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Biomedical subjects

S M Lewis

Publications and source records attributed to S M Lewis.

At least 181 records · Page 10Linked to original sources
PubMed1982

Radionuclide angiographic exercise left ventricular performance in chronic aortic regurgitation: relationship to resting echographic ventricular dimensions and systolic wall stress index.

Forty-five patients with chronic aortic regurgitation (AR) underwent first-pass radionuclide angiocardiography (RNA) at rest and during upright bicycle exercise, as well as M-mode echocardiography at rest. Abnormal left ventricular (LV) exercise reserve, defined by the absolute change in ejection fraction (EF), was present in 16 of 45 patients (36%). Seven of ten patients with abnormal resting EF (less than 50%) and three of seven symptomatic patients had normal LV exercise responses. Patients with normal LV exercise reserve by RNA had LV dimensions by echo at end diastole (5.9 +/- 0.2 vs 6.5 +/- 0.3 cm, p = NS) and end systole (3.9 +/- 0.2 vs 4.4 +/- 0.3 cm, p = NS) comparable to those in patients wht abnormal LV exercise reserve. However, the mean corrected LV end-diastolic (LVED) radius/wall thickness ratio was significantly greater in AR patients with abnormal LV exercise reserve than in those with normal LV exercise reserve (395 +/- 15 vs 315 +/- 16, p less than 0.01). There data suggest that resting echocardiographic LV dimensions as well as the corrected echo LVED radius/wall thickness ratio have a variable relationship to RNA LV exercise performance in patients with chronic AR.

Adolescent↗
PubMed1982

Optimal inputs for parameter determination of inert gas washout from the lung.

The nitrogen washout test will yield more information about the distribution of pulmonary ventilation if a pattern of inspired gas concentrations is utilized other than the standard series of 100% oxygen breaths. The input breathing pattern which yields optimal results will vary with the specific features of the lung being studied but typically includes breaths of air, particularly in the last third of the washout. Using computerized, mathematical techniques, optimal inputs were selected for washout tests of duration 10, 20, 30 and 40 breaths for each of six lung models, ranging from a unicompartmental to a highly non-uniform 'diseased' lung. Knowing these optimal inputs we were able to devise a nominal input which was similar to the optimal inputs for all models. For a 10 breath test this nominal input pattern utilized a breath of air at breath 7. For a 20 breath test, air is utilized at breaths 12, 14, 15, 19; for 30, air at 19, 21, 22, 23, 29 and for a 40-breath test, air at breaths 19, 24, 28, 30, 31, 32 and 39. The 30-breath nominal sequence was compared with the conventional oxygen-only washout and a 31-breath pseudo-random binary (PRB) input. Comparisons were made using computer simulated washouts as well as actual tests on human subjects. The 30-breath nominal input was always superior to the standard washout and was superior to the PRB input for all models except the lung ventilated with vital capacity breaths. We conclude that a significant advantage is gained by substituting the recommended sequences of breaths in studies of the dynamics of gas exchange in the lung.

Humans↗
PubMed1982

Kinetics of heat damaged autologous red blood cells. Mechanism of clearance from blood.

The kinetics of radiolabelled heat damaged red cell (HDRBC) distribution have been studied in humans using a gamma camera, and compared with the kinetics of other blood cells. Liver uptake of 111In labelled HDRBC was completed within about 10 min of injection; splenic uptake was biphasic with a half time of about 5 min over the first 20 min following injection, and a later half time much longer than this. Activity initially present in the lung fields cleared within 24 h. The rate constants of liver uptake of 99mTc labelled HDRBC and of 111In labelled platelets were very similar; the rate constants of splenic uptake of these 2 particles were also very similar up to about 20 min following injection when the splenic platelet levels became constant and the HDRBC level continued to slowly rise. Splenic uptake and blood clearance of red cells coated with IgG (IgG-RBC), in contrast to HDRBC, were monoexponential. It was concluded that: (1) the blood clearance of HDRBC was due to pooling within, and to irreversible extraction by, the spleen; (2) liver uptake of HDRBC, which was irreversible, was completed within 10 min of injection; (3) IgG-RBC clearance was due to irreversible extraction by the spleen; (4) HDRBC uptake in the lung was unrelated to reticuloendothelial function, and represented prolonged transit through the lung microvasculature.

Blood Platelets↗
PubMed1982

Elution of 111Indium from reticuloendothelial cells.

Measurement of isotope accumulation in an organ is often used to assess that organ's removal of blood cells labelled with the isotope. This technique is only valid if the isotope does not elute from the organ. Elution of 111In from the liver and spleen has been investigated in 14 subjects following intravenous injection of heat-damaged erythrocytes labelled with 111In. The elution rate from the spleen was found to be low, about 2% of the initial activity per day. The liver accumulated activity with respect to its initial uptake at a rate of about 5% per day. Bone marrow was not visualised except in two patients in whom it was identifiable in the initial scan.

Erythrocytes↗
PubMed1982

Distribution of specific ventilation in cystic fibrosis.

Continuous distributions of specific tidal ventilation were recovered from nitrogen washouts in 29 patients with cystic fibrosis and 22 normal subjects along with other pulmonary parameters to assess the utility of the recovered distribution in describing the progress of the disease. Normal subjects showed predominantly unimodal distributions of a pattern showing a small amount of ventilation going to units with high specific ventilation. Multimodal distributions were the rule in the cystic population with only subjects with normal pulmonary function having unimodal distribution.

Adolescent↗
PubMed1981

Analysis of heat-damaged erythrocyte clearance curves.

The rate of clearance from the blood of heat-damaged erythrocytes (HDE) is used routinely as a quantitative assessment of splenic function. The time taken for the value at 3 min to fall by 50% (t0.5)is usually taken as the index of function. The clearance of HDE is dependent on three processes: splenic blood flow, splenic HDE extraction ratio and intrasplenic transit time of "unextracted' HDE, returning to the circulation. Exponential analysis of the clearance curve can resolve these three functions. Simple methods of analysis, however, such as t0.5, which are applied directly to the curve, may be weighted in favour of any one of them. In this paper, a large number of clearance curves have been analysed and the components of splenic function resolved. The t0.5, the percentage fall in HDE between 8 and 28 min (C20), the rate constant at 8 min (K8) and the rate constant of the tail of the curve (alpha 2) have been correlated with these components. K8 showed a close correlation with splenic blood flow, and alpha 2 with the rate of HDE phagocytosis. In general, the correlation between the various components of splenic function was better with C20 than with t0.5. This is explained predominantly by the fact that the t0.5 includes liver clearance. The t0.5 should therefore be used with caution as an estimate of splenic function, which can be usefully assessed by applying alternative simple methods of analysis described.

Erythrocytes↗
PubMed1981

Measurement of red cell volume and splenic red cell pool using 113m indium.

Using the lipophilic chelating agent, acetylacetone, red cells have been radiolabelled with the short-lived, generator-produced isotope, 113mIn. Following re-injection of these labelled cells, red cell volume has been measured and compared with corresponding values using 99mTc labelled red cells in 18 patients, and with 51Cr labelled red cells in five patients. 99mTc slightly overestimated red cell volume in relation to 113mIn, but 51Cr values were identical to 113mIn values. There was a close correlation between splenic red cell pool measured with 99mTc and with 113In. It was concluded that the intracellular stability and gamma emission of 113mIn make this isotope a superior alternative to 99mTc and 51Cr in measurements of red cell volume and splenic red cell pool.

Chromium Radioisotopes↗
PubMed1981

Automated platelet counting--a re-evaluation of the sedimentation method.

Platelet counting by means of the Coulter Thrombocounter, using the Thrombofuge method for specimen preparation has been evaluated in order to determine the cause of discrepancies in results obtained in interlaboratory quality assessment surveys. The method was assessed for accuracy, precision, drift and carry-over. When the method was used, as in routine practice, some discrepancies occurred; an important source of error was identified as being due to the level of sedimented plasma layer from which samples are removed. When the method was performed strictly in accordance with the manufacturer's instructions results were generally satisfactory and comparable to those obtained with the whole blood reference method, although, even with this standardized technique, the Thrombo-fuge tended to give higher platelet counts than the reference method with counts above 200 X 10(9)/l. This discrepancy to be independent of PCV, MCV or other identifiable factors.

Blood Platelets↗
PubMed1981

Measurement of splenic function in humans using heat damaged autologous red blood cells.

Functional hyposplenism, a clinical entity which has only recently been recognised, is usually assessed quantitatively by the rate of clearance of radiolabelled heat damaged erythrocytes (HDE) from the circulation. Based on recent observations on the kinetics of HDE, we have developed a 3 compartmental model of HDE distribution between the spleen and blood, and calculated, in a large series of clearance curves, splenic blood flow, HDE intrasplenic transit time and splenic HDE extraction ratio. Transit time (about 15 min) was of the same order as platelet transit time and extraction ratio (about 35%) was similar to that recorded in animals. Thr relationships between blood flow, transit time and extraction ratio provided evidence in support of 2 separate functional compartments, of which only one was engaged in phagocytosis, present within the spleen.

Erythrocytes↗
PubMed1981

Splenic atrophy in adult coeliac disease: is it reversible?

A study of splenic function in 28 patients with adult coeliac disease showed no significant correlation between the half life of heat-damaged red cells and either the duration of pre-treatment exposure to gluten or the length of time on a gluten free diet. A significant correlation was found between splenic size and duration of treatment; those patients who had been taking a gluten free diet for the longest time had the smallest spleens. Blood films from 11 of these 28 patients taken before treatment with a gluten free diet were compared with those taken between two and 15 years after the start of treatment. There was no tendency for the hyposplenic changes to regress. In the majority, the changes became more prominent despite strict adherence to the gluten free diet. These findings suggest that splenic atrophy in adult coeliac disease is not reversed by treatment with a gluten free diet and is unlikely to be related to the state of the jejunal mucosa or the duration of initial exposure to gluten.

Adolescent↗
PubMed1981

Spleen function and platelet kinetics.

In patients suffering from various platelet abnormalities, quantitative scanning after injection of indium-111 (111In) labelled platelets showed three different patterns of platelet destruction and distribution. In patients with a normal platelet life span but with evidence of increased splenic pooling, the spleen tended to be the main site of destruction. In patients with a moderately reduced platelet life span, the distribution of destruction in the system and variable destruction in the marrow. However, because of its rapidity this destruction was difficult to quantify, and it was difficult in these cases to distinguish reliably between spleen pool, sequestration, and destruction. Destruction of platelets on the liver appeared to be unimportant in all three groups. 111In, because of its physical characteristics, is preferable to chromium-51 as a platelet label in the assessment of abnormal platelet kinetics.

Adolescent↗
PubMed1981

Competitive inhibition of carbon monoxide transport: evidence against a carrier.

The existence of a saturable carbon monoxide (CO) carrier in the lung remains controversial. The carrier hypothesis was invoked to explain data that indicated that pulmonary diffusing capacity for CO (DLCO) decreases with increasing CO concentration. To test this hypothesis, we measured DLCO in 14 normal adult subjects at three alveolar CO concentrations (60, 660, and 2,060 ppm). Each mixture contained a constant amount of labeled C18O (60 ppm) and a balance of unlabeled C16O. If a saturable carrier exists at increasing CO concentrations, the unlabeled CO would compete for most of the sites on the carrier molecule, effectively inhibiting the uptake of the labeled C18O. C18O diffusing capacities (mean +/- SD) for the three levels of CO were 34.9 +/- 5.6, 33.0 +/- 6.0, and 34.7 +/- 7.8. There were no significant differences (P greater than 0.2) among the three levels. In another group of subjects we repeated the study using a gas mixture containing 130 ppm C18O. No significant differences were found. As a result, we find no evidence to support a CO carrier hypothesis.

Adolescent↗
PubMed1981

Distribution of ventilation and diffusing capacity in the normal and diseased lung.

Conventional tests of diffusing capacity (DL) consider the lung to be a uniform structure with regard to both ventilation and diffusion. These assumptions are incorrect even in normal subjects. We present a method for determining the distribution of both specific ventilation (SV) and DL from the washin and washout of C18O and simultaneous washout of argon. Both end-tidal and mixed-expired data are fit to a two-compartment lung model; parameters that define SV and DL are assigned to each compartment. From data generated by a model, the parameters recovered were found to be relatively insensitive to realistic levels of noise. Measurements in one subject were highly repeatable. We examined 15 normal subjects and 16 subjects with varying degrees of obstructive lung disease. In both groups the better ventilated spaces generally showed a higher DL. The sum of the total two-compartmental DL's correlated with, but was found to exceed, the value obtained using the steady-state method and generally exceeded the single-breath result. We conclude that this method has potential advantages over conventional methods and is worthy of further study.

Adolescent↗