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Biomedical subjects

R W Frater

Publications and source records attributed to R W Frater.

At least 73 records · Page 4Linked to original sources
PubMed1990

Diastolic viscous properties of the intact canine left ventricle.

The viscoelastic model of the ventricle predicts that the rate of change of volume (strain rate) is a determinant of the instantaneous pressure in the ventricle during diastole. Because relaxation is not complete before the onset of filling, one cannot distinguish the individual effects of relaxation and viscosity unless the passive and active components that determine the ventricular pressure are separated. To overcome this problem, we used the method of ventricular volume clamping to compare the pressures in the fully relaxed ventricle at a given volume at zero strain rate (static pressure) and high strain rate (dynamic pressure). Six open-chest, fentanyl-anesthetized dogs were instrumented with micromanometers and an electronically controlled mitral valve occluder in series with the electromagnetic flow probe. We reasoned as follows: If there were significant viscosity, then the dynamic pressure would be higher than the static pressure. The static pressure was measured when the ventricle was completely relaxed following a mitral valve occlusion after an arbitrary filling volume had been achieved. The dynamic pressure was determined by delaying the onset of filling until relaxation was complete and then measuring the pressure at the same volume that was achieved when the static pressure was measured. In 19 different hemodynamic situations, the dynamic and static pressures were identical (mean difference, 0.1 +/- 0.8 mm Hg), indicating that in the passive ventricle viscoelastic effects are insignificant and do not contribute to the left ventricular diastolic pressure under normal filling rates.

Animals↗
PubMed1990

Immunogenicity of glutaraldehyde-tanned bovine pericardium.

Glutaraldehyde-tanned bovine pericardium was tested for its ability to induce immunologic responses in vivo. Sections of glutaraldehyde-tanned bovine pericardium were implanted between the abdominal muscles of rats and guinea pigs. Control animals received Dacron implants. Lymphocytes and sera from animals were isolated at 2 and 4 weeks after implantation (four animals per group per time). Tritiated thymidine incorporation and an enzyme-linked immunosorbent assay were used to measure T- and B-lymphocyte responses to glutaraldehyde-tanned bovine pericardium antigens. At the same time points, implants and surrounding tissue from all animals were processed for histologic data. Results show that T-lymphocytes from animals with glutaraldehyde-tanned bovine pericardium implants responded significantly (p less than 0.001) to glutaraldehyde-tanned bovine pericardium antigens in vitro but not to Dacron. In contrast, lymphocytes from animals with Dacron implants failed to respond to glutaraldehyde-tanned bovine pericardium or Dacron preparations. Results of enzyme-linked immunosorbent assay show that animals with glutaraldehyde-tanned bovine pericardium implants produced antibody directed against glutaraldehyde-tanned bovine pericardium antigens. Histologic study revealed a dense mononuclear and multinuclear giant cell infiltrate at the interface between glutaraldehyde-tanned bovine pericardium and surrounding host tissues, with focal degradation of implant collagen. Dacron elicited a nonspecific lymphocytic and foreign body-type reaction. These results indicate that glutaraldehyde-tanned bovine pericardium can induce immunologic responses in vivo consistent with a host-versus-graft reaction.

Abdominal Muscles↗
PubMed1990

Chordal replacement in mitral valve repair.

Chordal replacement greatly extends the possibility of repair of atrioventricular valves. Both glutaraldehyde-tanned xenograft pericardial chordae (GTXP) and extruded polytetrafluorethylene chordae (ePTFE) heal to papillary muscles and cusps. Neither type elongates or shrinks. GTXP may thicken and stiffen with time. ePTFE is covered by a normal fibrosa and intima (a new chorda is grown around the ePTFE suture) experimentally and in small sizes (e.g., CV 5), retains flexibility. The results of late follow-up (5-10 years) with GTXP chordae and early follow-up (6-58 months) with ePTFE chordae are encouraging.

Adult↗
PubMed1989

Human immunodeficiency virus and the cardiac surgeon: a survey of attitudes.

The decision to operate on carriers of the human immunodeficiency virus (HIV) who need an urgent cardiac operation is difficult. There is a lack of knowledge about the effect of the presence of HIV on operative risk, about the effect of cardiopulmonary bypass on the progression of HIV infection to acquired immunodeficiency syndrome (AIDS), and about the risk to the cardiac surgical team of operating on 1 or more HIV carriers. This lack of knowledge is exacerbated by the strict regulations surrounding testing. We polled the board-certified cardiac surgeons in the United States on their willingness to perform open cardiac procedures on HIV carriers and AIDS patients. Fifty-three percent of the surgeons responded. Two thirds of them will operate on HIV carriers who need an urgent cardiac operation but regard the presence of AIDS as a contraindication to cardiopulmonary bypass. This is presumably a medical judgment. Those who will not operate on HIV carriers are apparently motivated by fear rather than moral judgments concerning the patients. Virtually all surgeons want to be able to test "high-risk" patients, and a substantial majority would test all patients.

AIDS Serodiagnosis↗
PubMed1989

Cardiac surgery in human immunodeficiency virus (HIV) carriers.

UNLABELLED: Intravenous drug addicts have always been at risk for acquiring infective endocarditis. In the United States in recent years, as many as 50% of addicts have become infected also with the human immunodeficiency virus (HIV). Since testing became available in late 1984, we have knowingly performed open cardiac surgery for endocarditis 11 times in HIV-positive patients. In 7, signs of infection were still presented at the time of surgery. Four died within 2 months of continued or recurrent sepsis. The others are alive, although 1 has returned to IV drug abuse. Open heart surgery was performed 4 times in patients whose endocarditis had been cured by antibiotics but who were left with destroyed valves and severe congestive cardiac failure. All these patients left hospital alive and well. One has since died of AIDS. Ten addicts with endocarditis coming to surgery in the pre-AIDS era had similar valvular pathology but only 2 with uncontrolled infection. All were cured by the combination of antibiotics and surgery. CONCLUSIONS: in HIV-positive patients with endocarditis, continued sepsis despite appropriate antibiotic therapy signals a potentially very serious prognosis which may be due to an already seriously impaired immune state. By contrast, in the absence of uncontrolled infection, HIV-positive patients appear to have a normal response to open cardiac surgery. Data on the risk to the patient of progressing to AIDS and the risk to the surgical team of acquiring HIV infection are unknown. Testing is vital for answering these questions.

Acquired Immunodeficiency Syndrome↗
PubMed1988

Passive properties of canine left ventricle: diastolic stiffness and restoring forces.

Left ventricular (LV) diastolic pressure-volume (P-V) relations arise from a complex interplay of active decay of force (i.e., relaxation), passive elastic myocardial properties, and time-varying inflow across the mitral orifice. This study was designed to quantify the passive properties of the intact ventricle and the effects of elastic recoil by separating filling from relaxation with a method of LV volume clamping with a remote-controlled mitral valve. Eleven open-chest fentanyl-anesthetized dogs were instrumented with aortic and mitral flow probes, LV and left atrium micromanometers, and a remote-controlled mitral valve. We prevented complete (end-systolic volume clamping) or partial filling at different times in diastole. The ventricle thus relaxed completely at different volumes, and we generated P-V coordinates for the passive ventricle that included negative, as well as positive, values of pressure. We then estimated ventricular volumes from ventricular weight in eight dogs, using regression equations based on data in the literature, to determine the equilibrium volume (V0), that is, volume at zero transmural pressure, in the working ventricle. We abandoned the traditional exponential approach and characterized by the P-V relation with a logarithmic approach that included maximum LV volume (Vm), minimum volume (Vd), and stiffness parameters (Sp and Sn) for the positive (p) and negative (n) phases: Pp = -Sp In[(Vm - V)/(Vm - V0)] and Pn = Sn In[(V - Vd)/(V0 - Vd)]. With this formulation, the chamber compliance, dP/dV, is normalized by the LV operating volume, and Sp and Sn are size-independent chamber stiffness parameters with the units of stress. In eight ventricles with LV weight = 131 +/- 20 g, Vm = 116 +/- 18 ml, V0 = 37 +/- 6 ml, and Vd = 13 +/- 2 ml, stiffness Sp = 14.6 mm Hg and Sn = 5.1 mm Hg were determined from the slopes of the log-linearized equations. Also, the duration of LV relaxation is increased by the process of ventricular filling (161 +/- 31 msec, filling versus 108 +/- 36 msec, nonfilling, measured from dP/dtmin, p less than 0.0001). We conclude that volume clamping is a useful method of studying restoring forces and that the logarithmic approach is conceptually and quantitatively useful in characterizing the passive properties of the intact ventricle.

Animals↗
PubMed1987

The use of glycerol-treated homologous pericardium as a substitute for cusps and chordae tendineae of the mitral valve in sheep.

In 11 weanling sheep chordae tendineae were replaced or a patch was implanted into the anterior mitral leaflet using homologous pericardium treated with 98% glycerol for 16.6 days on average. The sheep were electively sacrificed after 4, 6, 9, and 12 months. All animals showed competent mitral valves and good healing; only two sheep out of the patch-group showed small perforations at the suture line. Hemodynamic measurements and left ventricular angiography at rest and during stress test were normal except for the two cases. Histological examination revealed a distorsion and breakdown of pericardial collagen already after 4 months but the remnants of the graft were covered by a neointima of fibrous tissue. There were no signs of calcification and the new chordae tendineae and the patches were not shrunk, rigid or thickened. It is concluded that glycerol is a poor tanning agent, however, glycerol-treated pericardium seems to provide a lattice until fibrous tissue replacement has taken place. Therefore, we think it is a suitable material for mitral valve reconstruction.

Animals↗
PubMed1986

Development and use of a remote-controlled mitral valve.

A remote-controlled mitral valve was designed and constructed to occlude the mitral or tricuspid orifice at any time in the cardiac cycle. It is used to study ventricular properties in the anesthetized dog by controlling ventricular filling, atrial properties by controlling atrial emptying and interaction of the two chambers by uncoupling them. The device can produce transient or steady-state perturbations in filling volume which make possible studies of intrinsic control of cardiac output. When filling volume is transiently reduced, stroke volume and end-systolic volume are reduced. A compensatory increase in stroke volume of the next cycles occurs due to increased ventricular preload and reduced afterload. The compensation continues until the lost stroke volume is regained, at which time the system returns to its previous steady state.

Animals↗
PubMed1986

Influence of vegetation size on clinical outcome of right-sided infective endocarditis.

Endocarditis involving right-sided valvular structures is largely a disease of intravenous drug abusers. The majority of these patients respond to antibiotic therapy with clearing of their bacteremia and preservation of their hemodynamic status. This study evaluated the prognostic value of echocardiographically determined vegetation size in 23 episodes of right-sided valvular endocarditis in 21 patients. Right-sided vegetations were visualized in 19 of 23 episodes (83 percent). Of these, a vegetation of 1.0 cm or greater was found in 11. No patient with an echocardiographically determined vegetation size of less than 1.0 cm required surgery, whereas four of 11 (36 percent) of those episodes in which the vegetation size was 1.0 cm or greater required surgery for persistent pyrexia (p less than 0.05). In all patients requiring surgery, a bioprosthetic tricuspid valve was placed at the time of initial surgery and in no patient did early reinfection occur. This study reconfirms the benign prognosis of right-sided valvular endocarditis. Further, although vegetations of less than 1.0 cm identify those patients who will respond to medical therapy, echocardiographically documented vegetations of 1.0 cm or greater are associated with a significantly lower response rate to appropriate medical therapy. The association of fever that persists for more than three weeks in the absence of another source of infection with an echocardiographically demonstrable right-sided vegetation of 1 cm or more identifies those patients who will require surgical intervention. Finally, tricuspid valve replacement can be performed at the time of initial surgery without undue concern for early reinfection or valve dysfunction.

Adult↗
PubMed1986

Comparative study of calcification in the T6-treated and standard Hancock-I porcine xenografts: experimental study in weanling sheep.

We compared the morphological findings in 15 young sheep in which standard Hancock-I cardiac bioprostheses (7 animals) and T6-processed Hancock-I (8 animals) were implanted in the tricuspid position. The animals were sacrificed at intervals from 8 to 47 weeks after valve replacement. No valvular infection was detected. Six of the 7 untreated valves and 5 of the 8 T6-processed valves in the tricuspid position showed calcific deposits in the radiographic examination. Roentgenograms from all specimens showed a fairly uneven distribution of the mineralization sites with the commissures being the structure most frequently involved. Calcium in the aortic wall was more frequent in the T6-processed group while right coronary leaflet involvement more frequent in the control group. Histologic evaluation confirmed the above data and showed a fibrotic reaction with granulomatous degeneration of the muscular shelf in all valves. Comparison of linear regression lines of the evolution of tissue calcium content with time showed no statistically significant difference between the 2 groups. Under the conditions of this study, the T6-treatment does not reduce the extent of calcification in the Hancock-I porcine xenograft after implantation in the tricuspid position in young sheep.

Animals↗
PubMed1986

Left ventricular relaxation in the filling and nonfilling intact canine heart.

We studied left ventricular relaxation in the filling and transiently nonfilling working hearts of seven open-chest pentobarbital-anesthetized dogs by totally occluding the mitral annulus during one systole. In the completely isovolumic nonfilling cycle, the ventricle relaxes to a lower pressure minimum (usually negative) than in the normal filling cycle. By clamping the ventricle at end systole, we determined the pressure asymptote (Poo) under dynamic conditions. With this information, we evaluated the validity of a monoexponential characterization of relaxation. P = (P0 - Poo) exp(-t/T) + Poo (T, time constant, P0, pressure at t = 0). Plots of In(P-Poo) versus t are nonlinear and concave to the origin, thereby revealing that late relaxation is more rapid than predicted by a monoexponential relation. Nevertheless, the monoexponential T remains a useful index of relaxation and correlates well with other temporal indexes (isovolumic relaxation time and relaxation half-time). When T is calculated from a filling cycle by assuming a zero pressure asymptote, i.e., the conventional way, there is no significant difference with the true value based on the nonfilling cycle.

Animals↗
PubMed1986

Left ventricular filling dynamics: influence of left ventricular relaxation and left atrial pressure.

Peak rapid filling rate (PRFR) is often used clinically as an index of left ventricular relaxation, i.e., of early diastolic function. This study tests the hypothesis that early filling rate is a function of the atrioventricular pressure difference and hence is influenced by the left atrial pressure as well as by the rate of left ventricular relaxation. As indexes, we chose the left atrial pressure at the atrioventricular pressure crossover (PCO), and the time constant (T) of an assumed exponential decline in left ventricular pressure. We accurately determined the magnitude and timing of filling parameters in conscious dogs by direct measurement of phasic mitral flow (electromagnetically) and high-fidelity chamber pressures. To obtain a diverse hemodynamic data base, loading conditions were changed by infusions of volume and angiotensin II. The latter was administered to produce a change in left ventricular pressure of less than 35% (A-1) or a change in peak left ventricular pressure of greater than 35% (A-2). PRFR increased with volume loading, was unchanged with A-1, and was decreased with A-2; T and PCO increased in all three groups (p less than .005 for all changes). PRFR correlated strongly with the diastolic atrioventricular pressure difference at the time of PRFR (r = .899, p less than .001) and weakly with both T (r = .369, p less than .01) and PCO (r = .601, p less than .001). The correlation improved significantly when T and PCO were both included in the multivariate regression (r = .797, p less than .0001). PRFR is thus determined by both the left atrial pressure and the left ventricular relaxation rate and should be used with caution as an index of left ventricular diastolic function.

Angiotensin II↗