Quantitation of left-to-right shunt from a single earpiece dye-dilution curve

Non-invasive dye dilution method for measuring an atrial septal defect shunt size

Aims

Objective of this study was to evaluate the feasibility of the non-invasive dye dilution method to quantify shunt size related to atrial septal defects (ASD).

The diagnostic accuracy of shunt size determination in ASD’s has been suboptimal with common non-invasive methods. We have previously developed a cost-effective and time-effective non-invasive dye dilution method. In this method, the indocyanine green solution is injected into the antecubital vein and the appearance of the dye is detected with an earpiece densitometer.

Methods and results

We studied 192 patients with an ASD. Mean pulmonary blood flow/systemic blood flow (Qp/Qs) was measured with dye dilution technique and compared with following methods: Fick’s invasive oximetry (n=49), transoesophageal echocardiography (TEE) measuring ASD size (n=143) and cardiac MR (CMR) (n=9).

For the first 49 patients, Qp/Qs was 2.05±0.70 with the Fick’s invasive oximetry and 2.12±0.68 with dye dilution method with an excellent correlation between the two methods (R=0.902, p<0.001). In the second study sample, the ASD size by TEE was 15±6 mm on average, and the mean Qp/Qs 2.16±0.65 measured with dye dilution method with a good correlation between the methods (R=0.674, p<0.001). Qp/Qs measured with CMR was 1.87±0.40 resulting in a good correlation with the dye dilution method (R=0.696, p=0.037).

Conclusion

The dye dilution method with earpiece densitometer recording is a clinically feasible and reliable method to assess shunt size in ASDs.

Dextran sodium sulfate (DSS) induces colitis in mice by forming nano-lipocomplexes with medium-chain-length fatty acids in the colon

Inflammatory bowel diseases (IBDs), primarily ulcerative colitis and Crohn's disease, are inflammatory disorders caused by multiple factors. Research on IBD has often used the dextran sodium sulfate (DSS)-induced colitis mouse model. DSS induces in vivo but not in vitro intestinal inflammation. In addition, no DSS-associated molecule (free glucose, sodium sulfate solution, free dextran) induces in vitro or in vivo intestinal inflammation. We find that DSS but not dextran associated molecules established linkages with medium-chain-length fatty acids (MCFAs), such as dodecanoate, that are present in the colonic lumen. DSS complexed to MCFAs forms nanometer-sized vesicles ~200 nm in diameter that can fuse with colonocyte membranes. The arrival of nanometer-sized DSS/MCFA vesicles in the cytoplasm may activate intestinal inflammatory signaling pathways. We also show that the inflammatory activity of DSS is mediated by the dextran moieties. The deleterious effect of DSS is localized principally in the distal colon, therefore it will be important to chemically modify DSS to develop materials beneficial to the colon without affecting colon-targeting specificity.

Left-to-right shunt assessed by thermodilution during surgery for congenital heart disease

In nine children with congenital heart defects, left-to-right shunting was assessed during open-heart surgery by injecting cold 5% glucose solution through a left atrial line and detecting temperature change with a pulmonary arterial thermistor. The shunt was quantified by recording the temperature after injecting the same amount of cold glucose solution also through a central venous line. Oximetric determination of the left-to-right shunt was used as a reference. The result was expressed as shunt flow divided by pulmonary blood flow (Qshunt/Qp). The regression equation then obtained was Qshunt/Qp by thermodilution = 0.05 + 0.87 x Qshunt/Qp by oximetry. The residual standard deviation around the line of regression was 0.03. The thermodilution technique can be used for rapid assessment of the presence and magnitude of left-to-right shunting, provided that there is opportunity for the indicator to mix adequately in the main blood stream before shunting occurs.

Assessment of the magnitude of aortic regurgitation by dye injection into the descending aorta

A technique simpler than the angiographic method for estimating aortic regurgitant volume was tried with 31 patients with aortic insufficiency. During cardiac catheterization, we injected dye into the descending aorta while recording the dye dilution curve in the left ear. The distance between the aortic arch and the tip of the catheter at the lowest point from which the injected dye could be detected in the left ear was rated in terms of the number of corresponding vertebral bodies. This "distance score" closely correlated with the regurgitant stroke volume and with the fraction to total stroke volume, which were measured by angiocardiography (r = 0.927, p less than 0.001; and r = 0.900, p less than 0.001, respectively). The correlation coefficients of the aortographic grade to those parameters were not as high as they were in the relationship of the score to the same parameters. Therefore, these results indicate that the "distance score" is a practical method for assessing the magnitude of aortic regurgitant volume.

IV. Evaluation of dichromatic earpiece densitometry in children with left-to-right shunts

Earpiece densitometry was performed in 60 infants and children with left-to-right cardiovascular shunts. The method was found to possess a high diagnostic sensitivity with respect to identification of the left-to-right shunt. Earpiece densitometry was in this respect clearly superior to conventional method using oxygen saturation figures. Quantitation of pulmonary blood flow by both densitiometric and oxygen content technique in a small number of patients indicates that the dye dilution technique gives values somewhat in excess of the Fick method. It is concluded that quantitation of the magnitude of the left-to-right shunt and pulmonary blood flow is disturbed by the fact that indicator material is recirculated before the ascending limb of the primary curve is fully inscribed.