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Biomedical subjects

J B Scott

Publications and source records attributed to J B Scott.

At least 19 recordsLinked to original sources
PubMed1995

Clinical comparison of desired versus actual amount of surgical crown lengthening.

The actual length of clinically exposed tooth structure between planned restoration margin and alveolar crest ("biologic width") obtained during surgical crown elongation procedures was compared to the textbook goal of 3.0 mm. Sixteen (16) patients with 21 teeth requiring surgical crown lengthening for restoration placement participated. Oral hygiene instructions were given and optimal plaque control was mandatory. At each clinician's discretion, surgical techniques consisted of either gingivectomy or an apically positioned flap with and without osseous resection. Utilizing a reference stent, measurements were obtained at the facial, mesial-facial, lingual, and distal-lingual of the treated teeth both before and after osseous reduction. Parameters evaluated were gingival margin position, probing depth, mucogingival junction position, alveolar crest location, mobility, plaque index, and gingival index. These measurements were again recorded 8 weeks after surgery with the exception of alveolar crest. Statistical analysis with the paired t-test and linear correlation showed no significant change from baseline or among operators with varying experience in any of these parameters. Overall the results showed that the default objective of 3 mm between planned restoration margin and alveolar crest was not routinely achieved (mean 2.4 +/- 1.4 mm). The post-treatment distance from the planned restoration margin to the alveolar crest was greatest at the facial aspect of the teeth (mean 2.6 +/- 1.2 mm) and least at the distal-lingual (mean 2.2 +/- 1.7 mm). In addition, although more experienced periodontists removed a larger amount of bone, the amount of root surface exposed was still short of the initially desired biologic width.(ABSTRACT TRUNCATED AT 250 WORDS)

Alveolar Process↗
PubMed1984

Effect of equilibration zones on stability, uniformity, and homogeneity profiles of vapors and aerosols in the ADG nose-only inhalation exposure system.

A commercially available, inexpensive, nose-only exposure chamber was modified to include removable equilibration zones, and the effect of these zones on chamber performance was determined. Since limited performance data were available concerning this unit, a more extensive characterization was performed. EPA limit concentrations (greater than or equal to 5 mg/liter) of toluene vapor or corn oil aerosol, and relatively low concentrations of uranine aerosol (less than or equal to 50 micrograms/liter) were produced by standard techniques. The presence or absence of equilibration zones did not affect the stability or uniformity of toluene vapor atmospheres, with the coefficient of variation (CV) not exceeding 3.33% in all experiments. In contrast, the presence of two equilibration zones was found to progressively enhance the uniformity of the inhalable test aerosols in the animal exposure zone (CV less than or equal to 3.16%). Matrix sampling revealed that in both uranine and corn oil experiments, the center matrix point concentration was consistently lower than samples taken in the actual animal breathing zone. Equilibration zones markedly reduced the difference between breathing zone and center point concentrations. These performance data indicated that the modified ADG nose-only exposure system performed exceptionally well with the materials that were studied. Results were comparable to those describing whole-body chamber performance. The ready availability of this inexpensive prototype lends itself to standardization of techniques between laboratories.

Aerosols↗
PubMed1983

Effects of brain hypoxia on pulmonary hemodynamics.

The effects of acute brain hypoxia on pulmonary hemodynamics were investigated in anesthetized dogs with the vagus and carotid sinus nerves intact and cut. Following ligation of collateral vessels, brain hypoxia was induced by pumping arterial blood through a ventilated extracorporeal lung to the external carotid arteries for 5 min. In the intact-nerve group brain hypoxia caused no change in pulmonary and systemic vascular pressures and resistances. In the cut-nerve group brain hypoxia caused an increase in mean pulmonary artery, left atrial, pulmonary artery pulse, and mean aortic pressures. Cardiac output, dP/dt, central blood volume, and total peripheral resistance increased but pulmonary vascular resistance and lung extravascular thermal volume were unchanged. It is concluded that acute brain hypoxia does not increase pulmonary vascular resistance but may increase pulmonary blood volume resulting from increased left ventricular afterload.

Animals↗
PubMed1983

Effects of histamine on lung water and hemodynamics after beta-blockade.

The effects of 90 min intravenous histamine (10 micrograms base . kg-1 . min-1) with and without beta (propranolol)-receptor blockade on lung water and hemodynamics were studied. In anesthetized dogs cold 3% saline was used as the indicator to determine cardiac index, central blood volume, and lung extravascular thermal volume. Propranolol alone decreased stroke volume and cardiac index but increased central blood volume, total peripheral resistance, and mean pulmonary arterial and pulmonary arterial wedge pressures. Pulmonary vascular resistance, mean arterial pressure, and lung extravascular thermal volume were not changed. Histamine with propranolol further reduced stroke volume and cardiac index, whereas mean pulmonary arterial and pulmonary arterial wedge pressures returned to control values. Mean arterial pressure, central blood volume, and total peripheral resistance decreased, pulmonary vascular resistance increased, and lung extravascular thermal volume remained unchanged. In all experiments postmortem extravascular lung water-to-dry weight ratio was unchanged. We conclude that histamine does not increase lung water content and that beta-receptor blockade does not modify this response.

Adrenergic beta-Antagonists↗
PubMed1982

Local vasoactivity of oxygen and carbon dioxide in the right coronary circulation of the dog and pig.

1. Eight mongrel dogs were anaesthetized with sodium thiamylal and chloralose-urethane, ventilated, vagotomized and heparinized. Five Poland-China pigs were anaesthetized with sodium thiamylal and nitrous oxide, ventilated, vagotomized and heparinized. 2. Extracorporeal perfusion of the right coronary artery at constant pressure (100 mmHg) was instituted. A lung from a donor animal was interposed in the coronary perfusion circuit to effect changes in CO2 and O2 tensions in the coronary arterial blood while systemic blood gases were maintained at normal levels. 3. Local hypoxia (PO2 range 17-22 mmHg) produced a 25-75% decrease in coronary vascular resistance (P less than 0.05) and a 0-24% (not significant) decrease in right ventricular dP/dt. 4. Local changes in PCO2 over the range 8-105 mmHg were associated with a 17-58% decrease in coronary vascular resistance (P less than 0.05), a 19-24% decrease in right ventricular dP/dt (P less than 0.05) with no change in right ventricular end-diastolic pressure, and a 1-18% (not significant) decrease in heart rate. 5. These studies suggest that local decreases in O2 or increases in CO2 tensions produce decreases in right coronary vascular resistance that are in the opposite direction to those that would be expected from the observed changes in heart rate and contractility (two primary determinants of myocardial oxygen consumption). 6. These data support the hypothesis that CO2 and O2 are locally vasoactive in the coronary circulation.

Animals↗
PubMed1982

Central blood volume and lung extravascular thermal volume in dogs with dirofilariasis.

Central blood volume, lung extravascular thermal volume, cardiac output, and pulmonary and systemic vascular pressures were measured in clinically normal and heartworm-infected dogs. Central blood volume and cardiac output were significantly (P less than 0.05) decreased in heartworm-infected dogs compared with the in normal dogs. Pulmonary vascular resistance, total peripheral resistance, mean pulmonary artery, pulmonary artery wedge, and pulse pressures were significantly increased in heartworm-infected dogs compared with that in normal dogs. Significant differences between normal and heartworm-infected dogs were not found in lung extravascular thermal volume, pulmonary extravascular tissue weight, or extravascular lung water to extravascular dry-weight ratio. Lung extravascular thermal volume overestimated gravimetric pulmonary extravascular tissue weight by approximately 16%. A significant correlation (R = 0.83) existed between pulmonary extravascular tissue weight and lung extravascular thermal volume for all dogs.

Animals↗
PubMed1981

Vascular response of the chicken hindlimb to vasoactive agents, asphyxia, and exercise.

Previous studies in live chickens have measured heart rate, blood pressure, and cardiac output during drug administration or asphyxia and made assumptions concerning the peripheral vasculature. The present study employs a constant-flow, isolated hindlimb perfusion technique to measure directly changes in skeletal muscle vascular resistance induced either by local intra-arterial (i.a.) bolus, or continuous i.a. infusion, of various vasoactive substances. Prostaglandin E1 (0.5 microgram, bolus) produced arteriolar vasodilation lasting 10 min, as indicated by a fall ian perfusion pressure. Bolus injection of histamine (10 microgram diphosphate) or adenosine (5 and 10 microgram) produced vasodilation of less than 2-min duration. Theophylline infusion (5 microM infused at 1 mL/min, i.a.) blocked the effect of adenosine. Norepinephrine (1 microgram) produced vasoconstriction which was reduced 60% by systemic alpha-adrenergic blockade with phenoxybenzamine (7.5-10 mg/kg). Tracheal occlusion produced intense vasoconstriction which was reduced 70% by alpha-adrenergic blockade. Electrical stimulation of the peripheral end of the cut sciatic nerve (6 Hz) produced an immediate vasodilation lasting several minutes.

Acetylcholine↗
PubMed1981

Vascular and hematologic effects of hemorrhage in the chicken.

Chickens have been reported to have a rate of posthemorrhagic fluid mobilization twice that of mammals and lack a phase of shock irreversible to transfusion. In the present study we measured several hemodynamic and hematologic parameters in chickens subjected to sustained hemorrhagic hypotension. Total peripheral resistance was unaffected or fell slightly and skeletal muscle vascular resistance judged from changes in gastrocnemius resistance was not affected by hemorrhage. Blood compositional changes included a progressive hyperkalemia, hyperglycemia, and hemodilution as evidenced by linear falls in hematocrit, hemoglobin, and plasma total protein concentration. Plasma sodium and osmolality were unchanged, as were arterial pH and oxygen tension; however, there was a fall in carbon dioxide tension. These studies demonstrate that fluid mobilization in the chicken after hemorrhage does not require an increase in precapillary resistance and suggest that, because the chicken does not exhibit intense precapillary constriction, it is spared some of the deleterious effects of inadequate tissue perfusion. Thus, the findings tend to incriminate the peripheral action of the sympathetic nervous system as a major contributor to the development of irreversibility in other species.

Acid-Base Equilibrium↗
PubMed1981

Carotid sinus reflex vasoconstriction in right coronary circulation of dog and pig.

This study was designed to evaluate the effects of the sympathetic nervous system on right ventricular and right coronary hemodynamics in the anesthetized vagotomized dog and pig during constant-pressure coronary perfusion. Carotid occlusion in the dog resulted in an increase in heart rate, aortic pressure, right ventricular dP/dt, and a sustained 13% decrease in right coronary artery blood flow and a 14% increase in coronary vascular resistance. This coronary vasoconstriction was not modified during beta-blockade with propranolol but was prevented by alpha- blockade with phentolamine. Similar hemodynamic data was obtained in the pig and, in addition, it was found that the O2 consumption of the right ventricle is low (4.8 +/- 0.4 ml O2.min-1.100 g-1) and is only slightly increased (5.l5 +/- 0.8 ml.min-1.100 g-1) during carotid occlusion. These data suggest that baroreflex-mediated sympathetic stimulation to the heart evokes only a minor increase in metabolic activity in the right ventricular myocardium so that the direct neural (alpha-vasoconstrictor) effect predominates over the metabolic vasodilator mechanism.

Animals↗
PubMed1981

Flow through collapsible tubes at high Reynolds numbers.

The pressure-flow relationships of collapsible tubes were studied utilizing the Starling resistor model. Reynolds numbers much higher than previously reported were used to simulate high cardiac output states. Alterations which occur in vivo, including longitudinal tension, stretch, tubing diameter, length, and outflow resistance were also simulated and systematically investigated. The pressure-flow curves showed an initial rising phase, a plateau phase, as well as a late-rising phase which has not been reported previously. Self-induced oscillations occurred during the plateau phase and persisted throughout the late-rising phase. These perturbations were markedly increased by longitudinal tension and stretch, but were attenuated by increased diameter, length, and outflow pressure. These instabilities may prove to be an explanation for the "venous hum."

Animals↗
PubMed1981

Systemic and digital vascular effects of intravenous histamine in the pony.

The effects of a 60-minute IV infusion of histamine (0.5 mg of histamine base/minute) on the systemic, pulmonary, and digital vasculature were investigated in mature ponies. Immediately after the start of histamine infusion, there were a transient decrease in systemic pressure lasting less than 1 minute and then a brief period of systemic hypertension. Systemic pressure then returned to preinfusion levels for the remainder of the infusion period. Pulmonary arterial pressure increased transiently coincident with systemic hypotension. Histamine increased cardiac output and decreased both total peripheral and pulmonary vascular resistances. In the digit, blood flow increased for the duration of the systemic hypertension, but was otherwise unchanged. Digital lymph flow and protein concentration were unchanged by histamine. Hematocrit increased significantly after 60 minutes of histamine infusion, but plasma and blood volumes were unchanged. Histamine caused cyanosis, hyperpnea, and sweating in all ponies. The effects of histamine given IV do not mimic the systemic and digital vascular effects of acute alimentary laminitis.

Animals↗
PubMed1980

Effect of pulmonary venous pressure on steady-stage collateral resistance.

Steady-state collateral resistance (Rcoll), residual volume (RV), and lung pressure-volume (PV) relations were determined in an isolated perfused dog lung as pulmonary venous pressure (Ppv) was increased. Increased Ppv had no effect on the lung PV curve except for a significant increase in RV when Ppv equaled or exceeded 20 Torr. When compared to the value at Ppv = 5 Torr, significant decreases in Rcoll occurred when Ppv was raised to 15 Torr or above at transpulmonary pressure, PL = 0 cmH2O, to 20 Torr or above when PL = 2 cmH2O, and to 25 Torr or above when PL = 4 cmH2O. In most dogs the decrease in Rcoll with increased Ppv could be explained by increased lung volume.

Animals↗
PubMed1980

Flow through collapsible tubes at low Reynolds numbers. Applicability of the waterfall model.

The applicability of the waterfall model was tested using the Starling resistor and different viscosities of fluids to vary the Reynolds number. The waterfall model proved adequate to describe flow in the Starling resistor model only at very low Reynolds numbers (Reynolds number less than 1). Blood flow characterized by such low Reynolds numbers occurs only in the microvasculature. Thus, it is inappropriate to apply the waterfall model indiscriminately to flow through large collapsible veins.

Blood Vessels↗