Can an intermittent pneumatic compression system monitor venous filling in the leg?

OBJECTIVE

Intermittent pneumatic compression (IPC) systems are used for prophylaxis of venous thromboembolism. Both legs are wrapped with inflatable sleeves connected to a pneumatic controller to allow compression of the legs causing expulsion of venous blood. Venous refill between inflation periods causes leg expansion, which can be tracked by measuring pressure changes in the sleeve. The aim of our study, which utilized the SCD RESPONSE compression system in conjunction with an independent pressure transducer, was to investigate whether factors such as temperature changes within the sleeves during inflation and deflation affect the measured venous refill time (VRT).

METHODS

Transducers were used to measure air pressure in the middle chamber of the sleeve. A thermocouple was also inserted into the bladder to measure temperature changes. Inflation, deflation and refill measurements were made with the sleeves around model systems (static, rigid plastic pipes or compliant paper rolls, and dynamic, latex tubes inserted between a rigid pipe and the sleeve to simulate veins) and on 10 subjects in semi-recumbent, supine and sitting positions.

RESULTS

In all the experiments the maximum temperature change was 0.023 degrees C. With the static model systems, the pressure in the venous refill measuring bladder fell from the inflation pressure of 40 - 50 mmHg to 9 +/- 1 mmHg, but then rose by 2.1 +/- 0.2 mmHg (rigid pipes) and 1.4 +/- 0.2 mmHg (paper rolls). These pressure changes were associated with reported 'filling times' of 21 - 24 s (rigid pipes) and 22 - 29 s (paper rolls). In experiments on dynamic filling of the latex tube, there was a strong linear relationship between the filling time indicated by the SCD system and the time to empty the filling reservoir. In 170 measurements on human subjects, there were only three VRTs less than 30 s and 36 less than 35 s. VRT increased in all subjects when going from supine (34.6 +/- 1.8 s) to semi-recumbent (38.9 +/- 1.9 s) to sitting (42.6 +/- 0.9 s) positions.

DISCUSSION

In all cases, temperature changes during the refill phase were too small to result in significant pressure changes that would affect VRT. The pressure increases observed with the static models after deflation appeared to be due to viscoelastic relaxation. Viscoelastic responses were present in human subjects, but the effect on VRT was negligible. This indicates that the increased VRT observed in humans is due to blood return. Body position affected VRTs, indicating the system's ability to detect changes in filling times and venous blood volume.

Rapid hyperspectral fluorescence lifetime imaging

We report a rapid hyperspectral fluorescence lifetime imaging (FLIM) instrument that exploits high-speed FLIM technology in a line-scanning microscope. We demonstrate the acquisition of whole-field optically sectioned hyperspectral fluorescence lifetime image stacks (with 32 spectral bins) in less than 40 s and illustrate its application to unstained biological tissue.

Toward the clinical application of time-domain fluorescence lifetime imaging

High-speed (video-rate) fluorescence lifetime imaging (FLIM) through a flexible endoscope is reported based on gated optical image intensifier technology. The optimization and potential application of FLIM to tissue autofluorescence for clinical applications are discussed.

High-speed wide-field time-gated endoscopic fluorescence-lifetime imaging

We report the development of a high-speed wide-field fluorescence-lifetime imaging (FLIM) system that provides fluorescence-lifetime images at rates of as many as 29 frames/s. A FLIM multiwell plate reader and a potentially portable FLIM endoscopic system operating at 355-nm excitation have been demonstrated.

Spectroscopic imaging of arteries and atherosclerotic plaques

Fourier transform infrared (FTIR) spectroscopic imaging using a focal plane array detector has been used to study atherosclerotic arteries with a spatial resolution of 3-4 microm, i.e., at a level that is comparable with cellular dimensions. Such high spatial resolution is made possible using a micro-attenuated total reflection (ATR) germanium objective with a high refractive index and therefore high numerical aperture. This micro-ATR approach has enabled small structures within the vessel wall to be imaged for the first time by FTIR. Structures observed include the elastic lamellae of the tunica media and a heterogeneous distribution of small clusters of cholesterol esters within an atherosclerotic lesion, which may correspond to foam cells. A macro-ATR imaging method was also applied, which involves the use of a diamond macro-ATR accessory. This study of atherosclerosis is presented as an illustrative example of the wider potential of these ATR imaging approaches for cardiovascular medicine and biomedical applications.

Studying biological tissue with fluorescence lifetime imaging: microscopy, endoscopy, and complex decay profiles

We have applied fluorescence lifetime imaging (FLIM) to the autofluorescence of different kinds of biological tissue in vitro, including animal tissue sections and knee joints as well as human teeth, obtaining two-dimensional maps with functional contrast. We find that fluorescence decay profiles of biological tissue are well described by the stretched exponential function (StrEF), which can represent the complex nature of tissue. The StrEF yields a continuous distribution of fluorescence lifetimes, which can be extracted with an inverse Laplace transformation, and additional information is provided by the width of the distribution. Our experimental results from FLIM microscopy in combination with the StrEF analysis indicate that this technique is ready for clinical deployment, including portability that is through the use of a compact picosecond diode laser as the excitation source. The results obtained with our FLIM endoscope successfully demonstrated the viability of this modality, though they need further optimization. We expect a custom-designed endoscope with optimized illumination and detection efficiencies to provide significantly improved performance.

Carotid artery wall motion estimated from B-mode ultrasound using region tracking and block matching

The motion of the carotid atheromatous plaque relative to the adjacent wall may be related to the risk of cerebral events. A quantitative method for motion estimation was applied to analyse arterial wall movement from sequences of 2-D B-mode ultrasound (US) images. Image speckle patterns were tracked between successive frames using the correlation coefficient as the matching criterion. The size of the selected region-of-interest (ROI) was shown to affect the motion analysis results; an optimal size of 3.2 x 2.5 mm(2) was suggested for tracking a region at the wall-lumen interface and of 6.3 x 2.5 mm(2) for one within the tissue. The results showed expected cyclical motion in the radial direction and some axial movement of the arterial wall. The method can be used to study further the axial motion of the carotid artery wall and plaque and, thus, provide useful insight into the mechanisms of atherosclerosis.

Fluorescence lifetime system for microscopy and multiwell plate imaging with a blue picosecond diode laser

We report a wide-field fluorescence lifetime imaging (FLIM) system that uses a blue picosecond pulsed diode laser as the excitation source. This represents a significant miniaturization and simplification compared with other time-domain FLIM instruments that should accelerate the development of clinical and real-world applications of FLIM. We have demonstrated this instrument in two configurations: a macroimaging setup applied to multiwell plate assays of chemically and biologically interesting fluorophores and a microscope system that has been applied to imaging of tissue sections. The importance of the adjustable repetition rate of this laser source is discussed with respect to noise reduction and precision in the lifetime determination, illustrating a further significant advantage over conventional mode-locked solid-state lasers.

Sulphorhodamine-B-labelled albumin uptake around the ostium of the renal artery in rabbits: changes with age

Because protein transport between blood and artery wall is important in atherogenesis, we have measured the uptake of fluorescently labelled albumin around the aorto-renal branch, an important site for lesions. Tracer concentrations in artery wall sections were quantified using digital fluorescence microscopy. Short-term experiments indicated endothelial permeability, while longer ones indicated the steady-state distribution of native proteins within the wall. In sexually immature rabbits (65-75 days), the permeability of the aorta was greater downstream of the renal ostium than upstream (p < 0.004). However, in mature rabbits (120-156 days), the permeability was greater, on average, at the upstream site compared to downstream. This change in pattern of uptake around the renal ostium with age appears to be due to increased uptake at the upstream site in mature animals, which was over fourfold greater than that measured at the equivalent site in immature animals (p < 0.01). In the renal artery itself, permeability was low and age independent. In mature animals, endothelial permeability did not correlate with steady-state wall concentrations, suggesting that the latter may be more dependent upon the rate of exit of protein and/or available space in the wall, rather than the rate of entry. The age-dependent changes in the spatial pattern of permeability correspond to the different distributions of spontaneous lipid accumulation in immature and mature vessels of both rabbits and humans, implying that permeability of the wall is important in atherogenesis.

A ratiometric method of autofluorescence correction used for the quantification of Evans blue dye fluorescence in rabbit arterial tissues

Evans blue dye (EBD) conjugates with albumin in the circulation and is frequently used to measure vascular protein leakage. The fluorescence of the dye from tissue sections can be used to measure its uptake at very specific anatomical locations, but problems arise with dye quantification because tissue components also fluoresce; so-called autofluorescence. We have measured uptake of EBD by blood vessel walls at various points around the aorto-renal branch of rabbits. High resolution, digitised, fluorescence images of histological sections of artery wall allowed detailed microscopic analysis of EBD accumulation; and a ratiometric method was developed to enable autofluorescence to be separated from EBD fluorescence. When EBD-free tissue sections were illuminated with blue light, the ratio of red to green fluorescence was constant throughout the tissue (0.59 +/- 0.03, mean +/- S.D., n = 32). Therefore, at each individual pixel, the level of red autofluorescence could be determined by multiplying the green intensity at that pixel by the calculated red to green ratio. Since EBD fluorescence was detected only in the red region of the spectrum, intensity values of the dye alone were obtained from EBD-exposed tissue by subtracting the red autofluorescence estimated by this ratiometric method. In such cases the red to green fluorescence ratio was measured from adjacent sites known to be free of EDB (0.59 +/- 0.02, mean +/- S.D., n = 56). We were therefore able to increase the sensitivity of tracer quantification by complete elimination of background autofluorescence on a pixel-by-pixel basis. Use of EBD standards allowed calibration of corrected fluorescence intensities and calculation of mass transfer coefficients for albumin into the artery wall. Spatial variations in the permeability of the artery wall around the renal ostium were detected with the present high resolution technique, with an average mass transfer coefficient of (6.8 +/- 0.9) x 10(-8) cm s(-1) for all sites combined (n = 56). The present ratiometric method could potentially be applied to other quantitative fluorescence-based techniques.

Time-domain whole-field fluorescence lifetime imaging with optical sectioning

A whole-field time-domain fluorescence lifetime imaging (FLIM) microscope with the capability to perform optical sectioning is described. The excitation source is a mode-locked Ti:Sapphire laser that is regeneratively amplified and frequency doubled to 415 nm. Time-gated fluorescence intensity images at increasing delays after excitation are acquired using a gated microchannel plate image intensifier combined with an intensified CCD camera. By fitting a single or multiple exponential decay to each pixel in the field of view of the time-gated images, 2-D FLIM maps are obtained for each component of the fluorescence lifetime. This FLIM instrument was demonstrated to exhibit a temporal discrimination of better than 10 ps. It has been applied to chemically specific imaging, quantitative imaging of concentration ratios of mixed fluorophores and quantitative imaging of perturbations to fluorophore environment. Initially, standard fluorescent dyes were studied and then this FLIM microscope was applied to the imaging of biological tissue, successfully contrasting different tissues and different states of tissue using autofluorescence. To demonstrate the potential for real-world applications, the FLIM microscope has been configured using potentially compact, portable and low cost all-solid-state diode-pumped laser technology. Whole-field FLIM with optical sectioning (3D FLIM) has been realized using a structured illumination technique.

Whole-field five-dimensional fluorescence microscopy combining lifetime and spectral resolution with optical sectioning

We report a novel whole-field three-dimensional fluorescence lifetime imaging microscope that incoporates multispectral imaging to provide five-dimensional (5-D) fluorescence microscopy. This instrument, which can acquire a 5-D data set in less than a minute, is based on potentially compact and inexpensive diode-pumped solid-state laser technology. We demonstrate that spectral discrimination as well as optical sectioning minimize artifacts in lifetime determination and illustrate how spectral discrimination improves the lifetime contrast of biological tissue.

Application of the stretched exponential function to fluorescence lifetime imaging

Conventional analyses of fluorescence lifetime measurements resolve the fluorescence decay profile in terms of discrete exponential components with distinct lifetimes. In complex, heterogeneous biological samples such as tissue, multi-exponential decay functions can appear to provide a better fit to fluorescence decay data than the assumption of a mono-exponential decay, but the assumption of multiple discrete components is essentially arbitrary and is often erroneous. Moreover, interactions, both between fluorophores and with their environment, can result in complex fluorescence decay profiles that represent a continuous distribution of lifetimes. Such continuous distributions have been reported for tryptophan, which is one of the main fluorophores in tissue. This situation is better represented by the stretched-exponential function (StrEF). In this work, we have applied, for the first time to our knowledge, the StrEF to time-domain whole-field fluorescence lifetime imaging (FLIM), yielding both excellent tissue contrast and goodness of fit using data from rat tissue. We note that for many biological samples for which there is no a priori knowledge of multiple discrete exponential fluorescence decay profiles, the StrEF is likely to provide a truer representation of the underlying fluorescence dynamics. Furthermore, fitting to a StrEF significantly decreases the required processing time, compared with a multi-exponential component fit and typically provides improved contrast and signal/noise in the resulting FLIM images. In addition, the stretched-exponential decay model can provide a direct measure of the heterogeneity of the sample, and the resulting heterogeneity map can reveal subtle tissue differences that other models fail to show.

Effect of altered flow on the pattern of permeability around rabbit aortic branches

Uptake of circulating macromolecules by the aortic wall is greater downstream than upstream of branch sites in immature rabbits, but the opposite pattern is seen at later ages. The mature pattern is nitric oxide dependent; we tested whether it is also flow dependent. Intercostal arteries of anesthetized rabbits were occluded, sham operated, or left alone. Uptake of rhodamine-labeled albumin was assessed by quantitative fluorescence microscopy of the sections through the aorta. In mature animals, uptake was higher upstream than downstream of the control and sham-operated branches, but the pattern was reversed at occluded branches. In young animals, uptake was not significantly different between regions upstream and downstream of control, sham-operated, or occluded branches. The absence of the normal immature pattern may reflect an influence of anesthesia and will assist in the elucidation of mechanisms underlying this pattern. The data for mature animals provide the first direct evidence that flow determines permeability near arterial branches and may account for the inverse spatial correlation between shear stress and disease prevalence at branches of adult human arteries.

Whole-field optically sectioned fluorescence lifetime imaging

We describe a novel three-dimensional fluorescence lifetime imaging microscope that exploits structured illumination to achieve whole-field sectioned fluorescence lifetime images with a spatial resolution of a few micrometers.

Fluorescence lifetime imaging with picosecond resolution for biomedical applications

We describe a novel whole-field fluorescence lifetime imaging system, based on a time-gated image intensifier and a solid-state laser oscillator-amplifier, that images lifetime differences of less than 10 ps. This system was successfully applied to discrimination between biological tissue constituents.

Influence of hypercholesterolemia and adventitial inflammation on the development of aortic aneurysm in rabbits

Abdominal aortic aneurysms are characterized by intimal atherosclerosis, disruption and attenuation of the elastic media, and a variable adventitial inflammatory infiltrate. We have developed an animal model of this disorder to evaluate the contribution of hypercholesterolemia, medial injury, and adventitial inflammation to aneurysmal dilatation. To accomplish this, we used periaortic application of calcium chloride, which induced both medial injury with calcification and endothelial injury. Ultrasonography was used to demonstrate the dilatation and thickening of the aortic wall. Over the first 3 weeks after periaortic application of 0.25 mol/L CaCl2, the external aortic diameter increased from 3.5 +/- 0.5 to 4.2 +/- 0.8 mm, but the ID remained unchanged. This apparent wall thickening was accompanied by vascular remodeling, and biochemical changes included approximately 50% reduction in tissue hydroxyproline concentration and increased activity of gelatinases (matrix metalloproteinase [MMP]-2 and MMP-9). Independently, cholesterol feeding to induce hypercholesterolemia or the concomitant periaortic application of thioglycollate had little effect on the histological, biochemical, or diameter changes. Together, hypercholesterolemia and thioglycollate were associated with rapid aortic dilatation in CaCl2, treated animals but not controls: after 3 weeks, the ID and OD had doubled, the OD increasing from 3.5 +/- 0.4 to 7.1 +/- 0.4 mm, P = .005. The remarkable feature that accompanied this dilatation was the infiltration of cells, mostly foamy macrophages, into the adventitia, with a further reduction in hydroxyproline concentration. Adventitial inflammation may provide the critical stimulus to dilatation of an aorta with preexisting intimal and medial injury.

Plasma protein entry and retention in the vascular wall: possible factors in atherogenesis

Various experiments are described that relate to measuring the uptake of plasma proteins by the walls of various large blood vessels of the rabbit. The rate of uptake across the intimal surface is not uniform, there being punctate regions of elevated transport. In addition, the rate of transport appears to be considerably higher across veins, pulmonary vessels, and the ascending aorta than across more peripheral arteries. Although larger proteins such as fibrinogen and low-density lipoprotein are transported more slowly than smaller ones, they appear to be retained to a greater extent in the inner layers of arteries than in pulmonary vessels and veins. Retention is greatly enhanced when collars are placed around the arteries and may be involved in the intimal hyperplasia that is seen in such vessels. Thus it appears that it may be the relative extent of entrapment of large atherogenic proteins that determines the appearance of lesions at different sites in the cardiovascular system, in addition to the rates at which they exchange across the blood-wall interface.

Blood velocity profiles in the human renal artery by Doppler ultrasound and their relationship to atherosclerosis

Blood velocity profiles were measured in the renal branch (diameter 5.9 +/- 1.3 mm) of the aortorenal bifurcation using a 20-MHz 80-channel pulsed Doppler velocimeter during retroperitoneal surgery in 10 patients. The peak Reynolds number was 1145 +/- 140 and the frequency parameter (Wormersley parameter) was 3.0 +/- 0.8. Immediately distal to the ostium of the renal artery, reverse flow, indicating flow separation, was observed near the cranial wall mainly during the first part of the cardiac cycle. There were flows from the cranial to the caudal side of the artery at this location, indicating the presence of strong secondary flows. Two diameters downstream of the ostium, the velocity profiles were skewed to the caudal side in all patients. Four diameters downstream, the flow profile was symmetrical (3 patients) or only slightly skewed (7 patients) and virtually parabolic throughout the cardiac cycle. These observations mean that the flow on the cranial side of the renal branch of the human aortorenal bifurcation is characterized by (1) a bidirectional oscillation of the flow, (2) separation of the flow during systole, and (3) low time-averaged shear rate. These blood velocity patterns may be related to the localization and development of atheromatous plaque that occurs preferentially in this region of the renal artery. Conversely, the unidirectional, axisymmetrical flow found in more distal parts of the renal artery are associated with a very low incidence of lesions.

Influence of heart rate and vasoactive drugs on blood flow patterns at the canine ilio-femoral bifurcation

OBJECTIVE

The aim was to study the effects of altered heart rate and vasoactive drugs on the blood velocity patterns in the region of an arterial bifurcation.

METHODS

Blood velocity profiles were measured in an exposed iliofemoral bifurcation of paced dogs using a pulsed Doppler ultrasound velocimeter with high temporal and spatial resolution.

RESULTS

Decrease of the heart rate from 120 beats.min-1 (2 Hz) to 60 beats.min-1 (1 Hz) increased the peak forward velocity (30%), the peak reverse velocity (20%), and the duration of reverse flow (25%). Each drug caused qualitatively similar changes in velocity patterns at both heart rates. The systemic administration of angiotensin II reduced peak forward velocity (-26% at 2 Hz and -33% at 1 Hz) and forward flow duration (-15% at 1 Hz), the peak reverse velocity (-30% at 1 Hz), and reverse flow duration (-20% at 2 Hz and -28% at 1 Hz). Glyceryl trinitrate also reduced the peak forward velocity (-19% at both 2 and 1 Hz) but prolonged forward flow duration (28% at 2 Hz and 17% at 1 Hz) and that of reverse flow (45% at 2 Hz and 24% at 1 Hz), and also decreased the degree of oscillation (-16% at 2 Hz). Barnidipine hydrochloride (a calcium channel antagonist) also increased the duration of forward flow (48% at 1 Hz) and of reverse flow (31% at 2 Hz) but reduced the peak reverse velocity (-29% at 1 Hz) and flow oscillation (-22% at 2 Hz and 20% at 1 Hz).

CONCLUSIONS

These dramatic changes in the pattern of blood flow, including alterations in the amplitudes and durations of the different phases of the flow cycle, are expected to have important consequences on the shear dependent responses of endothelial cells in the region of the bifurcation.

Effects of high molecular weight solutes on fluid flux across the arterial wall

To investigate the mechanisms controlling the flux of plasma proteins into and through the walls of blood vessels, we have studied the effects of two inert protein analogues, Dextran 500 and Poly(ethylene)oxide (PEO) on fluid transport across the walls of intact rabbit common carotid arteries. Transmural fluxes were first measured in vessels pressurized to 150 cmH2O with a solution containing 10 mg/ml albumin alone (control solution) and then with one containing 10 mg/ml albumin plus 10 or 50 mg/ml dextran, or 10 or 30 mg/ml PEO (test solutions). The macromolecule solutions caused a decrease in transmural filtration; the ratios of fluxes with the test solutions to those with the control solutions were 0.89 +/- 0.11 (7), 0.63 +/- 0.08 (8), 0.69 +/- 0.24 (9) and 0.41 +/- 0.09 (4), respectively (Mean +/- SD (n)). These reductions in fluid movement through the vessel wall may be explained quantitatively in terms of the formation of concentration-polarized layers of the macromolecules at the luminal surface or interactions of the macromolecules with the endothelial glycocalyx, causing a decrease in its permeability.

The effect of luminal flow in rabbit carotid artery on transmural fluid transport

The steady-state flow of fluid across the wall of the isolated rabbit common carotid artery has been measured in the presence and absence of flow within the lumen of the vessel. The perfusate solution contained either 10 or 40 mg ml-1 albumin and transmural flux was measured by monitoring the rate of movement of fluid into a chamber enclosing the artery. Vasomotion was minimized by the inclusion of the vasodilator sodium nitrite in both the perfusate and the outer bathing solution. A relatively slow luminal flow caused a reversible increase in the transmural flux by 20-30% relative to the value in the absence of flow. The mechanism responsible for the increase is not clear, but since it was not affected by the H1 antagonist, mepyramine, it would not appear to have been mediated by histamine release.

Blood velocity profiles in the origin of the canine renal artery and their relevance in the localization and development of atherosclerosis

Using a 20-MHz 80-channel pulsed Doppler velocimeter and 30-MHz high-resolution echo ultrasound, we investigated the in vivo hemodynamics at the origin of the renal artery by measuring the velocity profiles and bifurcation geometry of a surgically exposed left renal artery in 10 anesthetized dogs. The angle between the aorta and the renal artery ranged from 60 degrees to 90 degrees (mean, 84 degrees) although the bifurcation did not lie in a single anterodorsal plane and the diameter of the renal artery ranged from 1.5 to 3.5 mm (mean, 2.4 mm). Despite different geometries, the velocity profiles in the different aortorenal bifurcations were similar. Although regions of reverse velocity were observed, the net flow in the renal artery was in the forward direction throughout the cardiac cycle. The peak Reynolds' number was 486 +/- 63. The velocity profiles in the proximal renal artery in the plane parallel to the bifurcation showed velocity vectors directed toward the caudal wall throughout the cardiac cycle. Reverse flow, indicating flow separation, was observed near the cranial wall even during systole. When the probe was placed on the cranial wall perpendicular to the wall, a velocity component from the cranial side to the caudal side was observed. At a distance of four diameters from the renal ostia, velocity profiles were almost parabolic. These results indicate that the velocity pattern near the cranial wall at the renal ostia, at which atherosclerotic lesions are prone to develop, are characterized by 1) a low time-averaged shear rate, 2) separation of the flow, and 3) a time-varying oscillation of the flow.

Blood velocity distributions within intact canine arterial bifurcations

As local variations in blood flow are implicated in atherogenesis at bifurcations, we measured in vivo blood velocities in different planes within exposed iliofemoral arterial bifurcations in 8 dogs using 20-MHz, 80-channel Doppler ultrasound velocimetry. Cardiac frequency was fixed at 2 Hz by pacing. Local geometry was characterized using 25-MHz, B-mode ultrasound images, photographs, and methacrylate casts. The bifurcations were asymmetrical and planar to within 5 degrees, the diameter ratios of the daughter vessels ranged from 1.47 to 2.00, and the angles between them ranged from 40 to 76 degrees. Measured velocities indicated that just upstream of the bifurcation mean peak Reynolds numbers ranged from 196 to 564 and Womersley (frequency) parameters ranged from 2.00 to 4.1. At the level of the bifurcation, secondary flows were insignificant in the normal plane but strong in the plane of the bifurcation. As a result, two-dimensional velocity fields, reconstructed by vector addition of velocities measured in the plane of the bifurcation, differed markedly from the one-dimensional profiles calculated assuming flow parallel to the vessel axis. In the two-dimensional velocity fields, forward flow was directed toward the flow divider and reversal occurred earliest near the outer wall. Wide spatial and temporal variations in the shear stress at the endothelium are implied by these detailed, in vivo measurements of the bifurcation velocity fields.

Effects of isosorbide dinitrate on the pattern of arterial blood flow in healthy human subjects

1. Blood velocity measurements have been made in the superficial femoral artery, 10 cm downstream of the common femoral artery bifurcation, in healthy human subjects, using a multi-channel Doppler ultrasound device. 2. In a randomized double-blind protocol, the effects of isosorbide dinitrate were examined during a 2 h period. 3. The changes induced by isosorbide dinitrate include: (i) an increase in the width of the artery and a reduction in brachial arterial blood pressure, implying relaxation of arterial smooth muscle; (ii) an increase in reverse flow and a decrease in time-averaged mean velocity associated with a relatively small decrease of the velocity excursion during the cardiac cycle, implying an increase in flow pulsatility; and (iii) an alteration of the flow pattern both in the core and near the vessel walls.

Albumin and Cr-EDTA uptake by systemic arteries, veins, and pulmonary artery of rabbit

Experiments have been performed both in vivo and in vitro to measure the steady-state uptake of labeled albumin and Cr-ethylenediaminetetraacetate by various blood vessels of the rabbit: the ascending and descending portions of the thoracic aorta, the carotid artery, the pulmonary artery, and the inferior vena cava. The in vitro experiments indicated that the wall tissues of the pulmonary artery and the vena cava have much greater distribution volumes for albumin than do the systemic arteries. This may in part explain the differences in wall tissue concentrations in vivo and, in turn, the differences between vessels in their susceptibility to atherosclerosis.

Changes in vein interstitium following distension for aortocoronary bypass

Some patients who undergo aortocoronary bypass develop lesions in the graft and recurrence of symptoms. Hydraulic distension is used for preparation of veins. We have studied properties of vein interstitium, before and after peroperative distension, in 30 consecutive unselected patients. Segments of vein were studied for water content, swelling behaviour, tracer distribution, and uronic acid content. Initial water content was the same in distended and undistended vein; initial uronic acid content was slightly lower in distended veins, 8.7 (SD = 2.3) micrograms/m, n = 4 vs 10.5 (SD = 5.1) micrograms/mg dry weight, n = 6, not significant. The initial ratio, uronate/hydroxyproline was less in distended veins, 0.14 (SD = 0.05) n = 4 vs 0.19 (SD = 0.07), n = 6 in controls, not significant. Distended veins swelled less during incubation in saline. Average weight gain/initial weight was 0.65 (SD = 0.45), n = 27, and 1.1 (SD = 0.66), n = 25 in controls (p less than 0.01); change in water content/dry weight was 1.2 (SD = 1.1), n = 22, and 1.7 (SD = 1), n = 23 (p less than 0.02), in controls. Distended veins desorbed less uronic acid into the bath; 0.40 (SD = 0.2) microgram/mg wet tissue, n = 26 and 0.59 (SD = 0.3), n = 25 in controls (p less than 0.01). The pattern of uptake of two tracers 125I Serum albumin and 51Cr EDTA, was similar in both groups. These findings suggest alteration of the interstitial matrix of veins during distension. Histologic examination of glutaraldehyde-fixed tissue by light and electron microscopy revealed mural thinning and endothelial cell damage in distended veins.(ABSTRACT TRUNCATED AT 250 WORDS)

Coronary vasodilatation induced by calcitonin gene-related peptide in the anaesthetised pig

The ability of CGRP to increase blood flow in the coronary circulation of the anaesthetized pig was studied in a constant pressure perfusion model. Human alpha-CGRP, when infused close-arterially into the left anterior descending coronary artery perfused at constant pressure, produced a marked and prolonged dose-related increase in coronary flow, at doses above 10 pmol min-1. The gradient of the flow/pressure curves at each dose increased with an increase in pressure, indicating a drop in the resistance of the coronary bed. No significant change was observed in heart rate, left ventricle pressure, mean arterial pressure or cardiac output.

The effect of varying albumin concentration of the hydraulic conductivity of the rabbit common carotid artery

Rabbit common carotid arteries were cannulated in situ, after ligation of their branches, and transferred to a perfusion apparatus in such a way that they were maintained at their physiological dimensions and the endothelium remained intact. The vessels were pressurized to 150 cm H2O with Krebs solution and the wall smooth muscle was relaxed with 10(-4) M NaNO2. The rate of inflow of perfusate into the vessels was measured by following the movement of a bubble in a calibrated capillary which, when steady, was taken to indicate the transmural filtration rate. The filtration rate was 1.48 +/- 0.26 X 10(-6) cm sec-1 (11) (mean, SD, n) with 1 g/dl bovine serum albumin in Krebs solution. The values with 0, 4, 7, and 10 g/dl, normalized by the 1 g/dl value were 1.38 +/- 0.16 (7), 0.80 +/- 0.05 (9), 0.65 +/- 0.03 (8), and 0.47 +/- 0.06 (9), respectively. The hydraulic conductivity of the wall was also found to depend on perfusate albumin concentration. The 1 g/dl value was 0.92 +/- 0.17 X 10(-8) cm sec-1 (cm H2O)-1 (11) and the values with 0, 4, 7 and 10 g/dl normalized by the 1 g/dl value were 1.35 +/- 0.16 (7), 0.87 +/- 0.06 (9), 0.81 +/- 0.03 (8), and 0.72 +/- 0.06 (9), respectively. The findings were analyzed in relation to models involving interaction of albumin with the endothelial glycocalyx, concentration polarization at the blood/wall interface, dependence of flux on solvent viscosity and dependence of the porosity of the wall interstitium on solvent flux. Both concentration polarization and variation of the porosity of the wall interstitium provide reasonable quantitative explanations for the findings.

Effect of pressure and intimal damage on 131I-albumin and [14C]sucrose spaces in aorta

To measure the distribution volume for sucrose and albumin in the media of the rabbit thoracic aorta, we studied the uptake of tracers in vitro. In most cases the tracers were applied to both luminal and adventitial surfaces at the same concentration. When transmural convection was prevented by pressurization of the arteries with air, there was a decrease in sucrose space (19% at 70 mmHg and 28% at 180 mmHg) and in albumin space (60% at 70 mmHg and 66% at 180 mmHg), compared with the respective spaces in relaxed arteries (0.42 for sucrose and 0.08 for albumin). Much smaller changes were found when intact vessels were pressurized with liquid (insignificant for sucrose, decreases of 24% at 70 mmHg and 14% at 180 mmHg for albumin). Removal of the endothelium, which increases transmural fluid flux, increased the space for sucrose (not significantly at 70 mmHg and 17% at 180 mmHg) and particularly for albumin (100% at 70 mmHg and 250% at 180 mmHg). We conclude that the interstitial volume and consequently the protein space within the media can be modified both by distending stresses applied to the vessel and by transmural fluid flux.

Effect of cigarette smoking on the pattern of arterial blood flow: possible insight into mechanisms underlying the development of arteriosclerosis

By means of non-invasive multichannel doppler ultrasound measurements, cigarette smoking in healthy subjects was shown to increase arterial wall stiffness and to alter the pattern of arterial blood flow, decreasing the pulsatility index. The pattern of blood flow seems to be a contributory factor in the development of arteriosclerosis, and these findings may provide insight into the underlying mechanisms.

The interaction of convection and diffusion in the transport of 131I-albumin within the media of the rabbit thoracic aorta

The interaction of convection and diffusion in the transport of 131I-labeled albumin within the wall of rabbit thoracic aorta was studied in vessels excised at in vivo length. They were pressurized with a solution containing no tracer and immersed in a solution containing labeled albumin. The label then entered the wall tissue via the adventitia and had to diffuse against the convective flux which occurred from the lumen to the adventitia. Experiments were performed on intact and deendothelialized vessels pressurized to 70 and 180 mm Hg. At the end of each experiment the vessels were subjected to sequential frozen sectioning parallel to the lumenal surface. The radioactivity of the 20-micron-thick sections was determined and expressed as a tissue:labeled solution concentration ratio. Transmural profiles of these ratios were thus obtained. The steady state was found to be achieved by about 90 minutes. When the convection was enhanced by removal of the endothelium, the average ratios were lower than when the endothelium was intact, and the profile was much flatter. The results suggest that convection influenced macromolecular transport within the arterial wall, even in vessels with intact endothelium.

Filtration through damaged and undamaged rabbit thoracic aorta

The influence of luminal pressure and endothelial removal on fluid filtration across the arterial wall has been studied in the rabbit thoracic aorta. Segments of aorta were excised in such a way as to prevent shortening and depressurization and were filled with a 4% albumin-Tyrode solution. Experiments were carried out at two controlled pressure levels (70 and 180 mmHg). The hydraulic conductivity (Lp) of the total wall, calculated from the filtration data, was 4.00 +/- 1.31 and 2.44 +/- 0.80 (SD) X 10(-8) cm/(s X mmHg) in intact wall at 70 and 180 mmHg, respectively (P less than 0.01), whereas values for deendothelialized arteries were higher (P less than 0.01), being 5.36 +/- 1.62 and 5.27 +/- 0.84, respectively. The apparent pressure dependence of conductivity of the intact wall may be due to altered strain of the interstitial matrix. Removal of the endothelium can increase the hydration and porosity of the medial interstitium but, assuming that the conductivity of the deendothelialized wall at 70 mmHg is the same as that of the normal media, the calculated conductivity of the endothelium is 15.76 X 10(-8) cm/(s . mmHg).

Factors influencing arterial wall mass transport

Arterial wall mass transport has particularly attracted attention because it may be implicated in the development of arterial disease, including arteriosclerosis. A short review is presented of the structure of the arterial wall and of studies of mass transport within it. Recent findings confirm that mass transport occurs across the entire arterial wall apparently from the lumen to the adventitial lymphatics. Evidence has emerged of inhomogeneity of the distribution volume for extracellular tracers in different layers of the wall. An attempt is made to interpret results which indicate that distension per se of arteries and increase of medial smooth muscle tone tend to compact the medial interstitium whereas pressure driven convection across the wall tends to expand that tissue. These findings imply a potentially important role of endothelial permeability, smooth muscle tone and luminal pressure in influencing solute transport in the wall and wall transport properties.

Effect of vasoactive agents and applied stress on the albumin space of excised rabbit carotid arteries

Experiments were undertaken on excised rabbit common carotid arteries to assess whether the distribution volume for radioactively labelled albumin is influenced by smooth muscle tone or externally applied stress. In arteries at relaxed length and zero transmural pressure, the distribution volume in the media was reduced by noradrenaline at concentrations exceeding 10(-9) M and increased by both sodium nitrite and isosorbide dinitrate at concentrations exceeding 10(-4) M. The distribution volume was lower in both the media and adventitia of segments at in vivo length pressurized with air to prevent convection through the wall, than in segments at relaxed length and zero transmural pressure. Noradrenaline decreased and sodium nitrite increased the medial distribution volume of the tracer in these air-pressurized segments. The vasoactive agents did not change the [51Cr]EDTA space in vessels at relaxed length and zero transmural pressure, although there were small alterations of medial water content. Transient conditions raise interpretative difficulties because of uncertainty about endothelial permeability and time-dependent changes of wall properties. The changes of the distribution volume for labelled albumin are thought to reflect changes in the properties of the interstitium.

Effect of noradrenaline, sodium nitrite and isosorbide dinitrate on albumin transport in the wall of the excised rabbit common carotid artery

The effects of noradrenaline (NA), sodium nitrite (NaNO2) and isosorbide dinitrate (ISDN) on the steady state distribution of 125I-labelled albumin in the wall of excised rabbit common carotid arteries were studied. The vessels were incubated in Tyrodes solution either at relaxed length and zero transmural pressure (non-pressurized) or at in vivo length and a transmural pressure of 70 mm Hg (pressurized). Label was applied in the same concentration at both the luminal and outer surfaces. The mean medial uptake in pressurized vessels was greater after treatment with 10(-7) M NA than after additional treatment with either 10(-3) M NaNO2 or 10(-3) M ISDN. The opposite was found for non-pressurized vessels. The medial uptake by NA-treated pressurized vessels was greater than that by NA-treated non-pressurized vessels, while the reverse was found for NaNO2- or ISDN-treated vessels. We conclude that the different patterns of uptake seen in these vessels results from the relative effects of externally applied stress (elongation and pressurization), smooth muscle tone and convection through the wall, on the properties of the interstitium, and possibly from the effects of the vasoactive agents on endothelial permeability.

Net albumin transport across the wall of the rabbit common carotid artery perfused in situ

We have studied the transport of radioactively labelled albumin in the rabbit common carotid artery perfused in situ at 100 cm H2O luminal pressure in the anaesthetized living animal, assessing the distribution of concentration across the wall by means of sequential frozen sectioning. We have compared the findings with those of experiments in which we have attempted to saturate the wall with label. Our findings support the belief that there is a net transport of macromolecules across the arterial wall. They show in addition that the wall is inhomogeneous. The distribution volume for label is greater in the adventitia than the media, which appears to offer a larger resistance. The transport process is seemingly dominantly diffusional.

Acid-base curve nomogram for chimpanzee blood and comparison with human blood characteristics

An acid-base nomogram for chimpanzee blood was constructed. Blood was drawn from eight lightly anesthetized chimpanzees. Each sample of blood was oxygenated and nine aliquots were prepared with three different concentrations of hemoglobin and three different amounts of added acid or base. Each aliquot was equilibrated at two PCO2 levels and the pH was measured and plotted on pH-logPCO2 coordinates. Using the intersection point of these pH-logPCO2 lines as a point of equal hemoglobin-independent "base excess" for each condition, values for true base excess were plotted. Connecting these values provided a Cartesian PCO2-pH base excess nomogram for the chimpanzee comparable to that devised by Siggaard-Andersen for humans. Examination of blood from normal human subjects by the same methods showed no appreciable differences from the original Siggaard-Andersen nomogram. However, the PCO2-pH-base excess nomogram for chimpanzee blood deviated slightly from that for human blood. It is possible that the deviation is related to an arterial bicarbonate concentration in the chimpanzee slightly higher than that in human.

Experimental studies of the deposition of particles in the human lungs

Measurements of deposition, De, during steady breathing through the mouth of particles between 0.5 and 2.5 micons diameter and density 0.92 g/cm3 show that it is related to the tidal volume, VT, expiratory reserve volume, Vr, and a "normal" volume, Vro, by the formula 100 De= Vt/B+C/FD- E- Vr-Vro/A where B, C, D and E are constants which depend on particle size but do not vary from subject to subject enough to have much influence on corresponding values of De. A and and Vro are independent of particle size but relate to the individual subject, especially Vro. A new method is described of correlating the numerous experimental results, which involve six variables, and of evaluating the subject's 'normal' expiratory reserve volume, Vro, for any subject.

Experiments on the genesis of bubbles as a result of rapid decompression

1. The time course of intravascular bubble formation in mice after rapid decompression from 150 Lb/sq. in. has been followed in vivo in a flap preparation of thoracic and abdominal skin.2. Gas appeared first in the arteries, moving distally after a latent period of 3 min or more. Then bubbles appeared, moving centrally, in the venous system.3. The arterial bubbles could not be attributed to air forced into the circulation from the lungs or lumen of the gut.