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Biomedical subjects

E L Rolett

Publications and source records attributed to E L Rolett.

At least 19 recordsLinked to original sources
PubMed2000

Critical oxygen tension in rat brain: a combined (31)P-NMR and EPR oximetry study.

The relationship between cerebral interstitial oxygen tension (Pt(O(2))) and cellular energetics was investigated in mechanically ventilated, anesthetized rats during progressive acute hypoxia to determine whether there is a "critical" brain Pt(O(2)) for maintaining steady-state aerobic metabolism. Cerebral Pt(O(2)), measured by electron paramagnetic resonance oximetry, decreased proportionately to inspired oxygen fraction. (31)P-nuclear magnetic resonance measurements revealed no changes in P(i), phosphocreatine (PCr)/P(i) ratio, or intracellular pH when arterial blood oxygen tension (Pa(O(2))) was reduced from 145.1 +/- 11.7 to 56.5 +/- 4.4 mmHg (means +/- SE). Intracellular acidosis, a sharp rise in P(i), and a decline in the PCr/P(i) ratio developed when Pa(O(2)) was reduced further to 40.7 +/- 2.3 mmHg. The corresponding Pt(O(2)) values were 15.1 +/- 1.8, 8.8 +/- 0.4, and 6.8 +/- 0.3 mmHg. We conclude that over a range of decreasing oxygen tensions, cerebral oxidative metabolism is not sensitive to oxygen concentration. Oxygen becomes a regulatory substrate, however, when Pt(O(2)) is decreased to a critical level.

Animals↗
PubMed1997

Histological assessment of rodent CNS tissues to EPR oximetry probe material.

The effects of the paramagnetic oxygen sensing material, lithium phthalocyanine (LiPc) and fusinite were assessed in the brain of Mongolian gerbils and the spinal columns of rats respectively, to determine if there are histologically discernible changes in the tissue surrounding the probe material. This information is essential for the evaluation of the role of EPR oximetry in the measurements of pO2 in the CNS; the technique has great potential value for such measurements because it reports on the pO2 accurately and sensitively and, after the initial placement, measurements can be made repeatedly without invasive procedures or anesthesia. Histologic assessments demonstrated the inert nature of both the fusinite and LiPc EPR probes in rodent CNS tissue over relatively long (2 month) time periods. The fusinite suspensions and LiPc crystals (size range of approximately 100-200 microns) remained well localized to the point of injection and created mild acute tissue reaction on implantation (which appeared to resolve quickly) and virtually no tissue reaction at later times. The majority of the implanted fusinite and LiPc material was present extracellularly in the brain and spinal cord. MRI provided an accurate, noninvasive assessment of probe placement and was able to investigate pathologic effects (hemorrhage, edema, necrosis) associated with the probe placement and treatment effects.

Animals↗
PubMed1995

High resolution renal diffusion imaging using a modified steady-state free precession sequence.

A modified steady-state free precession (SSFP) diffusion sequence is proposed for high resolution renal imaging. A pair of bipolar diffusion gradients was used to minimize the errors in measured apparent diffusion coefficient (ADC) caused by variations in T1, T2, and RF flip angle that have been observed with previously employed SSFP diffusion sequences. Motion sensitivity was reduced by the use of compensated gradients, frame-by-frame averaging, and a repetition time of 22 ms, which for a single-acquisition 128 x 128 image requires only 3 s. High resolution was achieved by signal averaging. The modified sequence was applied to in vivo diffusion measurements. In six normal rat kidneys the ADCs (mean +/- SD; x 10(-3) mm2/s) of the cortex, outer medulla, and inner medulla were 2.28 +/- 0.05, 2.38 +/- 0.10, and 2.95 +/- 0.05, respectively. The technique requires relatively large gradients to achieve adequate diffusion weighting.

1-Propanol↗
PubMed1990

Beta 2-adrenergic stimulation does not prevent potassium loss from exercising quadriceps muscle.

During exercise K+ is released from contracting muscle and plasma K+ concentration rises. Because beta 2-adrenergic agonists stimulate K+ uptake by skeletal muscle in vitro, we tested whether terbutaline, a selective beta 2-agonist, would reduce the loss of K+ from working muscle. Dynamic quadriceps muscle exercise was performed by 12 healthy male volunteers for 50 or 80 min at an average workload of 38 W. A steady K+ loss estimated at 0.16 +/- 0.02 mmol.min-1.kg working muscle-1 and a 0.30 +/- 0.05 mM elevation of arterial plasma K+ concentration were observed. The addition of terbutaline during exercise caused leg blood flow to increase 13% from 5.10 +/- 0.16 to 5.75 +/- 0.13 l/min and arterial K+ concentration to fall monoexponentially by 0.90 +/- 0.05 mM with a rate constant of 0.26 min-1. Terbutaline increased, rather than decreased, the washout of K+ from working quadriceps by 40% to an average value of 0.23 +/- 0.02 mmol.min-1.kg muscle-1. In an additional subject who exercised to exhaustion, terbutaline failed to diminish muscle K+ loss. We conclude that terbutaline does not augment Na(+)-K+ pump activity to a degree sufficient to prevent K+ loss from exercising muscle in humans. On the other hand, the rapid reduction in plasma K+ concentration observed with beta 2-adrenergic stimulation is compatible with an uptake of K+ by nonexercising tissue at an estimated maximal rate of 0.5 micromol.g-1.min-1.

Adrenergic beta-Agonists↗
PubMed1987

Two-dimensional ultrasonic tissue characterization: backscatter power, endocardial wall motion, and their phase relationship for normal, ischemic, and infarcted myocardium.

To understand the possible differences in reflected ultrasonic energy from normal, ischemic, and infarcted myocardium, we studied 20 open-chest dogs with a commercially available two-dimensional ultrasonic scanner. Echocardiographic radiofrequency images of anterior myocardium were obtained serially during complete coronary occlusion for 2 hr (n = 15) or 5 hr (n = 10), or after temporary coronary clamping for 15 min with release for 1 hr (n = 5). We investigated two variables: the cyclic backscatter power and the phase difference among endocardial wall motion (EWM), cyclic backscatter power (BSP), and left ventricular pressure (LVP). The cyclic BSP decreased from a control (nonischemic) level of 5.1 +/- 0.8 to 2.3 +/- 0.7 dB during ischemia (up to 30 min after coronary ligation). The phase difference between the EWM and BSP progressed from a control (nonischemic) value of 38 +/- 20 to 115 +/- 23 degrees during ischemia. For the infarction period (2 to 5 hr after coronary ligation), the cyclic BSP progressively returned toward baseline control levels to 4.0 +/- 1.2 dB, but the phase had increased further to 170 +/- 28 degrees. The reperfusion study showed a similar decrease in cyclic BSP and an increase in phase after arterial clamping and both returned to near-normal nonischemic values upon arterial release. Simultaneous LVP recordings were performed to assess the phase contribution of endocardial dyskinesis to the total phase difference measurement. At 5 hr the dyskinesis had contributed 46% to the total phase difference, while the backscatter power contributed 54%. However, the EWM contribution occurred immediately while BSP contribution changed progressively during the 5 hr study period.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Two-dimensional ultrasonic variation in myocardium throughout the cardiac cycle.

This study was performed to investigate the two-dimensional unprocessed radiofrequency (rf) ultrasonic backscatter from myocardium throughout the cardiac cycle. Eleven mongrel dogs underwent left lateral thoracotomy and had two-dimensional echocardiographic studies performed using a 5 MHz transducer. Regions of interest, selected to encompass a portion of the myocardium, were transported at 33 ms intervals to a host computer and disc. Results show a reproducible cyclic variation in backscatter power throughout the cardiac cycle for the anterior wall. The backscatter power was highest during diastolic relaxation and lowest during systolic contraction. The average change was 4.5 dB.

Animals↗
PubMed1984

Characterization of the human right ventricular pressure-volume relation: effect of dobutamine and right coronary artery stenosis.

Right ventricular function was assessed in 15 patients using right ventricular pressure-volume loops. Right ventricular pressure using a micromanometer-tipped catheter, thermodilution cardiac output and gated blood pool scintigrams were simultaneously obtained. To help isolate the right ventricle, a slant hole collimator was used. The measurements were repeated during dobutamine infusion, which was titrated so there was minimal change in systemic pressure and heart rate. The right ventricular pressure-volume loop resembles the usual left ventricular loop except that the isovolumic contraction phase is often not as distinct, and right-sided ejection may continue well beyond right ventricular peak systolic pressure. Systolic but not diastolic function improved with dobutamine administration. There was no significant difference in right ventricular systolic function (ejection fraction, stroke work index, stroke volume index and cardiac index) or in end-diastolic volume index between patients without (Group I) and with (Group II) significant right coronary artery stenosis. However, there was a small but significant difference in right ventricular end-diastolic pressure (5.3 +/- 2.5 and 8.1 +/- 1.8 mm Hg [p less than 0.05]) for Group I and II, respectively. Thus, the right ventricular pressure-volume loop can be used to graphically display right ventricular function and improvement in contractility with dobutamine. The right ventricular isovolumic contraction phase and ejection phase differ from those in the usual left ventricular loop. Although there was a small difference in right ventricular end-diastolic pressure in patients with and without right coronary artery stenosis, the right ventricular pressure-volume loop did not provide additional discriminatory information between these two groups of patients.

Adult↗
PubMed1981

Short-term threshold behavior of human ventricular pacing electrode: noninvasive monitoring with a multiprogrammable pacing system.

Twenty-two patients were studied for 8 to 12 weeks following pacemaker implantation. A unipolar multiprogrammable pacing system was used to assess and compensate for early post-implant changes in pulse width threshold (PWT). Changes in PWT were estimated by noninvasive measurements of the lowest pulse width required for 100% capture at constant voltage. All patients showed an early increase in PWT. The magnitude of this change was unpredictable and ranged from 2- to 10-fold. For pacing, we selected an appropriate margin of safety to be a pulse width three times the PWT. During the study period, 4 patients showed critical increases in PWT, requiring reprogramming to an increased pulse width as above, whereas only one patient required lead repositioning. The majority of patients achieved a stable low PWT and were reprogrammed to a reduced pulse width. The programmable pacing system provides a safe accurate technique for monitoring early changes in PWT, defines the need for appropriate alterations in programmable functions, decreases the risk of early pacemaker failure, and offers promise for improved pacemaker longevity in many patients.

Aged↗
PubMed1979

Quantitative coronary angiography: measurement of the "critical" stenosis in patients with unstable angina and single-vessel disease without collaterals.

Quantitative angiographic assessment of proximal coronary artery stenosis was performed in 15 patients with consecutive presentations in two categories defined by clinical and angiographic criteria. Group 1 consisted of 10 patients who had new onset of refractory rest angina and ischemic ST-T changes, but no infarction, single-vessel coronary disease without collateralization, and normal left ventricular (LV) angiograms. Group 2 consisted of five patients who were similar to patients in group 1, but had subendocardial infarction (SEI). Quantitative coronary arteriography, using paired perpendicular angiographic views and digital computation, yielded statistically different lesion dimensions and hemodynamic predictions for the two groups. Minimum stenosis diameters were 0.88 +/- 0.14 (SD) and 0.64 +/- 0.08 mm, respectively, for groups 1 and 2. This corresponded to 72% and 78% diameter reduction and 92% and 95% cross-sectional area reduction for the two groups. These small dimensional differences among lesions in the two groups resulted in large differences in their hemodynamic impact as predicted from classic fluid mechanics theory. We conclude that there are characteristic lesion dimensions for the isolated "critical" stenosis in these selected patients with rest angina. Further small increases in lesions severity result in SEI. Certain practical applications and limitations of these observations are discussed.

Angina Pectoris↗
PubMed1978

Left-ventricular ejection fraction and segmental wall motion by peripheral first-pass radionuclide angiography.

A computerized edge-detection method was developed to obtain radionuclide ventriculograms for analysis of left-ventricular ejection fraction and segmental wall motion from first-pass studies following i.v. injection of radionuclide. The accuracy of this technique was examined in 21 patients undergoing cardiac catheterization. Tc-99m DTPA was injected into an antecubital vein, with data acquisition in the 30 degrees RAO projection by a gamma scintillation camera interfaced to a computer. A computerized profile analysis was used to determine objectively the edge of the left-ventricular blood pool. Time-activity curves were generated, and the ejection fraction was calculated from sequential end-diastolic and end-systolic count rates. The values for ejection fraction correlated well with those obtained by single-plane contrast ventriculography (r = 0.95). End-diastolic and end-systolic images were reconstructed from the time-activity curve. To analyze segmental wall motion, the left-ventricular outline was divided into five segments and the motion of each segment was graded qualitatively from 1 to 5. Seventy-five of 105 segments had the same grade as the wall motion determined by contrast angiography, and 102 of 105 were within one grade. (P less than 0.001). These findings demonstrate the accuracy of this improved technique for objective, rapid, and noninvasive determination of left-ventricular function.

Adult↗
PubMed1972

Relaxing effects of catecholamines on mammalian heart.

1. The effect of catecholamines on the time course and amplitude of contraction and on KCl-induced contractures has been studied in mammalian hearts.2. Marked and reproducible contractures could be obtained in mammalian ventricular trabeculae and papillary muscles after beta-adrenergic block with propanolol or if the hearts were depleted of their catecholamine stores by reserpine or by chemical denervation with 6-hydroxydopamine.3. In neonatal hearts with lower endogenous catecholamine stores and poorly developed sarcoplasmic reticulum KCl contractures are easily produced.4. Catecholamines potentiate twitch tension and relax the contracture tension under all of the above circumstances.5. The relaxant effect of catecholamines is present during the time course of a twitch. This increased relaxation rate as well as the shortening of the time-to-peak of tension is independent of the variation in the duration of the action potential.6. The shortened relaxation time is present when the action potential is shortened with anodal repolarization or prolonged with cathodal depolarization (voltage-clamp).7. The relaxant effect of catecholamines on the twitch is temperature and rate dependent. The effect is observed in the presence of high or low concentrations of calcium.8. The presence of catecholamines is necessary for full relaxation of mammalian heart muscle under high performance conditions or states of calcium overload.9. It is proposed that catecholamines exert their relaxant effect independent of their positive inotropic effect by stimulating the sequestering system (sarcoplasmic reticulum, mitochondria or sarcolemma) for calcium.

Action Potentials↗