Using laboratory measurements to predict in-flight desaturation in respiratory patients: are current guidelines appropriate?

In an attempt to guide physicians asked by respiratory patients for advice on flight fitness, the British Thoracic Society (BTS) have published guidelines on fitness to fly. The main potential hazard is hypobaric hypoxia, and efforts have focused on the prediction of hypoxia in individuals. The present study examines 10 years' experience of hypoxic challenge (HC) of respiratory patients to evaluate if the guidelines recommended by the BTS are appropriate. One hundred and eighteen patients (67 female, mean age 65.6+/-11.4 (SD) years) were referred for assessment. Patients underwent HC using a 40% Venturi mask supplied with 100% N(2) which lowered the F(i)O(2) to 15.1%. A further 13 patients on long-term oxygen therapy also underwent HC whilst receiving supplemental oxygen. In agreement with the BTS guidelines, all patients with a sea level SpO(2) of over 95% maintained their SpO(2) > or = 90% during HC. One third of patients with sea level SpO(2) of 92-95%, but no other risk factor (as defined by the guidelines) also desaturated below 90% during HC. Thirty-two patients were assessed as fit to fly with supplemental oxygen. Our results support the BTS guidelines for patients with a sea level SpO(2) > 95% but suggest that some revision is required for patients with a sea level SpO(2) of 92-95%. It was not possible to predict from either initial SpO(2) or spirometry which individuals were at risk of desaturation below 90% during hypoxic challenge.

Inappropriate inhaler use: assessment of use and patient preference of seven inhalation devices. EDICI.

Inefficient inhaler technique is a common problem resulting in poor drug delivery, decreased disease control and increased inhaler use. The aim of this study was to assess patients' use of different inhaler devices and to ascertain whether patient preference is indicative of ease of use and whether current inhaler use has any influence on either technique or preference. We also wished to define the most appropriate method of selecting an inhaler for a patient, taking into account observed technique and device cost. One hundred patients received instruction, in randomized order, in the use of seven different inhaler devices. After instruction they were graded (using predetermined criteria) in their inhaler technique. After assessment patients were asked which three inhalers they most preferred and which, if any, they currently used. Technique was best using the breath-actuated inhalers; the Easi-Breathe and Autohaler, with 91% seen to have good technique. The pressurized metered dose inhaler (pMDI) fared poorly, in last position with only 79% of patients showing good technique, despite being the most commonly prescribed. The Easi-Breathe was by far the most popular device with the patients. The Autohaler came in second position closely followed by the Clickhaler and Accuhaler. The majority of patients (55%) currently used the pMDI but the pMDI did not score highly for preference or achieve better grades than the other devices. Only 79% of patients tested could use the pMDI effectively even after expert instruction yet it continues to be commonly prescribed. This has important repercussions for drug delivery and hence disease control. Prescribing a patient's preferred device increases cost but can improve efficiency and therefore be cost effective in the long term. Using an inexpensive device (pMDI) when technique is good and the patient's preferred inhaler device when not is one way to optimize delivery and may even reduce cost.

Detection of benzene and other gases with an open-path, static Fourier-transform UV spectrometer.

Releases of benzene and other gases have been detected and quantified using a novel optical, open-path instrument based on a deuterium light source and a static Fourier-transform spectrometer. The spectrometer uses Wollaston prisms to form an interferogram in the spatial domain that is recorded by use of a detector array. The instrument is designed to operate in the ultraviolet region of the spectrum between 200 and 270 nm, which coincides with strong absorption features in the spectra of many gases of environmental and health interest. Using the instrument with a 5-s measurement period provides a path-integrated concentration sensitivity to benzene of 2 parts in 10(6) times meter, which corresponds to a 20-parts in 10(9) detection limit over a typical path length of 100 m.

The distribution of carnosine and related dipeptides in rat and human tissues.

Carnosine and anserine are present in high concentrations in most skeletal muscles. In addition, carnosine and homocarnosine have been detected in brain and cardiac muscle. Other tissues have been found to be devoid of these histidine-containing dipeptides. However, Flancbaum et al. reported that carnosine was present in every rodent and human tissue analyzed. These authors postulated that carnosine serves as a non-mast cell reservoir for histidine which becomes available for histamine synthesis during periods of physiological stress. We have analyzed many rat and human tissues using an immunohistochemical procedure. Carnosine and related dipeptides were detected in skeletal muscle, cardiac muscle and brain, but not in kidney, liver, lung or several other organs. These negative results seem valid since the immunoassay gave positive staining in the tissues generally known to contain carnosine.

Localization of a novel pathway for the liberation of GABA in the human CNS.

Serum carnosinase is a dipeptidase, which is synthesized in human brain, where it hydrolyzes homocarnosine to release free GABA. Immunohistochemical procedures were used to demonstrate the presence of this enzyme in several layers of the retina and in certain neuronal tracts of the cerebral cortex, cerebellar cortex, olfactory bulb, hippocampus, and in disseminated tracts presumably from the internal capsule, interspersed among the basal ganglia. The enzyme was also present in the epithelial cells of the choroid plexus and in corpora amylacea, which were seen in many regions of the CNS. Homocarnosine was localized either in the same tracts or in nearby neurons. For example, the Purkinje cells of the cerebellar cortex contained homocarnosine, whereas serum carnosinase was localized in adjacent neuronal projections apparently originating from outside the cerebellar cortex and having probable synaptic contact with the Purkinje cells. These findings suggest that in addition to glutamate decarboxylation, a second metabolic reaction for the formation of free GABA exists in specific neuronal tracts of the human CNS where GABA is released from homocarnosine by the action of serum carnosinase.

Breath-actuated inhalers in chronic asthma: comparison of Diskhaler and Turbohaler for delivery of beta-agonists.

An open, randomized, cross-over study was performed to compare the efficacy and acceptability of two breath-actuated inhalers, the Turbohaler (T) and Diskhaler (D), for delivery of beta-agonists. Thirty six adults with chronic asthma requiring beta-agonists four times daily were treated with terbutaline 500 micrograms via T and salbutamol 400 micrograms via D four times daily, each period lasting four weeks. Additional bronchodilator via pressurized aerosol was permitted as required. Peak expiratory flow (PEF) was recorded in the morning (before and after beta-agonist) and in the evening. The mean morning PEF was higher during the first two weeks using T (295 l.min-1) than whilst using D (281 l.min-1, p < 0.01), but this difference did not persist during the second two weeks and there were no differences in post-bronchodilator PEF or rescue beta-agonist use. After four weeks, > 90% of patients used both inhaler devices efficiently and they were equally acceptable in terms of ease of use and convenience to carry. The Diskhaler and Turbohaler achieve similar clinical efficacy for delivery of beta-agonists.

Homocarnosinosis patients and great apes have a serum protein that cross-reacts with human serum carnosinase.

A specific polyclonal antiserum to human serum carnosinase was raised in rabbits and was used to prepare an agarose-protein A-antibody matrix. An antigen capture procedure showed that sera from homocarnosinosis patients, which lack carnosinase activity, contain an immunoreactive protein (M(r) 75,000) indistinguishable from the carnosinase band from normal serum. Other higher primates have active serum carnosinase and a similar immunoreactive M(r) 75,000 protein. The immunoaffinity matrix was used in a facile procedure to isolate pure carnosinase from human plasma with a yield of 69%. The antiserum inhibited human serum carnosinase strongly, but the maximum inhibition attained averaged only 71%. The antiserum inhibited human and chimpanzee serum carnosinases more effectively than gorilla or other higher primate serum carnosinases.

The use of a new breath-actuated inhaler by patients with severe airflow obstruction.

The ability of patients with severe airflow limitation (forced expiratory volume in one second less than 1.0 l or peak expiratory flow rate less than 200 l.min.1) to use a new breath-actuated inhaler (BAI) was assessed. One hundred and fifty six patients attending two respiratory units entered and completed the study. Subjects were instructed how to use the device and after attempting to trigger the BAI had flow-volume loops measured. One hundred and fifty one (97%) were able to actuate the inhaler on their first (146) or second (5) attempt. The five unsuccessful patients did not have the most severe airways obstruction. It is concluded that this new device, which is actuated at low inspiratory flow rates, can be used by patients with severe airflow limitation and represents an important advance in inhaler technology.

Purification and properties of human serum carnosinase.

Carnosinase from human plasma was purified 18,000-fold to apparent homogeneity in a four step procedure. The dipeptidase was partially inactivated during DEAE-cellulose chromatography; however, it reactivated slowly when concentrated and stored at 4 degrees C. In the second purification step, hydroxylapatite column chromatography, two forms of the enzyme were separated from one another. Human serum carnosinase was found to be a glycoprotein with a pI of 4.4 and a subunit Mr of 75,000; the active enzyme was a dimer, the two subunits being connected by one or more disulfide bonds. The enzyme was especially active in hydrolyzing carnosine and anserine, preferring dipeptides with histidine in the C-terminal position. In most human tissues, the concentration of serum carnosinase was proportional to the percentage of trapped blood in the sample. However, the brain contained about 9 times more enzyme than expected, based on the amount of trapped blood present. The physiological function of this enzyme seems to be the hydrolysis of homocarnosine in the brain and the splitting of carnosine and anserine in the blood stream. Six higher primates were found to have serum carnosinase. Twelve nonprimate mammals were tested; all were lacking the serum enzyme except for the Golden hamster, which had very high concentrations of a carnosinase having somewhat different properties than the higher primate enzyme.

Separation and characterization of two carnosine-splitting cytosolic dipeptidases from hog kidney (carnosinase and non-specific dipeptidase).

High performance anion-exchange chromatography was used to separate two carnosine-hydrolysing dipeptidases from hog kidney. Both enzymes (peaks I and II) were cytosolic and were activated and stabilized by Mn2+ and dithiothreitol. Peak I had a narrow specificity when assayed without added metal ions, but a broad specificity in the presence of Mn2+ or Co2+. Peak II was inactive unless both Mn2+ and dithiothreitol were present. Bestatin and leucine inhibited peak II, but not peak I. Peak I had a Km of 0.4 mM carnosine, a pI of 5.5 and a Mr of 57,000. Peak II had a Km of 5 mM carnosine, a pI of 5.0 and a Mr of 70,000. Hog and rat brain and liver carnosinase activity was completely inhibited by bestatin, indicating that these organs contained peak II, with little or no peak I enzyme. Hog kidney peak I contained the classical carnosinase of Hanson and Smith, who first described this enzyme. It also contained activity against homocarnosine ("homocarnosinase") and showed "manganese-independent carnosinase" activity. These three activities could not be separated using 8 different chromatographic procedures; it was concluded that they are attributable to one enzyme. It is recommended that the name carnosinase be retained for this enzyme and the names "homocarnosinase" and "manganese-independent carnosinase" be withdrawn. The properties of hog kidney peak II closely resembled those of human tissue carnosinase (also known as prolinase, a non-specific dipeptidase), mouse "manganese-dependent carnosinase" and a rat brain enzyme termed "beta-Ala-Arg hydrolase". Since these terms appear to represent closely related enzymes with broad specificity, the recommended name for each is "non-specific cytosolic dipeptidase".

Human cytosolic carnosinase: evidence of identity with prolinase, a non-specific dipeptidase.

In separate papers published in 1985, human cytosolic carnosinase and prolinase were purified and characterized for the first time. Prolinase had activity against many dipeptides not containing proline; carnosinase also had broad specificity. The present paper reports that carnosinase and prolinase activities were not separated from one another during chromatography on columns of DEAE-cellulose, AGMP-1, gel filtration media, hydroxylapatite or butyl-agarose. Both activities had identical pH-stability curves at 50 degrees C, being stabilized by manganese ions and dithiothreitol. Prolinase substrates competitively inhibited carnosinase activity and carnosinase substrates inhibited prolinase activity. Bestatin was a potent inhibitor of both activities, while cilastatin inhibited neither. It was concluded that prolinase and carnosinase activities reside in the same enzyme. High performance anion-exchange chromatography of extracts from kidney, liver or brain separated the enzyme into two forms having isoelectric points of 5.6 and 5.1. Because of the broad specificity of this dipeptidase, it is recommended that it be termed "human cytosolic non-specific dipeptidase".

Inborn errors of carnosine and homocarnosine metabolism.

Serum carnosinase deficiency with carnosinuria has been reported in 23 children with neurological signs and/or mental retardation. In adults four cases in one family had serum carnosinase deficiency, carnosinuria, and in addition elevated homocarnosine in CSF and in the brain. The mother was one of these cases but had no clinical symptoms; however her three children have spastic paraparesis, retinitis pigmentosa and mental retardation. Serum carnosinase deficiency alone is not the cause of the neurological symptoms. When two of the affected children consumed carnosine, anserine or homocarnosine, they metabolized these compounds much less rapidly than did two normal control individuals.

Bestatin inhibition of human tissue carnosinase, a non-specific cytosolic dipeptidase.

Bestatin is a dipeptide containing a unique beta-amino acid. It is usually referred to as an aminopeptidase inhibitor. Current interest has focused on the immunostimulating activity of bestatin and several clinical trials have demonstrated that it is an effective adjunct to radiation or chemotherapy in the treatment of certain types of cancer. We found that bestatin was much more effective against human tissue carnosinase than against aminopeptidases. Inhibition was competitive, with a Ki of 0.5nM. Carnosinase did not hydrolyse bestatin and the enzyme-inhibitor complex formed rapidly. A hog kidney dipeptidase similar to human tissue carnosinase was equally sensitive to this inhibitor. Bestatin has a backbone structure identical to that of carnosine; however, our results indicate that the inhibitory activity of this compound is primarily attributable to the side chains of the beta-amino-acid moiety. Human tissue carnosinase is a non-specific dipeptidase, actively hydrolysing many dipeptides, including prolinase substrates. Inhibition of this cytosolic enzyme is probably at least partially responsible for the intracellular accumulation of dipeptides which occurs following the in vivo administration of bestatin.

Characterization of human tissue carnosinase.

Human tissue carnosinase (EC 3.4.13.3) had optimum activity at pH9.5 and was a cysteine peptidase, being activated by dithiothreitol and inhibited by p-hydroxymercuribenzoate. By optimizing assay conditions, the activity per g of tissue was increased 10-fold compared with values in the literature. The enzyme was present in every human tissue assayed and was entirely different from serum carnosinase. Highly purified tissue carnosinase had a broader specificity than hog kidney carnosinase. Although tissue carnosinase was very strongly inhibited by bestatin, it did not hydrolyse tripeptides, and thus appears to be a dipeptidase rather than an aminopeptidase. It had a relative molecular mass of 90 000, an isoelectric point of 5.6, and a Km value of 10 mM-carnosine. Two forms of kidney and brain carnosinase were separated by high-resolution anion-exchange chromatography, although only one form was detected by various electrophoretic methods. Homocarnosinase and Mn2+-independent carnosinase were not detected in human tissues, although these enzymes are present in rat and hog kidney.

Cathepsins J and K: high molecular weight cysteine proteinases from human tissues.

Human tissue extracts contained two high Mr proteinases active in hydrolyzing the fluorogenic substrate Cbz-phe-arg-aminomethylcoumarin. By gel filtration chromatography, cathepsins J and K had apparent molecular weights of 230,000 and 650,000, respectively. Both enzymes were cysteine proteinases with optimum activity at pH 6.2-6.8; neither had aminopeptidase activity. Human kidney, lung and spleen were rich sources of these enzymes, while liver contained moderate amounts. Cathepsins J and K were partially characterized and appeared to differ from the mammalian high Mr cysteine proteinases described in the literature. In rat liver and kidney and in mouse liver, cathepsin J was localized in the particulate fraction, whereas cathepsin K was not detected in these tissues.

Homocarnosinosis: lack of serum carnosinase is the defect probably responsible for elevated brain and CSF homocarnosine.

Patients afflicted with homocarnosinosis have elevated concentrations of homocarnosine in brain and CSF. It has been reported that they lack brain homocarnosinase. However, we have found that these patients are deficient in serum carnosinase, a dipeptidase which hydrolyzes homocarnosine about 5% as rapidly as it splits carnosine. Homocarnosinase could not be detected in normal human brain extracts after isoelectric focusing or DEAE-cellulose column chromatography. The ability of brain extracts to hydrolyze homocarnosine thus appears to be attributable solely to the serum carnosinase which is present because of serum trapped in the brain sample. Preliminary data indicate that homocarnosinase is probably not present in 13 other human tissues. Normal CSF contained serum carnosinase, whereas the CSF of a homocarnosinosis patient was lacking this enzyme. Thus it appears that the elevated concentrations of homocarnosine in the CSF of homocarnosinosis patients are attributable to serum carnosinase deficiency.