Robert L. Piziali

A system for ultrasonically imaging the human heart in three dimensions

Abstract A hardware and software system capable of collecting and storing three-dimensional time-varying ultrasonic data is described. Display capabilities consist of two dimensional cross-sectional views at selected points, orientations, and times. The accuracy of the system was verified by imaging stationary objects of known shape. An in vivo human heart was then isonified. Adjacent cross sections were viewed to find a cross section containing heart structures. This cross section was then viewed throughout the heart cycle. Important structures can be clearly identified and their anatomical relationship observed during all phases of the heart cycle.

The function of the primary ligaments of the knee in varus-valgus and axial rotation

Abstract Four in vitro human knee specimens have been loaded, two with varus-valgus femoral rotations and two with internal and external axial tibial rotations. Each specimen has been tested in full extension and in 30° of flexion. All orthogonal components of applied force and moment required to cause the rotations were measured as were all resultant orthogonal components of load on the femur. Curves fit to the data were studied to establish the portions of the applied load transmitted by each ligament.

The function of the primary ligaments of the knee in anterior-posterior and medial-lateral motions

Abstract The functions of the primary ligaments of the human knee have been investigated during anterior, posterior, medial and lateral tibial displacements. The ligaments of in vitro knee specimens have been loaded to large load levels and all three resultant orthogonal components of force and of moment acting on the femur as a result of the applied tibial displacements have been measured. Least squares cubic spline curves fit to the data have been analyzed to determine what percentage of a given applied load is transmitted by each ligament. These curves can also provide data for a computer model of the human leg.

Distribution of waste anesthetic gases in the operating room air.

Epidemiologic and animal studies identify a relationship between chronic exposure to anesthetic gases and health hazards. Efforts to reduce exposure of personnel require an understanding of the distribution of anesthetic waste gases in the operating room air. Concentrations ol nitrous oxide and halothane were measured at numerous stations throughout an operating room and a delivery room in the absence of personnel. Air conditioning flow rates and flow patterns were varied, as was the height of the anesthetic gas source. Air flow patterns were found to dominate the anesthetic gas distribution, while buoyaney effects were neligible. Venting waste gases at the floor does not significantly reduce exposure of personnel. Areas of high concentration were observed; their occurrences and locations varied strongly with air flow patterns. The exhaust grille is the best location for a single measurement of the average room concentration. Recirculating air-conditioning systems reduce energy costs; however, only the non-recirculating portion of the air exchanges reduces waste gas concentrations.

Natural frequency analysis of a human tibia

Abstract A beam type finite element computer model is used to predict the natural frequency response of a human tibia with varying geometries, mass formulations and boundary conditions. Results are compared to analytic solutions and to published computer and experimental results. Variations between lumped and consistent mass formulations were found to be small, but significant. The effects of tibial twist and curvature were generally of the same order as the mass effects, with notable exceptions depending on boundary conditions. In fact, the major changes in predicted frequencies occurred with changes in boundary conditions. Variable springs at the boundaries were introduced to show a more continuous variation between free and fixed boundary conditions. Accuracy and repeatability of experimental and analytic results are examined in light of possible clinical applications.

An extended structural analysis of long bones—Application to the human tibia

Abstract A computer model is used to investigate the importance of several assumptions associated with whole bone modeling. The importance of shearing deformations relative to bending deformations, and the coupling between transverse loading and torsion are shown to be negligible. A more rigorous solution for torsion in hollow, irregular solids, the three dimensional twisted geometry of the tibia and the values chosen for Youngs modulus and Poissons ratio are all shown to be significant factors. The material properties are assumed to be linear, elastic and isotropic. The analysis is concerned primarily with modeling the response of the whole bone to loads transmitted through the epiphyses, and with detailed stress distributions in the diaphysis. An outline of the computer model and the experimental data are presented.

Measurement of the nonlinear, coupled stiffness characteristics of the human knee.

Abstract The structural characteristics of the human knee have been determined using the stiffness influence coefficient method. The nonlinear load-displacement data is approximated by a least squares polynomial and differentiated to determine the stiffness coefficient as a function of displacement. Cross axes coupling produces a full matrix and individual stiffness curves are seen to be a function of the initial displacement state of the joint. The resulting data provides a complex, but accurate description of joint stiffness in a format consistent with matrix structural analysis. The methods are described in detail; the data is taken from a single fresh human knee.

GEOMETRIC PROPERTIES OF HUMAN LEG BONES

Abstract In analytical models of human lower extremities, the geometric properties of the bones are needed along with the material properties of compact and cancellous bone. This paper presents the geometric data for the right and left femurs, tibias and fibulas from a single donor, along with the results of two additional tibias. Data includes the areas, polar moments of inertia, torsional rigidities, angles from anatomical axes to principal axes, and the position of the centers of mass along the lengths of the bones. The results from a single speciment provide data for entire limb models.

Effect of boundary conditions on the ultrasonic‐beam characteristics of circular disks

The ultrasonic‐beam characteristics of piston (case 1) are first reviewed and then two radially symmetric velocity distributions—a simply supported disk Ussd [1 − (r/R)2] (case 2), and a clamped disk Ucd[1 − (r/R)2]2 (case 3)—are used to calculate the axial intensity and directivity of the resulting ultrasonic beam. The oscillations in axial intensity for both cases 2 and 3 are less than that for case 1. The axial intensities are compared both for equal maximum velocities and equal source strengths. According to the Fraunhofer equation, the diverging portion of the beam from a piston begins at approximately 1.6 R2/λ; not at the position of the last axial maximum, approximately R2/λ. The position of the last axial maximum lessens from R2/λ for case 1, to 3/4 R2/λ for case 2, and 9/16 R2/λ for case 3, Directivity calculations show that the conical half‐angle for case 2 is 20% greater than for case 1, and for case 3, it is 60% greater than case 1. The first side lobes for cases 2 and 3 are 7 and 13 dB down, ...

Monitoring occupational exposure to inhalation anesthetics.

Air monitoring, an essential feature of the waste gas control program, is best based on measurement of total leakage in time-weighted sampling of N2O present in the anesthetists breathing zone during clinical anesthesia. Leakage in the high-pressure N2O system is measured separately in a survey of the empty rooms. The infrared N2O analyzer used for these measurements is also useful as a teaching device and in enhancing the safety of the patient.