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Biomedical subjects

J T Walsh

Publications and source records attributed to J T Walsh.

At least 19 recordsLinked to original sources
PubMed2000

Pulmonary capillary wedge pressure in mitral stenosis accurately reflects mean left atrial pressure but overestimates transmitral gradient.

Current opinion varies as to whether pulmonary capillary wedge pressure assessment of transmitral gradient in mitral stenosis is accurate; we therefore compared transmitral gradient in 36 patients awaiting balloon valvuloplasty using both pulmonary capillary wedge pressure and direct left atrial pressure. Mean pulmonary capillary wedge pressure correlated well with mean left atrial pressure (limits of agreement -1.5 to +3.7 mm Hg), but mean diastolic mitral gradient calculated using pulmonary capillary wedge pressure differed significantly from that calculated using left atrial pressure (limits of agreement -1.2 to +9.8 mm Hg): wedge pressure-assessed transmitral gradient is therefore misleading, routinely overestimating stenosis severity.

Blood Pressure↗
PubMed2000

Comparison of central venous and inferior vena caval pressures.

Inferior vena caval pressures were measured in 60 patients undergoing cardiac catheterization and compared with central venous pressure from within the right atrium. Mean pressures within the abdominal inferior vena cava were essentially the same as mean right atrial pressure, suggesting that the inferior vena cava provides a useful safe alternative for measuring central venous pressure.

Aged↗
PubMed2000

Coronary angiography in the presence of peripheral vascular disease: femoral or brachial/radial approach?

Peripheral vascular disease is considered a relative contraindication to the femoral approach for coronary angiography, but no data exist comparing the femoral and brachial/radial routes under these circumstances. We examined the influence of vascular approach on outcome. Two hundred and ninety-seven patients, mean age 67.1 +/- 8.4 years, with clinical or radiographic evidence of aortofemoral peripheral arterial disease underwent diagnostic coronary angiography during a 3-year period at this cardiothoracic center. The approach was successful in 121 of 154 femoral cases (79%) compared with 130 of 143 brachial/radial cases (91%; P < 0.01). Of the 33 failed femoral cases, 15 were then approached from the other femoral artery, with success in 6 (40%), while 18 were approached from the arm, with success in all (100%; P < 0.01). Brachial/radial cases took significantly longer than femoral cases (51 +/- 19 vs. 42 +/- 22 mins; P < 0.01). In cases where the femoral pulse was considered normal, the femoral approach nonetheless failed in 19 of 95 (20%). Major vascular complications (e.g., pulseless limb, arterial dissection, hemorrhage, or false aneurysm) occurred in nine femoral cases vs. zero brachial/radial cases (P < 0.01). Patients with peripheral vascular disease who undergo coronary angiography from the femoral artery have a 1-in-5 risk of procedural failure, necessitating use of an alternative vascular approach, and a 1-in-20 risk of a major vascular complication. Normality of femoral arterial pulsation is not a good predictor of femoral success. Brachial/radial approaches take longer, but succeed more frequently and have a negligible major vascular complication rate. We believe that patients with peripheral vascular disease should undergo coronary angiography via brachial or radial approach. Cathet. Cardiovasc. Intervent. 49:32-37, 2000.

Aged↗
PubMed2000

Laser skin welding: in vivo tensile strength and wound healing results.

BACKGROUND AND OBJECTIVE: Laser skin welding was investigated as a general model for laser tissue closure. Scanned delivery of near-infrared laser radiation in combination with a dye can produce strong welds with limited thermal damage. STUDY DESIGN/MATERIALS AND METHODS: Two-centimeter-long, full-thickness incisions were made on the backs of guinea pigs. Wounds were closed either by laser welding or sutures and then biopsied at 0, 3, 6, 10, 14, 21, and 28 days postoperatively. Welding was achieved by using continuous-wave, 1. 06-micrometer, Nd:YAG laser radiation scanned over the incisions to produce a dwell time of approximately 80 msec. The cooling time between scans was fixed at 8 seconds. A 4-mm-diameter laser spot was maintained during the experiments, and the power was kept constant at 10 W. The operation time was fixed at 10 minutes per incision. India ink was used as an absorber of the laser radiation at the weld site, and clamps were used temporarily to appose the incision edges. RESULTS: Acute weld strengths of 2.1 +/- 0.7 kg/cm(2) were significantly higher than suture apposition strengths of 0.4 +/- 0.1 kg/cm(2) (P < 0.01), and weld strengths continued to increase over time. Lateral thermal damage in the laser welds was limited to 200 +/- 40 micrometer near the epidermal surface with less thermal damage deeper within the dermis. CONCLUSION: Our welding technique produced higher weld strengths and less thermal damage than reported in previous skin welding studies and may represent an alternative to sutures.

Animals↗
PubMed2000

Sealant bond strengths of CO(2) laser-etched versus acid-etched bovine enamel.

BACKGROUND AND OBJECTIVE: The purpose of this study was to evaluate sealant shear bond strength on bovine enamel with standard acid etching compared with CO(2) laser etching. STUDY DESIGN/MATERIALS AND METHODS: Bovine enamel was prepared either by acid or laser etching and divided into four experimental groups, either acid or laser-etched teeth with or without a primer. A gelatin capsule was used to place the sealant on the prepared enamel surface and the bond tested in shear. Also surface roughness was evaluated by using a surface analyzer and an atomic force microscope. RESULTS: Shear bond strength results were the following: acid etch = 8.8 +/- 3.8 MPa, acid etch with primer = 10.3 +/- 5.5 MPa, laser etch = 4.0 +/- 1.1 MPa, and laser etch with primer = 6.2 +/- 2.3 MPa. Analysis of variance statistical analysis found no significant difference in bond strength between the acid-etched groups. However, the laser-etched groups had significantly lower bond strengths from the acid-etched teeth. In addition, a significant difference was observed between the laser-etched groups, where the use of the primer helped to increase the bond strength of the sealants. The surface roughness was significantly greater on the laser-etched teeth at the microm level (by using a surface analyzer) from the acid-etched and the control specimens. No difference in roughness (by using an atomic force microscope) was observed at the nanometer level between the laser and acid-etched teeth. CONCLUSION: For these particular settings, the laser-etched teeth resulted in lower bond strengths to enamel and the use of a primer increased the bond strength for laser-etched teeth only.

Acid Etching, Dental↗
PubMed2000

Cryogen spray cooling during laser tissue welding.

Cryogen cooling during laser tissue welding was explored as a means of reducing lateral thermal damage near the tissue surface and shortening operative time. Two centimetre long full-thickness incisions were made on the epilated backs of guinea pigs, in vivo. India ink was applied to the incision edges then clamps were used to appose the edges. A 4 mm diameter beam of 16 W, continuous-wave, 1.06 microm, Nd:YAG laser radiation was scanned over the incisions, producing approximately 100 ms pulses. There was a delay of 2 s between scans. The total irradiation time was varied from 1-2 min. Cryogen was delivered to the weld site through a solenoid valve in spurt durations of 20, 60 and 100 ms. The time between spurts was either 2 or 4 s, corresponding to one spurt every one or two laser scans. Histology and tensile strength measurements were used to evaluate laser welds. Total irradiation times were reduced from 10 min without surface cooling to under 1 min with surface cooling. The thermal denaturation profile showed less denaturation in the papillary dermis than in the mid-dermis. Welds created using optimized irradiation and cooling parameters had significantly higher tensile strengths (1.7 +/- 0.4 kg cm(-2)) than measured in the control studies without cryogen cooling (1.0 +/- 0.2 kg cm(-2)) (p < 0.05). Cryogen cooling of the tissue surface during laser welding results in increased weld strengths while reducing thermal damage and operative times. Long-term studies will be necessary to determine weld strengths and the amount of scarring during wound healing.

Anesthetics↗
PubMed1999

Radiometric surface temperature measurements during dye-assisted laser skin closure: in vitro and in vivo results.

BACKGROUND AND OBJECTIVE: A thermal camera was used to measure surface temperatures during laser skin welding to provide feedback for optimization of the laser parameters. STUDY DESIGN/MATERIALS AND METHODS: Two-centimeter-long, full-thickness incisions were made in guinea pig skin in vitro and in vivo. India ink was applied to the incision edges, which were then mechanically apposed. Continuous-wave, 1.06-microm Nd:YAG laser radiation was scanned over the incisions, producing an effective pulse duration of approximately 100 msec. Cooling durations between scans of 1.6, 4.0, and 8.0 sec were studied in vitro. A 5-mm-diameter laser spot was used with the power kept constant at 10 W. Thermal images were obtained at 30 frames per second with a thermal camera detecting 3-5 microm radiation. Surface temperatures were recorded at 0, 1, and 6 mm from the center line of the incision. RESULTS/CONCLUSIONS: Cooling durations of 1.6 and 4.0 seconds in vitro resulted in temperatures at the weld site that remained above approximately 65 degrees C for prolonged periods of time. Cooling durations of 8.0 seconds were sufficient both in vitro and in vivo to prevent a significant rise in baseline temperatures at the weld site over time.

Animals↗
PubMed1999

Surfactant-spreading and surface-compression disturbance on a thin viscous film.

Spreading of a new surfactant in the presence of a pre-existing surfactant distribution is investigated both experimentally and theoretically for a thin viscous substrate. The experiments are designed to provide a better understanding of the fundamental interfacial and fluid dynamics for spreading of surfactants instilled into the lung. Quantitative measurements of spreading rates were conducted using a fluorescent new surfactant that was excited by argon laser light as it spread on an air-glycerin interface in a petri dish. It is found that pre-existing surfactant impedes surfactant spreading. However, fluorescent microspheres used as surface markers show that pre-existing surfactant facilitates the propagation of a surface-compression disturbance, which travels faster than the leading edge of the new surfactant. The experimental results compare well with the theory developed using lubrication approximations. An effective diffusivity of the thin film system is found to be Deff = (E*gamma)/(mu/H), which indicates that the surface-compression disturbance propagates faster for larger background surfactant concentration, gamma, larger constant slope of the sigma*-gamma* relation, -E*, and smaller viscous resistance, mu/H. Note that sigma* and gamma* are the dimensional surface tension and concentration, respectively, mu is fluid viscosity, and H is the unperturbed film thickness.

4-Chloro-7-nitrobenzofurazan↗
PubMed1999

Ventricular dilatation in the absence of ACE inhibitors: influence of haemodynamic and neurohormonal variables following myocardial infarction.

OBJECTIVE: To examine the relation between patterns of ventricular remodelling and haemodynamic and neurohormonal variables, at rest and during symptom limited exercise, in the year following acute myocardial infarction in patients not receiving angiotensin converting enzyme (ACE) inhibitors. DESIGN: A prospective observational study. PATIENTS: 65 patients recruited following hospital admission with a transmural anterior myocardial infarction. METHODS: Central haemodynamics and neurohormonal activation at rest and during symptom limited treadmill exercise were measured at baseline before hospital discharge, one month later, and at three monthly intervals thereafter. PATIENTS were classified according to individual patterns of change in left ventricular end diastolic volumes at rest, assessed at each visit using transthoracic echocardiography. RESULTS: In most patients (n = 43, 66%) ventricular volumes were unchanged or reduced. Mean (SEM) treadmill exercise capacity and peak exercise cardiac index increased at month 12 by 200 (24) seconds (p < 0.001 v baseline) and by 0.8 (0.4) l/min/m2 (p<0.05 v baseline), respectively, in this group. In patients with limited ventricular dilatation (n = 11, 17%) exercise capacity increased by 259 (52) seconds (p < 0.001 v baseline) and peak exercise cardiac index improved by 0.8 (0.7) l/min/m2 (NS). In the remaining 11 patients with progressive left ventricular dilatation, exercise capacity increased by 308 (53) seconds (p< 0. 001 v baseline) and peak exercise cardiac index similarly improved by 1.3 (0.7) l/min/m2 (NS). There were trends towards increased atrial natriuretic factor (ANF) secretion at rest and at peak exercise in this group. CONCLUSIONS: Ventricular dilatation after acute myocardial infarction is a heterogeneous process that is progressive in only a minority of patients. Compensatory mechanisms, including ANF release, appear capable of maintaining and improving exercise capacity in most patients for at least 12 months, even in those with a progressive increase in ventricular size.

Adult↗
PubMed1998

Coronary angiography from the radial artery--experience, complications and limitations.

AIMS: to assess the outcomes, complications and limitations of coronary angiography performed via percutaneous radial artery puncture. METHODS AND RESULTS: two hundred and fifty patients underwent diagnostic coronary angiography from the radial artery, 182 (72.8%) of whom had contraindications to the femoral approach, for example due to peripheral vascular disease (n=85), therapeutic anticoagulation (29), or failed femoral approach (17). Procedural success in this high-risk population was achieved in 231 patients (92.4%). Principle reasons for failure were unsuccessful radial access (5) and arterial spasm (5). Procedure duration (SD) for an operator's first 20 cases compared with cases thereafter (min) was 47.7 (16.7) vs. 41.5 (14.6), P=0.0004; fluoroscopy time (min) 9.7 (7.1) vs. 6.6 (5.1), P=0.0001 and procedural success 89.6% vs. 94.1%, P=ns. Complications included two deaths associated temporally with catheterisation, three cases of arterial dissection without ischaemic sequelae and one transient ischaemic attack. CONCLUSIONS: coronary angiography can be performed successfully from the radial artery, but this approach has limitations, which include the need to demonstrate dual palmar vascular supply, the prolonged learning phase, the procedural failure rate, patient discomfort and a demonstrable incidence of vascular and haemodynamic complications. We believe that radial coronary angiography should only be undertaken when there is a contraindication to the femoral approach.

Chi-Square Distribution↗
PubMed1998

Comparison of radial versus brachial approaches for diagnostic coronary angiography when the femoral approach is contraindicated.

One hundred patients with contraindications to the femoral approach were randomized to undergo diagnostic coronary angiography via percutaneous radial puncture or brachial artery cutdown. Procedure duration, fluoroscopy time, and total radiation dose were significantly less via the radial route, whereas procedural success, complication rates, and pain scores were comparable; we conclude that the radial technique should be the arm approach of choice for new trainees, although there will be occasions when radial access fails and a brachial approach is required.

Aged↗
PubMed1998

Birefringence measurement of rapid structural changes during collagen denaturation.

Linear birefringence, an optical property that results from a material's structure and composition, can be used to study dynamic changes in tissue structure. Single, 200 microseconds-long pulses from a Ho:YAG laser emitting 2.1 microns radiation were used to induce changes in the linear birefringence of rat tail tendon. Such changes were measured on a millisecond timescale. The measured rate coefficients describing the denaturation are not predicted by previous studies of collagen denaturation induced by slower, lower-temperature heating. Two types of laser-induced collagen denaturation can be differentiated: thermal denaturation, which appears rate-limited, and thermomechanical denaturation, which is observed at higher laser radiant exposures. Neither process is described by standard Arrhenius-type kinetic models.

Animals↗
PubMed1997

Relation of daily activity levels in patients with chronic heart failure to long-term prognosis.

Symptom-limited, laboratory-based exercise tests are often used to define prognosis in patients with chronic heart failure, but they do not relate to measures of normal daily activity. Invasive measures of central hemodynamics similarly relate poorly to outcome. Pedometer scores of weekly walking are markedly reduced in patients with heart failure, but whether this less artificial measure of exercise capacity is important in predicting prognosis is not known. Eighty-four patients with chronic heart failure were followed for a mean of 710 days during which 44 died and 3 underwent cardiac transplantation. Symptom-limited treadmill exercise capacity using 2 different protocols did not predict survival, whereas reduced weekly pedometer scores were strong predictors of death (p < 0.001). Other variables that predicted death included resting cardiac output, arterial blood pressure, diuretic requirements, New York Heart Association class, increased bilirubin, and hyponatremia (all p < 0.01). Reduced levels of daily activity are strong predictors of death in chronic heart failure and appear more powerful than laboratory-based exercise tests. This type of assessment is valuable in identifying patients at high risk and provides an objective measure of incapacity during normal daily life. The exercise capacity of patients unable to exercise in the laboratory could also be assessed using this technique. This may prove invaluable in clinical and mortality trials.

Activities of Daily Living↗
PubMed1997

Quantitative measurements of linear birefringence during heating of native collagen.

BACKGROUND AND OBJECTIVE: Linear birefringence is an anisotropic property of rat tail tendon, which is largely composed of collagen. Our goal is to show that the dynamic range and sensitivity of the linear birefringence loss of collagen during heating are sufficient for kinetic modeling of the reaction. STUDY DESIGN, MATERIALS AND METHODS: The linear birefringence loss was quantified for tendon denatured via both a heated-isotonic-saline bath and a heated stage. All measurements were made with a polarizing transmission microscope equipped with a Berek compensator. RESULTS: The data show that the loss of linear birefringence is a first-order kinetic reaction. The native rat tail tendon birefringence, delta n = 3.0 +/- 0.6 x 10(-3) (mean +/- std. err.), is lost after denaturation occurs (delta n = 0). Application of the Arrhenius equation to the linear birefringence data yields the activation energy (Ea = 89 +/- 1 kcal/mole), pre-exponential coefficient (A = e130 +/- 1 s-1), enthalpy (delta H = 88 +/- 1 kcal/mole) and entropy (delta S = 197 +/- 2 cal/degree K.mole). CONCLUSION: This study shows that dynamic changes in linear birefringence can be used to monitor thermally induced changes in collagen.

Animals↗
PubMed1997

Effects of amlodipine in patients with chronic heart failure.

The role of calcium antagonists in patients with ischemic heart failure is currently unclear. We examined the effects of amlodipine on exercise capacity and central and regional hemodynamics in 32 patients with mild to moderate chronic heart failure in a single-center, double-blind, randomized placebo-controlled trial. All were taking at least 40 mg of furosemide daily with an angiotensin-converting enzyme inhibitor. Ischemic heart disease was the most common cause of heart failure, but no patient had symptom-limiting angina. Mean treadmill exercise capacity in patients taking amlodipine increased by 96 seconds (95% confidence interval -23 to 215) and 50 seconds (-34 to 135) in the placebo group; mean difference in change between treatments was 70 seconds (-90 to 233), p = 0.38. Active treatment with amlodipine did not affect self-paced corridor walking times. Similarly, there were no significant effects on cardiac output, oxygen uptake, heart rate, and mean arterial pressure at rest or during exercise. Calf and renal blood flow were also unchanged by treatment. The lack of significant effect demonstrated by these data suggests a limited role for amlodipine in patients with ischemic cardiomyopathy, although it may prove beneficial in those with nonischemic disease. More data are required before amlodipine can be recommended for all patients with chronic heart failure.

Aged↗
PubMed1997

Abnormalities of skeletal muscle metabolism in patients with chronic heart failure: evidence that they are present at rest.

OBJECTIVE: To investigate abnormalities of skeletal muscle metabolism in patients with congestive heart failure. SETTING: A university teaching hospital. METHODS: 43 patients (22 New York Heart Association (NYHA) grade II, 21 grade III) and 10 controls were studied. A forearm model of muscle metabolism was used, with a cannula inserted retrogradely into an antecubital vein of the dominant forearm. Maximum voluntary contraction (MVC) was measured using handgrip dynamometry. Subjects performed handgrip exercise, 5 s contraction followed by 5 s rest for 5 min at 25%, 50%, and 75% of MVC or until exhaustion. Blood was taken at rest and 0 and 2 min after exercise for measurement of lactate and ammonia. After 30 min the procedure was repeated with fixed workloads of 7 kg, 14 kg, and 21 kg. RESULTS: MVC (kg, mean (SEM)) was lower in patients than in controls (control 42.45 (2.3); NYHA II 34.13 (1.3), P = 0.003; NYHA III 33.13 (1.94), P = 0.008). Resting lactate (mmol/l) was higher in patients than controls (control 0.65 (0.06); NYHA II 0.84 (0.08), P = 0.13; NYHA III 1.18 (0.1), P = 0.002). Resting ammonia (mumol/l) was higher in NYHA III (65.7 (6.0)) than in NYHA II (48.0 (3.7), P = 0.016); no difference was found between controls (48.0 (7.1)) and patients. The overall lactate and ammonia response to exercise was greater in NYHA III than in NYHA II and controls (P < 0.05). At volitional exhaustion, peak lactate (mmol/l: NYHA III 3.31 (0.26); NYHA II 2.56 (0.16); controls 2.71 (0.22); P = 0.022 NYHA III v NYHA II) and ammonia (mumol/l: NYHA III) 126.4 (8.97); NYHA II 92.9 (7.23); controls 109 (16.3); P = 0.006 NYHA III v NYHA II) were higher in severe congestive heart failure. CONCLUSIONS: Skeletal muscle metabolism is abnormal at rest in congestive heart failure. During exercise, the degree of metabolic abnormality is related to the symptomatic status of the patient.

Adult↗