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Biomedical subjects

R A Stein

Publications and source records attributed to R A Stein.

At least 19 recordsLinked to original sources
PubMed1995

Intracoronary ST-T alternans during coronary balloon angioplasty.

To evaluate the presence and clinical significance of electrical alternans during PTCA, intracoronary electrocardiography (ic-ECG) was performed in 65 consecutive lesions. ST-T alternans, defined as a beat-to-beat difference in the ST elevation > or = 1 mm, was present in five lesions (7.7%), all in the proximal left anterior descending (LAD) coronary artery. The phenomenon was seen only after 130 sec (mean 174 +/- 57) of balloon inflation. Only two of the five showed ST-T alternans simultaneously on both surface and ic-ECG. One of five patients had premature ventricular contractions following ST-T alternans. Three of these five lesions required a second balloon inflation with duration of > or = 300 sec; there was no ST-T alternans on the second inflation in any of these lesions. We conclude: (1) the detection of ST-T alternans during PTCA is enhanced by use of ic-ECG, (2) electrical alternans during PTCA was seen only in proximal LAD lesions, implicating a large amount of ischemic myocardium as a requisite for the phenomenon, (3) electrical alternans is not immediate, requiring a certain duration of balloon occlusion and hence ischemia to occur, and (4) the absence of ST-T alternans during second balloon inflations suggests ischemic preconditioning may abolish this phenomenon.

Adult↗
PubMed1994

Light distribution of ocular endophotocoagulator probes and its surgical implications.

Ophthalmic endophotocoagulator probe cone angle affects the spot size, working distance, laser output power requirement, tissue exposure time, and uniformity of tissue irradiance, which all affect ease and safety of clinical use. The cone angle and irradiance distribution of several ophthalmic endophotocoagulator delivery systems were studied by directing the laser energy emitted by them on a CCD video sensor at several angles of incidence. The irradiances followed a Gaussian distribution. The measured irradiances were compared to a mathematical model of tissue irradiance that adjusted for the cone angle, probe-tissue distance, and angle of incidence. Using this model, laser irradiances produced by endophotocoagulator probes can be estimated under a wide variety of conditions. At highly oblique angles of incidence, wide-angle probes produce unexpectedly higher and uneven tissue irradiance. When numerous characteristics are considered, probes with a cone angle in the range of 10 degrees have many advantages over narrower or wider angle probes.

Fiber Optic Technology↗
PubMed1992

Changes in left ventricular size, wall thickness, and function in anemic patients treated with recombinant human erythropoietin.

Left ventricular size and function were evaluated in 15 anemic chronic hemodialysis patients before and after the administration of recombinant human erythropoietin (rHuEPO). All patients were studied with two-dimensional and M-mode echocardiographic examinations before the initiation of rHuEPO (T1) and at 28 +/- 7 weeks of rHuEPO therapy (T2). The two-dimensional targeted M-mode echocardiographic measurements obtained were: end-diastolic dimension (EDD); end-systolic dimension (ESD); stroke dimension (SD); dimensional shortening (SD/EDD); systolic posterior wall thickness (PWs); diastolic posterior and interventricular septal thickness; end-systolic wall stress (ESWS); and left ventricular mass. Mean hematocrit in these patients increased almost 50%. The EDD decreased from a mean value (+/- SEM) of 6.41 +/- 0.33 to 4.93 +/- 0.21 cm (p less than 0.05). ESD decreased from a mean value of 4.16 +/- 1.2 to 2.77 +/- 0.06 cm (p less than 0.05). The calculated mean SD decreased slightly but not significantly from 2.21 +/- 0.69 to 2.19 +/- 0.60 cm. The calculated SD/EDD increased from a mean 0.35 +/- 0.09 to 0.44 +/- 0.07 (p less than 0.05). ESWS fell from 59.2 +/- 12.2 to 37.6 +/- 9.3 gm/cm2 (p less than 0.01), and left ventricular mass fell (p less than 0.05) from 347 +/- 15.2 to 227 +/- 59 gm. There was no significant difference in resting heart rate or systolic blood pressure between T1 and T2. The increase in dimension shortening reflects afterload reduction, as indicated by the fall in end-systolic wall stress.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Segmentation of high-frequency ultrasound images of atherosclerotic coronary arteries.

High-frequency epicardial echocardiography (HFE) is an ultrasound imaging technique capable of visualizing coronary arteries in cross-section. Use of this imaging technique in the intra-operative setting can provide information about the structure of coronary arteries. As a result of time constraints imposed in this setting, there is a need for rapid, on-line analysis of HFE images. An algorithm for segmenting HFE images of coronary arteries into wall and luminal regions is described in this paper. The algorithm is more objective and time efficient than manual methods. A validation study with post-mortem human hearts demonstrated an excellent correlation (r = 0.99 for luminal areas, r = 0.99 for wall areas) between HFE images segmented with the algorithm and by manual methods, and a good correlation (r = 0.90 for luminal areas, r = 0.86 for wall areas) between HFE images segmented with the algorithm and manually segmented images of histological samples of the corresponding coronary arterial segments. Use of the algorithm for intra-operative HFE image segmentation may reduce the amount of time required for HFE image analysis and allow for an increased amount of data collection and analysis in the operating room.

Algorithms↗
PubMed1991

Exercise in hemodialysis patients after treatment with recombinant human erythropoietin.

To assess the effect of substantial increases in blood hemoglobin (Hb) caused by treatment with recombinant human erythropoietin (rhEPO) on exercise capacity in maintenance hemodialysis patients, we evaluated 10 patients (7 men and 3 women) at a mean age of 44.3 +/- 8.4 years on maintenance hemodialysis for a mean of 29.7 +/- 30.2 months by treadmill exercise to exhaustion. The patients were tested before administration of rhEPO and after a minimum 1 g/dl rise in Hb. With a change in Hb from 7.1 +/- 1.4 to 9.8 +/- 2.1 g/dl, peak oxygen consumption (VO2 peak) with exercise increased 50.3 +/- 9% (T1 = 15.1 +/- 5.3, T2 = 22.7 +/- 4.6 ml O2/kg/min, p less than 0.05). Respiratory exchange ratio (RER) at a given submaximal exercise level (3 mph, 6% of elevation) decreased significantly (T1 = 1.13 +/- 0.24, T2 = 0.92 +/- 0.08, p less than 0.05). The rhEPO-mediated increase in Hb was associated with an increased VO2 peak--an improvement of the peak exercise capacity and a reduced submaximal RER--reflecting a reduction in anaerobic metabolism at activities of daily living.

Adult↗
PubMed1991

Lipid and lipoprotein profiles relate to peak aerobic power in spinal cord injured men.

The relationship between peak VO2 and serum lipids, lipoproteins, and apolipoproteins was assessed in nine traumatic spinal cord injured (SCI), active, male volunteers. Mean (SD) age, height, and weight were 30.6 (11.6) yr, 171.1 (11.3) cm, and 74.2 (12.5) kg, respectively. Peak VO2 (X = 2.13 l.min-1) was assessed by a graded arm-crank test to maximum, percent body fat (X = 28.7%) by densitometry, and lipid profile by measures of serum triglycerides, total cholesterol (TC), high and low density lipoprotein cholesterol (HDL-C and LDL-C, respectively), apolipoproteins (apoA-1, apoB), and various ratios of lipids, lipoproteins, and apolipoproteins. Significant inverse relationships emerged between peak VO2 and TC/HDL-C (r = -0.86; P less than 0.01), apoB/apoA-1 (r = -0.75; P less than 0.05), triglycerides (r = -0.73; P less than 0.05), and LDL-C/HDL-C (r = -0.72; P less than 0.05). Direct correlations (P less than 0.05) were demonstrated between peak VO2 and apoA-1/apoB (r = 0.71) and HDL-C/apoA-1 (r = 0.64). The present results indicate that, for active, mid-to-lower thoracic SCI men, the putative atherogenic and antiatherogenic lipid, lipoprotein, and apolipoprotein indices are significantly related to peak VO2 in a manner similar to that described for the able-bodied. These findings indicate the relevance of aerobic fitness assessment in planning CHD prevention strategies for the SCI.

Adult↗
PubMed1990

Time-resolved rotational dynamics of phosphorescent-labeled myosin heads in contracting muscle fibers.

We have measured the microsecond rotational motions of myosin heads in contracting rabbit psoas muscle fibers by detecting the transient phosphorescence anisotropy of eosin-5-maleimide attached specifically to the myosin head. Experiments were performed on small bundles (10-20 fibers) of glycerinated rabbit psoas muscle fibers at 4 degrees C. The isometric tension and physiological ATPase activity of activated fibers were unaffected by labeling 60-80% of the heads. Following excitation of the probes by a 10-ns laser pulse polarized parallel to the fiber axis, the time-resolved emission anisotropy of muscle fibers in rigor (no ATP) showed no decay from 1 microsecond to 1 ms (r infinity = 0.095), indicating that all heads are rigidly attached to actin on this time scale. In relaxation (5 mM MgATP but no Ca2+), the anisotropy decayed substantially over the microsecond time range, from an initial anisotropy (r0) of 0.066 to a final anisotropy (r infinity) of 0.034, indicating large-amplitude rotational motions with correlation times of about 10 and 150 microseconds and an overall angular range of 40-50 degrees. In isometric contraction (MgATP plus saturating Ca2+), the amplitude of the anisotropy decay (and thus the amplitude of the microsecond motion) is slightly less than in relaxation, and the rotational correlation times are about twice as long, indicating slower motions than those observed in relaxation. While the residual anisotropy (at 1 ms) in contraction is much closer to that in relaxation than in rigor, the initial anisotropy (at 1 microsecond) is approximately equidistant between those of rigor and relaxation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Effects of exercise on the signal-averaged electrocardiogram in coronary artery disease.

The effects of exercise on the signal-averaged electrocardiogram (SAECG) were investigated in 52 patients with stable coronary artery disease. The SAECG was recorded before and immediately after the exercise test and analyzed at 25 to 250 Hz and 40 to 250 Hz. All patients had SAECG with noise level less than or equal 0.8 microV at 25 Hz and less than or equal to 0.6 microV at 40 Hz and with the difference in noise level between control SAECGs and SAECGs after exercise less than or equal to 0.2 to 0.3 microV. Twenty-eight patients developed ST changes consistent with transient subendocardial ischemia that persisted during the SAECG recording after exercise. There was no significant difference between control SAECGs and SAECGs after exercise in patients with or without a positive exercise test. The absence of significant change on the SAECG was not related to the presence or absence of prior myocardial infarction, site of infarction, development of exercise-induced ventricular arrhythmias or presence of an abnormal recording at baseline. These data suggest that exercise-induced electrophysiologic changes and ventricular arrhythmias may not be related to the anatomic-electrophysiologic substrate that underlies late potentials on the SAECG.

Arrhythmias, Cardiac↗
PubMed1990

Effects of different exercise training intensities on lipoprotein cholesterol fractions in healthy middle-aged men.

Exercise training has been associated with decreases in total cholesterol and increases in high-density lipoprotein (HDL) cholesterol. The effect of the intensity of the exercise on alterations in cholesterol and lipoprotein fractions has not been defined and is the subject of this study. We divided 49 healthy men (aged 44 +/- 8 years) into four groups and evaluated them before and after 12 weeks of cycle ergometer exercise training at (1) an intensity of 65% of maximal achieved heart rate, (2) 75% maximal heart rate, (3) 85% maximal heart rate, and (4) a 12-week nonexercise control period. Pre- and post-training evaluations included maximal ergometer exercise ECG examinations with measurement of maximal minute oxygen consumption and serum total cholesterol, HDL cholesterol, and triglyceride levels. Low-density (LDL) and very low-density lipoprotein (VLDL) cholesterol levels were calculated. Dietary histories were obtained before and after the training period, and body weight and percentage of body fat were measured. Post-training oxygen uptake was significantly increased (training effect) in the groups exercising to 65%, 75%, and 85% maximal heart rate. Results of within-group analysis showed significant increases in the HDL cholesterol fractions in the 75% and 85% groups but not in the 65% group or the control group. Significant decreases in calculated LDL fractions occurred only in the 75% exercise-trained group with maximal heart rate. Aerobic exercise training favorably alters plasma lipoprotein profiles. A minimum training intensity equal to 75% maximal heart rate is required to the increase HDL cholesterol level.

Adult↗
PubMed1988

Small hydrocarbons formed by the peroxidation of squalene.

Experiments were undertaken to determine whether peroxidized squalene forms isoprene in a manner such that peroxidation could be considered as a possible route for the formation of in vivo human breath isoprene. Small hydrocarbons derived from peroxidation of positions 1-6 of squalene were identified in the head space. The most unusual product, proposed to arise from peroxidation of carbon 1 and intramolecular cyclization, was a mixture of dimethylcyclopentadiene isomers. Sonication of an aqueous mixture or low O2 partial pressure favored isoprene formation.

Chemical Phenomena↗
PubMed1987

Fatigue, acid-base and electrolyte changes with exhaustive treadmill exercise in hemodialysis patients.

Aerobic conditioning exercises have been shown to be beneficial for maintenance hemodialysis patients, but biochemical changes during exhaustive exercise in these functionally anephric patients have been less thoroughly studied. We evaluated serum biochemical changes in 7 patients during and after treadmill exercise to patient exhaustion. Duration of exercise was limited by lower leg fatigue without claudication. At exhaustion, only mild changes from baseline rest values were noted in arterial pH (7.39 +/- 0.03-7.33 +/- 0.04) and lactate (0.94 +/- 0.3-5.73 +/- 2.68 mmol/l) despite normal exercise-induced intracellular fluid shifts as evidenced by albumin concentration increases (44.9 +/- 2.8-49.3 +/- 3.1 g/l). Increases in serum K+ concentrations are also modest (change in K from baseline = 0.87 +/- 0.22 mmol/l). An explanation for these minimal biochemical alterations at exhaustion is unclear, but could relate to exercise being limited well below estimated maximum cardiac output and muscle O2 extraction levels by early, unexplained muscle fatigue. Fatigue in hemodialysis patients does not appear to be due to muscle hypoxia.

Acid-Base Equilibrium↗
PubMed1986

A survey of diagnostic stress testing centers in New York City.

Exercise electrocardiography (ECG) is widely employed for diagnosis of coronary heart disease (CHD) and for assessment of aerobic fitness prior to starting an exercise training program. This study surveyed stress testing centers in New York City (NYC) to determine practices currently used and to compare these practices with those suggested by the American Heart Association (AHA). A questionnaire was sent to 46 known centers in New York City and 18 responded. Of these, two did not list diagnosis of CHD as one of their purposes and were excluded from the sample, thus leaving 16 to be considered for this report. The most noteworthy findings were: most tests (56%) are conducted on asymptomatic adults, a population in whom the sensitivity and specificity of exercise ECG is relatively poor; only four centers employed qualified exercise physiologists, the profession specifically trained to perform fitness testing and exercise prescription for asymptomatic adults; over 50% of the centers terminate the test in the absence of symptoms when the client reaches a heart rate of 75%-95% of age-predicted maximal, even though maximal testing is suggested by the AHA; most centers did not include submaximal physiological responses in their test reports to clients and referring physicians; and most centers did not have a clearly established plan for handling emergencies. By bringing their practices into closer agreement with recommendations of appropriate professional organizations, testing centers can probably enhance the effectiveness and safety of their services to the public.

American Heart Association↗
PubMed1985

Acid-catalyzed formation of isoprene from a mevalonate-derived product using a rat liver cytosolic fraction.

Isoprene formation in a rat liver cytosolic fraction is shown to be increased 146-fold by acid treatment. This acid catalysis is dependent upon prior incubation of the cytosolic fraction with DL-mevalonate and is stimulated when the incubation also contains ATP. Formation of isoprene proceeds linearly through 5 h of acid treatment and is nearly complete at 10 h. These results suggest that the acid-catalyzed isoprene formation arises from the decomposition of dimethylallyl pyrophosphate via a carbonium ion mechanism. Chemical model studies using 3-methyl-2-buten-1-ol and 3-methyl-3-buten-1-ol (the alcohols corresponding to dimethylallyl pyrophosphate and isopentenyl pyrophosphate, respectively) confirm this hypothesis. At a pH less than or equal to 1, an 85% decomposition of 3-methyl-2-buten-1-ol to isoprene occurred after 24 h, while 3% of 3-methyl-3-buten-1-ol was converted to isoprene under identical conditions and time. It is concluded that the predominant immediate precursor of isoprene is dimethylallyl pyrophosphate and at low pH the ultimate fate of dimethylallyl pyrophosphate is complete conversion to isoprene. These conclusions have important biochemical and methodological implications.

Adenosine Triphosphate↗
PubMed1984

In vitro biosynthesis of isoprene from mevalonate utilizing a rat liver cytosolic fraction.

The in vitro biosynthesis of isoprene from DL-mevalonate in the cytosolic fraction of rat liver is described. Evidence is provided suggesting a non-enzymatic formation of isoprene from isopentenyl pyrophosphate and/or dimethylallyl pyrophosphate. Furthermore, the data establish an alternate fate of the mevalonate carbon skeleton providing the first evidence that breath isoprene is linked to cholesterol biosynthesis.

Adenosine Triphosphate↗