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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.

Pressure pulses were recorded simultaneously at the aortic/external iliac junction and in the abdominal aorta of six normal dogs at a distance 7—10 cm upstream of the junction. The matched abdominal aortic equitrifurcation was then transformed, in vivo, to an unmatched equibifurcation by temporary occlusion of the central branch and the pressure recording procedure repeated. An increase in the oscillatory pressure amplitudes at the junction was observed as a result of the unmatching procedure. At the upstream site the amplitude increase was similar to the junction site for only the first two harmonics of the pressure pulse. These changes were interpreted as being due to increased reflection from the unmatched junction and alteration in the peripherally reflected pressure waves reaching the aorta.

— A review is presented of thirty cases, in the dog, where repair of rupture of the anterior cruciate ligament was undertaken using skin as a ligament substitution material. The results of this series are examined and the authors recommend the employment of whole thickness skin grafts for cruciate ligament replacement. Resume— Une etude est presentee de trente cas de reparation de la rupture du ligament croise anterieur chez le chien, utilisant la peau come materiel de substitution de tissu ligamentaire. Les resultats obtenus dans ce groupe sont etudies et les auteurs recommandent l'emploi de greffes de peau entiere pour le remplacement de ligaments croises. Zusammenfassung— Es werden dreissig Falle beschrieben, in denen bei Hunden ein Riss des vorderen Kreuzbandes unter Verwendung von Haut als Ligamenturnersatz ausgebessert wurde. Die Ergebnisse dieser Serie wurden untersucht, und die Autoren empfehlen, Hauttransplantate ganzer Dicke zur Ausbesserung des gerissenen Kreuzbandes zu verwenden.

The fluid impedance of the abdominal aorta was measured in anaesthetized dogs before and during the occlusion of the central branch of the aortic/external iliac junction. Aortic impedance increased during the occlusion due to a change in the terminal impedance of the peripheral beds and an increase in reflection from the aortic junction. The higher harmonics of impedance were relatively unaffected by changes in the terminal impedance and hence the increase found for these harmonics may be attributed to reflection from the junction alone. The reflection coefficient calculated from the impedance values of the higher harmonics (> 3rd) agreed well with the theoretical value from the Womersley model of a junction set in an infinite line.

The dynamic and static elastic response of the abdominal aorta was studied in beagle dogs of similar age and weight. The dynamic response was measured in situ by means of an optical transmission wedge resting on the exposed vessel to record the pulsatile changes in wall displacement and the pressure pulse recorded at the same site via a hypodermic needle. The static response was recorded (1) in situ by observing the change in radius which occurred with a change in the mean blood pressure, (2) post mortem using both transmission wedge and radiographic techniques. The change in radius (deltaR) for a change in pressure (deltaP=20 mm Hg[2.67kPa]) was calculated for both the dynamic and static cases. It was found that the aorta was stiffer for the dynamic case, the extent of the stiffening being dependent on the mean pressure. At pressures less than 80 mm Hg (10.64 kPa) the dynamic/static deltaR ratio was 1.8 decreasing to 1.1 at 160 mm Hg (21.28 kPa). This behaviour is interpreted in terms of smooth muscle relaxation and the subsequent transference of circumferential tension to collagen.

The arterial pressure wave, Pm, is composed of a forward travelling wave, Pt, and a backward travelling wave, Pb, resulting from partial reflection of Pt 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 vascoactive 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 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.