Transcranial Doppler sonography during pulsatile and non-pulsatile extracorporeal circulation

Transcranial Doppler sonography (TCD) was used to determine the mean blood flow velocity of the middle cerebral artery (Vm-MCA) and pulsatility (systolic/diastolic flow velocity = S/D) in 25 patients undergoing aortocoronary bypass grafting before, during, and after extracorporeal circulation (ECC). Preoperatively, none of the patients had signs or symptoms of cerebrovascular disease. ECC was performed with 2.4 l/min per m2 under mild hypothermia (34 degrees C) using membrane oxygenators. After 20 min of nonpulsatile perfusion, ECC was switched to the pulsatile mode for 20 min. Nonpulsatile perfusion was applied for the remaining ECC period. Vm-MCA, S/D, mean arterial blood pressure (MABP), and nasopharyngeal temperature (T.np) were recorded continuously throughout the operation. Hematocrit and paCO2 were determined before, during, and after ECC. Following hemodilution after the introduction of ECC, Vm-MCA was significantly increased compared with the baseline values before ECC. With hematocrit and paCO2 varying insignificantly during ECC, the onset of pulsatile ECC decreased Vm-MCA and MABP simultaneously. After the re-establishment of nonpulsatile ECC, both Vm-MCA and MABP increased again. However, a linear relationship between the two variables could not be documented statistically. During pulsatile ECC, pulsatility (S/D) of the obtained TCD wave forms did not reach baseline values. In 4 cases, TCD showed cessation of diastolic blood flow velocity after induction of ECC or onset of pulsatile ECC. An increase in MABP or changes in ECC regimen promptly restored diastolic TCD signals in these cases. Our results support the concept of increased cerebral blood flow under mild hypothermic ECC. Compared with the nonpulsatile perfusion mode, we found Vm-MCA reduced during pulsatile ECC.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effects of pulsatile and non-pulsatile cardiopulmonary bypass on renal blood flow and function

The physiologic effects of pulsatile and non-pulsatile flow in cardiopulmonary bypass were compared in terms of the relationship between different flow rates and what effects these had on pulsatile and non-pulsatile flow. Forty adult mongrel dogs were used in this study and divided into 5 groups, each comprised of 8 animals, according to the flow rate during cardiopulmonary bypass, namely; 40, 60, 80, 100, or 120 ml/kg/min. The animals were perfused with either pulsatile or non-pulsatile flow for 1 hour, given randomly at the same mean flow rate. At flow rates of 80 and 100 ml/kg/min, the mean arterial blood pressure and total peripheral vascular resistance were significantly lower in pulsatile flow than in non-pulsatile flow, and the renal blood flow was significantly greater in pulsatile flow than in non-pulsatile flow. The renal arterial-venous lactate difference was significantly less in pulsatile flow than in non-pulsatile flow at a flow rate of 80 ml/kg/min, and the renal lactate extraction was significantly higher in pulsatile flow than in non-pulsatile flow at the same flow rate. The renal excess lactate was significantly lower in pulsatile flow than in non-pulsatile flow at a flow rate of 100 ml/kg/min. There were no significant differences in these parameters between the two types of perfusion at flow rates of 40, 60 or 120 ml/kg/min. Pulsatile flow was therefore apparently advantageous, when compared to non-pulsatile flow, in terms of hemodynamics, renal circulation, and metabolism of the kidney at flow rates of 80 and 100 ml/kg/min. However, when the flow rate was 120 ml/kg/min, pulsatile flow and non-pulsatile flow had the same effects.     

The effects of pulsatile and non-pulsatile cardiopulmonary bypass on renal blood flow and function

The physiologic effects of pulsatile and non-pulsatile flow in cardiopulmonary bypass were compared in terms of the relationship between different flow rates and what effects these had on pulsatile and non-pulsatile flow. Forty adult mongrel dogs were used in this study and divided into 5 groups, each comprised of 8 animals, according to the flow rate during cardiopulmonary bypass, namely; 40, 60, 80, 100, or 120 ml/kg/min. The animals were perfused with either pulsatile or non-pulsatile flow for 1 hour, given randomly at the same mean flow rate. At flow rates of 80 and 100 ml/kg/min, the mean arterial blood pressure and total peripheral vascular resistance were significantly lower in pulsatile flow than in non-pulsatile flow, and the renal blood flow was significantly greater in pulsatile flow than in non-pulsatile flow. The renal arterial-venous lactate difference was significantly less in pulsatile flow than in non-pulsatile flow at a flow rate of 80 ml/kg/min, and the renal lactate extraction was significantly higher in pulsatile flow than in non-pulsatile flow at the same flow rate. The renal excess lactate was significantly lower in pulsatile flow than in non-pulsatile flow at a flow rate of 100 ml/kg/min. There were no significant differences in these parameters between the two types of perfusion at flow rates of 40, 60 or 120 ml/kg/min. Pulsatile flow was therefore apparently advantageous, when compared to non-pulsatile flow, in terms of hemodynamics, renal circulation, and metabolism of the kidney at flow rates of 80 and 100 ml/kg/min. However, when the flow rate was 120 ml/kg/min, pulsatile flow and non-pulsatile flow had the same effects.     

Brain damage in dogs immediately following pulsatile and non-pulsatile blood flows in extracorporeal circulation

The brains of dogs subjected to total cardiac bypass were examined for early signs of ischaemic nerve cell changes. Diffuse nerve cell changes were found immediately following two- and three-hour non-pulsatile perfusions but not following pulsatile perfusions of the same durations. The nerve cell changes found in the brains were acute cell swelling and early ischaemic cell change. Acute cell swelling was found only in the cerebellar Purkinje cells. Ischaemic cell change was found in several regions of the brain but the cerebral cortex and cerebellar Purkinje cells were most frequently affected. Diffuse nerve cell changes are attributed to non-pulsatile blood flow but some complicating factors are recognized.     

Comparison of pulsatile and non-pulsatile cardiopulmonary bypass on regional renal blood flow in sheep

OBJECTIVE--The purpose of the present study was to evaluate the effects of pulsatile cardiopulmonary bypass (CPB) on sheep regional renal blood flow by comparing pulsatile and non-pulsatile perfusion at two different flow rates. DESIGN--Seven female Suffolk sheep were used and the animals were perfused with pulsatile and non-pulsatile CPB at flow rates of 60 and 100 ml/min/kg. Regional renal blood flow was measured by the colored microsphere method. General linear model ANOVA was performed to analyze the data. RESULTS--Regional renal blood flow was significantly higher in both outer and middle cortices of pulsatile CPB compared with non-pulsatile CPB (outer cortex: pulsatile CPB, 381+/-192 ml/min/100 g, non-pulsatile CPB, 255+/-151 ml/min/100g, p=0.002; middle cortex: pulsatile CPB, 239+/-114 ml/min/100 g, non-pulsatile CPB, 176+/-80 ml/min/100 g, p=0.02). The increase of flow rate from 60 to 100 ml/min/kg improved renal cortical blood flow significantly. CONCLUSION--The regional renal blood flow was significantly higher in both outer and middle cortices of pulsatile CPB compared with the non-pulsatile CPB.     

Brain damage and mortality in dogs following pulsatile and non-pulsatile blood flows in extracorporeal circulation

In a series of 20 dog experiments, total cardiac bypass was followed by a high rate of mortality during the first 12 postoperative hours. Only five dogs survived for one week, but a further three dogs were perfuse-fixed after shorter periods of survival. All dogs developed pulmonary alveolar haemorrhages and seven of the eight perfuse-fixed brains exhibited brain damage. Diffuse nerve cell changes were found in the brains of dogs subjected to non-pulsatile blood flow. Focal brain lesions were found following both pulsatile and non-pulsatile blood flows. The lesions varied from staining pallor and rarefaction of the neuropil to total nerve cell loss and glial infiltration depending upon the duration of survival. When considered in conjunction with a previous series of experiments, these results show that the diffuse nerve cell changes associated with roller pump perfusions can be avoided by using a new pulsatile pump, but focal brain damage was not eliminated, and lung damage and mortality were not reduced.     

In vitro characterization of aortic retrograde and antegrade flow from pulsatile and non-pulsatile ventricular assist devices.

BACKGROUND: Many advances have been made in left ventricular assist device (LVAD) development including the introduction of smaller, non-pulsatile pumps. However, controversy exists over the potential significance of non-pulsatile blood flow. In addition, some newer LVADs incorporate descending aortic anastomosis (and therefore retrograde ascending aortic flow) for outflow rather than the traditional ascending aortic anastomosis. This, combined with non-pulsatile flow, may significantly increase the risks of ascending aortic thrombus formation, especially if native cardiac function is negligible and the aortic valve remains closed. The purpose of this study was to compare pulsatile and non-pulsatile flow generated by LVADs with outflow to the ascending aorta and descending aorta. METHODS: An in vitro mock circulatory loop, driven by either a pulsatile or a non-pulsatile LVAD, was anastomosed to transparent aortic models at either the ascending or descending aortic position. The aortic valve was kept closed, modeling no native cardiac output. Normal saline was used as a blood analog. Methylene blue dye was injected into the ascending aorta and aortic arch to demonstrate flow patterns. Dye washout time (in seconds) was used as a marker of flow stagnation and potential thrombogenicity. LVAD flow, rate, after-load and coronary flow were measured. RESULTS: Dye washout times at a flow rate of 5 liters/min were 1.7 +/- 0.75, 2.1 +/- 0.71, 4.7 +/- 0.82 and 9.9 +/- 4.4 seconds for pulsatile ascending (PA), non-pulsatile ascending (NPA), pulsatile descending (PD) and non-pulsatile descending flow (NPD), respectively. Coronary flow averaged 294 ml/min over all set-ups. Dye washout times at a flow rate of 4-liters/min were 3.0 +/- 1.0, 3.0 +/- 0.8, 14.0 +/- 3.8 and 25.0 +/- 9.1 seconds for PA, NPA, PD and NPD, respectively. Coronary flow averaged 227 ml/min over all set-ups. Ascending aortic anastomoses were associated with shorter dye washout times compared with descending aortic anastomoses, regardless of flow type (p < 0.001). There was no difference in washout time between pulsatile and non-pulsatile flow in the ascending aortic position (p = 0.23 and 0.12 for 5 and 4 liters/min, respectively). Pulsatile flow in the descending aorta had shorter washout times than non-pulsatile flow in the descending aorta (p < 0.001 and p = 0.004 for 5 and 4 liters/min, respectively). CONCLUSIONS: LVAD descending aortic anastomosis and retrograde aortic flow is associated with increased flow stagnation in the ascending aorta. This may increase the risk for thrombus formation in patients relying solely on retrograde aortic flow, especially if cardiac function and antegrade blood flow returns.     

Critical oxygen delivery during cardiopulmonary bypass in dogs: pulsatile vs. non-pulsatile blood flow

BACKGROUND AND OBJECTIVE: To determine the minimal oxygen delivery and pump flow that can maintain systemic oxygen uptake during normothermic (37 degrees C) pulsatile and non-pulsatile cardiopulmonary bypass in dogs. METHODS: Eighteen anaesthetized dogs were randomly assigned to receive either non-pulsatile (Group C; n = 9) or pulsatile bypass flow (Group P; n = 9). Oxygen delivery was reduced by a progressive decrease in pump flow, while arterial oxygen content was maintained constant. In each animal, critical oxygen delivery was determined from plots of oxygen uptake vs. oxygen delivery and from plots of blood lactate vs. oxygen delivery using a least sum of squares technique. Critical pump flow was determined from plots of lactate vs. pump flow. RESULTS: At the critical point, oxygen delivery obtained from oxygen uptake was 7.7 +/- 1.1 mL min(-1) kg(-1) in Group C and 6.8 +/- 1.8 mL min(-1) kg(-1) in Group P (n.s.). These values were similar to those obtained from lactate measurements (Group C: 7.8 +/- 1.6 mL min(-1) kg(-1); Group P: 7.6 +/- 2.0 mL min(-1) kg(-1)). Critical pump flows determined from lactate measurements were 55.6 +/- 13.8 mL min(-1) kg(-1) in Group C and 60.8 +/- 13.9 mL min(-1) kg(-1) in Group P (n.s.). CONCLUSIONS: Oxygen delivery values greater than 7-8 mL min(-1) kg(-1) were required to maintain oxygen uptake during normothermic cardiopulmonary bypass with either pulsatile or non-pulsatile blood flow. Elevation of blood lactate levels during bypass helps to identify inadequate tissue oxygen delivery related to insufficient pump flow.     

Experimental evaluation of the influence of complete artificial circulation on renal circulation and tissue metabolism -comparative study of pulsatile vs nonpulsatile circulation.

In this study, pulsatile and nonpulsatile assisted circulation were compared to evaluate renal circulation under complete artificial circulation. In addition, differences were also compared between animals supported by high (assist rate 80%)- and low (assist rate 60%)-level artificial circulation. Using 20 pigs, ventricular fibrillation was induced after cardiogenic shock, assist by mechanical support by pulsatile and nonpulsatile artificial circulation. Hemodynamics and renal circulation were evaluated by measuring renal arterial blood flow, renal cortical blood flow, renal medullar blood flow, cortical/medullar flow ratio, serum urea nitrogen levels, blood creatinine levels, urinary beta(2)-microglobulin (MG) levels, and serum beta(2)-MG levels. Tissue metabolism was evaluated by comparing arterial ketone body ratios and lactic acid/pyruvic acid ratios. During the acute stage of cardiogenic shock, redistribution of renal blood flow and tissue metabolism were improved in the pigs with pulsatile artificial circulation, suggesting the usefulness of pulse pressure. In nonpulsatile artificial circulation, the possibility of irreversible renal dysfunction was suggested. Although changes in renal blood flow were smaller in high-level artificial circulation than in low-level artificial circulation, physiological maintenance of renal circulation was better in pulsatile artificial circulation than in nonpulsatile artificial circulation. These results suggest that this effect of pulsatile assisted circulation may become more marked when evaluated in the early state after cardiogenic shock.     

Comparative clinical study of pulsatile and non-pulsatile perfusion in 350 consecutive patients.

Pulsatile perfusion has been shown to offer significant haemodynamic advantages over non-pulsatile perfusion in many experimental studies. Clinical acceptance of pulsatile perfusion during cardiac surgical procedures has, however, been hampered by the lack of technologically satisfactory pulsatile pump systems, and by inadequate clinical experience of routine use of pulsatile perfusion. The recent introduction of reliable pulsatile pump systems with low haemolysis characteristics has made possible the clinical validation of the previous experimental studies. We describe the results of a prospective study of mortality, haemodynamic morbidity, and haematological status, in 350 consecutive adult patients submitted to cardiopulmonary bypass procedures in a surgical unit over a 12-month period. One hundred and seventy five patients were perfused with conventional non-pulsatile flow and 175 with pulsatile flow, using a modified roller-pump pulsatile system (Cobe-Stockert). The groups were closely similar in terms of preoperative characteristics, referral category, and pathology requiring surgery. Operative techniques, bypass parameters, and anaesthetic regime were standardised in both groups. The results were as follows. (1) Total mortality was significantly lower in the pulsatile group (4.6%) compared with the non-pulsatile group (10.3%), p = 0.06. (2) The incidence of deaths attributable to post-perfusion low cardiac output was significantly lower in the pulsatile group (1.1% compared with 6.3%, p = 0.02). (3) Requirement for mechanical (intra-aortic balloon) or drug circulatory support was significantly lower in the pulsatile group. (4) The use of pulsatile perfusion was not associated with any increase in haemolysis, blood cell depletion, or postoperative bleeding problems.     

Perfusion cooling by pulsatile flow

Organ temperature changes and the temperature gradient between organs with cooling and rewarming were studied in rabbits using pulsatile flow perfusion. The temperature gradient between organs was within 3°C. At the initial stage of cooling and rewarming, organ temperatures changed rapidly. During circulatory arrest, organ temperatures rose gradually. Brain temperature changes were similar to other organs.     

Strategies for temporary mechanical support: contemporary experience with pulsatile and non-pulsatile support systems

Despite advances in mechanical circulatory support, cardiogenic shock continues to have a high mortality. We reviewed our experience with pulsatile versus non-pulsatile temporary mechanical support at our institution to determine optimal strategy for survival. From January 2001 to December 2003, mechanical support for cardiogenic shock was instituted in 38 patients. Non-pulsatile devices (NP group) were used in 22 patients and pulsatile devices (P group) in 16 patients. Indications for the NP group were post-cardiotomy shock (PCS) in 17, myocardial infarction in 2, and isolated post-cardiotomy right ventricular failure in 3 patients. In the P group, 9 had the device placed for PCS, 3 for viral myocarditis, 1 after myocardial infarction, and 3 for right ventricular (RV) failure. Overall, bleeding, limb ischemia, and multi-system organ failure were higher in NP group with 5 weaned and 3 surviving to discharge (14%). In the P group, survivors included 7 weaned and 3 transplanted patients (63%). With the exception of isolated RV failure, we obtained a dismal survival result with ECMO/centrifugal circuits for treatment of cardiogenic shock. For refractory pump failure, improved survival was achieved by using intermediate-term pulsatile devices with early transition to a chronic device and/or heart transplantation.     

Coronary flow distribution and dynamics during continuous and pulsatile extracorporeal circulation in the pig

Four extracorporeal perfusion conditions (continuous beating, continuous fibrillating, pulsatile beating, and pulsatile fibrillating) were tested for 15 minutes each in pigs. Coronary flow, endocardial-epicardial flow ratio, phasic coronary flow, myocardial oxygen consumption, and myocardial lactate extraction were measured. No significant differences in any of these variables were found between pulsatile and continuous flow states in either fibrillating or beating hearts (p greater than 0.05). In both fibrillating conditions, significant elevations of myocardial oxygen consumption and decreases in endocardial-epicardial flow ratios were found (p less than 0.05). Lactate extraction occurred in all conditions, and phasic coronary flows were similar in both beating conditions. These data suggest caution in the expectation that pulsatile perfusion will reverse the coronary flow and myocardial oxygen consumption changes seen with fibrillation.