Feasibility of Conjunctival Hemodynamic Measurements in Rabbits: Reproducibility, Validity, and Response to Acute Hypotension (original) (raw)
Related papers
Analysis of Variance of Microspheres Blood Flow Measurements in Rabbits
Experimental Eye Research, 1997
As part of a larger study on the interpretation of angiographically derived hemodynamic parameters, blood flow in several ocular tissues was measured using the radioactively labelled microspheres technique. As an unexpected secondary result, it was found that the microspheres data gave quantitative information on hyperaemic effects in the eye. This is the subject of the present paper. The measurements were made in 13 anaesthetized pigmented rabbits. In each animal, three blood flow measurements were performed at three different ocular perfusion pressures (60-15 mmHg). The perfusion pressures of the experimental eye were varied by changing the intra-ocular pressure. The contra-lateral eye served as a control. Labelled microspheres were used as a non-recirculating blood flow indicator, enabling the estimation of regional blood flows, in this case for the iris, ciliary body, peripheral choroid and peripapillary choroid separately. Using analysis of variance with perfusion pressure as covariate and taking into account the blood flow of the control eye, hyperaemia could be quantified in the experimental eye. Apart from a difference amongst animals, hyperaemia depended on tissue type. The amount of hyperaemia proved to be more pronounced in the anterior part of the eye, iris and ciliary body, and to decrease towards the posterior pole. With regard to the causes of this hyperaemia one could speculate about the invasive handling (anterior eye needles) topical administration of tropicamide, in combination with the general anaesthesia.
New Methods to Study the Microcirculation
American journal of hypertension, 2017
Essential hypertension is associated with structural alterations in the microvessels; in particular, an increase in the media thickness to internal lumen ratio of small resistance arteries (MLR) and a reduction in capillary density have been observed. The evaluation of the morphological characteristics of small resistance arteries in humans is challenging. The gold standard method is generally considered to be the measurement by wire or pressure micromyography of MLR of subcutaneous small vessels obtained by local biopsies. However, non-invasive techniques for the evaluation of retinal arterioles were recently proposed; in particular, two approaches, scanning laser Doppler flowmetry (SLDF) and adaptive optics (AO), seem to provide useful information. Both of them provide an estimation of the wall to lumen ratio (WLR) of retinal arterioles. Moreover, a non-invasive measurement of basal and total capillary density may be obtained by videomicroscopy/capillaroscopy. It has been recently...
Blood velocity pulse quantification in the human conjunctival pre-capillary arterioles
Microvascular Research, 2010
Axial red blood cell velocity pulse was quantified throughout its period by high speed video microcinematography in the human eye. In 30 conjunctival precapillary arterioles (6 to 12 microm in diameter) from 15 healthy humans, axial velocities ranged from 0.4 (the minimum of all the end diastolic values) to 5.84 mm/s (the maximum of all the peak systolic values). With the velocity pulse properly quantified, two parameters can be estimated: (1) the average velocity of the pulse during a cardiac cycle AVV (average velocity value) and (2) the magnitude of the pulsation using Pourcelot's resistive index RI. These parameters are important for the estimation of other hemodynamic parameters such as the average volume flow and the average shear stress. The results of this study revealed that the AVV in the human precapillary arterioles ranged between 0.52 and 3.26 mm/s with a mean value for all microvessels of 1.66 mm/s+/-0.11(SE). The RI ranged between 35.5% and 81.8% with a mean value of 53.1%+/-2.2. Quantitative information was obtained for the first time on the velocity pulse characteristics just before the human capillary bed.
Quantitative assessment of conjunctival microvascular circulation of the human eye
Microvascular Research, 2010
Accessibility to the bulbar conjunctival microvasculature provides a means to assess blood supply to the cerebral cortex and thus optimize therapeutic interventions designed to prevent or reduce the risk of cerebral vascular disease and stroke. The feasibility of a method for quantitative measurements of conjunctiva blood vessel diameter, blood velocity, and flow in the human eye is reported. The method is based on slit lamp biomicroscope digital imaging coupled with a space time image analysis technique. A sequence of conjunctiva microvasculature images were captured at a rate of 50 Hz. The images were analyzed to determine blood vessel diameter, velocity and flow. Blood vessel diameter measurements ranged between 8.7 and 24.3 microns, with a mean value of 15.5 microns. Blood flow rate ranged between 27.3 and 296.9 pl/s, with a mean value of 111.8 pl/s. The relationship between blood flow and vessel diameter was fit with a power law curve (R = 0.87). The application of this technique for in vivo quantitative assessment of blood flow dynamics has potential to impact diagnosis and monitoring of various cardiovascular and blood disorders.
Microvascular blood flow: evidence indicating a cubic dependence on arteriolar diameter
American Journal of Physiology-Heart and Circulatory Physiology, 1983
The primary objectives of this study were 1) to determine the functional relationship between microvascular blood flow (Q) and arteriolar internal diameter (D) and 2) to determine whether this relationship conformed to a theoretical optimality prediction--that blood flow is proportional to the cube of the diameter (Q = kD3). Paired blood velocity and arteriolar diameter measurements in the cremaster muscle microvasculature of eight normotensive (WKY) and eight hypertensive (SHR) rats were made under control conditions and following maximal dilation of the microvasculature with topically applied adenosine. A total of 160 paired flow-diameter measurements were made in arteriolar vessels with diameters ranging from 6 to 108 micron. Analysis of this data showed that Q and D were functionally linked by Q = kDm with k = 417 and m = 3.01 with D expressed in centimeters. Confidence intervals at the 99.9% level were 331-503 and 2.86–3.14 for k and m, respectively. A theoretical development b...
Assessment of Human Ocular Hemodynamics
Survey of Ophthalmology, 1998
Vascular abnormality and altered hemodynamics play important roles in many ophthalmic pathologies. Much of our knowledge of ocular hemodynamics was gained from invasive animal research, although a number of noninvasive methods suitable for in vivo use in humans have been developed. Data from these methods now produce a significant literature of their own. Understanding the origins of the data and appreciating their limitations can be difficult. Modern hemodynamic assessment techniques each examine a unique facet of the ocular circulation. No single facet provides a complete description of the hemodynamic state of the eye. These methods have contributed a great deal to our understanding of normal hemodynamics. More importantly, they continue to add to our understanding of altered hemodynamics found in disease. Some have found their way into limited clinical practice. The predominant ocular hemodynamic assessment techniques are reviewed with the aims of introducing the fundamental principles behind each, highlighting their inherent advantages and limitations, highlighting their contributions to understanding ocular physiology, and considering their potential to provide signs for diagnosis.
Journal of Biomedical Optics, 2009
The use of laser Doppler perfusion imaging ͑LDPI͒ and laser speckle perfusion imaging ͑LSPI͒ is well known in the noninvasive investigation of microcirculatory blood flow. This work compares the two techniques with the recently developed tissue viability ͑TiVi͒ imaging system, which is proposed as a useful tool to quantify red blood cell concentration in microcirculation. Three systems are evaluated with common skin tests such as the use of vasodilating and vasoconstricting drugs ͑methlynicotinate and clobetasol, respectively͒ and a reactive hyperaemia maneuver ͑using a sphygmomanometer͒. The devices investigated are the laser Doppler line scanner ͑LDLS͒, the laser speckle perfusion imager ͑FLPI͒-both from Moor Instruments ͑Axminster, United Kingdom͒-and the TiVi imaging system ͑Wheels-Bridge AB, Linköping, Sweden͒. Both imaging and point scanning by the devices are used to quantify the provoked reactions. Perfusion images of vasodilatation and vasoconstriction are acquired with both LDLS and FLPI, while TiVi images are acquired with the TiVi imager. Time acquisitions of an averaged region of interest are acquired for temporal studies such as the reactive hyperaemia. In contrast to the change in perfusion over time with pressure, the TiVi imager shows a different response due its measurement of blood concentration rather than perfusion. The responses can be explained by physiological understanding. Although the three devices sample different compartments of tissue, and output essentially different variables, comparisons can be seen between the three systems. The LDLS system proves to be suited to measurement of perfusion in deeper vessels, while FLPI and TiVi showed sensitivity to more superficial nutritional supply. LDLS and FLPI are insensitive to the action of the vasoconstrictor, while TiVi shows the clear boundaries of the reaction. Assessment of the resolution, penetration depth, and acquisition rate of each instrument show complimentary features that should be taken into account when choosing a system for a particular clinical measurement.
Microvascular Research, 1996
Autoregulation of blood flow in response to changes in perfusion pressure is known to occur in a number of tissues including the human retina. Defective autoregulation may play a part in the pathophysiology of several retinal diseases. Laser Doppler velocimetry has been used to study retinal blood flow. Technically superior measurements are obtained from veins by this method but arterial measurements might provide additional information. The response of the normal human retina to an acute elevation of systemic blood pressure induced by isometric exercise was investigated in nine normal volunteers using laser Doppler velocimetry and computer-assisted image analysis. Measurements were taken from retinal veins and arteries. Autoregulation was demonstrated by an 8.4% rise in flow in response to a 34% rise in perfusion pressure (P Å 0.0007) using data derived from veins and a 4.8% rise in flow in response to a 33% rise in perfusion pressure (P Å 0.01) using data derived from arteries. Arteries constricted by 3.4% (P Å 0.002) and veins dilated by 1.6% (P Å 0.02). Red cell velocity rose in veins by 5.0% (P Å 0.008) and in arteries by 12.2% (P Å 0.02). The variability in velocity change derived from veins (SD 3.4%) was lower than that from arteries (SD 12.1%). A similar pattern of flow change was found in both sets of data. This makes venous measurements more useful for obtaining statistically reliable results from these techniques.
Review of Scientific Instruments, 2007
Microcirculation is the generic name of vessels with internal diameter less than 100 m of the circulatory system, whose main functions are tissue nutrition and oxygen supply. In microcirculatory studies, it is important to know the amount of oxyhemoglobin present in the blood and how fast it is moving. The present work describes improvements introduced in a classical hardware-based instrument that has usually been used to monitor blood flow velocity in the microcirculation of small animals. It consists of a virtual instrument that can be easily incorporated into existing hardware-based systems, contributing to reduce operator related biases and allowing digital processing and storage. The design and calibration of the modified instrument are described as well as in vitro and in vivo results obtained with electrical models and small animals, respectively. Results obtained in in vivo studies showed that this new system is able to detect a small reduction in blood flow velocity comparing arteries and arterioles ͑p Ͻ 0.002͒ and a further reduction in capillaries ͑p Ͻ 0.0001͒. A significant increase in velocity comparing capillaries and venules ͑p Ͻ 0.001͒ and venules and veins ͑p Ͻ 0.001͒ was also observed. These results are in close agreement with biophysical principles. Moreover, the improvements introduced in the device allowed us to clearly observe changes in blood flow introduced by a pharmacological intervention, suggesting that the system has enough temporal resolution to track these microcirculatory events. These results were also in close conformity to physiology, confirming the high scientific potential of the modified system and indicating that this instrument can also be useful for pharmacological evaluations.