In vivo calibration of the T2* cardiovascular magnetic resonance method at 1.5 T for estimation of cardiac iron in a minipig model of transfusional iron overload

Background Non-invasive estimation of the cardiac iron concentration (CIC) by T2* cardiovascular magnetic resonance (CMR) has been validated repeatedly and is in widespread clinical use. However, calibration data are limited, and mostly from post-mortem studies. In the present study, we performed an in vivo calibration in a dextran-iron loaded minipig model. Methods R2* (= 1/T2*) was assessed in vivo by 1.5 T CMR in the cardiac septum. Chemical CIC was assessed by inductively coupled plasma-optical emission spectroscopy in endomyocardial catheter biopsies (EMBs) from cardiac septum taken during follow up of 11 minipigs on dextran-iron loading, and also in full-wall biopsies from cardiac septum, taken post-mortem in another 16 minipigs, after completed iron loading. Results A strong correlation could be demonstrated between chemical CIC in 55 EMBs and parallel cardiac T2* (Spearman rank correlation coefficient 0.72, P < 0.001). Regression analysis led to [CIC] = (R2* − 17.16)/41.12 for the calibration equation with CIC in mg/g dry weight and R2* in Hz. An even stronger correlation was found, when chemical CIC was measured by full-wall biopsies from cardiac septum, taken immediately after euthanasia, in connection with the last CMR session after finished iron loading (Spearman rank correlation coefficient 0.95 (P < 0.001). Regression analysis led to the calibration equation [CIC] = (R2* − 17.2)/31.8. Conclusions Calibration of cardiac T2* by EMBs is possible in the minipig model but is less accurate than by full-wall biopsies. Likely explanations are sampling error, variable content of non-iron containing tissue and smaller biopsies, when using catheter biopsies. The results further validate the CMR T2* technique for estimation of cardiac iron in conditions with iron overload and add to the limited calibration data published earlier.

Interstitial Glucose and Lactate Levels Are Inversely Correlated With the Body Mass Index: Need for In Vivo Calibration of Glucose Sensor Results With Blood Values in Obese Patients

Background: Continuously measured glucose and lactate levels in interstitial fluid (ISF) may markedly differ from their respective blood levels. Methods: Combining microdialysis with a bioanalytical microsystem, the interstitial glucose and lactate concentrations of eight male volunteers with different body mass index (BMI) were monitored during a 2-fold glucose tolerance test over the period of three hours. Results: Significant correlations were found between abdominally measured sensor results and reference measurements ( R2 = .967 for glucose and R2 = .936 for lactate, P < .05). The physiological delay of the abdominally observed glucose appearance in the ISF correlated positively with the BMI ( R2 = .787, P < .05). The relative in vivo recovery of glucose and lactate was inversely proportional to the BMI of the volunteers ( R2 = .540 for glucose, R2 = .609 for lactate, P < .05). One subject with a BMI of > 34 kg/m2 showed abdominally as well as the antebrachially significantly reduced tissue glucose values compared to blood glucose values ( P < .001). Conclusions: A very good correlation between abdominally measured sensor results and the results of the reference method verified the reliability of the BioMEMS. The abdominally measured glucose level in ISF decreased significantly with increasing BMI. Therefore, an in vivo calibration of glucose levels in ISF with blood levels seems to be necessary especially in markedly obese subjects.

Clinical evaluation of the new BMU 40 in-line blood analysis monitor

Background: Accurate information about different blood parameters is essential in maintaining haemodynamics, perfusion and gas exchange during cardiopulmonary bypass (CPB). For this purpose, precise, accurate and continuous measurement and monitoring, preferably visually available, is needed.The objective of this clinical study was to compare the newly developed continuous in-line blood parameter monitoring system (CIBPMS) BMU 40 with a reference laboratory analyser with regards to the precision and accuracy of blood parameter measurement. Methods: Thirty adult patients underwent elective cardiac surgery, CPB and mild hypothermia (32°C). At five predetermined time points (S1 — S5) arterial and venous blood samples were analysed using the BMU 40 for five different parameters (PaO2(37°C), PaO2(act), SvO2, Hb(ven) and Hct(ven)) and these results were compared to the gold standard laboratory analyser, the ABL 700. Results: A total of 150 paired blood samples were included to compare means, to analyse correlation, and to calculate measures of bias, precision, limits of agreement and 95% confidence intervals. Results revealed good agreement between the two devices for all parameters. Bias ± precision of S2 — S5 PaO 2(37°C) were: 2.17 ± 9.61; PaO2(act) 2.58 ± 9.54; SvO2 -1.44 ± 2.35; Hb(ven) 0.01 ± 0.42; Hct(ven) 0.04 ± 1.29. Statistically significant differences were detected for SvO2 (p<0.00001) at S1. Correlations after this first time point (S1) improved following an in vivo calibration. Conclusion: The BMU 40 is a precise, accurate and reliable continuous in-line blood parameter measuring system that can easily be used within a standard CPB setup. However, present data suggest an in vivo calibration of the BMU 40 should be performed.