Doppler methods for quantitative measurement and localization of peripheral arterial occlusive disease by analysis of the blood flow velocity waveform.
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Arteries↗
Biomedical subjects
R S Cobbold
Publications and source records attributed to R S Cobbold.
An automatic, multi-function pressure cuff control unit.
A fully automatic blood pressure cuff control system is described. The system is designed for use in the assessment of peripheral vascular disease and helps reduce the amount of operator attention required to carry out such measurements properly. It also provides repeatable control of specific functions, thereby eliminating a potential source of variability. The system incorporates a pneumatic control system, an integrated silicon pressure transducer, and a digital readout. The design, modes of operation, safety features, and use of the system are described.
Blood Pressure Determination↗
Errors and artifacts of Doppler flowmeters and their solution.
Continuous-wave Doppler ultrasound flowmeters are essential instruments for the vascular surgeon. Unfortunately, when used for quantitative purposes, they yield a flow velocity waveform that is substantially in error. Current directional continuous-wave Doppler velocimeters used a O-crossing detector to convert the Doppler signal to a waveform. Unfortunately, there are several inherent problems with this technique, and velocity waveforms are produced that have significant artifacts or errors. In this report, it is shown that a multifilter system is a simple, inexpensive alternative to systems using a O-crossing detector, and furthermore, permits real-time display of the Doppler waveform. The severity of the underlying arterial disease can be quantified by the calculation of pulsatility index. The pulsatility index was calculated from the Doppler waveforms recorded from peripheral arteries in 155 limbs and showed an excellent correlation with the severity of atherosclerosis as assessed by arteriography.
Animals↗
Systolic pressure slope: system for automated display and calculation.
The rate of rise of arterial blood pressure--the systolic pressure slope--has been measured noninvasively at the ankle and has been shown to be reduced by minor degrees of peripheral arterial stenosis. This report describes an electronic system used to display the systolic part of the arterial pressure wave. The system uses noninvasive data from an ECG, a blood pressure cuff, and a Doppler ultrasound detector. From these data the systolic pressure slope is measured automatically. One hundred and sixty-eight recordings from the limbs of 10 normal subjects were analyzed in detail and confirmed the reproducibility of the system. The points used to calculate the systolic slope fell close to a straight line, with correlation coefficients averaging 0.96. An average of eight repeat measurements were made per limb, and the coefficients of variation averaged 6.5%. Mean values for the normalized systolic pressure slope agreed with previously published data.
Adult↗
Inaccuracies of a zero-crossing detector for recording Doppler signals.
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Arterial Occlusive Diseases↗
Negative feedback applied to pressure transducers.
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Catheterization↗
Characteristics of a multicathode polarographic oxygen electode.
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Electrodes↗
Critical evaluation of continuous-wave Doppler probes for carotid studies.
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Carotid Arteries↗
Computer diagnosis of skin disease: system design and preliminary results.
A system for computer-assisted diagnosis of dermatological disease is described. This is an 'expert system' whose knowledge base has been prepared with the aid of a dermatological specialist. The user enters the key elements of the patient's disease history and physical examination into the computer. The computer then returns a summary of the patient's medical record, and a differential diagnosis. The rules of operation by which a given diagnosis was included or rejected is accessible to the user. The system is currently being evaluated in a large dermatology clinic. Preliminary evaluation of the accuracy of diagnosis by the computer indicates that while it nearly always includes the correct diagnosis in its differential diagnosis (94% of cases), it frequently also includes diseases thought to be inappropriate (34% of diseases listed).
Diagnosis, Computer-Assisted↗
Relationship between Doppler pulsatility index and direct femoral pressure measurements in the diagnosis of aortoiliac occlusive disease.
One hundred and seventy-five aortofemoral segments were studied in order to determine the role of CW Doppler ultrasound combined with real-time spectral analysis in the assessment of aortoiliac disease. The pulsatility index (PI), determined from the maximum velocity waveform, was compared to the systolic pressure difference between the aorta and common-femoral artery as measured at the time of angiography. Receiver operating characteristic curves were constructed and the optimum sensitivities and specificities measured. Results show that if a PI(max) of 5.5 is taken as the threshold level, then the PI is 95% sensitive and specific in detecting hemodynamically significant aortoiliac disease that corresponds to a resting aortofemoral pressure difference of 10 mm Hg or greater. We also carefully examine those technical aspects of Doppler recording and analysis that influence the accuracy of PI measurements.
Aortic Valve Stenosis↗
An in vitro model and its application for the study of carotid Doppler spectral broadening.
A new in vitro model has been developed for studying the changes in the ultrasound Doppler spectrum that occur in the region of a stenosis. Pulsatile flow in rigid acrylic tubes was produced by means of a modified hemodialysis pump. The Doppler spectral waveforms were measured using a continuous wave Doppler system, a probe of a known field pattern, a real-time high resolution frequency analyzer, and a video display and recording system. The flow velocity waveforms were found to be nearly identical to those seen in the human carotid. Measurements were made to determine the critical stenosis and the results are similar to those reported from in vivo studies. In a preliminary study, the extent of spectral broadening was found to be dependent on the recording site in relation to the stenosis, the severity of the stenosis, and the flow rate. Using qualitative methods it was not possible to determine either the influence of the shape of the stenosis or the phase of the cardiac cycle on spectral broadening.
Carotid Arteries↗
Comparative study of four methods for quantifying Doppler ultrasound waveforms from the femoral artery.
Currently, there is no agreement as to the best method for quantifying Doppler ultrasound recordings from peripheral arteries in order to detect occlusive disease. The four methods assessed in this study are: the pulsatility index, height-width index, path length index, and a Laplace transform function index. Recordings of the Doppler ultrasound spectral waveforms from the common femoral artery of 232 limbs were digitized to obtain the maximum velocity waveforms. This data was analyzed and the various indices were computed and then compared with the arteriographic grades. The effect of distal disease was also examined. The diagnostic accuracy of each index was determined from receiver operating characteristics curves. We concluded that all four indices were capable of detecting significant aortoiliac disease with approximately equal diagnostic accuracy of 90-95% but that pulsatility index had the advantages of simplicity and ease of calculation.
Angiography↗
Quantitative estimation of spectral broadening for the diagnosis of carotid arterial disease: method and in vitro results.
For the quantitative assessment of carotid arterial disease using continuous wave Doppler ultrasound, the choice of an index to describe the degree of spectral broadening is important. It is shown that a spectral broadening index (SBI) given by 100(1 - fmean/fmax) and evaluated over a 25 msec period around peak systole is relatively insensitive to artifacts and has potential for achieving good clinical sensitivity. Furthermore, it can be implemented very simply on a microcomputer for on-line display. A description of a microcomputer based system, together with the results obtained using an in vitro flow model that closely approximates the carotid flow velocity waveform, are presented. Results relating the SBI to the degree of stenosis, recording site, and angle of insonation, are given. In addition, the results obtained with a commercial system that computes SBI based on the power spectrum, are presented for comparison.
Carotid Artery Diseases↗
Simulation of red blood cell aggregation in shear flow.
A simulation model has been developed for red blood cell (RBC) aggregation in shear flow. It is based on a description of the collision rates of RBC, the probability of particles sticking together, and the breakage of aggregates by shear forces. The influence of shear rate, hematocrit, aggregate fractal dimension, and binding strength on aggregation kinetics were investigated and compared to other theoretical and experimental results. The model was used to simulate blood flow in a long large diameter tube under steady flow conditions at low Reynolds numbers. The time and spatial distribution of the state of aggregation are shown to be in qualitative agreement with previous B-mode ultrasound studies in which a central region of low echogenicity was noted. It is suggested that the model can provide a basis for interpreting prior measurements of ultrasound echogenicity and may help relate them to the local state of aggregation.
Cell Adhesion↗
Aggregation effects in whole blood: influence of time and shear rate measured using ultrasound.
Ultrasound B-mode imaging (7 MHz) was used to measure blood echogenicity and velocity profiles simultaneously as they developed with axial distance for a steady flow of 28% hematocrit whole blood flowing in a long (> 60 D) large diameter (D = 2.54 cm) tube. At selected sites along the flow axis, velocity profiles were measured using block matching (cross correlation) between successive digitized images with a known time separation; from these shear rate profiles were calculated. The corresponding echogenicity profiles were also determined by averaging the digitized images. It was found that over a range of low shear rates, the echogenicity is enhanced in a manner similar to the previously reported influence on aggregation. Evidence is presented confirming the important role of aggregation in controlling the echogenicity. The transient effects of abrupt flow stoppage were studied and shown to provide useful insights into aggregation kinetics. Based on the above results, a detailed explanation is provided of the echogenicity variations seen in B-mode ultrasound images of slow-moving blood.
Animals↗