Experimental Investigation on the Impact of Graphite Electrodes Grain Size on Technological Parameters and Surface Texture of Hastelloy C-22 after Electrical Discharge Machining with Negative Polarity.

Electrical discharge machining (EDM) is a rapidly evolving method in modern industry that manufactures highly complex components. The physical properties of a tool electrode material are significant factors in determining the effectiveness of the process, as well as the characteristics of the machined surfaces. The current trend of implementing graphite tool electrodes in manufacturing processes is observed. Innovative material engineering solutions enable graphite production with miniaturized grain size. However, the correlation between the graphite electrode grain size and the mechanism of the process removal in the EDM is a challenge for its widespread implementation in the industry. This research introduces a new method to evaluate the impact of the graphite electrode grain size and machining parameters on the material removal effectiveness, relative tool wear rate, and surface roughness (Ra) of Hastelloy C-22 following EDM with negative polarity. The study utilized new graphite materials with a grain size of 1 µm (POCO AF-5) and 10 µm (POCO EDM-180). An assessment of the impact of the EDM process parameters on the technological parameters and the development of the surface roughness was carried out. Electrical discharge machining with fine-grained graphite electrodes increases process efficiency and reduces tool wear. Graphite grains detached from the tool electrode affect the stability of electrical discharges and the efficiency of the process. Based on the experimental results, mathematical models were developed, enabling the prediction of machining effects to advance state-of-the-art manufacturing processes. The obtained mathematical models can be implemented in modern industrial EDM machines as guidelines for selecting adequate machining parameters depending on the desired process efficiency, tool wear rate, and surface roughness for advanced materials.

Finishing Additively Manufactured Ti6Al4V Alloy with Low-Energy Electrical Discharges.

Additive manufacturing has garnered significant interest in various industries due to its flexibility and capability to produce parts with complex shapes. However, issues related to surface quality, such as roughness and microstructural defects, necessitate the use of post-processing techniques to achieve the desired properties. Ti6Al4V alloy, produced additively, was finished using low-energy discharges, and the new surface integrity properties resulting from the induced heat energy were investigated. To further understand the influence of discharge energy on the formation of the new layer, roughness parameters and power spectral density were used to characterize the surface topography. SEM and EDS analyses were performed to examine the morphology and microstructural defects such as microcracks. The results indicate that the heat energy induced by the discharge improved the properties of the surface. SEM analysis revealed that the new layer was characterized by a reduction in defects such as unmelted particles, the balling effect, and microcracks. At the lowest investigated discharge energy of E = 0.21 mJ, surface roughness, Sa, was reduced by about 69%, which is equal to about 2 µm, accompanied by a significant decrease in microcracks. EDS analysis indicated that the diffusion of copper and zinc from the electrode to the top surface was related to the discharge energy. Furthermore, prediction models of the influence of wire electrical discharge polishing parameters, including discharge energy, wire speed, and time interval, on the surface roughness and material removal rate (MRR) were developed using the response surface methodology.

Functional aortic annulus 3-dimensional remodelling during bicuspid aortic valve repair: complete external and internal annuloplasty.

The internal geometric ring provides full three-dimensional annular stability while minimizing the dissection of the aortic root, pulmonary artery and right ventricle and avoids reimplanting the coronaries. The external annuloplasty provides a secondary stabilization of the easily accessed fibrous portion of the annulus using the sutures for the internal annuloplasty device and minimizes the sutures above the leaflets. Together they form a complete remodelling of the ventriculo-aortic junction following its exact course. The junction together with stabilization of the subcommissural triangles defines functional aortic annulus remodelling. External annuloplasty supports the virtual basal ring.

Experimental Investigation of Technological Indicators and Surface Roughness of Hastelloy C-22 after Electrical Discharge Machining Using POCO Graphite Electrodes.

Modern industry is focused on looking for new and effective technologies to manufacture complex shapes from alloys based on nickel and chromium. One of the materials widely used in the chemical and aerospace industry is Hastelloy C-22. This material is difficult to machine by conventional methods, and in many cases, unconventional methods are used to manufacture it, such as electrical discharge machining (EDM). In the EDM process, the material is removed by electrical discharges between a workpiece and a tool electrode. The physical and mechanical properties of the tool electrodes have a direct impact on the process efficiency, machining accuracy, and surface roughness. Currently, there has been a significant increase in the use of graphite as a material for tool electrodes due to the low purchase cost of the raw material, good machinability, and high sublimation temperature. In this work, an experimental investigation of the influence of the grain size of the graphite tool electrode on material removal rate (MRR), tool wear rate (TWR), and surface roughness (Ra) of Hastelloy C-22 was carried out. Two POCO graphite tool electrodes with a grain size of 1 µm (AF-5) and 10 µm (S-180) were used. Based on the experimental studies, empirical models describing the influence of machining parameters on technological indicators and the condition of the surface texture were determined. The research indicates that graphite with a larger grain provides higher process efficiency with high relative wear of the tool electrode. The lowest surface roughness was obtained for graphite with a smaller grain size (AF-5). The analysis of the machining parameters proves that the discharge current and pulse duration are the main factors determining the MRR and Ra values for both AF-5 and S-180 graphite. The time interval is the dominant parameter with regard to the relative wear of the graphite electrode.

Custodiol HTK versus Plegisol: in-vitro comparison with the use of immature (H9C2) and mature (HCM) cardiomyocytes cultures.

BACKGROUND: Although cardioplegia is used since the '70s of the last century, debate on cardioprotection during cardio-surgical procedures is still actual. The selection of a particular method depends mainly on the preferences and experience of a specific center or even surgeon. Crystalloid cardioplegia is an aqueous ion solution similar to intracellular (Custodiol HTK) or extracellular (Plegisol) fluid. The potensional clinical advantages of relatively new idea of cardioplegia solution based on intracellular composition (Custodiol HTK) justifies futher research, but only a few used cultured cells in laboratory conditions. METHODS: In this study, the authors sought to compare Custodiol HTK with Plegisol cardioplegia solutions using an in-vitro model simulating cardioplegic arrest. The efficacy of myocardial protection during ischemia was investigated with susceptible indicators like the appearance of the deleterious effect of reactive oxygen species and oxidative stress markers. Immersed human cardiomyocytes and rat cardiomyoblasts H9C2 in cardioplegia for 4 h were examined for expression of oxidative stress markers (MnSOD, iNOS, HSP27), cardioplegic solutions cytotoxicity, and peroxidation damage of the cell's lipids and proteins. All tests were performed after 0.5 h, 1 h, 2 h, and 4 h of incubation in identical physical and biological conditions, which is difficult to achieve in clinical trials. RESULTS: The lower cytotoxicity index performed on matured cells of human cardiomyocytes and highest dehydrogenase level showed after incubation with Custodiol HTK. This did not apply to tests on immature cells H9C2. Custodiol HTK induced significantly stronger iNOS expression. The decrease of HSP27 concentration has been instantaneous and maintained troughout the study only in both cultures incubated with Custodiol HTK. The other tests: lipid peroxidation, carbonyl groups concentration and MnSOD expression show no clear superiority evidence of used cardioplegic solutions. CONCLUSIONS: Considering proceeded examinations on cultured cardiomyocytes, Custodiol HTK appears to be safer than Plegisol.

St. Thomas Modified Cardioplegia Effects on Myoblasts' Viability and Morphology.

Background and Objectives: The cardioplegic arrest of the heart during cardiosurgical procedures is the crucial element of a cardioprotection strategy. Numerous clinical trials compare different cardioplegic solutions and cardioprotective protocols, but a relatively small number of papers apply to in vitro conditions using cultured cells. This work aimed to analyze whether it is possible to use the rat heart myocardium cells as an in vitro model to study the protective properties of St. Thomas cardioplegia (ST2C). Methods: The rat heart myocardium cells-H9C2 were incubated with cold cardioplegia for up to 24 h. After incubation, we determined: viability, confluency, and cell size, the thiol groups' level by modifying Ellman's method, Ki67, and Proliferating Cell Nuclear Antigen expression (PCNA). The impact on cells' morphology was visualized by the ultrastructural (TEM) study and holotomograpic 3D imaging. Results: The viability and confluency analysis demonstrated that the safest exposure to ST2C, should not exceed 4h. An increased expression of Ki67 antigen and PCNA was observed. TEM and 3D imaging studies revealed vacuolization after the longest period of exposure (24). Conclusions: According to obtained results, we conclude that STC can play a protective role in cardiac surgery during heart arrest.

Experimental Investigation and Optimization of Rough EDM of High-Thermal-Conductivity Tool Steel with a Thin-Walled Electrode.

The industrial application of electrical discharge machining (EDM) for manufacturing injection molding, in many cases, requires forming depth cavities with high length-to-width ratios, which is quite challenging. During slot EDM with thin-walled electrodes, short-circuits and arcing discharges occur, as a result of low efficiency in removing debris and bubble gas from the gap. Furthermore, unstable discharges can cause increases in tool wear and shape deviation of the machined parts. In order to characterize the influence of the type of electrode material and EDM parameters on the deep slot machining of high-thermal-conductivity tool steel (HTCS), experimental studies were conducted. An analytical and experimental investigation is carried out on the influence of EDM parameters on discharge current and pulse-on-time on the tool wear (TW), surface roughness (Ra), slot width (S)-dimension of the cavity, and material removal rate (MRR). The analyses of the EDS spectrum of the electrode indicate the occurrence of the additional carbon layer on the electrode. Carbon deposition on the anode surface can provide an additional thermal barrier that reduces electrode wear in the case of the copper electrode but for graphite electrodes, uneven deposition of carbon on the electrode leads to unstable discharges and leads to increase tool wear. The response surface methodology (RSM) was used to build empirical models of the influence of the discharge current I and pulse-on-time ton on Ra, S, TW, and MRR. Analysis of variance (ANOVA) was used to establish the statistical significance parameters. The calculated contribution indicated that the discharge current had the most influence (over 70%) on the Ra, S, TW, and MRR, followed by the discharge time. Multicriteria optimization with Derringer's function was then used to minimize the surface roughness, slot width, and TW, while maximizing MRR. A validation test confirms that the maximal error between the predicted and obtained values did not exceed 7%.

Bicuspid aortic valve repair: outcomes after 17 years of experience.

OBJECTIVES: This study presents the results of 17 years of experience with bicuspid aortic valve (BAV) repair and the analysis of factors associated with repair failure and early echocardiographic outcome. METHODS: Between 2003 and 2020, a total of 206 patients [mean age: 44.5 ± 15.2 years; 152 males (74%)] with BAV insufficiency with or without aortic dilatation underwent elective aortic valve repair performed by a single surgeon with a mean follow-up of 5 ± 3.5 years. The transthoracic echocardiography examinations were reported. RESULTS: There were no deaths during the hospital stay, and all but 1 patient survived the follow-up period (99.5%). Overall, 10 patients (5%) developed severe insufficiency and 2 (1%) developed aortic dilatation requiring reoperation. Freedom from reoperation at 7 years reached 91.8%. Type 2 BAV configuration [hazard ratio (HR) 3.9; 95% confidence interval (CI): 1.01-60; P = 0.049], no sinotubular junction remodelling (HR 7; 95% CI: 1.7-23; P = 0.005), no circumferential annuloplasty (HR 3.9; 95% CI: 1.01-64; P = 0.047) and leaflet resection (HR 5.7; 95% CI 1.2-13. P = 0.017) have been identified as a risk factor of redo operation. Parameters of the postoperative left ventricle reverse remodelling improved significantly early after the operation and later at 2 years evaluation. CONCLUSIONS: The repair of BAV offers good short- and mid-term results providing a significant reverse left ventricular remodelling. Type 0 BAV preoperative configuration, circumferential annuloplasty and sinotubular junction remodelling are associated with better repair durability.

Upregulated sulfatase and downregulated MMP-3 in thoracic aortic aneurysm.

BACKGROUND: Thoracic aortic aneurysm (TAA) formation is accompanied by degradation of extracellular matrix components (EMC). Numerous matrix metalloproteinases (MMPs) have been implicated in the process, but the involvement of MMP-3 remains unclear. Additionally, the changes in proteoglycan (PG) structure can alter the signal transduction pathways in TAA, though the enzymatic systems which originate them are not fully understood. OBJECTIVES: To measure MMP-3 and sulfatase levels in aneurysmal tissue, comparing them with non-aneurysmal vessels, and to investigate possible correlations with patients' serum levels in order to evaluate their potential usefulness in aiding aneurysm detection and monitoring. MATERIAL AND METHODS: The study included 74 patients (TAA: n = 42; control group: n = 32). Sulfatase activity was measured colometrically and MMP-3 levels were measured immunoenzymatically. RESULTS: Sulfatase activities were higher (p = 0.03) and MMP-3 concentrations lower (p = 0.014) in aneurysmal tissue than in normal aortic tissue. Medium-sized dilatations were associated with lower tissue MMP-3 concentrations than small dilatations (p = 0.033). No differences in sulfatase activity or MMP-3 concentration in the serum of TAA patients were observed in comparison with the controls. The serum and tissue levels of MMP-3 were correlated (r = 0.41; p < 0.001). The serum levels of MMP-3 were significantly lower in the female patients than in the male patients (p = 0.006). CONCLUSIONS: Our studies confirmed the lower MMP-3 levels in aneurysmal tissue, but the lack of a statistically confirmed reduction of MMP-3 in the blood serum seems to preclude its usefulness for diagnostic purposes. Our study points to the differences in MMP-3 behavior between TAA and abdominal aortic aneurysms. Significantly higher sulfatase activity in TAA tissue suggests a possible impact of sulfatase on signal transduction pathways involved in aneurysm formation.

Lipomatous hypertrophy of the atrial septum - a benign heart anomaly causing unexpected surgical problems: a case report.

BACKGROUND: Lipomatous hypertrophy of the atrial septum (LHAS) is an anomaly of the heart. It is characterized by an infiltration of adipocytes into myocytes of the interatrial septum, sparing the fossa ovalis, which gives a characteristic hourglass-shaped image. Due to the progress in imaging techniques, it can be recognized more frequently, but it is still often misdiagnosed. CASE PRESENTATION: We present a case of 65-year-old woman with an incidentally discovered lipomatous hypertrophy of the atrial septum during cardiac surgery, which has caused the technical problems for surgeons with bicaval cannulation and visualization of the operated structures of the heart. Due to the unclear shadow in the lung parenchyma, the patient had preoperative computed tomography (CT) done, but the study report focused only on the lung description, neglecting visible changes in the structure of the heart. Based on the standardly performed intra-operative transesophageal echocardiography (TEE), as well as by analyzing the chest X-ray and CT scans, the diagnosis of LHAS was made. It allowed the surgeon to leave the mass intact, thus not increasing the risk of the baseline surgery. CONCLUSIONS: LHAS is a rare but increasingly recognized anomaly of the heart. Contemporary diagnostic methods allow to diagnose and make the right therapeutic decisions. The utility of TEE and analysis of X-ray images, in this case, allowed the surgeon to recognize LHAS, and because of its histologically benign nature and asymptomatic course, to leave this change intact. Surgical treatment should be limited only to cases of patients with life-threatening cardiovascular complications.

Computed tomography angiography of aorta subjected to external wrapping.

BACKGROUND: External wrapping is a surgical technique used in patients with dilated ascending aorta. To date, there is no available data describing the radiographic features of the aorta subjected to external wrapping using a straight corrugated Dacron vascular prosthesis. The aim of this study was to find distinctive radiographic features of an externally constricted aorta. METHODS: Preoperative and early postoperative (7th postoperative day) CT angiography images of ten patients who underwent wrapping procedures were assessed and compared. The images were analyzed in order to find characteristic features of CT angiography images of the ascending aorta subjected to external wrapping. RESULTS: The CT-angiography images showed that the aortic wall deformed significantly (the wall plicated) after the wrapping procedure in one patient, whose aortic diameter was decreased by 47 %. The remaining nine patients did not have significant aortic wall deformations. All patients presented with a periaortic mass. This was a collection of blood clots and pericardial fluid that filled the empty space in the pericardium following a decrease in the diameter of the ascending aorta. A very thin (<1 mm) crescent-shaped uncontrasted layer was noticed between the aorta and the periaortic area in all patients. This, in turn, was an empty space between the aorta and the corrugated vascular prosthesis. CONCLUSIONS: The CT-angiography images of the aorta subjected to external wrapping may have unique features that are not observed after other operations on the ascending aorta. The knowledge about the details of this surgical procedure helps to correctly assess these images.

Single center experience with wrapping of the dilated ascending aorta.

BACKGROUND: External wrapping is a surgical technique performed in patients with a dilated ascending aorta. The aim of this study is to present the mid-term results of wrapping of the dilated ascending aorta. METHODS: 34 patients (mean age: 64.4 ± 10.8 years, 21 males) with a dilated ascending aorta were operated on at a single cardiac surgery center using a wrapping technique. The aortas were wrapped with 32-36 mm straight Dacron vascular prostheses. The aortic wall was not excised in any of the patients. Wrapping was performed concomitant to other cardiac surgery procedures in 30 patients (88 %), which involved surgery on the aortic valve in 28 patients (82 %). RESULTS: The mean follow-up time was 19.5 ± 8.3 months (median: 18 months, range: 12-36 months). None of the patients died or had aortic complications during the hospital stay and the follow-up period. A rethoracotomy had to be performed due to excessive postoperative bleeding in two patients. One patient was diagnosed with a transient ischemic attack on the 4th postoperative day, while another had respiratory failure requiring prolonged intubation. No redilatation of the ascending aorta or dislocation of the wrap was noticed in any of the patients. CONCLUSIONS: According to our study, external wrapping of the ascending aorta has good short-term results and may be regarded as a safe surgical option for patients with a moderately dilated ascending aorta.

Temporary resolution of chronic atrial fibrillation after cardiac surgery and the prolongation of ventricular repolarization.

BACKGROUND: Chronic atrial fibrillation may temporarily resolve after cardiac surgery. Prolongation of the ventricular repolarization period may be the electrophysiological background for this phenomenon. OBJECTIVES: The aim of the study was to assess the association between resolution of atrial fibrillation and changes in the duration of the ventricular repolarization period in patients with pre-operative chronic atrial fibrillation who underwent cardiac surgery. MATERIAL AND METHODS: A retrospective analysis of the medical recordings of patients with chronic atrial fibrillation who underwent cardiac surgery was performed. After exclusions the study group comprised 51 patients with chronic atrial fibrillation who underwent surgery in the Cardiac Surgery Department of Wroclaw Medical University in 2008 and 2009. The 12-lead EKGs performed before and after the surgery were assessed and the QT and R-R intervals were measured. The patients were divided into Group 1, in whom atrial fibrillation persisted after the cardiac surgery, and Group 2, whose atrial fibrillation resolved after the surgery. RESULTS: In 31 patients (60.8%) atrial fibrillation disappeared during the first 24 hours after cardiac surgery. A significant prolongation of the QT interval after the surgery was found in Group 2 that was not observed in Group 1. Multiple regression analysis revealed that QT interval duration after surgery is related to the resolution of atrial fibrillation independently from the duration of the R-R interval duration and the need for cardiac pacing. CONCLUSIONS: Spontaneous temporary resolution of atrial fibrillation is a common finding after cardiac surgery in patients with chronic atrial fibrillation. This phenomenon is related to a prolonged QT interval, therefore it may have an electrophysiological basis rather than a hemodynamic background. Further studies are required to assess the clinical importance of the prolongation of the QT interval after cardiac surgery.

Electroporation-induced changes in normal immature rat myoblasts (H9C2).

Application of a high electric field causes an electric shock to the heart. This is utilized in defibrillation to reestablish normal contraction rhythms during dangerous arrhythmias or in cardiac arrest. If shock-induced transmembrane potentials are large enough, they can cause tissue destruction due to irreversible electroporation (EP). Also electrochemotherapy of nearby tissues may have an adverse effect on the heart. Herein, we present experimental data on effects of electroporation in culture of cardiac cells (H9C2). The electric field was applied in short pulses of 25-3250 V/cm, 50 µs each. The viability of cells was tested by MTT assay after 24 hours. For detection of DNA fragmentation, associated with apoptosis, alkaline and neutral comet assays were performed after EP. Additionally phase contrast images of cells obtained directly after EP were analyzed. Although cell images indicated disruption of cell membranes after EP with high intensities, only a few percent of apoptotic cells and no necrotic effects in the cell nucleus could be observed in comet assay tests performed 2 hours post EP. MTT viability test showed that pulse intensities above 375 V/cm are destructive for myocytes viability.

Is remote ischaemic preconditioning of benefit to patients undergoing cardiac surgery?

A best evidence topic in cardiac surgery was written according to a structured protocol. The question addressed was whether remote ischaemic preconditioning (RIPC) is of benefit to patients undergoing cardiac surgery. Altogether, more than 264 papers were found using the reported search, 16 of which represented the best evidence to answer the clinical question. The authors, journal, date and country of publication, patient group studied, study type, relevant outcomes and results of these papers are tabulated. We conclude that RIPC is a safe protocol which could potentially be used in cardiac surgery to provide additional cardiac protection against ischaemia reperfusion injury, although it may not be appropriate for patients on K(+) ATPase channel blockers (sulphonylureas) as they seem to eliminate the effect of RIPC. In our study, we found two meta-analyses of cardiac surgery with or without RIPC. Both unequivocally showed 0.81 and 0.74 standardized mean reduction in myocardial necrosis markers in patients receiving RIPC and cardiac or vascular surgery. No difference in perioperative myocardial infarction incidence or 30-day mortality were found. In adult cardiac surgery, we found 11 randomized control trials (RCTs) ranging in size from 45 to 162 patients. Two representative studies reported no difference in postoperative cardiac troponin I concentration in RIPC vs. controls. In one of the studies (CABG ± RIPC) no additional benefit could have been observed for RIPC regarding intra-aortic balloon pump usage (controls 8.5 vs. RIPC 7.5%), inotropic support (39 vs. 50%) or vasoconstrictor usage (66 vs. 64%). On the other hand, in the other study [CABG ± AVR (aortic valve replacement) ± RIPC] significant reduction of troponin I at 8 h postoperatively (controls, 2.90 µg/l vs. RIPC, 2.54 µg/l, P = 0.043) was shown. Marked reduction in cardiac necrosis markers was also found in several smaller RCTs concerning coronary artery bypass grafting (CABG) patients receiving RIPC preoperatively: with cold crystalloid cardioplegia (44.5% reduction), with cross-clamping and fibrillation (43% reduction) and with cold blood cardioplegia (42.4% reduction). The proof of concept trials summarized here give some early evidence that RIPC may potentially provide some reduction in myocardial injury. If confirmed, in future clinical studies this technique may one day lead to a method to reduce reperfusion injury in clinical practice.

The estimation of oxidative stress markers and apoptosis in right atrium auricles cardiomyocytes of patients undergoing surgical heart revascularisation with the use of warm blood cardioplegia.

Oxidative stress markers and apoptosis were estimated during elective surgical heart revascularization. Eight patients with good ejection fraction underwent coronary artery bypass grafting (CABG) with the use of warm blood cardioplegia. Two right atrium auricle biopsy specimens were collected before and after the operation. Specimens underwent immunocytochemical analysis of mitochondrial manganese superoxide dismutase (MnSOD) expression and apoptosis estimation by the TUNEL method. Ultrastructure analysis under electron microscope was made. Satisfactory results of the operation were obtained. After CABG the MnSOD expression increase in sections of auricles was observed through the increase of stain intensity and the percentage of cells with positive stain (from 30 to 80%). The apoptotic cells percentage remained at approximately the same level. Under the electron microscope insignificant pathological changes were observed. On this basis one may assume that in the case of cardiosurgical procedures with short aorta cross-clamping time and low operation risk level the application of cardioplegia sufficiently prevents reactive oxygen forms (ROF) cytotoxic activity although it does not inhibit the expression of oxidative stress (OS) markers. In our opinion the method of examining right atrium sections is safe and provides results comparable with other publications. It may also be a voice in the discussion on new methods of heart protection during cardiac surgery procedures.

The influence of controlled hypotension on splanchnic mucosal perfusion using gastric tonometry in patients undergoing resection of meningioma.

BACKGROUND: The aim of our research was to evaluate the influence of general anesthesia with controlled nitroglycerin-induced hypotension on splanchnic mucosal perfusion using gastric tonometry. MATERIAL/METHODS: In six patients (1 female, 5 males, median age 46 years, range 32-62) undergoing elective resection of meningiomas, measurements of gastric mucosal perfusion were taken by nasogastric tonometry. Controlled hypotension was initiated after craniotomy and terminated prior to hemostasis procedures. The mean arterial blood pressure (MAP) was maintained 25-30% below initial parameters during controlled hypotension. The adequacy of perfusion was defined by the intramucosal pH (pHi) and the difference between arterial and intramucosal pH (pHGAP). All parameters were analyzed before the induction of controlled hypotension, after the 1st, 2nd, and 3rd hour, and 1 hour after the termination of controlled hypotension. RESULTS: The MAP decreased during controlled hypotension by ca. 26.5% (min. 21.1%; max 31.6%). The lower MAP was accompanied by a statistically significant increase in heart rate. A significant increase from baseline in regional prCO2 was seen after the 1st, 2nd, and 3rd hour of controlled hypotension. Intramucosal pH values decreased significantly during the same period, from 7.428+/-0.032 to 7.372+/-0.015. Despite these statistically significant differences during controlled hypotension, the pHi values were always greater than 7.35, and the pHGAP values were lower than 0.05, which were recognized as being within the normal range. CONCLUSIONS: Controlled hypotension allows accurate evaluation of the blood flow quality at the level of microcirculation. Mild controlled hypotension slightly alters splanchnic mucosal perfusion, but does not lead to ischemia and hypoxia in tissues.