Lee E. Ostrander

The relationship of surface reflectance measurements to optical properties of layered biological media

Reflectance from a turbid biological tissue is discussed for a diffusive light source illuminating the surface of the medium, and is related to the optical property distribution within the medium and to photon propagation through the medium. A three-dimensional photon diffusion model with closed form is developed to describe the photon diffuse intensity in a homogeneous medium. The solution is extended by numerical methods to the medium with layered structure. The concepts of photon flux paths and of reflectance indexes are utilized, together with reflectance data, to extract information about the internal optical properties of a medium. The flux path concept was corroborated by successfully detecting in vivo and ex vivo layered differences in optical properties within the biological medium. These studies suggest that the optical properties of subdermal tissue can be measured from light reflectance and that the effect of the upper skin layers can be eliminated.<<ETX>>

Effect of lumbar sympathectomy on muscle blood flow: Distribution of perfusion measured by hydrogen clearance in skeletal muscle

Measurements of local tissue blood flow using a technique of hydrogen clearance were used to examine the effect of lumbar sympathectomy on skeletal muscle blood flow. Polarographic recordings on 25 hydrogen desaturations were obtained with platinized platinum electrodes. Lumbar sympathectomies were done on five canines leaving the contralateral limb as a control. The hydrogen clearance data were modeled with biexponential curves: the initial rapid component and the second slow component yielded a weighted average perfusion through tissue. Average volumetric blood flow in the control limb was 6.08 +/- 0.45 ml/min/100 g tissue while the sympathectomized limb averaged 9.54 +/- 0.61 ml/min/100 g tissue (p less than 0.005). Average blood flow increases ranged from 33 to 83 percent in the sympathectomized limb over the control limb. This significant increase in muscle blood flow following lumbar sympathectomy, if of prolonged duration, may be cause for re-evaluation of the role of sympathectomy in the management of arteriosclerotic occlusive disease.

The Spinal Cord-Injured Patient: Comprehensive Management

Covers the broad issues involved in the care of spinal cord injured patients. Scope includes diagnostic and evaluation methods, spinal cord injury, pathophysiology, medical/surgical management of complications of treatment, and issues of specialized care.

Presentation of the clinical engineering role to hospital administrators.

This paper constitutes a presentation to health care managers on the clinical engineering role in the hospital. Guidelines are covered that were issued in 1976, by the Joint Commission for the Accreditation of Hospitals: the engineering problems, goals, and solutions addressed in the clinical engineering function; the education of the clinical engineer; and the alternative methods of delivering engineering support services to the hospital. The material included in this paper can form the basis for presentations intended to increase awareness of the role of clinical engineering, improve compliance with JCAH requirements, and to stimulate action to make effective use of engineering.

On-Line Blood and Respiratory Gas Analysis

Data from a patient receiving ventilatory assistance are processed by computer to calculate pulmonary shunt, dead space/tidal volume ratio, oxygen uptake and delivery, and carbon dioxide elimination and delivery. The computations are based on routines described by Kelman and by Severinghaus, but modified to match limitations of testing imposed by the requirements for ventilatory assistance. Analyses are performed sequentially on arterial and venous blood samples and on respiratory gas samples. The output of the blood gas analyzers is fed on-line to a computer together with other data, such as patient identification, which are manually entered at a keyboard and with thumb-wheel switches. The computer processing begins with determining the concentration of oxygen and carbon dioxide in whole blood and of bicarbonate in plasma. The shunt equation is used to calculate a virtual shunt at therapeutic concentrations of inspired oxygen. Dead space/tidal volume ratios are corrected for mechanical dead space in the respiratory circuit. The analyzed results are returned to the operator within seconds via a video display. Since the data include blood samples from multiple patient sites, a cross-comparison is made by the computer and the operator is informed of unusually large differences in values.

A compartment model for fluorometric indication of tissue perfusion

A theoretical analysis incorporating a multicompartmental model for dye distribution is applied to describe the relationship among perfusion, dye kinetics, and fluorescence readings. Errors in calculating perfusion from fluorescence are related to dye concentrations and to measurement errors. These error sources are minimized by selecting the measurement time. The alternatives of measurement during wash-in or wash-out of dye are compared, as well as the alternatives of introducing dye by bolus injection or by constant infusion. Compensation of wash-in measurements for differences in skin pigmentation is accomplished by the matching of skin optical properties between incident and fluorescing wavelengths. A laboratory study at 80 measurement sites (from ten graded-perfusion canine flaps) demonstrated a correlation of wash-in and wash-out perfusion data ranging from 0.88 to 0.96 at typical levels of fluorescein in blood. Since wash-in can be completed in a matter of a few minutes, this is likely to be preferable in the clinical setting to wash-out, which can take much longer to complete.<<ETX>>

Inductive 27.12 MHz diathermy in arterial peripheral vascular disease

Ten patients with moderate to severe arterial peripheral vascular disease (PVD) were monitored during treatment with inductive pulsed electromagnetic diathermy therapy. The therapy consisted of 20 daily treatments lasting one-half hour each per day and spread over one month. The application of the electromagnetic energy to the mid-anterior thigh and plantar surface of the foot of the treated leg was accomplished by the use of two inductive application heads and resulted in tissue heating. Patient measurements included surface temperature, transcutaneous partial pressure of oxygen (tcpO/sub 2/), segmental Doppler blood pressure, and superficial blood flow measured with a laser Doppler flowmeter, in addition to the patients subjective assessments of their overall condition. Temperature measurements indicated a repeatable heating pattern for each patient. The maximum temperature was not reached within 20 minutes of heating at the maximum output, while at 10% of maximum output for 10 minutes after maximum output a temperature plateau was reached. TcpO/sub 2/ indicates that the non-treated limb was also affected by the treatment. Sixty percent (60%) of the subjects indicated their belief that the therapy had some discernible therapeutic effect on their condition. The remaining 40% of the subjects experienced no perceptible change during or after the treatment. Based upon the small sample of patients the studies suggest that there is a maximum heating rate applicable to long duration heating using this modality of diathermy. The principle effect on PVD for the subjects studied appears to have been the stimulation of vasodilation.<<ETX>>

Testing viscoelastic properties of biological soft tissue

The goal in this study is to assess instrumentation and methods for measuring the pressure and deformation of soft body tissues. The design of an instrument and the form of the resulting data are discussed in this paper. Applications include the evaluation of edema, the compartment syndrome, monitoring of peripheral vascular disease and the evaluation of pressures associated with use of a prosthesis with the residual limb following amputation.

Clinical engineering as an academic discipline.

This paper includes sections written by the current or former Clinical Engineering coordinators of five universities on common problems faced by Clinical Engineering (CE) educational programs and the different solutions adopted on various campuses. The problems discussed include student recruitment, financial support, containment of student credit hours and faculty time, retention of CE graduates in the profession, and differentiation between Clinical Engineering and Biomedical Engineering Technology.

A Computer Algorithm to Calculate P50 from a Single Blood Sample

We have developed an iterative computer-based algorithm which determines Pso while avoiding direct inversion of the relationship between blood oxygen partial pressure and oxyhemoglobin saturation. Blood sample measurements and the value of P50 are used, together with carboxyhemoglobin data, as necessary, to calculate blood oxyhemoglobin saturation and oxygen content.