Some failings of pulsatility index and damping factor

Pulsatility index (PI) is a commonly used method of objective assessment of the Doppler waveform. PI falls with increasing proximal stenosis and is raised by increasing peripheral resistance. Damping factor (DF) for an arterial segment is calculated by dividing the proximal by the distal PI. DF rises with increasing severity of disease of the arterial segment. DF is not, however, sufficiently accurate to be used alone but is usually combined with transit time measurements to provide information of diagnostic use. Both PI and DF have been examined in a canine model of combined segment disease. With increasing stenosis, distal PI falls as expected but so also does proximal PI. Such a stenosis is, in effect, a flow-throttling resistance so that although the characteristics of blood flow are altered by its presence, similar changes are observed both above and below the stenosis. The reduction of PI by a stenosis distal to the insonation site may result in the false interpretation of a low PI as indicating disease proximal to the insonation site. The observed similarity between PI proximal and distal to a stenosis reduces the usefulness of pulsatility index damping factor, particularly in the assessment of the femoro-popliteal segment in combined segment disease.     

Doppler evaluation of fetal hemodynamics

Human umbilical hemodynamics was investigated in 27 pregnant patients with gestational ages from 29 to 43 weeks using a pulsed Doppler flowmeter. The signals were analyzed by Fast Fourier Transform using a minicomputer. Coherent averaging of the signals, along with the computation of maximum velocity, mean velocity and the first moment of Fourier spectra about the zero frequency axis were performed. Hemodynamic indices were measured utilizing a comprehensive feature characterization technique of the blood flow velocity waveform. It was observed that coherent averaging reduced spectral variance thus relatively simplifying the analyses. The Pulsatility Index based on the first moment of the Fourier spectra indicated a higher umbilical flow change during the fetal cardiac cycle, than that predicted by the peak velocity Pulsatility Index. We also observed a high Pulsatility Index in association with three cases of oligohydramnios indicating the possibility of an elevated placental circulatory impedance. Variation in the peak velocity up to 20% was also noted with fetal breathing movements. Further studies are necessary to determine the clinical relevance of these findings.     

Physiological interpretation of Doppler-shift waveforms-II. Validation of the laplace transform method for characterisation of the common femoral blood-velocity/time waveform

The blood-velocity/time waveform over the cardiac cycle from the common femoral artery is investigated using Fourier transform and curve-fitting techniques. This results in a third order Laplace transform whose coefficients can be related to distal impedance, proximal lumen diameter and elastic modulus. The validity of the method is investigated by determining the coefficients of the Laplace transform, derived from the common femoral waveform, and from these values, reconstructing the waveform and comparing with the original. The Fourier transform, curve fitting, and reconstruction procedures are shown for each waveform so that all stages of the method can be critically assessed.     

Quantitative assessment of the common femoral to popliteal arterial segment using continuous wave Doppler ultrasound

The common femoral to popliteal segments of 123 patients with radiologically confirmed arterial disease have been compared with those of 43 volunteers apparently free from disease. The comparisons have been based upon parameters derived from Doppler-shifted, continuous wave ultrasound.Simultaneous recordings of the Doppler signal were made from over the common femoral artery and the popliteal artery; these were analyzed subsequently to reveal variations of maximum frequency with time. Fifteen parameters were obtained from each segment. Of these the Pulsatility Index (P.I.) the Damping Factor(Δ), the pulse wave transit time(TT) the rise time ratio(RTR) from each segment were examined in detail. The Doppler results from the patient groups were compared also with the findings from arteriography.On the basis of these comparisons it was found that the RTR was simpler to measure than other more commonly used parameters such as Pulsatility Index and at least as sensitive for the differentiation between severe arterial disease and the mildly affected or normal state. However, none of these parameters was sufficiently sensitive to distinguish between mild to moderate disease and normal.     

Transcutaneous detection of subcritical arterial stenoses by Doppler signal spectrum analysis.

Early clinical studies showed significant data overlap when Doppler signal spectral analysis was used to differentiate normal carotid vessels from those with slight stenoses. A canine common carotid model has been used to study the ability of spectral analysis to detect subcritical stenoses, i.e., those with 20 to 50 per cent diameter reductions. Using the ratio of peak systolic frequency at the stenosis site to that proximal to the stenosis, significant differences from controls were found for all degrees of stenosis. The mean peak frequency ratio was 1.15 +/- 0.05 for 20 per cent stenoses, increasing to 1.68 +/- 0.50 for 50 per cent stenoses. The peak frequency ratios for Doppler signal spectra recorded from a site 1 cm distal to the stenosis exceeded control values only for 40 and 50 per cent stenoses; at a site 3 cm from the stenosis no spectra were significantly different from controls. Spectral analysis can be a direct, sensitive method to evaluate slight carotid arterial stenoses, but careful examination technique is necessary and Doppler signals must be taken from the stenotic site itself.     

Detection of renal artery stenosis: experimental and clinical analysis of velocity waveforms

Mass screening of hypertensive patients by a noninvasive method could uncover the 10% of those cases where renal artery stenosis is the primary etiology. Treatment by transluminal angioplasty or surgery could replace a long-term medical regimen. To investigate an ultrasonic technique, normal velocity waveforms were obtained from the abdominal aorta, celiac artery and renal arteries in seven mongrel dogs using a 5 MHz, continuous-wave Doppler detector. Renal artery pressure gradients, volume flow rates and velocity recordings were subsequently made during induced proximal renal artery stenoses. The ratio of peak renal artery frequency to peak aortic frequency was 88% sensitive to stenoses of greater than 20 mm Hg pressure gradient, while the renal artery systolic frequency window was 79% sensitive to the same obstructions. Ninety-five hypertensive and vascular surgical patients were examined using a 3 MHz duplex scanner with 175 of the 190 (92%) renal arteries adequately detected (clear signal with high diastolic component). Analysis of velocity waveforms based on peak frequency, proximal to distal peak frequency changes, evidence of flow disturbances and associated bruit were compared to contrast arteriograms in 84 vessels. Of the 76 (90%) arteries adequately examined by duplex scanning, 59 of 61 (97%) with 0-59% diameter reduction, 10 of 12 (83%) with 60-99% diameter reduction and 1 of 3 (33%) occlusions were correctly identified. Velocity waveform analysis can accurately detect renal artery stenosis and may prove effective in mass screening of hypertensive patients for renovascular disease.     

Echocardiographic evaluation of aorto-iliac occlusive disease

Several studies demonstrated feasibility of visual assessment of the common femoral artery Doppler waveform, in an indirect evaluation of aorto-iliac segment stenosis. Patients with cardiac diseases referred for echocardiography often have coexistent arterial pathology. Since many of them are potential candidates for endovascular procedures, we decided to study, whether echocardiography can be useful for detection of aorto-iliac occlusive disease. We evaluated 92 patients with abdominal aortic aneurysm or peripheral artery occlusive disease, referred from the vascular surgery department for cardiac evaluation before surgery. At the end of an echocardiographic examination, evaluation of flow in the distal external iliac arteries with an echocardiographic probe was performed. The Doppler waveform was classified into normal-with early diastolic flow reversal or abnormal-without early diastolic flow reversal. Echocardiographic results were compared in a blinded fashion with reports from computed tomography angiography. Overall there were 58 iliac segments with significant (≥70%) area stenosis or occlusion and 126 iliac segments without significant disease on computed tomography angiography. Abnormal Doppler waveform was found in 56 out of 58 abnormal iliac segments-sensitivity 97%, and normal waveform was found in 106 out of 126 normal iliac segments-specificity 84%. Positive predictive value of abnormal Doppler waveform for significant iliac disease was 74%, and negative predicting value was 98%. Detection of significant stenoses in aorto-iliac segments is feasible with echocardiography. Further studies are necessary to evaluate its potential utility in a population of patients with cardiac disease referred for echocardiographic study.     

High-frequency ultrasound for in vivo measurement of colon wall thickness in mice

Mouse models are becoming increasingly important in the study of molecular mechanisms of colorectal disease and in the development of novel therapeutics. To enhance this phase of preclinical research, cost-effective, easy to use noninvasive imaging is required to detect and monitor changes in the colon wall associated with disease pathology. This study investigated the feasibility of using 40-MHz (high frequency) B-mode ultrasound (HF-US) to image the normal mouse colon and measure its thickness in vivo by establishing a robust imaging protocol and conducting a blinded comparison of colon wall thickness (CWT) measurement between and within operators. The in vivo and ex vivo appearance of mouse colon under HF-US revealed distinct patterns. Colon wall thickness was reproducibly and accurately measured using HF-US compared with histology measurement. The technique was more sensitive in detecting changes in CWT in distal than proximal colon as it showed the highest level of inter- and intraoperator reproducibility. Using the protocol described, it is possible to detect changes in thickness of 0.09 mm and 0.25 mm in distal and proximal colon, respectively. In conclusion, HF-US provides an easy to use and noninvasive method to perform anatomical investigations of mouse colon and to monitor changes in CWT.     

猪腹主动脉下端及髂总动脉不同程度狭窄引起股总动脉血流动力学变化的比较

目的 探讨腹主动脉下端、髂总动脉不同程度狭窄引起股总动脉血流动力学变化的差异.方法 幼年家猪6只,利用血管夹夹闭腹主动脉下端、左侧髂总动脉侧壁依次造成1/3、1/2、3/4管腔狭窄,记录对应股总动脉血流频谱波形,测算PSV、Vmin、S/D、D/S.分析所有实验数据并进行统计学处理,观察血流参数与狭窄程度的相关性,并比较腹主动脉下端、髂总动脉相同程度狭窄引起股总动脉血流动力学变化的差异.结果 超过1/2管腔狭窄时反向波消失,出现持续正向波.PSV与狭窄程度呈线性负相关,D/S在管腔狭窄超过1/3后与狭窄程度呈线性正相关.左侧髂总动脉狭窄时,右侧股总动脉血流参数无显著性变化.髂总动脉狭窄较同等程度腹主动脉狭窄引起股总动脉血流动力学改变显著.结论 根据一侧股总动脉血流频谱波形的改变可以推断其上游存在狭窄性病变和反应狭窄下游有效循环血容量的情况,离心脏越远处的分支动脉管腔狭窄引起其下游血流动力学改变越显著.     

Quantitative angiographic follow-up studies on the development of coronary artery disease: which coronary segments should be analyzed?

Angiographic follow-up studies on the evolution of coronary artery disease are of increasing relevance. It has still to be evaluated which coronary segments are predominantly involved in the process of atherosclerosis and, thus, should be preferably included in the analysis. Therefore, the correlation of progression and regression of coronary disease with the diameter and location (proximal, mid or distal) of coronary segments was investigated from the data of the INTACT-study, in which 25 different coronary segments were defined including anatomic variants of rather distal segments. In 348 patients with coronary artery disease, standardized coronary angiograms were repeated within 3 years and were quantitatively analyzed (CAAS). In 1063 coronary stenoses (% diameter stenosis > 20%) compared from both angiograms, progression and regression were not influenced by diameter nor location of arterial segments. In the follow-up angiograms, the number of new lesions (stenoses and occlusions) per coronary segment differed with regard to segment diameter (> 3 mm: 64/1125 (6%); 2–3 mm: 139/1967 (7%);<2 mm: 44/1756 (2%); p<0.001) and location of segments (proximal: 86/1285 (7%); mid: 84/1193 (7%); distal: 77/2370 (3%); p<0.001). Out of 77 distal new lesions, only 25 (32%) were found in segments<2 mm in diameter. Since the absolute number of new lesions was high in distal coronary segments, but low in segments with diameters<2 mm, angiographic follow-up studies should analyze coronary segments at any location, but may neglect segments with diameters smaller than 2 mm.     

Validation of a non-invasive method for localization of atherosclerotic occlusive disease in the legs

Summary. The accuracy in determining the level of haemodynamically significant occlusive arterial disease (stenosis of ≥50%) in the leg by a combination of segmental blood pressure measurements and evaluation of pulses with the Doppler shift technique was assessed in 50 patients (100 legs), using angiography as the reference method. For aorto-iliac disease the sensitivity was 72%, the specificity 97% and the diagnostic accuracy 87%. For femoro-popliteal disease the corresponding figures were 87%, 78% and 85%, respectively. The accuracy of a positive diagnosis was 93% for both levels. Similar results were obtained for combined aorto-iliac and femoro-popliteal disease. The accuracy in detecting calf disease was poor.     

Response of left ventricular myocardial perfusion and cavity size to beta-blockade by acebutolol.

The effect of beta-blockade by acebutolol on global and regional myocardial perfusion (133Xenon wash-out) was studied in 10 patients with coronary artery disease. Another group of 10 similar patients was used to study the effect of acebutolol on left ventricular cavity size (metal markers--spot film camera). Global perfusion responses roughly paralleled the changes in rate-pressure variable which decreased in 8 patients and increased in 2 who had spontaneous angina pectoris. Regional perfusion decreased more in areas distal to less than 75% stenoses than in those distal to less than 75% stenoses (29 vs 12%; p = 0.10 less than 0.20). Left ventricular asynergy did not modify the response, nor did the presence or absence of collateral vessels. No evidence was found to support the thesis that beta-blockade may evoke a redistribution in perfusion which favours the potentially ischaemic areas of myocardium. Left ventricular cavity size remained unchanged after acebutolol, a cardioselective beta-blocking compound with some degree of agonist activity.     

Potential intrinsic error of noninvasive coronary angiography.

PURPOSE: With current noninvasive techniques compromises have to be accepted for coronary imaging, e.g., partial coverage of the coronary artery tree. The aim of the study was to estimate the potential intrinsic error of partial coverage from a database of invasive angiograms. METHODS AND RESULTS: The localization and severity of coronary artery stenoses and, if percutaneous coronary intervention (PCI) was performed, the balloon and stent size were extracted from a large database of 21,335 selective coronary angiograms. Of stenoses with >50% diameter reduction, 31.4% were located in distal segments and minor side branches, constituting 28.8% of interventional treatment. In 5% of patients undergoing their first invasive angiogram, the most proximal relevant stenosis was found in a distal segment or minor side branch. Most interventions (83.5%) were performed in main coronary artery segments. CONCLUSION: Coronary artery stenoses were found and interventional treatment performed in all coronary segments. Therefore, noninvasive coronary imaging of only proximal and medial segments and major side branches is an inadequate strategy for complete diagnosis or as a guide to therapeutic decisions. However, the currently available noninvasive techniques allow the detection of relevant stenoses in 95% of patients with suspected coronary artery disease (CAD) to prepare for further invasive diagnostic and therapeutic planning.     

The Effect of Shock Configuration and Delivered Energy on Defibrillation Impedance

Shock impedance is an important determinant of defibrillation efficacy. Lead configuration, shock polarity, and delivered energy can affect shock impedance, but these variables have not been studied in active can lead systems. The present study was a prospective evaluation of 25 patients undergoing initial transvenous defibrillator implantation. In all patients, a dual coil lead and pectoral emulator were placed and three lead configurations were tested in random order: Lead (distal to proximal coil), unipolar (distal coil to can), and triad (distal coil to can + proximal coil). Shock energies of 0.1- to 15-J shock were evaluated. Impedance increased a mean of 21% as delivered energy was decreased (P < 0.001), an effect independent of lead configuration. At all delivered energies, impedances in the unipolar configuration were about 40% higher than triad, while the lead configuration was about 20% higher than triad (ps < 0.001). Polarity did not affect impedance. These results indicate that transvenous lead configurations and delivered energy, but not polarity, significantly influence shock impedance. The magnitude of the increase of impedance at low energies is independent of the shocking pathway. This effect has important implications for low energy shocks used to terminate atrial fibrillation or ventricular tachycardia.     

Review of the assessment of single level and multilevel arterial occlusive disease in lower limbs by duplex ultrasound.

The purpose of this article is to review the performance of duplex ultrasound scanning in assessing lower limb arterial disease with emphasis on patients with multisegmental occlusive lesions. Several studies have reported that duplex scanning can be as accurate as angiography to localize arterial stenoses. In spite of these promising results, there still remain some difficulties and controversies. Among them, it has been reported that multisegmental disease may affect the accuracy of duplex scanning. Indeed, some studies have indicated a lower sensitivity for detecting significant stenoses distal to severe or total occlusions. It also was demonstrated that second-order stenoses were detected with lower sensitivity compared to first-order stenoses. The main reason proposed to explain this lower sensitivity is that the highly reduced flow distal to occluded or highly stenotic segments increases the difficulty of detecting significant Doppler velocity changes in the distal or secondary stenoses. The intrinsic limitations of the peak systolic velocity ratio used as a classification criterion are presented. Finally, new and promising developments in power Doppler imaging and ultrasound contrast agents are discussed, because they may allow expansion of the capabilities of current ultrasound scanning systems and provide more accurate diagnosis of patients with multiple disease.     

Physiological interpretation of Doppler shift waveforms: The femorodistal segment in combined disease

A new method is presented for assessing the femorodistal segment in multisegmental arterial disease, using the Laplace transform technique of Doppler waveform analysis.Blood velocity/time waveforms were obtained at femoral and ankle levels in three groups of limbs—50 without arterial disease, 12 with isolated aortoiliac stenoses, and 32 with femoropopliteal occlusions, with and without proximal disease. The waveforms were analyzed for Laplace transform and pulsatility index values.The ω₀ coefficients of the Laplace transform analysis at femoral and ankle levels were compared in each subject, as the ω₀ gradient (femoral/ankle ω₀): and pulsatility index damping factor (femoral/ankle Pl) was also calculated. The ω₀ gradient was shown to detect femoropopliteal occlusion in the presence of multisegmental arterial disease and to give some indication of its haemodynamic significance. The diagnostic accuracy of the ω₀ gradient was superior to that of pulsatility index damping factor.When combined with its existing ability to detect aortoiliac stenosis, this new application of the Laplace transform method offers the possibility both of a system for complete localisation of significant arterial lesions, and potential for follow-up of vascular surgical procedures in the lower limb, from two simple Doppler recordings.     

Changes in Doppler waveforms can predict pressure reduction across internal carotid artery stenoses

Cerebral ischemia can result from either embolism or be due to hemodynamic failure. The purpose of this study was to evaluate whether Doppler waveforms, obtained distal to an internal carotid artery (ICA) stenosis, could predict the degree of hemodynamic compromise in terms of reduction in cerebral perfusion pressure. Forty-nine patients were examined consecutively with ultrasound Doppler prior to carotid endarterectomy. Pulsatility index (PI), pulse rise-time (RT), and systolic width (SW) were related to angiographic degree of stenosis and the ratio of distal ICA blood pressure to common carotid artery (CCA) blood pressure (ICA/CCA pressure ratio). The latter was determined during surgery. All three waveform parameters were significantly correlated with the ICA/CCA pressure ratio when calculated from the mean frequency curve (p less than 0.001). A reduction in ICA pressure of 20% could be predicted with an accuracy of 90-95%. Correlating the waveform parameters with arteriography was less convincing, reaching the level of statistical significance for PI only. ICA Doppler waveforms, obtained as distal in the neck as possible can accurately predict the degree of hemodynamic compromise. It is recommended as a simple adjunct to routine Doppler evaluation of carotid stenoses.     

A Definition of Proximal and Distal Tubular Compliance: PRACTICAL AND THEORETICAL IMPLICATIONS

Micropuncture studies were carried out in the rat to evaluate the in situ distensibility characteristics of the proximal and distal tubules under a variety of experimental conditions. In the first phase, we determined the response of tubular diameter (D) to changes in tubular pressure (P) induced by partially obstructing single tubules. The response observed under these conditions (i.e., when interstitial pressure is presumed to be constant) has been defined as the compliance of the tubule. Over the range of tubular pressures studied (10-35 mm Hg for the proximal tubule, 5-25 mm Hg for the distal tubule) the compliance characteristics of the proximal and distal tubule were found to be markedly different; the proximal tubular pressure-diameter relationship was linear, DeltaD/DeltaP = 0.45 mum/mm Hg, whereas the distal pressure-diameter relationship was curvilinear, DeltaD/DeltaP = c(-0.1xP+2.2).In the second phase we used the compliance data to construct a series of theoretical pressure-diameter curves that define the response of the tubule to increments in interstitial as well as intratubular pressure. These curves indicate that changes in distal diameter should provide a sensitive index of a rise in interstitial pressure under conditions in which the transtubular pressure gradient is increased by a small amount, but that proximal diameter should provide a more sensitive index of changes in interstitial pressure when the transtubular pressure gradient is increased by a large amount. In subsequent experiments in which furosemide was administered, we observed that the pressure-diameter relationships for both the proximal and distal tubule were indistinguishable from the compliance curves, a finding consistent with the interpretation that interstitial pressure was not appreciably changed from control. By contrast, when mannitol was administered, both proximal and distal tubular pressure-diameter relationships were significantly altered in a fashion consistent with a large increase in interstitial pressure. Neither with furosemide nor mannitol administration did it appear likely that significant changes in tubular compliance could account for the observed behavior of the tubule.Finally, we propose that a knowledge of tubular compliance will be useful in exploring the interrelationships between tubular and peritubular pressures, tubular anatomy, and transtubular ionic permeability. Recent studies linking changes in the geometry of lateral intercellular spaces of the tubule to changes in passive ion movement suggest that an investigation of such anatomical-functional correlates should be productive.     

LaPlace transform analysis of femoral artery Doppler signals: the state of the art

A followup study was conducted to validate our previous experience with the LaPlace Transform Analysis (LTA) method for processing Doppler ultrasound signals from the common femoral artery to detect significant stenosis of the aorto-iliac segment. The first phase used the same instantaneous mean velocity signal processor as used in the prior study. A comparison of the Doppler examinations with angiograms in 98 legs yielded a sensitivity = 92% and sensitivity = 94% in the identification of 50% or greater stenosis of the aorta-iliac segment, results almost identical to the last study. Because of theoretical disadvantages of using the instantaneous mean velocity signal we carried out a second phase using a peak velocity detector. In 148 limbs sensitivity = 87% and specificity = 98%. The presence or absence of superficial femoral artery occlusion did not affect the accuracy of the waveform analysis in the detection of proximal disease. The LTA parameter related to distal resistance, G, was not found to have clinical value in the assessment of the femoral-popliteal segment.     

Artificial neural network analysis of common femoral artery Doppler shift signals: classification of proximal disease.

The aim of this study was to apply artificial neural networks (ANNs) to the problem of the diagnosis of aorto-iliac arterial disease on the basis of the profile of the common femoral artery (CFA) Doppler flow velocity waveform. The maximum frequency envelopes obtained from the CFA of 180 subjects were used to create sets of training and testing vectors for a back-propagation ANN. The ANN had three outputs: one representing the absence of significant aorto-iliac disease (i.e., < 50% diameter stenosis), one representing the presence of a hemodynamically significant aorto-iliac stenosis (i.e., 50-99% stenosis), and the other representing the presence of an aorto-iliac occlusion. After training, the ANN correctly classified 80% of "no significant disease" testing data, 45% of "significant stenosis" data and 85% of "occlusion" data. This work, thus, demonstrated the ability of an ANN to identify the severity of aorto-iliac disease from the CFA waveform. Although the ANN outperformed standard univariate methods and visual classification of the data, it would appear that further work is needed to increase the accuracy of the ANN to a clinically acceptable standard.