Some aspects of ultrasound in the diagnosis and assessment of aortoiliac disease

Development of Ultrasound Techniques for Assessment of Aortoiliac Obstructive Disease

The development of ultrasound techniques for assessment of aortoiliac obstructive disease is described. This period started in 1959 with the detection of blood flow with an ultrasonic device. Continuous-wave Doppler devices were designed, and the pulse waves of readily accessible vessels like the common femoral artery were examined. It was soon recognized that the functional status of the aortoiliac arteries could be assessed by the Doppler characteristics of the common femoral artery pulse wave. Qualitative and quantitative methods were used to analyze the femoral Doppler signal. The introduction of duplex scanning made it possible to evaluate the hemodynamics of aortoiliac arteries directly. At present, duplex scanning offers the best method of evaluating the aortoiliac arteries noninvasively.

The pulsating brain: A review of experimental and clinical studies of intracranial pulsatility

The maintenance of adequate blood flow to the brain is critical for normal brain function; cerebral blood flow, its regulation and the effect of alteration in this flow with disease have been studied extensively and are very well understood. This flow is not steady, however; the systolic increase in blood pressure over the cardiac cycle causes regular variations in blood flow into and throughout the brain that are synchronous with the heart beat. Because the brain is contained within the fixed skull, these pulsations in flow and pressure are in turn transferred into brain tissue and all of the fluids contained therein including cerebrospinal fluid. While intracranial pulsatility has not been a primary focus of the clinical community, considerable data have accrued over the last sixty years and new applications are emerging to this day. Investigators have found it a useful marker in certain diseases, particularly in hydrocephalus and traumatic brain injury where large changes in intracranial pressure and in the biomechanical properties of the brain can lead to significant changes in pressure and flow pulsatility. In this work, we review the history of intracranial pulsatility beginning with its discovery and early characterization, consider the specific technologies such as transcranial Doppler and phase contrast MRI used to assess various aspects of brain pulsations, and examine the experimental and clinical studies which have used pulsatility to better understand brain function in health and with disease.

Postocclusive Reactive Hyperemia During Vascular Reconstruction

The purpose of this basic investigation was to clarify the postocclusive reactive hyperemia during vascular reconstruction using laser Doppler flowmetry (LDF). For the fundamental experiment, thirty-nine limbs with arteriosclerosis obliterans (ASO) in Stage II according to Fontaine's classification and 33 limbs without arterial or venous disease were chosen. In the supine position, a thigh cuff was applied to the lower thigh of a subject. Systolic Doppler thigh pressure was obtained and thigh/arm pressure index (TPI) was calculated. A LDF probe was then fixed to the bottom of the first toe and cutaneous blood flow was measured continuously before, during, and after femoral artery occlusion by the thigh cuff. The occlusion time was 3 and 6 minutes. For the clinical study, thirty-three lower limbs with arterial occlusive disease were selected. During the vascular surgery, the LDF probe was attached to the bottom of the first toe and cutaneous blood flow was monitored continuously before, during, and after the vascular clamping. In the fundamental experiment, after the release of the occlusion, the maximum blood flow of the reactive hyperemia (peak flow) appeared. The period between the release of the occlusion and the peak flow was called the peak time. When the occlusion time was longer, the reactive hyperemia appeared later and was bigger. When TPI decreased, the peak time lengthened and the peak flow after a 6-minute occlusion decreased. In the clinical study, the more severe the degree of the preoperative limb ischemia was, the longer was the peak time. The longer the intraoperative clamping time, the longer the peak time. In conclusion, postocclusive reactive hyperemia during vascular surgery was influenced by the degree of the preoperative limb ischemia and the length of the vascular clamping time.

Postocclusive hyperaemic duplex scan: a new method of aortoiliac assessment

Aortoiliac duplex scanning, while accurate, is time-consuming and technically demanding. This study aimed to develop a fast, non-invasive screening test for aortoiliac disease. Colour duplex scanning was used to record common femoral Doppler ultrasonographic waveforms following 3 min of arterial occlusion using a thigh cuff in 25 patients with normal aortoiliac segments and 25 patients with significant aortoiliac disease. The latter patients had a prolonged period of postocclusive hyperaemic flow compared with the former. End diastolic velocity, 70 s after cuff release, was a significant discriminant between the two groups (sensitivity of 88 per cent, accuracy of 92 per cent). The postocclusive hyperaemic duplex (PHD) test performed well when used prospectively in a further 50 limbs (sensitivity of 86 per cent, accuracy of 84 per cent). The test was more sensitive than femoral pulse palpation and compared favourably with arteriography. The PHD test provides a simple, noninvasive assessment for aortoiliac disease that can be performed on the initial outpatient clinic visit.

Assessment of stenoses in the aortoiliac tract by calculation of a vascular resistance change ratio before and after exercise

OBJECTIVES

Intraarterial pressure measurement is the most reliable method to assess haemodynamically significant stenoses in the aortoiliac tract. We have tried to develop a simple and quick, non-invasive method to assess stenoses of this type.

DESIGN

Prospective semi-blinded clinical study.

METHODS

It was postulated that a haemodynamically significant aortoiliac tract stenosis would result in a lesser degree of vascular resistance decrease after vasodilatation, compared to patients only suffering from femorodistal stenoses. We approximated vascular resistance by: (brachial pressure-ankle pressure)/femoral artery mean Doppler velocity. By dividing vascular resistance at rest by vascular resistance after exercise, we calculated the Resistance Change Ratio (RCR).

PATIENTS AND RESULTS

In 34 patients (50 legs) with arterial stenoses, the pressure gradient over the aortoiliac segment was compared to the RCR. Legs were divided in three groups: group 1 consisted of 22 legs that showed a pressure gradient > 10 mmHg at rest; group 2 showed a pressure gradient > 10 mmHg after papaverine; group 3 showed a pressure gradient of 10 mmHg or less. The median RCR was: 0.74 (range: 0.23-4.04) for group 1, 0.71 (range: 0.36-1.80) for group 2 and 0.93 (range 0.36-2.06) for group 3. There was no significant difference between the groups (p = 0.19).

CONCLUSION

The RCR could not be used to accurately detect stenoses in the aortoiliac.

Noninvasive hemodynamic assessment of the internal mammary artery in myocardial revascularization

Using transthoracic B-mode imaging and Doppler spectrum analysis it was found that the luminal diameter of the internal mammary artery and its hemodynamics were not significantly different among 15 preoperative patients (64 +/- 10 years) who underwent myocardial revascularization using the left internal mammary artery and young and older control groups (25 +/- 3 years and 61 +/- 9 years, respectively). These data indicate that older age does not significantly adversely influence the degree of intimal thickening and compliance in the internal mammary artery. Doppler spectrum analysis of the internal mammary artery in the patients who were operated on revealed conversion from a triphasic systolic waveform preoperatively to a unidirectional combined systolic/diastolic waveform at 1 week and 2 and 6 months postoperatively, characterized by a significant increase in the diastolic blood flow velocity and a significant decrease in the systolic blood flow velocity and the pulsatility and resistance indices. This study indicates that transthoracic B-mode imaging and Doppler spectrum analysis are promising noninvasive techniques in the preoperative assessment of internal mammary artery morphology and physiology. In addition, Doppler spectrum analysis can also be used in the long-term serial assessment of the internal mammary artery conduit after myocardial revascularization.

Experimental variations in renovascular resistance in normal man as detected by means of ultrasound

The pulsatility index (PI) of blood flow velocities has been reported to vary with changes in peripheral vascular resistance. Since blood flow velocities can easily be detected with the Echo-Color-Doppler technique in interlobar arteries of normally positioned kidneys, we tried in six healthy volunteers to estimate pharmacological induced variations in renal plasma flow (RPF) and renovascular resistance (RVR) by means of PI measurements. In this study no significant correlation between the absolute values of PI and RVR was found. In order to correct PI for different blood pressure-inputs to the renal artery, PI was divided by the pulsatility of the systemic arterial pressure, i.e. the 'blood pressure index' [BPI = (SAD-DAP)/MAP)], resulting in the 'velocity blood-pressure index' (VBI = PI/BPI), which was significantly correlated with RVR (r = 0.54, P less than 0.01). The pharmacological induced changes of RPF and RVR (delta RPF, delta RVR) were also correlated to the respective changes of PI and VBI (delta PI, delta VBI), with the highest significance when delta VBI was plotted against delta RVR (r = 0.83, P less than 0.0001). VBI, i.e. the pulsatility index of blood flow velocities as corrected for the pulsatility of the driving force, may be a tool for noninvasive assessment of changes in RVR and thereby of importance for the diagnosis and follow-up of renovascular diseases.

Detrimental sequelae on the hemodynamics of the upper left limb after subclavian flap angioplasty in infancy

The long-term effect of two surgical techniques for repair of coarctation of the aorta in infancy, namely, resection and end-to-end anastomosis (RETE) and subclavian flap angioplasty (SFA) on the blood supply of the upper left limb, was quantified by Doppler spectrum analysis of blood flow velocities in the left brachial artery at rest and during postocclusive reactive hyperemia. Twenty-three patients participated in this study: nine patients after SFA (median age, 8 years), 14 patients after RETE (median age, 8 years), and 10 control subjects (median age, 9.5 years). At rest, a highly significant decrease of blood flow velocities in the left brachial artery was measured in all patients of the SFA group compared with those of the RETE and control groups, as documented by various Doppler spectrum parameters: maximal frequency of advancing curve (p = 0.0001), pulsatility index (p = 0.0005), and resistance index (p = 0.039). During reactive hyperemia, a moderate capacity of physiologic augmentation of blood flow velocities was observed in five patients of the SFA group. This capacity was marginal in two patients with complaints of claudication in the left upper limb during strenuous exercise, which can be related to the number of branches of the left subclavian artery ligated during operation. This study indicates that SFA in infancy may lead to compromised hemodynamics of the upper left limb with potential for symptoms of ischemia during exercise.

Resting ankle-arm pressure index in vascular diseases of the lower extremities

The authors calculated 442 values of resting ankle-arm indices in 222 patients, of whom 114 reported exercise pain of the lower extremities (51.3%) and 34 reported rest pain (15.3%). Tissue necrosis was diagnosed in 55 patients (24.8%) and other disorders in 19 (8.6%). Obliterating atherosclerosis was found in 186 patients (83.8%), Buerger's disease in 16 (7.2%), and other vascular diseases in 20 patients (9%). The studied index value in 262 examined lower extremities was 1.3-1.0 in 54, 0.9-0.8 in 29, 0.7-0.6 in 66, 0.5-0.4 in 55, and 0.3-0.0 in 58 lower extremities. Respective values for contralateral lower extremities (180) were the following: 69, 54, 33, 14, and 10.

Quantitative Doppler ultrasound evaluation of occlusive arterial disease in the lower limb

Forty consecutive patients with lower limb arterial disease were evaluated using a multi-gated pulsed Doppler system. Doppler signals were sampled at 4 sites in each limb, and following spectral analysis, the pulse rise time (PRT) was measured. The value obtained at the location giving the longest duration of PRT was used for comparison with ankle/brachial pressure index (A/B index) and angiography. A highly significant correlation was found between PRT and A/B index (r = -0.75, P less than 0.001). Based on receiver operating characteristic curves an overall diagnostic accuracy of 90% in diagnosing a pressure reduction greater than 20% was obtained. The diagnostic accuracy in detecting an angiographic stenosis greater than 50% was almost identical. Based on combined quantitative and qualitative analysis of Doppler signals sampled at the common femoral and popliteal artery, the aorto-iliac segments and the femoro-popliteal segments were evaluated separately. Comparison with arteriography revealed overall accuracies of 96% in the aorto-iliac segments and 87% in the femoro-popliteal segments. It is concluded that simple quantitatively measurable parameters in the Doppler spectrum may accurately predict and localize hemodynamically significant arterial lesions of the lower extremities.

Duplex scanning for diagnosis of aortoiliac and femoropopliteal disease: a prospective study

We compared ultrasonic duplex scanning and angiography for the localization and classification of arterial stenoses and occlusions in 32 patients. The criteria for the detection of a greater than 50% diameter reducing stenosis was an increase in peak systolic velocity of greater than 100%, loss of reverse flow, and spectral broadening. Duplex studies and angiograms were evaluated in a blinded fashion. The agreement between duplex scanning and angiography for the 383 arterial segments studied was not significantly different than the previously reported agreement between two different radiologists reading the same angiograms (kappa of 0.55 vs 0.63). For detecting stenoses that were greater than 50% diameter reducing by angiography, duplex scanning had a sensitivity of 82%, a specificity of 92%, a positive predictive value of 80%, and a negative predictive value of 93%. These results are as good as previously reported comparisons between two different radiologists' readings of the same angiograms.

Criteria from intra-arterial femoral artery pressure measurements combined with reactive hyperaemia to assess the aorto-iliac segment; a prospective study

Direct femoral artery blood pressure measurements combined with reactive hyperaemia (FAP study) were performed on 50 extremities (45 patients) with multilevel arterial occlusive disease of the lower extremities. In a previous retrospective study we established criteria for detection of significant aorto-iliac occlusive disease. These criteria were used in a prospective way in this study. Twenty-seven extremities were subjected to a proximal and 23 extremities to a distal reconstruction. The half-year postoperative results were evaluated. The criteria used were 86 per cent sensitive, 100 per cent specific and 93 per cent accurate in relation to predicting the postoperative haemodynamic result. The positive predictive value was 100 per cent and the negative predictive value 89 per cent. The criteria are presented and compared with data from the literature. It is concluded that FAP studies are a simple and excellent way to assess the aorto-iliac segment and to predict the outcome of a reconstruction in multilevel arterial occlusive disease.

Prospective assessment of the aorto-iliac segment by visual interpretation of frequency analysed Doppler waveforms--a comparison with arteriography

In a group of 83 patients the prospective Doppler assessment of disease in the aorto-iliac segment, obtained from visual interpretation of the frequency analysed Doppler waveforms, is compared with subsequent arteriographic findings. The Doppler technique proved to be particularly accurate in the severely diseased vessels (sensitivity 87%, specificity 88%) but tended to underestimate the extent of the minimal/moderate disease.

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.

Spectral analysis of doppler ultrasound: its clinical application in lower limb ischaemia

Twenty-nine patients with symptomatic lower limb ischaemia were studied using a continuous wave Doppler ultrasound spectrum analyser. Frequency spectra were recorded from the peripheral arteries to determine the pulsatility index, damping factor and pulse wave transit time, and the results were related to arteriography.

In the aortofemoral segment, the pulsatility index at the common femoral artery decreased significantly with increasing stenosis, but the transit time was only prolonged with total occlusion. In the femoropopliteal segment there were significant differences in all parameters between each grade of stenosis. Accurate Doppler and radiological assessments of the calf vessels were possible in only 31 limbs; ultrasound did not enable differentiation between patent and occluded vessels.

The pulsatility index at the common femoral artery may be helpful in detecting aortofemoral disease, and accurate assessment of the femoropopliteal segment is possible, but spectral analysis is of no value in assessing the calf vessels.