Spread of cochlear excitation during stimulation with pulsed infrared radiation: inferior colliculus measurements

Infrared neural stimulation (INS) has received considerable attention over the last few years. It provides an alternative method to artificially stimulate neurons without electrical current or the introduction of exogenous chromophores. One of the primary benefits of INS could be the improved spatial selectivity when compared with electrical stimulation. In the present study, we have evaluated the spatial selectivity of INS in the acutely damaged cochlea of guinea pigs and compared it to stimulation with acoustic tone pips in normal-hearing animals. The radiation was delivered via a 200 µm diameter optical fiber, which was inserted through a cochleostomy into the scala tympani of the basal cochlear turn. The stimulated section along the cochlear spiral ganglion was estimated from the neural responses recorded from the central nucleus of the inferior colliculus (ICC). ICC responses were recorded in response to cochlear INS using a multichannel penetrating electrode array. Spatial tuning curves (STCs) were constructed from the responses. For INS, approximately 55% of the activation profiles showed a single maximum, ∼22% had two maxima and ∼13% had multiple maxima. The remaining 10% of the profiles occurred at the limits of the electrode array and could not be classified. The majority of ICC STCs indicated that the spread of activation evoked by optical stimuli is comparable to that produced by acoustic tone pips.

Acoustic modulation and photon-phonon scattering in optical coherence tomography

Acousto-optic interactions allow the measurement of nonoptical material properties with high-resolution optical methods. We modulated a sample with ultrasound while simultaneously imaging with a traditional optical coherence tomography (OCT) system. The measured acousto-optic signal then depends on the mechanical response of the tissue to the applied modulation. The acquired acoustically enhanced OCT signals are consistent with established acousto-optic theory and provide enhanced contrast to OCT images.

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.

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.

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.

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.

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.

Polarized light propagation through tissue phantoms containing densely packed scatterers

We demonstrate that polarized light is maintained differently in densely packed versus dilute suspensions of polystyrene microspheres. The degrees of linear and circular polarization were measured versus scatterer concentration in aqueous suspensions of 0.48-, 0.99-, 2.092-, and 9.14-mum-diameter polystyrene microspheres. The results indicate that, for dilute suspensions of microspheres where independent scattering is assumed, the degrees of linear and circular polarization decrease as the scatterer concentration increases. For dense suspensions, however, the degree of polarization begins to increase as the scatterer concentration increases. The preferential propagation of linear over circular polarization states in dense suspensions is similar to results seen in biological tissue.

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.

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.

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.

Comparison of polarized-light propagation in biological tissue and phantoms

We demonstrate significant differences in the propagation of polarized light through biological tissue compared with two common tissue phantoms. Depolarization of linearly and circularly polarized light was measured versus propagation distance by use of two independent measurement techniques. The measurements were performed on adipose and myocardial tissues and on tissue phantoms that consisted of polystyrene microsphere suspensions and Intralipid. The results indicate that, in contrast with results obtained in tissue phantoms, linearly polarized light survives through longer propagation distances than circularly polarized light in biological tissue.

Polarization discrimination of coherently propagating light in turbid media

We describe the use of degree of polarization to discriminate unscattered and weakly scattered light from multiply scattered light in an optically turbid material. We use spatially resolved measurements of the degree of polarization to compare how well linearly and circularly polarized light survives in a sample. Experiments were performed on common tissue phantoms consisting of polystyrene and Intralipid microsphere suspensions and on adipose and arterial tissue. The results indicate that polarization is maintained even after unpolarized irradiance through each sample has been extinguished by several orders of magnitude. The results also show that polarized light propagation in common tissue phantoms is distinctly different from polarized light propagation in the two tissues investigated. Further, these experiments illustrate when polarization is an effective discrimination criterion and when it is not. The potential of a polarization-based discrimination scheme to image through the biological and nonbiological samples investigated here is also discussed.

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.

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.

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.

Dye-assisted laser skin closure with pulsed radiation: an in vitro study of weld strength and thermal damage

Previous laser skin welding studies have used continuous wave delivery of radiation. However, heat diffusion during irradiation prevents strong welds from being achieved without creating large zones of thermal damage. Previously published results indicate that a thermal damage zone in skin greater than 200 μm may prevent normal wound healing. We propose that both strong welds and minimal thermal damage can be achieved by introducing a dye and delivering the radiation in a series of sufficiently short pulses. Two-cm-long incisions were made in guinea pig skin, in vitro. India ink and egg white (albumin) were applied to the wound edges to enhance radiation absorption and to close the wound, respectively. Continuous wave (cw), 1.06 μm, Nd:yttrium-aluminum-garnet laser radiation was scanned over the weld producing ∼100 ms pulses. The cooling time between scans and the number of scans was varied. The thermal damage zone at the weld edges was measured using a transmission polarizing light microscope. The tensile strength of the welds was measured using a tensiometer. For pulsed welding and long cooling times between pulses (8 s), weld strengths of 2.4±0.9 kg/cm2 were measured, and lateral thermal damage at the epidermis was limited to 500±150 μm. With cw welding, comparable weld strengths produced 2700±300 μm of lateral thermal damage. The cw weld strengths were only 0.6±0.3 kg/cm2 for thermal damage zones comparable to pulsed welding. © 1998 Society of Photo-Optical Instrumentation Engineers.

Tricuspid regurgitation following central line insertion in a patient undergoing haemodialysis

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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.

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.

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.

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.

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.

Inspiratory muscle endurance in patients with chronic heart failure

OBJECTIVE

To assess the significance of changes in respiratory muscle endurance in relation to respiratory and limb muscle strength in patients with mild to moderate chronic heart failure using a threshold loading technique.

SUBJECTS

20 patients with chronic heart failure (17 male) aged 63.8 (SD 7.4) years and 10 healthy men aged 63.1 (5.6) years. Heart failure severity was New York Heart Association (NYHA) grade II (n = 11) and NYHA grade III/IV (n = 9).

METHODS

Respiratory muscle strength was measured from mouth pressures during maximum inspiratory effort (MIP) at functional residual capacity (FRC) and limb muscle strength was measured using a hand grip dynamometer. Inspiratory muscle endurance was measured using a threshold loading technique. The total endurance duration, the maximum threshold pressure achieved (P-Max), and the inspiratory load (% ratio of P-Max/MIP) were recorded in all subjects.

RESULTS

Inspiratory muscles were weaker in patients with heart failure than in the controls [MIP 53.6 (16.5) v 70.9 (20.2) cm H2O, P < 0.05]. Hand grip strength was similar in both subject groups [31.6 (SD) v 36.1 (15.9) dynes]. Total endurance duration was significantly reduced in the patient group [494 (223) v 996 (267) s, P < 0.01], as was the maximal threshold pressure achieved [P-Max 18.5 (6.4) v 30.7 (6.6) cm H2O, P < 0.01]. When expressed as a percentage of MIP, P-Max was also lower in the patients [35.2 (11.8) v 44.8 (11.4)%, P < 0.05]. There was no significant correlation between any measure of endurance and limb muscle strength.

CONCLUSIONS

Respiratory muscle endurance is reduced in patients with chronic heart failure. These changes probably reflect a generalised skeletal myopathy and provide further evidence of respiratory muscle dysfunction in patients with this disease. Respiratory muscle endurance needs now to be related to symptoms and the effects of treatment and respiratory muscle training should also be explored.

Dynamic 193-nm optical properties of water

Previous assumptions that water is not a 193-nm chromophore during ArF excimer laser tissue ablation are based on room-temperature data and ignore spectroscopic literature that suggests a strong temperature dependence of far-ultraviolet water absorption. By the use of a Q-switched Er:YAG laser as a pump source and an ArF excimer laser as a probe source, thermal generation and relaxation of 193-nm water absorption were characterized under nonequilibrium high-temperature and high-pressure conditions. At volumetric energy densities as small as 2 kJ/cm(3) relative to room temperature, the 193-nm absorption coefficient of water was measured to increase by more than 5 orders of magnitude. These results are consistent with the hypothesis that the absorption of 193-nm radiation by water may play a role in ArF excimer laser ablation of tissue.

Erbium laser ablation of dental hard tissue: effect of water cooling

BACKGROUND AND OBJECTIVE

Several lasers have been explored for hard dental tissue applications; used alone they have resulted in potentially harmful temperature increases in the pulp chamber.

MATERIALS AND METHODS

An Er:YAG laser (lambda = 2.94 microns) was used to ablate hard dental tissues. Ablation rates with and without a water-cooling spray were measured. Subsequent experiments investigated the cooling effects of the water. Initially single channels were drilled into dentin; further studies involved ablating rectangular areas with repetition rates up to 10 Hz.

RESULTS

The water spray minimally reduced the ablation rates of dentin and did not affect the ablation rates of enamel. The water spray effectively cooled the teeth; while using the maximum average power investigated (10 Hz, 360 mJ/pulse), a water flow rate of 4.5 ml/min limited the temperature rise in the pulp chamber to less than 3 degrees C.

CONCLUSION

The studies confirm the feasibility of using an Er:YAG laser in conjunction with a water spray to safely and effectively remove hard dental tissues.

Shear strength of composite bonded to Er:YAG laser-prepared dentin

An Er:YAG laser coupled with a cooling stream of water effectively removes dental hard tissues. However, before such a system can be deemed clinically viable, some safety and efficacy issues must be addressed. We compared the bonding of composite to dentin following the preparation of the dentinal surface with either an Er:YAG laser (lambda = 2.94 microns) or a standard dental bur and with and without a subsequent acid-etching treatment. The crowns of extracted human molars were removed, revealing the underlying dentin. We removed an additional thickness of material with either a dental handpiece or an Er:YAG laser (350 mJ/pulse at 6 Hz) by raster-scanning the samples under a fixed handpiece or laser. Comparable surface roughnesses were obtained. Several samples from each group received an acid-conditioning treatment. A cylinder of composite was bonded onto the prepared surfaces. The dentin-composite bond was then shear-stressed to failure on a universal testing apparatus. The results indicate that laser-irradiated samples had improved bond strengths compared with acid-etched and handpiece controls. SEM photographs of the surfaces show exposed tubules following the laser treatment: tubules could also be exposed with acid etching. We conclude that Er:YAG laser preparation of dentin leaves a suitable surface for strong bonding or an applied composite material.

Erbium laser ablation of dental hard tissue: effect of water cooling

BACKGROUND AND OBJECTIVE

Several lasers have been explored for hard dental tissue applications; used alone they have resulted in potentially harmful temperature increases in the pulp chamber.

MATERIALS AND METHODS

An Er:YAG laser (lambda = 2.94 microns) was used to ablate hard dental tissues. Ablation rates with and without a water-cooling spray were measured. Subsequent experiments investigated the cooling effects of the water. Initially single channels were drilled into dentin; further studies involved ablating rectangular areas with repetition rates up to 10 Hz.

RESULTS

The water spray minimally reduced the ablation rates of dentin and did not affect the ablation rates of enamel. The water spray effectively cooled the teeth; while using the maximum average power investigated (10 Hz, 360 mJ/pulse), a water flow rate of 4.5 ml/min limited the temperature rise in the pulp chamber to less than 3 degrees C.

CONCLUSION

The studies confirm the feasibility of using an Er:YAG laser in conjunction with a water spray to safely and effectively remove hard dental tissues.

Water flux from partial-thickness skin wounds: comparative study of the effects of Er:YAG and Ho:YAG lasers

BACKGROUND AND OBJECTIVE

The clinical use of lasers to cut and coagulate tissue necessitates a better understanding of how the residual thermal damage affects healing. This study was designed to evaluate the effects of varying degrees of thermal damage on the healing process.

STUDY DESIGN, MATERIALS AND METHODS

Partial-thickness lesions were created in guinea pig skin using an Er:YAG laser, a Ho:YAG laser, and a scalpel. To monitor recovery of the stratum corneum, water flux from the wound sites was quantified and histological data obtained for approximately one week.

RESULTS

The data indicate an exponential water loss pattern from all wounds. Water flux from the scalpel- and the Er:YAG laser-induced wounds was initially high but decreased rapidly with decay rates (mean +/- SE) of 0.46 +/- 0.01 day-1 and 0.38 +/- 0.01 day-1, respectively. The Ho:YAG laser-induced wounds demonstrated a different pattern of decay with lower water flux values initially and a decay rate of only 0.13 +/- 0.01 day-1.

CONCLUSION

Histological and water flux data reveal that Er:YAG laser-induced wounds achieve epidermal integrity only slightly after scalpel-induced lesions, and Ho:YAG laser-induced wounds heal substantially slower and contain more granulation tissue.

Failure of "effective" treatment for heart failure to improve normal customary activity

OBJECTIVES

To examine the effects of drug treatment on laboratory exercise tests in relation to measures of daily activity in patients with chronic heart failure.

SETTING

University teaching hospital.

SUBJECTS

18 patients with mild to moderate chronic heart failure (New York Heart Association functional class II-III) and 10 age matched healthy controls.

METHODS

Assessments were made before and after 12 weeks of vasodilator drug treatment. Exercise capacity was measured during two different types of treadmill exercise, one using a ramp protocol and the other a fixed work load. Corridor walk tests at three self selected speeds were also undertaken and measures of customary activity assessed from pedometer scores.

RESULTS

Exercise times were significantly increased from baseline (P < 0.01) with both treadmill protocols after 12 weeks of drug treatment, with a positive correlation between the duration of treadmill exercise for both protocols (r = 0.69, P < 0.01). Corridor walk tests of 100 m at a self selected slow speed also improved (P < 0.02) but these did not correlate with the changes in treadmill exercise time. The pedometer scores of the patients with heart failure were greatly reduced compared with those of the controls (258 (45) x 10(2) v 619 (67) x 10(2) steps/week, P < 0.001) and after 12 weeks of treatment were unchanged (261 (42) x 10(2) steps/week).

CONCLUSIONS

These data confirm the need to use different exercise protocols when assessing the benefits of drug treatment in patients with chronic heart failure. Treatments that seem effective with conventional laboratory based exercise tests may not improve daily activities. This may reflect a failure of apparently successful treatment and should be considered when interpreting clinical trials.

ACE for whom? Implications for clinical practice of post-infarct trials

OBJECTIVE

To determine how many lives would be saved if patients were routinely treated with ACE inhibitors after myocardial infarction according to the criteria of four recent major clinical trials, and to estimate the costs and benefits of these approaches.

DESIGN

Retrospective survey.

SETTING

The Nottingham Health District.

PATIENTS

Data from 7855 patients admitted between 1989 and 1990 were combined and the selection criteria of four major clinical trials (AIRE, SAVE, GISSI-3, and ISIS-4) were applied.

RESULTS

Of the patients admitted in Nottingham with confirmed myocardial infarcts 39% were eligible for AIRE and 8% for SAVE. In patients with suspected myocardial infarction as defined by the major trials, 60% would have been eligible for GISSI-3 and 63% for ISIS-4. Treating appropriate patients in accordance with these trials would have saved 20 (AIRE), 3 (SAVE), 4 (GISSI-3) and 5 (ISIS-4) lives each year in Nottingham at a drug cost of 5400 pounds, 33 pounds 791, 2730 pounds, and 4116 pounds per life per year saved respectively.

CONCLUSIONS

Short-term treatment with ACE inhibition appears to be cheaper but such an approach would save fewer lives. The AIRE study is the most applicable to current clinical practice but ACE inhibitors should be offered routinely to patients satisfying the criteria of any of the four major clinical trials.

Effects of captopril and oxygen on sleep apnoea in patients with mild to moderate congestive cardiac failure

OBJECTIVES

To determine the effects of captopril and oxygen on sleep quality in patients with mild to moderate cardiac failure.

DESIGN

An open observational study.

PATIENTS

12 patients with New York Heart Association class II-III heart failure were studied at baseline. 9 of these patients were then examined at the end of 1 month of treatment with captopril; 9 of the patients were separately assessed during a single night of supplementary oxygen.

MAIN OUTCOME MEASURES

Sleep patterns by polysomnography, overnight oximetry, and subjective sleep assessment using visual analogue scores.

RESULTS

Abnormal sleep was present in all baseline studies. Complete polysomnograms after treatment with captopril were obtained in 8 patients. Light sleep (stages 1 and 2) was reduced (mean (SEM) 61%(8)% to 48%(6)% actual sleep time, P < 0.05) but slow wave (stages 3 and 4) and REM (rapid eye movement) sleep increased (25%(6)% to 31%(5)%, 14%(2)% to 21%(5)% actual sleep time, P < 0.05). Apnoeic episodes (242(59) to 118(30), P < 0.05), desaturation events (171(60) to 73(37), P < 0.05), and arousals (33(5) to 18(3) P < 0.01) were reduced. Visual analogue scores of sleep quality increased 49(5) to 69(5), P < 0.01). Complete polysomnograms were obtained in 7 patients treated with oxygen. Light sleep duration was reduced (55% (7)% to 42%(5)% actual sleep time, P < 0.05) and slow wave sleep increased (30%(5)% to 38%(6)% actual sleep time, P < 0.05). REM sleep duration was not significantly different. Total arousals (33(6)% to 20(2) P < 0.05), desaturation events (140(33) to 38(10), P < 0.01), and apnoeic episodes (212(53) to 157(33), P < 0.05) were reduced. Visual analogue scores of sleep quality were unchanged.

CONCLUSIONS

Captopril and oxygen may improve sleep quality and reduce nocturnal desaturation in patients with mild to moderate cardiac failure. Improved sleep quality could explain the reduction in daytime symptoms seen after treatment in patients with chronic heart failure.

Haemodynamic and hormonal response to a stream of cooled air

Many patients with angina note that their symptoms deteriorate in cold weather, although the precise physiological mechanism that explains this remains unclear. Exposure of the face to cool winds may be a contributory factor. The cardiovascular and hormonal response to a localised stream of room (22 degrees C) and cold (4 degrees C) air during submaximal treadmill exercise was therefore studied in nine normal subjects. Cardiac output and respiratory gases were measured with a mass spectrometer, using the indirect Fick principle. Blood samples were taken for plasma noradrenaline. A localised stream of air at 5 m.s-1 produced significant cardiovascular effects at rest, some of which persisted during exercise. In response to cold air, stroke volume, cardiac output, blood pressure and oxygen uptake increased (all P < 0.05). There was a trend towards a reduction in heart rate at rest and increase in plasma noradrenaline. Room air caused a reduction in blood pressure (P = 0.01) but stroke volumes and oxygen uptake were unchanged. The results of this study demonstrate significant cardiovascular effects of a cooled air facial stimulus at rest and during exercise. They may, in part, explain the effects of cold winds on patients with angina.

Lasers in dentistry

Since the development of the ruby laser by Maiman in 1960, there has been great interest among dental practitioners, scientists, and patients to use this tool to make dental treatment more pleasant. Oral soft tissue uses are becoming more common in dental offices. The possible multiple uses of lasers in dentistry, beyond soft tissue surgery and dental composite curing, unfortunately, have not yet been realized clinically. These include replacement of the dental drill with a laser, laser dental decay prevention, and laser decay detection. The essential question is whether a laser can provide equal or improved treatment over conventional care. Safe use of lasers also must be the underlying goal of proposed or future laser therapy. With the availability and future development of different laser wavelengths and methods of pulsing, much interest is developing in this growing field. This article reviews the role of lasers in dentistry since the early 1960s, summarizes some research reports from the last few years, and proposes what the authors feel the future may hold for lasers in dentistry.

ERISA estoppel: say what you mean and mean what you say

Estoppel is rapidly becoming part of ERISA litigation. However, as employers, TPAs and other entities associated with ERISA plans learn to take precautions against erroneous representations, estoppel litigation may subside.

Unruptured aneurysm of the left sinus of Valsalva presenting with atrial fibrillation

Congenital aneurysms arising from the left sinus of Valsalva are extremely uncommon, and when unruptured often asymptomatic. Abnormalities of rhythm are more commonly associated with dilatation of the right coronary sinus although the reason for this is unclear. We report the first case of an unruptured aneurysm involving the left sinus of Valsalva presenting with paroxysmal atrial fibrillation. Two-dimensional echocardiography confirmed the diagnosis.

Pharmacokinetics of hydroxyurea in nude mice

Extrachromosomal DNA is the predominant form of gene amplification in human tumors. Hydroxyurea (HU) concentrations of 100-150 microM have been promising in vitro for extrachromosomal DNA elimination. The study objective was to determine the HU dose-concentration relationship in nude mice with HU doses from 0 to 200 mg/kg. For HU t1/2 determination, mice were injected with HU 100 mg/kg. A plasma concentration of 159 microM was achieved and a t1/2 of 11.3 min determined. Based on these findings, In vivo elimination studies will require frequent administration of HU to maintain plasma concentrations from 100 to 150 microM.

Er:YAG laser ablation of prairie dog gallbladder epithelium for the prevention of gallstones

We hypothesized that laser ablation of gallbladder epithelium would prevent gallstone formation in prairie dogs. An Er:YAG laser (lambda = 2.94 microns) was used to ablate the gallbladder epithelium of 24 prairie dogs; 20 sham-irradiated and 12 non-operated prairie dogs served as controls. Prairie dogs were sacrificed at time periods of 4 days, 2 weeks, and 8-12 weeks and evaluated for the presence of gallstones and cholesterol crystals. Laser-irradiated gallbladders demonstrated a lower rate of gallstone formation at 8-12 weeks than the sham-irradiated gallbladders (39% vs. 79%: P < .02). Crystal formation, however, was not different between laser-irradiated (88%) and sham-irradiated (100%) animals. The laser-irradiated group had less epithelium than the non-operated group at all time periods (P < or = .002) and compared to the sham-irradiated group at 4 days and 8-12 weeks (P < or = .001). These data suggest that laser ablation of gallbladder epithelium can reduce the rate of gallstone formation although this effect may be temporary.

Effect of the dynamic optical properties of water on midinfrared laser ablation

Water is a primary tissue chromophore in the midinfrared. Absorption of midinfrared radiation by water is a function of temperature and pressure, both of which rise rapidly during an ablative laser pulse. Data show that the absorption coefficient of water changes, by as much as two orders of magnitude, during a high-irradiance laser pulse. We present an ablation model that is fundamentally based upon Beer's Law but considers changes in the absorption coefficient. The model predicts that Er:YAG laser cuts will be deeper than Er:YSGG laser cuts; an opposite prediction would be made based upon the static, low-intensity absorption coefficient of water. The results of in vitro ablation of skin confirm that the dynamic optical properties of tissue need to be considered in the understanding of laser ablation as well as the design, manufacture, use, and regulation of clinical laser systems.

Double minutes are frequently found in ovarian carcinomas

Double minutes (dmins) are acentric chromosomal-like entities that are important in the etiology of cancer because they are known to harbor amplified oncogenes and drug resistance genes. Because dmins can be unequally partitioned at mitosis they have the ability to confer genetic diversification rapidly. Selective pressures operative in vitro may be quite different than those in vivo; therefore, tumor cells which harbor dmins could be selected against during short-term in vitro propagation. We wanted to determine the incidence of dmins in human ovarian cancer cells obtained from fresh ovarian specimens with an absolute minimum of culture time (6-24 hours). In "direct" chromosomal preparations obtained from these clinical specimens we found dmins present in 88% of these samples. This remarkable finding that dmins are found so frequently in ovarian cancers underscores the importance of gene amplification in human tumor biology. Therefore, the presence of dmins in patient specimens indicates that these unstable genetic elements may play a significant role in the maintenance or progression of malignancy.