GATOR1 Mutations Impair PI3 Kinase-Dependent Growth Factor Signaling Regulation of mTORC1

GATOR1 (GAP Activity TOward Rag 1) is an evolutionarily conserved GTPase-activating protein complex that controls the activity of mTORC1 (mammalian Target Of Rapamycin Complex 1) in response to amino acid availability in cells. Genetic mutations in the GATOR1 subunits, NPRL2 (nitrogen permease regulator-like 2), NPRL3 (nitrogen permease regulator-like 3), and DEPDC5 (DEP domain containing 5), have been associated with epilepsy in humans; however, the specific effects of these mutations on GATOR1 function and mTORC1 regulation are not well understood. Herein, we report that epilepsy-linked mutations in the NPRL2 subunit of GATOR1, NPRL2-L105P, -T110S, and -D214H, increase basal mTORC1 signal transduction in cells. Notably, we show that NPRL2-L105P is a loss-of-function mutation that disrupts protein interactions with NPRL3 and DEPDC5, impairing GATOR1 complex assembly and resulting in high mTORC1 activity even under conditions of amino acid deprivation. Furthermore, our studies reveal that the GATOR1 complex is necessary for the rapid and robust inhibition of mTORC1 in response to growth factor withdrawal or pharmacological inhibition of phosphatidylinositol-3 kinase (PI3K). In the absence of the GATOR1 complex, cells are refractory to PI3K-dependent inhibition of mTORC1, permitting sustained translation and restricting the nuclear localization of TFEB, a transcription factor regulated by mTORC1. Collectively, our results show that epilepsy-linked mutations in NPRL2 can block GATOR1 complex assembly and restrict the appropriate regulation of mTORC1 by canonical PI3K-dependent growth factor signaling in the presence or absence of amino acids.

Antisense oligonucleotides targeting the miR-29b binding site in the GRN mRNA increase progranulin translation

Heterozygous GRN (progranulin) mutations cause frontotemporal dementia (FTD) due to haploinsufficiency, and increasing progranulin levels is a major therapeutic goal. Several microRNAs, including miR-29b, negatively regulate progranulin protein levels. Antisense oligonucleotides (ASOs) are emerging as a promising therapeutic modality for neurological diseases, but strategies for increasing target protein levels are limited. Here, we tested the efficacy of ASOs as enhancers of progranulin expression by sterically blocking the miR-29b binding site in the 3' UTR of the human GRN mRNA. We found 16 ASOs that increase progranulin protein in a dose-dependent manner in neuroglioma cells. A subset of these ASOs also increased progranulin protein in iPSC-derived neurons and in a humanized GRN mouse model. In FRET-based assays, the ASOs effectively competed for miR-29b from binding to the GRN 3' UTR RNA. The ASOs increased levels of newly synthesized progranulin protein by increasing its translation, as revealed by polysome profiling. Together, our results demonstrate that ASOs can be used to effectively increase target protein levels by partially blocking miR binding sites. This ASO strategy may be therapeutically feasible for progranulin-deficient FTD as well as other conditions of haploinsufficiency.

Young children's use of syntactic cues to learn proper names and count nouns

In 6 experiments, 144 toddlers were tested in groups ranging in mean age from 20 to 37 months. In all experiments, children learned a novel label for a doll or a stuffed animal. The label was modeled syntactically as either a count noun (e.g., "This is a ZAV") or a proper name (e.g., "This is ZAV"). The object was then moved to a new location in front of the child, and a second identical-looking object was placed nearby. The children's task was to choose 1 of the 2 objects as a referent for the novel word. By 24 months, both girls (Experiment 2) and boys (Experiment 5) were significantly more likely to select the labeled object if they heard a proper name than if they heard a count noun. At 20 months, neither girls (Experiments 1 and 6) nor boys (Experiment 1) demonstrated this effect. By their 2nd birthdays, children can use syntactic information to distinguish appropriately between labels for individual objects and those for object categories.

Young children's use of syntactic cues to learn proper names and count nouns

In 6 experiments, 144 toddlers were tested in groups ranging in mean age from 20 to 37 months. In all experiments, children learned a novel label for a doll or a stuffed animal. The label was modeled syntactically as either a count noun (e.g., "This is a ZAV") or a proper name (e.g., "This is ZAV"). The object was then moved to a new location in front of the child, and a second identical-looking object was placed nearby. The children's task was to choose 1 of the 2 objects as a referent for the novel word. By 24 months, both girls (Experiment 2) and boys (Experiment 5) were significantly more likely to select the labeled object if they heard a proper name than if they heard a count noun. At 20 months, neither girls (Experiments 1 and 6) nor boys (Experiment 1) demonstrated this effect. By their 2nd birthdays, children can use syntactic information to distinguish appropriately between labels for individual objects and those for object categories.

[Evaluation of a program designed to develop social competence in kindergarten children]

This paper presents an evaluation of the implementation and impact of a program promoting social competence among kindergarten children. This program was conducted experimentally in 8 schools (10 classrooms, n = 165) in Montreal; 5 classrooms (n = 74) from 5 other schools formed the control group. Analysis of the impact reveals significant gains in self-esteem and conflict resolution skills in the experimental group compared to the control group. However, there was no significant change in pro-sociality and social withdrawal. Finally, an unexpected result was found in the area of boys' aggression. Analysis of the implementation indicates that teachers found the program's activities easy to use and adapt. In addition, great diversity in the utilization of these activities was observed. These results lead to areas of discussion concerning: (a) the links between gains realized by children and the emphasis teachers place on some aspects of the program; (b) the development of social competence among preschoolers; (c) the evaluation of the this type of program.

The fluctuant nature of precipitating antibodies in dairy farmers

Four hundred and forty five of 888 dairy farmers studied in an epidemiological survey four years previously were restudied to determine change in precipitins and in clinical features. Subjects answered the same questionnaire, which was filled in by the same nurse in the same winter months, and had blood withdrawn for precipitin analysis (double diffusion technique). Of the 445 subjects retested, 48 (10.8%) had been precipitin positive at the first study; of these, 34 remained positive four years later and 14 had reverted to negative. Twenty eight subjects previously negative for precipitins had become positive, so that 62 subjects in all were precipitin positive when restudied (13.9%). Of the 445 farmers, 369 were precipitin negative at both studies. The prevalence of symptoms, including cough, sputum production, wheezing, dyspnoea, and fever and chills, was similar for subjects who were consistently negative for precipitins and consistently positive and for those who changed from one to the other. Only one subject developed farmer's lung; he had precipitins in both studies. This study shows a fluctuation in the precipitin state of dairy farmers, suggesting that more farmers have precipitins at least once in their lifetime than are identified by screening at a single point in time. Relatively few develop farmer's lung or other respiratory symptoms. The presence of precipitins in a symptomless farmer appears to have no clinical importance.

Prognostic significance of bronchoalveolar lymphocytosis in farmer's lung

In 1983, we studied and reported the clinical and bronchoalveolar lavage (BAL) data of 26 patients with a history of previous farmer's lung. Most of these subjects (24 of 26) had a BAL lymphocytosis. In 1985, we restudied 14 of these subjects. Each subject had a clinical evaluation, chest roentgenogram, pulmonary function tests, and bronchoalveolar lavage. Results show that only 1 subject had evidence of an episode of acute recurrent disease, and only 1 had clinically progressive disease; however, 6 complained of chronic cough and sputum production. There were some fluctuations in individual pulmonary functions, with a significant decrease in FVC during the 2-yr period. The total number of cells on repeated lavage was 55.20 X 10(6) +/- 41.10 X 10(6) (mean +/- SD). This was not statistically different from the results obtained 2 yr earlier (69.5 X 10(6) +/- 43.01 X 10(6)). The percentage of BAL lymphocytes was also similar between the 2 studies, with abnormal values (greater than 20%) in 13 of 14 subjects (47.2 +/- 19.2). The BAL lymphocyte subsets, measured by monoclonal antibody in 8 subjects, showed a wide range of values, with individual OKT4/OKT8 ratios remaining similar at both studies. There were no correlations between changes seen in individual pulmonary function and BAL lymphocytosis. We conclude that a high intensity lymphocytic alveolitis, which persists after an acute episode of farmer's lung, does not predict the outcome of the disease.

Characterization of digoxin and related cardiac glycosides by fast atom bombardment mass spectrometry

The potential of using fast atom bombardment mass spectrometry for the detection and the characterization of digoxin and a series of related cardenolide analogues was investigated. The spectra were dependent upon the type of support-matrix in which they were recorded; thioglycerol proved to be satisfactory for the characterization of digoxin and allowed for its detection in human urine extract spiked with ca 11 ng ml(-1).

Effect of mefenamic acid on bronchial tone in vivo

Prostaglandins (PG) are very potent mediators which can dilate or constrict the bronchi. In order to evaluate the role of PG in the homeostasis of bronchial tone, we studied the effects of mefenamic acid, a potent cyclooxygenase inhibitor, on the pulmonary function tests of 20 volunteers. The subjects were studied randomly in two sessions, one with a placebo and one with mefenamic acid. Tablets (drug or placebo) were taken for 2 days with the pulmonary function tests performed in the afternoon of the second day. Sessions were performed at least 2 days apart. Parameters measured, including forced vital capacity, forced expiratory volume in 1 s, expiratory flows, functional residual capacity and specific airway conductance (SGaw), were similar in both sessions. The SGaw, which was previously reported to increase with cyclooxygenase inhibitors, was 0.23 +/- 0.06 s-1 X cm H2O-1 in the placebo session and 0.24 +/- 0.06 in the mefenamic acid session (mean +/- SD). This study shows that cyclooxygenase inhibitors have no effect on airway tone and strongly suggests that endogenous PG do not participate in the homeostasis of normal bronchial tone.

Persistent bronchoalveolar lymphocytosis in asymptomatic farmers

We previously demonstrated that 14 of 23 asymptomatic dairy farmers with positive precipitins and 5 of 20 without precipitins had an alveolar lymphocytosis (greater than 22%). To verify the outcome of this lymphocytosis, we restudied, 2 or 3 yr later, 27 of these subjects. No subject had had symptoms suggestive of farmer's lung disease either prior to the initial study or between the 2 studies. All were still on their farm. Physical examination and chest roentgenograms were normal for all subjects at both studies. Pulmonary function tests showed a small but significant change in RV (101.8 +/- 20.4% to 118.7 +/- 27.6% of predicted, p less than 0.05) and FVC (98.0 +/- 12.6% to 94.3 +/-9.5%, p less than 0.05), whereas TLC, FEV1, and DLCO showed no changes. Lymphocytes from BAL were still increased in 9 of 12 subjects, whereas 3 had returned to normal; of the 15 subjects with previous normal values, 3 now had an abnormal lavage lymphocytosis. There was no correlation between lung function variations and the percentage of lymphocytes in the previous or the present BAL. We conclude that a bronchoalveolar lymphocytosis is a persistent phenomenon in a large number of asymptomatic dairy farmers, and that this finding is not related to significant disease, at least in the time span studied.

Relationships between radiographic change, pulmonary function, and bronchoalveolar lavage fluid lymphocytes in farmer's lung disease

Ninety four dairy farmers were investigated by chest radiography, pulmonary function tests, and bronchoalveolar lavage. They were divided into five groups--1: 11 subjects with acute farmer's lung; 2: 25 subjects with previously diagnosed farmer's lung who had stayed on their farm; 3: 15 farmers with previously diagnosed farmer's lung who had left the farm; 4: 23 precipitin positive symptomless farmers; 5: 20 precipitin negative symptomless farmers. The study evaluated the relationships between radiographic changes measured with a scoring system derived from the International Labour Office (ILO) classification, the results of pulmonary function tests, and bronchoalveolar lavage fluid. Thirty eight subjects had radiographic evidence of interstitial pulmonary infiltrates. Group 1 had the highest percentage of lymphocytes recovered by bronchoalveolar lavage (mean 66.3 (SD 19.2]. For all subjects carbon monoxide transfer factor (TLCO) and total lung capacity were negatively correlated with radiographic changes (r = -0.45 and -0.30; p less than 0.001 and less than 0.01 respectively). TLCO was also negatively correlated with radiographic change in group 2 (r = -0.59, p less than 0.005). The percentage of lavage lymphocytes was correlated with radiographic changes for all subjects (r = 0.36, p less than 0.001), but this correlation was not seen within groups. This study shows good correlation between radiographic abnormalities, pulmonary function changes and the cellular composition of bronchoalveolar lavage fluid.

Relationship among antigen contact, alveolitis, and clinical status in farmer's lung disease

We studied 41 subjects with a history of farmer's lung disease who had been free of acute episodes for at least one year. Twenty-six were still in daily contact with hay (group 1), and 15 had ceased all antigenic exposure (group 2). While the incidence of dyspnea was similar in both groups, coughing and sputum were more frequent in group 1. Inspiratory crackles were frequent in group 1 subjects (15 of 26) and absent in all group 2 subjects. In both groups, a high percentage of lymphocytes was demonstrated by bronchoalveolar lavage: 52.5% +/- 21.1% (mean +/- SD) and 26.3% +/- 18.7%, respectively. Lymphocytic alveolitis (greater than 22% lymphocytes) was more common in group 1 (23 of 26) than in group 2 (6 of 15). There was no relationship between functional abnormalities and the intensity of the alveolitis. We conclude that lymphocytic alveolitis may persist after an acute episode of farmer's lung disease, but the intensity of the alveolitis is not associated with functional alterations.

Fast atom bombardment mass spectrometry in the pharmaceutical analysis of drugs

The principles, techniques and value of fast atom bombardment mass spectrometry are summarized in this revïew. Applications of the method in such areas as molecular weight determination, standard and metabolic studies, and peptide sequencing, as well as direct quantitative analysis, are surveyed, with examples from several classes of compounds with pharmacological activity.

Role of prostaglandins in marihuana-induced bronchodilation

In vitro evidence suggests that physiological effects of marihuana may be mediated by prostaglandins via the stimulation of phospholipase A2. To verify if marihuana could act by this route in vivo, we tested the effects of acetylsalicylic and mefenamic acids, inhibitors of cyclooxygenase, on marihuana-induced bronchodilation and tachycardia. In 11 healthy volunteers, marihuana smoking (7 mg/kg, 1.7% delta 9-tetrahydrocannabinol) produced a significant increase in specific airway conductance (from 0.262 +/- 0.033 to 0.360 +/- 0.050 s-1 X cm H2O-1, mean +/- SE, p less than 0.01), forced expiratory volume in 1 s (4.02 +/- 0.22-4.27 +/- 0.25 liter, p less than 0.05) and heart rate (73.2 +/- 2.0-108.5 +/- 5.2 beats/min, p less than 0.001). In a second session, acetylsalicylic or mefenamic acid was taken for 30 h before marihuana smoking. No inhibition of marihuana-induced increase of specific airway conductance, forced expiratory volume in 1 s and heart rate was found. These findings suggest that the bronchodilation and the tachycardia induced by marihuana smoking in humans are not mediated by prostaglandins.

Long-term physiologic outcome after acute farmer's lung

We performed a follow-up study of 61 patients who had an acute episode of farmer's lung (54 men and seven women). Twenty-four subjects had ceased all contact with the barn, while 37 had continued farming. Pulmonary function tests for all subjects showed an initial improvement after the acute episode: 92.4 +/- 36.9 percent of predicted for carbon monoxide diffusing capacity (Dco) after one year, compared to 61.5 +/- 28.5 percent at diagnosis (p less than 0.01); and 6.01 +/- 1.50 L for total lung capacity (TLC) after three years, compared to 5.35 +/- 1.42 L (p less than 0.05). Subsequently, pulmonary function decreased over time. Five years or more after the acute episode, pulmonary function tests in subjects who had continued farm work were not worse than those of subjects who had ceased contact for Dco (68.1 +/- 21.4 percent of predicted vs 80.6 +/- 27.7 percent, respectively [p greater than 0.1]) and for TLC (5.55 +/- 1.31 L vs 5.90 +/- 0.84 L [p greater than 0.2]). This study shows that during a long-term follow-up, subjects with farmer's lung who stayed on the farm have subnormal values for pulmonary function but comparable values to those who left their farm.

Absence of correlation between the degree of alveolitis and antibody levels to Micropolysporum faeni

Specific IgG antibody (Ab) levels to Micropolysporum faeni (MF) antigen were measured in three study groups: 29 farmers of whom one had acute, two chronic and 26 with a past history of Farmer's lung disease (FLD), 91 clinically asymptomatic but exposed farmers and 23 unexposed donors. This study confirms the greater sensitivity of enzyme linked immunosorbent assay (ELISA) over double immunodiffusion (DID): 34 (37%) sera negative by DID were positive by ELISA and only two (4%) were positive by DID and negative by ELISA. Antibody levels to MF were higher in the serum of farmers whether symptomatic (113.2 +/- 196.1 u) or not (25.2 +/- 64.7 u) than in that of unexposed donors (1.05 +/- 1.46 u), (P less than 0.001). In a subgroup of farmers, antibody levels were compared in the serum and bronchoalveolar lavage (BAL) fluid; the levels were higher in the serum than in BAL fluids in all farmers except the only patient with acute FLD. A significant correlation was seen between Ab levels of the serum and BAL fluids. Finally, no correlation was seen between the serum antibody levels and the total number of cells or the percentage of lymphocytes found in BAL fluids, either in the subjects with a history of FLD or the asymptomatic group.

Factors influencing the development of serum precipitins to farmer's lung antigen in Quebec dairy farmers

A total of 888 randomly selected dairy farmers participated in an epidemiological study to evaluate the prevalence of precipitins to farmer's lung antigens, and the socioeconomic factors associated with their presence. Precipitins were present in 75 farmers (8.4%) (65 to Micropolyspora faeni, seven to Aspergillus spp, two to both Aspergillus and Micropolyspora faeni, and one to Aspergillus and Thermoactinomyces vulgaris). The titres ranged from a dilution of 1/32 to a concentration of X 2 (Ouchterlony's double diffusion method). In the study population there were 544 who had never smoked, 146 ex-smokers, and 198 smokers. Sixty nine precipitin positive subjects were either never smokers or ex-smokers; only six were smokers. The negative relationship between cigarette smoking and precipitins was highly significant (p = 0.004). Factors positively associated with positive precipitin reactions were: size of farm, time spent in the barn, and the presence of a family member previously diagnosed as having farmer's lung disease. Interestingly, positive precipitin reactions were not associated with any of the following: use of silos, hay conditioners, or hay dryers; the presence or quantity of mouldy hay; or the presence of respiratory symptoms. It is concluded that precipitin analysis is not useful as a screening method for farmer's lung, though it can be of diagnostic value in acute farmer's lung disease.

Abnormal bronchoalveolar lavage in asymptomatic dairy farmers. Study of lymphocytes

Bronchoalveolar lavage (BAL) was performed on 24 asymptomatic dairy farmers. Thirteen had serum precipitins to Micropolyspora faeni (MF) antigens (Group 1), and 11 were seronegative control subjects (Group 2). All were nonsmokers and had no history of previous lung disease. Thirteen of 24 subjects (9 in Group 1 and 4 in Group 2) had a high percentage of lymphocytes (greater than or equal to 20%) in their BAL. The T-lymphocyte subpopulations as estimated by OKT3, OKT4, and OKT8 monoclonal antibody reactivity were measured in peripheral blood lymphocytes; OKT3 = 58.5 +/- 15.6% for Group 1, and 58.5 +/- 8.7% for Group 2; OKT4 = 40.6 +/- 10.7% and 39.9 +/- 10.0%; OKT8 = 21.5 +/- 10.6% and 22.4 +/- 8.0%, respectively (p = NS). These lymphocyte characteristics were also similar when subjects with a high percentage of lymphocytes in BAL were compared to those with a normal percentage. Specific (MF-coated) chicken erythrocyte lymphocytotoxicity (Group 1, 45.2 +/- 29.5%, Group 2, 49.2 +/- 23.4%), and nonspecific lymphocytotoxicity (Group 1, 43.9 +/- 28.6%, Group 2, 37.9 +/- 18.0%) were also similar. We conclude that a large number of asymptomatic dairy farmers have an increased percentage of lymphocytes in their BAL ("alveolitis") and that peripheral blood lymphocytes in these subjects have normal subpopulations, as assessed by monoclonal antibodies, and normal lymphocytotoxicity.

Quantification of the effect of gas exchange on the slope of phase III

It was previously shown that gas exchange could contribute to the rising slope of phase III of the single-breath nitrogen (SB-N2) test. This study was done to quantify this role. We studied eight normal volunteers with a series of SB-N2 derived tests where the RV gas was progressively changed from room air to 90% O2 and 10% N2, by 10% increments in O2 and 10% decreases in N2 concentrations (i.e. room air, 70% N2 30% O2, 60% N2 40% O2, etc.). A similar series of SB-R (single-breath reversed gradients test) derived tests was done. Here the RV contained 100% O2 by previous washout, while the inspired gas was changed by 105 steps from room air to 10% N2 90% O2. We therefore have a situation where dilutional N2 gradients change with the % N2, in either the RV or the inspired gas. However, the alveolar volume loss remains the same for all tests. The mean +/- SD slope of phase III in the SB-N2 series for our eight subjects decreased from 0.87 +/- 0.25 with room air to 0.14 +/- 0.07 with 10% N2 90% O2, while its steepness in the SB-R series decreased from 0.62 +/- 0.23 with the inspired room air to 0.11 +/- 0.06 with the final inspiration being 10% N2 90% O2. From these data, we could calculate that the mean % contribution of gas exchange to the slope of phase III was 10.2%.

Metabolic gas effect on phase III slopes of single-breath nitrogen tests

This study was designed to estimate the relative contribution of gas exchange to the slope of phase III and the mean respiratory quotient (R) during this maneuver. With eight normal volunteers, we studied single-breath nitrogen tests and single-breath reversed tests (SB-N2, SB-R) without and with CO2 added to the test inspiration (SB-N2CO2, SB-RCO2). With an inspired CO2 of about 6% the slope of phase III in SB-N2 and SB-N2CO2 increased from 0.87 +/- 0.24 (mean +/- SD) to 1.03 +/- 0.21% N2.l-1 (P less than 0.01); however, in SB-R an SB-RCO2 the steepness of the slope of phase III decreased from 0.65 +/- 0.13% to 0.50 +/- 0.14% N2.l-1 (P less than 0.01). From these data we can calculate that gas exchange accounted for 13% of the slope of phase III in SB-N2 and SB-R. The mean R value during the slope of phase III for this effect was between 0.6 and 0.7. R was further decreased when CO2 was added, and its influence was increased to 26% of the slope of phase III.

The role of gas exchange in phase IV of the single-breath nitrogen test

Because at the end of a prolonged expiration the respiratory quotient is less than 1, ongoing gas exchange could add to the rising N2 concentration in phase IV of the single-breath nitrogen (SB-N2) test. To verify this, 7 normal subjects performed SB-N2 and reversed gradients (SB-R) tests with and without a 20-s apnea at the onset of closing volume. In the SB-R test, the residual gas is 100% O2 and the final VC inspiration is room air. This gives a downward slope of phase IV (delta N2IV). Apnea, by prolonging total expiratory time, should increase the contribution of gas exchange and therefore increase the delta N2IV in the SB-N2 test and decrease it in the SB-R test. In the SB-N2 test, the delta N2IV increased, with the apnea, from 5.58 +/- 1.35 to 8.12 +/- 1.52 (mean +/- SD, p less than 0.01). In the SB-R test, the delta N2IV decreased from 4.31 +/- 1.65 to 1.43 +/- 1.45 (p less than 0.01). These results suggest that 10% of the N2 changes in the delta N2IV in the normal SB-N2 test may be related to gas exchange.

Contribution of residual volume to the increased alveolar plateau with bronchoconstriction

We studied 10 normal volunteers with single-breath nitrogen tests before and after methacholine-induced bronchoconstriction. On the first day we challenged each subject with increasing methacholine concentrations to obtain a 20% drop in the partial forced expired volume in 1 s/partial forced vital capacity ratio. This resulted in an increased residual volume (RV) from 1,536 +/- 138 to 2,371 +/- 216 ml (mean +/- SEM, p less than 0.01). On the following day we did single-breath nitrogen tests from RV, RV + delta V (delta V is the individual's RV increase after bronchoprovocation) and after a similar methacholine rechallenge. Baseline slope of phase III was 0.88 +/- 0.11% N2/1 (mean +/- SEM), 1.36 +/- 0.22% N2/1 with the RV + delta V test (p less than 0.01), and 2.84 +/- 0.68% N2/1 with bronchoconstriction (p less than 0.05). The results show that the changes in RV per se accounted for 24% of the increase in the slope of phase III seen with bronchoprovocation.

Contribution of gas exchange to slope of phase III of the single-breath nitrogen test

To study the influence of gas exchanges on the slope of phase III, single-breath nitrogen tests (SB-N2) and reversed tests (SB-R) were performed with 10 normal volunteers at expiratory flows of 100 ml.s-1, 500 ml.s-1,11.s-1, and 21.s-1. During the prolonged expiration required for the SB-N2 test, more O2 is consumed that CO2 eliminated. This factor could contribute to the rising slope of phase III. However, if one obtains a reversed slope of phase III (by having O2 as the residual gas and room air as the inspired gas), factors increasing N2 concentration with time of expiration should decrease the steepness of this reversed slope. Our data show that, at an expiratory flow of 100 ml.s-1, the slope of phase III was steeper in SB-N2 than in SB-R by 0.92 +/- 0.31% N2 1-1 (mean +/- SD, p less than 0.01). As the expiratory flow was increased to 500 ml.s-1, this difference decreased to 0.33 +/- 0.19% N2 1-1, and both slopes became similar in magnitude but opposite in direction at an expiratory flow of 1 1.s-1. These data suggest that active gas exchange has a significant influence on the slope of phase III of the SB-N2 test.

The influence of active gas exchange on the slope of phase III at rest and after exercise

Because exercise increases the slope of phase III of the single-breath nitrogen (SB-N2) test in normal persons, we hypothesized that this increase might be due to increased O2 consumption. During the prolonged expiration implicit in the SB-N2 test, the amount of O2 absorbed is greater than the amount of CO2 eliminated. The decrease of gas in volume and the proportional increase in N2 concentration that result might, therefore, increase the slope of phase III, even at rest, but much more after exercise. To test this hypothesis, we had 10 normal volunteers perform SB-N2 tests and reversed SB-N2 tests (SB-R) before and after graded bicycle ergometer exercises. The SB-R test yielded a negative slope for phase III; however, an increasing N2 concentration during prolonged expiration tended to flatten this slope. At rest, the positive slope of phase III for the SB-N, test was steeper than the negative slope of phase III in the SB-R test by a mean +/- SD of 0.23 +/- 0.05% N2/L. After exercise, the slope of phase III of the SB-N2 test increased, while that of the SB-R showed no change. These data suggested that active gas exchange, rather than mechanical factors, is responsible for the increased slope of phase III after exercise. The data also raised the possibility that the slope of phase III at rest is partly the result of gas exchange.

[Influence of sequential breath-holding on the slope of phase III (author's transl)]

Many factors contribute to the slope of phase III of the single-breath nitrogen test (SB-N2). By its effect of nitrogen concentrations, alveolar oxygen exchange may be responsible for a fraction of this slope. In fact, the slope of phase III is steeper when expiratory time is prolonged. We studied the effect of two sequential breath-holding periods of 20 seconds each with ten healthy young male volunteers, by SB-N2 and a reverse technique (SB-R). We observed a sudden increase (mean 1.27%) in the expired nitrogen concentration after each breath-holding period. Closing volume remained the same in all tests, but the slope of phase IV decreased by 44% in SB-N2A (SB-N2 with breath-holding) and increased by 55% in SB-RA. Expiratory vital capacity was significantly less after breath-holding. These data suggest that gas exchange during expiration is partly responsible for the slope of phase III.