Bruce E. Keogh

The effect of intestinal hypoperfusion on intestinal absorption and permeability during cardiopulmonary bypass

BACKGROUND/AIMS Mean arterial pressure is reduced during hypothermic cardiopulmonary bypass. The aim of this study was to assess whether this was associated with intestinal hypoperfusion and whether it affected intestinal absorption and permeability. METHODS Twenty-six patients undergoing coronary artery bypass grafting underwent an intestinal absorption-permeability test involving ingestion of 3-O-methyl-D-glucose, D-xylose, L-rhamnose, and lactulose. Ingestion took place 2 days before, within 3 hours, and 5 days after hypothermic cardiopulmonary bypass. Hemodynamic parameters and gastric mucosal laser Doppler blood flow were measured perioperatively in eight patients. RESULTS Hypothermic (28 degrees C), nonpulsatile cardiopulmonary bypass resulted in a 25% reduction in mean blood pressure, 10% reduction in cardiac index, and a 46% reduction in gastric mucosal laser Doppler blood flow. There was 85.4%, 85.5%, and 73.6% reduction (P < 0.01) in active (3-O-methyl-D-glucose) and passive (D-xylose) carrier-mediated transport and passive, nonmediated transcellular (L-rhamnose) transport in the immediate postoperative period, respectively. The differential urine excretion of lactulose/L-rhamnose increased sixfold. All parameters returned to control levels by the fifth postoperative day. CONCLUSIONS Cardiopulmonary bypass, while maintaining generally acceptable levels of hemodynamic performance, is associated with significant intestinal hypoperfusion and malabsorption of monosaccharides, which may have implications for enteral drug treatment in the immediate postoperative period.

Effects of cardiopulmonary bypass on gut blood flow, oxygen utilization, and intramucosal pH

Studies documenting rises in endotoxin after cardiopulmonary bypass (CPB) have postulated gut mucosal hypoperfusion. We have investigated alterations in jejunal blood flow by laser Doppler flow measurement, intramucosal pH (pHi) by tonometry, and oxygen utilization in a canine model of hypothermic CPB (n = 11 dogs). After 10 minutes of hypothermic CPB, despite no major reduction in superior mesenteric artery flow, mucosal laser Doppler flow decreased to -38.2% +/- 9.3% of levels obtained before bypass (p = 0.008) and serosal laser Doppler flow, to -47.3% +/- 11.4% (p = 0.006). During the hypothermic phase, mesenteric oxygen consumption fell from 0.18 +/- 0.01 to 0.098 +/- 0.01 mL.min-1.kg-1 (p = 0.005), and mesenteric oxygen delivery fell from 1.97 +/- 0.39 to 1.14 +/- 0.12 mL.min-1.kg-1 (p = 0.05). There was no change in jejunal pHi. During the rewarming phase, there was a substantial increase in mucosal laser Doppler flow, peaking at +69.8% +/- 15.2% (p = 0.03), whereas serosal laser Doppler flow returned to values seen prior to CPB (-16.4% +/- 21.5%; p = 0.25). These changes coincided with a surge in oxygen consumption (0.33 +/- 0.042 mL.min-1.kg-1; p = 0.009), while mesenteric oxygen delivery remained depressed at 1.09 +/- 0.12 mL.min-1.kg-1 (p = 0.04). Jejunal pHi fell from a value of 7.36 +/- 0.04 before CPB to 7.12 +/- 0.07 (p = 0.02), thus indicating mucosal hypoxia. During the rewarming phase of hypothermic CPB, there is a disparity between mesenteric oxygen consumption and oxygen delivery with villus tip ischemia; these findings may explain the pathophysiology of endotoxemia during CPB.

Intracoronary endothelin induces myocardial ischemia by small vessel constriction in the dog

Abstract Since the original observations made with acetylcholine, 1 several vasodilators have been shown to cause smooth muscle relaxation by stimulating the secretion of endothelium-derived relaxing factors. 2 It has also been shown that the vasoconstrictor effect of noradrenaline, neuropeptide Y, thrombin and hypoxia may be mediated by diffusable endothelium-derived contracting factors, 3,4 such as the pressor agent present in the supernatant of cultured endothelial cells described by Hickey et al. 5 Subsequently, Yanagisawa et al 6 have isolated endothelin, a vasoconstrictor peptide, from the supernatant of cultured porcine aortic endothelial cells. This 21 amino acid peptide induces potent, prolonged dose-dependent contraction of isolated arterial and vein preparations from several mammalian species, including porcine coronary and human pulmonary arteries. 6 In vitro endothelin is the most potent mammalian vasoconstrictor known to date, with a median effective concentration of less than the values reported for angiotensin II, neuropeptide Y and vasopressin. 7,8 We have investigated the effects of locally infused endothelin on the canine coronary circulation in vivo.

Assessment of the value of the immediate postoperative chest radiograph after cardiac operation

The value of the immediate postoperative chest radiograph upon a patients return to the intensive care unit after a cardiac surgical procedure is uncertain. This study represents a prospective analysis of the immediate postoperative radiograph in 100 consecutive adult patients undergoing cardiac operations. In 11 patients it was found that the routine postoperative radiograph was of value when it was necessary either to clarify or confirm clinical findings or to check the position of an intraaortic balloon catheter. For those chest radiographs that were deemed unnecessary, only one of 89 were found to be of clinical value. Furthermore, in those situations in which an emergency radiograph was obtained, the routine radiograph was not found to be contributory to patient management. We conclude that the policy of obtaining routine, immediate postoperative chest radiographs in the absence of a specific clinical indication provides virtually no additional clinical yield. Residents should therefore request radiographs only to check the position of an intraaortic balloon catheter, and to clarify or confirm a clinical diagnosis.

Co-expression of renin-angiotensin system component genes in human atrial tissue.

Objectives To detect co-expression of genes coding for components of the rennin—angiotensin system and investigate the potential for variation in the level of angiotensin converting enzyme (ACE) gene expression in the right atrial appendage of patients undergoing heart surgery. Design The right atrial appendage was collected at the time of surgery from 30 randomly chosen patients and was rapidly frozen in liquid nitrogen prior to extraction of messenger (m)RNA. Surgical samples of heart valve (n = 6) and papillary muscle (n = 3) were also examined. Methods Aliquots of purified mRNA were reverse-transcribed for analysis of gene expression by a polymerase chain reaction amplification assay. Primers specific for angiotensinogen, renin, ACE, cardiac chymase, atrial natriuretic peptide, glyceraldehyde-3-phosphate dehydrogenase, adenosine deaminase and the transferrin receptor were used for a qualitative analysis of co-expression of these genes within the same sample. In a subgroup of eight patients, a quantitative comparison of the relative levels of ACE gene expression was performed using a competitive polymerase chain reaction. Results Angiotensinogen and ACE expression were detected in all atrial, valve and ventricular samples examined, at levels similar to those of ‘housekeeping’ genes such as the transferrin receptor. Atrial renin and chymase expression were more difficult to detect, being demonstrable in only 70 and 63% of the samples, respectively. Higher levels of chymase were detected in ventricular samples than in atrial tissues. A quantitative analysis of ACE expression in eight atrial samples provided evidence of interindividual variation in the relative level of atrial ACE expression. Conclusions The essential components of the rennin—angiotensin system are co-expressed at a low level in the right atrial appendage and are detectable in other regions of the human heart. Renin and chymase genes are expressed at a lower level than the angiotensinogen and ACE genes and exhibit regional differences in expression. Interindividual variation in the relative level of ACE expression can be detected by a competitive polymerase chain reaction.

Carcinoid heart disease: Early failure of an allograft valve replacement☆

A woman who had carcinoid syndrome and carcinoid heart disease underwent tricuspid and pulmonary valve replacements with a xenograft and a cryopreserved allograft, respectively. Within 3 months of the operation severe pulmonary regurgitation and pulmonary hypertension refractory to medical therapy developed. Autopsy found the biomechanical tricuspid valve to be free of disease but the allograft in the pulmonary position was involved by carcinoid heart disease in a fashion similar to the excised native pulmonary valve.

Angiosarcoma of the heart causing cardiac rupture: a rare cause of hemopericardium.

Cardiac rupture as a complication of primary cardiac tumors has rarely been reported in the literature. The diagnosis is difficult to establish preoperatively, but echocardiography may provide the best assessment of cardiac damage. We found a loculated pericardial effusion on two-dimensional echocardiography, a finding that has been documented in two of the previous four case reports. A case of right atrial rupture is reported with review of other cases from the literature.

Endothelin-1 Is a Potent Long-Lasting Vasoconstrictor in Dog Peripheral Vasculature in vivo

Summary Endothelin-1 (ET-1), a 21 amino acid peptide, has recently been identified and shown to produce a potent and prolonged constriction of mammalian blood vessels in vitro. We have studied the effect of local infusion of this peptide on resistance vessels in the hindlimb of the anesthetized greyhound dog. Incremental doses of ET-1 (3–200 pmol/min) were infused into the left femoral artery. Doses above 10 pmol/min produced a slowly progressive reduction in hindlimb blood flow in a dose dependent fashion, maximally reducing flow by 79.5%

Intravascular delivery of laser energy with metal-capped optical fibers: The potential hazard of distal embolism

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