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Biomedical subjects

M Saeed

Publications and source records attributed to M Saeed.

At least 55 records · Page 3Linked to original sources
PubMed2000

Coronary sinus flow measurement by means of velocity-encoded cine MR imaging: validation by using flow probes in dogs.

PURPOSE: To validate coronary sinus flow measurements for quantification of global left ventricular (LV) perfusion by means of velocity-encoded cine (VEC) magnetic resonance (MR) imaging and flow probes. MATERIALS AND METHODS: Measurements of coronary sinus flow were performed in seven dogs by using VEC MR imaging at baseline, single coronary arterial stenosis, dipyridamole stress, and reactive hyperemia. These measurements were compared with flow probe measurements of coronary blood flow (CBF) in the left anterior descending coronary (LAD) and circumflex (CFX) arteries (CBF(LAD+CFX)) and coronary sinus. LV blood perfusion was calculated in milliliters per minute per gram from coronary sinus flow, and LV mass was obtained by using VEC and cine MR imaging. LV mass was validated at autopsy. RESULTS: CBF(LAD+CFX) and coronary sinus flow at VEC MR imaging showed close correlation (r = 0.98, P: <.001). The difference between CBF(LAD+CFX) and MR coronary sinus flow was 3.1 mL/min +/- 8.5 (SD). LV mass at cine MR imaging was not significantly different from that at autopsy (73.2 g +/- 12.8 vs 69. 4 g +/- 12.8). At baseline, myocardial perfusion was 0.40 mL/min/g +/- 0.09 at VEC MR imaging, and CBF(LAD+CFX) was 0.44 mL/min/g +/- 0. 08 (not significant). Reactive hyperemia resulted in 2.7- and 2. 3-fold increases in coronary sinus flow at VEC MR imaging and flow probe CBF(LAD+CFX), respectively. CONCLUSION: VEC MR imaging has the potential to measure coronary sinus flow during different physiologic conditions and can serve as a noninvasive modality to quantify global LV perfusion in patients.

Animals↗
PubMed2000

Multiparameter trend monitoring and intelligent displays using wavelet analysis.

An Intelligent Patient Monitoring (IPM) framework is defined for the analysis and display of multiparameter trends from ICU patients. Wavelet analysis was utilized for detection of physiological events and artifacts in long-term trends. A group of 58 patients from the MIMIC database were identified in which the heart rate (HR), arterial blood pressure (ABP), and pulmonary artery pressure (PAP) were monitored. An estimated cardiac output (CO) signal, using HR and ABP, was shown to correlate strongly (r=.67) with actual CO measurements. Using wavelet analysis, automated artifact and physiological event detection algorithms were developed to monitor left ventricular hemodynamic function. Finally, an intelligent display system is presented for presentation of the data in ICU monitors.

Algorithms↗
PubMed1999

Identification of a novel circular single-stranded DNA associated with cotton leaf curl disease in Pakistan.

Recent reports have suggested that cotton leaf curl virus (CLCuV), a geminivirus of the genus Begomovirus, may be responsible for cotton leaf curl disease in Pakistan. However, the causal agent of the disease remains unclear as CLCuV genomic components resembling begomovirus DNA A are unable to induce typical disease symptoms when reintroduced into plants. All attempts to isolate a genomic component equivalent to begomovirus DNA B have been unsuccessful. Here, we describe the isolation and characterisation of a novel circular single-stranded (ss) DNA associated with naturally infected cotton plants. In addition to a component resembling DNA A, purified geminate particles contain a smaller unrelated ssDNA that we refer to as DNA 1. DNA 1 was cloned from double-stranded replicative form of the viral DNA isolated from infected cotton plants. Blot hybridisation using probes specific for either CLCuV DNA or DNA 1 was used to demonstrate that both DNAs co-infect naturally infected cotton plants from different geographical locations. DNA 1 was detected in viruliferous Bemisia tabaci and in tobacco plants infected under laboratory conditions using B. tabaci, indicating that it is transmitted by whiteflies. Sequence analysis showed that DNA 1 is approximately half the size of CLCuV DNA but shares no homology, indicating that it is not a defective geminivirus component. DNA 1 has some homology to a genomic component of members of Nanoviridae, a family of DNA viruses that are normally transmitted by aphids or planthoppers. DNA 1 encodes a homologue of the nanovirus replication-associated protein (Rep) and has the capacity to autonomously replicate in tobacco. The data suggest that a nanovirus-like DNA has become whitefly-transmissible as a result of its association with a geminivirus and that cotton leaf curl disease may result from a mutually dependent relationship that has developed between members of two distinct DNA virus families that share a similar replication strategy.

Amino Acid Sequence↗
PubMed1999

Assessment of myocardial function and perfusion in a canine model of non-occlusive coronary artery stenosis using fast magnetic resonance imaging.

Magnetic resonance (MR) functional and perfusion imaging were employed in a canine model of coronary artery stenosis (n = 6) for the quantification of functional and perfusion deficits before and after dipyridamole administration. Left anterior descending and circumflex (LCX) coronary blood flow were measured continuously after placing Doppler flowmeters. Inversion recovery gradient echo images during the transit of MR contrast medium gadolinium-benzyloxypropionictetraacetate dimeglumine (Gd-BOPTA/Dimeg) and fast breath-hold cine MR images were acquired at baseline, during LCX stenosis in basal state, and during LCX stenosis with vasodilation (dipyridamole 0.5 mg/kg). The extent of the functional defect and perfusion defect was expressed as percent of left ventricle (LV) circumference. During stenosis (LCX flow: 62.6 +/- 5.6% of baseline) the extent of the functional defect was slightly larger than the perfusion defect (11.0 +/- 1.8% versus 6.3 +/- 1.70% of LV circumference, respectively; P < 0.01). During vasodilation the extent of the functional defect was considerably smaller than the perfusion defect (25.3 +/- 2.5% versus 35.3 +/- 3.5%; P < 0.01). Thus, the sizes of ischemic regions displayed by MR perfusion defect and functional defect differ from each other.

Animals↗
PubMed1999

MRI of acute myocardial ischemia: comparing a new contrast agent, Gd-DTPA-24-cascade-polymer, with Gd-DTPA.

A new macromolecular contrast agent, gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA)-24-cascade-polymer, was compared with Gd-DTPA for time-dependent delineation of acute myocardial ischemia. Acute myocardial ischemia was produced in 12 rats by occluding the anterior branch of the left coronary artery for 20-40 minutes. Dynamic spin-echo magnetic resonance imaging (MRI) was performed for 30 minutes after injection of Gd-DTPA (n = 6) or the cascade polymer (n = 6) using equimolar doses (0.1 mmol of Gd/kg). The contrast agent-induced changes in signal intensity (deltaSI) in normal and ischemic myocardium were observed. In normal myocardium, both contrast agents caused a sharp increase in deltaSI, followed by a decline to baseline values over the 30-minute period. Enhancement in the ischemic myocardium was attenuated. Gd-DTPA showed greater deltaSI in ischemic myocardium than the cascade polymer, which gave rise to virtually no enhancement. Significant differences (P<0.05) in signal enhancement between normal and ischemic myocardium persisted for only 6 minutes using Gd-DTPA but for 18 minutes with the cascade polymer. Use of Gd-DTPA-24-cascade-polymer extends the temporal window of dynamic contrast-enhanced MRI for the differentiation of ischemic and normal myocardium. Identification of the ischemic zone is easier with the cascade polymer, which demonstrates virtually no signal enhancement in this territory.

Animals↗
PubMed1999

Detection of acute myocardial ischemia using first-pass dynamics of MnDPDP on inversion recovery echoplanar imaging.

Previous studies used manganese N,N'-bis-(pyridoxal 5-phosphate)ethylenediamine-N,N'-diacetic acid (MnDPDP) to detect myocardial ischemia at a dose of 0.4 mmol/kg with spin echo imaging. The purpose of this study was to detect acute myocardial ischemia using MnDPDP at a dose range near that approved for hepatobiliary imaging (0.005 mmol/kg) in conjunction with inversion recovery echoplanar imaging (IR EPI). Regional ischemia was produced in 26 rats by occluding the left coronary artery for 20-30 minutes before imaging. Consecutive 32 IR EP images (inversion time [TI]/TR/TE 700/2000/10 msec) were obtained to monitor the first pass of MnDPDP at four incremental doses (0.005, 0.01, 0.02, or 0.04 mmol/kg, n = 6-8). MnDPDP produced dose-dependent enhancement of left ventricular blood and normal myocardium, but not ischemic myocardium. Quantitative analysis revealed a difference in signal intensities (P<0.05) between normal and ischemic myocardium at the time of peak enhancement in all groups. However, differential enhancement between normal and ischemic myocardium produced clear visual delineation of the ischemic region only at doses > or =0.01 mmol/kg. In conclusion, acute myocardial ischemia can be detected with IR EPI using doses close to the clinically approved dose of MnDPDP.

Animals↗
PubMed1999

Contrast-enhanced MRI for quantification of myocardial viability.

During the past 10 years substantial advances have taken place in magnetic resonance imaging (MRI) capabilities and in contrast media development. Furthermore, knowledge of in vivo contrast media interactions with surrounding water and distribution into tissue has increased, permitting regional quantification of concentration-time profiles in the myocardium. The combination of these advances has substantially improved the capability of contrast-enhanced MRI characterization of myocardial ischemic injury, including its ability to discriminate viable from nonviable zones. Discrimination of viable from nonviable myocardial subregions is important for patient management and for research applications. This review addresses recent progress toward the goal of defining viable and nonviable myocardium based on MRI detection of contrast media effects. J. Magn. Reson. Imaging 1999;10:694-702.

Animals↗
PubMed1999

Selective impairment of glucose storage in human sepsis.

BACKGROUND: Glucose utilization in sepsis is impaired but the mechanisms are unclear. This study examined the effect of sepsis on total glucose utilization, oxidation and storage, and the energetic costs of these metabolic processes. METHODS: Glucose infusion rate (GIR), glucose oxidation rate (GOR), non-oxidative disposal rate and the energetic cost of glucose storage were studied in 24 patients with abdominal sepsis and in 26 healthy controls, using indirect calorimetry and the euglycaemic hyperinsulinaemic clamp with insulin infusion rates of 40 and 240 mU m-2 min-1. RESULTS: Basal GOR was significantly lower in septic patients than in controls (1.5 versus 2.3 mg per kg fat-free mass (FFM) per min, P < 0.001). Septic patients had a significantly lower GIR at 40 mU m-2 min-1 (4.2 versus 9.1 mg per kg FFM per min) and at 240 mU m-2 min-1 (7.5 versus 11.8 mg per kg FFM per min), relative to controls (P < 0.001). GOR was similar in septic and control subjects at both rates of insulin infusion whereas non-oxidative disposal was significantly lower in septic patients (P < 0.001) and accounted entirely for the reduction in GIR. The energetic cost of glucose disposal was unaffected by sepsis. CONCLUSION: Sepsis is associated with selective impairment of glucose storage but the energetic cost of non-oxidative disposal is unaffected.

Blood Glucose↗
PubMed1999

Measurement of the distribution volume of gadopentetate dimeglumine at echo-planar MR imaging to quantify myocardial infarction: comparison with 99mTc-DTPA autoradiography in rats.

PURPOSE: To measure the fractional distribution volume of gadopentetate dimeglumine in normal and reperfused infarcted myocardium at magnetic resonance (MR) imaging by using the fractional distribution volume of technetium 99m-diethylenetriaminepentaacetic acid (DTPA) as an independent reference. MATERIALS AND METHODS: Rats were subjected to 1 hour of coronary artery occlusion and 1 hour of reperfusion before inversion-recovery echo-planar imaging or autoradiography. Regional change in relaxation rate (delta R1) ratios for myocardium over blood were compared with radioactivity ratios for myocardium over blood after the injection of 99mTc-DTPA. RESULTS: Both delta R1 and radioactivity ratios demonstrated equilibrium distribution and hence represent partition coefficients (lambda). The fractional distribution volumes were greater in infarcted myocardium (0.90 +/- 0.05 for gadopentetate dimeglumine and 0.89 +/- 0.04 for 99mTc-DTPA) than in normal myocardium (0.23 +/- 0.02 for gadopentetate dimeglumine and 0.16 +/- 0.01 for 99mTc-DTPA). Area at risk at autoradiography was not significantly different from that at histomorphometry. The infarction size defined by using triphenyltetrazolium chloride was 13% +/- 4 smaller than that defined by using autoradiography. CONCLUSION: The fractional distribution volumes of gadopentetate dimeglumine and 99mTc-DTPA are similar and indicate extracellular distribution in normal myocardium and intracellular as well as extracellular distribution in reperfused infarction. Because the failure of cells to exclude these agents is indicative of necrosis, contrast medium-enhanced MR imaging may be useful to quantify myocardial infarction.

Animals↗
PubMed1999

Reperfused myocardial infarction as seen with use of necrosis-specific versus standard extracellular MR contrast media in rats.

PURPOSE: To measure the difference in size of reperfused myocardial infarction with necrosis-specific (bis-gadolinium-mesoporphyrin [hereafter, mesoporphyrin]) and standard extracellular (gadopentetate dimeglumine) magnetic resonance (MR) contrast media. MATERIALS AND METHODS: Echo-planar (for T1 measurement) and spin-echo (for infarction size) MR imaging were conducted in 32 rats subjected to reperfused reversible (n = 16) and irreversible (n = 16) myocardial injuries. All animals received gadopentetate dimeglumine 1 hour after reperfusion and underwent imaging. Sixteen rats received mesoporphyrin at 2 hours, the other 16 rats received gadopentetate dimeglumine at 24 hours, and all animals underwent imaging at 24 hours. RESULTS: Mesoporphyrin produced prolonged (22 hours) reduction in T1 in irreversibly, but not in reversibly, injured myocardium. The size of the mesoporphyrin-enhanced region (37% +/- 4 [SEM] of left ventricular surface area) closely correlated with the true infarction size as measured by means of histomorphometry (36% +/- 3, r = 0.90). The size of the gadolinium-enhanced region overestimated (48% +/- 2 and 43% +/- 1 at 1 and 24 hours of reperfusion, respectively) the size of true infarction (36% +/- 3, P < .05, r = 0.02), but it was close to the size of the area at risk (r = 0.93). CONCLUSION: The sizes of hyperenhanced regions displayed by using mesoporphyrin and gadopentetate dimeglumine differed from each other. The difference in size of the hyperenhanced region demarcated by mesoporphyrin and gadopentetate dimeglumine may provide an estimation of potentially salvageable myocardium.

Animals↗
PubMed1999

Serum leptin concentrations and their relation to metabolic abnormalities in human sepsis.

Circulating leptin concentrations are raised in animal models of inflammation and sepsis. The purpose of this study was to determine the effect of sepsis on serum leptin concentration in humans and to examine the relationship between leptin and the metabolic consequences of sepsis. Resting energy expenditure, insulin sensitivity, and fasting serum leptin, plasma insulin, and cortisol concentrations were measured in 20 subjects with intra-abdominal sepsis and 20 healthy control subjects, before and during a 2-h period of euglycemic hyperinsulinemia. Fasting serum leptin concentrations were similar in septic and control subjects. In simple regression analysis, serum leptin concentrations correlated significantly with percent body fat in both septic patients (r = 0. 64, P < 0.005) and healthy subjects (r = 0.75, P < 0.0001). Multiple regression analyses additionally indicated that percent body fat, fasting plasma insulin, and plasma cortisol, but not sepsis, were significant and independent determinants of serum leptin concentration. No relationship between leptin and resting energy expenditure or insulin sensitivity was identifiable. A major metabolic role for leptin in human sepsis therefore appears unlikely.

Adipose Tissue↗
PubMed1999

Value of blood pool MR contrast agents in imaging of the heart and blood vessels.

Magnetic resonance (MR) imaging has emerged as a new diagnostic technique for evaluation of the cardiovascular system. The diagnostic benefits of MR contrast agents have been demonstrated in the laboratory and in clinical research that has taken place during the past 12 years. Contrast agents enhance the sensitivity of MR angiography and improve early detection and characterization of myocardial and microvascular injuries. Clinically approved MR contrast agents are not confined to the intravascular space due to their small molecular size (standard extracellular MR contrast agents) and, therefore, they produce peak vascular enhancement for only a short period of time (< 30 min). In recent years remarkable progress has been seen in the development of blood pool agents for MR imaging. Impetus for creation of these agents has come in part from a growing appreciation of MR angiography. Vascular mapping has become an important application of medical imaging. Ample experimental evidence has shown that blood pool agents may play a significant role in coronary, peripheral and pulmonary angiography. In addition to their ability to increase vascular contrast, blood pool agents provide physiological information such as rate of entry, rate of accumulation and rate of elimination. In the heart, blood pool contrast agents are useful for estimating relative myocardial perfusion, discriminating between occlusive and reperfused infarction, differentiating between reversible and irreversible myocardial injury and detecting microvascular integrity. Blood pool agents are currently being investigated in humans. Initial clinical trials have demonstrated their safety and feasibility and, hopefully, future trials will demonstrate their efficacy. The purpose of this review is to focus on the rationale and value of blood pool MR contrast agents in imaging of the heart and blood vessels.

Journal Article↗
PubMed1998

Studies on the effects of piperidine derivatives on blood pressure and smooth muscles contractions.

Ten substituted phenacyl derivatives of 4-hydroxypiperidine were synthesized and studied for their effects on the mean arterial blood pressure (MABP) in normotensive anaesthetized rats and smooth muscles contractions of isolated rabbit jejunum. Two derivatives caused fall in blood pressure at the dose of 10-20 mg/kg and one rise in blood pressure at the dose of 20 mg/kg. Two compounds exhibited biphasic response (hypotensive followed by hypertensive) and one gave triphasic response at 10 mg/kg dose. Rest of four derivatives were found devoid of any effect on mean arterial blood pressure up to the dose of 30 mg/kg. All the derivatives except two caused relaxant effect on the spontaneous contraction of rabbit jejunum at the dose range of 0.1-2 mg/kg.

Animals↗
PubMed1998

Value of blood pool contrast agents in magnetic resonance angiography of the pelvis and lower extremities.

Our objective was: (1) to determine the appropriate dose of new ultrasmall superparamagnetic iron oxide particles for magnetic resonance angiography (MRA). This agent comprised of a single iron oxide crystal stabilized with a carbohydrate-polyethylene glycol coat (PEG-Ferron/NC 100150 injection); (2) to determine the proper flip angle for PEG-Ferron-enhanced 3 D time-of-flight (TOF) MRA sequence; and (3) to compare the enhancement of peripheral vessels following PEG-Ferron and GdDTPA-BMA. MRA parameters were: TR/TE = 50/2.1 ms, NEX = 1, FOV = 30 x 30 x 1.8 cm, and matrix = 256 x 128 x 64. In anesthetized beagle dogs (n = 10), the effects of PEG-Ferron and GdDTPA-BMA on regional signal were monitored for 45 min and compared. The lowest dose of PEG-Ferron (0.05 mmol/kg) produced the best enhancement of primary, secondary and tertiary vessels. The flip angle 60 degrees provided better enhancement than 20 degrees on contrast enhanced images. Unlike GdDTPA-BMA, PEG-Ferron allowed prolonged delineation (> 45 min) of the pelvis and lower extremities circulation. PEG-Ferron provided greater Contrast-to-noise ratio CNR (80.2 +/- 6.2, P < 0.05) than GdDTPA-BMA (63.5 +/- 2.5). It may be possible for blood pool contrast-enhanced 3 D TOF MRA to provide valuable information for visualization of vascular tree including guiding interventions.

Animals↗
PubMed1998

Integrated MR imaging approach to valvular heart disease.

With development of cine and velocity encoded magnetic resonance imaging, it is now feasible to detect and quantify aortic and mitral stenosis and regurgitation accurately. In addition, magnetic resonance imaging has the capabilities to assess simultaneously left and right ventricular mass, volumes, and function precisely. The high accuracy and reproducibility of magnetic resonance imaging in quantification of regurgitation and ventricular function has the potential to provide improved monitoring of therapy and optimal timing of surgery in patients with valvular dysfunction. In comparison to echocardiography and angiography, some current limitations of magnetic resonance imaging to an integrated approach of valvular heart disease exist, which may be removed with future refinement of magnetic resonance imaging technology for cardiovascular imaging.

Heart Valve Diseases↗
PubMed1998

Microvascular injury in reperfused infarcted myocardium: noninvasive assessment with contrast-enhanced echoplanar magnetic resonance imaging.

OBJECTIVES: The purpose of this study was to measure the accumulation of labeled albumin and to visualize its distribution pattern in reperfused infarcted myocardium as a function of time between onset of reperfusion and administration of the tracer. BACKGROUND: Myocardial microvascular injury leads to leakage of albumin from the intravascular space. Quantitative measurements of GdDTPA-albumin with inversion recovery echoplanar imaging (IR-EPI) may allow noninvasive monitoring of microvascular injury. METHODS: After 1 h of coronary artery occlusion, 56 rats were injected with GdDTPA-albumin or 123I-GdDTPA-albumin either immediately before reperfusion or 1/2, 1 or 24 h after reperfusion. GdDTPA-albumin in blood, normal myocardium and reperfused infarction was dynamically measured with IR-EPI during 1 h postinjection (PI). Autoradiograms were obtained at 15 min PI. Accumulation of labeled albumin in myocardium was expressed as the ratio of myocardial to blood content. RESULTS: In normal myocardium, the ratio of changes of relaxation rate-ratio (deltaR1-ratio) was 0.12+/-0.01 and did not change over 1 h. In reperfused infarction, however, the deltaR1-ratio increased after administration. Animals given GdDTPA-albumin before reperfusion exhibited fastest accumulation (deltaR1-ratio 15 min PI: 0.56+/-0.03) and essentially homogeneous distribution. The accumulation was slower when administered at 1/2, 1 and 24 h after reperfusion (deltaR1-ratios 15 min PI: 0.39+/-0.03; 0.31+/-0.04; 0.16+/-0.01; p < 0.001 compared to administration before reperfusion). Moreover, the tracer accumulated predominantly in the periphery of the injury zone. CONCLUSIONS: Amount and distribution pattern of labeled albumin in reperfused infarction are modulated by duration of reperfusion. The accumulation of GdDTPA-albumin can be quantified by IR-EPI. Thus, IR-EPI may be useful to noninvasively monitor myocardial microvascular injury in reperfused infarction.

Albumins↗