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Biomedical subjects

T K Goldstick

Publications and source records attributed to T K Goldstick.

At least 37 records · Page 2Linked to original sources
PubMed1985

Hyaluronate increases intraocular pressure when used in cataract extraction.

A prospective randomised study of 26 eyes (24 patients) following uncomplicated intracapsular cataract surgery was carried out with three groups in which different agents were used to re-form the anterior chamber: air, seven eyes; sodium hyaluronate, seven eyes; and a combination of hyaluronate plus systemic acetazolamide, 12 eyes. The intraocular pressure (IOP) was measured by Goldmann applanation tonometry 16 hours before surgery and every eight hours after surgery for 72 hours. The IOP doubled in the two hyaluronate-treated groups for the first day following cataract surgery. By contrast, the IOP in the group receiving air initially decreased slightly. Throughout the study the effect of using acetazolamide was never statistically significant. After the first day and a half the differences in IOP among the three treatment groups disappeared, and the pressures returned to their preoperative values.

Acetazolamide↗
PubMed1985

Ocular massage before cataract surgery.

We used the Honan intraocular pressure reducer, a balloon that applies a constant force, to the eyes in ten subjects with senile cataracts. An initially significant decrease in intraocular pressure after removal disappeared exponentially with a half-time of 9.6 minutes, indicating that the benefits derived from the Honan balloon do not result from a sustained reduction in intraocular pressure. Measurements made on a phantom eye showed both marked variability and unexpectedly high intraocular pressure during typical preoperative digital massage by a group of ophthalmic surgeons. Measurements made on a cadaver eye after application of the Honan balloon showed that very high intraocular pressures may be achieved under some conditions.

Cataract Extraction↗
PubMed1984

Diabetic oxygen-hemoglobin equilibrium curves evaluated by nonlinear regression of the Hill equation.

The oxygen-hemoglobin equilibrium curves ( OHECs ) were measured on whole blood samples from 131 individuals (33 normal and 26 diabetic adults and 30 normal and 42 diabetic juveniles) using a Radiometer Dissociation Curve Analyzer (DCA-1). All measurements were made in the morning following an overnight fast and without exogenous insulin. The saturation versus Po2 data were fitted to the Hill equation using a previously described nonlinear regression algorithm to yield the parameters describing the position (P50) and shape (n) of each OHEC . It was found that the Hill model could be used to describe OHECs of both normal and diabetic subjects. A small (approximately 10%) but significant decrease in P50 was found for the diabetic juveniles compared to normal juveniles. There appeared to be no change in P50 with diabetes in adults. However, in these diabetic subjects, the P50 had been increased by the somewhat elevated levels of 2,3-DPG. No difference in n was found between either group of diabetics and their corresponding group of normals but n was approximately 5% lower in juveniles than in adults. The ability of blood to release oxygen to tissue may be transiently impaired in diabetic juveniles because of the left shift of their OHECs .

Adult↗
PubMed1984

Retinal oxygen tension in diabetic dogs following insulin infusion.

We measured preretinal oxygen tensions using a microelectrode in dogs made diabetic with alloxan. The intravenous administration of insulin did not affect preretinal oxygen tension over the two hours it could be continuously accurately measured. Furthermore, the oxygen-hemoglobin equilibrium curves measured before and two hours after insulin administration did not change.

Animals↗
PubMed1984

Renal tissue oxygenation following induced hypotension in dogs.

Renal oxygenation was studied during induced hypotension in mongrel dogs, anaesthetized with 1-1.5% halothane in oxygen. Hypotension was induced with an infusion i.v. of sodium nitroprusside (SNP) 70 +/- 17 micrograms kg-1 min-1 (mean +/- SEM) or trimetaphan (TMP) 36 +/- 16 micrograms kg-1 min-1, or by controlled arterial haemorrhage (45 +/- 6 ml/kg of body weight). Mean arterial pressure (MAP), cortical (Pcto2) and medullary (Pmto2) tissue oxygen tensions, arterial (Pao2), renal venous (Prvo2), and urine (Puo2) oxygen tensions were measured during the 40-min control, hypotension, and recovery periods. MAP was decreased to approximately 60% of the control value. Pcto2 decreased significantly (P less than 0.05) in all three groups while Pmto2 decreased significantly only in the haemorrhage group. Upon restoration of MAP to normal values, renal tissue oxygen tensions recovered in all groups, somewhat more rapidly in the SNP group. There were no significant differences in Pao2, Prvo2, and Puo2 during control, hypotension and recovery periods in the three groups. Tissue oxygen tension values followed the changes in MAP, but were not hypoxic, leading us to believe that both SNP and TMP are hypotensive agents safe for the kidney.

Animals↗
PubMed1984

Retinal oxygen tension and oxygen reactivity in retinopathy of prematurity in kittens.

In the first series of experiments, preretinal oxygen tensions were measured using microelectrodes in newborn kittens, at 6 +/- 2 days of age, following their placement in an atmosphere of 80 to 90% oxygen for 5 +/- 1 day. The oxygen exposure caused an obliteration of the normally developing retinal vasculature. Preretinal oxygen tensions in the resultant avascular retina were close to zero while those in the vascular retina were near normal. The avascular retina was a "sink" for ocular oxygen. Oxygen breathing resulted in expected increases in preretinal oxygen tension, but, surprisingly, the preretinal oxygen tension decreased with continued oxygen administration. Because the oxygen tension in the avascular retinal area is determined primarily by the choroidal circulation, we speculated that increased oxygen caused a decreased choroidal blood flow. In the second series of experiments, however, choroidal blood flow was measured in the kittens by applying a temperature probe to the sclera and oxygen breathing did not appear to have an effect. These results did not support the initial speculation. It may be that the decrease in preretinal oxygen tension observed with continued oxygen administration resulted from progressive increase in utilization.

Animals↗
PubMed1983

Effects of oxygen and carbon dioxide on the retinal vasculature in humans.

Mixtures of carbon dioxide and oxygen are commonly used in the treatment of central retinal artery obstruction to improve retinal oxygenation. While oxygen alone causes retinal vasoconstriction, it is thought that the carbon dioxide balances this effect, even causing a net vasodilatation. To test this hypothesis, normal, healthy volunteers were given 100% oxygen, a mixture of 95% oxygen and 5% carbon dioxide, and a mixture of 5% carbon dioxide in air to breathe. The caliber of large, fluorescein-filled retinal arteries and veins was then measured using computer processing of digitized television images. The marked decrease in arterial and venous caliber caused by 100% oxygen was not reversed by the subsequent addition of 5% carbon dioxide. Moreover, 5% carbon dioxide in air did not cause substantial vasodilatation of the retinal vasculature. The efficacy of adding 5% carbon dioxide to oxygen to treat retinal vascular obstructive diseases is questioned.

Adult↗
PubMed1983

Characterization of oxygen-hemoglobin equilibrium curves using nonlinear regression of the Hill equation: parameter values for normal human adults.

Measurements of oxygen concentration versus PO2 in blood from 33 normal adults were fitted, using a special nonlinear regression analysis, to the Hill equation to obtain the parameters describing the position (P50) and shape (n) of each oxygen-hemoglobin equilibrium curve (OHEC). Data between 20% and 97% saturation were described well by this empirical two-parameter model. The mean (+/- SD) P50 and n were found to be 26.2 (+/- 0.8) torr and 2.50 (+/- 0.07), respectively, in good agreement with previously published values. Some normal individuals, however, deviated markedly from the averages indicating that the published values cannot be applied to everyone.

Adult↗
PubMed1983

Hyperglycemia impairs retinal oxygen autoregulation in normal and diabetic dogs.

Preretinal oxygen tensions were measured continuously using microelectrodes in four normal dogs and four dogs made diabetic with alloxan. The latter were kept under poor control for 8 months. Glucose administered intravenously in 30 to 90 sec to all the dogs when they were normoglycemic caused an immediate increase in preretinal oxygen tension lasting approximately 10 min. When the dogs were given 100% oxygen to breathe, their preretinal oxygen tensions increased. This increase in preretinal oxygen tension was 36.6 +/- 8.5 mmHg (+/-SE) when the animals were normoglycemic and 63.5 +/- 9.2 mmHg when the animals were made hyperglycemic. This suggests that hyperglycemia impairs oxygen autoregulation. Moreover, the diabetic dogs appeared to exhibit a larger preretinal oxygen tension increase than normal dogs when both were given 100% oxygen to breathe. The small number of animals studied, however, makes a comparison between the two groups difficult. These data lead one to speculate that in diabetes there may be an impairment of the normal retinal vascular homeostasis. This could play a role in both the development and in the severity of diabetic retinopathy.

Animals↗
PubMed1982

Effect of pulsatility on oxygen transport to the human arterial wall.

Oxygen transfer in fully-developed, pulsating, laminar flow in rigid and distensible tubes was simulated as part of a study of vessel-wall hypoxia and atherogenesis. The model used for the computations is based on dimensions and flows in the human thoracic aorta. The pulsatile velocity fields employed are based on those of Womersley with the modification that the radial convection is written relative to the moving wall. Womersley-type pulsatility, superposed on an axial Poiseuille flow, was found to negligibly affect oxygen transport to the wall. Caution should be exercised, however, in extending this conclusion to the complex pulsatility in actual living vessels.

Aorta, Thoracic↗
PubMed1982

Arterial wall oxygen consumption rate varies spatially.

The ratio of the O2 consumption rate (Q) to the O2 transmissibility (diffusivity-solubility product, Dk) was estimated by curve-fitting O2 tension profiles measured in vascular strips in vitro and in blood vessels in vivo. For rabbit aortic tissue in vitro, Q/Dk was 2.51 +/- 0.28 (SE) X 10(5) Torr/cm2 (n = 9). For various dog vessels in vivo, Q/Dk ranged from 0.15 to 47 X 10(5) Torr/cm2. In most cases, Q/Dk was higher near the endothelium than in the outer wall. This difference appears to be caused by a higher Q. Computer simulations using a two-layer O2 transport model with estimated Q/Dk indicate that the O2 supply from the vasa vasorum is essential to prevent medial wall hypoxia.

Animals↗
PubMed1982

Effect of photocoagulation on ocular blood flow.

The effect of panretinal photocoagulation on ocular blood flow was studied in pigmented rabbits by means of labeled microsphere impaction and in monkeys by indocyanine-green-dye clearance. In the rabbits, one eye of each animal was photocoagulated and the follow eye of the same animal was used as the control. Twenty-six rabbits received full-scatter panretinal photocoagulation (300 +/- 20 burns, one half burn apart) and an additional 32 rabbits received partial-scatter panretinal photocoagulation (150 +/- 20 burns, one burn apart). After full-scatter photocoagulation there was a significant decrease in choroidal-retinal blood flow measured at 1 to 2 hr, 24 hr, 2 weeks, 4 weeks, and 3 months, but no change in iris-ciliary body blood flow. After partial scatter photocoagulation there was no consistent change. In one monkey, 100 burns were placed around the macular area and in a second monkey 100 burns were placed in the inferior half of the ocular fundus. Choroidal blood flow was significantly reduced in both monkeys for the initial hour during which is was continually measured.

Animals↗
PubMed1980

The contrast sensitivity of cat retinal ganglion cells at reduced oxygen tensions.

1. These experiments were done to investigate the effect of various degrees of hypoxia on the function of retinal ganglion cells (recorded in the optic tract) and on retinal oxygen tension. 2. The contrast sensitivity of the centre of X and Y cells, the surround of X cells and the non-linear subunits of Y cells were measured separately by choosing appropriate spatial and temporal parameters of a sinusoidal grating pattern. 3. Retinal oxygen tension was measured with a bipolar polarographic oxygen electrode positioned in the vitreous humor close to the retina. 4. The time course of changes in ganglion cell sensitivity and retinal oxygen tension was similar. However, oxygen tension frequently overshot the prehypoxic value at the end of hypoxia, while sensitivity did not. 5. The cat retina was rather resistant to hypoxia. Contrast sensitivity and mean firing rate did not change provided the arterial oxygen tension was above about 35 mmHg, but usually dropped precipitously at lower arterial values. 6. The apparent reason for this resistance is that retinal oxygen tension was well regulated, falling only 0.14 mmHg per mmHg of arterial oxygen tension for arterial values above about 35 mmHg, which corresponds to a retinal oxygen tension of about 10 mmHg. Retinal oxygen tension decreased more sharply (0.62 mmHg per mmHg) at lower values of arterial oxygen tension, where sensitivity also decreased. 7. The centre, surround and subunits reacted similarly to hypoxia. This suggests that lateral pathways (i.e. surround) and pathways which might be expected to use more synapses than the centre (i.e. surround and subunits) are not more susceptible to hypoxia.

Action Potentials↗