Current concerns in haematology. 3: Blood count calibration.
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Blood Cell Count↗
Biomedical subjects
S M Lewis
Publications and source records attributed to S M Lewis.
Intra-aortic balloon counterpulsation support in the high-risk cardiac patient undergoing urgent noncardiac surgery.
Patients with a recent myocardial infarction, congestive heart failure, sever angina, or uncorrected multivessel coronary artery disease are at increased risk of cardiac complications after major noncardiac surgery. Although invasive hemodynamic monitoring and preoperative optimization of cardiac status may lead to some reduction in the rate of perioperative cardiac events, the mortality from such events remains high. We report our experience with the use of perioperative intra-aortic balloon counterpulsation in eight patients with unstable coronary syndromes or severe coronary artery disease who underwent urgent noncardiac surgery. There were no perioperative cardiac events while the intra-aortic balloon pump (IABP) was in place. There were two postoperative cardiac events (non-fatal myocardial infarction, congestive heart failure) in the first postoperative week after the IABP was removed. One patient required emergent femoral thrombectomy as a result of intra-aortic balloon counterpulsation and subsequently died of a gastrointestinal hemorrhage. Intra-aortic balloon counterpulsation should be considered as an adjunct to maintain hemodynamic stability for the high-risk cardiac patient about to undergo urgent or emergent noncardiac surgery.
Aged↗
Coronary artery disease in the octogenarian: angiographic spectrum and suitability for revascularization.
The angiographic findings of 84 consecutive octogenarians presenting with symptoms of coronary artery disease (CAD) were examined to determine the extent of CAD as well as suitability for both coronary artery bypass grafting (CABG) and percutaneous transluminal coronary angioplasty (PTCA). The frequency of 0-, 1-, 2-, and 3-vessel and left main CAD was 7, 14, 21, 57 and 13%, respectively. Based on angiographic criteria, 69 of 78 patients (88%) with significant CAD had suitable coronary anatomy for CABG. Only 24 patients (31%) had coronary anatomy amenable to PTCA. CABG was performed in 19 patients with an operative mortality of 16% and major complication rate of 37%. PTCA was performed in 12 patients with a clinical success rate of 83%, mortality of 8% and major complication rate of 8%. It is concluded that in octogenarians with CAD, cardiac catheterization will often reveal coronary anatomy that is suitable for CABG but less suitable for PTCA. The morbidity and mortality associated with these interventions are high.
Aged↗
Lassa fever in the United States. Investigation of a case and new guidelines for management.
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Adult↗
Factorial designs for crossover clinical trials.
When measuring the joint effect of two factors it is advantageous to use a factorial design. If the application is suitable, efficiency may be further improved by using a crossover design. This paper presents a flexible method for amalgamating these two devices. Designs are constructed from smaller designs, known as bricks, generated cyclically from tabulated initial sequences. The bricks have known efficiencies for estimation of direct treatment main effects and interactions; the efficiencies can be simply combined to approximate the efficiencies of the whole design. This allows the user to build a design that is tailored to the particular objectives of the experiment. Three and four periods, and two factors with up to four levels are considered.
Antihypertensive Agents↗
Cardiogenic oscillations of He and SF6 in expired gas in dogs.
Quantitative analysis of cardiogenic oscillations of He and SF6 during airway and venous loading demonstrated that both VA/Q and VA/VA inequalities were involved in the lung gas inhomogeneity producing cardiac oscillations in the expirogram. Both inequalities were coupled in such a manner that low VA/Q units had high VA/VA. The oscillations were modified in conducting airways where SF6 oscillations were attenuated more than He oscillations, probably by laminar Taylor dispersion.
Animals↗
Silent myocardial ischemia and infarction in diabetics with peripheral vascular disease: assessment by dipyridamole thallium-201 scintigraphy.
We investigated the incidence of silent myocardial ischemia and infarction as assessed by dipyridamole thallium scintigraphy in 30 diabetic patients with peripheral vascular disease and without clinical suspicion of coronary artery disease. Seventeen patients (57%) had thallium abnormalities, with reversible thallium defects compatible with ischemia in 14 patients (47%) and evidence of prior, clinically silent myocardial infarction in 11 patients (37%). Thallium abnormalities were most frequent in patients with concomitant hypertension and cigarette smoking (p = 0.001). These results suggest that unsuspected coronary artery disease is common in this particular group of patients with diabetes mellitus.
Adult↗
Detection and functional assessment of accessory splenic tissue (splenunculi) with radiolabelled heat damaged autologous erythrocytes.
Eight patients (six with idiopathic thrombocytopenic purpura, one with immune pancytopenia, and one with autoimmune haemolytic anaemia), who had previously been splenectomized, were found to have splenunculi using radioactively labelled heat damaged autologous erythrocytes. In all patients the splenunculi were found to have significant 'splenic function'. However, there was a poor correlation between the size and the function of the splenunculi. Splenunculectomies were carried out in two patients. This led to a complete haematological remission in one patient and partial remission in the other. In three patients, where splenunculectomies could not be undertaken, the patients had to remain on significant doses of immunosuppressive therapy. In one patient complete remission was achieved using a course of immunosuppressive therapy alone and in the remaining two there was insufficient information to draw valid conclusions. Blood clearance kinetic studies of heat damaged erythrocytes were found to provide an accurate functional assessment of the splenunculi in all patients. However, the presence of a functional splenunculus was found to be the cause of disease relapse in only some patients. Therefore, the management of similar patients should perhaps be along the same lines as that at their initial presentation, that is, immunosuppressive therapy should be tried if they are not on any at the time of relapse, if they are already on it, then splenunculectomy should be done.
Adolescent↗
Standardization and harmonization of the blood count: the role of International Committee for Standardization in Haematology (ICSH).
Scientific principles of standardization were first applied in haematology in 1963 when the International Committee for Standardization in Haematology was established with a primary objective to improve the measurement of haemoglobin. Subsequently, ICSH has established Expert Panels on a wide range of haematological topics, including especially a Panel on Cytometry. The purpose of haematological standardization is to obtain precision, accuracy, specificity and harmonization of results between different laboratories in all countries and also between different instruments or methods in the same laboratory. To achieve these objectives ICSH sponsors collaborative studies by scientists from academic centres and from industry and uses a consensus procedure for establishing standards on the basis of the scientific data, followed by an educational programme to ensure that the standards are adopted worldwide. ICSH defines material standards and standardized methods. Material standards are classified as primary international standards, certified reference materials, secondary standards and calibrators. These must be distinguished from control preparations which are intended exclusively for quality control. Standardization of methods must also be considered at four levels: definitive, reference, selected and routine. Each has a place in practice but their roles must be clearly defined. ICSH has an established protocol for evaluation of automated blood cell counters. This defines the levels of precision and accuracy of instrument performance. It is also necessary to assess "clinical utility". The main requirement of the practising haematologist is clinical reliability and harmonization of results for comparability. One of the major functions of ICSH is to provide an interface for collaboration between the manufacturers who develop the instruments and the users in order to achieve this goal.
Anticoagulants↗
Evaluation of a prototype for a reference platelet counter.
A semiautomated single channel aperture-impedance particle counter was developed as a prototype for a reference platelet count for assigning values to reference preparations used in automated blood cell counts. The instrument is equipped with sheath flow and an aperture orifice of 50 microns in diameter and 60 microns in length to eliminate non-axial flow and minimise coincidence errors. Use of fixed volume and red blood cell:platelet ratios obviate dilution errors. The counter was assessed in accordance with the International Committee for Standardization in Haematology protocol for evaluation of automated blood cell counters. The counter provided a high level of linearity and precision, accurate coincidence correction, controlled volume, stability and negligible carryover.
Erythrocyte Count↗
Cardiogenic oscillations in He and SF6 expirograms during airway and venous loading.
Cardiogenic oscillations in the expired partial pressure profiles of two inert gases (He and SF6) were monitored in seven anesthetized paralyzed mechanically ventilated dogs. He and SF6 were administered either intravenously by a membrane oxygenator and partial arteriovenous bypass [venous loading (VL)] or by washin into lung gas [airway loading (AL)]. The single-breath expirograms obtained during constant-flow expiration after inspiration of test gas-free air displayed distinct and regular cardiogenic oscillations. The relative oscillation amplitude (ROA), calculated as oscillation amplitude divided by mixed expired-inspired partial pressure difference, was in the range of 1-8%. The ROA for both He and SF6 was approximately 4.2 times higher in VL than in AL, which indicated that among lung units that emptied sequentially in the cardiac cycle, the effects of alveolar ventilation-perfusion (VA/Q) inequality were more pronounced than those of alveolar ventilation-alveolar volume (VA/VA) inequality. In AL, He and SF6 oscillations were 180 degrees out of phase compared with CO2 and O2 oscillations and with He and SF6 oscillations in VL, which suggests that regions with low VA/VA had high VA/Q and very low Q/VA. The ROA was practically unaffected by breath holding in both AL and VL, which indicates that there was little diffusive or convective (cardiogenic) mixing between the lung units that were responsible for cardiogenic oscillations. The ROA was consistently higher for He than for SF6, and the He-to-SF6 ratio was independent of route of test gas loading, averaging 1.6 in both AL and VL. This result may be explained by laminar Taylor dispersion, whereby oscillations generated in peripheral lung regions are dissipated in inverse proportion to diffusion coefficient during transit through the proximal (larger) airways.
Administration, Inhalation↗
Dietary fiber for dogs: I. Effects of graded levels of dietary beet pulp on nutrient intake, digestibility, metabolizable energy and digesta mean retention time.
The optimal level of beet pulp (BP) inclusion in a meat-based dog diet and the effects of graded levels of dietary BP on fecal excretion responses and mean retention time of marked fiber in the gastrointestinal tract of the dog were evaluated using 30 female English Pointers assigned to isonitrogenous diets containing 0, 2.5, 5.0, 7.5, 10.0 or 12.5% BP (DM basis). Beet pulp replaced portions of dietary cornstarch. Digestibilities of DM and OM decreased by an average of 6% when comparing diets containing BP to the control diet, and quadratic and cubic responses were noted in digestibilities of fiber constituents (lower values at the 7.5 and 10.0% levels, higher values at the 2.5, 5.0 and 12.5% levels). Digestible energy (DE) and ME intakes (kcal/d) were not affected by treatment, but when expressed as a percentage of GE, values decreased (4.8% for DE; 6.2% for ME) linearly with increasing BP levels. Wet weight of feces increased (from 117 to 374 g/d) linearly as percentage of dietary BP increased. Frequency of defecation was higher (P less than .05) for dogs fed the diet containing 12.5% BP than for dogs fed the other diets (5.2 vs mean value of 2.8/24 h). Mean retention time of marked fiber decreased linearly (high value of 23.4 h for the 2.5% BP treatment, low value of 13.0 h for the 10.0% BP treatment) with increased level of BP. Beet pulp levels up to 7.5% of diet DM appear acceptable as a dietary fiber source in a meat-based canine diet.
Animal Feed↗
Blood film evaluations as a quality control activity.
Correlation of the blood film with the blood-count parameters provides a means of quality control of results obtained by the counter. This requires the observer to be skilled in identifying significant morphological abnormalities. Reliable blood film assessment must avoid potentially misleading information resulting from cell distribution bias and morphological artefact produced by poor techniques in the preparation and staining of films. Thus, whilst concordance between instrument results and manual films provides control on the sensitivity, specificity and predictive value of the counter, conversely blood count results provide a check on the reliability of the blood film. The experiences with the United Kingdom external quality assessment program illustrate the strengths as well as weaknesses of the blood film evaluation.
Hematologic Tests↗
Surrogate materials for calibration and control: the use of latex particles as calibrants for red cell volume measurements.
Latex particles, including BCR Certified Reference Material CRM 166a, have important applications for checking linearity and for calibrating aperture-impedance instruments used to determine red-cell volumes. Studies performed on Coulter Counters, e.g. the ZBi/C1000, ZM/C256 and Model S Plus IV, using a series of three different mono-sized latex particles have shown linearity but non-zero intercepts. This emphasizes the importance of calibrating instruments at more than one point. Latex particles also have an important role in calibration of red-cell volume measurements provided that a relative latex: red-cell shape factor has been assigned when the instrument is calibrated with fresh blood. Such relative shape factors are independent of latex particle size but need to be specific for instrument type and probably also for the orifice and diluent to be used. Nevertheless latex calibrants can serve an important role in standardizing red-cell volume measurements.
Calibration↗
Predictive value of quantitative dipyridamole-thallium scintigraphy in assessing cardiovascular risk after vascular surgery in diabetes mellitus.
Cardiac complications represent a major risk to patients undergoing vascular surgery. Diabetic patients may be particularly prone to such complications due to the high incidence of concomitant coronary artery disease, the severity of which may be clinically unrecognized. Attempts to stratify groups by clinical criteria have been useful but lack the predictive value of currently used noninvasive techniques such as dipyridamole-thallium scintigraphy. One hundred one diabetic patients were evaluated with dipyridamole-thallium scintigraphy before undergoing vascular surgery. The incidence of thallium abnormalities was high (80%) and did not correlate with clinical markers of coronary disease. Even in a subgroup of patients with no overt clinical evidence of underlying heart disease, thallium abnormalities were present in 59%. Cardiovascular complications, however, occurred in only 11% of all patients. Statistically significant prediction of risk was not achieved with simple assessment of thallium results as normal or abnormal. Quantification of total number of reversible defects, as well as assessment of ischemia in the distribution of the left anterior descending coronary artery was required for optimum predictive accuracy. The prevalence of dipyridamole-thallium abnormalities in a diabetic population is much higher than that reported in nondiabetic patients and cannot be predicted by usual clinical indicators of heart disease. In addition, cardiovascular risk of vascular surgery can be optimally assessed by quantitative analysis of dipyridamole-thallium scintigraphy and identification of high- and low-risk subgroups.
Angina Pectoris↗
An electron paramagnetic resonance study of skeletal muscle membrane fluidity in malignant hyperthermia.
Skeletal muscle sarcolemma (SL), transverse tubule (TT) and heavy sarcoplasmic reticulum (HSR) membranes were isolated from malignant hyperthermia susceptible (MHS) and normal pigs, and the rotational dynamics of lipid hydrocarbon chain motion was examined by electron paramagnetic resonance (EPR) spectroscopy. The stearic acid spin probe 16-SASL was incorporated into MHS and normal membranes and both the order parameter (S) and effective correlation time (tau r) of probe motion were calculated from spectra recorded over the temperature range of 2 to 40 degrees C. At any given temperature, TT membranes exhibited significantly greater values for both the S and tau r of probe motion than did SL, which exhibited significantly greater values than did HSR membranes. The order of decreasing S and tau r values for 16-SASL mobility correlated with the decreasing cholesterol content of these membranes (TT greater than SL greater than HSR), however there was no difference in the S or tau r values for a given membrane fraction isolated from both MHS and normal muscle. Arrhenius plots of 16-SASL mobility in SL, TT and HSR were linear from 2 to 40 degrees C, indicating no abrupt thermotropic change in the lipid hydrocarbon phase of any of the membrane types studied. Apparent activation energies (Ea), calculated from the Arrhenius plots, were similar for MHS and normal membranes derived from a given cellular location. However, the Ea of probe motion for TT membranes (2.3 +/- 0.1 and 2.4 +/- 0.1 kcal/mol/degree for MHS and normal, respectively) was significantly less than for SL (3.4 +/- 0.4 and 2.9 +/- 0.1 kcal/mol/degree for MHS and normal, respectively) which, in turn, was significantly less than the Ea for HSR (3.7 +/- 0.1 and 3.7 +/- 0.1 kcal/mol/degree for MHS and normal, respectively). Since 16-SASL motion was similar in MHS and normal membranes, we conclude that there is no evidence for a generalized membrane defect affecting lipid mobility in these MHS muscle membranes.
Animals↗
Coincidence correction in red blood cell counting.
A method has been developed for accurate correction of red blood cell count for coincidence in aperture-impedance electronic blood cell counters. It is based on extrapolation of the slope of regression of the counts which are obtained with sequential dilutions of the samples.
Erythrocyte Count↗
Allogeneic bone marrow transplantation for primary myelofibrosis.
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Adult↗