Electronic measurement of blood flow

Duplex scanning for the intraoperative assessment of infrainguinal arterial reconstruction: a useful tool?

Duplex scan, arteriography, and graft flow rates were used intraoperatively to assess 56 infrainguinal arterial reconstructions for technical error. Intraoperative duplex scan identified a technical defect or low graft flow velocity in 22 of 56 (39%) grafts. Eleven of the defects were judged to be clinically significant and were corrected. Four of these defects were missed by the completion arteriogram. One technical defect identified by completion arteriography was missed by duplex scan. Fifty percent (5/10) of grafts with an abnormal intraoperative duplex scan which were not corrected occluded within 30 days. Graft flow rates measured by the electromagnetic flowmeter were neither predictive of technical defect nor early graft outcome. Although the sensitivity of arteriography and duplex scan (88% sensitivity for both) were both high for predicting early graft occlusion, the combination of duplex scan and completion arteriography was significantly more accurate (p less than .0001) in predicting early graft outcome than either study alone. Duplex scan identified significant graft defects which were not detected by completion arteriography or graft flow rate measurement. The duplex scan also provided hemodynamic information which was predictive of early graft outcome. The duplex scan can be an important adjunct to completion arteriography for the intraoperative assessment of infrainguinal arterial reconstruction.

Hemodynamic effects in dogs of nitrous oxide-meperidine and meperidine, respectively, in comparison with nitrous oxide

The aim of this investigation on dogs, was to examine the hemodynamic effects of nitrous oxide (N2O) plus meperidine and of meperidine with room air ventilation, respectively, compared with those of N2O on its own. When meperidine (bolus dose 3 mg.kg-1 and continued infusion 4 mg.kg-1.h-1) was added to 80% N2O, mean arterial blood pressure fell from about 20 to 10 kPa (150 to 75 mmHg), as a result of a decrease in peripheral vascular resistance, but no compensatory changes in cardiac output were seen. When N2O was withdrawn, during continued meperidine infusion, cardiac output and stroke volume increased, while peripheral resistance remained low. Coronary vasodilation was noted when meperidine was added to N2O, and persisted when N2O was withdrawn. In the pulmonary circulation a different response was found. Here, no effects were observed when meperidine was added to N2O, while pressure and resistance decreased when N2O was withdrawn and meperidine continued.

Intraoperative use of ultrasound in arterial surgery

Technical perfection is the goal of any arterial reconstruction so as to avoid postoperative complications. Experimental and clinical studies have clearly shown that these operations are imperfect and that some form of intraoperative surveillance is required to decrease the incidence of correctable technical defects. Ultrasound technology is uniquely suited for this role. This article describes the distinct advantages of duplex ultrasound for the intraoperative monitoring of vascular reconstructions.

Hypovolemic shock, pancreatic blood flow, and pancreatitis

Electromagnetic blood flow determinations were carried out on the superior pancreatic duodena (SPDA), the splenic (SA) and the superior mesenteric (SMA) arteries and compared to cardiac output (CO, thermodilution technique) in 12 anesthetized dogs submitted to hypovolemic shock of various duration: 5 dogs underwent a one-hour and 7 a three-hour period of shock. A 50 mm Hg level of mean arterial blood pressure (MABP) was maintained throughout hypovolemia. Dogs were then reinfused. Control preshock values were 4.12 l/min for CO, 38.0 ml/min for SPDA, 405.9 ml/min for SA, and 963.6 ml/min for SMA. SPDA, SA and SMA flows expressed as % of CO amounted to 0.9, 9.8 and 23.4% respectively. No significant changes in SPDA and SMA flows were noted within the first hour of shock. However, from the end of the second hour on, both flows differed significantly (P less than 0.01), SMA increasing from -75.6% of its control value at the end of bleeding to -61.0%, and SPDA decreasing from -75.6 to -86.9%. Similar observations were made when respective flows were considered as % of CO. The SA behaved somewhat in an intermediate fashion. This relative spoliation in pancreatic blood supply as hypovolemia proceeds supports an ischemic etiology of acute pancreatitis (AP), which could account for some of the so-called idiopathic cases of AP.

Some immediate hemodynamic consequences of closure of atrial septal defects of the secundum type

The circumclusion method for surgical closure of atrial septal defects (ASDs) of the secundum type makes it possible, during surgery, to close and reopen the defect as desired. In each of 23 patients the following statistically significant pressure and flow changes were found when the ASD was closed: increasing mean pressures in the ascending aorta (from 74 to 87 mm Hg), left atrium (from 10 to 18 mm Hg), and right pulmonary artery (from 20 to 24 mm Hg); increasing mean flows in the ascending aorta (from 84 to 111 ml/min/kg); decreasing mean pressures in the right atrium (from 9.0 to 7.7 mm Hg); and decreasing mean flows in the right pulmonary artery (from 78 to 46 ml/min/kg). Surprisingly, no correlation between shunt size determined before and during surgery was found. However, in the calculation of the intraoperative shunt, several factors might have contributed to an erroneous result. In 17 patients a right heart catheterization was performed in the third to thirteenth postoperative month and the following statistically significant changes from the intraoperative results with closed ASD were found: The intraoperative mean pressure in the left atrium (18 mm Hg) decreased to 7.3 mm Hg after surgery (pulmonary wedge pressure), the pulmonary arterial pressure decreased from 23 to 13 mm Hg, and the right atrial pressure from 8.2 to 1.6 mm Hg.

Factors determining outcome of reversed saphenous vein femoropopliteal bypass grafts

The investigation was designed to study factors that might be of predictive value in femoropopliteal vein bypass grafting. A series of 146 grafts had a cumulative 5-year graft patency of 82.5 per cent. Five-year limb survival rate in salvage cases was 77.9 per cent. These results are encouraging. However, taking certain factors into account, the patency rates varied. In limbs with claudication, the 5-year graft patency rate was significantly higher than in salvage procedures (P < 0.05). Basal and maximal (during pharmacological vasodilatation) intraoperative graft flow rates were also significantly higher in claudicating limbs (P < 0.01). Reconstructions in limbs with a good run-off had better patency and flow rates than in limbs with a poor run-off (P < 0.001). This suggests that progression of distal atherosclerosis is a major factor for late graft thrombosis. The incidence of graft thrombosis was correlated with the flow rates (P < 0.01). Age, the presence of diabetes, graft diameter and the site of the distal anastomosis did not affect patency.

The advantages of the great saphenous vein as a femoropopliteal graft. A report on its clinical use

As a majority of vascular surgeons prefer the autologous saphenous vein as a bypass graft below the inguinal ligament, the need of alternative graft materials or reconstructive techniques is confined to patients with unavailable or unsuitable saphenous veins. The aim of this investigation was to ascertain how often these alternative procedures are necessary. From 1973 to June 1979, the great saphenous vein was used as a femoropopliteal graft without regard to fixed limitations in the diameter and the quality of the vein. During this period, vascular reconstruction was required in 148 limbs due to symptomatic atherosclerotic occlusion of the superficial femoral artery. In 144 of these cases, the ipsilateral (138) or the contralateral (6) great saphenous vein was used for a femoropopliteal bypass reconstruction. Thus, the vein could not be utilized in only 4 of 148 cases (2.7%). As graft patency rate was not subject to the size and quality of the vein and as cumulative patency rates in the 144 grafts were most satisfactory (97.9, 92.0 and 81.9% at 1 month, 1 year and 5 years, respectively), although all these veins were used regardless of their calibre and quality, we conclude that the great saphenous vein can be used more liberally as a graft for femoropopliteal occlusion. In approximately only 3% of patients requiring operation, alternative reconstructive techniques, such as "non-vein" bypass grafts and thrombendarterectomy are needed.

Intra-operative graft blood flow related to failure of femoro-popliteal bypass grafts

The prognostic significance of intra-operative blood flow, as measured by electromagnetic flowmetry, was investigated in 127 limbs, which were operated on with a reversed femoropopliteal saphenous vein bypass graft because of symptomatic atherosclerotic occlusion of the superficial femoral artery. Thromboses occurring in the first postoperative month are defined as early failures and thereafter as late failures. There were three early graft failures. The basal and augmented flow rates during pharmacological vasodilation of these grafts were less than half those of the grafts remaining patent. Eight additional late graft occlusions occurred. Whereas the basal blood flow of these grafts did not differ significantly from that of the grafts which remained patent, the maximal flow rate was significantly lower (p less than 0.05). The overall incidence of graft failure at basal and maximal flow rates of 100 ml/min or less and 150 ml/min or less, respectively, was 35%, while, at higher flow rates, this incidence was reduced to 5% (p less than 0.001). This study emphasizes that intra-operative femoropopliteal vein graft flow provides prognostic indications of graft failure.

LEg venous oxygen saturation in the evaluation of intra-operative blood flow during arterial reconstructive surgery

In twenty-four patients, undergoing a femoro-popliteal saphenous vein bypass graft for symptomatic atherosclerotic occlusion of the superficial femoral artery, oxygen saturation values for the femoral and popliteal veins were compared to the directly measured blood flows in the common femoral artery and in the bypass graft, respectively. Blood flow and venous oxygen saturation increased significantly after transfusion of 900 ml of blood. Pharmacological vasodilation caused a significant increase in blood flow both before and after transfusion, whereas the changes in venous oxygen saturation were significant only before blood transfusion. A close statistical relationship was found between initial femoral venous oxygen saturation and initial blood flow in the common femoral artery as well as between initial popliteal venous oxygen saturation and initial byapss blood flow. However, especially at low saturation values, the evaluation of blood flow was very uncertain. Whole leg and lower leg oxygen uptakes were not altered by intraoperative changes in blood volume. It is concluded that blood flow in the common femoral artery and the bypass graft can be roughly estimated from analysis of oxygen saturation in the femoral and popliteal veins, respectively. Furthermore, by determining leg venous oxygen saturation both before and after flow augmentation, induced by pharmacological vasodilation, a conception of the load on the vascular system may be obtained.

Leg haemodynamics during reconstructive vascular surgery

The aim of this study was to find the best haemodynamic variables for a correct assessment of the function of a femoropopliteal bypass graft. The results are based on intraoperative measurements performed on 11 patients undergoing surgical reconstruction of the femoral artery with a femoropopliteal reversed saphenous vein bypass graft.

Both blood transfusion and local intra-arterial injection of 40 mg of papaverine resulted in a significant increase in common femoral arterial and graft blood flows as well as in femoropopliteal pressure difference. At the same time there was a significant decrease in total leg and lower leg resistance, whereas the resistance over the graft was not significantly altered by changes in blood volume or by pharmacological vasodilatation.

It was shown that, for a complete assessment of the bypass function, both the resistance in the graft and in the lower leg must be evaluated. This can be effected by simultaneously measuring both the blood pressure and the blood flow. It was also shown that the femoropopliteal pressure difference per se does not indicate the true capacity of the graft. It is concluded that, during reconstructive vascular surgery, leg haemodynamic variables are influenced by variations in blood volume and vasomotor tone. This is of importance for the correct interpretation of a single haemodynamic variable and for the correct quantitative evaluation of the results of vascular surgery.

Release of renal prostaglandins during endotoxin-induced hypotension

The appearance of prostaglandins in dog's blood during endotoxin-induced hypotension was studied by use of the dialysis modification of the blood bathed organ technique. An increase in prostaglandins, mainly E2 and F2alpha was found in renal venous blood, whereas no such increase was seen in blood from the abdominal aorta, the inferior vena cava or the femoral vein. Three possible trigger mechanisms for this increase i.e. hypotension, reduced flow and reflexogenic sympathetic stimulation, have been investigated. It is suggested that, in addition to these three factors, circulating hormones such as noradrenaline, angiotensin or bradykinin, play a role in this release mechanism. Administration of indomethacin produced a restoration of the systemic blood pressure to its pre-endotoxin value; concomitantly a disappearance of the prostaglandins from the circulation was observed. It is concluded that prostaglandins contribute to the hypotension induced by endotoxin. Whether they are beneficial or detrimental remains to be resolved.

The haemodynamic effects of nitrous oxide anaesthesia on myocardial blood flow in dogs

The effects of ventilation with nitrous oxide in oxygen on myocardial blood flow any oxygen metabolism were investigated in 31 mongrel dogs. The results of this study showed that, compared with controls, hyperoxic nitrous oxide mixtures did not cause any great changes in myocardial haemodynamics, despite a decrease in cardiac output and an increase in systemic vascular resistance. Normoxic nitrous oxide mixtures produced an increase of the coronary blood flow due to decreased coronary vascular resistance. To what extent this coronary vasodilatation resulted from a increased myocardial metabolism or from a direct effect of nitrous oxide on the coronary vascular bed cannot be quantified from the present results.

The haemodynamic effects of nitrous oxide anaesthesia on systemic and pulmonary circulation in dogs

The haemodynamic effects of nitrous oxide in normoxia (20% oxygen) and in hyperoxia (50% oxygen) were investigated in 13 dogs. Nitrous oxide in hyperoxia caused a significant rise in total peripheral resistance and a significant decrease in cardiac output, heart rate, myocardial contractility (dP/dt max) and cardiac work. On the other hand, nitrous oxide in normoxia seemed to reverse these findings and did not exert negative inotropic effects on the myocardium. The results indicate that the earlier reported sympathetic activation of the circulation may be related to hyperoxia and not to nitrous oxide as such.

Estimation of pancreatic IRI output rate and its relations to glucose tolerance in normal anasthetized dogs

The pancreaticoduodenal and portal venous blood flows were recorded electromagnetically in anaesthetized dogs. Blood glucose and IRI were measured in the arterial, portal, and peripheral venous as well as in the intestinal venous blood. By a mathematical model the actual net IRI output of the whole pancreas was estimated. Under basal conditions it is 10.2 +/- 2.4 mU/min (n = 30; 26 kg mean body wt.). After i.v. glucose injection, IRI output is rapidly enhanced. The biphasic nature of this reaction was unequivocally demonstrated by consideration of the ratio IRI output : blood glucose. Pancreaticoduodenal blood flow increases transiently in relation to the increased blood glucose concentration. The IRI secretion rate is well correlated with the blood glucose concentration and to the amounts of glucose or of blood reaching the whole pancreas. It is also correlated with the portal IRI Concentration. The overall peripheral venous or arterial IRI concentrations are correlated with the IRI secretion rate, but not in all individual experiments. The different phases of IRI output (basal rate, stimulated output 1-10 min and 10-60 min) show no influence on each other, nor are they correlated with the peripheral IRI concentration area. Basal IRI output is negatively correlated with the glucose assimilation constants. These constants or the peripheral BG areas, however, are independent of the stimulated IRI output rate. However, both the assimilation constants and the peripheral BG areas are related to the peripheral IRI concentration areas. Hepatic uptake of insulin and dynamics of pancreatic blood flow seem to contribute considerably to the estimated correlation pattern.

Continuous, long-term measurement of cardiac output after open-heart surgery

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Hemodynamic responses to glucagon: an experimental study of central, visceral and peripheral effects

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Clinical blood flow measurement--evaluation of a current method

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