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Biomedical subjects

J T Walsh

Publications and source records attributed to J T Walsh.

At least 55 records · Page 3Linked to original sources
PubMed1990

Thermal damage produced by high-irradiance continuous wave CO2 laser cutting of tissue.

Thermal damage produced by continuous wave (cw) CO2 laser ablation of tissue in vitro was measured for irradiances ranging from 360 W/cm2 to 740 kW/cm2 in order to investigate the extent to which ablative cooling can limit tissue damage. Damage zones thinner than 100 microns were readily produced using single pulses to cut guinea pig skin as well as bovine cornea, aorta, and myocardium. Multiple pulses can lead to increased damage. However, a systematic decrease in damage with irradiance, predicted theoretically by an evaporation model of ablation, was not observed. The damage-zone thickness was approximately constant around the periphery of the cut, consistent with the existence of a liquid layer which stores heat and leads to tissue damage, and with a model of damage and ablation recently proposed by Zweig et al.

Animals↗
PubMed1989

Er:YAG laser ablation of tissue: effect of pulse duration and tissue type on thermal damage.

The thermal damage caused by 2.94-micron Er:YAG laser ablation of skin, cornea, aorta, and bone was quantified. The zone of residual thermal damage produced by normal-spiking-mode pulses (pulse duration approximately 200 microseconds) and Q-switched pulses (pulse duration approximately 90 ns) was compared. Normal-spiking-mode pulses typically leave 10-50 microns of collagen damage at the smooth wall of the incisions; however, at the highest fluences (approximately 80J/cm2) tears were produced in cornea and aorta and as much as 100 microns of damaged collagen is found at the incision edge. Q-switched pulses caused less thermal damage, typically 5-10 microns of damage in all tissues.

Animals↗
PubMed1989

Er:YAG laser ablation of tissue: measurement of ablation rates.

The ablation of both soft and hard tissue using the normal-spiking-mode Er:YAG laser has been quantified by measuring the number of pulses needed to perforate a measured thickness of tissue. Bone is readily ablated by 2.94 microns radiation; however, at per pulse fluences greater than 20 J/cm2, plasma formation decreases ablation efficiency. At low fluence, desiccation can prevent efficient ablation of bone. The ablation efficiency for aorta and skin is higher than for bone. The ablation efficiency, 540 micrograms/J, and the ablation depth per pulse, greater than 400 microns, for skin are too high to be readily explained by simple models of ablation and thus provide evidence for a more complex explosive removal process.

Animals↗
PubMed1989

Pulsed CO2 laser ablation of tissue: effect of mechanical properties.

The ablation rate of guinea pig skin and bovine aorta, myocardium, and liver by a CO2 laser emitting 2-microseconds-long pulses was quantified. Ablation efficiency was found to be strongly dependent upon the ultimate tensile strength of the tissue; the ablation efficiency of liver is seven times that of skin. Gluteraldehyde cross linking of skin, which is known to greatly increase tissue stiffness but not significantly affect ultimate tensile strength, did not change the ablation rate. The water content of the tissues, which largely determines the optical and thermal properties, was measured and found to vary only slightly. The results demonstrate that tissue mechanical properties are important in the interpretation and modeling of pulsed laser ablation of tissue and that variations in these mechanical properties can lead to drastically different cutting rates for different tissues.

Animals↗
PubMed1988

Pulsed CO2 laser tissue ablation: effect of tissue type and pulse duration on thermal damage.

Tissue removal by infrared lasers is accompanied by thermal damage to nonablated tissue. The extent of thermal damage can be controlled by a choice of laser wavelength, irradiance, and exposure duration. The effect of exposure duration has been studied in vivo by using CO2 lasers with pulse widths that vary from 2 microseconds to 50 msec. Pulse widths of 50 msec, typical of a shuttered, continuous-wave CO2 laser, produce damage regions 750 micron wide in normal guinea pig skin; the use of a 2-microseconds-long pulse reduced this damage zone to as little as 50 micron. Using 2-microseconds-long pulses, in vitro studies showed that the minimum zone of thermal damage varied significantly with tissue type. The thermal denaturation of these tissues has been studied and correlated with damage. The effect of denaturation temperature and pulse duration on the width of the damage zone is explained by a simple model.

Animals↗
PubMed1988

Pulsed CO2 laser tissue ablation: measurement of the ablation rate.

Ablation of guinea pig skin using a CO2 laser emitting 2-mu sec-long pulses has been quantified by measuring the mass of tissue removed as a function of incident fluence per pulse. The mass-loss curves show three distinct regimes in which water evaporation, explosive tissue removal, and laser-induced plasma formation dominate. The data are fit to two models that predict that the mass removed depends either linearly or logarithmically on fluence. Although the data are best fit by a linear dependence upon fluence, plasma formation at high fluences prohibited obtaining data over a wide enough fluence range to differentiate unambiguously between the two models. Ablation efficiency, ablation thresholds, and the optical penetration depth at 10.6 micron were obtained from the measurements.

Animals↗
PubMed1987

Increasing daytime vascular resistance with progressive hypertension in ambulant patients.

Twenty-four-hour recordings of intra-arterial blood pressure, heart rate, and calculation of the index of peripheral vascular resistance were obtained in 20 untreated ambulant hypertensive patients during their routine activities outside the hospital. Blood pressures and heart rates were higher during the day, with a mean night-to-day increase of 22%, 34%, and 26%, for systolic, diastolic, and mean pressures, respectively. The average increase in the heart rate was 32%. Overall, the index of resistance was lower (12%) during the day. However, eight patients (40%) demonstrated no change or an increase in the peripheral vascular resistance. Six of these eight patients had an average daytime mean pressure above 120 mm Hg. There was a significant decrease in the index of resistance during exercise in all but one of the 16 subjects. Hemodynamic parameters of 1 hour before and 1 hour after awakening were similar to the values obtained during the entire night and the rest of the day, respectively. Our data suggest that in patients with "progressive" hypertension, the ability to decrease vascular resistance from night to day is compromised.

Adult↗
PubMed1986

Relative tachycardia in ambulant children with borderline hypertension.

Borderline hypertensives who demonstrate tachycardia have a tendency toward the development of essential hypertension. However, the documentation of tachycardia in previous studies has been generally based on brief periods of observation. In the present study, we measured heart rates through a 24-hour period in 16 ambulatory mildly hypertensive subjects (ages 5 to 23 years). When compared with normal matched controls, significantly (p less than 0.05) higher heart rates were observed during the waking periods (99 +/- 9 vs 90 +/- 11) and sleep periods (72 +/- 12 vs 62 +/- 7). Similar observations were also made for 24 hours (90 +/- 8 vs 79 +/- 8). In addition, hypertensives also demonstrated thickened (during diastole) left ventricular posterior wall (0.96 +/- 0.17 vs 0.85 +/- 0.13 cm; p less than 0.05) and interventricular septum (0.98 +/- 0.17 vs 0.84 +/- 0.19 cm; p less than 0.05). It is suggested that tachycardia may be an early manifestation of borderline hypertension in children.

Adolescent↗
PubMed1985

The lowering of daytime blood pressures with a single daily dose of acebutolol in ambulant hypertensives.

Intra-arterial blood pressure recordings were studied in 10 ambulant subjects with essential hypertension to evaluate the effect of a single daily dose of acebutolol. Blood pressures and heart rates, measured on a beat-to-beat basis were averaged over every hour, for the daytime, night-time, and for the total 24 hours. Acebutolol significantly lowered the average daytime systolic pressure (160 to 142 mmHg, p = less than 0.01), diastolic pressure (78 to 66 mmHg, p = less than 0.01), and the heart rate (92 to 77 beats/min, p = less than 0.001). Significantly lower pressures were demonstrated up to 11 hours after the last dose of acebutolol. The effect on heart rate lasted up to 13 hours. The observed lowering of pressures and heart rate during the remaining 11 hours did not reach statistical significance.

Acebutolol↗
PubMed1985

Evaluation of an index of peripheral vascular resistance in human subjects.

Based on evidence in animal studies, an index of resistance in man has been evaluated. In 10 human subjects, ranging in age from 31 to 60 years, direct brachial arterial pressure was measured, and a computer program using linear regression calculated the index of resistance from the slope of the logarithm of the pressure versus time during the second half of diastole. Resistance was independently calculated from 20-s averages of pressure and cardiac output obtained by thermodilution. Resistance was varied by infusion of phenylephrine and nitroprusside. The values of the index of resistance were compared with independently calculated resistance by linear regression and correlation. The index of resistance was variably correlated with independently calculated resistance. However, when the comparison was limited to points with a model correlation coefficient greater than or equal to 0.98 (i.e. a good fit of a straight line to the logarithm of pressure versus time), the correlation of the index of resistance with calculated resistance approached or exceeded 0.9 in eight of 10 subjects. In the two subjects showing poor correlation of the index with calculated resistance, estimated compliance from the same model was much lower than in the other subjects. In the same two subjects pressure dependence of estimated compliance was much higher than in the other subjects, suggesting the presence of significant atherosclerosis. We concluded that the diastolic decay of pressure may be used to calculate a useful index of resistance, provided that a single exponential decay fits the observed diastolic waveform well, and arterial compliance is not significantly reduced by atherosclerosis.

Adult↗
PubMed1985

An index of peripheral vascular resistance.

An index of peripheral vascular resistance, derived from directly measured arterial pressure, has been developed and tested in an animal model. Assuming a mono-exponential character for diastole, the time constant for direct arterial pressure decay in the central aorta was obtained with high-fidelity recording techniques from six anaesthetized dogs. Changes in peripheral resistance were induced by infusion of phenylephrine or nitroprusside. The time constant correlated well with resistance determined from 1-min averages of pressure divided by integrated electromagnetic flow (r = 0.845). A portable system used for direct arterial pressure recording in ambulant outpatients yielded a mean correlation of 0.822 with resistance. In a study of patients undergoing cardiac catheterization, a time constant obtained from the brachial artery (the site of pressure recording in the ambulant subjects) correlated well with the aortic time constant (n = 6, r = 0.964). The results of the present work suggest that the time constant derived from direct arterial pressure waveform may be a useful index in the evaluation of the peripheral vascular resistance. Furthermore, with the help of the portable system it might be used for the continuous monitoring of resistance changes in ambulatory subjects.

Animals↗
PubMed1985

A non-invasive index of leg arterial perfusion pressure during walking, derived from cutaneous toe temperature.

This article describes and evaluates a non-invasive technique for continuous monitoring of hemodynamic changes in the legs during walking. The method involves monitoring of cutaneous toe temperature. In six normal subjects we have shown that, during exercise under carefully controlled conditions, a unique steady-state toe temperature exists for any given leg arterial perfusion pressure, when perfusion pressure is varied by means of an external occluding ankle cuff. Further, we have demonstrated a strong correlation between this external ankle cuff pressure and the time rate of changes of toe temperature during the test-period following occlusion. Correlation coefficients, r1, were between -1 and -0.88 (mean -0.95; standard deviation +/- 0.03) for big toe and between -1 and -0.87 (mean -0.94; standard deviation +/- 0.03) for third toe. We conclude that during walking the time profile of toe temperature changes is a useful index of changes in leg perfusion pressure. Therefore, toe temperature may be used to study the dynamics of leg arterial circulation in atherosclerotic occlusive diseases.

Adult↗
PubMed1984

An isolated rat liver model for the evaluation of thermal techniques to quantify perfusion.

An isolated, thermally regulated, perfused rat liver model system is presented. The model was developed to evaluate thermal methods to quantify perfusion in small volumes of tissue. The surgically isolated rat liver is perfused with an isothermal oxygenated Krebs-Ringer bicarbonate buffer solution via the cannulated portal vein. A constant-pressure head variable-resistance scheme is utilized to control the total flow to the liver. Total flow is quantified by hepatic vein collection. The spatial distribution of perfusion within the liver is determined using two independent methods. In the first method, radio-labelled microspheres are injected into the portal vein, and the regional flow distribution is determined from the relative radioactivity of each section of tissue. In the second method, the tissue is thermally perturbed, and the time constant of the tissue temperature recovery is measured. The regional distribution is determined from the relative time constants of each section of tissue. Both methods require the measurement of total liver flow to determine the absolute perfusion at each point. Results obtained by the two methods were well correlated (0.973). The rat liver system offers a stable, controllable, and measurable perfusion model for the evaluation of new perfusion measurement techniques.

Animals↗
PubMed1982

Familial glaucoma with sleep apnoea: a new syndrome?

Sleep apnoea was combined with glaucoma in five members of two generations of a family The three surviving members with heavy snoring and glaucoma with intraocular pressure maxima in the morning and a fourth with heavy snoring only all had clinical sleep apnoea. The more severe glaucoma, resistant to surgery and medication, correlated with a greater number and duration of episodes of sleep apnoea. In all those who had recordings made episodes of sleep apnoea tended to occur and be more prolonged in rapid-eye-movement sleep. Oxygen desaturation was greater in rapid-eye-movement sleep and could occur without evidence of impaired respiration. In the third generation of this family there is as yet no evidence of impaired respiration in sleep or of glaucoma.

Aged↗
PubMed1981

Naloxone and focal epilepsy: a study with depth electrodes.

Intravenous injections of naloxone (0.8 to 2.4 mg) were given to patients with focal epilepsy who had had electrodes implanted in cortical and subcortical structures. There were no changes in interictal spike activity, responses to electrical stimulation, of frequency of spontaneous seizures. These data do not support the hypothesis that opiate peptides are involved in human focal epilepsy.

Action Potentials↗
PubMed1977

Prostaglandin biosynthesis in the epidermis and dermis of young mouse skin, and the effects of calcium and cyclic nucleotides.

Homogenates of skin from 2- to 3-day old mice converted labeled eicosa-8,11,14-trienoic acid to prostaglandins (PGs) PGE1, D1, and F1alpha. For several reasons PGD2 has been overlooked as a possible major PG in skin. The relative formation of each PG was modified by the presence of reduced glutathione (GSH), chelating agents (EDTA, EGTA), and L-epinephrine. Chelating agents and l-epinephrine increased conversion, espeicially to PGE1 but this effect was not due to inactivation of Ca++ which was shown to have no control over the reaction. Cyclic nucleotides including cyclic AMP (cAMP) and cyclic GMP (cGMP) were also ineffective. The conversion occurred mostly in the epidermis. Epidermal preparations were more efficient in the conversion than those from whole skin. Indomethacin (0.2 mM) completely inhibited the reaction.

8,11,14-Eicosatrienoic Acid↗