Estimation of filler macro-dispersion in rubber matrix by radiometric stereo microscopy.

A new microscopic principle based on radiometric stereo microscopy is presented, which is designed for investigating macro-dispersion of filler in rubber. The image acquisition is combined with a stereological method of estimating the volume-weighted size distribution of the filler particles. Experimental results for carbon black filler in rubber obtained by radiometric stereo microscopy are compared with those from microtomography using synchrotron radiation, and, furthermore, a simulation study is used for evaluation. It turns out that using the new three-dimensional microscopic method, the size distribution of the filler particles can be estimated from fresh cuts of rubber with high accuracy, and thus it is an interesting alternative to well-established dark field microscopy. LAY DESCRIPTION: Macro-dispersion of globular filler particles in a rubber matrix is an important quantity that depends on manufacturing parameters and influences various rubber properties. Therefore, it must be carefully adjusted during the incorporation process and investigated by industrial quality control (ASTM D7723-18). Quality control is usually based on freshly made planar sections so-called fresh cuts through rubber specimen. After stress retention of the rubber one obtains a rough cutting surface in which the filler particles appear as imprints or bumps, called nodges. These nodges can be made visible by classical light microscopy under dark field (DFM) illumination. The systems disperGRADER+ or the disperGRADER Alpha View were specifically designed for rubber inspection. However, it has proved to be very difficult estimating the size distribution of the filler particles from the observed white spots in the DFM image. In any case it is still necessary to compute the size distribution of the filler particles from an estimated size distribution of the section profiles. The latter is numerically unstable, i.e. small errors of the estimated size distribution of the section profiles lead to large errors of the computed filler size distribution. Applying DFM combined with filler dispersion estimation as described in ASTM D7723-18 appears to be a fingerprint method only. For this reason, the new microscope nSPEC 3D was applied for rubber inspection. The principle used for surface imaging is based on radiometric stereo allowing for perfect three-dimensional reconstruction of curved surfaces of fresh cuts. From this reconstruction it is possible to measure the height of particle nodges as well as their volumes. Furthermore, we present a new stereological method for estimating the filler size distribution from samples of the height and the volume of the nodges. Finally, microtomography with synchrotron radiation and computer simulation are applied to evaluate accuracy of the presented method.

Young adults with cystic fibrosis have altered trabecular microstructure by ITS-based morphological analysis.

UNLABELLED: Young adults with cystic fibrosis have compromised plate-like trabecular microstructure, altered axial alignment of trabeculae, and reduced connectivity between trabeculae that may contribute to the reduced bone strength and increased fracture risk observed in this patient population. INTRODUCTION: The risk of fracture is increased in patients with cystic fibrosis (CF). Individual trabecular segmentation (ITS)-based morphological analysis of high-resolution peripheral quantitative computed tomography (HR-pQCT) images segments trabecular bone into individual plates and rods of different alignment and connectivity, which are important determinants of trabecular bone strength. We sought to determine whether alterations in ITS variables are present in patients with CF and may help explain their increased fracture risk. METHODS: Thirty patients with CF ages 18-40 years underwent DXA scans of the hip and spine and HR-pQCT scans of the radius and tibia with further assessment of trabecular microstructure by ITS. These CF patients were compared with 60 healthy controls matched for age (±2 years), race, and gender. RESULTS: Plate volume fraction, thickness, and density as well as plate-plate and plate-rod connectivity were reduced, and axial alignment of trabeculae was lower in subjects with CF at both the radius and the tibia (p < 0.05 for all). At the radius, adjustment for BMI eliminated most of these differences. At the tibia, however, reductions in plate volume fraction and number, axially aligned trabeculae, and plate-plate connectivity remained significant after adjustment for BMI alone and for BMI and aBMD (p < 0.05 for all). CONCLUSIONS: Young adults with CF have compromised plate-like and axially aligned trabecular morphology and reduced connectivity between trabeculae. ITS analysis provides unique information about bone integrity, and these trabecular deficits may help explain the increased fracture risk in adults with CF not accounted for by BMD and/or traditional bone microarchitecture measurements.

Neutral Hydrogen Structures Trace Dust Polarization Angle: Implications for Cosmic Microwave Background Foregrounds.

Using high-resolution data from the Galactic Arecibo L-Band Feed Array HI (GALFA-Hi) survey, we show that linear structure in Galactic neutral hydrogen (Hi) correlates with the magnetic field orientation implied by Planck 353 GHz polarized dust emission. The structure of the neutral interstellar medium is more tightly coupled to the magnetic field than previously known. At high Galactic latitudes, where the Planck data are noise dominated, the Hi data provide an independent constraint on the Galactic magnetic field orientation, and hence the local dust polarization angle. We detect strong cross-correlations between template maps constructed from estimates of dust intensity combined with either Hi-derived angles, starlight polarization angles, or Planck 353 GHz angles. The Hi data thus provide a new tool in the search for inflationary gravitational wave B-mode polarization in the cosmic microwave background, which is currently limited by dust foreground contamination.

Defects in cortical microarchitecture among African-American women with type 2 diabetes.

SUMMARY: Patients with type 2 diabetes mellitus (DM2) have increased fracture risk. We found that African-American women with DM2 have increased cortical porosity and lower cortical bone density at the radius than non-diabetic controls. These cortical deficits are associated with hyperglycemia and may contribute to skeletal fragility associated with DM2. INTRODUCTION: Fracture risk is increased in patients with type 2 diabetes mellitus (DM2) despite normal areal bone mineral density (aBMD). DM2 is more common in African-Americans than in Caucasians. It is not known whether African-American women with DM2 have deficits in bone microstructure. METHODS: We measured aBMD at the spine and hip by DXA, and volumetric BMD (vBMD) and microarchitecture at the distal radius and tibia by HR-pQCT in 22 DM2 and 78 non-diabetic African-American women participating in the Study of Women Across the Nation (SWAN). We also measured fasting glucose and HOMA-IR. RESULTS: Age, weight, and aBMD at all sites were similar in both groups. At the radius, cortical porosity was 26% greater, while cortical vBMD and tissue mineral density were lower in women with DM2 than in controls. There were no differences in radius total vBMD or trabecular vBMD between groups. Despite inferior cortical bone properties at the radius, FEA-estimated failure load was similar between groups. Tibia vBMD and microarchitecture were also similar between groups. There were no significant associations between cortical parameters and duration of DM2 or HOMA-IR. However, among women with DM2, higher fasting glucose levels were associated with lower cortical vBMD (r=-0.54, p=0.018). CONCLUSIONS: DM2 and higher fasting glucose are associated with unfavorable cortical bone microarchitecture at the distal radius in African-American women. These structural deficits may contribute to the increased fracture risk among women with DM2. Further, our results suggest that hyperglycemia may be involved in mechanisms of skeletal fragility associated with DM2.

A white paper--consensus and recommendations of a global harmonization team on assessing the impact of immunogenicity on pharmacokinetic measurements.

The Global Bioanalysis Consortium (GBC) set up an international team to explore the impact of immunogenicity on pharmacokinetic (PK) assessments. The intent of this paper is to define the field and propose best practices when developing PK assays for biotherapeutics. We focus on the impact of anti-drug antibodies (ADA) on the performance of PK assay leading to the impact on the reported drug concentration and exposure. The manuscript describes strategies to assess whether the observed change in the drug concentration is due to the ADA impact on drug clearance rates or is a consequence of ADA interference in the bioanalytical method applied to measure drug concentration. This paper provides the bioanalytical scientist guidance for developing ADA-tolerant PK methods. It is essential that the data generated in the PK, ADA, pharmacodynamic and efficacy/toxicity evaluations are viewed together. Therefore, the extent for the investigation of the PK sensitivity to the presence of ADA should be driven by the project needs and risk based.

Molecular properties of bacterial multidrug transporters.

One of the mechanisms that bacteria utilize to evade the toxic effects of antibiotics is the active extrusion of structurally unrelated drugs from the cell. Both intrinsic and acquired multidrug transporters play an important role in antibiotic resistance of several pathogens, including Neisseria gonorrhoeae, Mycobacterium tuberculosis, Staphylococcus aureus, Streptococcus pneumoniae, Pseudomonas aeruginosa, and Vibrio cholerae. Detailed knowledge of the molecular basis of drug recognition and transport by multidrug transport systems is required for the development of new antibiotics that are not extruded or of inhibitors which block the multidrug transporter and allow traditional antibiotics to be effective. This review gives an extensive overview of the currently known multidrug transporters in bacteria. Based on energetics and structural characteristics, the bacterial multidrug transporters can be classified into five distinct families. Functional reconstitution in liposomes of purified multidrug transport proteins from four families revealed that these proteins are capable of mediating the export of structurally unrelated drugs independent of accessory proteins or cytoplasmic components. On the basis of (i) mutations that affect the activity or the substrate specificity of multidrug transporters and (ii) the three-dimensional structure of the drug-binding domain of the regulatory protein BmrR, the substrate-binding site for cationic drugs is predicted to consist of a hydrophobic pocket with a buried negatively charged residue that interacts electrostatically with the positively charged substrate. The aromatic and hydrophobic amino acid residues which form the drug-binding pocket impose restrictions on the shape and size of the substrates. Kinetic analysis of drug transport by multidrug transporters provided evidence that these proteins may contain multiple substrate-binding sites.

Contribution of villous atrophy to reduced intestinal maltase in infants with malnutrition.

BACKGROUND: It has been known for many years that small intestinal maltase activities are reduced in malnourished infants and in other patients with villous atrophy. The recent availability of human maltase-glucoamylase cDNA provides the opportunity to test the hypothesis that villous atrophy accounts for the reduced maltase enzyme activity in malnourished infants. METHODS: Mucosal biopsy specimens obtained for clinical evaluation of malnourished infants with poor responses to refeeding were examined by quantitative methods for enzyme activity and mRNA levels. RESULTS: Maltase activity and maltase-glucoamylase mRNA were reduced (approximately 45% of normal). When maltase-glucoamylase message was normalized to villin message, a structural protein expressed only in enterocytes, a preservation of maltase messages in surviving enterocytes was documented. The luminal glucose transporter-villin message was also preserved. CONCLUSIONS: The loss of maltase-glucoamylase message paralleled the reduction in villin message and degree of villous atrophy. The reduced maltase-glucoamylase message also paralleled sucrase-isomaltase message, previously found to be decreased in proportion to villous atrophy of malnourished infants. The data directly demonstrate, for the first time, that the terminal steps of starch 1-4 starch digestion and sucrase-isomaltase 1-6 starch digestion are decreased in malnourished infants, secondary to villous atrophy. These data in prior and present reports suggest that mechanisms underlying the chronic villous atrophy of malnutrition should be a priority for investigations in malnourished infants with slower than expected weight gain during refeeding.

Molecular pharmacological characterization of two multidrug transporters in Lactococcus lactis.

The active extrusion of cytotoxic compounds from the cell by multidrug transporters is one of the major causes of failure of chemotherapeutic treatment of tumor cells and of infections by pathogenic microorganisms. A multidrug transporter in Lactococcus lactis, LmrA, is a member of the ATP-binding cassette superfamily and a bacterial homolog of the human multidrug resistance P-glycoprotein. Another multidrug transporter in Lactococcus lactis, LmrP, belongs to the major facilitator superfamily, and is one example of a rapidly expanding group of secondary multidrug transporters in microorganisms. Thus, LmrA and LmrP are transport proteins with very different protein structures, which use different mechanisms of energy coupling to transport drugs out of the cell. Surprisingly, both proteins have overlapping specificities for drugs, are inhibited by the same set of modulators, and transport drugs via a similar transport mechanism. The structure-function relationships that dictate drug recognition and transport by LmrP and LmrA represent an intriguing area of research.

The purified and functionally reconstituted multidrug transporter LmrA of Lactococcus lactis mediates the transbilayer movement of specific fluorescent phospholipids.

Lactococcus lactis possesses an ATP-binding cassette transporter, LmrA, which is a homolog of the mammalian multidrug resistance (MDR) P-glycoprotein, and is able to transport a broad range of structurally unrelated amphiphilic drugs. A histidine tag was introduced at the N-terminus of LmrA to facilitate purification by nickel affinity chromatography. The histidine-tagged protein was overexpressed in L. lactis using a novel protein expression system for cytotoxic proteins based on the tightly regulated, nisin-inducible nisA promoter. This system allowed us to get functional overexpression of LmrA up to a level of 30% of total membrane protein. For reconstitution, LmrA was solubilized with dodecylmaltoside, purified by nickel-chelate affinity chromatography, and reconstituted in dodecylmaltoside-destabilized, preformed liposomes prepared from L. lactis phospholipids. The detergent was removed by adsorption onto polystyrene beads. The LmrA protein was reconstituted in a functional form, and mediated the ATP-dependent transport of the fluorescent substrate Hoechst-33342 into the proteoliposomes. Interestingly, reconstituted LmrA also catalyzed the ATP-dependent transport of fluorescent phosphatidylethanolamine, but not of fluorescent phosphatidylcholine. These data demonstrate that LmrA activity is independent of accessory proteins and support the notion that LmrA may be involved in the transport of specific lipids or lipid-linked precursors in L. lactis.

Structure-function analysis of multidrug transporters in Lactococcus lactis.

The active extrusion of cytotoxic compounds from the cell by multidrug transporters is one of the major causes of failure of chemotherapeutic treatment of tumor cells and of infections by pathogenic microorganisms. A multidrug transporter in Lactococcus lactis, LmrA, is a member of the ATP-binding cassette (ABC) superfamily and a bacterial homolog of the human multidrug resistance P-glycoprotein. Another multidrug transporter in L. lactis, LmrP, belongs to the major facilitator superfamily, and is one example of a rapidly expanding group of secondary multidrug transporters in microorganisms. Thus, LmrA and LmrP are transport proteins with very different protein structures, which use different mechanisms of energy coupling to transport drugs out of the cell. Surprisingly, both proteins have overlapping specificities for drugs, are inhibited by the same set of modulators, and transport drugs via a similar transport mechanism. The structure-function relationships that dictate drug recognition and transport by LmrP and LmrA represent an intriguing area of research.

The secondary multidrug transporter LmrP contains multiple drug interaction sites.

The secondary multidrug transporter LmrP of Lactococcus lactis mediates the efflux of Hoechst 33342 from the cytoplasmic leaflet of the membrane. Kinetic analysis of Hoechst 33342 transport in inside-out membrane vesicles of L. lactis showed that the LmrP-mediated H(+)/Hoechst 33342 antiport reaction obeyed Michaelis-Menten kinetics, with a low apparent affinity constant of 0.63 microM Hoechst 33342 (= 0.5 mmol Hoechst 33342/mol phospholipid). Several drugs significantly inhibited LmrP-mediated Hoechst 33342 transport through a direct interaction with the protein rather than through dissipation of the proton motive force or reduction of the membrane partitioning of Hoechst 33342. The characterization of the mechanism of inhibition of LmrP-mediated Hoechst 33342 transport indicated competitive inhibition by quinine and verapamil, noncompetitive inhibition by nicardipin and vinblastin, and uncompetitive inhibition by TPP(+). The three types of inhibition of LmrP-mediated Hoechst 33342 transport in inside-out membrane vesicles indicate for the first time the presence of multiple drug interaction sites in a secondary multidrug transporter.

Multidrug resistance in lactic acid bacteria: molecular mechanisms and clinical relevance.

The active extrusion of cytotoxic compounds from the cell by multidrug transporters is one of the major causes of failure of chemotherapeutic treatment of tumor cells and of infections by pathogenic microorganisms. The secondary multidrug transporter LmrP and the ATP-binding cassette (ABC) type multidrug transporter LmrA in Lactococcus lactis are representatives of the two major classes of multidrug transporters found in pro- and eukaryotic organisms. Therefore, knowledge of the molecular properties of LmrP and LmrA will have a wide significance for multidrug transporters in all living cells, and may enable the development of specific inhibitors and of new drugs which circumvent the action of multidrug transporters. Interestingly, LmrP and LmrA are transport proteins with very different protein structures, which use different mechanisms of energy coupling to transport drugs out of the cell. Surprisingly, both proteins have overlapping specificities for drugs, are inhibited by the same set of modulators, and transport drugs via a similar transport mechanism. The structure-function relationships that dictate drug recognition and transport by LmrP and LmrA will represent an intriguing new area of research.

Restrictive use of detergents in the functional reconstitution of the secondary multidrug transporter LmrP.

The histidine-tagged secondary multidrug transporter LmrP was overexpressed in Lactococcus lactis, using a novel protein expression system for cytotoxic proteins based on the tightly regulated, nisin-inducible nisA promoter. LmrP-mediated H+/drug antiport activity in inside-out membrane vesicles was inhibited by detergents, such as Triton X-100, Triton X-114, and Tween 80, at low concentrations that did not affect the magnitude or composition of the proton motive force. The inhibition of the activity of LmrP by detergents restricted the range of compounds that could be used for the solubilization and reconstitution of the protein because low concentrations of detergent are retained in proteoliposomes. Surprisingly, dodecyl maltoside did not modulate the activity of LmrP. Therefore, LmrP was solubilized with dodecyl maltoside, purified by nickel-chelate affinity chromatography, and reconstituted in dodecyl maltoside-destabilized, preformed liposomes prepared from Escherichia coli phospholipids and egg phosphatidylcholine. Reconstituted LmrP mediated the transport of multiple drugs in response to an artificially imposed pH gradient, demonstrating that the protein functions as a proton motive force-dependent multidrug transporter, independent of accessory proteins. These observations are relevant for the effective solubilization and reconstitution of multidrug transporters belonging to the major facilitator superfamily, which, in view of their broad drug specificity, may strongly interact with detergents.

Estrogen production in endometriosis and use of aromatase inhibitors to treat endometriosis.

Estrogen is the most important known factor that stimulates the growth of endometriosis. Estrogen delivery to endometriotic implants was classically viewed to be only via the circulating blood in an endocrine fashion. We recently uncovered an autocrine positive feedback mechanism, which favored the continuous production of estrogen and prostaglandin (PG)E2 in the endometriotic stromal cells. The enzyme, aromatase, is aberrantly expressed in endometriotic stromal cells and catalyzes the conversion of C19 steroids to estrogens, which then stimulate cyclooxygenase-2 to increase the levels of PGE2. PGE2, in turn, is a potent inducer of aromatase activity in endometriotic stromal cells. Aromatase is not expressed in the eutopic endometrium. Aromatase expression in endometriosis and its inhibition in eutopic endometrium are controlled by the competitive binding of a stimulatory transcription factor, steroidogenic factor-1, and an inhibitory factor, chicken ovalbumin upstream promoter-transcription factor to a regulatory element in the aromatase P450 gene promoter. In addition, we find that endometriotic tissue is deficient in 17beta-hydroxysteroid dehydrogenase type 2, which is normally expressed in eutopic endometrial glandular cells and inactivates estradiol-17beta to estrone. This deficiency is another aberration that favors higher levels of estradiol-17beta in endometriotic tissues in comparison with the eutopic endometrium. The clinical relevance of local aromatase expression in endometriosis was exemplified by the successful treatment of an unusually aggressive form of recurrent endometriosis in a postmenopausal woman using an aromatase inhibitor.

Deficient 17beta-hydroxysteroid dehydrogenase type 2 expression in endometriosis: failure to metabolize 17beta-estradiol.

Aberrant aromatase expression in stromal cells of endometriosis gives rise to conversion of circulating androstenedione to estrone in this tissue, whereas aromatase expression is absent in the eutopic endometrium. In this study, we initially demonstrated by Northern blotting transcripts of the reductive 17beta-hydroxysteroid dehydrogenase (17betaHSD) type 1, which catalyzes the conversion of estrone to 17beta-estradiol, in both eutopic endometrium and endometriosis. Thus, it follows that the product of the aromatase reaction, namely estrone, that is weakly estrogenic can be converted to the potent estrogen, 17beta-estradiol, in endometriotic tissues. It was previously demonstrated that progesterone stimulates the inactivation of 17beta-estradiol through conversion to estrone in eutopic endometrial epithelial cells. Subsequently, 17betaHSD type 2 was shown to catalyze this reaction, and its transcripts were detected in the epithelial cell component of the eutopic endometrium in secretory phase. Because 17beta-estradiol plays a critical role in the development and growth of endometriosis, we studied 17betaHSD-2 expression in endometriotic tissues and eutopic endometrium. We demonstrated, by Northern blotting, 17betaHSD-2 messenger ribonucleic acid (RNA) in all RNA samples of secretory eutopic endometrium (n=12) but not in secretory samples of endometriotic lesions (n=10), including paired samples of endometrium and endometriosis obtained simultaneously from eight patients. This messenger RNA was not detectable in any samples of proliferative eutopic endometrium or endometriosis (n=4) as expected. Next, we confirmed these findings by demonstration of immunoreactive 17betaHSD-2 in epithelial cells of secretory eutopic endometrium in 11 of 13 samples employing a monoclonal antibody against 17betaHSD-2, whereas 17betaHSD-2 was absent in paired secretory endometriotic tissues (n=4). Proliferative eutopic endometrial (n=8) and endometriotic (n=4) tissues were both negative for immunoreactive 17betaHSD-2, except for barely detectable levels in 1 eutopic endometrial sample. Finally, we sought to determine whether deficient 17betaHSD-2 expression in endometriotic tissues is due to impaired progesterone action in endometriosis. We determined by immunohistochemistry the expression of progesterone and estrogen receptors in these paired samples of secretory (n=4) and proliferative (n=4) eutopic endometrium and endometriosis, and no differences could be demonstrated. In conclusion, inactivation of 17beta-estradiol is impaired in endometriotic tissues due to deficient expression of 17betaHSD-2, which is normally expressed in eutopic endometrium in response to progesterone. The lack of 17betaHSD-2 expression in endometriosis is not due to alterations in the levels of immunoreactive progesterone or estrogen receptors in this tissue and may be related to an inhibitory aberration in the signaling pathway that regulates 17betaHSD-2 expression.

Effects of malnutrition on expression and activity of lactase in children.

BACKGROUND & AIMS: Many malnourished infants have reduced lactase specific activity in the small intestine. The aim of this study was to test the hypothesis that the hypolactasia of malnourished infants results from transcriptional suppression of lactase expression. METHODS: Biopsy specimens were studied from two groups of infants: 29 with malnutrition and 10 normally nourished controls with normal morphology and lactase activity. RESULTS: In malnourished infants, lactase messenger RNA (mRNA) was reduced to 32% and sucrase to 61% of normal. Lactase and sucrase enzyme proteins and activities were lower in malnourished infants, and partial villus atrophy was present. The genotype of adult hypolactasia was not present. CONCLUSIONS: Because the hypolactasia of malnourished children was associated with much lower lactase than sucrase mRNA abundance and because the epigenetic suppression, which accounted for the reduction of sucrase mRNA, was inadequate to explain the greater reduction of lactase mRNA, this study concludes that malnutrition suppresses lactase gene transcription or mRNA stability in infants. The reductions of lactase mRNA, distinct from those found in adults with genetic hypolactasia, explain the low lactase activities commonly found in malnourished infants.

Energetics and mechanism of drug transport mediated by the lactococcal multidrug transporter LmrP.

The gene encoding the secondary multidrug transporter LmrP of Lactococcus lactis was heterologously expressed in Escherichia coli. The energetics and mechanism of drug extrusion mediated by LmrP were studied in membrane vesicles of E. coli. LmrP-mediated extrusion of tetraphenyl phosphonium (TPP+) from right-side-out membrane vesicles and uptake of the fluorescent membrane probe 1-[4-(trimethylamino)phenyl]-6-phenylhexa-1,3,5-triene (TMA-DPH) into inside-out membrane vesicles are driven by the membrane potential (Deltapsi) and the transmembrane proton gradient (DeltapH), pointing to an electrogenic drug/proton antiport mechanism. Ethidium bromide, a substrate for LmrP, inhibited the LmrP-mediated TPP+ extrusion from right-side-out membrane vesicles, showing that LmrP is capable of transporting structurally unrelated drugs. Kinetic analysis of LmrP-mediated TMA-DPH transport revealed a direct relation between the transport rate and the amount of TMA-DPH associated with the cytoplasmic leaflet of the lipid bilayer. This observation indicates that drugs are extruded from the inner leaflet of the cytoplasmic membrane into the external medium. This is the first report that shows that drug extrusion by a secondary multidrug resistance (MDR) transporter occurs by a "hydrophobic vacuum cleaner" mechanism in a similar way as was proposed for the primary lactococcal MDR transporter, LmrA.

Myasthenia gravis and upper airway obstruction.

Respiratory impairment in myasthenia gravis is usually attributed to weakness of the diaphragm and thoracic chest wall muscles, and is rarely attributed to upper airway obstruction. Myasthenia gravis is characterized by weakness of the striated muscles and usually affects those innervated by the bulbar cranial nerves. Weakness of these bulbar and upper airway muscles can lead to upper airway obstruction. To our knowledge, there are only five case reports in the literature associating upper airway obstruction with myasthenia gravis. Therefore, we attempted to further define its occurrence in myasthenia gravis patients by reviewing their flow volume loops. We present a case of upper airway obstruction causing respiratory symptoms in a myasthenia gravis patient. We then surveyed a total of 61 patients with myasthenia gravis who were tested in our pulmonary function laboratory between February 1990 and August 1993. Of these 61 patients, 12 had flow volume loops and 7 of these 12 disclosed a pattern of extrathoracic upper airway obstruction. The FVC was 80% or more in five of seven patients. Our data suggest that upper airway obstruction is much more common in patients with myasthenia gravis than previously recognized. In conclusion, we recommend the performance of flow volume loops in patients with myasthenia gravis to evaluate their respiratory impairment.