Biomedical subjects

J E Grunwald

Publications and source records attributed to J E Grunwald.

68 records · Page 4Linked to original sources

PubMed1985

Blood velocity and volumetric flow rate in human retinal vessels.

The distributions of blood velocity and volumetric flow rate in individual vessels of the normal human retina were determined as a function of vessel diameter. The mean velocity of blood, Vmean, was calculated from the centerline velocity measured by bidirectional laser Doppler velocimetry (LDV). Volumetric flow rate was determined from Vmean and the vessel diameter, D, measured from monochromatic fundus photographs. Diameter of the arteries and veins at the site of the LDV measurements ranged from 39 to 134 microns and 64 to 177 microns, respectively. Flow velocity correlated with D (P less than 0.001 for both arteries and veins). Volumetric flow rate varied with D at a power of 2.76 +/- 0.16 for arteries and 2.84 +/- 0.12 for veins, in close agreement with Murray's law. Calculated from 12 eyes, the average total arterial and venous volumetric flow rates were 33 +/- 9.6 and 34 +/- 6.3 microliters/min, respectively. The good agreement between both flow rates suggests that the technique and the assumptions for calculating flow yield results that satisfy mass conservation. Total arterial and venous volumetric flow rates correlated with total arterial and venous vessel cross-section. Volumetric flow rate in the temporal retina was significantly greater than in the nasal retina, but the difference is likely to be due to the larger area of the temporal retina. No difference in flow rate was observed between the superior and inferior retinal hemispheres. Finally, blood velocity in the major retinal vessels measured under normal experimental conditions appears remarkably constant over short (hours) and long (months) periods of time.

Blood Flow Velocity↗

PubMed1984

Retinal autoregulation in open-angle glaucoma.

The macular blood flow response to an induced change in intraocular pressure (autoregulation) was studied using the blue field entopic phenomenon in 11 open angle glaucoma patients, eight glaucoma suspects and 13 normal volunteers. A suction cup was used to raise the intraocular pressure (IOP) above its resting state (IOPrest). IOPmax, the highest acutely increased IOP for which blood flow can be maintained constant by autoregulation, was 24.9 +/- 1.5 mmHg (+/- 1 SD) in the glaucoma patients, 30.8 +/- 4.6 mmHg in the glaucoma suspects and 29.9 +/- 3.6 mmHg in the normal subjects. The values for IOPmax - IOPrest were 3.7 +/- 4.3 mmHg, 4.7 +/- 3.3 mmHg, and 14.3 +/- 3.1 mmHg, respectively. After the release of the suction cup, a hyperemic response was observed by 16 of 17 normal eyes, 10 of 14 glaucoma suspect eyes and only 9 of 19 glaucomatous eyes. These results suggest an abnormal autoregulation of macular retinal blood flow in open-angle glaucoma.

Adult↗

PubMed1984

Altered retinal vascular response to 100% oxygen breathing in diabetes mellitus.

The effect of 100% oxygen breathing on retinal blood flow was investigated using laser Doppler velocimetry in 19 normal eyes, and in 41 eyes of insulin treated diabetic patients. Of the diabetic eyes studied, nine had no retinopathy, 18 had background diabetic retinopathy, seven had proliferative diabetic retinopathy, and seven had proliferative diabetic retinopathy that had been previously treated by argon panretinal photocoagulation. Five minutes of 100% oxygen breathing produced an average decrease in blood flow of 61% (SD = 8) in normal eyes, 53% (SD = 10) in NR eyes, 38% (SD = 13) in background diabetic retinopathy eyes, 24% (SD = 18) in proliferative diabetic retinopathy eyes and 54% (SD = 8) in panretinal photocoagulation eyes. In six eyes with proliferative retinopathy measured before and after panretinal photocoagulation, a significant increase in vascular response to O2 was observed following photocoagulation (Wilcoxon signed rank test, P less than 0.05).

Adult↗

PubMed1984

Effect of pure O2-breathing on retinal blood flow in normals and in patients with background diabetic retinopathy.

The noninvasive Laser Doppler velocimetry technique was applied in normal volunteers and in patients with background diabetic retinopathy to determine retinal blood flow during pure oxygen breathing at atmospheric pressure. In normal subjects, five minutes of oxygen breathing produced a 63 +/- 6% decrease in retinal blood flow. In the diabetic patients blood flow decreased by only 36 +/- 15%. A significant correlation between the decrease in blood flow and that of the diameter of the veins was found in the diabetic patients. This was not the case for the normal subjects.

Adult↗

PubMed1984

Dynamics of an oscillating viscoelastic sphere: a model of the vitreous humor of the eye.

The vitreous humor of the eye is modelled as a homogeneous viscoelastic sphere. The analysis provides a relation for the displacement amplitude and phase following oscillatory and step excitations, as functions of the storage and loss moduli of the vitreous gel, and allows calculation of the resolution requirements for a non-invasive optically-based diagnostic method for the viscoelastic properties of the vitreous.

Elasticity↗

PubMed1983

Laser Doppler Velocimetry study of the effect of pure oxygen breathing on retinal blood flow.

The noninvasive Laser Doppler Velocimetry (LDV) technique was used in normal volunteers to determine retinal blood flow, F, during pure oxygen breathing at atmospheric pressure. Changes in blood flow were calculated based on Poiseuille relation, F = (pi D2/4) X Vmax, where Vmax is the red blood cell maximum or center-line velocity and D, the diameter of the vessel at the site of the LDV recordings. After five minutes of pure oxygen breathing, Vmax decreased by about 53%, vessel diameter by 12%, and retinal blood flow by about 60%. In arteries, pulsatility of red blood cell velocity (Vmax, systole/Vmax, diastole) during the cardiac cycle increased by about 10%. Decrease in red blood cell velocity was detectable within 1-1 1/2 min. From these LDV flow measurements and the changes in retinal mean circulation time (MCT) reported by other investigators, based on the relation F = v/MCT, a 45% decrease in retinal blood volume (v) during 100% O2 breathing was obtained.

Adult↗

PubMed1983

Reactivity of the human retinal circulation to darkness: a laser Doppler velocimetry study.

Bidirectional laser Doppler velocimetry (LDV) and fundus photography were applied to investigate the effects of light and darkness on retinal blood flow. Blood flow had increased by an average of 67% after 5 min of darkness. This increase persisted for periods of darkness as long as 80 min (the longest period tested). The magnitude of this elevation, its time course, and its neutralization by the breathing of 100% O2 suggest that, in vivo, the retina consumes more O2 in the dark than in light. This effect is, most probably, associated with the maintenance of the photoreceptor dark current. LDV in light and darkness may become a useful probe of retinal function.

Blood Flow Velocity↗

PubMed1982

Retinal vascular autoregulation in diabetes mellitus.

The blue field entoptic technique was used to study autoregulation of the macular retinal circulation in response to acute alterations of intraocular pressure in 71 diabetic eyes and 30 normals matched for age, systemic blood pressure, and ophthalmic artery diastolic pressure. IOPmax, the maximal intraocular pressure at which flow is maintained normal by autoregulation, was normal in eyes with no retinopathy (30 +/- 3.2 mm Hg) but decreased with progression of retinopathy, approaching the resting intraocular pressure in eyes with proliferative retinopathy. The hyperemia observed by normals to an acute reduction of intraocular pressure was not observed frequently in the diabetics with no retinopathy. The frequency of observation of the hyperemia decreased with progression of retinopathy and was uniformly absent in eyes with proliferative retinopathy. A group of eyes with minimal microangiopathy was found to have an abnormal IOPmax and no hyperemic response. The prognostic significance of these parameters remains to be established.

Adolescent↗

PubMed1982

Laser Doppler measurement of relative blood velocity in the human optic nerve head.

The Doppler shift frequency spectrum (DSFS) of laser light scattered from red blood cells (RBCs) moving in the microcirculation of the optic nerve head has been recorded in normal volunteers by means of a fundus camera laser Doppler velocimeter. The width of the DSFS, which varies in proportion to the speed of the RBCs, has been characterized by a parameter alpha. With the use of a model for the scattering of light by tissue and RBCs and for the RBC velocity distribution, values of alpha recorded at normal intraocular pressure (IOP) suggest that the RBCs that contribute to the Doppler signal are flowing in capillaries. The parameter alpha was found to vary markedly with the IOP and with the phase of the ocular pressure pulse at elevated IOP. The return of the speed of RBCs toward normal, which is observed after a step increase of IOP above normal and after a step decrease below normal, has been attributed to an autoregulatory response of the optic nerve circulation.

Blood Flow Velocity↗

PubMed1982

Autoregulation of the retinal circulation in response to decrease of intraocular pressure below normal.

The autoregulatory response of the retinal circulation to a short-term reduction in intraocular pressure (IOP) to hypotonic levels was studied in 15 normal subjects by means of the blue-field entoptic phenomenon. This phenomenon allows the perception of the leukocytes flowing in one's own retinal macular capillaries. Subjects were asked to compare the leukocyte speed in one eye with that in the fellow eye while a scleral suction cup was used to raise the IOP in one eye to levels above 25 mm Hg for approximately 12 min. The release of the suction cup caused a drop in IOP to levels between 4 and 7 mm Hg, at which time all subjects reported a higher leukocyte speed (hyperemia) in this eye than in the fellow eye. After an average of 4 min the speed was observed to be equal in both eyes. The average IOP at which the equalization occurred was 6.8 +/- 1.3 mm Hg. The retina can therefore normalize leukocyte capillary speed and presumably blood flow at IOPs at least as low as 6.8 mm Hg. The results of 16 experiments on the same eye of one subject suggest that under these experimental conditions, the lowest IOP for which the retina can fully autoregulate is around 6 to 7 mm Hg.

Adult↗

PubMed1981

Blue field entoptic phenomenon in amblyopia.

The blue field entoptic phenomenon allows the perception of leukocytes moving in the retinal capillaries of one's own retina. This phenomenon is not affected by media opacities provided that enough blue light reaches the retina. The phenomenon was investigated in 63 amblyopic patients to determine if the perception of the leukocytes in the amblyopic eye differs from that in the good eye. A difference in perception would provide a means of assessing amblyopic in eyes with opaque media. Ninety-four percent of the amblyopic eyes perceived less sharp particles, 83% perceived fewer particles and 60% perceived slower particles than in the good eyes. In 86% of the amblyopic eyes, the tails were shorter than in the good eyes or absent entirely. The degree of amblyopia correlated with the difference in the number of leukocytes observed in each eye. No differences in the perception of leukocytes were reported by 20 normal subjects.

Adolescent↗

PubMed1981

Is the pulsating vascular tree entoptic phenomenon an indicator of ophthalmic artery pressure?

The relation between the intraocular pressure (IOP) at which the pulsating vascular tree (PVT) entoptic phenomenon is first observed and the ophthalmic artery diastolic pressure measured by ophthalmoscopic examination of the central retinal artery was determined in 25 normal volunteers. The PVT entoptic phenomenon consists in perceiving black stripes in the shape of branches of a tree appearing and disappearing synchronously with each heartbeat when the intraocular pressure is increased. The average IOP at which the entoptic phenomenon was first observed was 51.4 +/- 7.5 mm Hg, and the average ophthalmic artery diastolic pressure was 51.8 +/- 7.5. The correlation coefficient between both sets of numbers was r = 0.97 (p less than 0.01). These results show that the ophthalmic artery diastolic pressure can be measured accurately with the perception of the PVT phenomenon as an end point. Because the perception of the phenomenon is not disturbed by ocular media opacities, this method enables the determination of the ophthalmic artery diastolic pressure in eyes where an ophthalmoscopic examination is not possible.

Adult↗

PubMed1981

Autoregulation of retinal circulation in response to decrease of perfusion pressure.

Autoregulation of the retinal circulation in response to an acute elevation of intraocular pressure was investigated in 17 subjects (23 eyes) with no ocular abnormalities, by means of the blue field entoptic phenomenon. This phenomenon allows a person to observe leukocytes flowing in his own macular capillaries. Subjects were instructed to compare the speed of their leukocytes in one eye with that in the other eye. All subjects perceived equal speed in both eyes. During their observation of the leukocytes, the intraocular pressure (IOP) was rapidly raised in one eye to a level at which autoregulation was not sufficient to maintain normal blood flow. At that level of IOP, subjects described the leukocytes moving slower in this eye than in the fellow eye. The IOP was then decreased in steps of 2 to 3 mm Hg until the subjects reported observing equal leukocyte speeds in both eyes. The IOP at which this occurred, IOPmax, represents the highest IOP (lowest mean perfusion pressure P min) at which the retina is able to maintain normal blood average IOPmax was 29.6 +/- 2.0 mm Hg, corresponding to an average of P min of 27 +/- 6 min Hg and demonstrating that a decrease of 36% or less in perfusion pressure is adequately compensated by retinal vascular autoregulation.

Adult↗

PubMedDate not supplied

Effect of niacin on retinal vascular diameter in patients with age-related macular degeneration.

PURPOSE: Niacin is a B vitamin well-known for causing vasodilation and flushing. The purpose of this study was to investigate its effect on the retinal vasculature of patients with age-related macular degeneration (AMD). METHODS: Twelve patients with AMD were enrolled in a double-blind, randomized, placebo-controlled, crossover trial. Fundus photographs of the posterior pole were taken at baseline, 30 min, and 90 min after a single dose of niacin or placebo. The protocol was repeated after a washout period using the alternate study drug. The diameters of two veins and one artery on each image were measured. RESULTS: An analysis of variance for repeated measures comparing the effects of niacin with those of placebo demonstrated a significant increase in the inferior temporal retinal artery diameter (p = 0.01), with a 5.3 +/- 7.7% increase at 30 min (p = 0.05) and 5.8 +/- 5.0% increase at 90 min (p = 0.003). No significant changes were observed in the temporal retinal veins. CONCLUSIONS: Our results suggest that niacin produces vasodilatation of retinal arterioles. Further studies are needed to ascertain whether niacin treatment may be beneficial in retinal ischemic diseases.

Aged↗