Pulsatile flow during cardiopulmonary bypass. Evaluation of a new pulsatile pump

The effects of pulsatile cardiopulmonary bypass on cerebral and renal blood flow in dogs

OBJECTIVE

The purpose of this study was to determine the effects of pulsatility on cerebral blood flow, cerebral metabolism, and renal blood flow over a range of cardiopulmonary bypass temperature and flow conditions.

DESIGN/SETTING

The investigation was prospective, randomized, and performed in a canine physiology laboratory at the Mayo Foundation.

PARTICIPANTS AND INTERVENTIONS

Anesthetized dogs were studied during pulsatile (n = 9) or nonpulsatile (n = 10) cardiopulmonary bypass at two flow rates (2.4 and 1.2 L/min/m2) at each of three temperatures (37 degrees, 32 degrees, and 27 degrees C). Pulsatility was achieved by use of a pediatric intraaortic balloon pump. Cerebral blood flow and metabolic rate were determined using the sagittal sinus outflow method. Renal blood flow was determined by a periarterial ultrasonic flow probe.

MEASUREMENTS AND MAIN RESULTS

In the pulsatile group, a pulse pressure of 29 mmHg had no effect on cerebral blood flow or metabolism at any temperature under either flow condition. Renal blood flow was also unaffected by pulsatility, but decreased with hypothermia and reduced pump flow. Pulsatility also did not attenuate the systemic effects of normothermic hypoperfusion.

CONCLUSIONS

Pulsatility has no significant effect on cerebral or renal perfusion over a broad range of cardiopulmonary bypass temperature and flow conditions. Cerebral blood flow and metabolism were functions of temperature but not pulsatility or flow rate. Renal blood flow was affected by both temperature and cardiopulmonary bypass flow rate but not by pulsatility. Finally, central nervous system perfusion may be preserved under low-flow cardiopulmonary bypass conditions by shunting of perfusion from splanchnic vascular beds.

Swine as a model for cardiovascular research: improved cardiopulmonary bypass techniques

A large-animal model is essential for the assessment of functional parameters in cardiovascular surgical research. To date the canine model has been used successfully because of its availability and tolerance to cardiopulmonary bypass. However, because of decreased availability and increased cost, an alternative animal model is now needed. The swine model has been used in experimental cardiac procedures, but complications during cardiopulmonary bypass have presented a formidable challenge. These complications include enormous fluid shifts from the vascular bed, increased metabolic acidosis, and marked hemoglobinuria. To eliminate these deleterious complications within the swine model, a number of technical alterations were achieved. The priming solution used for the extracorporeal circuit was altered to consist of 1000 mL lactated Ringer's solution. 500 mL 20% mannitol, 500 mL 6% dextran in 5% detrose solution. 50 mEq sodium bicarbonate, and 10,000 IU heparin. The extracorporeal circuit employed the use of membrane oxygenation. Three different blood flow rates (150, 175, and 200 mL/kg min-1) were studied. We conclude that the optimum blood flow rate for cardiopulmonary bypass in swine is in the range of 175-200 mL/kg min-1. Membrane oxygenation results in less damage to blood during cardiopulmonary bypass. The asanguinous hyperosmolar priming solution is beneficial for cardiopulmonary bypass in swine to greatly reduce fluid shifts, prevent metabolic acidosis, and eliminate hemoglobinuria.

A pulsatile pump for cardiopulmonary bypass and its clinical use

A pulsatile pump driven by a coil spring, which was designed and constructed by us, is described in this report. It consists of two main parts, a disposable blood chamber and a driving section. The blood chamber has two leaflet valves and a piston, which is covered with two bellofram rolling diaphragms and moves into the housing to draw in and eject the blood. The driving section consists of three cams, an electric motor and a coil spring. The ejection force is wholly produced by the compressed coil spring and is transmitted to the piston in the blood chamber by a rod. This pump allows the ejection pressure, the beat rates, and the stroke volume all to be changed independently. The performance of the pump was tested by using a circulation model where the beat rate was adjusted from 30 to 250 bpm. The output subsequently increased from 0.8 l/min to 5.7 l/min and the stroke volume, from 20.4 ml to 36.7 ml. This new pump has been used for clinical cardiopulmonary bypasses in 24 patients of open heart surgery and the pressure traces during perfusion resembled those of the patients' own hearts.

Brain oedema and blood-brain barrier permeability in pulsatile and nonpulsatile cardiopulmonary bypass

In pigs subjected to pulsatile or nonpulsatile cardiopulmonary bypass (CPB) at normothermia for 3 hours, evaluation was made of water content in brain tissue (specific gravity measurements), blood-brain permeability to serum proteins (immunocytochemical demonstration of extravasated proteins, using peroxidase-antiperoxidase technique) and histopathology (paraffin sections). The specific gravity in parietal cortex was higher after pulsatile than after nonpulsatile CPB or in control pigs, the change corresponding to a 6.3% water increase. The tissue water content was unchanged in the internal capsule, basal ganglia and nucleus accumbens after CPB. The vascular permeability to serum proteins was unchanged after nonpulsatile CPB, but after pulsatile CPB minute foci of extravasated serum proteins appeared. All the animals showed dark neurons in cortical and subcortical regions, but these could have been artefacts in immersion-fixed tissue. There were no other signs of ischaemic tissue damage. The study indicated that cortical oedema may follow pulsatile CPB, the cause being altered permeability of the blood-brain barrier to serum proteins.