Jerry C. Collins

Comparison of two laser doppler flowmetry systems for bone blood flow analysis

SummaryThe development of laser Doppler flowmetry (LDF) has provided a real-time, reliable method for monitoring capillary perfusion in multiple tissues. LDF has potential for the experimental and clinical assessment of bone blood flow. To compare the accuracy and ease of use of two commercially available laser Doppler flowmeters with different mechanisms for processing the Doppler-shifted component of light, estimates of bone blood flow were obtained in a sheep model using the two systems, and the values derived then compared with estimates of bone blood flow also obtained in a sheep using the technique of injection of labeled microspheres. The single-channel laser Doppler flowmeter, the LD 5000, processes the reference and Doppler-shifted beams on the surface of a single photodetector using optical heterodyning for measurement. The dual-channel flowmeter, the Periflux 2, uses two optical fibers to transmit reference and Doppler-shifted light to two separate photodetectors. The differential amplification and detection system improves the signal-to-noise ratio. Measurement of both metaphyseal (cancellous) and diaphyseal (cortical) blood flow using both LDF systems was compared with values obtained with an injection of85Sr-labeled microspheres in three sheep. The LDF measurements were repeated after occlusion of the left femoral artery, and a46Sc microsphere injection was performed prior to animal sacrifice. Two of the animals developed vasomotor instability, resulting in poor correlation between the measurements obtained with the Periflux 2, which is motion sensitive, and the values obtained with the microsphere method. High correlation was apparent in two of the three animals for the LD 5000 and the microsphere values. Four additional sheep were evaluated using only the Periflux 2, and the data collected yielded R values of 0.6–0.98. Both the single- and dual-channel LDF systems offer accurate assessment of local cortical and cancellous bone blood flow.

Direct, real time measurement of meniscal blood flow: An experimental investigation in sheep

The functional microcirculatory system of the meniscus was investigated in nine sheep using laser Doppler flowmetry (LDF). The highest blood flows recorded were found at the periphery and at the anterior and posterior horns, and this finding was confirmed by india ink injections in five sheep and by meniscal autoradi ographs following intraatrial injection of 20 million Cs46 microspheres in four sheep. LDF provides accurate and reproducible assessment of meniscal blood flow. If adequate probes can be developed, this method offers great promise in the clinical assessment of blood flow within the substance of meniscal tears, thus offering the surgeon initial information in the decision to repair or resect a meniscal tear.

MR imaging parameters in the study of lung water. A preliminary study.

The use of magnetic resonance (MR) to evaluate lung water is made difficult by several factors: paucity of proton signal from normal lung, respiratory and cardiac motion, and long relaxation times of lung fluids. To optimize scanning parameters for this use, and to test MRs ability to detect and quantitate regional and temporal variations in signal intensity in hydrostatic pulmonary edema, in vivo experiments were performed with a 0.5 tesla whole body MR imaging device. Human volunteers were studied in prone and supine positions using spin echo technique (TE = 30 msec) with varying TR, and with respiratory and cardiac gating. In addition, sedated, intubated, chronically prepared sheep were paralyzed to control extraneous motion and allow the use of a high frequency ventilator, thereby eliminating respiratory gating. Elevated pulmonary hydrostatic pressure was induced in these sheep by inflation of a left atrial balloon. Relative signal intensity from the lung rises with lengthening TR. Cardiac gating diminishes motion artifact, but masks extravascular water by enhancing signal from slowly flowing blood by an average of 44%. A gravity-dependent gradient of signal intensity predictably shifts in supine and prone positions. The use of longer TRs, respiratory gating, and cardiac gating all proportionally prolong data acquisition times to an objectionable degree. Without the use of gating, a gradual rise in relative signal intensity is seen in the sheep lung following the establishment of elevated hydrostatic pressure in the pulmonary circuit, and is most pronounced in the dependent portion of the lung.(ABSTRACT TRUNCATED AT 250 WORDS)

Indistinguishability and identifiability analysis of linear compartmental models

Two compartmental model structures are said to be indistinguishable if they have the same input-output properties. In cases in which available a priori information is not sufficient to specify a unique compartmental model structure, indistinguishable model structures may have to be generated and their attributes examined for relevance. An algorithm is developed that, for a given compartmental model, investigates the complete set of models with the same number of compartments and the same input-output structure as the original model, applies geometrical rules necessary for indistinguishable models, and test models meeting the geometrical criteria for equality of transfer functions. Identifiability is also checked in the algorithm. The software consists of three programs. Program 1 determines the number of locally identifiable parameters. Program 2 applies several geometrical rules that eliminate many (generally most) of the candidate models. Program 3 checks the equality between system transfer functions of the original model and models being tested. Ranks of Jacobian matrices and submatrices and other criteria are used to check patterns of moment invariants and local identifiability. Structural controllability and structural observability are checked throughout the programs. The approach was successfully used to corroborate results from examples investigated by others.

Prostacyclin reduction of regional ischemic injury in the canine myocardium

The effect of prostacyclin (PGI2) on the myocardium of the awake dog subjected to coronary artery occlusion was examined. Animals were randomly administered PGI2 200 ng/kg/min (n = 6), PGI2 100 ng/kg/min (n = 6), or the vehicle control (n = 6), beginning 30 min prior to coronary artery occlusion. Radiolabeled microspheres (15 microns) were used to measure myocardial blood flow. The myocardial region at risk was determined by fluorescein injection, and infarct size was assessed by triphenyl tetrazolium staining. Segmental myocardial function was evaluated from the systolic ejection shortening (SES) by subendocardial ultrasonic dimension crystals in normal, ischemic, and border zones. PGI2 200 ng/kg/min produced significant decreases in aortic pressure and systemic vascular resistance. PGI2 100 ng/kg/min, which achieves 95% platelet inhibition, had no significant hemodynamic effects. Animals receiving PGI2 200 ng/kg/min had significantly higher blood flow to the ischemic region, better border zones SES, and a smaller infarct. PGI2 ameliorates myocardial injury and reduces functional impairment produced by ischemia in doses that elicit vasodilation. This beneficial effect of PGI2 does not appear to be mediated solely by an antiplatelet mechanism.

The VaNTH ERC: A Vehicle for Continuing Education in Bioengineering

The Vanderbilt–Northwestern–Texas–Harvard/MIT Engineering Research Center in Bioengineering Educational Technologies is the only such National Science Foundation sponsored Center specifically focused on educational technologies. The Center teams bioengineering, learning science and learning technology specialists in universities and industry to determine what bioengineers should learn, how it should be conveyed, and how learning should be assessed. Potential industrial and practice partners include companies and national laboratories that practise bioengineering, those that provide enabling technologies for construction of learning modules and assembly into courseware, and major publishers and others who will assist in courseware dissemination. Modular design should make Center courseware useful in continuing as well as curricular education. Continuing education marketing strategies include recruiting companies to provide employee, client, customer, and patient groups as test-beds and customers for courseware, and advertising for continuing education through professional societies and advocacy groups.

Effects Of Meals On Heart Rate Spectra

Sympathetic activity (SA) and parasympathetic activity (PA) before and after meals has been assessed using power spectral analysis of heart rate (HR) variability. Spectral analysis was performed using Welch’s method of averaging modified periodograms with Bartlett windowing. The power spectrum was divided into three bands--low frequency, 0.02 to 0.08 Hz; mid-frequency, 0.08 to 0.15 Hz; and high frequency, 0.15 to 0.40 Hz. The spectral area in each band was calculated pre-meal and post-meal. The results showed an elevation after meals in the Lf/(Lf+Mf+Hf) parameter as well as a decrease in the Hf/(Lf+Mf+Hf) parameter. Also, the ratio of Lf area to Hf area showed an increase after meals. These findings may be interpreted as a postprandial increase in SA and decrease in PA. This acknowledges the basis of increased HR following meals. In addition, a linear correlation was found betweenA HR andALf/Hf ratio. Spectral analysis of HR variability is a promising tool and may be utilized in the assessment of SA and PA.

Effects of blood flow reduction and lymphatic ligation on coronary transport in dogs

We studied the effects of reduced-flow coronary ischemia and coronary lymphatic ligation on transcapillary movement of albumin. We infused 125I-albumin intravenously into four groups of five anesthetized, open-chest dogs in which external carotid-to-coronary arterial cannulas had been placed. One group was subjected to both lymphatic ligation and ischemia; a second group to lymphatic ligation only; a third group ischemia only; and the fourth was a control group. After 1 hr, 85Sr-microspheres were injected into the cannula. After 2 hr, the animals were sacrificed. Extravascular albumin activities in heart sections that were perfused from the cannula were normalized to extravascular albumin in normal-flow regions. This variable was greater in the lymph-ligated and ischemic groups than in the control, and greater in the combined lymph-ligated and ischemic group than any other group. Relative increase in coronary vascular resistance over the protocol interval correlated significantly with normalized albumin content in the cannulated sections. Although both ischemia and lymph ligation lead to increased extravascular albumin accumulation, their mechanisms are different. Increased extravascular albumin after ischemia may be due to increased capillary permeability.

Patient monitoring systems: criteria for evaluation & selection.

Patient monitoring is more than just the acquisition and accumulation of physiological data. In order for it to be efficacious in patient diagnosis and treatment, the professional staff must be continuously involved in protocol development, evaluation, and modification. Given the constraints of these tasks, of cost limitations, and of staff interest and expertise, the clinical engineer should develop a rationale for making judgments about patient monitoring systems at his particular site. This rationale should include: evaluation of design criteria from medical, nursing, and engineering standpoints; consideration of the considerable and increasing effect of computers on monitoring; and the intelligent appraisal of technique and system development performed at other sites.

Perspectives on Ethical Development: Reflections from Life and Profession

I was born and grew up in Nashville, Tennessee, in the 1940s. Nashville was a politically conservative, historically racially segregated city. My family was in a Christian conservative religious movement. They were loving but strong-willed; some might say controlling. I was an early reader and precocious. At the age of five, when I spoke to my grandmother (with whom our family shared a house) about my ability to read and do math, she said “Do not brag!” I stopped what I was saying. I was a pleaser, but parts of me were rebellious and combative. When I was six, I took a small comic book stuck to a cereal box in our neighborhood grocery from the box, hid it in my pocket, and took it home. My father found it, asked where I got it, and made me take it back to the grocer and apologize. These and similar instances awakened or helped develop in me a sense of right and wrong. I am still coming to terms with how my early history affected my ethical sensitivities. In those early years, racial awareness formed a large part of my ethical awakening. I was aware that my household included Mertella, an AfricanAmerican woman who worked as a maid during the day and helped to care for my great-grandmother. I was also aware that our church included quarters for a 38 Perspectives on Ethical Development: Reflections from Life and Profession