Biomedical subjects

B L Petrig

Publications and source records attributed to B L Petrig.

At least 19 recordsLinked to original sources

PubMed1998

Blood flow in the human optic nerve head during isometric exercise.

Investigating blood flow autoregulation in the optic nerve is important to understand the physiopathology of various ocular diseases such as glaucoma. This investigation requires that one establishes the relationship between optic nerve blood flow and perfusion pressure. Previous work has documented the effect of lowering the perfusion pressure on optic nerve blood flow. The purpose of the present study was to investigate the effect of elevated perfusion pressure on blood flow in this tissue. Laser Doppler flowmetry was applied to measure relative mean velocity, volume and flux of red blood cells in the tissue of the optic nerve head. These parameters were measured in 13 subjects during isometric exercise consisting of squatting. In the range of perfusion pressures from 56+/-4 to 80+/-5 mmHg (30+/-8%), there was no significant variation of mean velocity, volume and flux of red blood cells, but vascular resistance increased by about 50%. Intraocular pressure was increased significantly above baseline at the end of squatting and decreased during recovery. The results suggest that the maintenance of constant blood flow is achieved by an increase in vascular resistance taking place either at the arterioles feeding or at the veins draining the blood from the ONH or at the ophthalmic artery and/or vessels between this artery and the site of LDF measurements. Combining the results of this study with those of a previous one where perfusion pressure was decreased by increasing the intraocular pressure, we show the entire relationship between perfusion pressure and optic nerve blood flow in man.

Adolescent↗

PubMed1998

[Flicker stimulation induces retinal vasodilation in man].

BACKGROUND: Previous studies have demonstrated, in the cat, a vasodilatation of retinal vessels in response to neuronal activity induced by diffuse luminance flicker. The aim of this study was to determine whether a similar diameter variation is detectable in humans. MATERIALS AND METHODS: Nine normal subjects were exposed to 1 min of sinusoidally varying diffuse luminance flicker (10 Hz, 30 degrees around optic nerve head). Monochromatic fundus pictures before and after the stimulation were taken. The diameter of retinal arteries and veins was measured on the digitised photographs with the NIH-Image software and an own algorythm. RESULTS: The diameter immediately after flicker was significantly larger than the pre-stimulus diameter by 4.2 +/- 2.2% (p < 0.014) (mean +/- SD) for the retinal arteries and 2.7 +/- 1.7% (p < 0.001) for the retinal veins. Six seconds after cessation of the flicker, arterial diameter was not significantly different from that of pre-flicker value. CONCLUSIONS: Diffuse luminance flicker induces an increase in retinal vessel diameter. This suggest that retinal blood flow is coupled with neuronal activity as previously evidenced by the blue field simulation technique in the macula.

Adolescent↗

PubMed1998

[Blood flow measurement in the optic nerve head during isometric exercise].

PURPOSE: Autoregulation of optic nerve head blood flow (Fonh) in response to decreases in perfusion pressure has been demonstrated in animals and humans. The aim of this study was to determine change in Fonh when systemic blood pressure is increased. METHODS: Blood flow parameters, i.e. relative mean velocity, number, and flux of red blood cells in the ONH tissue (Velonh, Volonh and Fonh, respectively) were measured by laser Doppler flowmetry in one eye of 13 normal subjects (aged 16 to 58 years), at baseline, during, and after isometric exercises consisting of squatting. Brachial artery blood pressure was measured by sphygmomanometry. IOP was measured at baseline and at the end of squatting. RESULTS: During squatting mean arterial pressure increased from 103 +/- 6 mm Hg to 139 +/- 58 mm Hg (average +/- 95% confidence interval), IOP increased from 13 +/- 0.5 to 17 +/- 1 mm Hg. An average increase in PPm from 56 +/- 4 to 80 +/- 7 mm Hg induced no significant (p > 0.05) change in the blood flow parameters. The sensitivity (detection threshold) of the blood flow changes was 8%. CONCLUSION: This study shows for the first time in human autoregulation of Fonh when PPm is increased by increasing the systemic blood pressure.

Adolescent↗

PubMed1997

[Measuring leukocyte velocity in macular capillaries using a miniaturized blue field simulator: effect of aperture of the pupil].

BACKGROUND: In this paper we present a miniaturized blue field simulator (BFS) which allows the measurement of the velocity (V) pulsatility (P) and number (D) of leukocytes in the macular retinal capillaries. A study on the effect of the aperture size of the blue light source at the subject's pupil on the measured flow parameters was performed. METHODS: A blue field entoptoscope with a small halogen lamp was used to induce the perception of the "flying corpuscles" and a flat color screen was selected to display a computer simulation of this entoptic phenomenon. The aperture of the blue light source at the pupil was varied by a diaphragm placed at a conjugate pupil plane while the size and retinal irradiance of the blue field stimulus at the fundus was held constant. RESULTS: The results show significant correlations between log pupil area and both V (-18% per log unit) and D (+42% per log unit). When the retinal illuminance is expressed in Log Trolands, V shows no dependency, but D is strongly correlated (+40% per log Troland). CONCLUSIONS: When applying the BFS technique, the size of the blue light stimulus at the pupil, if undilated, must be well controlled to minimize instrument-related variations of the blood flow measurements.

Adult↗

PubMed1997

[Effect of changes in ocular perfusion pressure on choroid ischemia in man].

BACKGROUND: The effect of changes in ocular perfusion pressure (PPm) on the choroidal blood flow (ChBF) in man was studied with the laser Doppler flowmetry (LDF) technique. MATERIALS AND METHODS: We changed the PPm by increasing the intraocular pressure (IOP) or by increasing the blood pressure (BP) with isometric exercises. RESULTS: We observed that a) ChBF was not significantly different from baseline up to an IOP of 27 mm Hg and b) ChBF remained constant even if PPm increased by as much as 72%. CONCLUSION: Our results suggest that ChBF is autoregulated in response to an increase in IOP up to about 27 mm Hg. ChBF remains also constant in spite of an increase in systemic BP, probably due to a vasoconstriction induced by increased sympathetic activity.

Adult↗

PubMed1997

Effect of acute decreases of perfusion pressure on choroidal blood flow in humans.

PURPOSE: To investigate the relationship between choroidal blood velocity (ChBVel), blood volume (ChBVol) and blood flow (ChBF) in the foveal region of the human ocular fundus and ocular perfusion pressure and to determine whether the choroidal circulation has some autoregulatory capacity. METHODS: Measurements of ChBVel, ChBVol and ChBF were obtained by laser Doppler flowmetry in healthy subjects (age range, 21 to 57 years) with normal eye examination results. Measurements were performed at normal intraocular pressure (IOP) and during successive step increases in IOP induced by scleral suction. In experiment 1, in six eyes (five subjects), the IOP was increased rapidly, in steps of 50 to 100 mm Hg of suction pressure, which each lasted approximately 10 seconds to a level above diastolic ophthalmic artery blood pressure (IOP = approximately 72 mm Hg). In experiment 2, in 14 eyes (seven subjects), the IOP was increased slowly in four successive steps at 2-minute intervals to a level of approximately 42 mm Hg. We also determined the pulsatility of the flow parameters during the heart cycle, pulsatility = 1 - diast value/syst value. RESULTS: For both rates of suction cup increase, the relationship between ChBFm (mean ChBF over the heart cycle) and mean perfusion pressure was not linear. At high pressure, ChBFm was less affected by decreases in the pressure than expected from a passive vascular system. In some cases, no change in ChBFm was detectable, although significant changes in PChBF occurred. Further decreases in perfusion pressure resulted in a proportional decrease in ChBFm. On release of suction, a significant increase in ChBFm over baseline value was detectable in experiment 1. CONCLUSIONS: The relationship between ChBFm and ocular mean perfusion pressure appears to be bilinear and reveals some autoregulation for moderate step decreases in perfusion pressure. The temporal characteristics of the ChBFm-response suggest a neural or passive hemodynamical process rather than a myogenic or metabolic compensatory mechanism.

Adult↗

PubMed1997

[Autoregulation in ischemia of the optic nerve in the human].

BACKGROUND: Autoregulation is defined as the maintenance of constant blood flow in a vascular system in spite of changes in perfusion pressure (PPm). MATERIALS AND METHODS: PPm was decreased by increasing the intraocular pressure (IOP) with a suction cup and optic nerve blood flow was measured with the laser Doppler flowmetry technique (LDF) in 9 normal volunteers. RESULTS: The blood flow was autoregulated down to a PPm of 13 mm Hg (IOP = 47 mm Hg). CONCLUSIONS: These results confirm previous studies in cats and monkeys. The mechanism of autoregulation is probably a decrease in resistance due to capillary recruitment.

Adult↗

PubMed1997

Choroidal blood flow during isometric exercises.

PURPOSE: To investigate the response of choroidal blood flow in the foveal region of the human eye to increases in mean perfusion pressure (PPm = mean ophthalmic artery pressure - intraocular pressure; IOP) induced by isometric exercises. METHODS: Using laser-Doppler flowmetry, changes in velocity (ChBVel), number (ChBVol), and flux (ChBF) of red blood cells in the choroidal vascular system in the foveal region of the fundus were measured in both eyes of 11 normal subjects (ages 18 to 57 years) during isometric exercises. RESULTS: During 90 seconds of squatting, PPm increased by an average of 67%, from 46 to 77 mm Hg. This resulted in a significant increase of 12% in ChBFm (the mean of ChBF during the heart cycle), mainly caused by an increase in ChBVelm. A further increase in PPm to a value approximately 85% above baseline resulted in a 40% increase in ChBFm. A significant negative correlation was found between the changes in ChBVelm and ChBVolm, during squatting. CONCLUSIONS: Previous studies have demonstrated that during isometric exercise, blood pressures in the ophthalmic and brachial arteries rise in parallel. These observations and the current results indicate that an increase in PPm up to 67% induces an increase in choroidal vascular resistance that limits the increase in choroidal blood flow to approximately 12%. This regulatory process fails when PPm is further increased.

Adolescent↗

PubMed1996

Effect of decreased ocular perfusion pressure on blood flow and the flicker-induced flow response in the cat optic nerve head.

The effect of decreased ocular mean perfusion pressure (PPm), defined as mean arterial blood pressure minus intraocular pressure (IOP), on optic nerve head blood flow (Fonh) and on the response of this flow (RFonh) to diffuse luminance flicker was investigated in 19 anesthetized cats using laser Doppler flowmetry. PPm was decreased by increasing the IOP. The flicker stimulus consisted of 20-msec flashes delivered at 10 Hz for 30-60 sec. It illuminated a 30 degrees diameter area of the fundus, centered at the optic disk. Decreasing PPm by 10-35% from its resting value resulted in a 23% increase in RFonh (supranormal RFonh). With further decreases in PPm, RFonh decreased, reaching zero at a PPm below 20 mmHg. Fonh remained constant until PPm was < 40 mmHg and then decreased thereafter. When PPm was brought back to resting value after having been decreased for approximately 45 min, Fonh first increased by approximately 380% and then returned to its value at rest within approximately 4.5 min. At low PPm, hyperoxia decreased Fonh by 23% and restored the attenuated RFonh back to the value at resting PPm and hypoxia did not increase Fonh, as it did at normal PPm. This study confirms that the optic nerve head circulation is autoregulated over a wide range of PPm and reveals, for the first time, a hyperemic response to a prolonged decrease in PPm. It suggests that hypoxia plays a role in abolishing RFonh at low PPm and that the supranormal RFonh at moderately decreased PPm is due to an increase in the flicker-induced ganglion cell activity.

Animals↗

PubMed1995

Strict control of glycaemia: effects on blood flow in the large retinal vessels and in the macular microcirculation.

AIMS: The purpose of this study was to investigate the effect of instituting strict diabetic glycaemic control on the retinal macular microcirculation and to compare this effect with that observed in the main retinal veins. METHODS: In 28 insulin dependent diabetic patients with poor glycaemic control a regimen of strict diabetic control, consisting of four daily insulin injections was instituted and maintained for 6 months. Retinal haemodynamics were investigated in the macular microcirculation by the blue field simulation technique and in the major retinal veins by a combination of bidirectional laser Doppler velocimetry and monochromatic fundus photography. Progression of diabetic retinopathy was assessed from fundus photographs taken at baseline and at the end of the study. RESULTS: Institution of strict diabetic control resulted in a significant increase in leucocyte velocity in the macular circulation (p = 0.013). No significant difference in this increase was observed between eyes that showed progression (n = 8) and no progression (n = 20) of retinopathy during the study. Significant correlations were found between relative changes over time of blood flow measured in the main retinal veins and relative changes of leucocyte velocity determined in the macular microcirculation at 2 months (p = 0.008) and 6 months (p = 0.001) but not at 5 days (p = 0.49). In the eight eyes that showed progression of retinopathy, the product of leucocyte velocity and density at baseline was significantly higher than normal (p < 0.05). During the length of this study, this product was also significantly higher in the eight eyes that showed retinopathy progression than in the 20 eyes that did not show progression (p = 0.005). CONCLUSION: Our results suggest that increased flow in the macular microcirculation may be associated with progression of retinopathy, thus supporting the hypothesis that increased blood flow may play a role in the development of diabetic microangiopathy. Although there are correlations between the changes detected in the macular microcirculation and those measured in the main retinal vessels, there are also differences which need to be further investigated in order to better understand pathogenetic mechanisms.

Adolescent↗

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↗