Bone-methyl methacrylate interfacial shear strength: an experimental study of dogs.

Bone-methyl methacrylate interfacial shear strength at failure in chronically implanted hip prostheses was studied. Gorman total hip prostheses fixed with methyl methacrylate bone cement were implanted in 6 large dogs. Interface shear strength studies were performed at 8, 16, and 24 weeks. Mechanical testing determined that the mean interfacial shear strength was 15.2 +/- 13.0 kg/cm2. Variability of the data was too great to allow conclusions to be drawn from statistical analysis, but trends in the data were observed. It was concluded that the interfacial bond had sufficient strength to withstand axial loads 3 to 6 times greater than those applied under normal physiologic conditions.

Ultrasonic pulsed Doppler transoesophageal measurement of aortic haemodynamics in humans.

Centreline blood velocity and exterior wall motion were measured in the descending aorta of humans using an oesophageal probe, a pulsed ultrasound Doppler velocity meter and an ultrasonic echo tracking system. The development of a method for easily measuring haemodynamics in the thoracic region using an oesophageal probe will provide an essentially non-invasive method for the assessment of cardiac function and the nature of blood vessels in that region. Detailed anatomical studies of the thorax were conducted by cross-sectioning of the thorax of a cadaver. Blood velocity waveforms were recorded from the descending aorta both during rest and exercise. In one volunteer, the peak centreline velocity increased from a resting value of approximately 30 cm s-1 to an exercise value of approximately 50 cm s-1. Vessel diameter waveforms similar to those for pressure were also recorded showing diameter changes of 1.8 mm. The accuracy and resolution of the technique would be improved by multicrystal probes and multigate ultrasonic flowmeters allowing for accurate calculation of the Doppler angle, imaging of vascular flow regions, and measurement of pulse wave velocity.

Ultrasonic detection of cardiovascular flow disturbances.

Blood flow that is disturbed or turbulent may have a significant effect on the development of cardiovascular disease. A method is presented here for detecting periods of disturbed flow using autocorrelograms of the audio signal from a pulsed ultrasound Doppler velocity meter (PUDVM). Autocorrelograms describe quantitatively how the form of a signal changes over time. We produced steady laminar and turbulent pipe flow in a hydraulic test tank, and computed autocorrelograms of the audio signal of the centerline velocity as detected by the PUDVM using fast Fourier transform techniques. We have shown that the autocorrelation coefficient averaged over a short length of time (64 ms) is significantly higher for laminar than for turbulent flow. We have also produced pulsatile flow in our hydraulic tank and computed the mean autocorrelation coefficient at different phases of the flow cycle. The regions of disturbed and undisturbed flow were predicted from the steady flow results. The disturbed flow first appears during the period of the highest forward velocities. These results indicate that the mean autocorrelation coefficient can serve as an indicator of the presence of flow disturbances.

Ultrasonic transesophageal measurement of hemodynamic parameters in humans.

A noninvasive method has been developed to monitor centerline blood velocity waveforms and vessel diameter in the descending aorta and pulmonary artery of conscious humans. An esophageal endoscope fitted with miniature ultrasound transducers is swallowed and positioned in the esophagus near vessels of interest. The transducers are connected to ultrasound Doppler velocimeters and echotrack instrumentation to obtain the pertinent hemodynamic parameters. This paper describes the design and fabrication of the esophageal ultrasound transducers and the techniques involved in human applications. In addition, blood velocity and wall motion measurements obtained in conscious men at rest and during exercise are described.

Blood velocity patterns in coronary arteries.

A pulsed ultrasound Doppler velocity meter has been used to map the time varying velocity waveforms in the exposed left coronary arteries of anesthetized ponies. Velocity measurements were made without invading the vessels or disturbing the hemodynamic patterns. Typical recordings of velocity waveforms and calculated velocity profiles in the main, descending and circumflex branches are presented. Marked velocity fluctuations in the frequency range of 5 to 10 Hz were measured in the major coronary branches and may influence the stability of the flow and the development of separated flows. Peak Reynolds numbers normally ranged from 300 to 600 and the Womersley unsteadiness parameter based on the heart frequency was usually less than 4.0. Maximum shear rates at the wall were estimated from the calculated velocity profiles and ranged from 400 to 600 sec-1.

The mechanical properties of immature osteopetrotic bone.

The elastic properties of the longer bones of the fore and hind limbs of an osteopetrotic Angus calf were measured using an ultrasonic technique. The same bones of a second Angus calf with unaffected bone tissue were also studied. The osteopetrotic bones were found to exhibit statistically significant lower values of density and mineral content than did the unaffected bones (P = .0054 and P = .0492, respectively). This result is contrary to what has been reported in the literature. The variations of the elastic properties and the density around the circumference of both the immature osteopetrotic femur and the unaffected femur were found to be similar to those previously measured on normal adult bovine femora.