Pressure, flow and diameter were measured in the abdominal aorta of five anesthetized dogs during normal heart beats and heart beats with a superimposed impulse (generated by rapidly injecting a small volume of saline into the system). From Fourier analysis it was found that the impulse enhanced the amplitudes of the higher harmonics so that frequencies up to 80 Hz could be studied. Both the input impedance and apparent phase velocity above 20 Hz were independent of frequency and their average values were designated as characteristic impedance and true phase velocity. Average characteristic impedance for all five animals was 2.0 ± 0.1 × 108 Nsm−5 and average phase velocity was 8.3 ± 0.6 ms−1. Phase velocities calculated from characteristic impedance (1.76−2.39 × 108 Nsm−5) and from the slope of the pressure-diameter relation (0.102–0.25 × 10−8 Nm−3) were similar to the true phase velocity as defined above (6.79–9.85 ms−1). It may be concluded that the input impedance converges to characteristic impedance and apparent phase velocity converges to phase velocity for high frequencies.

Analogues of arterial stenoses and aneurysms were constructed from latex tubing containing inserts of various lengths, and with diameters and elastic properties that differed from those of the surrounding tube. A pressure impulse (duration <10ms). was generated at one end of the tube and its transmission and reflection were monitored at various points within the system using a catheter-tip manometer. The complex waveforms produced by multiple reflections from either end of the insert were analysed and compared with those generated by a numerical model in which the reflection sites were regarded as isolated junctions between two tubes of infinite length. There was close agreement between the synthesised and measured waveforms.

A viscoelastic shell theory model for transient pressure perturbations in fluid filled tubes is presented and tested against experiments involving water filled latex tubes. The agreement between theory and experiment is good.

Elastic mismatching is studied by an impulse technique. Elastic mismatches are created by joining two latex rubber tubes of the same internal diameter but different wall thickness. A short duration pressure impulse is generated at the entrance of the water-filled tube system and the transmission characteristics of the impulse are determined from a series of measurements along the tube system using a catheter-tip pressure manometer. This technique enables the magnitude and phase change of the reflection at the elastic discontinuity to be obtained. A number of tube combinations are examined and in all cases a good agreement is shown between the measured reflection coefficient and the value calculated theoretically.

The left anterior descending coronary artery in anaesthetized greyhounds was perfused at constant pressure with blood pumped from the carotid artery. Phasic and mean coronary flow, left ventricular pressure, dP/dt, cardiac output, ECG, heart rate and systemic pressure were measured. Leukotriene (LT) D4 was administered into the left anterior descending coronary artery as a bolus injection. LTD4 caused dose-related reductions in coronary flow. Other parameters showed little immediate change although a gradual decrease in left ventricular pressure, dP/dt, cardiac output and systemic pressure occurred after administration of LTD4. Following intracoronary administration of LTD4 small surface haemorrhages were observed over the area perfused. The reduction in coronary flow was not inhibited by indomethacin.

The variation of radius with pressure was measured in vitro in the carotid artery of ten rabbits. Experiments were performed without prior conditioning of the vessel, over an inflation-deflation cycle at pressures in the range 0 to 24 kPa during treatment with, and in the absence of noradrenaline (referred to as active and passive conditions). The effect of a step change in pressure (2.7 kPa) on the radius of the vessel was investigated on a further three specimens. Under passive conditions, the variation of the static and the real part of the dynamic incremental elastic modulus with pressure and stress was similar during both inflation and deflation. Under active conditions a large degree of pressure-radius hysteresis was observed. At physiological pressures smooth muscle activity was associated with a decrease in elastic modulus when compared to passive values at the same pressure or stress. At a stress above 2 x 10(5) N.m-2 yield of the constricted vessels was observed and on further inflation and subsequent deflation the pressure radius curve was identical to that obtained under passive conditions. We suggest that conditioning a vessel, by means of repeated inflation to a high pressure and deflation to zero pressure, before measuring its elastic properties may give misleading results when applied to the vessels of living animals.

The reflection of pressure pulses from rubber tube junctions, covering a range of hydrodynamic mismatching, was determined by an impulse technique. A 5 ms pressure impulse generated in the parent vessel was detected, together with any reflected pulse, by means of a catheter-tip pressure manometer. Similar measurements were carried out on the aortic trifurcation of an anaesthetised dog. In both cases the measured reflections agreed well with those calculated from area and elasticity measurements.

In vivo studies of the propagation characteristics of cardiac pressure or flow pulses along arteries are made difficult because of reflections from the peripheral beds. These reflections interfere with the forward going waves with the result that the two waves become partially superimposed. Consequently only apparent attenuation and propagation velocities may be determined directly. In an attempt to overcome this problem we have recently developed an impulse technique to study attenuation and reflection phenomena in the aorta of anaesthetised dogs (1). A pressure pulse of 10ms duration was produced by the impact of a solenoid operated hammer. The propagation of this impulse down the vessel was then recorded by means of a catheter tip pressure manometer. We have now extended this work to the study of the propagation characteristics of the impulse in excised arteries. The purpose of the investigation being an attempt to obtain information from human arterial specimens. The problem of reflection from terminations is more acute in in vitro preparations because of the limited lengths of the specimens. If the length is 10cm and the propagation velocity 5ms−1 then reflections will arrive at the proximal end of the specimen within 40msec.

The propagation of a transient pressure impulse in a viscoelastic medium was investigated by experiments using water-filled latex rubber tubing and the aorta of anaesthetised dogs. A 5 ms pressure impulse was produced by the impact of a solenoid driven hammer. The propagation characteristics of the impulse (attenuation and propagation velocity) along the vessel were determined by means of a catheter-tip pressure manometer placed at various distances distal to the impulse generator. The presence of stenoses of varying degrees of severity resulted in reflection of the impulse and the appearance of reflected pulses whose magnitude depended on the stenotic severity. The experiments suggest that for the technique to be used in the detection of local reflecting sites such as might result from vascular occlusive disease, the lesions should occlude at least 70% of the lumen and should be no more than 0.20 m distal to the impulse generator.

The arterial pressure wave, Pm, is composed of a forward travelling wave, Pf, and a backward travelling wave, Pb, resulting from partial reflection of PI at the peripheral beds. The magnitude of Pb depends on the degree of vasoconstriction. Total occlusion of the vessel distal to the pressure measurement site results in a wave which is equal to 2Pf. Subtraction of the derived Pf wave from Pm gives Pb, provided there is no re-reflection of Pb by proximal discontinuities. To test the validity of this total occlusion method for the determination of the components of Pm, measurements were carried out in an anaesthetised dog and the results compared with the method of Westerhof et al., (1972). The measurements were made at three arterial sites: 1. in the aorta just proximal to the junction of the renal artery; 2. at the termination of the aorta; and 3. in the femoral artery. The magnitude of Pb was varied by the infusion of vasoactive drugs. There was good agreement between the two methods at site 1 but at the other two sites the agreement was less good. It is shown that this is the result of re-reflection of the backward travelling waves produced by the occlusion at the aortic termination and the renal artery junction.

The uptake of 131I-albumin by the wall of the isolated pig thoracic aorta was investigated in vitro to achieve good control of the experimental conditions. The lumena of the arteries were perfused with a balanced salt solution (Hanks') containing the radioactively labelled albumin. Albumin flux was studied at three static intralumenal pressures, viz 6.7, 13.3 and 20 kPa (50, 100 and 150 mmHg) and uptake (normalised per unit dry tissue weight) was found to be approximately doubled on increasing the pressure from 6.7 to 20 kPa (50 to 150 mmHg). With a mean pressure of 6.7 kPa (50 mmHg) the uptake was studied in the presence of sinusoidal pressure oscillations of amplitude in the range 1.3 to 6.0 kPa (10 to 45 mmHg) at frequencies 1, 5 and 11 Hz. At each frequency the uptake was found to be dependent on the pressure amplitude. The dependence at 5 Hz was significantly stronger than at 1 Hz (P < 0.05) and although not significant there was a suggestion that the uptake was higher at 5 than 11 Hz. There was no significance and no suggestion of a difference at 1 and 11 Hz. The possible influence on uptake of the associated oscillatory wall shear component has been considered. The relevance of these findings to macromolecular transport and to the characteristic localisation of atheroma within the arterial tree is discussed.

An analogue of a stenosis in a uniform tube is proposed. The stenosis is modelled with an inertial term and loss term in series. The magnitude of the first term represents the mass of blood in the stenotic section whilst the magnitude of the second term is determined by entrance length effects, contraction and expansion losses. The uniform tube is represented as a series of inductance, capacitance and resistance networks and terminated by a modified Windkessel. This model is programmed on a digital computer. The changes in amplitude of sinusoidal pressure and flow waves proximal and distal to the stenosis are computed, as a function of frequency for a range of stenoses. The predictions of the model are in good agreement with experimental work using a hydraulic test line and with previously reported work on aortic stenosis in the dog.

Phase delays between flow velocity pulses have been measured at the proximal and distal ends of two arterial segments in dogs under two vasoactive conditions (vasoconstriction and vasodilation) using both the continuous wave Doppler-shift velocimeter and the electromagnetic flowmeter. The variation of phase velocity with frequency in the respective segments has been investigated with both techniques and a comparison of the results made. The agreements between the two methods as well as the suitability of the Doppler-shift technique for pulse propagation velocity measurements is discussed.

The propagation velocity (Cm) of the flow and pressure pulse has been measured in the abdominal aorta of anaesthetised dogs under vasoconstricted and vasodilated conditions. Simultaneously, measurements of the pressure strain elastic modulus (Ep) were obtained using a mercury in silastic strain gauge. These values of Ep were used to estimate a calculated propagation velocity (Cc) derived from the Moens Korteweg relationship. After Fourier analysing the pressure, flow and radius data it was found that Cc showed very little frequency dependence and that during vasodilatation Cm ≈ Cc to within a few percent for all harmonics above the first; whilst during vasoconstriction close agreement was observed at harmonics ≥ 6th. The mean values of Cm for these higher harmonics, and Cc for all harmonics, together with the mean propagation velocity (Cff) obtained from foot-to-foot time delays were, during vasodilation :Cm = 5.88 ± 1.2 (SD), Cc = 6.00 ± 1.04 and Cff = 5.79 ± 1.03 and during vasoconstriction Cm = 8.04 ± 1.27, Cc = 8.10 ± 1.04 and Cff = 8.00 ± 1.16. (units ms−1) Measurements in one dog of the impedance (ratio of pressure to flow) demonstrated that the contribution of peripheral reflections was negligible for the 6th and subsequent harmonics during vasoconstriction and above the first harmonic during vasodilatation, suggesting that the lack of agreement at lower frequencies between measured and calculated velocities was due to the presence of reflected waves. We conclude that within the frequency range in which reflected waves are negligible the Moens Korteweg equation in conjunction with measurements of pulse propagation velocity may be used to obtain accurate information on the elastic properties of the aorta.

The influence of abdominal aortic stenosis on the uptake of the protein-binding trypan blue dye and 131I human serum albumin (HSA) has been studied. The major change was a region of high uptake proximal to the stenosis, returning to normal by the level of the renal arteries. There was reduced uptake distal to the stenosis, apart from occasional small areas of high uptake probably due to turbulence. The increase in uptake immediately proximal to the stenosis was dependent on the severity and duration of the stenosis. Removal of the stenosis immediately before the injection of dye and 131I-HSA still resulted in elevated uptake in the proximal region. Some haemodynamic modifications resulting from a stenosis are described. It is suggested that the most satisfactory haemodynamic explanation of the observed uptake change is a proximal increase in oscillatory pressure/strain. The relevance of these findings to atherosclerotic development at and above arterial junctions is discussed.

Reflection from an arterial discontinuity, such as a stenosis, would be expected to produce partial standing waves of pressure and flow proximal to the stenosis. This phenomenon is demonstrated by determining the amplitude changes of the harmonic components of pressure and flow waves recorded at three sites at different distances from an experimental stenosis of the abdominal aorta in dogs. To minimise the effect of reflections from other arterial sites, such as the peripheral beds, the animals were vasodilated. Impedance and propagation velocity measurements were made to estimate the contribution of peripheral reflections in the harmonic components of the aortic pressure and flow pulses. In general, the peripheral contribution appeared to be small for harmonics greater than the first. The results indicate that, for the 'closed' type of reflection at the stenosis, a pressure antinode and a flow node occur immediately proximal to the stenosis. As the distance from the stenosis to the measurement site is increased, nodes and antinodes of pressure and flow occur at frequencies which correspond to integer multiples of lambda/4. Similar fluctuations take place in the impedance modulus proximal to the stenosis, such that close to the stenosis the modulus is a maximum, at the lambda/4 distance the modulus is a minimum and at the lambda/2 distance it is again a maximum. The extent of these impedance changes with distance indicates that the attenuation of the reflected, backwardgoing waves is greater than found for forwardgoing waves and that the diagnostic assessment of a vascular obstruction by means of a proximal measurement of pressure or flow may be subject to error if the measurement is not made close to the obstruction.

The uptake of trypan blue and [131I]human serum albumin (HSA) has been studied in the dog's abdominal aorta between 1 and 42 days after removal of an experimental stenosis (approximately 90%) applied 1 week previously. Previous work has shown that when the stenosis was present during circulation of these markers, their uptake was increased immediately proximal to the stenosis decreasing to normal by the renal artery level. Distal to the stenosis uptake was reduced apart from small areas of high uptake probably due to turbulent jet impacts. Within the stenosed section the uptake was normal. In this present study it was found that, after removal of the stenosis, proximal uptake initially remained elevated, returning to normal after approximately 15 days whilst the distal uptake returned to normal after approximately 10 days. In the previously stenosed section uptake was increased markedly following the release of the stenosis but returned to normal within approximately 20 days. The relationship of these findings to alterations in the local haemodynamic state and to possible changes in endothelial morphology are discussed.

Changes in the electrophoretic mobility of mammalian cells following irradiation with X, δ and β rays are reported. The cells investigated were human and cockerel erythrocytes and Ehrlich Ascites Tumour Cells. The electrophoretic mobility of the cells showed a biphasic response with dose. The general trend of the response was that the cockerel erythrocytes showed an initial increase in mobility, then a return to normal levels. Human erythrocytes and ascites cells exhibited an initial decrease in mobility before returning to the control values. The X and δ dose levels required for these changes were similar and substantially greater than when β radiations were used.