Clinical physiology and functional imaging
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Clin Physiol Funct Imaging · Nov 2016
Dynamic cerebral autoregulation to induced blood pressure changes in human experimental and clinical sepsis.
Previous studies have demonstrated that dynamic cerebral autoregulation to spontaneous fluctuations in blood pressure is enhanced following lipopolysaccharide (LPS) infusion, a human experimental model of early sepsis, whereas by contrast it is impaired in patients with severe sepsis or septic shock. In this study, we hypothesized that this pattern of response would be identical during induced changes in blood pressure. Dynamic cerebral autoregulation was assessed in nine healthy volunteers and six septic patients. ⋯ In healthy volunteers, thigh-cuff deflation caused a MAP reduction of 16 (13-20) % at baseline and 18 (16-20) % after LPS, while the MAP reduction was 12 (11-13) % in patients (P<0·05 versus volunteers at baseline; P<0·01 versus volunteers after LPS). The corresponding RoR values increased from 0·46 (0·31-0·49) s(-1) at baseline to 0·58 (0·36-0·74) s(-1) after LPS (P<0·05) in healthy volunteers, whereas they were similar to values observed in patients [0·43 (0·36-0·52) s(-1) ; P = 0·91 versus baseline; P = 0·14 versus LPS]. While our findings support the concept that dynamic cerebral autoregulation is enhanced during the very early stages of sepsis, they remain inconclusive with regard to more advanced stages of disease, because thigh-cuff deflation failed to induce sufficient MAP reductions in patients.
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Clin Physiol Funct Imaging · Mar 2016
Multicenter StudyThe accuracy of quantitative parameters in (99m) Tc-MAG3 dynamic renography: a national audit based on virtual image data.
Assessment of image analysis methods and computer software used in (99m) Tc-MAG3 dynamic renography is important to ensure reliable study results and ultimately the best possible care for patients. In this work, we present a national multicentre study of the quantification accuracy in (99m) Tc-MAG3 renography, utilizing virtual dynamic scintigraphic data obtained by Monte Carlo-simulated scintillation camera imaging of digital phantoms with time-varying activity distributions. Three digital phantom studies were distributed to the participating departments, and quantitative evaluation was performed with standard clinical software according to local routines. ⋯ The Tmax estimates showed a similar trend, but the difference was only significant for the right kidney. There was a significant bias in the measured DRF for all phantoms caused by different positions of the left and right kidney in the anterior-posterior direction. In conclusion, this study shows that virtual scintigraphic studies are applicable for quality assurance and that there is a considerable uncertainty associated with standard quantitative parameters in dynamic (99m) Tc-MAG3 renography, especially for patients with impaired renal function.
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Clin Physiol Funct Imaging · Sep 2015
Comparative Study Clinical TrialRelationship between pulse pressure variation and echocardiographic indices of left ventricular filling pressure in critically ill patients.
Pulse pressure variation (PPV) is a dynamic index of fluid responsiveness. This parameter helps clinicians in improving haemodynamic status while avoiding potential fluid overload. Echocardiographic indices, such as E/E' ratio and left atrial (LA) strain by speckle tracking echocardiography (STE), are used to estimate left ventricular (LV) filling pressures. This study aimed at exploring the relationship between PPV and echocardiographic indices of LV filling pressures in critically ill patients. ⋯ In a group of mechanically ventilated patients PPV, derived from pulse contour analysis, and echocardiographic preload parameters were well correlated. Global PALS by STE provided better estimation of PPV than mean E/E' ratio. PALS seems a potential alternative to PPV in assessing fluid responsiveness in critically ill patients.
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Clin Physiol Funct Imaging · Sep 2015
Local architecture of the vastus intermedius is a better predictor of knee extension force than that of the other quadriceps femoris muscle heads.
The purpose of this study was to determine whether the muscle architecture of each head of the quadriceps femoris (QF) at multiple regions can be used to predict knee extension force. Muscle thickness and pennation angle were measured using sonographic images from multiple regions on each muscle of the QF with the knee flexed to 90°. The fascicle lengths of the rectus femoris (RF), vastus lateralis (VL) and vastus intermedius (VI) muscles were estimated based on sonographic images taken along the length of the thigh. ⋯ The muscle thickness of the ant-VI was selected as an independent variable in the first step of the linear regression analysis (R(2) = 0.66, P<0.01). In the second step, pennation angle of the lat-VI was added to the model (R(2) = 0.91, P<0.01). These results suggest that among the four muscles that make up the QF, the muscle architecture of the VI is the best predictor of knee extension force.
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Clin Physiol Funct Imaging · May 2015
Comparative StudyExtra-cerebral oxygenation influence on near-infrared-spectroscopy-determined frontal lobe oxygenation in healthy volunteers: a comparison between INVOS-4100 and NIRO-200NX.
Frontal lobe oxygenation (Sc O2 ) is assessed by spatially resolved near-infrared spectroscopy (SR-NIRS) although it seems influenced by extra-cerebral oxygenation. We aimed to quantify the impact of extra-cerebral oxygenation on two SR-NIRS derived Sc O2 . ⋯ For all interventions, 35% of the INVOS-4100 signal reflected extra-cerebral oxygenation while, on the other hand, NIRO-200NX did not follow changes in a calculated estimate of cerebral capillary oxygenation. Thus, the NIRO-200NX and INVOS-4100 do not provide for unbiased evaluation of the cerebral signal.