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B S Gow

Publications and source records attributed to B S Gow.

At least 19 recordsLinked to original sources
PubMed1992

Detecting right ventricular volume changes using the conductance catheter.

The purpose of this study was to assess the role of conductance catheter position within the right ventricle in obtaining adequate indications of phasic changes in ventricular volume. Possible applications of this technology are in rate responsive pacemakers and implantable defibrilators. The conductance catheter was placed in the right ventricle by cannulation of a jugular or femoral vein or a branch of the pulmonary artery. Position within the ventricle was documented from biplane fluoroscopy. Stroke volume was perturbed by: bolus injection of blood, vagal stimulation, venous infusion of methylcholine chloride, or isoprenaline. Four criteria were used to assess the quality of volume signals: (1) volume signal phase relative to the electrocardiogram; (2) magnitude parity of volume change from each electrode pair; (3) freedom from artifact; and (4) indication of stroke volume change during interventions. Greyhound dogs of either sex (n = 33), weight 20-32 kg. A total of 236 recordings from 14 distinct catheter positions were analyzed. Catheter positions originating from a femoral cannulation and one position from the pulmonary artery gave markedly superior volume transduction compared to those from the jugular route. Although right ventricular volume transduction was possible from all catheter trajectories, those resulting from the femoral approach were clearly superior. In the right ventricle, the inability to transduce a sufficient proportion of ventricular volume, in concert with the potential sensitivity of the catheter to atrial volume changes, may seriously limit the potential of the conductance technique in the applications envisaged.

Animals↗
PubMed1992

Does vibration cause poststenotic dilatation in vivo and influence atherogenesis in cholesterol-fed rabbits?

Arterial post-stenotic dilatation (PSD) is a fusiform swelling immediately down-stream to a stenosis. It is characterized by the presence of turbulent blood flow and wall vibration which has been claimed by others to be causal by producing structural weakening. We tested the hypothesis that vibration causes PSD in vivo by attaching electromagnetic and pneumatic vibrators to the aortic wall in chronic rabbits. We also observed whether mechanical vibration of the aorta in vivo influenced the distribution of oil-red-O lesions during one percent dietary cholesterol feeding. Low mass vibration gauges were developed to measure the vibration. Electromechanical vibrators having a ceramic magnet slug within a coil supplied with 50 Hz were glued to the aorta of chronic rabbits and the vibration maintained for an average of 8 weeks. Despite greater amounts of energy imparted to the wall there was no dilatation or difference in oil-red-O staining from the controls. Five weeks vibration at 100 Hz and an amplitude equal to the normal diameter pulse also produced no dilatation. We conclude that vibration does not cause PSD in vivo and suggest that its cause is likely to involve the vascular muscle stimulated by the effect of turbulent flow on the endothelium.

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PubMed1989

Effect of radial position on volume measurements using the conductance catheter.

A finite-difference computer model has been used to determine the potential distributions arising from a dipole current source aligned parallel to the axis of bounding cylinders. The radial position of this source had large and nonlinear influence on the potentials along the dipole axis. The accuracy of the computer simulation was established from comparison with an analytic solution of a simple geometry. Measurements using a conductance catheter in saline-filled cylinders also demonstrated the dependence of the conductance on the radial position. The dependence of the potential distribution on the radial position of the dipole places limits on the ultimate accuracy of the conductance catheter technique when used for the measurement of ventricular volume. Radial movement of the catheter within the ventricular cavity, resulting in changes in the potential distribution, could explain some artefacts that appear on volume recordings from the conductance catheter.

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PubMed1989

Morphometric analyses of rabbit thoracic aorta after poststenotic dilatation.

The aim of this study was to quantify the morphological changes in the arterial wall resulting from poststenotic dilatation (PSD). PSD was produced by placing a split nylon ring around the thoracic aorta of the rabbits at a level of T6-7 during a sterile thoracotomy done under pentobarbital anesthesia. After period of PSD ranging from 1-51 months these rabbits were anesthetized, as were the control animals, and the descending thoracic aorta from the fourth to the eleventh ribs was removed following perfusion fixation with Karnovsky's solution at a constant pressure of 80 mm Hg. The extent of PSD development was variable even though the stenotic ring was the same size in all rabbits. Ultrastructural findings showed degenerative changes of the wall components in the PSD region and were more prominent in the aortas with greater dilatation. Morphometric measurements showed that the PSD was accompanied by a decrease in volume density of both smooth muscle cells (SMCs) and elastin and an increase in collagen and ground substance. These changes were well correlated with degree of dilatation and ratio of internal radius to wall thickness (hence, mean wall stress) but not with duration of PSD. While the number of SMCs per unit volume in the PSD aortas was significantly less than normal (p less than 0.05), there was no significant change in mean cell volume. Although the reduced muscle mass might be expected to lower the capacity of the vessel to maintain tone, previous results show that this does not occur.

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PubMed1987

Right ventricular volumetry by catheter measurement of conductance.

The electrical conductivity of blood is sufficiently higher than that of myocardium to make feasible the detection of cardiac volume changes by measurement of intraventricular fluid conductance. An eight-electrode catheter was used to inject an alternating current (100 microA or less, at 1500 Hz) via the two electrodes nearest the ventricular base and apex, then the resulting five voltage differences between adjacent pairs of the six intervening electrodes were measured. When current amplitude was held constant, the cross-sectional area of the ventricular cavity slice defined by planes perpendicular to the catheter through the relevant pair of electrodes was inversely proportional (to the first order) to the voltage difference. Measurement of multiple segments compensated for isovolumic cavity shape changes. The technique had previously been shown to measure left ventricular volume successfully, but the geometry of the right ventricle made this measurement more problematical. Using open-chested, anesthetized greyhounds, we compared the catheter-measured right ventricular volume change with stroke volume as measured by a pulmonary arterial electromagnetic blood flowmeter. With optimal catheter placement, good correlation between stroke volume and catheter-measured volume changes was achieved when stroke volume was perturbed on a beat-to-beat basis. In six data records from three dogs, involving two different means of varying stroke volume (rapid injection of blood and sinus node irritation), the correlations yielded r2 values between 0.82 and 0.98.(ABSTRACT TRUNCATED AT 250 WORDS)

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PubMed1983

Changes in the microindentation properties of aortic intimal surface during cholesterol feeding of rabbits.

A new microindentation technique using a small, loaded spherical probe (25 microns diameter) was developed to quantify early mechanical changes in the arterial intima during atherogenesis. Routine use of forces of 10 microN on normal intima for 10 S resulted in indentations of about 2.5 microns which gives an intimal compliance of 0.245 +/- 0.031 m/N. There was a decrease in intimal compliance in the proximal to distal direction in both the rabbit and the dog thoracic aorta. The region immediately distal to an intercostal orifice in the rabbit was often up to 1.6 times more compliant (softer) than surrounding areas while the corresponding region in the dog tended to be less compliant than elsewhere. Feeding a 1% cholesterol diet to rabbits for 8 weeks increased the intimal compliance to 0.368 +/- 0.041 m/N. The regions distal to the intercostal ostium were 32% more compliant after 4 weeks of cholesterol diet than non-orifice-related areas but after 8 weeks of the diet there was no significant difference between these regions. The time course of indentation (viscous component) was characterised by a rapid indentation phase which almost became non-exponentially asymptotic by 6 S and was 66 +/- 3% SD of this value by 1 S. Cholesterol feeding (8 weeks) altered this phase to 76 +/- 4% SD of the asymptotic value after 1 S of indentation, indicating a decrease in initial viscosity. A very slow indentation or creep was also found when the force continued for a period up to 25 min. Cholesterol feeding increased this rate of creep by approximately 15%. The results show that early atheromatous changes induced by cholesterol feeding are accompanied by softening and increased fluidity of the aortic intima.

Animals↗
PubMed1983

An improved microindentation technique to measure changes in properties of arterial intima during atherogenesis.

A fully automated instrument was developed that measured the amount and time-course of indentation of arterial intima by a spherical tipped probe 25 micrometers in diameter loaded routinely by forces of 10 microN. The relationship of depth of indentation to time was non-exponential but reached an apparent asymptotic value in about 6 s. Routine indentations were recorded 10 s after loading, the relationship of indentation and force being essentially linear between 0-100 microN. The instrument is an order of magnitude more sensitive than one previously described (Gow and Vaishnav, 1975, J. Appl. Physiol. 38, 344-350) and produces indentations of 1-4 micrometers in the intima of rabbit thoracic aorta with a reproducibility of 1-2%. Preliminary usage of the new microindentor has shown increases in the compliance of the thoracic aorta intima in rabbits during cholesterol feeding.

Animals↗
PubMed1980

A computerized scanner to quantify atherosclerosis.

A method is described for the quantitation of atherosclerotic lesion after excision and staining of the vessel. Essentially the device consists of a microscope with a computer-controlled stage which moves a photographic negative image over a square beam (o.1 mm sides) of light. At each translation-step of the stage a transmittance reading is taken using a photomultiplier tube for detection. The computer stores topographical values (typically around 6,000) and, by setting a threshold, can determine the fractional area of artery which is diseased.

Animals↗
PubMed1976

A comparative study of pulsatile arterial hemodynamics in rabbits and guinea pigs.

Pulsatile pressure and flow were measured in the ascending aorta and other arteries of 22 anesthetized rabbits and 16 anesthetized guinea pigs. Pressure/flow relationships were expressed as vascular impedance. Aortic flow waves were almost identical in the two species, but pressure waves were quite different. Reflected pressure waves returned earlier from the periphery in guinea pigs, augmenting pressure during late systole and resulting in relatively high external left ventricular work, an inappropriately larger difference between mean systolic and mean diastolic pressure and absence of any aortic diastolic pressure wave. Values of impedance modulus and phase were similar but differed in the frequency at which maxima and minima occurred. In both species, impedance curves were interpreted to indicate a functionally discrete reflecting site in the lower body whose position corresponded to the region of the aortic bifurcation. In addition, rabbits showed evidence of an upper body reflecting site approximately one-third as far distant from the heart. As in dogs, the arterial system in both species can be represented by an asymmetrical T-shaped model of realistic dimensions.

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PubMed1975

A microindentation technique to measure rheological properties of the vascular intima.

A microindentor was developed to measure the depth of indentation of the intimal surface of arterial tissue loaded by flat-ended, cylindrical probes. The depth of indentation depended on the initial stretch of the tissue which required a rigid support (plaster of Paris) beneath the adventitial surface. Probe tips used ranged from 550-mum down to 65-mum diameter while loads ranged from 800 to 15 mg. The depth of indentation was markedly time dependent; that obtained 30 s after loading (variation of 30) was reproducible and served as a useful parameter of viscoelasticity of the aortic intima and supporting tissues of dog and man. The mean variation of 30 (0.19-mm diam tip, 120-mg load), obtained from longitudinal series of indentations of nine dog aortas, ranged from 40.8 to 68.8 mum while coefficient of variation in these series ranged from 4.8 to 15.9%. Intimal pads were found to have greater resistance to identation than adjacent tissue; likewise the tissue on the dorsal, intimal surface of the aorta had lower variation of 30 values compared with the rest of the intima. Lipid-filled intimal regions were about twice as complaint as macroscopically spared areas. The technique should prove useful in understanding the microrheological response of the blood vascular interface to hydrodynamic stresses.

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