A culturally and gender responsive stress and chronic disease prevention intervention for low/no-income African American men: The MOCHA moving forward randomized control trial protocol

Low/no-income, African American men are disproportionally burdened by chronic disease resulting from a complex interplay of systemic, sociocultural, and individual factors. These disparities are related to poverty, racism, gender role strain, high levels of stress, low levels of physical activity, and malnutritious diet. Men of Color Health Awareness (MOCHA) is a community-driven movement to address the physical, mental, social, and spiritual needs of men of color. As part of ongoing programming, the MOCHA Standard intervention consists of a 10-week program including: (1) small group discussions of issues particularly relevant to men of color, (2) classes on health topics focusing on chronic disease control, such as nutrition, obesity, high blood pressure, fitness, and the social determinants of health; and (3) 60-min of moderately intensive aerobic exercise twice a week. While the MOCHA Standard intervention has yielded positive results, feedback from previous participants warranted an in-depth sociocultural tailoring of the curriculum to improve community receptiveness, in particular, revising the sessions to "narrativize" the materials to strengthen their potential effectiveness. This manuscript describes the novel recruitment strategies; the development of an enhanced MOCHA+ Stories Matter program that uses narrative communication strategies; and the methodology used to assess the comparative effectiveness of the MOCHA Standard relative to MOCHA+ Stories Matter program in lowering stress and risk of chronic diseases in a randomized controlled trial. The results of this research will contribute to the identification of effective interventions to address health disparities in low-income African-American men and the dissemination of effective chronic disease prevention programming.

Automated and semi-automated cell tracking: addressing portability challenges

Cell tracking is a key task in the high-throughput quantitative study of important biological processes, such as immune system regulation and neurogenesis. Variability in cell density and dynamics in different videos, hampers portability of existing trackers across videos. We address these potability challenges in order to develop a portable cell tracking algorithm. Our algorithm can handle noise in cell segmentation as well as divisions and deaths of cells. We also propose a parameter-free variation of our tracker. In the tracker, we employ a novel method for recovering the distribution of cell displacements. Further, we present a mathematically justified procedure for determining the gating distance in relation to tracking performance. For the range of real videos tested, our tracker correctly recovers on average 96% of cell moves, and outperforms an advanced probabilistic tracker when the cell detection quality is high. The scalability of our tracker was tested on synthetic videos with up to 200 cells per frame. For more challenging tracking conditions, we propose a novel semi-automated framework that can increase the ratio of correctly recovered tracks by 12%, through selective manual inspection of only 10% of all frames in a video.

Screening of some Australian Flacourtiaceae species for in vitro antioxidant, cytotoxic and antimicrobial activity

A total of 27 methanol extracts obtained from different plant parts of 10 species of rain forest trees belonging to four genera of the Flacourtiaceae and originating from Australia were investigated. In vitro cytotoxicity was measured by an ATP Lite-M assay method against the mouse P388 lymphocytic leukemia cell line. The total antioxidant activity has been assessed based on scavenging activity of stable ABTS free radicals. The minimum inhibition concentration (MIC) was determined by the dilution method performed in 96 well plates against four different microbes. The leaf extract of Casearia sp. (RB 3051), mature stem extract of Casearia grayi and stem extract of Scolopia braunii were found to have most antioxidant activity (IC50 = 2.9 microg/ml), cytotoxic activity (LC50 = 0.89 microg/ml) and antimicrobial activity against all four different microbes, respectively. The results obtained suggested that among the four genera studied Casearia is the most promising in respect of finding significant antioxidant, cytotoxic and also antimicrobial activity.

Artefacts in restored images due to intensity loss in three-dimensional fluorescence microscopy

Computational algorithms for three-dimensional deconvolution have proven successful in reducing blurring and improving the resolution of fluorescence microscopic images. However, discrepancies between the imaging conditions and the models on which such deconvolution algorithms are based may lead to artefacts and/or distortions in the images restored by application of the algorithms. In this paper, artefacts associated with a decrease of fluorescence intensity with time or slice in three-dimensional wide-field images are demonstrated using simulated images. Loss of intensity, whether due to photobleaching or other factors, leads to artefacts in the form of bands or stripes in the restored images. An empirical method for correcting the intensity losses in wide-field images has been implemented and used to correct biological images. This method is based on fitting a decreasing function to the slice intensity curve computed by summing all pixel values in each slice. The fitted curve is then used for the calculation of correction factors for each slice.

Blood-to-brain glucose transport, cerebral glucose metabolism, and cerebral blood flow are not increased after hypoglycemia

Recent antecedent hypoglycemia has been found to shift glycemic thresholds for autonomic (including adrenomedullary epinephrine), symptomatic, and other responses to subsequent hypoglycemia to lower plasma glucose concentrations. This change in threshold is the basis of the clinical syndromes of hypoglycemia unawareness and, in part, defective glucose counterregulation and the unifying concept of hypoglycemia-associated autonomic failure in type 1 diabetes. We tested in healthy young adults the hypothesis that recent antecedent hypoglycemia increases blood-to-brain glucose transport, a plausible mechanism of this phenomenon. Eight subjects were studied after euglycemia, and nine were studied after approximately 24 h of interprandial hypoglycemia ( approximately 55 mg/dl, approximately 3.0 mmol/l). The latter were shown to have reduced plasma epinephrine (P = 0.009), neurogenic symptoms (P = 0.009), and other responses to subsequent hypoglycemia. Global bihemispheric blood-to-brain glucose transport and cerebral glucose metabolism were calculated from rate constants derived from blood and brain time-activity curves-the latter determined by positron emission tomography (PET)-after intravenous injection of [1-(11)C]glucose at clamped plasma glucose concentrations of 65 mg/dl (3.6 mmol/l). For these calculations, a model was used that includes a fourth rate constant to account for egress of [(11)C] metabolites. Cerebral blood flow was measured with intravenous [(15)O]water using PET. After euglycemia and after hypoglycemia, rates of blood-to-brain glucose transport (24.6 +/- 2.3 and 22.4 +/- 2.4 micromol. 100 g(-1). min(-1), respectively), cerebral glucose metabolism (16.8 +/- 0.9 and 15.9 +/- 0.9 micromol. 100 g(-1). min(-1), respectively) and cerebral blood flow (56.8 +/- 3.9 and 53.3 +/- 4.4 ml. 100 g(-1). min(-1), respectively) were virtually identical. These data do not support the hypothesis that recent antecedent hypoglycemia increases blood-to-brain glucose transport during subsequent hypoglycemia. They do not exclude regional increments in blood-to-brain glucose transport. Alternatively, the fundamental alteration might lie beyond the blood-brain barrier.

Fast maximum-likelihood image-restoration algorithms for three-dimensional fluorescence microscopy

We have evaluated three constrained, iterative restoration algorithms to find a fast, reliable algorithm for maximum-likelihood estimation of fluorescence microscopic images. Two algorithms used a Gaussian approximation to Poisson statistics, with variances computed assuming Poisson noise for the images. The third method used Csiszar's information-divergence (I-divergence) discrepancy measure. Each method included a nonnegativity constraint and a penalty term for regularization; optimization was performed with a conjugate gradient method. Performance of the methods was analyzed with simulated as well as biological images and the results compared with those obtained with the expectation-maximization-maximum-likelihood (EM-ML) algorithm. The I-divergence-based algorithm converged fastest and produced images similar to those restored by EM-ML as measured by several metrics. For a noiseless simulated specimen, the number of iterations required for the EM-ML method to reach a given log-likelihood value was approximately the square of the number required for the I-divergence-based method to reach the same value.

Pulmonary angiotensin-converting enzyme (ACE) binding and inhibition in humans. A positron emission tomography study

Angiotensin-converting enzyme (ACE) inhibition attenuates pulmonary hypertension and delays the development of pulmonary vascular remodeling in animal models. Thus, ACE inhibition might be a useful treatment for primary pulmonary hypertension (PPH). To determine the dose of ACE inhibitor required to specifically block pulmonary ACE in humans, we measured the combined forward rate constant (CFRC) for [(18)F]-fluorocaptopril, which is proportional to the mass of ACE in the lung, using positron emission tomography (PET). In five normal subjects, CFRC was measured twice, 1 wk apart, to assess measurement reproducibility. The CFRC was 0.151 +/- 0.067 for the first measurement and 0.140 +/- 0.060 for the second measurement (p = not significant [NS]). In five normals, CFRC decreased on average 84%, from 0.177 +/- 0.053/s to 0.028 +/- 0.017/s (p < 0.05), after 1 wk ingestion of 5 mg enalapril orally once a day (the scans were performed 24 h after the last medication). Similarly, in five patients with PPH, CFRC decreased on average 76%, from 0.052 +/- 0. 020/s to 0.012 +/- 0.003 (p < 0.01), after 1 wk enalapril, despite much lower baseline values. We conclude that the total mass of pulmonary ACE appears to be significantly reduced in PPH and that only low doses of ACE inhibitors may be needed to block the effects of ACE on vascular remodeling in PPH.

Determination of octanol-water partition coefficient for terpenoids using reversed-phase high-performance liquid chromatography

Octanol-water partition coefficients (Kow) for 57 terpenoids were measured using a RP-HPLC method. Sample detection was achieved with standard UV and refractive index detectors and required no special column treatment. Measured log Kow values for the terpenoids ranged from 1.81 to 4.48 with a standard error of between 0.03 and 0.08 over the entire range. Partition coefficients determined by the RP-HPLC method were compared against shake flask, atom/fragment contribution, fragment and atomistic methods. The HPLC values were found to give the best correlation with shake flask results. Log Kow values calculated by the atom/fragment contribution method gave the best correlation with the HPLC values when compared to fragment and atomistic methods.

Parametric blind deconvolution: a robust method for the simultaneous estimation of image and blur

Blind-deconvolution microscopy, the simultaneous estimation of the specimen function and the point-spread function (PSF) of the microscope, is an underdetermined problem with nonunique solutions that are usually avoided by enforcing constraints on the specimen function and the PSF. We derived a maximum-likelihood-based method for blind deconvolution in which we assume a mathematical model for the PSF that depends on a small number of parameters (e.g., less than 20). The algorithm then estimates the unknown parameters together with the specimen function. The mathematical model ensures that all the constraints of the PSF are satisfied, and the maximum-likelihood approach ensures that the specimen is nonnegative. The method successfully estimates the PSF and removes out-of-focus blur. The PSF estimation is robust to aberrations in the PSF and to noise in the image.

Blood-to-brain glucose transport and cerebral glucose metabolism are not reduced in poorly controlled type 1 diabetes

To test the hypothesis that blood-to-brain glucose transport is reduced in poorly controlled type 1 diabetes, we studied seven patients with a mean (+/- SD) HbA1c level of 10.1 +/- 1.2% and nine nondiabetic subjects during hyperinsulinemic, mildly hypoglycemic (approximately 3.6 mmol/l, approximately 65 mg/dl) glucose clamps. Blood-to-brain glucose transport and cerebral glucose metabolism were calculated from rate constants derived from blood and brain time-activity curves--the latter determined by positron emission tomography (PET)--after intravenous injection of [1-(11)C]glucose using a model that includes a fourth rate constant to account for regional egress of 11C metabolites. Cerebral blood flow and cerebral blood volume were determined with intravenous H2(15)O and inhaled C(15)O, respectively, also by PET. At plateau plasma glucose concentrations of 3.6 +/- 0.0 and 3.7 +/- 0.1 mmol/l, rates of blood-to-brain glucose transport were similar in the two groups (23.7 +/- 2.2 and 21.6 +/- 2.9 micromol x 100 g(-1) x min(-1), P = 0.569, in the control subjects and the patients, respectively). There were also no differences in the rates of cerebral glucose metabolism (16.8 +/- 0.8 and 16.3 +/- 1.2 micromol x 100 g(-1) x min(-1), P = 0.693, respectively). Plasma epinephrine (1,380 +/- 340 vs. 450 +/- 170 pmol/l, P = 0.0440) and glucagon (26 +/- 5 vs. 12 +/- 1 pmol/l, P = 0.0300) responses to mild hypoglycemia were reduced in the patients with type 1 diabetes. We conclude that neither blood-to-brain glucose transport nor cerebral glucose metabolism is measurably reduced in people with poorly controlled type 1 diabetes.

Spinal cord stimulation revisited

The proportion of patients with intractable pain successfully managed with spinal cord stimulation (SCS) remains disputed. We analyze 27 consecutive patients with intractable pain treated with SCS using identical hardware (Itrel II System; Medtronic Neurological, Inc Minneapolis, MN, USA) by a single satisfactory diagnosis 1992 through 1995. A rigid selection protocol was used: 1. A satisfactory diagnosis of the pathologic process resulting in pain was made. 2. A corrective surgical procedure was judged not feasible by surgeons experienced in the particular pathology, e.g., vascular peripheral nerve, spine. 3. Lack of satisfactory response to noninterventional pain management modalities by an interdisciplinary pain clinic. 4. Independent psychological evaluation, including a structured interview was performed by a psychologist specialized in chronic pain management. In the last eight cases, a battery of self-report tests designed to assess psychosocial and behavioral consequences of the chronic pain problem were administered as well. All cases were of nonmalignant pain, except for one patient. Thirteen cases were diagnosed with failed back surgery syndrome (FBSS), one older patient with lumbosacral radiculopathy who refused decompression, one cervical radiculopathy and Klippel-Feil syndrome, six with reflex sympathetic dystrophy (RSD), two with peripheral vascular ischemic disease, one with post-thoracotomy pain syndrome, one with leg pain following resection of angiolipoma, one with traumatic superficial peroneal neuropathy, and one with Pancoast's tumor. Fifteen patients were female and twelve were male. All were Caucasian. Their ages ranged from 27 to 84 years (mean:48). The average follow-up was 21 months (range: 48-6). All patients underwent a three day trial screening with Pisces-Quad/Resume epidural leads connected to a temporary external stimulator. An Itrel II System pulse-generator was internalized in each of the 24 patients who had successful trial (three cervical and twenty-one thoracic-lumbar). There was no morbidity. Pain reduction was sustained in 22 out of the 24 patients who continue to use the stimulator. The same number would choose to receive in an electrical stimulator again. Normalization or improvement in Quantitative Sudomotor Axon Reflex Test (Q-SART) and Thermography was documented in the patients with RSD. We conclude that rigid selection protocol can maximize the proportion of patients with intractable pain who are successfully treated with SCS. Strict neurosurgical technique eliminates infection risk. Hardware selection minimizes incidence of malfunction.

Cerebral glucose transport and metabolism in preterm human infants

Few data regarding early developmental changes in cerebral (blood-to-brain) glucose transport (CTXglc) and CMRglc are available for humans. We measured CBF, CTXglc, and CMRglc with positron emission tomography at 4 to 7 days of life in six preterm human infants whose estimated gestational age was 25 to 34 weeks. The Michaelis-Menten constants Kt and Tmax were estimated from CTXglc and the calculated cerebral capillary plasma glucose concentration. Mean CMRglc was 8.8 mumol 100 g-1 min-1. The CMRglc did not correlate with plasma glucose concentration (r = .315, P = .543), whereas CTXglc showed a significant correlation with plasma glucose concentration (r = .836, P = .038). Estimation of the Michaelis-Menten constants from the best fit to the measured data produced values of Kt = 6.0 mumol mL-1 and Tmax = 32.6 mumol 100 g-1 min-1. These values for Kt in the developing human brain are similar to those that have been reported for the mature brain of adolescent and adult humans and adult nonhuman primates, indicating the affinity of the glucose transport protein for D-glucose is similar. However, Tmax is approximately one third to one half of the comparable values for mature brain, indicating a reduced number of available luminal transporters.

Effects of tea tree oil on Escherichia coli

Tea tree oil (TTO) stimulates autolysis in exponential and stationary phase cells of Escherichia coli. Electron micrographs of cells grown in the presence of TTO showed the loss of electron dense material, coagulation of cell cytoplasm and formation of extracellular blebs. Stationary phase cells demonstrated less TTO-stimulated autolysis and also had greater tolerance to TTO-induced cell death, compared to exponentially grown cells. It was also revealed that subpopulation of stationary phase cells demonstrated increased tolerance to TTO-bactericidal effects.

Positron emission tomography measurements of pulmonary vascular permeability with Ga-68 transferrin or C-11 methylalbumin

OBJECTIVE

To compare estimates of pulmonary endothelial barrier integrity obtained using two different tracer proteins.

DESIGN

Measure the pulmonary transcapillary escape rate with gallium (Ga)-68 labeled transferrin (PTCER(tf)) and positron emission tomography (PET) imaging and compare the results to similar measurements obtained with C-11 labeled methylalbumin (PTCER(alb)).

SETTING

Laboratory investigation.

SUBJECTS

Mongrel dogs.

INTERVENTIONS

No intervention in one group of dogs (n = 3); oleic-acid induced lung injury in another set (n = 4).

MEASUREMENTS AND MAIN RESULTS

Although PTCER(tf) was consistently higher than PTCER(alb) (mean difference: 50 x 10(-4)/min), the overall correlation between the two methods, after normalizing for differences in regression slope and intercept among the individual dogs, was excellent (r2 = .67).

CONCLUSION

The data support the continued use of PET and Ga-68 transferrin as an appropriate means of evaluating and quantifying lung injury.

In vivo kinetics of [18F](N-methyl)benperidol: a novel PET tracer for assessment of dopaminergic D2-like receptor binding

A novel D2-like receptor-binding radioligand, [18F](N-methyl)benperidol ([18F]NMB), was evaluated via positron emission tomographic (PET) imaging studies of baboons. [18F]NMB rapidly localized in vivo within dopaminergic receptor-rich cerebral tissues, and striatum-to-cerebellum ratios as high as 35 were achieved after 3 hours. Pretreatment of an animal with unlabeled receptor-specific antagonists before injection of [18F]NMB confirmed that the radioligand bound specifically to central D2-like receptors in vivo, and not to S2- or D1-like receptors. Unlabeled eticlopride displaced striatal [18F]NMB in vivo, showing that D2-like binding is reversible. Receptor-binding by the radioligand was resistant to competitive displacement by synaptic dopamine, as illustrated by the lack of effect of intravenous d-amphetamine on the in vivo localization of [18F]NMB. Studies involving sequential intravenous administration of [18F]NMB, d-amphetamine, and eticlopride show that the radioligand does not undergo agonist-mediated internalization with subsequent trapping. The feasibility of applying a three-compartment non-steady state model for quantification of [18F]NMB receptor binding was demonstrated. These in vivo characteristics give [18F]NMB distinct advantages over the PET radiopharmaceuticals currently used for clinical investigation of D2-like receptor binding.

Decreased [18F]spiperone binding in putamen in idiopathic focal dystonia

In this study we have investigated the pathophysiology of two idiopathic focal dystonias: hand cramp with excessive cocontractions of agonist and antagonist hand or forearm muscles during specific tasks, such as writing, and facial dystonia manifested by involuntary eyelid spasms (blepharospasm) and lower facial and jaw spasms (oromandibular dystonia). We used positron emission tomography (PET) to measure the in vivo binding of the dopaminergic radioligand [18F]spiperone in putamen in 21 patients with these two focal dystonias and compared the findings with those from 13 normals. We measured regional cerebral blood flow and blood volume in each subject as well as the radiolabeled metabolites of [18F]spiperone in arterial blood. A stereotactic method of localization, independent of the appearance of the images, was used to identify the putamen in all of the PET images. We analyzed the PET and arterial blood data with a validated nonsteady-state tracer kinetic model representing the in vivo behavior of the radioligand. An index of binding called the combined forward rate constant was decreased by 29% in dystonics, as compared with normals (p < 0.05). There were no significant differences between dystonics and normals in regional blood flow, blood volume, nonspecific binding, permeability-surface area product of [18F]spiperone or the dissociation rate constant. These findings are consistent with a decrease of dopamine D2-like binding in putamen and are the first demonstration of a receptor abnormality in idiopathic dystonia. These results have important implications for the pathophysiology of dystonia as well as for function of the basal ganglia.

Quantitation of myocardial fatty acid metabolism using PET

Abnormalities of fatty acid metabolism in the heart presage contractile dysfunction and arrhythmias. This study was performed to determine whether myocardial fatty acid metabolism could be quantified noninvasively using PET and 1-(11)C-palmitate.

METHODS

Anesthetized dogs were studied during control conditions; during administration of dobutamine; after oxfenicine; and during infusion of glucose. Dynamic PET data after administration of 1-(11)C-palmitate were fitted to a four-compartment mathematical model.

RESULTS

Modeled rates of palmitate utilization correlated closely with directly measured myocardial palmitate and total long-chain fatty acid utilization (r = 0.93 and 0.96, respectively, p < 0.001 for each) over a wide range of arterial fatty acid levels and altered patterns of myocardial substrate use (fatty acid extraction fraction ranging from 1% to 56%, glucose extraction fraction from 1% to 16% and myocardial fatty acid utilization from 1 to 484 nmole/g/ min). The percent of fatty acid undergoing oxidation could also be measured.

CONCLUSION

The results demonstrate the ability to quantify myocardial fatty acid utilization with PET. The approach is readily applicable for the determination of fatty acid metabolism noninvasively in patients.

Inhaled [13N]nitric oxide: a positron emission tomography (PET) study

Using positron emission tomography (PET) and nitric oxide radiolabeled with nitrogen-13 (half-life 9.97 min) we probed the distribution and kinetics of inhaled nitric oxide in anesthetized dogs. The washout of this gas after inhalation was much slower than that observed for [13N]nitrogen gas, demonstrating its uptake by lung tissue. The small fraction of radioactivity found in the plasma was determined to be in the form of [13N]nitrate. The administered gas contained < 1 ppm of nonradioactive nitric oxide, which is believed to be below the physiologic threshold for vasorelaxation.

Regional myocardial perfusion assessed with generator-produced copper-62-PTSM and PET

We have previously demonstrated that myocardial perfusion can be estimated accurately in experimental animals with the generator-produced positron-emitting tracer, 62Cu-pyruvaldehyde bis (N4-methylthio- semicarbazone)(62Cu-PTSM) and PET. This study evaluated the feasibility of quantifying regional myocardial blood flow using 62Cu-PTSM and PET in human subjects.

METHODS

Regional perfusion was estimated using a previously described and validated two-compartment model from dynamic PET scans obtained after an intravenous bolus of 62Cu-PTSM in 10 healthy volunteers and in 6 patients with coronary artery disease at rest: and in 9 of the volunteers and 4 of the patients after administration of dipyridamole intravenously. Flow estimates were compared with those obtained using H2(15)O.

RESULTS

Contrast was high between myocardium and blood or lung with 62Cu-PTSM, resulting in high-quality myocardial images. Liver uptake was also high. At flows of up to 1.5 ml/g/min, flow estimated with 62Cu-PTSM correlated closely with estimates obtained with H2(15)O (y = 0.71x .21, n = 169 regional comparisons, r = 0.66, p < 0.55), but this relationship was not maintained at higher flows.

CONCLUSION

The results demonstrate that quantification of myocardial perfusion with 62Cu-PTSM is feasible in human subjects but cannot be used to estimate hyperemic flows due most likely to the strong binding of the tracer to human serum albumin. Copper-62-PTSM congeners with less avidity for human albumin may prove more suitable for evaluation of hyperemic flows.

Cerebral transport and metabolism of 1-11C-D-glucose during stepped hypoglycemia

Attempts to measure blood-to-brain glucose transport and cerebral glucose metabolism with 11C-glucose have been hampered by methods that require jugular venous sampling or do not adequately account for the efflux of labeled metabolites from the brain. We performed eight positron emission tomography studies with 1-11C-D-glucose in macaques at arterial plasma glucose concentrations of 8.43 to 1.51 mumol ml-1 (152-27 mg dl-1) using a model that includes a fourth rate constant to account for regional egress of all 11C-metabolites. Values for blood-to-brain glucose influx, cerebral glucose metabolism, and brain free glucose concentration agreed closely with values obtained in mammals by other investigators. Values for net extraction fraction corresponded closely to simultaneously measured arteriovenous values. We demonstrated that utilization of a model that includes a fourth rate constant to account for regional egress of all 11C-metabolites with positron emission tomography and 1-11C-D-glucose provides accurate measurements of blood-to-brain glucose transport and cerebral glucose metabolism in vivo without need for jugular venous sampling, even under conditions of severe hypoglycemia.

In vivo measurements of pulmonary angiotensin-converting enzyme kinetics. II. Implementation and application

We measured pulmonary angiotensin-converting enzyme (ACE) kinetics with fluorine-18 captopril and positron emission tomographic (PET) imaging in five control dogs and in five dogs after 20-30 min of left caudal lobe (LCL) hypoxic ventilation. Time-activity data obtained with PET were interpreted with a compartmental receptor model relating changes in tissue and blood activity to one another within the region. In control dogs, the mean ratio of regional blood flow (measured by PET) between left and right dorsal lung regions was 0.90 +/- 0.16 (SD) vs. 0.54 +/- 0.24 (P < 0.05) in LCL hypoxic dogs. In control dogs, the amount of perfused unbound enzyme normalized to regional extravascular water concentration (Bmax/EVLW) averaged 13.3 +/- 8.9 x 10(-6) mmol ACE/ml EVLW; the ratio of regional values between the left and right sides was 1.02 +/- 0.18. In the LCL hypoxic dogs, Bmax/EVLW was 9.7 +/- 11.3 x 10(-6) mmol/ml hypoxic lung region and the ratio was 0.47 +/- 0.31 (P < 0.05). In control dogs, the coefficient of variation for Bmax/EVLW among regions was only 19 +/- 10%, although the between-dog variation was greater (64 +/- 4%). We conclude that this completely noninvasive method appears to be a promising approach for evaluating the expression of pulmonary ACE in vivo.

Measurement of regional pulmonary blood flow with PET

We have previously reported a method for measuring regional pulmonary blood flow (PBF) in experimental animals using 15O-water and PET. The method requires withdrawing blood from the pulmonary artery during the PET scan, so that the input function can be estimated for the one-compartment model used to analyze the data. The purpose of the present study was to modify and validate this technique for a more general use in humans.

METHODS

PBF was measured after injections of 15O-water in 15 normal subjects and in five patients with reduced cardiac output. In ten of the normal subjects, PBF was also measured after the injection of 68Ga-albumin macroaggregates (MAA). In the five other normal subjects and in the cardiomyopathy patients, PBF was measured twice after two separate 15O-water administrations. The input function was estimated from a region of interest (ROI) over the right ventricle (RV), with corrections when necessary, for time delays between RV and lung tissue.

RESULTS

The mean value for PBF in the normal subjects was 121 +/- 32 ml/min/100 ml lung, and was 57 +/- 33 ml/min/100 ml lung in the patients with cardiomyopathy. The correlation between PBF measured with 15O-water and PBF measured with 68Ga-MAA was r = 0.96. There was no significant difference in the mean value for PBF or the ventral-dorsal distribution of PBF when sequential measurements were made in the same individual. PBF increased in general in the ventral-dorsal direction in these supine subjects, although PBF was more evenly distributed in the cardiomyopathy patients.

CONCLUSION

Measurement of regional PBF with 15O-water and PET appears to be a valid, noninvasive approach for evaluating the pulmonary perfusion pattern of humans.

In vivo measurements of pulmonary angiotensin-converting enzyme kinetics. I. Theory and error analysis

We developed a procedure for measuring pulmonary angiotensin-converting enzyme kinetics with fluorine-18 fluorocaptopril and positron emission tomography (PET). The method is based on the application of a compartmental receptor model that represents the kinetics of two species of ligand, presumably the trans and cis conformers of captopril. The input function was characterized and includes corrections for the labeled metabolites of fluorocaptopril. Application of the procedure to lung time-activity data obtained with PET produced estimates of kinetic parameters demonstrating fast kinetics for one conformer and slower kinetics for the other. Simulation studies were performed to evaluate the sensitivity of the estimated parameters to errors in the model assumptions and in measured values for variables required for analysis of the PET data. Estimates for two of the kinetic parameters, the amount of perfused unbound functional enzyme normalized to regional lung volume and the association rate constant for the trans conformer, were relatively stable even with large errors in the input data, varying < 30% from true values for all perturbations. Thus, the procedure produces reliable estimates of the kinetics of the trans conformer of captopril as well as theoretical curves that are close to the observed data.

Measurement of regional cerebral blood flow with positron emission tomography: a comparison of [15O]water to [11C]butanol with distributed-parameter and compartmental models

To further our understanding of the best way to measure regional CBF with positron emission tomography (PET), we directly compared two candidate tracers ([15O]water and [11C]butanol, administered intravenously) and two popular implementations of the one-compartment (1C) model: the autoradiographic implementation representing a single PET measurement of tissue radioactivity over 1 min and a dynamic implementation representing a sequence of measurements of tissue radioactivity over 200 s. We also examined the feasibility of implementing a more realistic, and thus more complex, distributed-parameter (DP) model by assigning fixed values for all of its parameters other than CBF and tracer volume of distribution (Vd), a requirement imposed by the low temporal resolution and statistical quality of PET data. The studies were performed in three normal adult human subjects during paired rest and visual stimulation. In each subject seven regions of interest (ROIs) were selected, one of which was the primary visual cortex. The corresponding ROI were anatomically equivalent in the three subjects. Regional CBF, Vd, tracer arrival delay, and dispersion were estimated for the dynamic data curves. A total of 252 parameter sets were estimated. With [11C]butanol both implementations of the 1C model provided similar results (r = 0.97). Flows estimated using the 1C models were lower (p < 0.01) with [15O]water than with [11C]butanol. In comparison with the 1C model, the constrained version of the DP used in these studies performed inadequately, overestimating high flow and underestimating low flow with both tracers, possibly as the result of the necessity of assigning fixed values for all of its parameters other than CBF and Vd.

Sudden death in idiopathic dilated cardiomyopathy: role of ventricular arrhythmias

Sudden cardiac death (SCD) is associated with idiopathic congestive cardiomyopathy (IDCM) and most commonly is due to ventricular tachyarrhythmias. The recurrence rate of SCD in the absence of specific therapy is thought to be around 20%-30% per year. Asymptomatic and symptomatic ventricular arrhythmias are common in patients with IDCM and the direct causal link of such arrhythmias with SCD in IDCM patients remains to be established. Furthermore, therapy directed at suppressing these ventricular arrhythmias has not been shown to decrease the incidence of SCD. Various approaches such as ambulatory monitoring, electrophysiological testing, signal-averaged electrocardiogram, and hemodynamics have met with variable success in identifying patients prone to SCD. Additionally, therapeutic approaches to prevent SCD in IDCM patients have produced equivocal results. This article reviews the published studies addressing the causal link of ventricular arrhythmias to sudden death in patients with IDCM and the attempts to decrease the incidence of sudden.

Quantification of regional myocardial perfusion with generator-produced 62Cu-PTSM and positron emission tomography

BACKGROUND

Noninvasive assessment of regional myocardial perfusion at rest and after stress is important for the objective evaluation of the effects of coronary artery disease and its response to therapy. Centers that do not have cyclotrons rely on generator-produced radioisotopes for assessment of regional myocardial perfusion with positron emission tomography (PET). The aim of the present study was to develop and implement an approach to quantify regional myocardial perfusion using copper(II) pyruvaldehyde bis-(N4-thiosemicarbazone) (PTSM) labeled with the generator-produced, positron-emitting radionuclide 62Cu (t1/2 = 9.7 minutes).

METHODS AND RESULTS

Regional perfusion was estimated from dynamic PET scans after intravenous administration of 62Cu-PTSM in 21 studies in 13 intact dogs evaluated over a wide range of myocardial flow values. In 15 interventions in nine dogs, regional perfusion was also estimated with H2(15)O. Regional perfusion with 62Cu-PTSM was estimated from dynamic blood and tissue time-activity curves, along with the model parameter k1 (forward rate of transport) and the PET parameter FBM (fraction of blood pool activity observed in tissue), using a two-compartment kinetic model. Arterial blood activity was corrected for red blood cell-associated 62Cu. In 44 comparisons, estimates of regional perfusion with 62Cu-PTSM correlated well with estimates obtained with concomitantly administered radiolabeled microspheres (y = 0.90x +/- 0.15, r = 0.95, p < 0.05) over a flow range from 0.23 to 6.14 ml/g per minute. In five healthy human volunteers evaluated at rest with H2(15)O and 62Cu-PTSM, regional perfusion estimated with 62Cu-PTSM was not significantly different from that obtained with H2(15)O (1.05 +/- 0.36 versus 0.96 +/- 0.28 ml/g per minute). 62Cu-PTSM provided high-quality images of the heart.

CONCLUSIONS

The results of this study demonstrate that quantification of regional myocardial perfusion is feasible using generator-produced 62Cu-PTSM. Since 62Cu-PTSM can be used to estimate perfusion in the brain, kidney, and tumors as well as in the heart, it is an attractive tracer for centers that rely on generator-produced tracers for the evaluation of perfusion with PET.

The effects of regional pulmonary blood flow on protein flux measurements with PET

We used PET to evaluate whether changes in regional pulmonary blood flow (PBF) or plasma volume (PV) affect calculations of the pulmonary transcapillary escape rate (PTCER) for 68Ga-labeled transferrin. We reduced PBF in five dogs by inflating a right atrial balloon. Regional PBF decreased 25% to 174 +/- 40 ml/min/100 ml lung without a change in PV or PTCER. In eight other dogs, we decreased PBF and PV via controlled arterial hemorrhage. PBF decreased 45% to 110 +/- 33 ml/min/100 ml lung and PV decreased 22% without a change in PTCER. We also used a series of computer simulations to evaluate the effect of even greater reductions in regional PBF on PTCER calculations. These simulations showed, in support of the experimental data, that if PBF was greater than 40 ml/min/100 ml lung, PTCER could be accurately measured. However, below this level, PV was increasingly under-estimated and PTCER overestimated. The results indicate the sensitivity of the PTCER calculation to errors in the PV measurement, especially in regions of markedly reduced regional PBF.

Effects of nonideal input functions on PET measurements of pulmonary blood flow

Regional pulmonary blood flow (rPBF) can be measured with an intravenous infusion of 15O-labeled water and positron emission tomography (PET). The current method depends on two assumptions related to the input of activity to the lung during the scan: 1) the pulmonary arterial tracer input is constant (i.e., a "step function" in shape), and 2) the scan begins at the instant of arrival of the step function. To determine the effect that departures from these assumptions might have on the measurement of rPBF, we performed a series of mathematical simulations for three different input functions: 1) a step function that arrived either 1 or 2 s before or after scan start; 2) a dispersed input function, with activity rising during the scan period; and 3) a combination of these two errors. Calculated values, based on the standard assumptions, were compared against the "known" values used in generating the simulated data. The results show that timing errors associated with starting the scan late cause an overestimation of rPBF, whereas timing errors due to low regional flow or departures from the assumed step input function both cause an underestimation of true rPBF. Thus, in actual practice, the combined errors probably partially offset one another. Except for states of truly high rPBF and low lung density, the errors remain less than 15% of the true value. We conclude that PET measurements of rPBF are not highly sensitive to these presumably common departures from the assumed pulmonary arterial input function to lung regions of interest.

Implementation and evaluation of a two-compartment model for quantification of myocardial perfusion with rubidium-82 and positron emission tomography

Positron emission tomography offers the ability to noninvasively assess regional myocardial perfusion in absolute terms (i.e., milliliters per gram per minute). Accurate estimates have been difficult to achieve with generator-produced 82Rb because of the complex behavior of this tracer in the myocardium. The aim of the present study was to determine whether regional myocardial blood flow could be assessed quantitatively with 82Rb and positron emission tomography by using a two-compartment kinetic model. Regional perfusion in milliliters per gram per minute was estimated from dynamic tomographic scans after intravenous administration of 82Rb in 18 studies in 13 intact dogs studied without intervention, after 2 and 24 hours of induced ischemia, during reperfusion after transient occlusion, or at rest and after pharmacological hyperemia after induced coronary artery stenosis. Regional flow was estimated along with the forward and backward rates of transport (k1 and k2 [minutes-1]) after the relative volume of distribution of the first compartment was fixed to 0.53 ml/ml and the tomographic parameters, the recovery and spillover fractions, were fixed to averaged values obtained in previous studies. In 36 comparisons, estimates of regional flow with 82Rb correlated well with flow measured with concomitantly administered radiolabeled microspheres (r = 0.91, p less than 0.05) over the flow range from 0.14 to 4.25 ml/g/min. A putative index of viability, k2, increased significantly in regions with severe ischemia. The results suggest that quantification of regional myocardial perfusion is possible in centers using 82Rb for estimates of myocardial perfusion when a physiologically appropriate, two-compartment model is used.

Diagnostic implications of spectral and temporal analysis of the entire cardiac cycle in patients with ventricular tachycardia

BACKGROUND

Available methods for analysis of signal-averaged electrocardiograms (ECGs) have a low-positive predictive accuracy for identifying patients at risk for ventricular arrhythmias. Identification of the spectral and temporal features in ECGs that distinguish patients prone to ventricular tachycardia (VT) is a prerequisite to implementing refinements in methods that increase the diagnostic power of the signal-averaged ECG.

METHODS AND RESULTS

Fast Fourier transforms and time-domain reconstructions based on inverse fast Fourier transforms were computed over the entire cardiac cycle of signal-averaged ECGs of sinus beats from 40 patients with myocardial infarction and sustained VT, 41 with infarction without VT, and 20 normal controls. Ventricular depolarization and repolarization were analyzed by procedures that obviate limited resolution due to short data segments and window functions. Spectral magnitudes of ECGs from patients in each group were compared, and the phase data were used for time-domain reconstructions to determine the temporal distributions of distinguishing frequency bands during the cardiac cycle. Magnitudes of 1-7-Hz frequencies were increased (from p less than 0.05 to p less than 0.00001), and magnitudes of 13-56-Hz and 70-128-Hz frequencies were decreased (from p less than 0.05 to p less than 0.00001) in the spectra of ECGs from patients with VT compared with patients without VT. Time-domain reconstructions demonstrated that 1-7-Hz frequencies were detectable throughout the QRS complex, ST segment, and T wave in ECGs from each group. The 13-56-Hz and 70-128-Hz frequency bands not only contributed to the terminal QRS and ST segment but were also detectable throughout the QRS complex of ECGs from patients with VT.

CONCLUSIONS

Results define new spectral and temporal features in signal-averaged ECGs from patients with VT that are excluded from analysis by available techniques that limit the bandwidth or restrict interrogation to portions of the cardiac cycle. These findings provide an objective basis for developing new indexes for signal-averaged ECG analysis.

Noninvasive quantification of regional myocardial perfusion with rubidium-82 and positron emission tomography. Exploration of a mathematical model

Positron emission tomography (PET) centers without cyclotrons use generator-produced rubidium-82 (82Rb) for assessment of myocardial perfusion. The aim of the present study was to determine whether myocardial blood flow could be assessed quantitatively with 82Rb and PET. Because the myocardial extraction fraction of 82Rb varies inversely and nonlinearly with flow and cannot be measured conveniently with PET, we used an experimentally derived mathematical function defining the relation between single-pass extraction fraction of 82Rb and flow to obviate the necessity of measuring the extraction fraction directly. Myocardial blood flow in absolute terms (ml/g/min) was estimated from dynamic PET scans after intravenous administration of 82Rb in intact dogs and compared with flows measured with radiolabeled microspheres. In 36 comparisons in 13 dogs studied at rest, or after coronary occlusion, reperfusion, or after coronary hyperemia induced with intravenous dipyridamole, over the flow range from 0.2 to 2.0 ml/g/min, estimates of perfusion with rubidium correlated well with flows measured concomitantly with microspheres, although there was a slight underestimation of flow with rubidium (flow by 82Rb = 0.92 x flow by microspheres-0.021, r = 0.83). In general, estimates of flow in ischemic regions were less reliable than estimates for regions with normal flow. Thus, although the relation between myocardial extraction and retention of 82Rb and flow can vary under a variety of physiological and pathophysiological conditions, this study demonstrates the ability to obtain quantitative estimates of myocardial blood flow with 82Rb and PET under carefully defined conditions without measuring the extraction fraction directly.

Occupational medicine: new interface for family medicine?

Family physicians are naturally concerned with the work effects or causes of their patients' health problems. As occupational risk factors have become better understood, however, a new specialty of occupational medicine has been recognized by the Royal College of Physicians and Surgeons in 1984, two years after the Canadian Board of Occupational Medicine started its own certification. Occupational physicians are available to act as an extension of the family doctor's care and can provide trustworthy medical resources in the workplace. The family physician should be aware of some of the games poorly trained or ill-informed personnel managers may play in the workplace if they have no medical consultant to rely on. New human rights legislation has given more opportunities to rehabilitate workers back to their jobs, and occupational physicians and family physicians can achieve a great deal in co-operation as a result.

Noninvasive quantitation of myocardial blood flow in human subjects with oxygen-15-labeled water and positron emission tomography

Noninvasive measurement of myocardial blood flow in absolute terms (i.e., milliliters per gram per min) has been difficult to accomplish despite the intrinsically quantitative power of positron emission tomography because of the nonphysiologic nature of tracers that have been employed conventionally as well as the limited spatial resolution of currently available instruments. It was previously demonstrated that myocardial blood flow in animals can be quantitated accurately with the diffusible tracer oxygen-15-labeled water (H2(15)O) when the arterial input function and myocardial radiotracer concentration were measured directly. To extend the approach for completely noninvasive measurement of blood flow, a parameter estimation procedure was developed whereby effects of limited tomographic spatial resolution and cardiac motion were compensated for within the operational flow model. In validation studies in 18 dogs, myocardial blood flow measured with positron emission tomography after intravenously administered H2(15)O correlated closely with flow measured with concomitantly administered radiolabeled microspheres over the range of 0.29 to 5.04 ml/g per min (r = 0.95). Although regional ischemia was clearly identifiable tomographically, absolute flow could not be determined accurately in ischemic regions in four dogs because of poor count statistics related to wall thinning. Subsequently, myocardial blood flow was measured in 11 normal human subjects. Flow was homogeneous throughout the myocardium, averaged 0.90 +/- 0.22 ml/g per min at rest and increased to 3.55 +/- 1.15 ml/g per min after intravenous administration of dipyridamole. Therefore, positron emission tomography with H2 15O and the approach developed permits noninvasive measurement of myocardial blood flow in absolute terms in humans and should facilitate objective assessment of interventions designed to enhance nutritive perfusion.

Quantitation of myocardial blood flow with H2 15O and positron emission tomography: assessment and error analysis of a mathematical approach

Quantitation of regional myocardial blood flow (MBF) in absolute terms with positron emission tomography (PET) has been difficult to achieve in part because of errors induced by the relatively low spatial resolution of current tomographic instruments. We previously demonstrated that MBF could be accurately measured over a wide range of flows after intravenous administration of H2 15O when the arterial input function and myocardial radiotracer content were measured directly. To extend this quantitative approach for noninvasive estimates of MBF with PET. We recently developed and implemented a novel mathematical approach whereby partial volume and spillover effects were estimated along with flow within the operational one-compartment flow equation. Noninvasive estimates of flow correlated closely with flow measured directly with radiolabeled microspheres. In the present study, with the use of a commercially available cardiac phantom, we assessed our ability to obtain true time-activity curves from observed PET data contaminated by partial volume and spillover effects. Computer simulations demonstrated that the approach developed is relatively insensitive to most potential sources of error, but is sensitive to timing discrepancies between the arterial input function and the tissue time-activity curve. Implementation of this approach provides accurate quantitation of regional MBF in absolute terms and should be useful in noninvasive evaluation of the efficacy of treatments designed to enhance nutritional perfusion in human subjects.

Identification of patients with sustained ventricular tachycardia by frequency analysis of signal-averaged electrocardiograms despite the presence of bundle branch block

Previously, we have demonstrated distinguishing features in the fast Fourier transform (FFT) of signal-averaged electrocardiograms (ECGs) obtained during sinus rhythm in the absence of bundle branch block that differentiate patients with from those without sustained ventricular tachycardia (VT). The ECGs during sinus rhythm from many patients with sustained VT, however, exhibit intraventricular conduction abnormalities. Accordingly, this study was performed to determine whether the presence of bundle branch block during sinus rhythm precluded accurate identification of patients with sustained VT. Studies were performed in 28 normal subjects (group I) and 141 patients with organic heart disease grouped according to clinical characteristics. Group II comprised 40 patients without VT in whom the QRS duration during sinus rhythm was less than 120 msec. Group III included 21 patients without VT in whom the QRS duration during sinus rhythm was 120 msec or greater. Group IV comprised 43 patients with sustained VT having ECGs during sinus rhythm with QRS durations less than 120 msec. Group V included 37 patients with sustained VT in whom the QRS duration during sinus rhythm was 120 msec or greater. FFTs of the terminal QRS and ST segment of signal-averaged X, Y, and Z ECGs were computed. Transformed data were expressed as an FFT magnitude and the relative contribution and peak magnitudes of 20 to 50 Hz frequencies determined after first demonstrating that this FFT method was more appropriate, when compared with the energy spectrum, for analyzing ECG signals having a broad range of ST segment durations.(ABSTRACT TRUNCATED AT 250 WORDS)