Strategies preventing deep sternal wound infection in cardiac surgery review.

Deep sternal wound infection is a feared complication of cardiac surgery due to the negative impact on mortality, morbidity and long-term survival. Its incidence has remained more or less unchanged over the last three decades despite the significant increase in patients´ morbidity and complexity of cardiac surgery. The review summaries strategies to reduce the incidence of deep sternal wound reflecting general surgical site infection prevention and specificities of surgery performed through the median sternotomy. Furthermore, contemporary evidence-based recommendations for prevention of this complication are highlighted in the review. Key words: sternal infection - prevention - cardiac surgery.

Efficiency of riboflavin and ultraviolet light treatment against high levels of biofilm-derived Staphylococcus epidermidis in buffy coat platelet concentrates.

BACKGROUND AND OBJECTIVES: Staphylococcus epidermidis forms surface-attached aggregates (biofilms) in platelet concentrates (PCs), which are linked to missed detection during PC screening. This study was aimed at evaluating the efficacy of riboflavin-UV treatment to inactivate S. epidermidis biofilms in buffy coat (BC) PCs. MATERIALS AND METHODS: Biofilm and non-biofilm cells from S. epidermidis ST-10002 and S. epidermidis AZ-66 were individually inoculated into whole blood (WB) units (~106 colony-forming units (CFU)/ml) (N = 4-5). One spiked and three unspiked WB units were processed to produce a BC-PC pool. Riboflavin was added to the pool which was then split into two bags: one for UV treatment and the second was untreated. Bacterial counts were determined before and after treatment. In vitro PC quality was assessed by flow cytometry and dynamic light scattering. RESULTS: Bacterial counts were reduced during BC-PC production from ~106 CFU/ml in WB to 103 -104 CFU/ml in PCs (P < 0·0001). Riboflavin-UV treatment resulted in significantly higher reduction of S. epidermidis AZ-66 than strain ST-10002 (≥3·5 log reduction and 2·6-2·8 log reduction, respectively, P < 0·0001). Remaining bacteria post-treatment were able to proliferate in PCs. No differences in S. epidermidis inactivation were observed in PCs produced from WB inoculated with biofilm or non-biofilm cells (P > 0·05). Platelet activation was enhanced in PCs produced with WB inoculated with biofilms compared to non-biofilm cells (P < 0·05). CONCLUSION: Riboflavin-UV treatment was similarly efficacious in PCs produced from WB inoculated with S. epidermidis biofilm or non-biofilm cells. Levels of biofilm-derived S. epidermidis ≥103 CFU/ml were not completely inactivated; however, further testing is necessary with lower (real-life) bacterial levels.

Comparison of bacterial attachment to platelet bags with and without preconditioning with plasma.

BACKGROUND AND OBJECTIVES: Canadian Blood Services produces apheresis and buffy coat pooled platelet concentrates (PCs) stored in bags produced by two different manufacturers (A and B, respectively), both made of polyvinyl chloride-butyryl trihexyl citrate. This study was aimed at comparing Staphylococcus epidermidis adhesion to the inner surface of both bag types in the presence or absence of plasma factors. MATERIALS AND METHODS: Sets (N = 2-6) of bags type A and B were left non-coated (control) or preconditioned with platelet-rich, platelet-poor or defibrinated plasma (PRP, PPP and DefibPPP, respectively). Each bag was inoculated with a 200-ml S. epidermidis culture adjusted to 0·5 colony-forming units/ml. Bags were incubated under platelet storage conditions for 7 days. After culture removal, bacteria attached to the plastic surface were either dislodged by sonication for bacterial quantification or examined in situ by scanning electron microscopy (SEM). RESULTS: Higher bacterial adhesion was observed to preconditioned PC bags than control containers for both bag types (P < 0·0001). Bacterial attachment to preconditioned bags was confirmed by SEM. Bacteria adhered equally to both types of containers in the presence of PRP, PPP and DefibPPP residues (P > 0·05). By contrast, a significant increase in bacterial adherence was observed to type A bags compared with type B bags in the absence of plasma (P < 0·05) [Correction added on 16 June 2017, after first online publication: this sentence has been corrected]. CONCLUSION: The ability of S. epidermidis to adhere to preconditioned platelet collection bags depends on the presence of plasma factors. Future efforts should be focused on reducing plasma proteins' attachment to platelet storage containers to decrease subsequent bacterial adhesion.

Bacterial survival and distribution during buffy coat platelet production.

BACKGROUND AND OBJECTIVES: At Canadian Blood Services, buffy coat (BC) platelet concentrates (BC-PCs) show a generally lower bacterial contamination rate than apheresis PCs. This study investigated whether the PC production method contributes to this observation. MATERIALS AND METHODS: Whole blood (WB) inoculated with eight bacterial strains was processed using the BC method. Bacteria were enumerated throughout BC-PC production and subsequent PC storage. Endotoxin production and bacterial adhesion to PC bags were evaluated during PC storage. PC quality was monitored by CD62P expression (flow cytometry) and changes in dynamic light scattering (ThromboLUX® ). RESULTS: During overnight WB hold, Staphylococcus epidermidis titres remained unchanged, commercial Escherichia coli and Klebsiella pneumoniae were eliminated and the remaining organisms proliferated to high concentrations. Through BC-PC production, bacteria segregated preferentially towards the cellular fractions compared to plasma (P < 0·05). During PC storage, most bacteria adhered to the PC bags and Gram negatives produced clinically significant endotoxin levels. Changes in CD62P expression or ThromboLUX scoring did not consistently reflect bacterial contamination in BC-PCs. CONCLUSION: WB hold during BC-PC production does not have a broad-spectrum bactericidal effect, and therefore, other factors contribute to low rates of contamination in BC-PCs.

[Transplantation of allogeneic bone graft in the therapy of massive post-sternotomy defects - 6 years of experience with the method]. / Transplantace allogenního kostního stepu v lécbe rozsáhlých post-sternotomických defektu - 6 let zkuseností s metodou.

INTRODUCTION: Early complications due to deep sternal wound infection pose a serious problem in cardiac surgery, with an up to 40% risk of mortality. Massive loss of sternum bone tissue and adjacent ribs results in major chest wall instability difficult to resolve using classical AO osteosynthesis procedures, causing respiratory insufficiency making the disconnection from artificial pulmonary ventilation difficult, and additional defects of soft tissue healing. Based on orthopaedic experience with bone defect replacement, we used the allogeneic bone graft method to reconstruct the chest wall. METHODS: In the period of 20112015 we performed the transplantation of an allogeneic bone graft in 13 patients. In 10 cases, an allograft of the sternum was used, in one case an allograft of the calva bone and in two cases the crushed spongy bone was used. After primary cardiac surgery, a massive post-sternotomy defect of the chest wall developed in all the 13 patients due to deep sternal infection and osteomyelitis of the sternum and adjacent ribs. Vacuum wound drainage was applied in the treatment of all the patients. To stabilize the chest and the graft, transverse titanium plates were used, fixed using bicortical screws. The bone allograft was prepared by the official Tissue Centre. Crushed allogeneic spongy bone was applied to reinforce the line of contact of the graft and the edges of the residual skeleton. In 12 cases, the soft tissue was closed by direct suture of mobilized pectoral flaps. In one case, V-Y transposition of the pectoral flap was performed. RESULTS: In 8 cases, healing of the reconstructed chest wall occurred without further complications. In 4 cases, additional re-suture of soft tissues and skin in the lower pole of the wound was needed while the patients were still in the hospital. However, excellent chest wall stability along with adjustment of respiratory insufficiency and a very good cosmetic effect in the wound were achieved in all the 12 cases. In two cases, explantation of the plates was required. In one case, severe concomitant complications and no healing of the wound resulted in death within half a year after the reconstruction. The median follow-up period of all patients in the series was 21 months (136). In 5 cooperating patients, scintigraphy of the chest wall was performed repeatedly during the follow-up period showing a high healing activity of the graft and particularly of the crushed spongy bone. CONCLUSION: Our existing results show that allogeneic bone graft transplantation is a promising and easily applied method in the management of serious tissue loss in sternal dehiscence with favourable functional and cosmetic effects.Key words: sternotomy deep sternal wound infection massive post-sternotomy defect allogeneic bone graft.

Adhesion of anaerobic bacteria to platelet containers.

Anaerobic Propionibacterium acnes and Staphylococcus saccharolyticus are frequently isolated during platelet screening with anaerobic culture methods. Although neither P. acnes nor S. saccharolyticus proliferates during platelet storage, both species survive well in this environment. This study was aimed at determining whether strains of P. acnes and/or S. saccharolyticus form surface-attached bacterial cell aggregates, known as biofilms, under platelet storage conditions. We report that these organisms are able to adhere to the inner surface of platelet containers in tight interaction with activated platelets.

[Hepatic cein catheterisation -  selected assessment aspects]. / Katetrizace jaterních zil -  vybrané aspekty hodnocení

INTRODUCTION: Hepatic vein catheterisation and portal hypertension assessment using the value of portal hepatic gradient (HVPG) is currently a method of choice. METHODOLOGY: In our paper we shall compare HVPG with the so called direct gradient -  using the difference in pressure in the portal vein and free hepatic vein in 5 groups of patients with liver cirrhosis. RESULTS: Hepatic vein catheterisation is reliable for assessing the portal hypertension in the group of patients with liver cirrhosis of ethylic etiology. In patients with liver cirrhosis resulting from hepatitis B, Wilsons disease or primary biliary cirrhosis, a statistically significant difference between HVPG and the direct gradient has been found. In patients with liver cirrhosis resulting from hepatitis C the obtained values differed but without statistical significance. CONCLUSION: In catheterisation of hepatic veins the HVPG value in liver cirrhosis with a presinusoidal component may be reduced, which has to be primarily taken into account when assessing the relationship to some critical values of the portal hepatic gradient.

Serratia marcescens strains implicated in adverse transfusion reactions form biofilms in platelet concentrates and demonstrate reduced detection by automated culture.

BACKGROUND AND OBJECTIVES: Serratia marcescens is a gram-negative bacterium that has been implicated in adverse transfusion reactions associated with contaminated platelet concentrates. The aim of this study was to investigate whether the ability of S. marcescens to form surface-attached aggregates (biofilms) could account for contaminated platelet units being missed during screening by the BacT/ALERT automated culture system. MATERIALS AND METHODS: Seven S. marcescens strains, including biofilm-positive and biofilm-negative control strains and five isolates recovered from contaminated platelet concentrates, were grown in enriched Luria-Bertani medium and in platelets. Biofilm formation was examined by staining assay, dislodging experiments and scanning electron microscopy. Clinical strains were also analysed for their ability to evade detection by the BacT/ALERT system. RESULTS: All strains exhibited similar growth in medium and platelets. While only the biofilm-positive control strain formed biofilms in medium, this strain and three clinical isolates associated with transfusion reactions formed biofilms in platelet concentrates. The other two clinical strains, which had been captured during platelet screening by BacT/ALERT, failed to form biofilms in platelets. Biofilm-forming clinical isolates were approximately three times (P<0·05) more likely to be missed by BacT/ALERT screening than biofilm-negative strains. CONCLUSION: S. marcescens strains associated with transfusion reactions form biofilms under platelet storage conditions, and initial biofilm formation correlates with missed detection of contaminated platelet concentrates by the BacT/ALERT system.

PEGylation prevents bacteria-induced platelet activation and biofilm formation in platelet concentrates.

Bacterial contamination of platelet concentrates represents the greatest post-transfusion infectious risk. Biofilm formation in this environment resulting from platelet-bacteria interactions can lead to non-uniform contaminant distribution and thus missed detection. As formation of platelet-bacteria aggregates is largely based on receptor-ligand interactions, we examined whether shielding these events would result in reduced biofilm formation by contaminant bacteria. We introduced methoxypoly(ethylene glycol) to covalently modify the platelet surface using a process termed 'PEGylation'. In the first study of its kind, we demonstrate that PEGylated platelet concentrates inoculated with Staphylococcus epidermidis display a significant reduction in bacterial binding and biofilm formation.

Negative pressure therapy as a treatment modality for surgical site infection in cardiac surgery.

BACKGROUND: Negative pressure therapy (NPT), primarily introduced for the treatment of pressure ulcers or chronic debilitating wounds, has recently emerged as a novel treatment strategy in the field of cardiac surgery, providing superior results to the conventional therapeutic strategies. PATIENTS AND METHODS: From November 2004 to October 2005, 25 patients underwent NPT (negative pressure therapy). Four patients (16%) were treated for extensive leg-wound infections, 10 (40%) were treated for superficial sternal wound infections and 11 (44%) for deep sternal wound infections. The median age was 67.9 years (range 48 to 79) and the median BMI was 34.2 kg/m2 (range 28 to 41). Because of wound infection complications, 11 patients (44%) were re-admitted to the department. In 13 patients (52%), NPT was employed after the failure of the conventional treatment strategy. RESULTS: All 25 patients were successfully healed. In-hospital mortality was 0% and 30-day survival was 100%. The overall length of hospitalization reached 36.4 days (range 11 to 62). The median number of dressing changes was 4.9 (range 3 to 9). The median NPT treatment time until the surgical closure was 9.7 days (range 6 to 24 days). In 17 patients (68%), the excessive residual sternal defect required a local advancement flap transfer. One patient (4%) with a chronic wire-related fistula was re-admitted 6 months after NPT therapy. CONCLUSION: NPT therapy can be considered as an effective treatment strategy associated with a low risk of procedure failure and wound infection recurrence, particularly in the management of sternal wound infection after cardiac surgery.

[Vacuum-assisted closure as a treatment modality for surgical site infection in cardiac surgery]. / Podtlaková terapie (vacuum-assisted closure) v lébe ranných infekcních komplikací po kardiochirurgických výkonech.

BACKGROUND: The vacuum-asssited closure has represented an encouraging treatment modality in treatment of surgical site infection in cardiac surgery, providing superior results compared with conventional treatment strategies, particularly in the treatment of deep sternal wound infection. METHODS: From November 2004 to January 2007, 40 patients, undergoing VAC therapy (VAC system, KCI, Austria, Hartmann-Rico Inc., Czech Republic) for surgical site infection following cardiac surgery, were prospectively evaluated. Four patients (10%) were treated for extensive leg-wound infection, 10 (25%) were treated for superficial sternal wound infection and 26 (65%) for deep sternal wound infection. The median age was 69.9 +/- 9.7 years and the median BMI was 33.2 +/- 5.0 kg/m2. Twenty-three patients (57%) were women and diabetes was present in 22 patients (55%). The VAC was employed after the previous failure of the conventional treatment strategy in 7 patients (18%). RESULTS: Thirty-eight patients (95%) were successfully healed. Two patients (5%) died, both of deep sternal infetion consequences. The overall length of hospitalization was 36.4 +/- 22.6 days. The median number of dressing changes was 4.6 +/- 1.8. The median VAC treatment time until surgical closure was 9.7 +/- 3.9 days. The VAC therapy was solely used as a bridge to the definite wound closure. Four patients (10%) with a chronic fistula were re-admitted with the range of 1 to 12 months after the VAC therapy. CONCLUSION: The VAC therapy is a safe and reliable option in the treatment of surgical site infection in the field of cardiac surgery. The VAC therapy can be considered as an effective adjunct to convetional treatment modalities for the therapy of extensive and life-threatening wound infection following cardiac surgery, particurlarly in the group of high-risk patients.

[Pulmonary trombendarterectomy in the patient with the symptoms of massive pulmonary embolism: case report]. / Trombendarterektomie plicnice u nemocného s klinickými známkami masivní embolie plicnice: kazuistika.

The case-report of a 57-year-old patient with the symptoms of massive pulmonary embolism is presented. The patient was admitted to the hospital in the cardiogenic shock, ventilated and with high dose of inotropic support. It was impossible to find out the exact data from personal history. The patient was operated on urgently. The chronic occlusion of the right pulmonary artery due to the chronic tromboembolic disease was found out. Thromboendarterectomy of the pulmonary artery was successfully performed. Three month after operation the patient is in excellent clinical condition almost without any functional limitation. Some atypical features of this case are stressed in the discussion: the urgency of the operation for chronic tromboembolic disease with unilateral involvement, which simulated pulmonary embolism and operation in mild hypothermia without circulatory arrest.

[Long-term pharmacological treatment of portal hypertension]. / Dlouhodobá farmakologická lécba portální hypertenze.

Portal hypertension is an unavoidable complication of liver cirrhosis, which usually limits the survival (bleeding from esophageal varices, ascites). Increase in portal pressure is not only due to mechanical obstruction of portal circulation, but there is also a dynamic component (endothelial dysfunction of hepatic microcirculation) and increased blood flow through the splanchnic circulation. For the long-term treatment of portal hypertension two groups of medicaments are available at present: non-selective betablockers (vasoconstriction in splanchnic bed) and nitrates (lowering of intrahepatic resistance). Long-term treatment is necessary in these situations: Primary prophylaxis of bleeding from esophageal varices (in patients, who never bled, but with "risk" varices)--non-selective betablockers; secondary prophylaxis (in patients after variceal bleeding)--non-selective betablockers (possibly with nitrates) or endoscopic treatment. It is clearly documented, that this treatment lowers the risk of the first or repeated bleeding from varices and hence lowers the mortality and morbidity due to this complication in patients with liver cirrhosis. Another serious complication of liver cirrhosis is the spontaneous bacterial peritonitis. All patients after that infection have to receive prophylactic treatment with antibiotics. This treatment should be long life, till the disappearance of ascites or till the liver transplantation.

Effect of peroral administration of isosorbide dinitrate on portal pressure and blood flow in patients with cirrhosis of the liver.

The effect of slow-release isosorbide dinitrate, given orally four times daily for 14 days, on the portal circulation was studied in 10 patients with liver cirrhosis and oesophageal varices. Mean arterial pressure and heart rate were not influenced significantly by isosorbide dinitrate. Statistically significant dilation of the portal vein by 11.9% and an increase in blood flow velocity by 35.4% and in portal blood flow rate by 54.3% were observed at the end of therapy. The average wedged hepatic vein pressure was 32.9 mmHg before therapy and after therapy it was decreased to 60.5%. The slight decrease observed in free hepatic vein pressure was not statistically significant. Before treatment the portohepatic gradient was four times above normal and after therapy it fell to 9.5 mmHg. The results indicate that, in patients with portal hypertension, an improvement in haemodynamics can be achieved by the use of isosorbide dinitrate. This improvement may lead to the prevention of bleeding from oesophageal varices.

[The effect of the heptoprotective agent LIV 52 on liver damage]. / Vliv hepatoprotektiva LIV 52 na jaterní poskozeni.

BACKGROUND: The action of hepatoprotective drugs is a steady subject of discussions. Despite the equivocal character of action hepatoprotective drugs are used, despite the fact that the effect is partly a placebo effect. In the literature are reports on preparation LIV 52 which is a mixture of substances of plant origin and improves the subjective complaints of patients as well as the objective condition of patients with liver disease. METHODS AND RESULTS: The effect of preparation LIV 52 was investigated in a retrospective study in 19 patients with liver damage. In the majority liver damage caused by alcohol was involved, steatosis and persisting hepatitis without the finding of chronic hepatitis B and C. The authors investigated biochemical parameters (bilirubin, ALT, AST, ALP, TZR, cholesterol). The size of the liver was assessed by ultrasonography and the subjective status of the patients was recorded. Within one year of administration of the preparation subjective improvement occurred, hepatomegaly diminished and the activity of aminotransferases declined. CONCLUSIONS: Administration of LIV 52 can improve the subjective condition and clinical parameters in patients with liver damage, in particular in alcoholic liver damage and in steatosis. The effect is certainly due also to better motivation on the patients part, better lifestyle and dietary measures. After one year of treatment no undesirable side-effects were detected.

[Experimental study of the action of antimalarial agents with respect to therapy in porphyria. Combined effect of chloroquine and pyrimethamine]. / Experimentální studium mechanismu úcinku antimalarik se zretelem k terapii porfyrické choroby. Kombinovaný úcinek chlorochinu a pyrimetaminu.

On an experimental model created from semiaerobically cultivated yeast cells of Caccharomyces cerevisiae (RIMB-75) the authors tested the effect of antimalarics used or tested for treatment of symptomatic liver porphyria. Chloroquine and pyrimethamine inhibited the synthesis of porphyrins, whereby pyrimethamine was more effective. Chloroquine released moreover intracellular porphyrins, contrary to pyrimethamine, which caused their intracellular cumulation. An equimolar combination of the two preparations preserved the inhibitory action of pyrimethamine, and the intracellular porphyrin content was reduced. Based on experimental results the suggested combination of chloroquine and pyrimethamine was successfully tested in clinical work.

[The effect of diltiazem on hemodynamic parameters in patients with liver cirrhosis]. / Vliv diltiazemu na hemodynamické parametry u nemocných s jaterní cirhózou.

Previous investigations of authors abroad provided evidence of a reduction of portal pressure by blockers of slow calcium channels group II by verapamil. We decided to investigate the effect of a quite new preparation dilthiazem on the portal haemodynamics in patients with compensated cirrhosis of the liver and oesophageal varices. Doppler examinations of the width, rate of blood flow and flow through the trunk of the portal vein did not prove a statistically significant effect of dilthiazem on the investigated parameters. After the preparation a significant decline of the median pressure in the pulmonary artery was recorded at the 5% level of significance. The significantly elevated pressure values in the wedged position in the hepatic vein (WHVP) as well as of the portohepatic gradient (P-H) rose further after administration of the preparation (WHVP by 12.3%, p P-H by 15%). Even maximum doses of dilthiazem did not influence the portal flow in patients and did not lead to a reduction of the portohepatic gradient. From the results it is apparent that dilthiazem is not suitable for the treatment of portal hypertension.

[The effect of glucagon on portal hemodynamics in patients with liver cirrhosis]. / Ucinek glukagonu na portální hemodynamiku u nemocných s jaterní cirhózou.

The authors assessed in 12 patients with compensated cirrhosis of the liver, portal hypertension and oesophageal varices, using a Doppler flowmeter Toshiba SAL 50A/SDL 01 under basal conditions, changes in the width, rate of blood flow and blood flow though the trunk of the portal vein before and after intravenous administration of 1 mg glucagon. The width of the trunk of the portal vein did not change significantly during assessment. A statistically significantly increased flow through the portal vein was recorded starting during the 5th minute, and it correlated with the increased velocity of the blood flow. The increased flow persisted to the 20th minute after glucagon administration. The drop of pressure in a wedged position assessed in the hepatic veins after administration of the drug was not significant, the pressure in the free hepatic vein increased insignificantly. On the whole the portohepatic gradient declined by 10.5%, the drop was not significant. Glucagon in pharmacological doses has an early onset of action even in cirrhotic subjects whereby the increased flow through the portal vein does not lead to a rise of the portohepatic gradient. Glucagon administration thus does not increase the risk of haemorrhage from oesophageal varices during acute fibroscopy of the oesophagus and stomach in patients with portal hypertension.

[Trimethoprim in the therapy of symptomatic liver porphyria]. / Trimetoprim v lécbe symptomatické jaterní porfyrie.

Administration of antimalaria drugs to patients with symptomatic hepatic porphyria (porphyria cutanea tarda) at the First Medical Clinic made it possible due to previous experimental studies, to influence the porphyrim metabolism of yeasts. The effect of trimetoprim was investigated in clinical work in 12 hitherto not treated patients with the manifest form of symptomatic hepatic porphyria. The group comprised 9 men, mean age 56.4 years, and 3 women mean age 43.6 years. During the two-year clinical study dermatological symptoms of the disease became milder or receded. Concurrently there was a significant regression of porphyrinuria. In the whole group porphyrinuria declined to 11% of the original values. The porphyrin content of hepatic tissue declined considerably after two years treatment. In the group as a whole to 40% of the original values. Trimetoprim is another drug which influences porphyrin metabolism. The authors did not detect any undesirable side-effects of trimetoprim treatment. The effect of trimetoprim on clinical and biochemical parameters of the disease is less marked than the effect of chloroquine. This new treatment can be used in patients resistant to chloroquine or in combination with other anti-malaria drugs.

[Measurement of impedance in liver tissue]. / Zkusenosti s merením impedance v jaterní tkáni.

At the First Medical Clinic (First Medical Faculty, Charles University) a new method of assessment of impedance of hepatic tissue was developed. A special thin injection electrode was designed which makes it possible to take readings in deep tissue. The measurements are made and aimed throughout the procedure under ultrasonographic control. From the sites of assessment specimens were taken for cytological and histological examination. So far 44 operations were completed. In 33 patients according to ultrasonography focal changes were involved, in the remainder the liver parenchyma was homogeneous or there were slight diffuse changes. Based on the results of the histological examination, the group was divided into 11 subgroups some of which are very small and thus difficult to interpret. Therefore this is only a preliminary study. Its objective is to introduce the technique of a new method because even from the small hitherto assessed values of impedance by means of the injection electrode under ultrasonographic control the conclusion can be drawn that the assessed impedance values could provide more detailed information on the character of focal changes.