Search PubMed⌕ Search

Biomedical subjects

Cristina Pislaru

Publications and source records attributed to Cristina Pislaru.

13 recordsLinked to original sources
PubMed2005

Evaluating the dynamic performance of a fibre optic pressure microsensor.

The dynamic performance of a new fibre optic sensor intended for measuring physiological fluid pressures is assessed in water. The sensor's sensitivity is evaluated at 23 degrees, 35 degrees and 37 degrees C against a Millar pressure catheter for sinusoidal pressure inputs with frequency ranging from 0.5 to 10 Hz. We found that sensitivity versus frequency is flat to 6 Hz and decreases slightly between 6 and 10 Hz. The sensitivity is slightly lower at 23 degrees C than at 37 degrees C. The reproducibility of measurements is excellent (two separate calibration tests in two consecutive days). The output of the fibre optic system used shows a constant time delay (0.13 s) for all frequencies tested. Experiments suggest that, with current sensor design, its immersion in degassed water prior to use ensures a reliable performance.

Equipment Design↗
PubMed2004

Strain echocardiography tracks dobutamine-induced decrease in regional myocardial perfusion in nonocclusive coronary stenosis.

OBJECTIVES: This study was designed to determine whether strain echocardiography parameters reflect changes in regional myocardial perfusion during dobutamine stress. BACKGROUND: Strain echocardiography depicts regional myocardial mechanical activity. Ischemia has been shown to reduce systolic strain rate (sSR) and prolong the time to regional lengthening (T(RL)). In an experimental model, we tested whether sSR and T(RL) tracked dobutamine-induced changes in regional myocardial perfusion (regional myocardial blood flow [RMBF]), as measured by colored microspheres. METHODS: We used a closed-chest pig model of nonocclusive coronary stenosis (n = 14) created by inflating an angioplasty balloon in the proximal left anterior descending artery. Invasive hemodynamics, RMBF, and strain parameters were measured at baseline and peak dobutamine stimulation before and during the coronary stenosis. We compared segments with reduced RMBF versus those with preserved RMBF at peak dobutamine stimulation. RESULTS: Peak sSR correlated with RMBF (r = 0.70). In the absence of coronary stenosis, dobutamine stimulation caused a significant increase in RMBF and sSR and a decrease in T(RL). This response was blunted during coronary stenosis. Using the "best cutoff" method, the sensitivity and specificity for prediction of reduced RMBF (ischemia) was 81% and 91% for sSR and 65% and 91% for T(RL), respectively. These changes occurred in the absence of any change in global systolic and diastolic function (dP/dT(max), dP/dT(min), and tau). CONCLUSIONS: Novel strain parameters that depict regional myocardial mechanics are able to predict changes in RMBF during dobutamine stress. Quantitative strain parameters may complement current echocardiographic techniques for ischemia detection and potentially improve the accuracy and reproducibility of stress echocardiography.

Animals↗
PubMed2004

Ultrasound strain imaging of altered myocardial stiffness: stunned versus infarcted reperfused myocardium.

BACKGROUND: In this study we evaluate the diastolic deformation of ischemic/reperfused myocardium and relate this deformation to tissue elastic properties. METHODS AND RESULTS: Farm pigs were subjected to left anterior descending coronary artery occlusion followed by reperfusion to create either stunning (n=12) or transmural myocardial infarction (n=12). Ultrasound-derived radial strain rates (SR) and strain were measured in the ischemic and remote walls. Myocardial stiffness was estimated from diastolic pressure-wall thickness relationship obtained from preload alterations. At reperfusion, end-systolic strain (epsilon(sys)) was significantly reduced in both stunned and infarcted walls compared with their remote walls (3+/-3% versus 26+/-2% and 1+/-0% versus 33+/-5%, respectively; P<0.0001) or baseline values. Diastolic passive deformation (epsilon(A)) and rates of deformation during early (E(SR)) and late (A(SR)) diastole were comparable between stunned and remote walls (epsilon(A): 7.3+/-1.6% versus 7.9+/-1.9%; E(SR): -2.7+/-0.4 s(-1) versus -2.6+/-0.5 s(-1); A(SR): -1.8+/-0.2 s(-1) versus -1.9+/-0.3 s(-1); P=NS for all) but were of significantly lower magnitude in infarcted walls versus remote walls (epsilon(A): 1.1+/-0.2% versus 11.4+/-1.9%; E(SR): -0.3+/-0.1 s(-1) versus -2.4+/-0.4 s(-1); A(SR): -0.3+/-0.1 s(-1) versus -2.5+/-0.4 s(-1); P<0.0001 for all). Stiffness coefficient of exponential diastolic pressure-wall thickness relation was higher for infarcted (P<0.05) but not for stunned walls (P=NS) compared with their remote walls. CONCLUSIONS: Early after postischemic reperfusion and in the presence of severely reduced systolic deformation, diastolic passive deformation (and rates of deformation) can distinguish stiff, noncompliant, transmurally infarcted myocardial walls from those more compliant walls containing viable but stunned myocardium.

Animals↗
PubMed2004

Distinctive changes in end-diastolic wall thickness and postsystolic thickening in viable and infarcted myocardium.

OBJECTIVES: In this study, we sought to compare the magnitude of changes in end-diastolic wall thickness (WT(ed)) and postsystolic thickening (PST) in a swine model of stunning and reperfused acute myocardial infarction, and to explore the relationship between WT(ed) and PST. METHODS: Twenty-six pigs were subjected to left anterior descending coronary artery occlusion followed by reperfusion to induce stunning (n = 6), nontransmural (n = 8), or transmural (n = 12) myocardial infarction. Myocardial wall thickness was measured using intracardiac echocardiography. Transmural extent of necrosis (TEN) was quantified by triphenyltetrazolium chloride technique. RESULTS: During the first minutes of reperfusion, a marked increase in WT(ed) occurred in the myocardial walls with nontransmural and transmural infarct (42% and 102%, respectively) but less in those with stunning (19%). PST persisted at reperfusion in walls with stunning and nontransmural infarct (23% and 26%, respectively). In transmurally infarcted walls, PST progressively decreased either during occlusion (5/12 pigs) or shortly after reperfusion (7/12 pigs). PST at reperfusion was virtually absent when TEN was >70%. Both PST and the increase in WT(ed) at reperfusion correlated well with TEN (P <.0001 for both). Changes in PST at reperfusion were weakly correlated with changes in WT(ed). CONCLUSIONS: A marked increase in WT(ed) after reperfusion and absence of PST indicate transmural myocardial infarction. Presence of PST at reperfusion indicates viable tissue in more than 30% of wall thickness. The results suggest that amplitude of PST is modulated predominantely by factors related to the severity of ischemia and, to a smaller extent, by changes in wall thickness.

Analysis of Variance↗
PubMed2004

Both systolic and diastolic dysfunction characterize nonischemic inhibition of myocardial energy metabolism: an experimental strain rate echocardiographic study.

BACKGROUND: Ischemia is primarily a metabolic event. However, regional functional changes can be affected by structural alterations. We developed an experimental model of sole myocardial energy metabolism inhibition and characterized the resulting regional dysfunction. METHODS: In 12 pigs, we regionally inhibited creatine kinase (CK) and, consequently, myocyte high-energy phosphate transfer by intracoronary administration of iodoacetamide. Myocardial biopsies for CK activity and structural analyses and strain rate (SR) echocardiography scans were obtained at baseline and 60 minutes after iodoacetamide administration. Plasma levels of the CK isoenzyme MB and troponin I were assessed to determine possible myocardial damage. RESULTS: CK activity in the iodoacetamide-perfused myocardium decreased to 0.5% of the original value and was accompanied by a reduction in peak systolic SR ( P < .0001), end-systolic strain ( P < .0001), and peak SRs of myocardial early and late filling waves ( P < .0001). Microscopy showed contracture without sarcomere disruption. Plasma levels of CK isoenzyme MB and troponin I did not change. CONCLUSIONS: Regional inhibition of myocyte energetics leads to both systolic and diastolic dysfunction by SR echocardiography, but the presence of a residual phosphotransfer protects microstructural integrity.

Animals↗
PubMed2003

Chlamydia pneumoniae induces neointima formation in coronary arteries of normal pigs.

OBJECTIVES: We evaluated the role of intracoronary, intrapulmonary and macrophage-mediated delivery of C. pneumoniae (Cp) on coronary lesion formation. METHODS: Pigs were allocated to one of three coronary protocols (intracoronary, macrophage or control groups) or to a fourth-a pulmonary group. In the intracoronary group Cp was injected into the wall of the left anterior descending (LAD) and right coronary arteries (RCA) and vehicle into the circumflex (CX). In the macrophage group autologous macrophages preincubated with Cp or not were injected into the LAD and CX wall, respectively. Animals in the control group received vehicle in LAD and CX. In the pulmonary group aerosolised Cp was given intrabronchially, after a single injection of vehicle into the LAD wall. Delivery into the coronary artery wall was performed with a balloon catheter with low-profile injector ports. RESULTS: Seroconversion occurred in the following proportions: 5/6 (intracoronary group), 4/5 (macrophage group), 0/6 (control group), and 1/6 (intrapulmonary group). Significantly higher maximal intimal thickness (MIT) was observed in LADs of intracoronary and pulmonary groups when compared to corresponding CXs. The presence of Cp antigen was associated with higher MIT (r=0.73; P<0.0001). Injection of macrophages into the coronary artery wall did not induce proliferation. Arteries without coronary interventions were morphologically normal. CONCLUSIONS: Intracoronary and intrapulmonary but not macrophage-mediated Cp inoculation were associated with moderate intimal proliferation in the absence of a lipid-rich diet. Pre-existing coronary lesions seem a prerequisite for Cp-induced proliferation.

Animals↗
PubMed2003

Optimization of ultrasound-mediated gene transfer: comparison of contrast agents and ultrasound modalities.

AIMS: Ultrasound (US)-enhanced gene transfer for cardiovascular disease is an emerging technique with translational relevance. Prior to pre-clinical applications, optimization of gene transfer using various US contrast agents and parameters is required. In order to do so, two clinically relevant contrast agents (Optison and PESDA), and two US modalities (dedicated continuous wave system and diagnostic scanner) were tested in vitro and in vivo. METHODS AND RESULTS: In vitro, luciferase activity was measured after exposure of primary vascular cells to combinations of luciferase plasmid, contrast agents, and US exposures. US gene transfer was consistently superior to controls. PESDA was better than Optison; there was no significant difference between US modalities. In vivo, luciferase activity in skeletal muscle of rats was measured after injection of plasmid or adenovirus, expressing luciferase with or without US exposure. Diagnostic US was superior to continuous wave. US plasmid gene transfer was highly localized, and was superior to all controls except adenovirus which lacked spatial specificity. To deliver a secreted transgene product, US gene transfer of a plasmid expressing tissue factor pathway inhibitor (TFPI) to skeletal muscle resulted in a dose-related increase in plasma activity for up to 5 days after delivery. CONCLUSION: US-enhanced plasmid gene transfer is capable of transducing skeletal muscle in vivo either directly or via an intravascular route. This enhanced nonviral method is an alternative to plasmid DNA alone or viral vectors.

Animals↗
PubMed2002

Higher myocardial strain rates during isovolumic relaxation phase than during ejection characterize acutely ischemic myocardium.

OBJECTIVES: The aim of this study was to define an index that can differentiate normal from ischemic myocardial segments that exhibit postsystolic shortening (PSS). BACKGROUND: Identification of ischemia based on the reduction of regional systolic function is sometimes challenging because other factors such as normal nonuniformity in contraction between segments, tethering effect, pharmacologic agents, or alterations in loading conditions can also cause reduction in regional systolic deformation. The PSS (contraction after the end of systole) is a sensitive marker of ischemia; however, inconsistent patterns have also been observed in presumed normal myocardium. METHODS: Twenty-eight open-chest pigs underwent echocardiographic study before and during acute myocardial ischemia induced by coronary artery occlusion. Ultrasound-derived myocardial longitudinal strain rates were calculated during systole (S(SR)), isovolumic relaxation (IVR(SR)), and rapid filling (E(SR)) phases in both ischemic and normal myocardium. Systolic strain (epsilon(sys)) and postsystolic strain (epsilon(ps)) were calculated by integrating systolic and postsystolic strain rates, respectively. RESULTS: During ischemia, S(SR), E(SR), and epsilon(sys) in ischemic segments were significantly lower (in magnitude) than in nonischemic segments or at baseline. However, some overlap occurred between ischemic and normal values for all three parameters. At baseline, 18 of 28 animals had negative IVR(SR) (i.e., PSS) in at least one segment. During coronary artery occlusion, IVR(SR) became negative and larger in magnitude than S(SR) in all ischemic segments. The IVR(SR)/S(SR) and epsilon(ps) best differentiated ischemic from nonischemic segments. CONCLUSIONS: In the presence of reduced regional systolic deformation, a higher rate of PSS than systolic shortening identifies acutely ischemic myocardium.

Animals↗
PubMed2002

Time to onset of regional relaxation: feasibility, variability and utility of a novel index of regional myocardial function by strain rate imaging.

OBJECTIVES: Time to onset of regional relaxation (T(R)) has been proposed as a novel index of regional myocardial function. This study sought to prospectively establish the feasibility and variability of T(R) in healthy volunteers (CONTROL) and to examine its utility in patients with inducible ischemia (PATIENT). BACKGROUND: Strain rate imaging (SRI) depicts myocardial deformation and enables quantitation of regional myocardial function with high temporal and spatial resolution. Thus, regional mechanical events can be accurately timed with SRI. The time point of regional transition from contraction to relaxation is altered in pathologic states. METHODS: Resting mean segmental T(R) was determined in 60 subjects: 20 in the CONTROL group and 40 in the PATIENT group. T(R) was also measured at peak dobutamine stress in the PATIENT group. An automated image analysis program determined the time point of transition from regional contraction to relaxation activity, and calculated T(R), defined as the time, in milliseconds, from the electrocardiogram R-wave to this transition point. RESULTS: Automated T(R) measurements were feasible in more than 90% of the segments in CONTROL and PATIENT groups. Mean T(R) was 353 +/- 24 ms and was shorter in the mid segments compared to apical and basal segments. Intra- and interobserver variability were low (6% and 9%, respectively). In the PATIENT group, the percent decrease in T(R) during dobutamine stress was significantly higher in normal compared to ischemic segments (30% vs. 19%, respectively, p = 0.01). A percent change >20% in T(R) identified patients with an ischemic response during dobutamine infusion (sensitivity 92%, specificity 75%). CONCLUSIONS: T(R), a novel quantitative index of regional myocardial function, can be determined with low variability and satisfactory feasibility in routine clinical settings. Percent change in T(R) identifies ischemic segments during dobutamine stress echocardiography (DSE) and may allow quantitative assessment of DSE.

Adult↗
PubMed2002

Epicardial ultrasound guidance of coronary catheter placement in an experimental animal model.

We evaluated epicardial ultrasonography with a 10-MHz transducer for coronary catheter guidance in 18 normal pigs. A modified long-axis view of the aortic root was used to direct a coronary catheter into the root, and then with a short-axis view of the aortic root, the catheter tip was placed selectively into either the right or the left main coronary artery. Subsequently, with modified coronary views, an angioplasty infusion catheter was guided with precision to the exact location desired in the coronary artery. Position was confirmed by direct visualization and palpation of the epicardial vessels, and the procedure was completed within 5 to 15 minutes without complication. Epicardial ultrasonography is a suitable alternative to fluoroscopy for guidance of coronary catheter placement in an open-chest experimental model.

Animals↗
PubMed2002

Strain and strain rate echocardiography.

Strain and strain rate echocardiography is an emerging technique for assessing myocardial systolic and diastolic function. It is envisioned that this modality could change the quantitative assessment of regional wall motion and improve the accuracy and reproducibility of test readings. Myocardial strain and strain rate can detect inducible ischemia and at earlier stages than visual estimation of wall motion or wall thickening parameters. Changes in systolic strain rate and strain have potential to discriminate between different myocardial viability states. Measurement of diastolic rate of deformation can differentiate physiologic from pathologic hypertrophy, and restrictive from constrictive cardiomyopathy. This article reviews basic principles and current experimental and clinical applications of strain and strain rate echocardiography.

Animals↗
PubMed2002

Characterization of reperfused infarcted myocardium from high-frequency intracardiac ultrasound imaging using homodyned K distribution.

Myocardial changes caused by infarction/reperfusion (contraction band necrosis, hemorrhage, edema, etc.) may result in an increased scatterer density and a variation in scatterer arrangement. This paper, for the first time, models most of the scattering conditions resulting from the interaction of ultrasound and normal/reperfused infarcted myocardium using the homodyned K distribution. Furthermore, this method is used to characterize the change in scatterer density by calculating the effective scatterer number per resolution cell. The reliability and the effects of attenuation and scan conversion on effective scatterer number estimation are discussed. We used in vivo data acquired using high-frequency intracardiac ultrasound imaging (8.5 MHz) from the left and right ventricles of open-chest pigs in an acute infarction/reperfusion model. The results show that the homodyned K distribution describes the statistical distribution of backscattered signal from both normal and abnormal myocardium. A significant increase in scatterer density occurs in the infarcted region after reperfusion compared with the same region at baseline (normal myocardium prior to occlusion). The scatterer density of the normal region does not change significantly after reperfusion. We conclude that the homodyned K distribution may characterize normal and reperfused infarcted myocardium using high-frequency intracardiac ultrasound images.

Animals↗