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Biomedical subjects

D R Boughner

Publications and source records attributed to D R Boughner.

At least 91 records · Page 5Linked to original sources
PubMed1976

Low frequency dynamic viscoelastic properties of human mitral valve tissue.

The dynamic viscoelasticity of the anterior leaflet of human mitral valves was investigated by subjecting the ventricular aspect of membranous samples of the tissue to sinusoidal fluid pressures. The frequency range of the stressing function used was from 0.5 Hz to 5 Hz. The storage modulus of the tissue was found to be independent of the stressing frequency and an average value of 2.55 (SE = 0-12) X 10(8) dyn cm-2 was observed. Losses were small and the phase shift between stressing function and resulting strain and hence the loss modulus increased with frequency. For the frequency range investigated the phase shift varied from 0.04 to 0.06 rad and the loss modulus was of the order of 10(7) dyn cm-2. From the observed data it was concluded that any tissue substitute used in mitral valve replacement should be rather inextensible and have a low loss modulus. Also under normal physiological conditions, the mitral valve cannot bulge into the left atrium during peak ventricular systole and hence events in the cardiac cycle, such as the presence of the atrial pressure 'c' wave, that involve the distensibility of the valve need to be re-examined.

Elasticity↗
PubMed1976

Noninvasive assessment of mitral insufficiency by transcutaneous Doppler ultrasound.

Instantaneous aortic arch blood velocity was recorded transcutaneously from the suprasternal notch, using a 2.2 MHz Doppler ultrasound unit, in 18 normals and 16 patients undergoing cardiac catheterization who had murmurs of mitral regurgitation. In normals aortic blood velocity rose rapidly in early systole to a midsystolic peak then fell to zero velocity. These roughly parabolic patterns had area ratios beneath the first and second halves of the curves measuring 52:48 +/- 3 (SD). With increasingly severe mitral regurgitation the pattern became skewed leftward such that the percent in the first half of systole ranged from 53-79%. From the angiograms of our sixteen patients an estimate of true percent regurgitation was made using the Fick cardiac output and ventricular volume measurements. When compared with the area under the first half of the velocity curve a strong correlation was found (r = 0.84) indicating that this Doppler technique can be used to evaluate mitral insufficiency.

Adult↗
PubMed1976

The low frequency dynamic viscoelastic properties of human aortic valve tissue.

Membranous samples of human aortic valve cusps were subjected to sinusoidal fluid pressure variations (frequency range, 0.5-5 Hz) to assess their dynamic viscoelastic properties. The storage (elastic) and loss (viscous) moduli and phase lag between the stressing function and response were found to be independent of the frequencies applied. The respective average values were 1.35 (SE = 0.06) X 10(8) dynes cm-2, 4.14 (SE = 0.28) X 10(6) dynes cm-2, and 0.033 (SE = 0.002) rad. The small phase lag indicates that the tissue would recover almost completely to its original state on removal of any applied stress, and this and the relatively low extensibility should be considered in the design of leaflet-type valve prostheses. The storage modulus of the aortic valve cusps when compared to that of the mitral leaflet shows the mitral leaflet to be almost twice as stiff as the aortic valve cusps. This finding led us to conclude that the vibrations of these two cardiac valves alone cannot contribute in any significant way to the production of the observed lower frequency of the first and the higher frequency of the second heart sounds and that other factors must be considered to explain this finding.

Aged↗
PubMed1976

Morphology and relationship to extensibility curves of human mitral valve chordae tendineae.

Human mitral valve chordae tendineae in which elastic response curves are nonlinear have also been found to exhibit extensibility that increases with chordal size and decreases with chordal age. We used selective enzymatic digestion and scanning transmission electron microscopy to explain these observations. Removal of the outer elastin sheath by enzymatic digestion did not significantly affect the elastic response of this tissue. Scanning electron microscopy revealed that the collagen fibers in the central core of young chordae exhibited a very wavy pattern but the pattern in adult specimens was relatively straight. The increased waviness accounted for the greater extensibility of the young specimens. The collagen fibers from young and old chordae consisted of a network of collagen fibrils that became more collapsed when the tissue was fixed under tension. This network arrangement of the fibrils explains the nonlinearity in the elastic response of the tissue. Transmission electron micrographs showed that the density of collagen fibrils decreased as chordal size increased. The number of fibrils per 10(-8) cm2 of the central core decreased from 182.4 (SE = 1.3) to 131.3 (SE = 1.6) as average chordal cross-sectional area increased from 0.0016 cm2 to 0.0268 cm2. This difference in fibril density provides an explanation for the greater extensibility shown by the thicker chordae. The collagen fibril diameters ranged from 516 A to 552 A.

Adolescent↗
PubMed1975

Hypertrophic obstructive cardiomyopathy. Assessment by echocardiographic and Doppler ultrasound techniques.

Hypertrophic obstructive cardiomyopathy is a disease of the myocardium that can be assessed echocardiographic and transcutaneous Doppler ultrasound techniques. Four patients are presented with various patterns of the disease, and the frequently familial incidence is illustrated. The importance of ultrasonic evidence for asymmetric septal hypertrophy in all stages is emphasized and evidence of reduced septal contractility demonstrated. Abnormalities of mitral valve motion, slow diastolic closure rate and systolic anterior movement of the anterior leaflet, are shown in the obstructive form of the disease. Also partial mid-systolic aortic valve closure and aortic cusp flutter are shown with outflow obstruction. The outflow tract gradient can be calculated from mitral valve to septum systolic distances. Transcutaneous Doppler ultrasound shows a normal aortic velocity pattern in nonobstructive disease while consistent abnormalities are present with severe resting obstruction. Isoprenaline can be used to alter the normal velocity pattern associated with a minimal resting gradient to an abnormal pattern indicating the development of significant obstruction.

Adolescent↗
PubMed1975

Mechanical properties of human mitral valve chordae tendineae: variation with size and strain rate.

A knowledge of the mechanical properties of valve tissue is a necessary prerequisite for a better understanding of valvular behavior and design of prosthetic heart valves. Elastic response of chordae tendineae under strain rates of 0.05 cm min(-1)(6.25% min(-1)) to 12.7 cm min(-1)(1600% min(-1)) were obtained by the application of an uniaxial tensile stress using an Instron machine. The chordae exhibited viscoelastic properties in that extensibility decreased with increasing strain rates. The approximate maximum physiological strain rate of the chordae was estimated from echocardiographic traces at the instant of valve closure, and a high value of 29 (S.D. equals 9) cm s(-1) (2000% s(-1)) was found. The breaking strain and stress were found to have values of 21.4 plus or minus 0.5% and 3.1 plus or minus 0.1 times 10(8) dyn cm(-2) respectively, and were independent of strain rates (1 dyn equals 10(-5) N). These values are typical of collagen fibers. The final modulus, before the proportional limit, was found to be about 10(9) dyn cm(-2), which is again typical of collagen fibers. In addition, smaller chordae exhibited less extensibility than the larger chordae. This behavior could be due to structural and functional differences and allows the more centrally inserted chordae to maintain an even valve surface during valve closure.

Adolescent↗
PubMed1975

Assessment of aortic insufficiency by transcutaneous Doppler ultrasound.

Using a 2.2 MHZ directional Doppler ultrasound unit, the instantaneous peak aortic velocity pattern was recorded transcutaneously in 15 normal persons and 15 patients with aortic insufficiency. The transducer was positioned in the suprasternal notch and aimed posteriorly to cross the descending aortic arch at an angle approximately parallel to blood flow. The electrocardiogram, phonocardiogram, and carotid pulse tracings were recorded simultaneously. In patients with aortic insufficiency there was significant diastolic flow that was not present in normal persons. The planimetered area under the systolic and diastolic velocity tracings represents the distance forward and backward that the stroke volume moves. The ratio was used to approximate the percent regurgitation, which ranged from 9% to 68%. From left ventricular angiograms in the patients with aortic regurgitation single plane ventricular volume measurements were used to calculate ventricular output and when compared with the Fick cardiac output gave an estimate of true percent regurgitation. A strong correlation was obtained with the Doppler estimate (r=0.91), confirming that this simple ultrasound technique can accurately assess the degree of aortic insufficiency.

Aortic Valve Insufficiency↗
PubMedDate not supplied

Quantitative assessment of myocardial collagen with picrosirius red staining and circularly polarized light.

Collagen plays a major role in the structural organization of the heart and therefore direct visualization of collagen fibers is a crucial component of cardiac analysis. Although linearly polarized light has proven an effective tool for the examination of myocardial collagen in histologic sections, the use of circularly polarized light may offer advantages and additional possibilities. We examined the potential enhancement of collagen analysis using circularly polarized light in two ways. We first measured the brightness, and hence indirectly assessed the birefringence, of collagen fibers in scars examined at different times after myocardial infarction. Secondly, we measured collagen content in myocardial tissue and compared results obtained from brightfield analysis of trichrome stained sections with those obtained from circularly polarized light analysis of picrosirius red stained sections. We observed a progressive increase in the maximum brightness of collagen fibers in the scar with time, and a time-dependent shift in the relative distribution of collagen fiber brightness from lower to higher levels. We found consistently lower values of collagen content in trichrome stained versus picrosirius red stained tissue, and concluded that trichrome staining underestimated collagen content. The information provided by these studies could not be obtained by brightfield analysis and could be only partially obtained from linearly polarized light analysis. Thus, analysis using circularly polarized light has the ability to enhance histologic assessment of tissue and can provide additional insights into the composition and structure of myocardial collagen.

Animals↗
PubMedDate not supplied

Enhanced detection of cardiac myocyte damage by polarized light microscopy. Use in a model of coxsackievirus B3-induced myocarditis.

Although accurate detection of cardiac muscle damage is critical in the diagnosis of acute myocarditis or acute cellular rejection in both clinical and experimental settings, the histologic evaluation is frequently uncertain without specialized stains. In a study of adult male A/J mice infected with 2x10(5) plaque-forming units of myocarditic coxsackievirus B3, cardiac muscle injury causing myofibrillar disruption was detected as a loss of muscle birefringence by polarized light microscopy. The technique was corroborated by comparison with Masson's trichrome stain and was helpful for histologic examination especially at the early preinflammatory stages of lesion development or in fringe territories of focal lesions. Polarized light microscopy is thus an available means to enhance the histologic determination of cardiac myocyte damage and has specific advantage in an absence of specialized stains.

Animals↗
PubMedDate not supplied

Value of cardiac monitoring and echocardiography in TIA and stroke patients.

One hundred and eighty-four consecutive patients admitted to an Investigative Stroke Unit with transient ischemic attacks (TIA) and cerebral infarction (stroke) had 48-hour automated arrhythmia monitoring, 55 patients had additional Holter monitoring and 127 patients had 2-D echocardiography. One hundred and sixteen presented with stroke (63%) and 68 patients with TIA (37%). One hundred and twenty-two were men (66.3%) and 62 were women (33.7%), mean age 63.5 years, range 25-86. The monitoring identified twelve (6.5%) patients with significant arrhythmias undetected by history, examination and admission electrocardiogram: six with atrial fibrillation (AF), four with 2 degrees heart block type Mobitz II and one each with 3 degrees heart block and sick sinus syndrome. Two-D echocardiography showed a previously unknown potential source for cardiac emboli in 22 patients (17.3%): segmental ventricular disease in eleven, mitral valve prolapse in seven, left ventricular thrombus in six, left ventricular aneurysm in three and one each with mitral valve endocarditis and global myocardial dysfunction. Only the mitral valve findings were expected on the basis of a previous M-mode echocardiographic study carried out in our city on healthy elderly volunteers. From the clinical history and all cardiac investigations, we found 59 patients (32%) with a possible cardiac source for cerebral emboli. After cerebral angiography, 29 of these 59 patients also showed a vascular lesion in the appropriate carotid artery and we could not decide definitely which lesion was responsible for the cerebral embolus. In the remaining 30 patients (16.4%), the evidence implicated the heart as the most likely source.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMedDate not supplied

The effect of cast immobilization on meniscal healing. An experimental study in the dog.

A 1.5-cm longitudinal, full-thickness incision was made in the vascularized portion of the medial meniscus in 20 adult dogs and anatomically repaired. Postoperatively, the animals were either placed in a long leg cast (N = 9) or mobilized immediately (N = 11). The animals were sacrificed at 2 weeks (6 dogs), 4 weeks (6 dogs), or 10 weeks (8 dogs). Five medial menisci from the nonoperated side were used as controls. Collagen content was measured using a digital image analysis system, and the collagen percentage in the repair tissue in each postoperative treatment group was compared. In the 2-week and 4-week groups, there was no statistically significant difference in the percentage of collagen between those animals immobilized versus those that had early mobilization. The animals in the 10-week group that were mobilized had a significantly greater collagen percentage in the healing meniscal incision than those that were cast immobilized (44.6% +/- 10% versus 27.0% +/- 11%, P < 0.0001). There was no significant difference in the collagen percentages between the mobilized 10-week group and the contralateral control menisci group. All other menisci had a decreased collagen percentage compared with the controls. Prolonged immobilization decreases collagen formation in healing menisci. Thus, our results suggest that patients undergoing isolated meniscal repair either be immediately mobilized after surgery or immobilized for short periods only.

Animals↗