Enn Maripuu

One-lung ventilation induces hyperperfusion and alveolar damage in the ventilated lung: an experimental study

BACKGROUND One-lung ventilation (OLV) increases mechanical stress in the lung and affects ventilation and perfusion (V, Q). There are no data on the effects of OLV on postoperative V/Q matching. Thus, this controlled study evaluates the influence of OLV on V/Q distribution in a pig model using a gamma camera technique [single-photon emission computed tomography (SPECT)] and relates these findings to lung histopathology after OLV. METHODS Eleven anaesthetized and ventilated pigs (V(T)=10 ml kg(-1), Fio2=0.40, PEEP=5 cm H2O) were studied. After lung separation, OLV and thoracotomy were performed in seven pigs (OLV group). During OLV and in a two-lung ventilation (TLV), control group (n=4) ventilation settings remained unchanged. SPECT with (81m)Kr (ventilation) and (99m)Tc-labelled macro-aggregated albumin (perfusion) was performed before, during, and 90 min after OLV/TLV. Finally, lung tissue samples were harvested and examined for alveolar damage. RESULTS OLV affected ventilation and haemodynamic variables, but there were no differences between the OLV group and the control group before and after OLV/TLV. SPECT revealed an increase of perfusion in the dependent lung compared with baseline (49-56%), and a corresponding reduction of perfusion (51-44%) in non-dependent lungs after OLV. No perfusion changes were observed in the control group. This resulted in increased low V/Q regions and a shift of V/Q areas to 0.3-0.5 (10(-0.5)-10(-0.3)) in dependent lungs of OLV pigs and was associated with an increased diffuse alveolar damage score. CONCLUSIONS OLV in pigs results in a substantial V/Q mismatch, hyperperfusion, and alveolar damage in the dependent lung and may thus contribute to gas exchange impairment after thoracic surgery.

Regional lung perfusion estimated by electrical impedance tomography in a piglet model of lung collapse

The assessment of the regional match between alveolar ventilation and perfusion in critically ill patients requires simultaneous measurements of both parameters. Ideally, assessment of lung perfusion should be performed in real-time with an imaging technology that provides, through fast acquisition of sequential images, information about the regional dynamics or regional kinetics of an appropriate tracer. We present a novel electrical impedance tomography (EIT)-based method that quantitatively estimates regional lung perfusion based on first-pass kinetics of a bolus of hypertonic saline contrast. Pulmonary blood flow was measured in six piglets during control and unilateral or bilateral lung collapse conditions. The first-pass kinetics method showed good agreement with the estimates obtained by single-photon-emission computerized tomography (SPECT). The mean difference (SPECT minus EIT) between fractional blood flow to lung areas suffering atelectasis was -0.6%, with a SD of 2.9%. This method outperformed the estimates of lung perfusion based on impedance pulsatility. In conclusion, we describe a novel method based on EIT for estimating regional lung perfusion at the bedside. In both healthy and injured lung conditions, the distribution of pulmonary blood flow as assessed by EIT agreed well with the one obtained by SPECT. The method proposed in this study has the potential to contribute to a better understanding of the behavior of regional perfusion under different lung and therapeutic conditions.

Noise correlation in PET, CT, SPECT and PET/CT data evaluated using autocorrelation function: a phantom study on data, reconstructed using FBP and OSEM.

BackgroundPositron Emission Tomography (PET), Computed Tomography (CT), PET/CT and Single Photon Emission Tomography (SPECT) are non-invasive imaging tools used for creating two dimensional (2D) cross section images of three dimensional (3D) objects. PET and SPECT have the potential of providing functional or biochemical information by measuring distribution and kinetics of radiolabelled molecules, whereas CT visualizes X-ray density in tissues in the body. PET/CT provides fused images representing both functional and anatomical information with better precision in localization than PET alone.Images generated by these types of techniques are generally noisy, thereby impairing the imaging potential and affecting the precision in quantitative values derived from the images. It is crucial to explore and understand the properties of noise in these imaging techniques. Here we used autocorrelation function (ACF) specifically to describe noise correlation and its non-isotropic behaviour in experimentally generated images of PET, CT, PET/CT and SPECT.MethodsExperiments were performed using phantoms with different shapes. In PET and PET/CT studies, data were acquired in 2D acquisition mode and reconstructed by both analytical filter back projection (FBP) and iterative, ordered subsets expectation maximisation (OSEM) methods. In the PET/CT studies, different magnitudes of X-ray dose in the transmission were employed by using different mA settings for the X-ray tube. In the CT studies, data were acquired using different slice thickness with and without applied dose reduction function and the images were reconstructed by FBP. SPECT studies were performed in 2D, reconstructed using FBP and OSEM, using post 3D filtering. ACF images were generated from the primary images, and profiles across the ACF images were used to describe the noise correlation in different directions. The variance of noise across the images was visualised as images and with profiles across these images.ResultsThe most important finding was that the pattern of noise correlation is rotation symmetric or isotropic, independent of object shape in PET and PET/CT images reconstructed using the iterative method. This is, however, not the case in FBP images when the shape of phantom is not circular. Also CT images reconstructed using FBP show the same non-isotropic pattern independent of slice thickness and utilization of care dose function. SPECT images show an isotropic correlation of the noise independent of object shape or applied reconstruction algorithm. Noise in PET/CT images was identical independent of the applied X-ray dose in the transmission part (CT), indicating that the noise from transmission with the applied doses does not propagate into the PET images showing that the noise from the emission part is dominant. The results indicate that in human studies it is possible to utilize a low dose in transmission part while maintaining the noise behaviour and the quality of the images.ConclusionThe combined effect of noise correlation for asymmetric objects and a varying noise variance across the image field significantly complicates the interpretation of the images when statistical methods are used, such as with statistical estimates of precision in average values, use of statistical parametric mapping methods and principal component analysis. Hence it is recommended that iterative reconstruction methods are used for such applications. However, it is possible to calculate the noise analytically in images reconstructed by FBP, while it is not possible to do the same calculation in images reconstructed by iterative methods. Therefore for performing statistical methods of analysis which depend on knowing the noise, FBP would be preferred.

Ventilation Distribution Studies Comparing Technegas and "Gallgas" Using (GaCl3)-Ga-68 as the Label

Ventilation distribution can be assessed by SPECT with Technegas. This study was undertaken in piglets with different degrees of ventilation inhomogeneity to compare PET using 68Ga-labeled pseudogas or “Gallgas” with Technegas. Methods: Twelve piglets were studied in 3 groups: control, lobar obstruction, and diffuse airway obstruction. Two more piglets were assessed for lung volume (functional residual capacity). Results: In controls, SPECT and PET images showed an even distribution of radioactivity. With lobar obstruction, the absence of ventilation of the obstructed lobe was visible with both techniques. In diffuse airway obstruction, SPECT images showed an even distribution of radioactivity, and PET images showed more varied radioactivity over the lung. Conclusion: PET provides detailed ventilation distribution images and a better appreciation of ventilation heterogeneity. Gallgas with PET is a promising new diagnostic tool for the assessment of ventilation distribution.

Thallium-201 myocardial imaging at rest in male orienteers and other endurance athletes.

During the period 1979 to 1992, 16 sudden unexpected cardiac deaths were known to have occurred in young Swedish orienteers. Autopsy indicated myocarditis to be the most frequent finding, most often combined with extensive myocardial fibrosis. The aim of the present investigation was to explore whether young male orienteers show a higher frequency than other young elite endurance athletes (controls) in the occurrence of Thallium-201 myocardial perfusion defects at rest, suggestive of fibrosis evoked by myocarditis. Thallium-201 perfusion abnormalities at rest were more frequently found in the controls than in the orienteers (26% vs. 12%, p=0.03). Uneven Tl-201 perfusion was associated with left ventricular mass (r=0.32, r=0.24, p<0.01, p=0.02) and body weight (r=0.30, r=0.31, p<0.01, p=0.03) in orienteers and controls, respectively. Echocardiographic left ventricular wall motion abnormalities were found in 11 athletes (9 orienteers and 2 controls) but only two displayed an abnormal Thallium-201 perfusion scan at rest. Perfusion abnormalities at rest did not occur more frequently in the orienteers but were commonly found in both groups of apparently healthy athletes making it futile to discern abnormals from normals. Thallium-201 perfusion aberrations were not associated with left ventricular wall motion abnormalities obtained by echocardiography.

Evaluating abdominal oedema during experimental sepsis using an isotope technique

Purpose:  Abdominal oedema is common in sepsis. A technique for the study of such oedema may guide in the fluid regime of these patients.

Regional lung ventilation and perfusion by electrical impedance tomography compared to single-photon emission computed tomography

OBJECTIVE Electrical impedance tomography (EIT) is a noninvasive imaging modality that allows real-time monitoring of regional lung ventilation ([Formula: see text]) in intensive care patients at bedside. However, for improved guidance of ventilation therapy it would be beneficial to obtain regional ventilation-to-perfusion ratio ([Formula: see text]) by EIT. APPROACH In order to further explore the feasibility, we first evaluate a model-based approach, based on semi-negative matrix factorization and a gamma-variate model, to extract regional lung perfusion ([Formula: see text]) from EIT measurements. Subsequently, a combined validation of both [Formula: see text] and [Formula: see text] measured by EIT against single-photon emission computed tomography (SPECT) is performed on data acquired as part of a porcine animal trial. Four pigs were ventilated at two different levels of positive end-expiratory pressure (PEEP 0 and 15 cm H2O, respectively) in randomized order. Repeated injections of an EIT contrast agent (NaCl 10%) and simultaneous SPECT measurements of [Formula: see text] (81mKr gas) and [Formula: see text] (99mTc-labeled albumin) were performed. MAIN RESULTS Both [Formula: see text] and [Formula: see text] from EIT and SPECT were compared by correlation analysis. Very strong (r 2  =  0.94 to 0.95) correlations were found for [Formula: see text] and [Formula: see text] in the dorsal-ventral direction at both PEEP levels. Moderate (r 2  =  0.36 to 0.46) and moderate to strong (r 2  =  0.61 to 0.82) correlations resulted for [Formula: see text] and [Formula: see text] in the right-left direction, respectively. SIGNIFICANCE The results of combined validation indicate that monitoring of [Formula: see text] and [Formula: see text] by EIT is possible. However, care should be taken when trying to quantify [Formula: see text] by EIT, as imaging artefacts and model bias may void necessary spatial matching.

Rapid Bolus Administration Does Not Increase the Extravasation Rate of Albumin : A Randomized Controlled Trial in the Endotoxemic Pig

ABSTRACT Some experimental data suggest that rapid bolus administration of albumin causes less plasma-expanding effects than slow, continuous infusion. To determine whether rapid bolus administration, in comparison with slow infusion, results in greater extravasation of albumin in experimental septic shock we performed a randomized controlled trial with 32 endotoxemic pigs. The animals were monitored and ventilated with standard intensive care equipment and given 10 mL × kg−1 5% albumin labeled with Technetium-99m, either as a rapid 15-min bolus (Bolus group, n = 16) or as a 2-h infusion (Infusion group, n = 16). Radioactivity was monitored in plasma, extracellular microdialysate, and urine for 6 h. Physiological parameters were monitored hourly. Radioactivity in the liver, spleen, kidney, and lung was analyzed post mortem. The plasma area under the curve activity0–6 h was 4.4 ± 0.9 × 107 in the Bolus group and 4.4 ± 1.1 × 107 counts × min−1 × mL−1 × h in the Infusion group. Blood hemoglobin levels increased in both groups, suggesting severe capillary leakage. Yet, there were no group differences in albumin radioactivity in plasma, muscle tissue, urine, or in the post-mortem analysis of the organs. Following albumin administration, circulatory and respiratory parameters were similar in the two groups. In conclusion, the present results suggest that albumin might be given as a bolus without leading to increased extravasation of albumin, in contrast to previous animal experiments in rodents.

0976. Similar effect of albumin given either as a rapid bolus or slow infusion in a large animal model of sepsis

The strategy of fluid resuscitation in severe sepsis and septic shock is a matter of ever-ongoing debate. Current sepsis guidelines recommend albumin in patients requiring large amounts of crystalloids for circulatory stability. Although the same guidelines also recommend bolus administration of fluid, concerns have been raised that fluid boluses might lead to increased extravasation of albumin leading to sustained tissue edema in patients with sepsis-induced activation of the systemic inflammatory response.

Mechanical ventilation worsens abdominal edema and inflammation in porcine endotoxemia.

IntroductionWe hypothesized that mechanical ventilation per se increases abdominal edema and inflammation in sepsis and tested this in experimental endotoxemia.MethodsThirty anesthetized piglets were allocated to one of five groups: healthy control pigs breathing spontaneously with continuous positive pressure of 5 cm H2O or mechanically ventilated with positive end-expiratory pressure of 5 cm H2O, and endotoxemic piglets during mechanical ventilation for 2.5 hours and then continued on mechanical ventilation with positive end-expiratory pressure of either 5 or 15 cm H2O or switched to spontaneous breathing with continuous positive pressure of 5 cm H2O for another 2.5 hours. Abdominal edema formation was estimated by isotope technique, and inflammatory markers were measured in liver, intestine, lung, and plasma.ResultsHealthy controls: 5 hours of spontaneous breathing did not increase abdominal fluid, whereas mechanical ventilation did (Normalized Index increased from 1.0 to 1.6; 1 to 3.3 (median and range, P < 0.05)). Endotoxemic animals: Normalized Index increased almost sixfold after 5 hours of mechanical ventilation (5.9; 4.9 to 6.9; P < 0.05) with twofold increase from 2.5 to 5 hours whether positive end-expiratory pressure was 5 or 15, but only by 40% with spontaneous breathing (P < 0.05 versus positive end-expiratory pressure of 5 or 15 cm H2O). Tumor necrosis factor-α (TNF-α) and interleukin (IL)-6 in intestine and liver were 2 to 3 times higher with mechanical ventilation than during spontaneous breathing (P < 0.05) but similar in plasma and lung. Abdominal edema formation and TNF-α in intestine correlated inversely with abdominal perfusion pressure.ConclusionsMechanical ventilation with positive end-expiratory pressure increases abdominal edema and inflammation in intestine and liver in experimental endotoxemia by increasing systemic capillary leakage and impeding abdominal lymph drainage.