- Email: [email protected]
Laser Doppler anemometer measurements of pulsatile flow in a model carotid bifurcation
Volume 7 Number 5 1May 1988
Abstracts 723
treatment only. The parameters were studied three times over a 3-month interval. In the unoperated patients the clinical score improved, paralleled by favorable changes in the EEG. However, this was no concomitant increase in cerebral blood flow. In patients undergoing extracranialintracranial (EC-IC) bypasses, there was deterioration of the clinical states after surgery but eventual improvement. ECG parameters did not change significantly and there was no increase in cerebral blood flow. In the group of patients undergoing carotid endarterectomy, there was a significant improvement in the patient’s clinical status, although it worsened shortly after the operative procedure. There was no change in the EEG nor in cerebral blood flow. In all cases cerebral blood flow varied between 100% and 96%. Unfortunately this study has several serious flaws. First, the three groups of patients are not comparable. The patients undergoing medical management have a clinical status score of 12.9 compared with 6.3 in the group of patients undergoing EC-IC bypass and with 2.4 in patients undergoing carotid endarterectomy. The reason for this difference is not clearly defined in the material and methods section. Second, the definition of stroke is also not clear. In half of these patients the defect was reversible; it was a transient ischemic attack or a reversible ischemic neurologic deficit. In addition, the interval between the first study and the stroke varied between 23.6 days in the medically treated group to 73.7 days in the EC-IC group to 65.2 days in the carotid endarterectomy group. The authors attempt to minimize this difference by statistically comparing the findings. They found no correlation between the time of the first study and the interval mentioned. For this reason, they deem it acceptable to compare the results of the EEG of the operated and unoperated patients. It should be pointed out that they did not correlate the EEG parameter nor the cerebral blood flow to the clinical status, which was certainly worse in the medically treated group. In addition, there is no attempt to correlate the angiographic tindings of these patients and their subsequent course. It is not surprising that in a patient with an ulcerative plaque and an embolic stroke, the cerebral blood flow would not necessarily increase. Why were the 51 patients not operated on? Was their anatomy different from that of the remaining patients who either had EC-IC bypass or carotid endarterectomy? Finally, the control group did not undergo any anesthetic manipulation, which may play an important role in the perioperative deterioration. Their operative mortality and morbidity data were not described. William Pearce, M.D. University of Colovado
Health
Sciences Center
Acute peripheral arterial occlusion associated with surgery for gynecologic cancer Townsend PA, Hutson DG, Lovecchio J, Averete HE. Gynecol Oncol 1986;25:108-14. One of the most challenging vascular traumas encountered by the general vascular surgeon is iatrogenic throm-
bosis or hemorrhage that occurs during operative procedures. This article describes four cases of acute lower extremity arterial occlusion associated with surgical therapy for gynecologic cancer. Although few articles have examined this subject, acute arterial thrombosis is not a rare occurrence in patients being treated for pelvic neoplasms. The importance of this article is its attempt to identify the etiologic factors leading to such thrombosis and to recommend a preventive management plan. Several factors characterized acute arterial occlusion in these patients. First, the problem occurred after some operative manipulation near the iliac arteries (e.g., periaortic and pelvic lymphadenectomy or ureteral dissection adjacent to the iliac arteries). Second, the occlusion usually involved the common and external iliac arteries. Occasionally, thrombus propagated proximally into the aorta or embolized distally to the lower leg. Third, the problem was generally recognized cr$& the operation in the recovery area or several days later. Lower limb pain, coolness, and no pulses were typical. Finally, most patients had some underlying predisposition to arterial thrombosis, such as aortoiliac arteriosclerosis or usage of oral contraceptives. Alleviation of the acute ischemia required thromboembolectomy and, in some cases, arterial reconstruction. Retrograde transfemoral theomboembolectomy with the Fogarty catheter sufficed if iliac artery thrombosis was not associated with significant atherosclerotic disease. However, advanced aortoiliac atherosclerosis required local endarterectomy or grafting to prevent recurrent thrombosis. Heparinization or antiplatelet drugs were used in most situations. Limb salvage was achieved in each case although chronic claudication continued in one of four patients. In conclusion, the authors recommended that gynecologic surgeons should screen their patients more carefully for symptoms or physical signs of underlying aortoiliac atherosclerosis. Pulse status should be documented preoperatively and lower limb pulses should be checked before closing the abdomen and leaving the operating room. Operative manipulation of arteries, particularly if sclerotic, should be minimized. Whether prophylactic heparin or antiplatelet drugs should be used in such patients is discussed but remains controversial. John W. Hallett, Mayo Clinic
Jr., M.D.
Laser Doppler anemomleter measurements of pulsatile flow in a model carotid bifurcation Ku DN, Giddens DP. J Biomech 1987;20:407-21. Hemodynamic factors related to low wall shear stress resulting from alterations in normal iaminar flow patterns have been postulated to play a pathogenetic role in the asymmetric development of atherosclerotic plaques at the carotid bifurcation. In this study a scale model of the normal carotid bifurcation was used to investigate flow velocity patterns that may be related to disease localization. A rigid bifurcation model was modified to include a
Jourd of VASCULAR SURGERY
724 .Abstvacts
compressible tube in the external carotid (ECA) outflow circuit. By embedding the tube in a pressurechamber, flow in the ECA could be varied through the pulse cycle, approximating the in vivo situation in which ECA flow is markedly reduced in diastole compared with that of the internal carotid artery (ICA). A pulsatile pump programmed to approximate a common carotid (CCA) waveform was used to propel the water-glycerine fluid, with silicon-carbide particles introduced as scatterers. Flow velocity information was obtained with a laser Doppler anemometer with signalsprocessedon a Fourier analyzer.Digitized signal data were ensemble-averaged over 10 pulse wave cycles,yielding data from planes parallel and perpendicular to the plane of the bifurcation. Velocity, wall shear stress, and flow disturbances in the CCA, carotid sinus, ECA, and ICA were assessed. CCA flow was determined to be laminar and symmetric with a blunt velocity profile during systole.Moderate shear stresswith relatively little flow disturbance was noted. Flow patterns in the sinus were complex-related in part to varying flow division between the ECA and ICA. High velocities were evident in both vesselsalong the flow divider with resultant high shear stress(mean 26 dynes/cm2). Little flow reversalwas evident. This pattern was maintained into the distal ICA as velocity is maintained related to a reduction in luminal area. In the sinus at the wall opposite the divider, lower velocitieswith systolicflow reversalwere
identified along with helical flow patterns. Wall shear was correspondingly reduced at this location (mean 0.5 dynes/cm2), oscillating from positive (9 dynes/ cmZ) to negative ( - 13 dynes/cm”) values.Flow disturbance in this model of the normal sinus was slight and occurred primarily in the deceleration phase of systole and in early diastole. The authors point out that in this pulsatile setting flow separation did not occur in early systole,unlike steady flow models, but in late systole the separation region was more than 50% larger than in steady flow. Lower shear stressat both inner and outer walls was also a feature of pulsatile compared with steady flow. They conclude that areas of bifnrcation in which intimal thickening appears to begin and where atherosclerotic plaques initially develop correlate with regions of low mean shear stress and oscillatory flow patterns, whereas regions of high wall shear stress tend to be delayed in the development of intimal disease. Disturbed flow did not appear to be a prominent feature of flow at the vesselwall and probably is not related to plaque initiation. However, because late systolic and diastolic flow disturbances were noted in this normal model, the authors questioned the accuracy of diagnosis of small carotid plaques on the basis of noninvasive detection of flow disturbance alone with Doppler ultrasound. Willianz M. Black&ear, Jr., MD. University of South Flotida Collefle of Medicine,
Tampa
Abstracts 723
treatment only. The parameters were studied three times over a 3-month interval. In the unoperated patients the clinical score improved, paralleled by favorable changes in the EEG. However, this was no concomitant increase in cerebral blood flow. In patients undergoing extracranialintracranial (EC-IC) bypasses, there was deterioration of the clinical states after surgery but eventual improvement. ECG parameters did not change significantly and there was no increase in cerebral blood flow. In the group of patients undergoing carotid endarterectomy, there was a significant improvement in the patient’s clinical status, although it worsened shortly after the operative procedure. There was no change in the EEG nor in cerebral blood flow. In all cases cerebral blood flow varied between 100% and 96%. Unfortunately this study has several serious flaws. First, the three groups of patients are not comparable. The patients undergoing medical management have a clinical status score of 12.9 compared with 6.3 in the group of patients undergoing EC-IC bypass and with 2.4 in patients undergoing carotid endarterectomy. The reason for this difference is not clearly defined in the material and methods section. Second, the definition of stroke is also not clear. In half of these patients the defect was reversible; it was a transient ischemic attack or a reversible ischemic neurologic deficit. In addition, the interval between the first study and the stroke varied between 23.6 days in the medically treated group to 73.7 days in the EC-IC group to 65.2 days in the carotid endarterectomy group. The authors attempt to minimize this difference by statistically comparing the findings. They found no correlation between the time of the first study and the interval mentioned. For this reason, they deem it acceptable to compare the results of the EEG of the operated and unoperated patients. It should be pointed out that they did not correlate the EEG parameter nor the cerebral blood flow to the clinical status, which was certainly worse in the medically treated group. In addition, there is no attempt to correlate the angiographic tindings of these patients and their subsequent course. It is not surprising that in a patient with an ulcerative plaque and an embolic stroke, the cerebral blood flow would not necessarily increase. Why were the 51 patients not operated on? Was their anatomy different from that of the remaining patients who either had EC-IC bypass or carotid endarterectomy? Finally, the control group did not undergo any anesthetic manipulation, which may play an important role in the perioperative deterioration. Their operative mortality and morbidity data were not described. William Pearce, M.D. University of Colovado
Health
Sciences Center
Acute peripheral arterial occlusion associated with surgery for gynecologic cancer Townsend PA, Hutson DG, Lovecchio J, Averete HE. Gynecol Oncol 1986;25:108-14. One of the most challenging vascular traumas encountered by the general vascular surgeon is iatrogenic throm-
bosis or hemorrhage that occurs during operative procedures. This article describes four cases of acute lower extremity arterial occlusion associated with surgical therapy for gynecologic cancer. Although few articles have examined this subject, acute arterial thrombosis is not a rare occurrence in patients being treated for pelvic neoplasms. The importance of this article is its attempt to identify the etiologic factors leading to such thrombosis and to recommend a preventive management plan. Several factors characterized acute arterial occlusion in these patients. First, the problem occurred after some operative manipulation near the iliac arteries (e.g., periaortic and pelvic lymphadenectomy or ureteral dissection adjacent to the iliac arteries). Second, the occlusion usually involved the common and external iliac arteries. Occasionally, thrombus propagated proximally into the aorta or embolized distally to the lower leg. Third, the problem was generally recognized cr$& the operation in the recovery area or several days later. Lower limb pain, coolness, and no pulses were typical. Finally, most patients had some underlying predisposition to arterial thrombosis, such as aortoiliac arteriosclerosis or usage of oral contraceptives. Alleviation of the acute ischemia required thromboembolectomy and, in some cases, arterial reconstruction. Retrograde transfemoral theomboembolectomy with the Fogarty catheter sufficed if iliac artery thrombosis was not associated with significant atherosclerotic disease. However, advanced aortoiliac atherosclerosis required local endarterectomy or grafting to prevent recurrent thrombosis. Heparinization or antiplatelet drugs were used in most situations. Limb salvage was achieved in each case although chronic claudication continued in one of four patients. In conclusion, the authors recommended that gynecologic surgeons should screen their patients more carefully for symptoms or physical signs of underlying aortoiliac atherosclerosis. Pulse status should be documented preoperatively and lower limb pulses should be checked before closing the abdomen and leaving the operating room. Operative manipulation of arteries, particularly if sclerotic, should be minimized. Whether prophylactic heparin or antiplatelet drugs should be used in such patients is discussed but remains controversial. John W. Hallett, Mayo Clinic
Jr., M.D.
Laser Doppler anemomleter measurements of pulsatile flow in a model carotid bifurcation Ku DN, Giddens DP. J Biomech 1987;20:407-21. Hemodynamic factors related to low wall shear stress resulting from alterations in normal iaminar flow patterns have been postulated to play a pathogenetic role in the asymmetric development of atherosclerotic plaques at the carotid bifurcation. In this study a scale model of the normal carotid bifurcation was used to investigate flow velocity patterns that may be related to disease localization. A rigid bifurcation model was modified to include a
Jourd of VASCULAR SURGERY
724 .Abstvacts
compressible tube in the external carotid (ECA) outflow circuit. By embedding the tube in a pressurechamber, flow in the ECA could be varied through the pulse cycle, approximating the in vivo situation in which ECA flow is markedly reduced in diastole compared with that of the internal carotid artery (ICA). A pulsatile pump programmed to approximate a common carotid (CCA) waveform was used to propel the water-glycerine fluid, with silicon-carbide particles introduced as scatterers. Flow velocity information was obtained with a laser Doppler anemometer with signalsprocessedon a Fourier analyzer.Digitized signal data were ensemble-averaged over 10 pulse wave cycles,yielding data from planes parallel and perpendicular to the plane of the bifurcation. Velocity, wall shear stress, and flow disturbances in the CCA, carotid sinus, ECA, and ICA were assessed. CCA flow was determined to be laminar and symmetric with a blunt velocity profile during systole.Moderate shear stresswith relatively little flow disturbance was noted. Flow patterns in the sinus were complex-related in part to varying flow division between the ECA and ICA. High velocities were evident in both vesselsalong the flow divider with resultant high shear stress(mean 26 dynes/cm2). Little flow reversalwas evident. This pattern was maintained into the distal ICA as velocity is maintained related to a reduction in luminal area. In the sinus at the wall opposite the divider, lower velocitieswith systolicflow reversalwere
identified along with helical flow patterns. Wall shear was correspondingly reduced at this location (mean 0.5 dynes/cm2), oscillating from positive (9 dynes/ cmZ) to negative ( - 13 dynes/cm”) values.Flow disturbance in this model of the normal sinus was slight and occurred primarily in the deceleration phase of systole and in early diastole. The authors point out that in this pulsatile setting flow separation did not occur in early systole,unlike steady flow models, but in late systole the separation region was more than 50% larger than in steady flow. Lower shear stressat both inner and outer walls was also a feature of pulsatile compared with steady flow. They conclude that areas of bifnrcation in which intimal thickening appears to begin and where atherosclerotic plaques initially develop correlate with regions of low mean shear stress and oscillatory flow patterns, whereas regions of high wall shear stress tend to be delayed in the development of intimal disease. Disturbed flow did not appear to be a prominent feature of flow at the vesselwall and probably is not related to plaque initiation. However, because late systolic and diastolic flow disturbances were noted in this normal model, the authors questioned the accuracy of diagnosis of small carotid plaques on the basis of noninvasive detection of flow disturbance alone with Doppler ultrasound. Willianz M. Black&ear, Jr., MD. University of South Flotida Collefle of Medicine,
Tampa