Search PubMed⌕ Search

Biomedical subjects

T Yeh

Publications and source records attributed to T Yeh.

50 records · Page 3Linked to original sources
PubMed1991

Skeletal muscle extraaortic counterpulsation. A true arterial counterpulsation.

Reduction of left ventricular work load during systole, a critical component of arterial counterpulsation, has not previously been documented for skeletal muscle-powered extraaortic counterpulsation. To assess its capacity for afterload reduction, a skeletal muscle extraaortic counterpulsator was connected to the thoracic aorta and counterpulsated. Canine hearts (n = 7) were instrumented with left ventricular Millar catheters (Millar Instruments, Inc., Houston, Tex.) for pressure measurements and with piezoelectric ultrasonic crystals for measurement of the left ventricular minor axis dimension and wall thickness. During systole, skeletal muscle extraaortic counterpulsation resulted in a significant change in all three determinants of left ventricular circumferential wall stress compared with control conditions (no counterpulsation). Pressure decreased (peak systole, 100 +/- 5 versus 75 +/- 6 mm Hg; p less than 0.05 by paired t test), minor axis dimension decreased (end systole, 46.4 +/- 1.1 versus 45.8 +/- 1.1 mm; p less than 0.05 by paired t test), and wall thickness increased (end systole, 10.4 +/- 0.7 versus 10.6 +/- 0.7 mm; p less than 0.05 by paired t test). Left ventricular wall stress/dimension work loops showed a shift downward and to the left, a shift consistent with afterload reduction. The mean systolic left ventricular wall stress was significantly reduced, from 67.3 +/- 10.6 to 47.7 +/- 8.1 10(3) dyne/cm2 (p less than 0.05 by paired t test). Skeletal muscle extraaortic counterpulsation increased the diastolic aortic pressure from 72 +/- 6 to 105 +/- 8 mm Hg (p less than 0.05 by paired t test). Our data, which documented the counterpulsator's direct effects on left ventricular functional mechanics, showed that skeletal muscle extraaortic counterpulsation is capable of both diastolic augmentation of arterial pressure and systolic unloading of the left ventricle. Skeletal muscle extraaortic counterpulsation has potential application for ventricular unloading in the treatment of chronic end-stage heart failure.

Animals↗
PubMed1991

Effects of dynamic cardiomyoplasty on left ventricular performance and myocardial mechanics in dilated cardiomyopathy.

We tested the hypothesis that dynamic cardiomyoplasty produces beneficial changes in the functional mechanics of the dilated, failing left ventricle. Chronic dilated cardiomyopathy was induced in seven mongrel dogs by rapid ventricular pacing (260 beats/min) for 3 to 4 weeks. After completion of the induction period, dynamic cardiomyoplasty was performed with the left latissimus dorsi muscle, paced synchronously with the R waves of the electrocardiogram (Medtronic SP1005). Instruments included an aortic flow probe, a left ventricular Millar pressure catheter, and piezoelectric sonomicrometric crystals on the left ventricle for measurements of wall thickness and minor and major axis dimensions. Data were obtained with the stimulator off and on. Statistical comparisons were made with Student's t test for paired data. Dynamic cardiomyoplasty increased the cardiac output of the failing heart (966 +/- 124 versus 1166 +/- 112 ml/min; p less than 0.01). Systolic shortening of both minor and major axis dimensions increased (3.1 +/- 0.3 versus 4.7 +/- 0.3 mm, p less than 0.01, and 4.6 +/- 0.3 versus 7.3 +/- 0.9 mm, p less than 0.05, respectively). Left ventricular end-diastolic pressure decreased by 16% (18 +/- 1 versus 15 +/- 1 mm Hg, p less than 0.01). Although skeletal muscle contraction increased the pressure development in the left ventricular chamber, mean systolic wall stress was diminished by concomitant changes in left ventricular dimensions (116,144 +/- 11,530 versus 101,268 +/- 7464 dynes/cm2, p less than 0.05). At end-systole, wall thickness increased (11.8 +/- 1.1 versus 12.7 +/- 1.1 mm, p less than 0.01), minor axis dimension decreased (51.3 +/- 1.4 versus 49.2 +/- 1.8 mm, p less than 0.01), and major axis dimension also decreased (85.6 +/- 3.3 versus 79.0 +/- 2.3 mm, p less than 0.05). Our detailed evaluation of left ventricular chamber mechanics suggests that dynamic cardiomyoplasty may have a role in ameliorating the functional and mechanical derangements associated with progression of dilated cardiomyopathy both by augmenting cardiac performance and by diminishing determinants of myocardial oxygen consumption. (All values are expressed as mean +/- standard error of the mean.)

Animals↗
PubMed1990

Superior myocardial preservation with modified UW solution after prolonged ischemia in the rat heart.

Cardiac transplantation remains constrained by poor graft tolerance of prolonged cold ischemia. University of Wisconsin solution has remarkably extended ischemic preservation in pancreas, kidney, and liver transplantation. To assess its efficacy in cardiac preservation, modified University of Wisconsin solution flush and storage were tested against St. Thomas' cardioplegia flush and normal saline solution storage after six hours of ischemia at 0 degrees C in 46 isolated rat hearts. After ischemia, groups were compared before and after reperfusion. After ischemia but before reperfusion, University of Wisconsin solution hearts had significantly less tissue water (3.8%), superior tissue sodium, potassium, calcium, and magnesium profiles, and elevated adenosine and inosine levels, and tended toward better histological preservation. After reperfusion, University of Wisconsin solution more effectively preserved left ventricular compliance (75% versus 35% of baseline), developed pressure (71% versus 45% of baseline), histological integrity, and tissue potassium and calcium profiles than St. Thomas' solution. The University of Wisconsin solution provided superior preservation of systolic and diastolic ventricular function, tissue histology, tissue water, and tissue electrolytes than did St. Thomas' cardioplegia and normal saline solution storage in this experimental model, and might result in improved graft tolerance of ischemia in clinical cardiac transplantation.

Adenine Nucleotides↗
PubMed1990

Altered contractile response in neonatal myocardium to citrate-phosphate-dextrose infusion.

The clinical use of citrate-phosphate-dextrose during blood-product transfusion is known to affect ionized calcium levels and can result in depression of myocardial contractility. The immature heart appears to have an intrinsic reduction in contractile state compared with the adult heart and may be more dependent on transsarcolemmal calcium flux for regulation of contraction. The myocardial contractile response to citrate infusion was compared in neonatal and adult rabbit hearts using clinically comparable citrate-phosphate-dextrose concentrations. Isovolumic left ventricular pressures were monitored in an isolated, crystalloid-perfused heart model before, during, and after 15 minutes of citrate-phosphate-dextrose infusion. Developed pressure decreased 42.1 +/- 4.9% from control within 1 minute in the neonatal group versus 24.3 +/- 4.3% in the adult group (p less than 0.02). The effect on diastolic function was paradoxical in the neonate with a 43.1 +/- 11.9% increase in end-diastolic pressure compared with a 9.7 +/- 7.8% decrease in the adult (p less than 0.01). These results indicate that the neonatal heart appears more sensitive to the myocardial effects of citrate infusion with impairment of both systolic and diastolic function. The decreased ventricular compliance in the neonate with citrate-phosphate-dextrose suggests that the myocardial effects may not be simply due to changes in ionized calcium concentration.

Animals↗
PubMed1990

Efficacy of recombinant-derived human superoxide dismutase on porcine left ventricular contractility after normothermic global myocardial ischemia and hypothermic cardioplegic arrest.

A porcine model of normothermic global ischemia (40 minutes) followed by systemic cooling to 25 degrees C with 4 degrees C crystalloid cardioplegic arrest (90 minutes) was used to assess the efficacy of recombinant-derived human superoxide dismutase (r-HSOD) on postreperfusion left ventricular function while on cardiopulmonary bypass. Isovolumic hemodynamic function was monitored, and adenine nucleotide pool was measured in myocardial biopsy specimens and coronary sinus effluent. The treatment group of pigs (n = 7) received 15 mg/kg r-HSOD immediately before warm reperfusion, both left ventricular peak systolic pressure and developed pressure were significantly better in the r-HSOD group of pigs (p less than 0.05 vs. placebo). This improvement persisted at 60 minutes of reperfusion (p less than 0.05 vs. placebo). Myocardial ATP and total adenine nucleotides did not differ, nor did adenine nucleotide catabolites in the coronary sinus effluent differ between treatment groups of pigs. The exception to this was the nucleotide catabolite inosine, which was significantly elevated in coronary sinus effluent of pigs treated with r-HSOD at 30 minutes of reperfusion (p less than 0.05 vs. placebo). In this model of global ischemia and reperfusion, a recombinant-derived human free-radical scavenger provides significant protection of systolic but not diastolic function. Values for myocardial ATP and total adenine nucleotide content suggest that the improvement in mechanical function during reperfusion is not due to enhanced preservation of myocardial bioenergetics.

Adenine Nucleotides↗
PubMed1990

Rapid cooling contracture of the myocardium. The adverse effect of prearrest cardiac hypothermia.

Hypothermic total circulatory arrest for repair of congenital heart lesions in neonates requires a period of rapid core cooling on cardiopulmonary bypass during which the myocardium is also exposed to hypothermic perfusion. Myocardial hypothermia in the nonarrested state results in an increase in contractility due to elevation of intracellular calcium levels. This study was designed to test the hypothesis that rapid myocardial cooling before cardioplegic ischemic arrest results in damage, with impaired recovery during reperfusion. Two groups of 10 rabbit hearts were perfused on an isolated Langendorff apparatus. Group N (normothermia) was perfused at 37 degrees C before 2 hours of cardioplegic ischemic arrest at 10 degrees C. Group C (cooling) was perfused at 15 degrees C in the unarrested state for 20 minutes before the same cardioplegic arrest conditions as group N. Left ventricular isovolumic pressure measurements, biochemical measurements from right ventricular biopsy specimens, and ventricular necrosis as defined by tetrazolium staining were used to compare the groups at 30 and 60 minutes of normothermic reperfusion. Developed pressure at a constant volume was preserved in group N at 90.7 +/- 4.5 mm Hg versus 76.9 +/- 6.3 in group C after reperfusion (p less than 0.05). Diastolic compliance showed significant deterioration in group C, with marked elevation of diastolic pressure during reperfusion (group N = 6.8 +/- 2.5 mm Hg versus group C = 38.9 +/- 6.1 after reperfusion; p less than 0.001). Adenosine triphosphate levels were significantly higher in group N both at end-ischemia and after reperfusion versus group C (group N = 17.0 +/- 1.1 nmol/mg protein versus group C = 7.7 +/- 1.0 after reperfusion; p less than 0.001). Group N had 0.4% +/- 0.4% necrosis of ventricular mass versus 19.3% +/- 2.2% with prearrest cooling in group C (p less than 0.0001). These results indicate that, when combined with cardioplegic ischemic arrest, rapid myocardial cooling in the unarrested state results in significant damage. The mechanism may be related to the cytosolic calcium loading effect of hypothermia that is not relieved during the subsequent period of cardioplegic arrest. Although hypothermia is an essential component to ischemic preservation, rapid cooling contracture can adversely influence cardioplegic myocardial protection.

Animals↗
PubMed1989

The effect of background luminance on cone sensitivity functions.

Implementations of the Wald-Marré technique have employed fixed luminance backgrounds to isolate cone sensitivity mechanisms. We evaluated the effect of varying the adaptation level on the relative isolation of the different cone types. For MWS and LWS cone isolation we used a 15 Hz flickering test light to isolate the achromatic channel, and we modelled the resulting spectral sensitivity functions as a linear sum of LWS and MWS input. We found only mild improvement in relative cone isolation with increasing adaptation level. The LWS and MWS cone mechanisms showed decreasing sensitivity with adaptation level and reached limiting Weber behavior above 1000 Td. SWS cones were isolated with a 2.4 Hz flickering light. SWS cone isolation improved with adapting level, reaching a plateau above 1000 Td. The SWS cone mechanism showed decreasing sensitivity with adaptation level but did not reach a limiting Weber region. Our data indicate that the use of fixed high adaptation levels has different effects on the cone mechanisms. Absolute sensitivity loss for LWS or MWS mechanism will not be revealed. LWS and MWS thresholds will appear normal unless there is an adaptation abnormality. On the other hand, the SWS cone thresholds would be sensitive to both absolute and increment sensitivity loss. More than one adaptation condition is needed to separate different types of sensitivity loss characteristic of eye disease.

Adaptation, Physiological↗
PubMed1987

DNA hybridization for diagnosis of enteric adenovirus infection from directly spotted human fecal specimens.

By using a genomic probe, DNA hybridization for adenovirus type 41 (Ad41) showed equivalent sensitivity with a direct spot method from clinical specimens compared with a more laborious DNA phenol extraction procedure. By using this direct spot preparation method, fecal specimens of 67 patients were examined under code for blind testing for the presence of adenovirus by DNA hybridization by using two Ad41 probes (genomic and cloned BglII-D) and an adenovirus type 2 genomic probe. Identical results were obtained with both of the Ad41 probes. Of the fecal specimens from 42 children with adenovirus gastroenteritis studied prospectively (16 of whom had enteric adenoviruses), 13 specimens (81%) were detected by DNA hybridization with a cloned Ad41 BglII-D probe. There were 14 fecal specimens that were positive by electron microscopy (EM) and culture for nonenteric adenovirus, and 2 specimens were positive by DNA hybridization (87% specificity); these 2 specimens may have been from a mixed enteric adenovirus and nonenteric adenovirus infection. None of 26 specimens from age-matched healthy control patients was positive for adenovirus by EM or DNA hybridization. Our data indicated that DNA hybridization gives highly reproducible results. The direct spot technique is the method of choice for specimen preparation in the diagnostic laboratory, since it requires only the simplest manipulations in specimen preparation. By using DNA hybridization with the BglII D fragment of a cloned enteric Ad41, both adenovirus type 40 and Ad41 were detected directly from fecal specimens, but it was less sensitive than EM following direct ultracentrifugation of specimens. The Bg1II-D Ad41 DNA probe was highly specific for enteric adenoviruses, and DNA hybridization with this probe could be a useful diagnostic test for these fastidious adenoviruses.

Adenoviridae Infections↗
PubMed1983

Studies on the blood-aqueous barrier after argon laser photocoagulation of the iris.

Breakdown and re-establishment of the blood-aqueous barrier (BAB) was studied following laser irradiation to the rabbit iris by quantitating leakage of protein, fluorescein, and fluorescein-labeled dextran (FLD-70, MW 70,000) into the aqueous humor. Breakdown of the BAB was more prolonged in pigmented than albino animals, possibly due to the increased laser energy absorbed by the pigmented iris. Fluorophotometry appeared to be a more sensitive method for evaluating BAB breakdown than aqueous protein measurements, and small molecule leakage (fluorescein) appeared to be more sensitive than macromolecule leakage (FLD-70). The noninvasive method of evaluating the BAB proved equally as effective as measuring aqueous protein content in assessing the sensitivity of laser-induced trauma to the ameliorating effect of the nonsteroidal anti-inflammatory agent indomethacin.

Animals↗
PubMed1978

Blood loss and bank blood requirement in coronary bypass surgery.

With the use of nonblood prime and refinement in perfusion and surgical techniques, blood requirement for coronary bypass operations has been reduced to a minimum. Of 240 patients (average number of bypasses, 3.07; average pump time, two hours and 22 minutes), no blood was used in pump prime or before perfusion. During perfusion, 29 patients (12%) received 34 units of blood in the pump-oxygenator, and after bypass 64 patients (27%) received 65 units of blood in the operating room (average intraoperative use, 203 ml per patient). For the total hospital stay, the blood requirement was 728 ml per patient. For the last 60 patients operated on, the figure was 328 ml. There were no surgical deaths, and only 1 reexploration for postoperative hemorrhage (0.4%). Discharge hemoglobin level averaged 11.8 gm, whereas the admission hemoglobin level had averaged 13.8 gm. Autotransfusion, avoidance of entry into the pleural space, shorter perfusion time, postoperative platelet count of more than 150,000, and normal partial thromboplastin time tend to reduce blood requirement, but not to a striking degree. Bank blood requirement for the coronary bypass program accounted for 3.7% of the hospital need and 2% of the community need.

Adult↗
PubMedDate not supplied

Receptive fields of primate retinal ganglion cells studied with a novel technique.

We have reinvestigated receptive-field structure of ganglion cells of the macaque parafovea using counterphase modulation of a bipartite field. Receptive fields were mapped with luminance, chromatic, and cone-isolating stimuli. Center sizes of middle (M) and long (L) wavelength cone opponent cells of the parvocellular (PC) pathway were consistent with previous estimates (Gaussian radii of 2-4 min of arc, corresponding to center diameters of 6-12 min of arc). We calculate that a large factor of the enlargement relative to cone radius could be blur due to the eye's natural optics. Maps were consistent with cone selectivity in surround mechanisms, which had radii of 5-8 min of arc. For magnocellular (MC) cells, center size estimates were also consistent with grating measurements from the literature (also Gaussian radii of 2-4 min of arc). The surround mechanism contributing the MC-cell frequency-doubled response to chromatic modulation appears to possess a subunit structure, and we speculate it derives from nonlinear summation of signals from M,L-cone opponent subunits, such as midget bipolar cells.

Animals↗
PubMedDate not supplied

Deficiency of plasma protein S, protein C, or antithrombin III and arterial thrombosis.

Protein C and protein S are vitamin K-dependent coagulation factors that together act as an anticoagulant, and antithrombin III is a plasma protein that inhibits several activated factors in the coagulation cascade. Although deficiencies of any of these three proteins have been associated with deficiencies of these factors. We report one patient with a protein S deficiency, another with a protein C deficiency, and a third with an antithrombin III deficiency, each of whom who had extensive arterial thrombosis. We suggest that deficiencies of these proteins may constitute risk factors for arterial thrombosis.

Adult↗