Biomedical subjects

B L Petrig

Publications and source records attributed to B L Petrig.

At least 37 records · Page 2Linked to original sources

PubMed1995

Effects of adenosine on ocular blood flow.

PURPOSE: To determine the effect of intravascular adenosine on blood flow in the ocular fundus and to examine indirectly whether the blood-brain barrier to adenosine, which exists in the cerebrovasculature of the cat, is present in the eye of this animal. METHODS: The noninvasive techniques of laser Doppler flowmetry and velocimetry along with fundus photography were used to measure the change in optic nerve head and choroidal and retinal blood flow during intravenous infusions of 0.18 and 0.6 mg/kg per minute of adenosine. RESULTS: Infusions of adenosine induced significant increases in choroidal blood flow (60% with 0.6 mg/kg per minute) but not in optic nerve head or retinal blood flows. CONCLUSIONS: The lack of effect of intravenously infused adenosine on the optic nerve and retinal circulations is most likely caused by the tight junctions in the vessels of these vascular beds, which prevent adenosine from reaching its receptors. Perivascular adenosine in the choroid most likely accounts for the increase in blood flow in this tissue.

Adenosine↗

PubMed1994

Strict metabolic control and retinal blood flow in diabetes mellitus.

The effects of strict diabetic control on retinal haemodynamics were studied to elucidate whether such effects are associated with retinopathy changes. In 28 patients with poorly controlled insulin dependent diabetes mellitus and non-proliferative retinopathy, retinal haemodynamics were investigated at baseline, 5 days, 2 months, and 6 months after the institution of strict diabetic control using the bidirectional laser Doppler velocimetry technique and monochromatic fundus photography. Changes in retinal blood flow measured in a major retinal vein (Q) on the fifth day of strict diabetic control correlated significantly with changes in retinopathy level observed at the end of the 6 months of this study (rank correlation 0.65, p < 0.01). On the fifth day of strict diabetic control, 16 out of 20 eyes that showed no progression (NP) of retinopathy at the end of the study had decreases in Q, whereas six out of eight eyes that showed progression (P) had increases in Q. The difference in these changes in Q between P and NP eyes was statistically significant (one way analysis of variance, p = 0.001). No significant changes in Q were detected at 2 months or 6 months. Following the institution of strict diabetic control, no significant changes in time were detected in the regulatory response to 100% oxygen breathing characterised as the percentage decrease in Q at 4-6 minutes of oxygen breathing (analysis of variance, p = 0.36). Changes in Q following institution of strict diabetic control are associated with progression of retinopathy. Measurements described in this study may help identify diabetic patients at risk of progression when their metabolic control is improved.

Adolescent↗

PubMed1994

Choroidal blood flow in the foveal region of the human ocular fundus.

PURPOSE: To develop a noninvasive method for the investigation of choroidal blood flow (ChBF) and its regulation in the foveal region of the human ocular fundus. METHODS: Measurement of ChBF was based on the technique of laser Doppler flowmetry (LDF). Sixteen normal subjects (age range, 20 to 64 years), with normal eye examination results, were asked to fixate on a diode laser beam (wavelength = 811 nm, 60 microW at the cornea) delivered to the undilated eye through a fundus camera. Light scattered by red blood cells in the tissue volume sampled by the incident laser beam was detected at the fundus image plane of the camera by an optical fiber. The diameter of the beam at the fundus of the emmetropic eye was about 300 microns. Relative ChBF was measured in both eyes by analyzing the Doppler signal with commercial skin blood flowmeters. The average pulsatile component of ChBF, ChBFP, was determined over the cardiac cycle, and its value was compared to the average total ChBF, ChBFAV. Responses of ChBF to various physiological stimuli, such as increased blood O2 and CO2 concentrations, rapid increases in intraocular pressure, and valsalva maneuvers, were documented. RESULTS: Significant correlations were obtained between the ChBFAV values measured with both flowmeters (P < 0.001) and between the ChBFAV values measured in the right and left eye (P < 0.001). ChBFP represented less than 23% of ChBFAV. ChBFAV was not significantly affected by 5 minutes of breathing 100% oxygen. Raising end-tidal CO2 in one subject from 37 to 59 mm Hg increased ChBFAV by approximately 40%. Acute elevation of the intraocular pressure by suction cup or finger pressure on the globe reduced ChBFAV by as much as 90%. Valsalva maneuvers induced reproducible responses that were very different from those recorded from the skin microcirculation. CONCLUSIONS: Although LDF of the choroidal circulation is still at an early stage of development, this noninvasive method appears to provide continuous and sensitive measurements of relative choroidal blood flow in the foveal region of the human fundus. Near-infrared laser diodes enable measurements through undilated pupils. Examples of responses suggest new avenues in the investigation by LDF of the effect of various physiological stimuli, pharmacologic agents, and pathologic processes on the choroidal circulation in man.

Adult↗

PubMed1994

Effect of flicker on macular blood flow assessed by the blue field simulation technique.

PURPOSE: To determine the effect of diffuse luminance flicker on the motion of leukocytes in the retinal macular capillaries of normal subjects. METHODS: Using the blue field simulation technique, subjects were asked to match the motion of simulated leukocytes displayed on a video monitor to that of their own entoptically seen white blood cells (WBCs). The changes in velocity and density of the WBCs were recorded after stimulation with diffuse luminance flicker of various durations (0 to 16 seconds), either immediately or at various delays (2, 4, 8 seconds) after cessation of the stimulus. RESULTS: White blood cell velocity increased as flicker duration increased from 0 to 16 seconds. After cessation of flicker, leukocyte motion decreased to baseline within 15 seconds. CONCLUSIONS: The authors' findings suggest a coupling between retinal neural activity and blood flow in the macular region of the retina. The rapidity of both the flicker-induced increase in WBC motion and the disappearance of the effect after flicker cessation resembles the time course of blood flow changes previously observed in the microcirculation of the cat optic nerve.

Adolescent↗

PubMed1993

Eye-tracking laser Doppler velocimeter stabilized in two dimensions: principle, design, and construction.

We developed an eye-tracking laser Doppler velocimeter to minimize eye-movement artifacts in the study of ocular hemodynamics in humans. The instrument compensates for both horizontal and vertical eye motions by using galvanometer mirrors controlled by a dual-Purkinje eye tracker. The performance of the instrument is demonstrated in a preliminary study of retinal arterial blood velocity in a normal subject. The subject's fixation point was adjusted manually to oscillate through a 2.3-deg span at 0.3 Hz. In spite of this motion the pulsatile velocity waveform of the heart cycle could be continuously recorded. Without eye tracking the velocity waveform was lost after the initiation of movement.

Adult↗

PubMed1992

Laser Doppler flowmetry in the optic nerve.

Laser Doppler flowmetry (LDF) is a technique that measures relative average velocity, number and flux (number times velocity) of red blood cells in a tissue. In this paper, we demonstrate its application in the optic nerve head tissue, describe the laser delivery and light scattering detection schemes and investigate the effect of the distance between the sites of illumination and detection. We also provide evidence that the flow measured by LDF varies linearly with actual blood flow in the optic nerve and examine the question of the depth of the sampled volume. Experiments in anesthetized cats illustrate potential applications which make use of the high temporal resolution of LDF. These include the response of blood flow to changes in the composition of the breathing gases and changes induced by neuronal stimulation with multiple and single flashes.

Animals↗

PubMed1992

Intravenous nicardipine in cats increases optic nerve head but not retinal blood flow.

The effect of intravenously injected nicardipine on retinal and optic nerve head (ONH) blood flow was studied in 27 cats using laser Doppler velocimetry and flowmetry, respectively. A dose of 20 micrograms/kg of nicardipine had little effect on retinal blood flow. A dose of 100 micrograms/kg, however, produced a significant transient decrease in flow. By contrast, both doses produced a significant increase in ONH blood flow despite a significant decrease of the mean arterial blood pressure. Measurements of the partial pressure of oxygen (PO2) with an oxygen-sensitive microelectrode, whose tip was placed in the vitreous just in front of the optic disc, showed a significant increase in the PO2 that paralleled the increase in ONH blood flow. These results demonstrate, for the first time to the authors' knowledge, a pharmacologically induced increase in ONH blood flow and suggest that nicardipine could have a beneficial effect on ONH tissue.

Animals↗

PubMed1992

The acute effect of topical epinephrine on macular blood flow in humans.

The acute effect of topical epinephrine HCl 2% on macular capillary blood flow was studied in 18 healthy human volunteers using the blue-field simulation technique. This technique provides a method for quantifying the velocity of leukocytes flowing in macular capillaries. Subjects adjusted the velocity of simulated leukocytes on a computer screen to match that of their own entoptically perceived leukocytes before instilling the drug and 2 hr thereafter. An artificial tear solution was instilled into the fellow eye for a control. Epinephrine instillation resulted in a 8% increase in macular leukocyte velocity and presumably blood flow (P less than 0.03, paired student t-test).

Administration, Topical↗

PubMed1991

Flicker evoked increase in optic nerve head blood flow in anesthetized cats.

The effect of diffuse luminance flicker stimulation of a large area (approximately 30 degrees diameter) on red blood cell flux (F) in the optic nerve head was measured in the anesthetized cat. F increased markedly during sustained flicker. The F-response to the initiation and cessation of the stimulation was found to occur within a few seconds. Upon sustained stimulation, the increase in F reached a plateau within approximately 2 min. Its level depended upon the intensity, frequency and wavelength of the stimulation and the state of adaptation of the retina. This stimulus offers a new and powerful means of investigating blood flow regulation in the optic nerve head (ONH).

Adaptation, Ocular↗

PubMed1991

New ocular micromanipulator for measurements of retinal and vitreous physiologic parameters in the mammalian eye.

A new ocular micromanipulator for introducing a microelectrode into the mammalian eye is described. Included is a technical description of the device, incorporating arched tracks and DC motors to provide for angular motion around a scleral entrance point. Applications for in vivo measurements of local PO2 in the retina and vitreous of miniature pigs and cats are shown. The new design features of this micromanipulator allow for smooth microelectrode movements over large retinal areas, facilitating the rapid collection of data in many different areas of the retina and vitreous.

Animals↗

PubMed1990

Rhythmic changes in velocity, volume, and flow of blood in the optic nerve head tissue.

Using laser Doppler flowmetry, slow variations in velocity, volume, and flux of red blood cells in the optic nerve head (ONH), choroid, and retina of the anesthetized minipig have been demonstrated. The variations of velocity and volume were highly regular and vigorous in the ONH and had frequencies ranging from 2.5 to 4.5 cycles/min. The flux variations were smaller or absent due to a phase shift of approximately 180 degrees between the volume and velocity changes. The volume fluctuations were synchronized to those of the PO2 measured in the vitreous, at approximately 50 microns from the surface of the ONH tissue. The fluctuations were less regular in the choroidal and the retinal vessels and their frequencies were higher than those in the ONH. The lack of correlation between the fluctuations in the ONH and those in the retinal and choroidal vessels points toward a local mechanism. The changes in blood volume in the ONH, the phase shift between volume and velocity changes, and the predominance of venules at the surface of the ONH are three factors suggesting that this mechanism involves a change in the diameter of the venules rather than in the arterioles.

Animals↗

PubMed1990

Diabetic glycemic control and retinal blood flow.

The effect of strict glycemic control on retinal volumetric blood flow rate (Q) was investigated in 13 insulin-dependent diabetic patients with laser Doppler velocimetry and monochromatic fundus photography. Strict glycemic control was achieved by glucose monitoring and four daily insulin injections. Q was determined in a major retinal vein at baseline and then 5 days, 2 mo, and 6 mo after the institution of strict control. Level of retinopathy was assessed from stereocolor fundus photographs taken at baseline and 6 mo. After 6 mo of strict diabetic control, five eyes demonstrated progression (P) by one or more retinopathy levels, and eight eyes showed no progression (NP). At 5 days, there was a significant decrease in Q of 1.4 +/- 0.9 microliters/min (P less than 0.005) in NP eyes and a nonsignificant increase in Q of 1.2 +/- 1.7 microliters/min in P eyes. Changes in Q from baseline observed at 5 days were strongly correlated with changes in retinopathy level at 6 mo (r = 0.79, P less than 0.005). No significant changes in Q from baseline were observed at 2 and 6 mo. A lack of decrease in Q at 5 days was associated with the progression of retinopathy that occurs in some patients after the institution of strict glycemic control and may serve as a predictor for progression of retinopathy.

Adult↗

PubMed1989

Retinal blood flow regulation and the clinical response to panretinal photocoagulation in proliferative diabetic retinopathy.

Bidirectional laser Doppler velocimetry and monochromatic fundus photography were used to investigate retinal hemodynamics before and after panretinal photocoagulation (PRP) in 25 eyes of 23 diabetic patients with proliferative retinopathy. After PRP, there was a significant decrease in retinal volumetric blood flow rate and an increase in the retinal vascular regulatory response to hyperoxia (R). A significant association was found between the presence or absence of regression of neovascularization and the increase or decrease in R after PRP. Eyes that showed regression of neovascularization had significantly larger average R after PRP than eyes that did not show regression. Lack of improvement in R after PRP may be related to the presence of remaining ischemia or hypoxia in eyes that continue to show proliferation after PRP.

Adult↗

PubMed1986

Laser Doppler velocimetry study of retinal circulation in diabetes mellitus.

Bidirectional laser Doppler velocimetry and monochromatic fundus photography were used to investigate retinal circulation in 26 normal subjects and in 51 insulin-treated diabetic patients with no retinopathy, background retinopathy (BDR), proliferative retinopathy (PDR), and patients with PDR who had been treated by panretinal photocoagulation (PDR-PRP). Measurements were obtained from main temporal retinal vessels in each eye. Venous diameter at the site of laser Doppler velocimetry measurements was significantly greater than normal in patients with BDR and PDR. The maximum velocity of red blood cells was significantly lower than normal in eyes with diabetic retinopathy. Calculated volumetric blood flow rate, however, was not significantly different from normal in eyes with no retinopathy, BDR, and PDR, and was significantly decreased from normal in patients with PDR who had been treated by panretinal photocoagulation. A comparison between this technique and the fluorescein dye dilution technique is provided.

Adult↗

PubMed1986

Effect of panretinal photocoagulation on retinal blood flow in proliferative diabetic retinopathy.

The effect of panretinal photocoagulation (PRP) on retinal volumetric blood flow rate and its regulatory response to hyperoxia was investigated in a main temporal vein of 15 eyes with proliferative diabetic retinopathy, using bi-directional laser Doppler velocimetry and monochromatic fundus photography. At an average of 4 +/- 2 months after the beginning of PRP, retinal venous diameter decreased from an average of 174 +/- 20 micron to 162 +/- 19 micron (P less than 0.01), red blood cell velocity decreased from 1.3 +/- 0.4 cm/sec to 1.1 +/- 0.4 cm/sec (P less than 0.01), and blood flow decreased from 11.5 +/- 3.8 microliter/min to 8.4 +/- 3.3 microliter/min (P less than 0.001). The regulatory response to hyperoxia, characterized by the percentage decrease in retinal blood flow during 100% oxygen breathing, improved from 20 +/- 15% prior to treatment to 45 +/- 12% following treatment (P less than 0.001). The decrease in retinal blood flow is most likely due to a decrease in viable retinal tissue and an improvement in retinal oxygenation following PRP. The increase in the regulatory response to 100% O2 breathing following PRP may also result from such an improved retinal oxygenation.

Adult↗

PubMed1986

Autoregulation of human retinal blood flow. An investigation with laser Doppler velocimetry.

The effect of acute changes in mean retinal perfusion pressure, P (2/3 of mean brachial artery blood pressure minus IOP), on retinal volumetric blood flow rate, Q, was investigated in normal volunteers. Changes in Q were determined from Q = k X Vmax X D2, where Vmax is the center line red blood cell velocity measured from temporal veins by laser Doppler velocimetry, D is the vessel diameter obtained by monochromatic fundus photography, and k is a constant of proportionality. A suction cup was used to induce step changes in IOP and, consequently, in P. The magnitude of the steps ranged from 10-32 mmHg. During the first 30 sec after a step decrease in P, Vmax and Q were significantly smaller than at rest by an amount proportional to the decrease in P. Thereafter, Vmax and Q increased markedly towards their values at rest, although P changed comparatively little during this period of time. Time constant of the corresponding decrease in vascular resistance, R(t) = P(t)/Q(t), was approximately 45 sec. There was no significant change in D during elevated IOP. Removal of the cup induced an immediate step increase in P, Vmax, D, Q, and R. Thereafter, Vmax, D, Q, and R returned to their values at rest (time constant of the change in R was about 30 sec), while P remained nearly constant. The rapid change in vascular resistance following a step decrease and increase in P can be attributed to an active process that attempts to maintain blood flow close to normal, in spite of changes in perfusion pressure (autoregulation).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1986

Retinal blood flow autoregulation in response to an acute increase in blood pressure.

The response of the retinal circulation to an acute elevation in systemic blood pressure was studied in three healthy normotensive volunteers using the noninvasive laser Doppler velocimetry (LDV) technique combined with retinal vessel size measurements. Isometric exercise was employed to induce the acute rise in arterial pressure. There was no detectable change in retinal blood flow until the mean brachial artery blood pressure was elevated to an average of 115 mm Hg, which represented an average rise in mean blood pressure of 41% above baseline values. Above this value, blood flow increased along with further increments in blood pressure. The parallel rise between the ophthalmic artery pressure and the brachial artery pressure indicates that the regulation of retinal blood flow observed in the above mentioned pressure range is achieved through an increase in retinal vascular resistance rather than by a mechanism that would act to maintain a constant ocular perfusion pressure.

Adult↗

PubMed1985

Does topical phenylephrine, tropicamide, or proparacaine affect macular blood flow?

The acute effect of topical phenylephrine HCl 10%, tropicamide 1% and proparacaine HCl 0.5% on macular capillary blood flow was studied in six healthy human volunteers using the blue field simulation technique. This technique provides a method for quantifying the velocity of leukocytes flowing in one's own retinal macular capillaries. Patients adjusted the velocity of computer simulated leukocytes moving on a CRT screen to match that of their own entoptically perceived leukocytes before instillation of each of the tested preparations and for 35 minutes immediately thereafter A 5% NaCl solution was used as a control. We found no significant difference in leukocyte velocity between the control drop and any of the tested drugs. With the six subjects tested, the calculated average minimum percentage change in leukocyte velocity detectable with this technique (P less than 0.05, paired t-test) was 9%. None of the tested drugs affected macular leukocyte velocity, and presumably blood flow, by more than this amount.

Administration, Topical↗