Mechanical evaluation of half-pin (type 1) external skeletal fixation in combination with a single intramedullary pin.

Half-pin (type 1) external skeletal fixators with four, three, and two fixation pins and an intramedullary pin, and four-pin external skeletal fixators without an intramedullary pin were applied to prepared canine femurs. Load to failure, load to yield, safe load, and stiffness under compressive and torsional loads were calculated. When tested in compression, all measurements for the four-pin fixators with an intramedullary pin were significantly higher than for the two-pin fixators with an intramedullary pin. The values for all parameters except load to yield were significantly higher for the four-pin fixators with an intramedullary pin than for the four-pin fixators without an intramedullary pin. When tested in torsion, all measurements for the four-pin fixators with an intramedullary pin were significantly higher than for the two or three-pin fixators with an intramedullary pin.

Effects of corticosteroids on mechanical strength of intervertebral joints and vertebrae in dogs.

Dogs with hyperadrenocorticism had a higher incidence of intervertebral joint disease, i.e., disc protrusion or spondylosis. In comparing cases of hyperadrenocorticism with age- and breed-matched controls with hypothyroidism, the incidence was significantly greater than expected. This was not seen, however, in beagle dogs in which the incidence was already high and attributed to chondrodystrophoid tendencies in this breed. To investigate the pathogenesis of this association and its possible relationship to steroid-induced osteopenia, adult dogs were given a placebo, prednisone, or prednisone plus calcium for six months. Torque testing of intervertebral joints revealed a consistent trend of lower force to failure in both prednisone-treated groups, but the difference was not statistically significant. In these dogs with mild to moderate hyperadrenocorticism, compression tests of intact vertebral bodies were not significantly different, but blocks of trabecular bone cut from the vertebral bodies failed at significantly lower compressive forces in both prednisone-treated groups compared with controls. Histomorphometric evaluation of lumbar vertebral trabecular bone revealed that the percentage of bone volume was not significantly decreased in the prednisone-treated groups. Nor was there any difference in the thickness or porosity of vertebral end-plates, which might contribute to weakening of intervertebral ligamentous insertions.

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 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.

Inverse effect of chronically elevated blood flow on atherogenesis in miniature swine.

The effect of chronically elevated blood flow on the development of atherosclerosis in miniature swine was studied. Fistulas connecting the right external iliac artery and vein were surgically created in four swine, while three were not fistulated. Pulsed Doppler velocity detection cuffs placed around the abdominal aorta and both iliac arteries of all pigs permitted chronic measurements of blood velocity, blood velocity distributions, and blood flow. All swine were fed an atherogenic diet consisting of 20% beef tallow, 3% cholesterol, and 5% cholic acid for 6 months. This diet elevated the serum cholesterol to values exceeding 500 mg/100 ml. Creation of the arteriovenous fistula (AVF) markedly elevated blood velocity and flow in the abdominal aorta and in the shunted iliac artery. In the shunted animals the aortic blood flow was 42.1 +/- 2.0 ml/sec compared with 17.3 +/- 1.4 ml/sec in the unshunted swine. The velocity distribution pattern across the vessel was also indicative of an elevated wall shear stress. After 6 months, the animals were killed and the arterial vessels examined macroscopically and microscopically for the presence of atherosclerotic lesions. In the shunted pigs, 17 +/- 15% of the lumenal surface was occupied by sudanophilic lesions, whereas 80 +/- 8% of the surface was covered by lesions in the unshunted (control) pigs. From these studies, it is apparent that mechanical factors related to blood flow rates can influence the development of atherosclerotic lesions in swine.

Ultrasonic blood flow measurements: transcutaneous compared with implanted cuff.

Experiments were undertaken in our laboratory to establish relationships between flow parameters calculated from implanted ultrasonic cuff signals and those obtained with a transcutaneous probe. Analog signals were received from crystals surgically implanted on the right carotid, right femoral, and abdominal aorta of a mature male beagle dog. Near these locations, transcutaneous measurements were made using a prescribed technique. From these ultrasonic signals, the following time dependent flow parameters were calculated: spatial velocities, velocity profiles, diameters, flows, and velocity frequency distributions. Using these measurements, a comparison between the implanted cuff and transcutaneous probe was made. In addition to high reproductibility, results confirm a strong correlation between the two techniques; consequently, the validity of the less traumatic transcutaneous method is substantiated.

Nontraumatic aortic blood flow sensing by use of an ultrasonic esophageal probe.

The measurement of blood velocity fields, volume flow, and arterial wall motion in the descending thoracic aorta provides essential hemodynamic information for both research and clinical diagnosis. The close proximity of the esophagus to the aorta in the dog makes it possible to obtain such data nonsurgically using an ultrasonic esophageal probe; however, the accuracy of such a probe is limited if the angle between the sound beam and the flow axis, known as the Doppler angle, is not precisely known. By use of a pulsed Doppler velocity meter (PUDVM) and a triangulation procedure, accurate empirical measurement of the Doppler angle has been obtained, allowing quantification of blood velocity scans across the aorta. Volume flow is obtained by integration of blood velocity profiles and arterial wall motion is measured with an ultrasonic echo tracking device. Accuracy of the probe was substantiated by comparison with ultrasonic and electromagnetic implanted flow cuff measurements. Use of the probe in measurement of blood velocity, volume flow and arterial wall motion at various locations along the 8- and 10-cm length of the descending thoracic aorta in adult beagle dogs is detailed. The simplicity, accuracy, and nontraumatic aspect of the technique should allow increasing use of such a probe in numerous research and clinical applications.