Inaccuracies in blood flow estimates in microvessels during arteriolar vasoconstriction

doi:10.1016/0026-2862(84)90026-8

Microvascular Research

Volume 28, Issue 1, July 1984, Pages 23-36

https://doi.org/10.1016/0026-2862(84)90026-8 Get rights and content

Abstract

The effect of vasomotor tone on blood flow estimates was evaluated in the hamster cheek pouch and cremaster muscle microcirculation. The products of arteriolar cross-sectional area and red blood cell velocity were calculated in three different cases: (1) at arteriolar bifurcations, (2) in short segments of an arteriole constricted by iontophoretic application of norepinephrine, and (3) at randomly selected second- and third-order arterioles. Vasodilation of the microcirculation was induced by topical application of adenosine. Vasoconstriction was induced by elevation of superfusion solution PO₂. If true volume flow is accurately estimated by this method then: (1) the sum of measured branch flows at a bifurcation should equal feed flow; (2) measured flow through constricted arteriolar segments should equal flow proximal or distal to the constricted segment; and, (3) following experimental manipulations, relative changes in estimated flow in second- and third-order arterioles should be equal. Our findings suggest that the blood flow estimates were not always accurate. The sum of branch flows was equal to feed flow only across bifurcations with low or resting vascular smooth muscle tone. During vasoconstriction, feed flow averaged 40% higher than the sum of downstream flows. In addition, estimated flow was 15% lower in constricted segments of an arteriole compared to dilated contiguous segments of the vessel. During alterations in vasomotor state, estimated fractional changes in flow in second- and third-order arterioles differed by more than sixfold. Therefore, blood flow estimates with the dual-slit method may not be reliable under conditions of high vasomotor tone. We speculate that the error may result largely from uncertainties in the diameter measurement.

References (20)

M. Baker et al.
On-line volume flow rate and velocity profile measurements for blood in microvessels
Microvasc. Res.
(1974)
E.C. Carlson et al.
Electron microscopic studies of cat mesenteric arterioles: a structure-function analysis
Microvasc. Res.
(1982)
D.N. Damon et al.
A comparison between mean blood velocities and center-line red cell velocities as measured with a mechanical image streaking velocitometer
Microvasc. Res.
(1979)
B.R. Duling
The preparation and use of the hamster cheek pouch for studies of the microcirculation
Microvasc. Res.
(1973)
B.R. Duling et al.
Microiontophoretic application of vasoactive agents to the microcirculation of the hamster cheek pouch
Microvasc. Res.
(1968)
S.L. Harper et al.
In vitro and in vivo measurement of red cell velocity with epi- and transillumination
Microvasc. Res.
(1983)
B.J. LaLone et al.
Estimation of arteriolar volume flow from dual slit red cell velocity: an in vivo study
Microvasc. Res.
(1978)
H.H. Lipowsky et al.
Application of the “two slit” photometric technique to the measurement of microvascular volumetric flow rates
Microvasc. Res.
(1978)
B.R. Duling et al.
A computerized system for densitometric analysis of the microcirculation
J. Appl. Physiol.
(1983)
P. Gaehtgens et al.
Blood flow measurement by dual slit photometry in small capillaries
Biomed. Eng. (Suppl)
(1976)

There are more references available in the full text version of this article.

Cited by (17)

Nicardipine reverses vasoactivity associated with university of Wisconsin solution in the rat peripheral circulation
2011, Transplantation Proceedings
Citation Excerpt :
The image was viewed with a high-resolution system, consisting of a digital camera (Q imaging; MicroPublisher 3.3RTV; www.qimaging.com), image capturing software (Qcapture Pro 6.0; http://www.qimaging.com), and desktop computer (Dell Precision T1500; http://www.dell.com) every 15 minutes. Measurement of arteriolar diameter and erythrocyte velocity, and calculation of blood flow were described previously.25,27 Analog blood pressure and erythrocyte velocity were digitized (DI-148U; http://www.dataq.com) and recorded using data acquisition software (Windaq 3.36; http://www.dataq.com).
The rapid uniform delivery of University of Wisconsin solution (UW) to the microcirculation may be compromised by its vasoactivity.
In 2 different rodent models, we tested whether UW-mediated vasoconstriction could be reversed with nicardipine.
In the perfused, splanchnic circulation, intravascular control solutions (lactated Ringers [LR], Hextend [HEX], histidine-tryptophan-ketoglutarate [HTK]) or UW (± nicardipine) evoked pressure changes in 3 protocols (series 1; n = 35). In the cremaster muscle, topical control solutions or UW (± nicardipine) evoked vascular responses measured by video microscopy in 4 protocols (series 2; n = 47). In series 1A, 37°C UW increased perfusion pressure, but there was no change caused by LR, HEX, or HTK. In series 1B, 4°C UW caused a similar, albeit transient, increase. In series 1C, nicardipine reversed 37°C UW-mediated vasoconstriction in a dose-related manner. In series 2A, UW caused a 30%–59% constriction that varied with arteriolar branching order. In series 2B, the recovery from UW-induced vasoconstriction varied with duration of exposure, but nicardipine fully reversed residual vasoconstriction. In series 2C, cold and warm UW were equipotent, near maximal, vasoconstrictors. In series 2D, UW potentiated no-reflow.
UW causes a potent temperature-independent vasoconstriction by a calcium-mediated mechanism and this effect can be mitigated with nicardipine.
Low-affinity hemoglobin increases tissue PO<inf>2</inf> and decreases arteriolar diameter and flow in the rat cremaster muscle
1996, Microvascular Research
The hypothesis that tissue oxygen delivery in excess of metabolic demand results in vasoconstriction and reduced blood flow was tested in the cremaster muscle of anesthetized Sprague–Dawley rats by studying the effects of an intravenous infusion of RSR-13, an allosteric effector of hemoglobin. RSR-13 reduces the affinity of hemoglobin for oxygen, causing a right shift in the oxygen dissociation curve. Thus, oxygen delivery to the tissues was increased without elevations in blood flow or blood pressure. Tissue PO₂, arteriolar diameter, and RBC velocity were measured and volume flow was calculated from diameter and RBC velocity in third-order arterioles. In rats receiving RSR-13 at a rate of 200 mg kg⁻¹in 15 min (n= 18), P₅₀(the PO₂at which hemoglobin is 50% saturated) increased from 36 ± 1 to 52 ± 3 mm Hg, and tissue PO₂increased to a maximum of 146 ± 12% above its control value. P₅₀and tissue PO₂did not change in the control group (n= 8) receiving vehicle at a rate equivalent to that in the experimental group. In a separate group of rats receiving RSR-13 (n= 7), P₅₀increased from 38 ± 1 to 51 ± 3 mm Hg, calculated arteriolar flow decreased from 9 ± 3 to a minimum of 1.4 ± 1 nl sec⁻¹, and arteriolar diameter decreased from 27 ± 3 to a minimum of 13 ± 3 μm. P₅₀, volume flow, and arteriolar diameter did not change in the control group (n= 10). These results suggest that an increased tissue oxygen delivery, caused by a right shift in the oxygen dissociation curve, may cause an increase in vascular resistance independent of an elevated blood flow.
Effect of irregularities of vessel cross-section on vascular resistance
1995, Fluid Dynamics Research
Irregularities of the vessel luminal geometry affect resistance to blood flow in microvessels. In the present study, the effect of the protrusion of endothelial cell nuclei into the vessel lumen on vascular resistance is numerically evaluated. It is assumed that nuclei of endothelial cells protrude regularly into the vessel lumen, which has an otherwise circular cross-section. The flow of an incompressible Newtonian fluid in these vessels is numerically analyzed by a finite element method applied to the Stokes equations, and the relationship of the flow rate and the pressure drop between upstream and downstream is used to calculate vascular resistance. It is found that the vascular resistance is constantly elevated compared to that for vessels without protrusions. The vascular resistance increases as the area of the vessel cross-section decreases, its shape is more distorted from the circular, or its variation along the vessel axis is more significant.
A narrow segment of the efferent arteriole controls efferent resistance in the hydronephrotic rat kidney
1990, Kidney International
A narrow segment of the efferent arteriole controls efferent resistance in the hydronephrotic rat kidney. We microscopically examined the narrow segment of the efferent arteriole (NSEA) in the hydronephrotic kidney of rats in vivo. This segment is routinely found at the proximal efferent arteriole adjacent to the glomerulus and is characterized by a narrowing due to a cellular structure which bulges into the lumen. The existence of NSEA has been described in a previous study from our laboratory, but it was not examined in detail; its functional behavior in particular is still unknown. In the present study, we measured changes in luminal diameter of NSEA during reduction of renal perfusion pressure and in response to angiotensin II (Ang II), saralasin, and nitroprusside. The mean luminal diameter of NSEA at its narrowest point was 5.1 μm and its effective length was 8.4 μm. Reduction of renal perfusion pressure from 115 to 90, 70, and 40 mm Hg decreased NSEA diameter by 9, 15, and 23%, respectively. Topical application of saralasin (10⁻⁵M) or nitroprusside (10⁻⁴M) to the kidney dilated NSEA by 10 or 20%, respectively, and attenuated the pressure-dependent constriction of NSEA. Intravenous infusion of Ang II at rates of 50, 100, 200, and 400 ng/min/kg constricted NSEA lumen by 7, 15, 20, and 21%, respectively. The vascular bed of the hydronephrotic kidney was scanned morphologically, and a mathematical model was developed from these data. With this model, we could calculate the effect of segmental diameter changes on total renal resistance as well as flow and pressure at different vascular levels. NSEA contributed 4% to the total renal resistance and 20% to the efferent resistance under control conditions. Lowering of renal perfusion pressure increased the efferent arteriolar resistance up to 50% above the control value mainly as a result of constriction of NSEA. Our data indicate that efferent resistance increases at reduced renal perfusion pressure and leads to a stabilization of glomerular pressure. The rise of efferent resistance is mediated primarily by NSEA constriction, and the renin-angiotensin system is involved in this regulation
Role of flow dispersion in the computation of microvascular flows by the dual-slit method
1989, Microvascular Research
Microvascular blood flow is commonly calculated from a “centerline” velocity derived from the dual-slit method. This is done by relating the computed centerline velocity to an average velocity through an empirically derived conversion factor. To determine the physical basis of the conversion factor, we utilized a Fourier transform and indicator dilution theory to model the parameters governing the conversion factor. We assumed Poiseuille flow from slit 1 to 2 and that the signals from the two slits were sinusoidal functions. Under these conditions, the conversion factor was found to depend primarily on a dimensionless time which is the product of the frequency of the sinusoidal signals and their time delay. Theory shows that if this dimensionless time is in the range of 3 to 7, the conversion factor lies within 1.5 to 1.7. Analysis of original dual-slit samples showed the conversion factor, obtained from the data of five arterioles and three venules, to be 1.58 ± 0.03, and independent of the microvessel diameter.
Numerical simulation of systemic O<inf>2</inf> and CO<inf>2</inf> exchange in a hyperbaric environment
1989, BioSystems
The process of gas exchange in systemic capillaries and its surrounding tissue is simulated numerically in a hyperbaric environment, taking into account the molecular diffusion, convection, saturation of haemoglobin with O₂ and CO₂, and the metabolic activity in the tissue. Krogh tissue-cylinder is used as a geometrical representation of the capillary-tissue system. The resulting system of non-linear governing equations together with the physiologically relevant boundary conditions is solved numerically. It is found that the concentration of oxygen decreases from the axis of the capillary to the tissue periphery whereas the concentration of carbon dioxide increases. It is shown that very little CO₂ is transported radially. The location of the vulnerable region from the point of view of CO₂ accumulation is found to be the rim (r = R₂, z = L) situated at the periphery of the tissue near the venous end of the capillary. It is also found that accumulation of O₂ decreases whereas that of CO₂ increases in a hyperbaric environment. Finally, it is surmised that one of the reasons in causing discomfort among divers could be excessive accumulation of CO₂ in the tissue.

View all citing articles on Scopus

View full text

Article preview

Microvascular Research

Abstract

References (20)

On-line volume flow rate and velocity profile measurements for blood in microvessels

Microvasc. Res.

Electron microscopic studies of cat mesenteric arterioles: a structure-function analysis

Microvasc. Res.

A comparison between mean blood velocities and center-line red cell velocities as measured with a mechanical image streaking velocitometer

Microvasc. Res.

The preparation and use of the hamster cheek pouch for studies of the microcirculation

Microvasc. Res.

Microiontophoretic application of vasoactive agents to the microcirculation of the hamster cheek pouch

Microvasc. Res.

In vitro and in vivo measurement of red cell velocity with epi- and transillumination

Microvasc. Res.

Estimation of arteriolar volume flow from dual slit red cell velocity: an in vivo study

Microvasc. Res.

Application of the “two slit” photometric technique to the measurement of microvascular volumetric flow rates

Microvasc. Res.

A computerized system for densitometric analysis of the microcirculation

J. Appl. Physiol.

Blood flow measurement by dual slit photometry in small capillaries

Biomed. Eng. (Suppl)

Cited by (17)

Nicardipine reverses vasoactivity associated with university of Wisconsin solution in the rat peripheral circulation

Low-affinity hemoglobin increases tissue PO<inf>2</inf> and decreases arteriolar diameter and flow in the rat cremaster muscle

Effect of irregularities of vessel cross-section on vascular resistance

A narrow segment of the efferent arteriole controls efferent resistance in the hydronephrotic rat kidney

Role of flow dispersion in the computation of microvascular flows by the dual-slit method

Numerical simulation of systemic O<inf>2</inf> and CO<inf>2</inf> exchange in a hyperbaric environment