A prospective polysomnographic study on the evolution of complex sleep apnoea.

Complex sleep apnoea (CompSA) may be observed following continuous positive airway pressure (CPAP) treatment. In a prospective study, 675 obstructive sleep apnoea patients (mean age 55.9 yrs; 13.9% female) participated. Full-night polysomnography was performed at diagnosis, during the first night with stable CPAP and after 3 months of CPAP. 12.2% (82 out of 675 patients) had initial CompSA. 28 of those were lost to follow-up. Only 14 out of the remaining 54 patients continued to satisfy criteria for CompSA at follow-up. 16 out of 382 patients not initially diagnosed with CompSA exhibited novel CompSA after 3 months. 30 (6.9%) out of 436 patients had follow-up CompSA. Individuals with CompSA were 5 yrs older and 40% had coronary artery disease. At diagnosis, they had similar sleep quality but more central and mixed apnoeas. On the first CPAP night and at follow-up, sleep quality was impaired (more wakefulness after sleep onset) for patients with CompSA. Sleepiness was improved with CPAP, and was similar for patients with or without CompSA at diagnosis and follow-up. CompSA is not stable over time and is mainly observed in predisposed patients on nights with impaired sleep quality. It remains unclear to what extent sleep impairment is cause or effect of CompSA.

ESPEN Guidelines on Enteral Nutrition: Cardiology and pulmonology.

These guidelines are intended to give evidence-based recommendations for the use of enteral nutrition (EN) in patients with chronic heart failure (CHF) and chronic obstructive pulmonary disease (COPD). They were developed by an interdisciplinary expert group in accordance with officially accepted standards and are based on all relevant publications since 1985. They have been discussed and accepted in a consensus conference. EN by means of oral nutritional supplements (ONS) or tube feeding (TF) enables nutritional intake to be maintained or increased when normal oral intake is inadequate. No data are yet available concerning the effects of EN on cachexia in CHF patients. However, EN is recommended to stop or reverse weight loss on the basis of physiological plausibility. In COPD patients, EN in combination with exercise and anabolic pharmacotherapy has the potential to improve nutritional status and function. Frequent small amounts of ONS are preferred in order to avoid postprandial dyspnoea and satiety as well as to improve compliance.

Major identity determinants for enzymatic formation of ribothymidine and pseudouridine in the T psi-loop of yeast tRNAs.

Almost all transfer RNA molecules sequenced so far contain two universal modified nucleosides at positions 54 and 55, respectively: ribothymidine (T54) and pseudouridine (psi 55). To identify the tRNA elements recognized by tRNA:m5uridine-54 methyltransferase and tRNA:pseudouridine-55 synthase from the yeast Saccharomyces cerevisiae, a set of 43 yeast tRNA(Asp) mutants were used. Some variants contained point mutations, while the others included progressive reductions in size down to a tRNA minisubstrate consisting of the T psi-loop with only one G.C base-pair as stem (9-mer). All substrates (full-sized tRNA(Asp) and various minihelices) were produced in vitro by T7 transcription and tested using yeast extract (S100) as a source of enzymatic activities and S-adenosyl-L-methionine as a methyl donor. The results indicate that the minimal substrate for enzymatic formation of psi 55 is a stem/loop structure with only four G.C base-pairs in the stem, while a longer stem is required for efficient T54 formation. None of the conserved nucleotides (G53, C56, A58 and C61) and U54 for psi 55 or U55 for T54 formation can be replaced by any of the other three canonical nucleotides. Yeast tRNA:m5uridine-54 methyltransferase additionally requires the presence of a pyrimidine-60 in the loop. Interestingly, in a tRNA(Asp) variant in which the T psi-loop was permuted with the anticodon-loop, the new U32 and U33 residues derived from the T psi-loop were quantitatively converted to T32 and psi 33, respectively. Structural mapping of this variant with ethylnitrosourea confirmed that the intrinsic characteristic structure of the T psi-loop was conserved upon permutation and that the displaced anticodon-loop did not acquire a T psi-loop structure. These results demonstrate that a local conformation rather than the exact location of the U-U sequence within the tRNA architecture is the important identity determinant for recognition by yeast tRNA:m5uridine-54 methyltransferase and tRNA:pseudouridine-55 synthase.

Enzymatic conversion of adenosine to inosine and to N1-methylinosine in transfer RNAs: a review.

Inosine (6-deaminated adenosine) is a characteristic modified nucleoside that is found at the first anticodon position (position 34) of several tRNAs of eukaryotic and eubacterial origins, while N1-methylinosine is found exclusively at position 37 (3' adjacent to the anticodon) of eukaryotic tRNA(Ala) and at position 57 (in the middle of the psi loop) of several tRNAs from halophilic and thermophilic archaebacteria. Inosine has also been recently found in double-stranded RNA, mRNA and viral RNAs. As for all other modified nucleosides in RNAs, formation of inosine and inosine derivative in these RNA is catalysed by specific enzymes acting after transcription of the RNA genes. Using recombinant tRNAs and T7-runoff transcripts of several tRNA genes as substrates, we have studied the mechanism and specificity of tRNA-inosine-forming enzymes. The results show that inosine-34 and inosine-37 in tRNAs are both synthesised by a hydrolytic deamination-type reaction, catalysed by distinct tRNA:adenosine deaminases. Recognition of tRNA substrates by the deaminases does not strictly depend on a particular "identity' nucleotide. However, the efficiency of adenosine to inosine conversion depends on the nucleotides composition of the anticodon loop and the proximal stem as well as on 3D-architecture of the tRNA. In eukaryotic tRNA(Ala), N1-methylinosine-37 is formed from inosine-37 by a specific SAM-dependent methylase, while in the case of N1-methylinosine-57 in archaeal tRNAs, methylation of adenosine-57 into N1-methyladenosine-57 occurs before the deamination process. The T psi-branch of fragmented tRNA is the minimalist substrate for the N1-methylinosine-57 forming enzymes. Inosine-34 and N1-methylinosine-37 in human tRNA(Ala) are targets for specific autoantibodies which are present in the serum of patients with inflammatory muscle disease of the PL-12 polymyositis type. Here we discuss the mechanism, specificity and general properties of the recently discovered RNA:adenosine deaminases/editases acting on double-stranded RNA, intron-containing mRNA and viral RNA in relation to those of the deaminases acting on tRNAs.

Effect of sleep position and sleep stage on the collapsibility of the upper airways in patients with sleep apnea.

Collapsibility of the upper airways has been identified as an important pathogenic factor in obstructive sleep apnea (OSA). Objective measures of collapsibility are pharyngeal critical pressure (Pcrit) and resistance of the upstream segment (Rus). To systematically determine the effects of sleep stage and body position we investigated 16 male subjects suffering from OSA. We compared the measures in light sleep, slow-wave sleep, REM sleep and supine vs. lateral positions. The pressure-flow relationship of the upper airways has been evaluated by simultaneous readings of maximal inspiratory airflow (Vimax) and nasal pressure (p-nCPAP). With two-factor repeated measures ANOVA on those 7 patients which had all 6 situations we found a significant influence of body position on Pcrit (p<0.05) whereas there was no significant influence of sleep stage and no significant interaction between body position and sleep stage. When comparing the body positions Pcrit was higher in the supine than in the lateral positions. During light sleep Pcrit decreased from 0.6 +/- 0.8 cm H2O (supine) to -2.2 +/- 3.6 cm H2O (lateral) (p<0.01), during slow-wave sleep Pcrit decreased from 0.3 +/- 1.4 cm H2O (supine) to -1.7 +/- 2.6 (lateral) (p<0.05) and during REM sleep it decreased from 1.2 +/- 1.5 cm H2O to -2.0 +/- 2.2 cm H2O (p<0.05). Changes in Rus revealed no body position nor sleep-stage dependence. Comparing the different body positions Rus was only significantly higher in the lateral position during REM sleep (p<0.05). The results indicate that collapsibility of the upper airways is not mediated by sleep stages but is strongly influenced by body position. As a consequence lower nCPAP pressure is needed during lateral positions compared to supine positions.

Effect of different levels of hyperoxia on breathing in healthy subjects.

We have recently shown that breathing 50% O2 markedly stimulates ventilation in healthy subjects if end-tidal PCO2 (PETCO2) is maintained. The aim of this study was to investigate a possible dose-dependent stimulation of ventilation by O2 and to examine possible mechanisms of hyperoxic hyperventilation. In eight normal subjects ventilation was measured while they were breathing 30 and 75% O2 for 30 min, with PETCO2 being held constant. Acute hypercapnic ventilatory responses were also tested in these subjects. The 75% O2 experiment was repeated without controlling PETCO2 in 14 subjects, and in 6 subjects arterial blood gases were taken at baseline and at the end of the hyperoxia period. Minute ventilation (VI) increased by 21 and 115% with 30 and 75% isocapnic hyperoxia, respectively. The 75% O2 without any control on PETCO2 led to 16% increase in VI, but PETCO2 decreased by 3.6 Torr (9%). There was a linear correlation (r = 0.83) between the hypercapnic and the hyperoxic ventilatory response. In conclusion, isocapnic hyperoxia stimulates ventilation in a dose-dependent way, with VI more than doubling after 30 min of 75% O2. If isocapnia is not maintained, hyperventilation is attenuated by a decrease in arterial PCO2. There is a correlation between hyperoxic and hypercapnic ventilatory responses. On the basis of data from the literature, we concluded that the Haldane effect seems to be the major cause of hyperventilation during both isocapnic and poikilocapnic hyperoxia.

Sleep-apnea in patients with end-stage renal disease and objective results.

BACKGROUND: A high prevalence of sleep apnea syndrome (SAS) of 54%-80% has been reported in patients with end-stage renal disease (ESRD). However, these studies were either done in highly selected small patient groups or without objective data using questionnaires only. PATIENTS AND METHODS: We, therefore, studied the prevalence of SAS in a large, unselected group of patients with ESRD. During a 6-month period 77 out of 84 unselected patients with ESRD filled out the sleep apnea questionnaire of the University of Marburg and the Epworth Sleepiness Scale. In 55 of these patients, snoring sounds, heart rate, body position and transcapillary arterial oxygen saturation were recorded with an ambulatory device during the night after hemodialysis. RESULTS: In the questionnaires, 70.3% of the patients reported of an excessive day-time sleepiness, 40.5% of unwillingly falling asleep during the daytime and 35.2% rated their ability to concentrate as decreased. 30.9% (40% male/15% female) of the patients showed evidence of sleep-disordered breathing with an apnea-hypopnea-index (AHI) equal or more than 5/hour. 16.4% (20% male/10% female) of the patients met the diagnostic criteria of SAS. Neither dialysis and biochemical data nor anamnestic parameters measured by the questionnaires correlated significantly with sleep-disordered breathing. CONCLUSION: The prevalence of SAS in this large unselected patient group was not as high as previously reported, but it is still considerably higher than in the general population. Objective recordings are essential, as questionnaires overestimate the prevalence of SAS in patients with ESRD. As SAS promotes hypertension and impairs quality of life, ESRD patients might benefit from a treatment of concomitant SAS.

Experience with new autotitrating nasal continuous positive airway pressure machines.

Since the introduction of nasal continuous positive airway pressure (nCPAP) in the treatment of sleep apnoea, enormous technical improvements in nCPAP devices have been achieved. nCPAP has become the most effective and widely used standard therapy for obstructive sleep apnoea. Recently, machines that automatically titrate the effective nCPAP pressure have become available. The question now is, whether and how they work and what the benefits and limitations of such devices are. The algorithms that control the machines are quite different and so is their effectiveness. Even in devices that generally work well, there may be some principal limitations. The algorithm may be mislead by artefacts, especially leaks. Apnoeas and arousal may occur because the pressure increase is too slow or breathing disturbances reoccur after a pressure decrease. Autotitrating nasal continuous positive airway pressure may reduce the work required to determine effective pressure. It is a valuable treatment option for patients who need high and variable nasal continuous positive airway pressure. It should not be used as an unattended pressure titration tool because this will lead to a loss of quality in patient care and a reduced acceptance of nasal continuous positive airway pressure, as pressure determination is only a small part of the adaptation of the patient to nasal continuous positive airway pressure.

[Pathophysiology and clinical aspects of global respiratory insufficiency]. / Pathophysiologie und Klinik der respiratorischen Globalinsuffizienz.

Patients in hypercapnic respiratory failure have got a poor prognosis. The recognition of pathophysiological mechanisms is required in order to choose adequate therapy. During the past years it has been shown that pathological respiratory events during sleep occur early in the disease process and that blood gas changes are usually most pronounced during sleep. Minute ventilation and functional residual capacity (FRC) decrease during sleep even in normal subjects and upper airway resistance increases markedly. PO2 slightly decreases and paCO2 increases. In most patients with hypercapnic respiratory failure episodes of marked hypoxemia and hypercapnia occur, mainly during REM sleep. Suggested pathomechanisms are worsening ventilation-/perfusion mismatching, impaired respiratory muscle function and a reduction in ventilatory drive, the latter two being of major importance. The relation between load and capacity is shifted towards an increased load and ventilatory drive is decreased at the same time. Therapeutic strategies that reduce the load of the respiratory pump, increase minute ventilation and prevent sleep related hypoventilation, thus noninvasive ventilation should be used. Symptoms of hypercapnic respiratory failure are often unspecific. Dyspnea, headache and awakening from sleep with dyspnea are often reported. Signs of right heart failure will be present in advanced disease stages. Early diagnosis and treatment provided, noninvasive ventilation achieves excellent improvement of both quality of life and life expectancy, especially if the primary disease progress is not rapidly progressive.

[Measuring hypoxic and hypercapnic respiratory response in patients with obstructive sleep apnea]. / Messung der hypoxischen und hyperkapnischen Atemantwort bei Patienten mit OSA.

The gas composition of breathing air is a very important stimulus for the control of breathing. The different partial pressures of O2 and CO2 independently trigger individually different reactions (respiratory response), which can be measured as a change of respiratory minute volume. Investigations of the respiratory control in patients with obstructive sleep apnoea (OSA) have up to now been restricted to an analysis of the breathing patterns at night. Therefore we have developed a computer-controlled device which allows a flexible composition of the air to be inhaled using a regulated feet-back circle. With this system it is possible to produce a hypercapnia test as well as a hyperoxia and an isocapnic hypoxia test. The simultaneous recording of all relevant respiratory parameters (AF, AMV, ETCO2, SpO2, FiO2) and the parallel recording of continuous blood pressure allow a quantitative description of the respiratory regulation of patients with OSA with exactly defined tests.

[Dependence of nocturnal bronchial obstruction on sleep position]. / Abhängigkeit Nächtlicher Bronchialobstruktionen von der Schlafposition.

Patients with bronchial obstructions often have problems to stay asleep at night. The interaction between sleep position and bronchial obstructions has not been investigated until now. A total of 20 patients was included in this study. All patients were recorded one night in our sleep laboratory with a parallel recording of lung sounds using a commercial Pulmotrack 1010 system. The bronchial obstructions were lower in lateral position than in supine position for both tracheal and chest sounds (p = 0,083 and p = 0,036; n.s.). This effect seemed to be especially high in patients with many obstruction episodes. From our results we can conclude that there is a small dependence of bronchial obstructions from sleep position. Further investigations are needed to verify this result.

Comparison of the effects of nebivolol and valsartan on BP reduction and sleep apnoea activity in patients with essential hypertension and OSA.

OBJECTIVES: To investigate the effect of nebivolol, a third generation beta-blocker, on blood pressure (BP) reduction and polysomnographic parameters in hypertensive patients with mild-to-moderate obstructive sleep apnoea (OSA). METHODS: In this double-blind, parallel group study, patients were randomized to nebivolol 5 mg or valsartan 80 mg once daily following a 14-day, placebo run-in period during which any antihypertensive medication were discontinued. BP and heart rate measurements and overnight polysomnography were performed at baseline and after 6 weeks of treatment. Safety and tolerability were assessed. RESULTS: Thirty-one patients were randomized to nebivolol (n = 16) or valsartan (n = 15). After six weeks both systolic and diastolic BP were effectively reduced by both treatments. Reductions in BP were not statistically significant different between agents, but mean heart rate was significantly decreased with nebivolol (compared with valsartan (p < 0.001). There was no statistically significant difference between both treatments for the change from baseline to treatment end for mean (+/-SD) Apnoea Hypopnoea Index (AHI) (nebivolol: 23.0 +/- 9.2 to 27.9 +/- 21.2 events/h; valsartan: 23.8 +/- 6.6 to 22.5 +/- 18.0 events/h; p = 0.48) or for any other sleep-related parameters. Both agents were well tolerated. CONCLUSION: Nebivolol has a significant BP reduction effect in patients with OSA that is similar to valsartan and reduces heart rate to a greater extent which may prove beneficial in selected patients.

[Relevance of sleep for patients with lung diseases]. / Bedeutung des Schlafs bei Patienten mit Lungenerkrankungen.

Sleep is characterized by a profound change of load and capacity of the respiratory system. Load increases due to a rise in upper and lower airway resistance. Capacity decreases due to reduced chemosensitivity, a decrease in muscle activity and minute ventilation. Whereas these changes do not lead to relevant blood gas changes and do not disturb sleep in healthy subjects, patients with respiratory diseases frequently show the first symptoms of their disease during sleep. Pulmonary diseases in which sleep plays an important role are asthma, COPD, hypercapnic respiratory failure, sleep disordered breathing, the overlap-syndrome and cystic fibrosis. Medical history should include sleep and complaints during the night. In asthmatics peak-flow measurements during the night may provide valuable information. In all other disorders mentioned, nocturnal ambulatory recording of respiration and arterial oxygen saturation often allow the detection of relevant disorders of breathing during sleep. If ambulatory monitoring reveals relevant pathology, then further evaluation and treatment in the sleep laboratory are warranted.

Growth, Gravitropism, and Endogenous Ion Currents of Cress Roots (Lepidium sativum L.) : Measurements Using a Novel Three-Dimensional Recording Probe.

A novel, three-dimensional recording, vibrating probe was used for measuring the density and direction of the endogenous ionic current of cress roots (Lepidium sativum L.) bathed in low salt media (artificial pond water, APW). Roots submerged in regular APW and growing vertically show the following current pattern. Current of 0.7 microampere/square centimeter density enters or leaves the root cap; the current changes direction frequently. Current of 1.6 microamperes/square centimeter enters the meristem zone most of the time. Maximum current with a density of 2.2 microamperes/square centimeter enters the apical elongating zone, i.e. between 0.8 and 1.2 millimeters behind the root tip. The current density decreases to 1.4 microamperes/square centimeter at 2 millimeters, i.e. in the central elongating zone, and to 1.0 microampere/square centimeter at 3 millimeters, i.e. in the basal elongating zone. The current direction changes from inward to predominantly outward between 1.2 and 3 millimeters behind the tip. Measurements on opposite flanks of the roots indicate that the current pattern is fairly symmetrical. After placing the roots horizontally, the density of the endogenous current remains stable, but the current direction changes at the root cap and in the meristem zone. The current leaves the root on the upper side and enters on the lower side, causing a highly asymmetrical current pattern at the very tip. The current pattern at the upper and lower side further away from the tip remains the same as in vertical roots. Roots submerged in low Ca(2+) APW show a very different current pattern, no gravitropism, and no change of the current pattern after horizontal orientation. In these roots current enters the root cap and the basal elongating zone and leaves the apical elongating zone. Three conclusions are drawn from these results: First, plant roots elongate by two different modes of growth that are correlated with different current directions. They grow by cytoplasmic enlargement at sites of inward current and by turgor-driven elongation at sites of outward current. Second, a change in the current pattern at the root cap and in the meristem zone is a clear indicator of later gravitropism. Third, Ca(2+) ions are involved in the gravistimulated change in the current pattern, probably affecting the activity of plasmalemma H(+)-ATPases.

[Sleep disorders and sleep-related breathing disorders]. / Schlafstörungen und schlafbezogene Atmungsstörungen.

Normal sleep consists of 4-5 sleep cycles including light-, deep- and rapid eye-movement sleep. Restoration of physical and psychological function are the main effects of sleep. In most cases, disturbances of normal sleep become clinically evident as problems of initiating and maintaining sleep and/or as increased daytime sleepiness. Approximately 10% of adults suffer from pronounced insomnia, a similar percentage from markedly increased daytime sleepiness. Sleep disorders cause high socio-economic costs due to increased accident risk, cardiovascular sequelae and sick leave. Most of the 88 distinct diagnoses summarized in the international classification of sleep disorders can be differentiated and managed according to patients history. In patients with severe daytime sleepiness - sleep disordered breathing being the most frequent cause - the diagnostic evaluation and treatment in the sleep laboratory is required. Effective therapeutic strategies are available for many sleep disorders. According to the underlying disorder, treatment includes a variety of measures like life style changes, differentiated medical treatment and the use of nasally applied positive pressure in patients suffering from sleep disordered breathing.

The yeast gene YNL292w encodes a pseudouridine synthase (Pus4) catalyzing the formation of psi55 in both mitochondrial and cytoplasmic tRNAs.

The protein products of two yeast Saccharomyces cerevisiae genes (YNL292w and CBF5) display a remarkable sequence homology with Escherichia coli tRNA:pseudouridine-55 synthase (encoded by gene truB). The gene YNL292w coding for one of these proteins was cloned in an E.coli expression vector downstream of a His6-tag. The resulting recombinant protein (Pus4) was expressed at high level and purified to homogeneity by metal affinity chromatography on Ni2+-NTA-agarose, followed by ion-exchange chromatography on MonoQ. The purified Pus4p catalyzes the formation of pseudouridine-55 in T7 in vitro transcripts of several yeast tRNA genes. In contrast to the known yeast pseudouridine synthase (Pus1) of broad specificity, no other uridines in tRNA molecules are modified by the cloned recombinant tRNA:Psi55 synthase. The disruption of the corresponding gene YNL292w in yeast, which has no significant effect on the growth of yeast cells, leads to the complete disappearance of the Psi55 formation activity in a cell-free extract. These results allow the formal identification of the protein encoded by the yeast ORF YNL292w as the only enzyme responsible for the formation of Psi55 which is almost universally conserved in tRNAs. The substrate specificity of the purified YNL292w-encoded recombinant protein was shown to be similar to that of the native protein present in yeast cell extract. Chemical mapping of pseudouridine residues in both cytoplasmic and mitochondrial tRNAs from the yeast strain carrying the disrupted gene reveals that the same gene product is responsible for Psi55 formation in tRNAs of both cellular compartments.

Ambulatory recording of sleep apnea using peripheral arterial tonometry.

Sleep related breathing disorders are common. A reliable diagnosis with relatively simple and portable methods is still needed. One approach is to make use of autonomous nervous system changes which accompany disordered breathing during sleep. The peripheral arterial tonometry (PAT) determines the peripheral arterial vascular tone using a plethysmographic method on the finger. The peripheral arterial tone is modulated by sympathetic activity, by peripheral blood pressure, and by the peripheral resistance of the vessels. We investigate a new ambulatory recording device which uses PAT, oximetry and actigraphy in order to detect sleep apnea. For this purpose we performed a comparative study on 21 patients referred to our sleep laboratory due to suspected sleep apnea. Of these 17 valid recordings were compared. The Watch-PAT was used in parallel with cardiorespiratory polysomnography and the validity was determined. The new system is able to detect apneas and hypopneas with a high reliability (r=0.89). It is very sensitive to arousals (r=0.77). Since arousal are not specific to sleep apnea the specificity of the new system could not be finally clarified in this study. We conclude that the new system is very well suited to perform control studies in patients with sleep apnea which are under therapy and require regular follow-up investigations to maintain a high CPAP compliance.

Automatic CPAP titration with different self-setting devices in patients with obstructive sleep apnoea.

Autotitrating continuous positive airway pressure (CPAP) devices automatically adjust the pressure according to upper airway obstructions. The aim of this study was to compare the treatment effects of different automatic CPAP devices (AutoSet, Horizon and Virtuoso) with conventional CPAP in patients with obstructive sleep apnoea independently of financial manufacturer support. Twelve male patients with obstructive sleep apnoea were submitted to a crossover study protocol with overnight polysomnography for 6 consecutive nights. After diagnostic polysomnography, the CPAP pressure was manually titrated. Over the next 4 nights, the patients were treated with any one of the three automatic CPAP devices or fixed CPAP in random order. The apnoea/hypopnoea index on the diagnostic night was 67.3+/-21.7 events h(-1), and was significantly reduced to 0.7+/-1.2, 3.0+/-2.9, 2.3+/-2.5 and 12.0+/-13.6 events x h(-1) with the fixed CPAP, AutoSet, Horizon and Virtuoso devices respectively. An apnoea/ hypopnoea index of <5 events h(-1), an indicator of optimal treatment, was achieved in all patients with fixed CPAP and in 10 patients using the Autoset and Horizon devices, but in only six of the 12 using the Virtuoso. The mean pressure was significantly lower with the AutoSet and Virtuoso devices, but not with the Horizon as compared to fixed CPAP. The maximum pressure was significantly higher with the Horizon. It is concluded that automatic continuous positive airway pressure devices produce a significant reduction in apnoea/hypopnoea index; however, there is considerable difference in the efficacy of the various devices.

Pseudouridine and ribothymidine formation in the tRNA-like domain of turnip yellow mosaic virus RNA.

The last 82 nucleotides of the 6.3 kb genomic RNA of plant turnip yellow mosaic virus (TYMV), the so-called 'tRNA-like' domain, presents functional, structural and primary sequence homologies with canonical tRNAs. In particular, one of the stem-loops resembles the TPsi(pseudouridine)-branch of tRNA, except for the presence of a guanosine at position 37 (numbering is from the 3'-end) instead of the classical uridine-55 in tRNA (numbering is from the 5'-end). Both the wild-type TYMV-RNA fragment and a variant, TYMV-mut G37U in which G-37 has been replaced by U-37, have been tested as potential substrates for the yeast tRNA modification enzymes. Results indicate that two modified nucleotides were formed upon incubation of the wild-type TYMV-fragment in a yeast extract: one Psi which formed quantitatively at position 65, and one ribothymidine (T) which formed at low level at position U-38. In the TYMV-mutant G37U, besides the quantitative formation of both Psi-65 and T-38, an additional Psi was detected at position 37. Modified nucleotides Psi-65, T-38 and Psi-37 in TYMV RNA are equivalent to Psi-27, T-54 and Psi-55 in tRNA, respectively. Purified yeast recombinant tRNA:Psisynthases (Pus1 and Pus4), which catalyze respectively the formation of Psi-27 and Psi-55 in yeast tRNAs, are shown to catalyze the quantitative formation of Psi-65 and Psi-37, respectively, in the tRNA-like 3'-domain of mutant TYMV RNA in vitro . These results are discussed in relation to structural elements that are needed by the corresponding enzymes in order to catalyze these post-transcriptional modification reactions.

Inosine and N1-methylinosine within a synthetic oligomer mimicking the anticodon loop of human tRNA(Ala) are major epitopes for anti-PL-12 myositis autoantibodies.

Sera of some patients afflicted with the inflammatory disease myositis contain antibodies of the anti-PL-12 type. A fraction of these polyclonal autoantibodies specifically precipitates the fully matured human tRNA(Ala) bearing the anticodon IGC (PL-12 antigen). Earlier work (Bunn & Mathews, 1987, Science 238:116-119) had shown that the epitopes are located entirely within the anticodon stem-loop of the tRNA(Ala). Here we demonstrate that human anti-tRNA(Ala) autoantibodies immunoprecipitate a synthetic polyribonucleotide containing inosine (I) and N1-methylinosine (m1I) separated by 2 nt as in the anticodon stem-loop of human tRNA(Ala). The shortest polyribonucleotide that can be immunoprecipitated corresponds to the pentanucleotide IpGpCpm1IpUp, which corresponds to part of the anticodon loop of human tRNA(Ala) and lacks the stem-loop structure. The efficiency of immunoprecipitation was about four times greater with longer polyribonucleotides capable of forming a stem-loop structure, and was abolished by altering the relative positions of I and m1I within the synthetic polynucleotide. Synthetic oligodeoxyribonucleotide analogs of the tRNA(Ala) stem-loop, containing the sequence dIpdGdCdm1Ip, are not antigenic. Our results show that human anti-tRNA(Ala) autoantibodies selectively recognize chemical details of modified nucleotides (the 6-keto group of inosine-34 and the 6-keto group and the N1-methyl groups of N1-methylinosine-37) within an anticodon loop structure of a tRNA molecule. We also describe the chemical synthesis of the phosphoramidite derivatives corresponding to N1-methylinosine and N1-methyl-2'-deoxyinosine for use in the automatic chemical synthesis of oligonucleotides containing N1-methylinosine and N1-methyl-2'-deoxyinosine.