Aortic distensibility and hypercholesterolaemia.
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Aorta↗
Biomedical subjects
R G Gosling
Publications and source records attributed to R G Gosling.
Non-invasive Doppler ultrasound technique for the in vivo assessment of aortic compliance.
A non-invasive Doppler ultrasound technique for the assessment of aortic compliance is described. This is based on the in vivo measurement of pulse wave velocity along the thoraco-abdominal aortic pathway. A structured protocol has been developed to improve the reproducibility of the technique as well as for the purposes of operator training. Preliminary results of a study of both the intra- and inter-observer variability of the method are provided and problems associated with the technique are discussed. Medical disorders such as atherosclerosis, diabetes mellitus and familial hypercholesterolaemia have all been shown to affect arterial wall compliance. We suggest that the measurement of aortic compliance in vivo may be a useful, non-invasive tool for assessing these patients' susceptibility to atheromatous arterial disease and for monitoring their response to therapy.
Adolescent↗
Non-invasive assessment of the Circle of Willis using transcranial pulsed Doppler ultrasound with angiographic correlation.
The ability of transcranial pulsed Doppler ultrasound (TCD) to provide a dynamic assessment of the functional capability of the Circle of Willis was assessed using conventional cerebral angiography for anatomic correlation. Eleven patients had normal four-vessel cerebral angiography prior to being investigated with ultrasound. Angiography and ultrasound both demonstrated a functional anterior communicating artery in nine of the eleven patients, giving complete agreement between the two techniques. Posterior communicating arteries were visualized angiographically in all eleven patients. Ultrasound identified bilateral functional vessels in nine, the other two patients having non-functional vessels. In these latter two patients, angiography demonstrated three of the four posterior communicating arteries to be hypoplastic and it was uncertain whether these vessels carried significant blood flow. The fourth posterior communicating artery was shown to have an absent proximal segment of the ipsilateral posterior cerebral artery, with a persistent fetal posterior communicating artery. This anatomical variation is a potential limitation of ultrasound for assessing functional posterior communicating arteries. These preliminary results indicate that a combination of the anatomical (angiographic) and dynamic (ultrasonic) data may prove to be complementary for assessing the Circle of Willis.
Adult↗
Aortic compliance in young patients with heterozygous familial hypercholesterolaemia.
1. Aortic compliance and plasma lipid and lipoprotein levels were measured in 20 young patients with heterozygous familial hypercholesterolaemia and in 20 age- and sex-matched control subjects. 2. Patients with familial hypercholesterolaemia had significantly higher plasma cholesterol, low-density lipoprotein-cholesterol and triacylglycerol levels than control subjects (P < 0.001, P < 0.001 and P < 0.005, respectively). The patients with familial hypercholesterolemia also had significantly more compliant (distensible) aortas than the control subjects (P < 0.001), a significant inverse correlation being observed between compliance and age (r = 0.73, P < 0.001) and between compliance and mean blood pressure (r = -0.60, P < 0.005). 3. When the effects of age and sex on aortic compliance were corrected for, the blood pressure effect disappeared, significant correlations being observed between normalized compliance and cholesterol (r = 0.50, P < 0.03), low-density lipoprotein-cholesterol (r = 0.54, P < 0.01), high-density lipoprotein-cholesterol (r = -0.44, P < 0.05), low-density lipoprotein-/high-density lipoprotein-cholesterol ratio (r = 0.60, P < 0.0006) and duration of disease (r = 0.67, P < 0.002). Multivariate regression analysis showed that the low-density lipoprotein-/high-density lipoprotein-cholesterol ratio (P < 0.03) and duration of disease (P < 0.04) were the best predictors of normalized compliance. 4. We suggest that the measurement of aortic compliance in young patients with familial hypercholesterolaemia may potentially be a useful, non-invasive, research tool for assessing their susceptibility to atheroma.
Adolescent↗
Arterial wall compliance in diabetes.
A non-invasive Doppler ultrasound technique, based on the measurement of pulse wave velocity along the aorta, has been used to deduce aortic compliance in 25 Type 1 and 25 Type 2 diabetic patients. Thirteen of the Type 1 diabetic group had their compliance measured within 1 year of diabetes first being clinically diagnosed. All compliance values were normalized for age and sex variations using data previously obtained from over 600 normal, non-diabetic subjects (mean normalized compliance +/- SD; 100 +/- 15%). The results show that Type 1 diabetic patients have significantly more distensible aortas (132 +/- 26%) than their age- and sex-matched non-diabetic counterparts (100 +/- 12%) (p less than 0.01), while Type 2 diabetic patients have significantly stiffer aortas (74 +/- 21%) than their age- and sex-matched non-diabetic counterparts (100 +/- 18%) (p less than 0.01). The young Type 1 diabetic patients measured within 1 year of diagnosis have aortas ranging up to 78% more distensible (151 +/- 15%) than their age- and sex-matched non-diabetic controls (100 +/- 11%) (p less than 0.001). These results support findings by other groups that adult diabetic patients have less distensible arteries than normal, but contradict reports in the literature dating back over 20 years that diabetic children have stiffer arteries than normal children.
Adolescent↗
Measuring aortic distensibility.
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Adolescent↗
Quickscan: Doppler ultrasound emulation of angiography--its value prior to arteriography in peripheral vascular disease.
The prevalence of peripheral vascular disease demands a quick, reliable, non-invasive technique for initial assessment. We have devised a new method which combines the two physical principles that (1) Doppler shift is proportional to blood velocity and (2) blood velocity is inversely proportional to arterial cross-section with the ability to track probe position using a non-contacting method. An image of the probe track and any arterial narrowing is shown superimposed on an outline of the patient. Pressure measurement, scan and graphics with final report take about 20 minutes. The accuracy of this system in peripheral vascular disease was evaluated. Thirty-one patients underwent quickscan (QS) and arteriography within an average time of 7 days. Abdominal aorta, common iliac-common femoral, superficial femoral and popliteal artery segments were graded independently as normal, significant stenosis (greater than 50% of diameter) or occluded by both techniques. Of 197 segments, QS correctly assessed 106 normal, 22 stenosed and 28 occluded segments. Four equivocal angiographic stenoses were normal on QS and three severe stenoses were graded occlusion. Fifteen segments on angiography and five on QS were not assessed. For the iliac and superficial femoral artery segments, sensitivity and specificity averaged 77% and 86%, respectively, for all grades. Aortic statistics were invalid (only one significant lesion). Six out of eight popliteal occlusions were correctly diagnosed by QS, but no popliteal stenoses were detected out of six shown on arteriography. Low numbers may contribute to this discrepancy but an improved popliteal scanning method may be necessary. We find initial QS an invaluable aid to direct percutaneous angiography and to indicate potential sites for angioplasty.
Adult↗
An online technique for estimating cerebral carbon dioxide reactivity.
A technique for measuring cerebral reactivity using transcranial pulsed Doppler ultrasound is described; the system includes a spectrum analyser and capnometer. Data acquisition and manipulation is under software control. Main stem middle cerebral artery blood velocity is monitored continuously using the transcranial Doppler technique, whilst the operator initiates data collection and controls the inspired gas composition. The calculation of cerebral CO2 reactivity is based upon linear regression analysis of normalized, time-averaged middle cerebral velocity on end-tidal pCO2 and is displayed graphically. Measurement of middle cerebral CO2 reactivities can be completed within 15 min. Results from two subjects, a healthy volunteer and a patient with occlusive disease, are shown to illustrate the technique.
Blood Flow Velocity↗
Aortic compliance measured by non-invasive Doppler ultrasound: description of a method and its reproducibility.
1. Aortic compliance (expressed as percentage increase in lumen diameter for a pulse pressure of 10 mmHg) was calculated from the characteristic pulse wave velocity deduced from 'foot to foot' transit times of the blood flow pulse over a measured length of aorta. Two continuous wave Doppler ultrasound transducers were used: one insonating the root of the left subclavian artery, the other the abdominal aorta proximal to its bifurcation. Measurements were made after the subject had been supine for 5 min to achieve stable conditions. 2. Transit times were calculated on-line in real-time from the delay between the start of the systolic upstroke in the flow velocity sonograms recorded by the two transducers. 3. Within-visit variation was minimized by measuring over 45 cardiac cycles repeated three separate times and calculating an overall mean value for aortic compliance. A full measurement took 5-10 min. 4. Reproducibility of this overall mean value of aortic compliance was assessed at 1 month in 30 subjects (aged 60 +/- 7 years, mean +/- SD) and at 3 months in 23 different subjects (59 +/- 8 years). Aortic compliance values ranged from 0.1 to 2.0%/10 mmHg. 5. The mean paired difference between aortic compliance values was -0.02 between 0 and 1 months, and 0.03 between 0 and 3 months, with respective 95% confidence limits of -0.06 to 0.03 and -0.03 to 0.09 embracing zero, thus not differing significantly from baseline.(ABSTRACT TRUNCATED AT 250 WORDS)
Aorta↗
Changes in carotid artery compliance with age.
Doppler-shifted ultrasound was used to measure arterial compliance non-invasively in the internal and external carotid pathways of 270 male and 388 female asymptomatic volunteers aged 5 to 90 years. There was a significant decrease in the compliance of both arteries from 5 to 50 years of age (p less than 0.001), when it then levelled out. Arteries of women were more compliant than those of men at ages 35 to 60 years.
Adolescent↗
On-line Doppler ultrasound measurement of aortic compliance and its repeatability in normal subjects.
An on-line technique is described for measuring aortic compliance using a two-probe Doppler ultrasound method. It is shown that automatic processing of blood velocity signals obtained simultaneously from the left subclavian artery and abdominal aorta enables real-time computation of the time delay observed between the systolic upstroke (or foot) of sonograms from these arteries during the same heart beat. An average foot-to-foot transit time (obtained from a number of cardiac cycles) and the physical separation between the two ultrasonic transducers is used to calculate aortic compliance. Using the above method, the reproducibility of aortic compliance measurements was studied in 12 healthy volunteers over different time intervals. Four of these subjects were measured 7 times each at 10 min intervals whilst the remaining eight subjects were measured 9 times each at hourly intervals. This reproducibility study indicated a significant variation of aortic compliance (P less than 0.001) in the same person regardless of time period. The coefficient of variation ranged approximately between 5% and 18%.
Aorta, Abdominal↗
Diagnosis of brain death by transcranial Doppler sonography.
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Brain Death↗
Chromaticity-coded Doppler blood velocity sonagrams: preliminary observations.
This paper describes the application of chromaticity to spectrally analysed Doppler blood velocity signals. Chromaticity enables a particular colour to be assigned to the power/frequency distribution within each instantaneous spectral sweep of a sonagram. Successive spectral sweeps of a sonagram can then be colour-coded in this fashion to produce a chromaticity-coded sonagram. Two chromaticity-coded sonagrams are presented to illustrate various blood flow features. Standard sonagram display formats are also presented for comparison purposes. It appears that the chromaticity-coded sonagram offers the ability to digitally encode the instantaneous power spectral distribution with a single chromaticity vector.
Blood Flow Velocity↗
The effect of arterial filtration on reduction of gaseous microemboli in the middle cerebral artery during cardiopulmonary bypass.
Noninvasive in vivo detection of gaseous microemboli in the middle cerebral artery, by transcranial Doppler ultrasound, was used to determine the effect of filtration in the arterial catheter using 25- and 40-microns filters and bubble oxygenators in patients undergoing cardiopulmonary bypass surgery. Eighteen patients undergoing coronary artery bypass surgery were studied using a closed cardiac (unvented heart) model. Group 1 patients (no filters) had the highest incidence of gaseous microemboli, as indicated by the ultrasound microemboli index, at both high and low oxygen flow rates. Group 2 patients (40-microns filters) had a significantly lower microemboli index, particularly at low oxygen flow rates (t = 4.9, p less than 0.001). The 25-microns group patients had the lowest values of all. No microemboli were detected at low oxygen flow rates, and microemboli were detected in only 0.1% of the samples at high oxygen flow rates. Additionally, observations on vented hearts in 3 patients undergoing cardiac valve surgery indicate that the origin of gaseous microemboli may be air trapped inside the heart.
Cardiopulmonary Bypass↗
Prevalence of severe internal carotid artery disease in hypertensive elderly patients.
Doppler-shifted ultrasound was used as a non-invasive test to determine the presence of severe (pressure dropping) internal carotid lesions in two groups of elderly patients. Group 1 consisted of 150 hypertensive patients; these were subdivided into 77 who had had no cerebrovascular incidents (mean age 75 years, range 65-97) and 73 who had previously suffered a stroke (mean age 75 years, range 65-91). Group 2 consisted of 44 normotensive asymptomatic elderly volunteers (mean age 76 years, range 68-90). In the hypertensive patients (group 1), severe disease was detected in the non-stroke patients in 15 (10%) of the internal carotid arteries (14% of the patients), and in the stroke patients in 23 (16%) of the internal carotid arteries (23% of the patients). None of the normotensive volunteers (group 2) had evidence of severe internal carotid disease. Statistical analysis confirmed a highly significant difference in the prevalence of severe carotid disease between the normotensive and hypertensive subjects. The difference between the non-stroke and stroke hypertensive patients was not statistically significant.
Aged↗
Transcranial Doppler assessment of cerebral collateral during carotid endarterectomy.
Sixteen patients (mean age 59 +/- 9 years) who were to undergo carotid endarterectomy were examined pre- and peroperatively using pulsed Doppler-shifted ultrasound; blood velocities in the middle cerebral artery were measured before and during common carotid compression in the conscious patient, and before and during measurement of carotid stump pressures at surgery in the anaesthetized patient. Measurements at endarterectomy showed a significant difference in middle cerebral artery blood velocities from patients with stump pressures of greater and less than 50 mmHg (t = 4.0, P less than 0.005). A threshold of 10 cm s-1 distinguished between stump pressures of greater and less than 50 mmHg in 15 of the 16 patients. Pre-operative blood velocity measurements during carotid compression did not correlate with those taken peroperatively at carotid clamping.
Adult↗
The detection of microemboli in the middle cerebral artery during cardiopulmonary bypass: a transcranial Doppler ultrasound investigation using membrane and bubble oxygenators.
Twenty-seven patients were examined who were undergoing cardiopulmonary bypass (CPB) surgery with either a bubble oxygenator or a capillary membrane oxygenator. The latter incorporated an arterial filter and bubble trap. A noninvasive Doppler ultrasound technique is described for monitoring irregularities in the Doppler flow signals attributable to gaseous microemboli detected in the middle cerebral artery during CPB. The ultrasound index for detecting gaseous microemboli (MEI) indicated the presence of such microemboli in 22 of the 27 patients during insertion of the aortic cannula. Measurements during CPB showed the MEI ranged from 4 to 39 in the 17 patients with a bubble oxygenator. However, all 10 patients with a membrane oxygenator had an MEI of 0. Varying the gas flow rates in 3 patients with bubble oxygenators showed a change in MEI from 4 +/- 4 (SD) at a flow rate of 2 L/min to 17 +/- 9 at a flow rate of 5 L/min. This observation supports the assumption that the MEI is providing quantitative information regarding the presence of gaseous emboli in the middle cerebral artery.
Cardiopulmonary Bypass↗
Pulsed Doppler ultrasound compared with thermodilution for monitoring cardiac output responses to changing left ventricular function.
To determine the responsiveness of the pulsed Doppler technique to pacing and drug induced changes in left ventricular function 125 simultaneous cardiac output measurements by pulsed Doppler ultrasound and thermodilution were compared in 12 patients. The Doppler velocity frequencies were analysed using a signal averaging process and the validity of this method first tested in vitro. This showed almost perfect linearity of pulsed Doppler and electromagnetic flow determinations in a test rig. Although data points showed greater scatter in the clinical study, a highly significant linear relation between cardiac output measurements by pulsed Doppler and thermodilution was confirmed by regression analysis (r = 0.88, p less than 0.001). Certain mean values for cardiac output by the two techniques differed, however, by up to 0.9 litre.min-1. Despite this, changes in cardiac output in response to pacing, inotropic stimulation with dobutamine, and vasodilatation with nitrates were directionally similar, indicating a useful role for the pulsed Doppler technique in monitoring responses to treatment in the intensive care unit. Pulsed Doppler also provided a simple measure of left ventricular contractile function. Thus the inotropic response to dobutamine produced a significant rise in peak aortic flow velocity, and this variable was unaffected by either pacing or nitrate induced vasodilatation.
Cardiac Output↗