Inverse relationship between heat stable enterotoxin-b induced fluid accumulation and adherence of F4ac-positive enterotoxigenic Escherichia coli in ligated jejunal loops of F4ab/ac fimbria receptor-positive swine.

Heat-labile enterotoxin (LT) produced by enterotoxigenic Escherichia coli (ETEC) increases bacterial adherence to porcine enterocytes in vitro and enhances small intestinal colonization in swine. Heat-stable enterotoxin-b (STb) is not known to affect colonization; however, through an induction of net fluid accumulation it might reduce bacterial adherence. The relationship between fluid accumulation and bacterial adherence in jejunal loops inoculated with ETEC strains that produce LT, STb, both, or neither toxin was studied. Ligated jejunal loops were constructed in weaned Yorkshire pigs in two independent experiments (Exp. 1, n=5, 8-week-old; Exp. 2, n=6, 6-8-week-old). Each pig was inoculated with six F4ac(+)E. coli strains: (1) LT(+), STb(+) parent (WAM2317); (2) STb(-) (ΔestB) mutant (MUN297); (3) MUN297 complemented with STb (MUN298); (4) LT(-) STb(-) (ΔeltAB ΔestB) mutant (MUN300); (5) MUN300 complemented with LT (MUN301); and (6) 1836-2 (non-enterotoxigenic, wild-type). Pigs were confirmed to be K88 (F4)ab/ac receptor-positive in Exp. 2 by testing for intestinal mucin-type glycoproteins and inferred to be receptor-positive in both Exp. 1 and 2 based on histopathologic evidence of bacterial adherence. Strains that produced STb induced marked fluid accumulation with the response (ml/cm) to WAM2317 and MUN298 significantly greater than that to the other strains (P<0.0001). Conversely, bacterial adherence scores based on immunohistochemistry and CFU/g of washed mucosa were both lowest in the strains that expressed STb and highest in those that did not. For the two experiments combined, the Pearson correlation coefficient (R) between fluid volume (ml/cm) and log CFU per gram was -0.57021 (P<0.0001); R(2)=0.3521 (n=197). These results support the hypothesis that enterotoxin-induced fluid accumulation flushes progeny organisms into the lumen of the bowel, thereby increasing the likelihood of fecal shedding and transmission of the pathogen to new hosts.

Development of a flexible inflow cannula with titanium inflow tip for the NEDO biventricular assist device.

A newly designed flexible inflow cannula has been developed for a biventricular assist device (BVAD). The inflow tip was designed for long-term ventricle drainage. Considering the anatomic differences between the right and left ventricles, a flexible inflow cannula, as a mass production model with a titanium tip, was developed and investigated in chronic BVAD animal experiments using the NEDO permanently implantable centrifugal blood pump. These flexible inflow cannulae consist of flexible plastic tubing with wire supported, titanium left and right tips. The right titanium inflow tip was designed with inner and outer stoppers to be inserted into the right ventricle wall and a beak shape to avoid sucking. The left tip was designed to be inserted into the left ventricle cavity. Five chronic BVAD bovine studies were performed to investigate the new beak shaped titanium tip. In these studies, the new beak shaped titanium tip and cannula prevented stenosis by a proliferation of pseudoneointimal, and supplied adequate blood flow to the pump without sucking. This newly designed inflow cannula with the beak shaped titanium tip was successfully implanted for 90 days.

Centrifugal blood pump with a hydraulically-levitated impeller for a permanently implantable biventricular assist device.

A permanently implantable biventricular assist device (BVAD) system has been developed with a centrifugal pump which is activated by a hydraulically-levitated impeller. The pump impeller floats hydraulically into the top contact position; this position prevents thrombus formation by creating a washout effect at the bottom bearing area, a common stagnant region. The pump was subjected to in vitro studies using a pulsatile mock circulation loop to confirm the impeller's top contact position and the swinging motion produced by the pulsation. Eleven in vivo BVAD studies confirmed that this swinging motion eliminated blood clot formation. Twenty-one pumps im-planted for up to three months did not reveal any thrombosis in the pumps or downstream organs. One exception was a right pump which was exposed to severe low flow due to the kinking of the outflow graft by the accidental pulling of the flow meter cable. Three ninety-day BVAD studies were achieved without thrombus formation.

In vivo evaluation of the NEDO biventricular assist device with an RPM dynamic impeller suspension system.

Since 1995, the Baylor College of Medicine group has been developing the NEDO Gyro permanent implantable (PI) pump. The Gyro PI pump has achieved outstanding results up to 284 days with no thrombus formation during the left ventricular assist device (LVAD) animal experiments. However, in biventricular assist device (BVAD) animal experiments, thrombus formation did occur. An in vitro experiment showed the reason for thrombus formation was caused by the missed magnetic balance between the impeller and the actuator. On the basis of this result, the revolutions per minute (RPM) impeller suspension system was developed. Six long-term animal studies were performed in bovine models. Survival periods were 90, 80, 60, 51, 48, and 37 days, respectively. No thrombus was observed in the pumps with the exception of one right pump. In that experiment, the thrombus formation may have occurred when the pump had a low flow because of outflow kinking. In this article, the antithrombogenic effect of this RPM impeller suspension system will be discussed.