 microns thickness. A subset of these was also sectioned tangentially. Measurements of the three-dimensional alignment of collagen and smooth muscle fibers within the vessel wall were made using polarized light microscopy and the universal stage attachment. Data were plotted and analysed using circular statistics. RESULTS: The IMA, structured like an elastic artery, is dominated by a media with discrete lamellae of wavy collagen and smooth muscle, aligned nearly circumferentially, with a low variability of alignment (mean circular SD 12 degrees). The SV is more variable in its size and structure, characteristically with a narrow circumferential media comprised mostly of collagen which is straightened and highly aligned at arterial pressures (mean circular SD 9 degrees). Circumferential collagen in the vein was often adjacent to longitudinal bundles of smooth muscle and collagen. CONCLUSIONS: The strikingly aligned structure of the SV complements the known high mechanical stiffness of this vessel when at arterial distending pressure. The high fraction of longitudinal muscle, in addition to the circumferential muscle cells in the SV make it vulnerable to any pre-implant surgical preparation, and to the cyclical luminal pressures and longitudinal strains characteristic for epicardial arteries.

Adult↗
PubMed1997

Myocardial collagen changes and edema in rats with hyperdynamic sepsis.

OBJECTIVE: To determine if sepsis, which is accompanied by both systolic and diastolic myocardial dysfunction, involves changes in myocardial collagen, as myocardial collagen changes can affect both myocardial compliance and contractility. DESIGN: Prospective, randomized, controlled study. SETTING: Animal laboratory at a university-affiliated hospital. SUBJECTS: Male Sprague-Dawley rats, weighing 310 to 396 g. INTERVENTIONS: Cecal ligation and perforation (to induce sepsis) for 24 (n = 9) or 48 hrs (n = 9); sham laparotomy for 24 (n = 10) or 48 hrs (n = 9) with saline fluid resuscitation or normal control (n = 5) groups. MEASUREMENTS AND MAIN RESULTS: Collagen content and interstitial space were determined, using polarized light microscopy and a computer video densitometry system. At 24 and 48 hrs post surgery, heart rate and cardiac index were increased, and systemic vascular resistance index was decreased significantly in the sepsis vs. the sham rats. Collagen content was decreased significantly in the sepsis vs. the sham groups both at 24 and 48 hrs following surgery (1.83 +/- 0.79 [SD] % [24 hrs], 1.76 +/- 0.31% [48 hrs] vs. 2.83 +/- 0.73% [24 hrs], 2.25 +/- 0.72% [48 hrs]; p < .01). Interstitial space was increased significantly in the sepsis vs. the sham groups (13.9 +/- 3.5% [24 hrs], 15.6 +/- 5.2% [48 hrs] vs. 8.6 +/- 4.2% [24 hrs], 9.9 +/- 4.8% [48 hrs]; p < .01). CONCLUSIONS: Sepsis is accompanied by changes in myocardial collagen content and myocardial edema. These changes may contribute to the systolic and diastolic myocardial dysfunction, and particularly to the ventricular dilation, observed in sepsis.

Animals↗
PubMed1996

Internal shear properties of fresh porcine aortic valve cusps: implications for normal valve function.

BACKGROUND AND AIMS OF THE STUDY: Several types of stress act on aortic heart valve tissue during the cardiac cycle. When closed the valve is subjected to primarily tensile stress due to the diastolic pressure, and upon opening bending stress occurs near the attachment with the aortic root and throughout the body of the cusps. Smooth bending requires internal tissue shearing. To measure the internal shear properties of the tissue a testing device was created which combined a high-precision linear actuator with a sensitive load cell. MATERIALS AND METHODS: Circular punch biopsy specimens from fresh porcine aortic valve cusps (n = 32) were examined. The shear stress versus shear strain characteristics were measured both in the circumferential (n = 17) and the radial (n = 13) direction, and the stress relaxation characteristics were also examined circumferentially (n = 15) and radially (n = 15). In addition seven specimens were tested repeatedly in both radial and circumferential directions for tissue isotropy. RESULTS: The results from the shear stress versus strain tests showed the tissue to behave non-linearly over the strain range between -0.9 and 0.9. The average moduli at the near zero strains were less than 300 Pa and increased to over 20 kPa at the extreme strains. The circumferential direction yielded slightly higher average moduli than the radial direction but this difference was not significant. The stress relaxation results indicated that valve tissue relaxation occurs in two distinct phases, an initial low slope region and a second high slope region with respective values of -7.5 log(s)-1 and -15 log(s)-1 and with no significant difference between test directions. CONCLUSIONS: Our results define and describe the pattern of internal shear properties of the aortic valve that are particularly important during the transition between the open and closed positions. This behavior pattern has particular application in the creation of accurate mathematical models of the valve tissue and may be important in understanding the mechanism of tissue failure in bioprosthetic valves.

Animals↗
PubMed1995

Glutaraldehyde fixation alters the internal shear properties of porcine aortic heart valve tissue.

Glutaraldehyde fixation noticeably alters the mechanical properties of porcine aortic valve tissue, subsequently affecting the function and durability of these tissues when used as prosthetic heart valves. Traditional uniaxial tensile testing techniques do not fully define the mechanical properties and we have devised a new approach to examine the important shear properties of the tissue. Altered shear properties would change the response of the valve tissue as it flexes open and closed. An apparatus combining a high-precision linear actuator with a gram-sensitive load cell was used to measure the shear characteristics of circular punch specimens taken from the center of each valve cusp. The tissue parameters measured showed significant differences between the fixed and fresh tissues. Glutaraldehyde-fixed tissue (n = 16) was about 100 times as stiff as fresh tissue (n = 32) between shear strain values of 0 and 0.2. The fixed tissue also had stress relaxation rates about 60% those of the fresh cusps and had about 70% of the hysteresis loss seen in fresh tissue. These results demonstrated the significant effects of glutaraldehyde fixation on the properties of porcine aortic valve cusp when tested in shear. Such changes could lead to altered tissue function and may increase internal stresses during opening and closing, contributing to valve fatigue.

Animals↗
PubMed1995

Bioprosthetic valve tissue viscoelasticity: implications on accelerated pulse duplicator testing.

Most of our knowledge of heart valve mechanics has been gained from low strain-rate studies much lower than physiologic levels. Using a high-speed materials testing system, we compared the low and high strain-rate viscoelastic behavior of porcine aortic valve cusps at extension rates of up to 40 mm/s. Circumferential and radial strips were stretched and then held in their stretched configuration to measure their "stress-relaxation" behavior. During low strain-rate stretching, only 6% of the initial stress dissipated or relaxed after 1 second, whereas 25% of the stress dissipated during high strain-rate stretching. This considerable difference in stress relaxation suggests a rate-dependent viscoelastic behavior that has not been accounted for in valve design and may have important implications for accelerated pulse testing. Even though the valve cusp is loaded for only 0.4 seconds during each heartbeat, at least 15% of the stress may relax over that period. During accelerated pulse testing, however, sufficient time may not be available to allow the tissue fibers to relax back to their natural state before the subsequent loading cycle, leading to a higher baseline preload. In addition, because valve tissue is not given sufficient time to relax before the next cycle, pulse testing subjects the valves to lower-magnitude cyclic stresses than does physiologic loading. Because both the baseline preload and the magnitude of cyclic stresses may lead to early fatigue failure, accelerated wear testing may either overestimate or underestimate valve durability. Clearly, the mechanism of stress-induced failure of biologic tissues must be elucidated before too much validity is placed on pulse duplicator studies.

Animals↗
PubMed1995

A comparison of macroscopic lipid content within porcine pulmonary and aortic valves. Implications for bioprosthetic valves.

Lipid droplets have been demonstrated within both explanted porcine bioprostheses and normal porcine aortic valves. Because of the increasing interest in pulmonary valves as an allograft or xenograft aortic valve substitute, we examined the incidence and distribution of such lipid deposits in 50 porcine aortic valves and 50 matched porcine pulmonary valves. All 300 cusps were removed with surgical scissors and, under a dissecting microscope, the ventricularis layer was removed to expose the spongiosal layer. Macroscopic extracellular lipid droplets analyzed by means of a dissecting microscope with an eyepiece grid and stereology point-counting techniques to provide an area-density average spatial probability map for each cusp. Only 8% of porcine aortic valves were free of lipid, with the distribution of the lipids being 52% +/- 14% right coronary cusp, 90% +/- 8% left coronary cusp, and 68% +/- 13% noncoronary cusp. Of the pulmonary valves, 60% were free of lipid, with the incidence of lipids being 26% +/- 12% left cusp, 6% +/- 7% right cusp, and 12% +/- 9% anterior cusp. Subsequently, lipid cluster samples underwent thin-layer chromatography, which showed them to be phospholipids, oleic acid (fatty acid), triglycerides, and unesterified cholesterol. One primary mode of bioprosthetic valve failure is leaflet calcification. The similarity of distribution within the spongiosal layer between leaflet calcification and intrinsic cusp lipids suggests that the observed lipids might act as a nucleation site for calcification. The substantially lower incidence of lipid in pulmonary valves therefore may represent a potential benefit when these valves are considered for use as aortic valve replacements.

Animals↗
PubMed1994

Oxygen uptake kinetics in cardiac transplant recipients.

Our purpose was to examine the gas exchange response to exercise in heart transplant (HT) patients and to characterize the O2 uptake kinetics (tau VO2) during successive square-wave on-transients from loadless cycling to moderate exercise. We hypothesized that with a slow heart rate response (and O2 transport limitation) O2 kinetics would be slowed but that with a repeated exercise initiated while the heart rate remained elevated the tau VO2 would be faster. Six male HT patients performed two ramp-function tests to determine peak O2 uptake (1.32 +/- 0.23 l/min) and ventilation threshold (1.02 +/- 0.16 l/min). Patients subsequently completed two repeats of a square-wave forcing function and repeated this on 2 days. Alveolar gas exchange was measured breath by breath. A monoexponential fit of signal-averaged data of the first exercise on-transient (between days) yielded a significantly slower tau VO2 in HT subjects than in healthy men (mean age 47 yr; n = 8) (77 +/- 26 vs. 45 +/- 4 s). With successive exercise (2nd transition) initiated while HR remained elevated the tau VO2 of HT patients was 46 +/- 17 s. The faster O2 kinetics of the second transition suggests that O2 delivery was enhanced and therefore that the tau VO2 may reflect bioenergetic processes controlling the rate of oxidative metabolism.

Blood Gas Analysis↗
PubMed1994

Emergency echocardiographic evaluation of penetrating chest trauma.

Penetrating chest trauma is the most common cause of acute cardiac tamponade. Clinical recognition of this potentially life threatening condition may be difficult despite well described physical signs. Failure to repair the injury causing acute cardiac tamponade may result in sudden decompensation with poor clinical outcome. Emergent use of two-dimensional echocardiography can be an extremely valuable tool in evaluating the presence of cardiac tamponade and directing subsequent clinical management.

Adult↗