Biomedical subjects
Publications and source records attributed to T S Padayachee.
Magnetic resonance imaging has been reported to have advantages over conventional angiography in the diagnosis of dural sinus thrombosis. A case report is presented describing the application of MR techniques including MR angiography, to diagnose and monitor therapy for dural sinus thrombosis.
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.
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.
The occurrence of neurological sequelae following cardiopulmonary bypass (CBP) surgery has stimulated interest in refining the techniques of extracorporeal circulation. Air micro-emboli originating from the oxygenator have been postulated as one source of cerebral damage. Since controversy still exists regarding the merits of bubble versus membrane oxygenators, this has prompted investigators to devise methods to determine the amount of micro-emboli produced during CPB. In this study, 27 patients undergoing CPB surgery for coronary artery disease (21) or valve replacement (6) were examined. The surgical and anaesthetic techniques were standardised in all patients except for the type of oxygenator used. A bubble oxygenator was used in 17 patients (Bentley Bio-10, William Harvey or Dideco) and a membrane oxygenator with a 25 microns filter in the remaining 10 patients (Bentley BOS CM50). Transcranial pulsed Doppler ultrasound was used to obtain blood velocity signals from the middle cerebral artery throughout CPB. A flow disturbance index (FDI) was defined which provided a representative index of the number of micro-emboli passing the ultrasound transducer. The FDI indicated the presence of gaseous micro-emboli during insertion of the aortic cannula in 22 of the 27 patients. In the 17 patients with a bubble oxygenator, the FDI ranged from 4-39. In the 10 patients with a membrane oxygenator, the FDI was always 0. Variation of gas flow rates in 3 patients with bubble oxygenators showed a change in the FDI from 4 +/- 4 at a flow rate of 2 l/min to 17 +/- 9 at 5 l/min.(ABSTRACT TRUNCATED AT 250 WORDS)
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.
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.
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.
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.
Data are presented from transcranial insonation of the middle cerebral artery (MCA) performed at intervals in 23 unconscious children for whom the outcome was subsequently poor. Once an MCA signal had been observed over a 30 minute period with time averaged velocity less than 10 cm s-1 and/or a direction of flow index, DFI, defined as 1 minus the ratio of reverse to forward flow of less than 0.8, recovery to forward flow throughout diastole was never observed and no patient recovered brain stem reflexes. Recovery of forward flow in diastole, and of brain stem function, was seen in cases with time averaged MCA velocity in the range 10 to 25 cm s-1 and with reverse flow but a DFI of greater than 0.8 for short periods of time. All but one of the 13 children fulfilling clinical criteria for brain stem death had MCA signals with time averaged velocity of less than 10 cm/s and DFI of less than 0.8. This type of signal was not observed in five children who were left in a persistent vegetative state.
Transcranial pulsed Doppler ultrasound and spectral analysis were used to monitor blood velocities in the middle cerebral artery of nineteen patients (mean age 61 +/- 9 years) during carotid endarterectomy. A Javid shunt was used in all patients. The intensity weighted mean Doppler frequency for each spectral sweep (at 5 ms intervals) was time-averaged over the cardiac cycle to obtain a mean value for blood velocity in the middle cerebral artery. The range of such values found in the 19 patients was: 12-38 cm s-1 after anaesthesia (baseline); 12-69 cm s-1 during diathermy; 0-30 cm s-1 during carotid clamping; 16-32 cm s-1 during shunting and 18-60 cm s-1 in the recovery room. The average change in middle cerebral artery blood velocity from baseline values showed significant increases during diathermy (P less than 0.005), shunting (P less than 0.05) and in the recovery room (P less than 0.005). Clamping of the internal carotid artery showed a significant decrease in middle cerebral artery blood velocities of all patients (P less than 0.005), three of whom showed no flow in the middle cerebral artery during clamping. Abnormally high amplitude Doppler signals at the commencement of shunting were detected in 17 of the 19 patients. Such Doppler signals are consistent with turbulent blood flow or the introduction of micro-air bubbles by the shunt. Backbleeding in the internal carotid artery before insertion of the shunt was associated with diminished flow in the ipsilateral middle cerebral artery of ten patients, oscillatory forward/reverse flow in three patients and cessation of flow in the remaining six patients.
Transcranial pulsed Doppler ultrasound and spectral analysis were used for detection of blood velocities in the basal cerebral arteries. The Doppler transducer was placed superior to the zygomatic arch and during insonation of the middle cerebral artery care was taken to obtain maximum Doppler-shift frequency signals since this allowed a small angle between the ultrasound beam and this artery. Doppler signals were obtained from the middle, anterior, and posterior cerebral arteries in 20 volunteers with the average depth of the Doppler gate at 4.9 (4.6-5.2 cm), 5.2 (4.9-5.4 cm), and 6.3 cm (6.0-6.9 cm), respectively. These measurements were in agreement with those obtained for 15 cadaver studies, in whom the distance from the proposed site of the Doppler transducer to each basal cerebral artery was measured as 4.7 +/- 0.6, 5.3 +/- 0.5, and 5.9 +/- 0.9 cm, respectively. The reproducibility of middle cerebral artery blood velocity values was tested in seven subjects and showed a variation of not more than 8% in any individual. The method was used in combination with common carotid compression to assess four patients who had occlusive extracranial carotid disease; in three the disease was more severe on one side and reversal of blood flow in the proximal ipsilateral anterior cerebral artery was demonstrated, consistent with cross flow from the contralateral side via the anterior communicating artery of the Circle of Willis. In the fourth patient augmentation of posterior cerebral artery blood velocities during common carotid compression indicated the major collateral source was from the vertebrobasilar system.
Blood velocities have been measured transcranially, at small Doppler angles, in the middle cerebral artery of normal volunteers. Cerebral blood flow was changed by varying carbon dioxide tension. In four volunteers, the relationships between arterial pCO2 and percentage change in intensity weighted mean, median, and maximum Doppler-shifted frequencies in the internal carotid and middle cerebral arteries were linear with slopes of 2.5 and 2.8% per mm Hg change in pCO2. In 38 volunteers, the relationship between end-expiratory pCO2 and time-averaged maximum Doppler frequency was linear over the range of pCO2 20-60 mm Hg with slopes of 2.5 and 2.9 percentage change per mm Hg, for internal carotid and middle cerebral, respectively. These results are very similar to those reported using direct methods of measuring cerebral blood flow. As the transcranial Doppler method is reproducible, this indicates that changes in middle cerebral blood velocity may be used to monitor changes in flow.
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Doppler-shifted ultrasound and spectral analysis were used to assess the carotid arteries of 77 elderly stroke patients, which represented 154 carotid bifurcations. Severe carotid disease was demonstrated at 19 of the 154 carotid bifurcations and in eight of these complete occlusion of the internal carotid artery was present. In 12 of the 19 instances the severe disease was in the internal carotid artery associated with the stroke. Localized carotid bruits were present in five patients and only three of these were associated with severe disease of the internal carotid artery. Minor disease was detected in 80 of the 154 carotid bifurcations and no disease was detected at the remaining 55 carotid bifurcations. An abnormally low ankle/arm systolic pressure ratio, which indicated occlusive arterial disease of the legs, was obtained in 19 of the 43 patients examined. No relationship was found between the severity of carotid artery disease and the presence of haemodynamically significant disease of the lower limbs. Ultrasound measurement of aortic compliance gave significantly lower values in elderly stroke patients compared to elderly asymptomatic volunteers. Comparison of flow-velocity transit times from the stroke-affected and non-affected limbs showed no consistent effect of the stroke on vascular tone in the patients assessed.
A method is described for non-invasively measuring the increase in lower limb blood flow during transfemoral lumbar aortography. Flow measurements were made using a continuous wave Doppler-shift ultrasound transducer placed over the contralateral femoral artery. The effect of the non-ionic contrast medium B15000 (Iopamidol), conventional contrast medium (Urografin 370) and Urografin 370 plus Lignocaine were compared in a double-blind trial. All three produced an increase in flow which reached a peak between 12 and 45 s after injection. The peak flow following Iopamidol was significantly lower than that from both Urografin 370 alone and with addition of Lignocaine. There was a difference of lesser degree between Urografin 370 plus Lignocaine and Urografin 370 alone; however, this was not statistically significant. The subjective assessments of pain and patient 'discomfort' paralleled these objective flow measurements.
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Doppler-shift ultrasound with spectral analysis permits the measurement of the relative heights of systolic peaks (the A/B ratio) in blood velocity sonograms from supra-orbital and common carotid arteries, the temporal artery occlusion test, the common carotid resistance index and transit times of flow-velocity waves in the internal carotid pathway. The results are compared with 201 carotid angiograms and expressed in terms of sensitivity (true positive) and specificity (true negative). Supra-orbital and common carotid A/B ratios, in combination with the temporal artery occlusion test, detected all grades of carotid artery disease with a sensitivity of 72 per cent and a specificity of 93 per cent. The corrected transit time gave a sensitivity of 57 per cent and a specificity of 89 per cent, whilst the Resistance Index gave a sensitivity of 60 per cent and a specificity of 80 per cent. The values of ultrasound parameters associated with severe disease, defined as reductions in lumen diameter of 75 per cent or more, of the internal carotid artery are examined. The temporal artery occlusion test gave a sensitivity of 91 per cent and a specificity of 94 per cent. These results were more accurate than those obtained for the corrected transit time (sensitivity 83 per cent, specificity 92 per cent) and for the Resistance Index (sensitivity 75 per cent and specificity 92 per cent). The results show that of the tests described the supra-orbital and common carotid artery A/B ratios, together with the temporal artery occlusion test, gave the best sensitivity and specificity for detection of both severe and minor carotid bifurcation disease.
Using continuous wave Doppler-shifted ultrasound and spectral analysis the response to the temporal artery occlusion test was compared when insonating the supraorbital and supratrochlear arteries of 203 internal carotid pathways. The test involved monitoring the periorbital artery whilst simultaneously compressing a single branch of the external carotid artery, the ipsilateral superficial temporal artery. In 41 instances carotid angiography demonstrated severe disease of the internal carotid artery, that is lesions of 75% or more reduction in lumen diameter. A positive response to the temporal artery occlusion test, when performed on the supraorbital artery, indicated severe disease with a sensitivity of 90% and a specificity of 89%. When this test was performed on the supratrochlear artery a low sensitivity of 36% was obtained, although specificity was high at 96%.