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Biomedical subjects

M R Miller

Publications and source records attributed to M R Miller.

At least 73 records · Page 4Linked to original sources
PubMed1997

Spirometry with a Fleisch pneumotachograph: upstream heat exchanger replaces heating requirement.

The exact temperature of the head of an unheated Fleisch pneumotachograph (PT) during recording is not known, and variation in its temperature may lead to errors in measuring spirometric indexes. We measured PT head temperature during blows from five normal subjects, recorded by using a PT with and without an upstream heat exchanger to condition the air to the ambient temperature that was set in a climate chamber. Group mean (+/- SD) temperature of a thermocouple (TC) placed inside the PT head was 11.8 +/- 1.9 degrees C with 7 degrees C ambient, 25.4 +/- 1.3 degrees C at 23 degrees C, and was 37.2 +/- 0.3 degrees C at 37 degrees C. The between-subject range of temperature for this TC was 7.5 degrees at 7 degrees C, 5.5 degrees at 23 degrees C, and 1.1 degrees at 37 degrees C. The mean within-subject within-blow variation of temperature for this TC was 10.0 degrees and 3.3 degrees C for ambient of 7 degrees and 23 degrees C, respectively. At the usual ambient temperature in a laboratory, these differences in temperature lead to a 3.6% between-subject bias in recording, and the within-subject differences lead to 2.6% underreading of peak expiratory flow and a 0.5% overreading later in the blow, which makes ATPS-to-BTPS correction erroneous or difficult to perform. With the use of an upstream heat exchanger, the group mean temperature was 8.7 +/- 0.4 degrees, 23.2 +/- 0.2 degrees, and 37.1 +/- 0.2 degrees C at the three ambient temperatures, respectively, and the within-subject within-blow variation was reduced to < 1 degrees C. A heat exchanger placed upstream of the PT satisfactorily conditioned expired air to the ambient temperature and removed the error.

Adult↗
PubMed1997

Gas compression in lungs decreases peak expiratory flow depending on resistance of peak flowmeter.

It has recently been shown (O. F. Pedersen T. R. Rasmussen, O. Omland, T. Sigsgaard, P. H. Quanjer. and M. R. Miller. Eur. Respir. J. 9: 828-833, 1996) that the added resistance of a mini-Wright peak flowmeter decreases peak expiratory flow (PEF) by approximately 8% compared with PEF measured by a pneumotachograph. To explore the reason for this, 10 healthy men (mean age 43 yr, range 33-58 yr) were examined in a body plethysmograph with facilities to measure mouth flow vs. expired volume as well as the change in thoracic gas volume (Vb) and alveolar pressure (PA). The subjects performed forced vital capacity maneuvers through orifices of different sizes and also a mini-Wright peak flowmeter. PEF with the meter and other added resistances were achieved when flow reached the perimeter of the flow-Vb curves. The mini-Wright PEF meter decreased PEF from 11.4 +/- 1.5 to 10.3 +/- 1.4 (SD) l/s (P < 0.001), PA increased from 6.7 +/- 1.9 to 9.3 +/- 2.7 kPa (P < 0.001), an increase equal to the pressure drop across the meter, and caused Vb at PEF to decrease by 0.24 +/- 0.09 liter (P < 0.001). We conclude that PEF obtained with an added resistance like a mini-Wright PEF meter is a wave-speed-determined maximal flow, but the added resistance causes gas compression because of increased PA at PEF. Therefore, Vb at PEF and, accordingly, PEF decrease.

Adult↗
PubMed1997

Effect of adult-onset deafness on the human central auditory system.

Degenerative change in the central auditory system was assessed in seven subjects with profound bilateral adult-onset deafness. The degree of transneuronal atrophy was determined by measuring cell size at three levels of the brain stem auditory pathway (anteroventral cochlear nucleus, medial superior olivary nucleus, and inferior colliculus). Within subjects, the relative degree of cell shrinkage was similar across all levels of the central pathway. Across subjects, the best neuronal preservation was seen in a case of viral labyrinthitis with 1 year of bilateral dearness and a near-normal population of cochlear ganglion cells. Reduction in cell size was greatest in cases of bacterial labyrinthitis or Scheibe degeneration with reduced populations of ganglion cells and longer periods of deafness. At the level of the cochlear nucleus, there was no consistent difference in cell size between the side stimulated by a functioning prosthetic device and the nonstimulated side.

Adult↗
PubMed1997

Preoperative risk factors for surface disease after penetrating keratoplasty.

We sought to identify the types of, prevalence of, and predisposing factors for the development of surface keratopathy after penetrating keratoplasty. We reviewed the records of 120 corneal grafts performed over a 15-month period. Twenty patients were excluded from the study. Fifty-three men and 47 women composed the group studied. All transplants were performed by the same surgeon. Retrospective data from patients' records were gathered preoperatively and from postoperative visits at 1 week and at 1, 2, 3, and 4 months. Data included preoperative medical and demographic data, operative time, postoperative medication regimens, assessment of the presence and degree, if present, of punctate epithelial keratopathy (PEK), hurricane keratopathy, macroepithelial defects, microcystic edema, bullous edema, and filamentary keratitis. In addition, information on the donor material was recorded. Surface disease and normal groups were compared to identify risk factors for the occurrence of surface abnormalities. Thirty-three of the patients demonstrated persistent surface abnormalities. Coarse PEK was the most common surface abnormality in the sample studied and was most prominent in the first week after surgery. Postoperative surface keratopathy was not statistically associated with preoperative diagnosis, donor age, death-to-preservation time, preservation-to-surgery time, or donor epithelial status. However, corneal recipients in the group with surface keratopathy were significantly older (mean, 68.7 years) than patients in the group with no surface abnormalities (mean, 52.6 years; Mann-Whitney U test, p < 0.001). Although many factors may contribute to the normal integrity of the corneal surface after keratoplasty, recipient age is of key importance in the development of surface disease.

Aged↗
PubMed1997

The Peak Flow Working Group: test of portable peak flow meters by explosive decompression.

In 1991, 50 new Vitalograph peak flow meters and 27 previously used mini-Wright peak flow meters were tested at three peak flows by use of a calibrator applying explosive decompression. The mini-Wright peak flow meters were also compared with eight new meters. For both makes of meter there was an excellent within-meter and between-meter variation. The accuracy, however, was poor, with a maximal overestimation of true flows of 50 and 70 L.min-1 in the interval from 200 to 400 L.min-1 for the Vitalograph and mini-Wright meters, respectively. The deviation is explained by the physical characteristics of the variable orifice peak flow meters. They have been supplied with equidistant scales, which give non-linear readings.

Calibration↗
PubMed1996

Pulmonary microsomal metabolism of benzo[a]pyrene following exposure of rats to silica.

Because some evidence suggests that there may be an increased incidence of lung cancer in silicosis and because previous studies have shown that exposure of rats to silica alters the pulmonary cytochrome P-450 system, we studied the effects of exposing rats to silica on the lung microsomal metabolism of benzo[a]pyrene (BaP). Rats were exposed to silica by intratracheal administration, lung microsomes were obtained 2 wk later from untreated and silica-treated animals, and the amounts of microsomal tissue and metabolites formed during the in vitro microsomal metabolism of BaP were measured. When the formation of BaP metabolites in equal amounts of lung microsomal tissue from the 2 treatment groups is compared, 3-OH BaP, BaP 4,5-diol, and BaP 9,10-diol are reduced by 45-70%, but the formation of BaP 7,8-diol or the BaP-quinones is not significantly altered following exposure to silica. In fact, the ratio of the BaP diols and BaP quinones, potentially toxic metabolites, to the relatively nontoxic 3-OH BaP produced by equal amounts of lung microsomal tissue is increased more than threefold following exposure of rats to silica. Since exposure of rats to silica leads to increased levels of lung microsomal protein, the amounts of BaP metabolites that could be produced by all microsomal tissue in the lungs were calculated. In silica-treated animals, the calculated total lung production of 3-OH BaP, BaP 4,5-diol, and BaP 9,10-diol tends to be increased by 1.2- to 2.0-fold, but BaP 7,8-diol and the BaP quinones are increased by 3.5-fold. These results demonstrate that exposure of rats to silica may alter the capacity of the lungs to metabolize benzo[a]pyrene, and the greatest effect seems to be enhanced accumulation of BaP 7,8-diol and the BaP quinones.

Animals↗
PubMed1996

Effect of altitude on spirometric parameters and the performance of peak flow meters.

BACKGROUND: Portable peak flow meters are used in clinical practice for measurement of peak expiratory flow (PEF) at many different altitudes throughout the world. Some PEF meters are affected by gas density. This study was undertaken to establish which type of meter is best for use above sea level and to determine changes in spirometric measurements at altitude. METHODS: The variable orifice mini-Wright peak flow meter was compared with the fixed orifice Micro Medical Microplus turbine microspirometer at sea level and at Everest Base Camp (5300 m). Fifty one members of the 1994 British Mount Everest Medical Expedition were studied (age range, 19-55). RESULTS: Mean forced vital capacity (FVC) fell by 5% and PEF rose by 25.5%. However, PEF recorded with the mini-Wright peak flow meter underestimated PEF by 31%, giving readings 6.6% below sea level values. FVC was lowest in the mornings and did not improve significantly with acclimatisation. Lower PEF values were observed on morning readings and were associated with higher acute mountain sickness scores, although the latter may reflect decreased effort in those with acute mountain sickness. There was no change in forced expiratory volume in one second (FEV1) at altitude when measured with the turbine microspirometer. CONCLUSIONS: The cause of the fall in FVC at 5300 m is unknown but may be attributed to changes in lung blood volume, interstitial lung oedema, or early airways closure. Variable orifice peak flow meters grossly underestimate PEF at altitude and fixed orifice devices are therefore preferable where accurate PEF measurements are required above sea level.

Adult↗
PubMed1996

Potential effects of correction of inaccuracies of the mini-Wright peak expiratory flow meter on the use of an asthma self-management plan.

BACKGROUND: Patient self-management plans for asthma use peak expiratory flow (PEF) meter readings for decisions on adjusting asthma treatment. PEF meters have been shown to be inaccurate and the effect of this inaccuracy on such treatment plans has been determined. METHODS: PEF measurements were made by 127 severe asthmatic patients at least twice a day for at least two weeks using a mini-Wright meter. The daily variation from "best" PEF and the within day PEF variability were calculated before and after correction for the meter's known inaccuracy. The effect of this data correction on the number of days when trigger points were reached for changing asthma therapy was then determined. RESULTS: Continuous PEF readings were available from 114 subjects with a median of 157.5 days of data per subject (range 15-489 days). Correction of the PEF data led to the number of days of satisfactory asthma control being reduced in 72% of subjects with just one subject showing an increase in satisfactory control. Data correction reduced the percentage of total days of satisfactory control from 46% to 36% of days, and increased the days requiring more inhaled steroids from 33% to 36%. The days on which a course of oral corticosteroids was required increased from 16% to 23%. CONCLUSIONS: The accuracy of PEF meters significantly influences the interpretation of currently used asthma self-management plans. Managing asthma with the corrected PEF data would have increased the amount of treatment received by these patients since the severity of the asthma was underestimated by the raw data.

Adolescent↗
PubMed1996

Peak expiratory flow and the resistance of the mini-wright peak flow meter.

The purpose of this study was to examine whether the resistance of the peak flow meter influences its recordings. One hundred and twelve subjects, (healthy nonsmokers and smokers and subjects with lung diseases) performed three or more peak expiratory flow (PEF) manoeuvres through a Fleisch pneumotachograph with and without a mini-Wright peak flow meter added in random order as a resistance in series. The results were as follows. In comparison with a pneumotachograph alone, peak flow measured with an added mini-Wright meter had a smaller within-test variation, defined as the difference between the highest and second highest values of PEF in a series of blows. The mean (SE) variation was 14 (1.3) L.min-1 and 19 (1.5) L.min-1 with and without meter added, respectively. In comparison with the pneumotachograph alone, the addition of the mini-Wright meter caused PEF to be underread, especially at high flows. The difference (PEF with meter minus PEF without meter) = -0.064 (average PEF) -8 L.min-1; R2 = 0.13. The mean difference was -7.8 (1.1) %, and increased numerically for a given PEF, when maximal expiratory flow when 75% forced vital capacity remains to be exhaled (MEF75%FVC) decreased. The reproducibility criteria for repeated measurements of peak flow are more appropriately set at 30 L.min-1 than the commonly used 20 L.min-1, because a within-test variation of less than 30 L.min-1 was achieved in 76% of the subjects without PEF meter inserted and in 88% with meter inserted, with no difference between healthy untrained subjects and patients. The resistance of the peak expiratory flow meter causes less variation in recordings but reduces peak expiratory flow, especially at high values and when the peak is large as compared with the rest of the maximal expiratory flow-volume curve.

Adolescent↗
PubMed1996

A cost-effectiveness analysis of typhoid fever vaccines in US military personnel.

Typhoid fever has been a problem for military personnel throughout history. A cost-effectiveness analysis of typhoid fever vaccines from the perspective of the US military was performed. Currently 3 vaccine preparations are available in the US: an oral live Type 21A whole cell vaccine; a single-dose parenteral, cell subunit vaccine; and a 2-dose parenteral heat-phenol killed, whole cell vaccine. This analysis assumed all vaccinees were US military personnel. Two pharmacoeconomic models were developed, one for personnel who have not yet been deployed, and the other for personnel who are deployed to an area endemic for typhoid fever. Drug acquisition, administration, adverse effect and lost work costs, as well as the costs associated with typhoid fever, were included in this analysis. Unique military issues, typhoid fever attack rates, vaccine efficacy, and compliance with each vaccine's dosage regimen were included in this analysis. A sensitivity analysis was performed to test the robustness of the models. Typhoid fever immunisation is not cost-effective for US military personnel unless they are considered imminently deployable or are deployed. The most cost-effective vaccine for US military personnel is the single-dose, cell subunit parenteral vaccine.

Cost-Benefit Analysis↗
PubMed1996

Correlation of flexural structural properties with bone physical properties: a four species survey.

The present investigation explores the relationship between animal and bone physical traits and the mechanical properties of whole bone from four species. Mechanical testing was performed using three-point flexure on the femora and tibiae of mice, rats, rabbits and cats. Interspecies correlations of the physical traits to the mechanical properties were used to elucidate the most likely physical predictors of mechanical properties within a single species. Physical traits measured were total bone length (BL), mid-diaphyseal cortical area (CA), body mass (BM), body mass times bone length (BMBL) and bone dry mass (DM). Bone mechanical parameters determined by flexure testing to failure were the structural properties of stiffness (S), elastic strength (Pe), maximum strength (Pm), and the material properties of modulus of elasticity (E), elastic stress (sigma e), and elastic strain (epsilon e). Linear regressions were used to relate the physical trait to the mechanical properties. Interspecies regressions of physical traits to mechanical characteristics implied bone dry mass (DM) is a significant predictor of bone structural properties. Further evidence of this relationship was obtained by exploring the linear relationship for the femora of a single species (rabbit, N = 17) in which age and bone size were allowed to vary. Strength at the elastic limit (in N) within a single species was described by the equation, Pe = 42.9*DM + 42.9 +/- 42.0N, where DM is in grams.

Animals↗
PubMed1995

Isolation and characterization of biliary epithelial cells from rainbow trout liver.

Lectin binding and density gradient centrifugation were explored for isolating epithelial cells from trout liver. Hepatocytes exhibited preferential attachment of coverslips coated with Phaseolus vulgaris erythroagglutinin. Biliary epithelial cells attached with glycine max agglutinin; however, significant attachment of cellular debris limited the use of glycine max agglutinin. Percoll-density gradient centrifugation separated liver cells into two distinct populations with biliary cells and hepatocytes banding at densities of 1.04 and 1.09, respectively. A discontinuous gradient composed of 13% Ficoll (wt/wt) separated biliary cells from hepatocytes. The recovery of highly enriched biliary epithelial cells from trout liver using Ficoll gradients yielded approximately 8 million cells (0.1 ml packed cells) from 10 g liver. Western blot analysis demonstrated that the cytokeratin profile for extracts from biliary epithelial cell-enriched populations differ significantly from those seen with whole liver extracts or with extracts with hepatocyte-enriched populations. Ficoll-gradient purified biliary cells and hepatocytes attached to culture plates coated with trout skin extract and carried out linear incorporation of leucine into protein and thymidine into DNA for 24 h. A mixture of growth hormones (insulin, epidermal growth factor, and dexamethasone) stimulated thymidine incorporation into DNA; however, long-term culture of dividing biliary epithelial cells was not achieved. Chemical analysis of neutral and acidic glycolipids indicated that hepatocytes and biliary cells have similar glycolipid profiles with an exception in the region of GM3 mobility, which is attributed to differences in the ceramide moiety. These studies provide a starting point for further characterization of unique cell types of the trout liver that may be important in their responses to toxic and carcinogenic agents.

Animals↗
PubMed1995

The performance of Mini Wright peak flow meters after prolonged use.

The accuracy of 84 new and 35 old Mini Wright peak flow meters were tested using a servo-controlled pump system. The 95% confidence limits for flow measurement across the range of the new meters was between +/- 151 min-1 at the lower end of the range and +/- 28 l min-1 at the top of the range. The readings for 22 (63%) of the old meters (age range 1-13 yr) were within these 95% confidence limits. For the remaining 13 old meters (age range 1-13 yr) whose readings were not within these limits, there were 11 meters with readings falling below and two meters with readings above these limits. Twelve of these old meters were washed and retested and there was no significant change in their readings. Twenty of the new meters were retested after 1 yr of continuous use and their readings were significantly higher with a median value of 5 l min-1 across the range, although only two of these 20 meters had readings outside the 95% confidence limits set from the 84 new meters. It is concluded that whilst Mini Wright meters aged up to 14 yr can give readings which are as good as new meters, some meters demonstrate significant changes in readings after only 1 yr and washing did not correct this change. It is recommended that clinicians prescribing peak expiratory flow (PEF) meters should be responsible for checking the patient's meter as well as their PEF readings at clinic visits.

Disinfection↗