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PubMed2003

Toxicity comparison of biosurfactants and synthetic surfactants used in oil spill remediation to two estuarine species.

The relative environmental toxicities of synthetic and biogenic surfactants used in oil spill remediation efforts are not well understood. Acute and chronic toxicities of three synthetic surfactants and three microbiologically produced surfactants were determined and compared in this study for the estuarine epibenthic invertebrate, Mysidopsis bahia and the inland silverside, Menidia beryllina. The toxicities of the surfactant were determined in standard laboratory static and static-renewal tests of 4-7 d duration. Results were specific to the surfactant, response parameter and test species. The LC50 values (nominal concentrations) for M. bahia ranged from 3.3 mg/l (Triton X-100) to >1000 mg/l (PES-61) and 2.5 mg/l (Triton X-100) to 413.6 mg/l (PES-61) for M. beryllina. Chronic first-effect concentrations (mg/l) for the six surfactants ranged from 2.3 to 465.0 (M. beryllina) and 1.0 to >1000.0 (M. bahia) based on reductions in growth and fecundity. Few generalizations could be made concerning the results due to their variability but M. bahia was generally the more sensitive species and the toxicities of the biosurfactants were intermediate to those of the synthetic surfactants.

Animals↗

PubMed1975

Considerations of delta 5-pregnenediol formation in ovarian tissue.

20Alpha-Hydroxypregn-4-ene-3-one (20alpha-DHP) in ovarian tissue could be formed directly from progesterone (Pathway 1) or from pregnenolone via a delta 5-intermediate, pregn-5-ene-3beta, 20alpha-diol (Pathway 2). The participation of Pathway 2 is demonstrated to the extent that pregnenediol can be formed from pregnenolone and that the delta 5-diol, in turn, can be a precursor to 20alpha-DH P in vitro, using ovarian tissue from cycling rats by both flask incubation and superfusion techniques. Pathway 2 would allow greater flexibility and local regulation with respect to potential steroid sulfate conjugates of delta 5-3beta-OH intermediates. The existence of two pathways leading to 20alpha-DH P could explain the occurrance of variable levels of this steroid without a necessary direct or inverse relationship to progesterone secretion levels at different stages of the estrous cycle.

Animals↗

PubMed2000

Exercise and oral contraceptive use suppress the normal age-related increase in bone mass and strength of the femoral neck in women 18-31 years of age.

Women who exercise during their second and third decades may increase their peak bone mass and lower their eventual risk for postmenopausal fracture. However, the effects of exercise in younger women can be modulated by the use of oral contraceptives, which may prevent the normal accretion of bone mass that would otherwise occur. We hypothesized that exercise intervention in young adult women would significantly increase both bone mass and the bending rigidity of the femoral neck. We further hypothesized that exercise intervention in the presence of oral contraceptive use would have a negative effect on bone mass and bending rigidity. Women 18-31 years of age (n = 123) were classified by oral contraceptive use (OC, NOC) and age (18-23, 24-31 years), and then randomized into exercise or nonexercise groups. The exercise protocol consisted of three sessions/week of aerobic and nonaerobic exercises, and continued for 2 years. Each 6 months, the femoral neck of each subject was scanned using a Lunar dual-energy X-ray absorptiometry (DEXA) scanner, and bone mineral content, density and geometric information were used to calculate estimated stresses and bending rigidity at the hip. Percent changes from baseline were analyzed using two-way analysis of variance (ANOVA) at 6, 12, 18, and 24 months. Women who neither exercised nor took oral contraceptives (NE/NOC) had the greatest percentage increases in cross-sectional area (4.98 +/- 2.29%), cross-sectional moment of inertia (9.45 +/- 2.37%), total bone mineral density (2.07 +/- 2.09%), fracture index (8.03 +/- 2.03%), and safety factor (20.03 +/- 5.79%) over the 24 month exercise program. Women who exercised and did not take oral contraceptives (E/NOC) declined on most variables related to femoral strength and bone mass, whereas those women who took oral contraceptives were usually intermediate between NE/NOC and E/NOC, whether they exercised or not. These data show that either exercise or OC use is associated with a suppression of the normal increase in bone mass and mechanical strength in the femoral neck in women 18-31 years old, but the combination of exercise and OC use appears to have a less suppressive effect.

Absorptiometry, Photon↗

PubMed2005

Mechanism of white phosphorus activation by three-coordinate molybdenum(III) complexes: a thermochemical, kinetic, and quantum chemical investigation.

White phosphorus (P(4)) reacts with three-coordinate molybdenum(III) trisamides or molybdaziridine hydride complexes to produce either bridging or terminal phosphide (P(3)(-)) species, depending upon the ancillary ligand steric demands. Thermochemical measurements have been made that place the MoP triple bond dissociation enthalpy at 92.2 kcal.mol(-)(1). Thermochemical measurements together with computational analysis rule out simple P-atom abstraction from P(4) as a step in the phosphorus activation mechanism. Kinetic measurements made by the stopped-flow method show that the reaction between the monomeric molybdenum complexes and P(4) is first-order both in metal complex and in P(4). Cyclo-P(3) complexes can be obtained when ancillary ligand steric demands are small, but kinetic measurements rule them out as monometallic intermediates in the P(4) activation mechanism. Also studied by calorimetric, kinetic, and in one case variable-temperature NMR methods is the process of mu-phosphide bridge formation. Post-rate-determining steps of the P(4) activation process were examined in a search for minima on the reaction's potential energy surface, leading to the proposal of two plausible, parallel, bimetallic reaction channels.

Journal Article↗

PubMed2000

New function for NF1 tumor suppressor.

The expression and subcellular localization of neurofibromatosis type 1 tumor suppressor was studied in keratinocytes induced to differentiate by increased Ca2+ concentration of the culture medium. Differentiating keratinocytes became intensely immunoreactive for neurofibromatosis type 1 protein, which was apparently associated with cellular fibrils. Double immunolabeling with antibodies to cytokeratin 14 and neurofibromatosis type 1 protein suggested an association of intermediate type cytoskeleton and neurofibromatosis type 1 protein. The presence of neurofibromatosis type 1 protein in cell preparations treated with cytoskeletal buffer indicated a high affinity interaction between intermediate filaments and neurofibromatosis type 1 protein. Further studies utilizing double immunolabelings revealed that the intense neurofibromatosis type 1 tumor suppressor signal on intermediate filaments was temporally limited to the period in keratinocyte differentiation in which the formation of desmosomes takes place. Keratinocytes were also cultured from nine patients with type 1 neurofibromatosis and were studied with respect to cell morphology, and association of neurofibromatosis type 1 protein with intermediate cytoskeleton. The results showed that keratinocytes cultured from patients with neurofibromatosis type 1 displayed a highly variable cell size and morphology compared to controls. The latter findings represent predicted alterations in a situation where cytoskeletal organization is disturbed. Furthermore, differentiating neurofibromatosis type 1 keratinocytes were characterized by a reduced number of cytokeratin bundles that were decorated neurofibromatosis type 1 protein. The results of this study suggest that neurofibromatosis type 1 tumor suppressor exerts its effects in part by controlling organization of cytoskeleton during the formation of cellular contacts.

Adult↗

PubMed1991

Calculation of protein conformation as an assembly of stable overlapping segments: application to bovine pancreatic trypsin inhibitor.

Conformations of bovine pancreatic trypsin inhibitor were calculated by assuming that the final structure as well as properly chosen overlapping segments thereof are simultaneously in low-energy (not necessarily the lowest-energy) conformational states. Therefore, the whole chain can be built up from building blocks whose conformations are determined primarily by short-range interactions. Our earlier buildup procedure was modified by taking account of a statistical analysis of known amino acid sequences that indicates that there is nonrandom pairing of amino acid residues in short segments along the chain, and by carrying out energy minimization on only these segments and on the whole chain [without minimizing the energies of intermediate-size segments (20-30 residues long)]. Results of this statistical analysis were used to determine the variable sizes of the overlapping oligopeptide building blocks used in the calculations; these varied from tripeptides to octapeptides, depending on the amino acid sequence. Successive stages of approximations were used to combine the low-energy conformations of these building blocks in order to keep the number of variables in the computations to a manageable size. The calculations led to a limited number of conformations of the protein (only two different groups, with very similar structure within each group), most residues of which were in the same conformational state as in the native structure.

Amino Acid Sequence↗

PubMed2005

Phylogeographic inferences concerning evolution of Brazilian Passiflora actinia and P. elegans (Passifloraceae) based on ITS (nrDNA) variation.

BACKGROUND AND AIMS: Passiflora actinia and P. elegans, two markedly parapatric species, have their southern and northern distribution limits, respectively, in the most southern part of the Brazilian Atlantic Rain Forest. Despite the fact that they are classified in different taxonomic series, previous phylogenetic studies of this genus revealed a high genetic similarity between them. The aim of the present work was to analyse in more detail their geographical range in this region of overlap, to investigate intraspecific genetic variability and phylogeographic structure, and to search for possible hybrids. METHODS: Eighty-two localities were searched for these species, and nuclear internal transcribed spacer (ITS) sequences were investigated for 32 individuals of P. actinia, 20 of P. elegans and one putative interspecific hybrid. Plastid trnL-trnF and psbA-trnH were examined for 12 plants of each species and the putative hybrid. KEY RESULTS: Both species showed a high level of intraspecific and intra-individual ITS variability. Network analysis revealed a north-south geographic gradient in their intra and interspecific relationships. Mismatch analyses suggested a recent population expansion of P. elegans. The plastid markers showed restricted variability but, together with the nuclear data, they contributed to the identification of an interspecific hybrid of intermediate morphology at the border of the distribution of these two species. Both genetic and morphological data indicate the absence of an extensive hybridization zone between these species. CONCLUSIONS: Gene flow between lineages is the possible cause for the presence of different ITS sequences within a given plant, the absence of homogenization being due to the high degree of vegetative reproduction in the two species. Differentiation of P. actinia into geographic groups and the origin of P. elegans may have been influenced by the Atlantic Forest migration towards southern Brazil. The genetic pattern of the interspecific hybrid indicates that plastid inheritance in these species is at least sometimes paternal.

Base Sequence↗

PubMed1996

Pituitary-testicular axis in men with beta-thalassaemia major.

Delayed puberty and hypogonadism are frequently observed in patients with homozygous beta-thalassaemia. We evaluated the pituitary-testicular axis in 30 thalassaemic men, aged from 17 to 35 years who were regularly transfused and underwent chelation therapy, while emphasis was given to pituitary reserves of gonadotrophins and the correlation of hormones with serum ferritin (SF). The investigation included endocrinological examination, evaluation of serum basal levels of follicle stimulating hormone (FSH), luteinizing hormone (LH), free testosterone and gonadotrophin-releasing hormone (GnRH) test and also spermiograms. According to the results, patients were divided into three groups: group A, which included 18 eugonadal patients with moderately elevated SF, group B which included six patients who had hypogonadotrophic hypogonadism and excessive elevation of SF, and group C, which included six patients characterized as intermediate, with regard to sexual maturation and SF levels. In conclusion, beta-thalassaemia major leads to variable pituitary iron overload and thus hypophyseal damage. This endocrine disturbance is becoming less frequent nowadays with early and intensive chelation therapy.

Adolescent↗

PubMed1985

Potential of a quantal response as a mechanism for oscillatory behavior: implications for our concepts of hormonal control mechanisms.

This article describes the potential of a quantal (i.e., all-or-none) response as a model for understanding the interactions between endocrine, paracrine and autocrine hormones. We review the general features of continuous and discontinuous (i.e., oscillating) quantal models including the role of a threshold. In addition, we also describe a few of the many different biochemical mechanisms which may give rise to quantal behavior. One of the more attractive schemes involves the coordinate regulation of opposing biochemical pathways resulting from phosphorylation of hormone receptors and/or rate-limiting enzymes. At least one hormone receptor (i.e., that for insulin) and many rate-limiting enzymes which control the flow of metabolites through a variety of metabolic pathways can be phosphorylated at multiple sites by one or more protein kinases. Phosphorylation may enhance or inhibit the activities of these proteins depending on which sites are modified. Furthermore, since phosphorylation of some sites on a protein may enhance the ability of phosphoprotein phosphatases to dephosphorylate other sites responsible for biological activity of the protein, phosphorylation also has the potential to produce a discontinuous quantal response. Quantal response mechanisms may alter our notions of endocrine regulation. When a quantal response mechanism is applied to a simple negative feedback model similar to that which was originally postulated to explain the interactions between gonadotropin and steroid hormonal levels, the model can account for the oscillations in hormone levels even when the input is constant. Conversely, when a graded mechanism is applied to the same negative feedback model, the model will almost certainly result in constant hormone levels. Further, the model illustrates that small changes in rate constants and thresholds of response, amplification of hormonal signals, and degradation of intermediate regulators can produce large shifts in the output of the system. These may account for the variability in hormonal levels observed in some endocrine systems. Finally, the high sensitivity of the quantal response mechanism accounts for the data which suggest that gonadotropins may play permissive rather than causal roles in regulation of gonadal function. Since increasing evidence suggests that all cells of a given type may not be equal in terms of hormonal responsiveness, measurements of response in single cells over short time periods will be needed before the role of a quantal response can be determined and endocrine regulation will be fully understood.

Animals↗

PubMedDate not supplied

Epileptic encephalopathies with myoclonic seizures in infants and children (severe myoclonic epilepsy and myoclonic-astatic epilepsy).

Myoclonic attacks are not characteristic of a specific syndrome. In infancy and early childhood, they are often observed in the context of syndromes that are associated with other types of seizures and with cognitive impairment but no obvious brain lesion. Characterization of the associated seizures and age of expression allows inclusion of a number of cases in two main subgroups: severe myoclonic epilepsy (SME, or Dravet syndrome) and myoclonic-astatic epilepsy (MAE). Severe myoclonic epilepsy is an epileptic encephalopathy with invariably poor outcome in which myoclonic seizures, though frequently observed, may be absent altogether in some children. Prolonged and repeated febrile and afebrile convulsive seizures starting in infancy are the main feature and are probably causally related to cognitive decline. One third of children harbor mutation of the SCN1A gene, but the genetics of SME is probably more complex than expected with simple monogenic disorders. Treatment is usually disappointing. Myoclonic-astatic epilepsy is perhaps more a conceptual category of idiopathic myoclonic epilepsy than a discrete syndrome. Childhood-onset myoclonic-astatic attacks are the characteristic seizures associated in most with episodes of nonconvulsive status and generalized tonic-clonic seizures. Outcome is unpredictable. Either remission within a few years with normal cognition or long-lasting intractability with cognitive impairment is possible. Likewise, the effectiveness of antiepileptic drugs is variable. A number of cases of myoclonic epilepsies in infancy and early childhood, however, remain unclassified, and intermediate forms between the different syndromes exist. They must be distinguished from other syndromes with frequent brief attacks and repeated falls, especially the Lennox-Gastaut syndrome. This differentiation is often difficult and may require extensive neurophysiologic studies.

Age Factors↗

PubMed2005

Coherence resonance in an atmospheric global circulation model.

Numerical evidence is presented of a coherence-resonant behavior, induced on an atmospheric global circulation model by a white (in time and space) additive Gaussian noise with amplitude A << 1 . Intermediate A values enhance the spatiotemporal regularity of vortical patterns that contribute to the intra-annual variability of the atmospheric component of the climate. Only weak patterns (those appearing in the summer hemisphere) become ordered by noise.

Journal Article↗

PubMed1995

Results of long-term deferiprone (L1) therapy: a report by the International Study Group on Oral Iron Chelators.

This report updates the combined experience of four centres involved in the long-term treatment of transfusional iron overload in 84 patients with the oral iron chelator deferiprone (L1) over 167 patient-years. The source of L1 was variable, including two university research laboratories and three pharmaceutical firms. Compliance was rated as excellent in 48%, intermediate in 36%, and poor in 16% of patients. On a mean L1 dose of 73-81 mg/kg/d, urinary iron excretion was stable, at around 0.5 mg/kg/d, with no indication of a diminishing response with time. Serum ferritin showed a very steady decrease with time from an initial mean +/- 1 SD of 4207 +/- 3118 to 1779 +/- 1154 micrograms/l after 48 months (P < 0.001). 17 patients abandoned L1 therapy. Major complications of L1 requiring permanent discontinuation of treatment included agranulocytosis (three), severe nausea (four), arthritis (two) and persistent liver dysfunction (one). The remaining patients abandoned treatment because of low compliance (three) and conditions unrelated to L1 toxicity (four). Lesser complications permitting continued L1 treatment included transient mild neutropenia (four), zinc deficiency (12), transient increase in liver enzymes (37), moderate nausea (three) and arthropathy (17). There was no treatment-related mortality. Although the complications associated with L1 treatment are significant and require close monitoring, they do not preclude effective long-term therapy in the vast majority of patients. Further well-controlled prospective studies of L1 are required in order to enable proper judgement of its suitability for general long-term clinical use.

Adult↗

PubMed2005

Properties of antiepileptic drugs in the treatment of idiopathic generalized epilepsies.

Although valproate is considered to be the drug of first choice for the treatment of idiopathic generalized epilepsies (IGEs), other antiepileptic drugs (AEDs), both old (ethosuximide, clobazam, and clonazepam) and new (lamotrigine, levetiracetam, topiramate, and zonisamide) are also available. These AEDs do not appear to have a common mechanism of action in that both inhibitory gamma-aminobutyric acid (GABA; e.g., clobazam, clonazepam, and valproate) and excitatory glutamate (e.g., lamotrigine and topiramate) mechanisms are involved. Ethosuximide primarily acts by blocking T-type voltage-gated calcium channels in thalamic neurones while topiramate and zonisamide have multiple mechanisms of action. In contrast, levetiracetam is unique in that it may act via a specific binding site in the brain. In terms of their pharmacokinetic characteristics, all eight AEDs are rapidly absorbed after oral ingestion with peak blood concentration being achieved within 1-4 hours. Bioavailability is 100% with the exception clonazepam (90%) and topiramate (81-95%). Plasma protein binding is variable with valproate (90%), clobazam (85%) and clonazepam (86%) showing substantial binding, lamotrigine (55%) and zonisamide (50%) intermediate binding, and levetiracetam (0%), ethosuximide (0%) and topiramate (10%) being minimally bound. However, the binding by zonisamide is complicated by its binding to erythrocytes as well as albumin. All AEDs, with the exception of lamotrigine and levetiracetam, undergo elimination as a result of extensive metabolism by hepatic cytochrome P450 enzymes, which are highly amenable to induction and inhibition by other drugs and therefore susceptible to pharmacokinetic interactions. Lamotrigine metabolism is via hepatic glucuronidation, a process that is also susceptible to induction and inhibition by concurrent drugs. Levetiracetam is minimally metabolized (by hydrolysis in blood), is excreted predominantly unchanged in urine, and to date has not been associated with any clinically significant pharmacokinetic interactions. Using a semiquantitative pharmacokinetic rating system, based on 16 pharmacokinetic characteristics, a direct comparison between AEDs is possible. Thus valproic acid, regarded as the drug of first choice in the treatment of IGEs, rates lowest with respect to favorable pharmacokinetic characteristics, mostly because of its nonlinear pharmacokinetics, extensive hepatic metabolism, and its high propensity to interact both with other AEDs and non-AEDs. Levetiracetam rates highest with topiramate in second place.

Anticonvulsants↗

PubMed1977

Correlations between serum ami- and nortriptyline concentrations and psychomotor performance.

Correlations of serum nortriptyline (NT) and amitriptyline (AT) levels with psychomotor performance choice reaction performance, eye-hand coordination, and divided attention was studied in two experiments each with 20 healthy subjects. In the first experiment serum NT level was measured with an isotope derivative method after treatment for 14 days with NT. In the second trial plasma AT and NT concentrations were measured with gas-chromatography after treatment for 14 days with AT. No linear correlations between the levels of the antidepressants and performance variables were found. Low levels of NT (less than 50 ng/ml) tended to shorten reaction time, and intermediate levels (50--80 ng/ml) to prolong it, when compared with the reaction times during placebo. The correlation between serum NT levels and the increase of the tyramine dose in the tyramine pressor test was not significant. A new assay method for AT and NT is presented.

Adult↗

PubMed1996

Predictors of smoking among male junior secondary school students in Riyadh, Saudi Arabia.

OBJECTIVE: To determine the prevalence and determinants of cigarette smoking among intermediate (junior secondary) schoolboys in Riyadh, Saudi Arabia. PARTICIPANTS: A sample of 1382 students (ages 12-19 years) in 45 classes randomly selected from 15 schools, using a two-stage stratified cluster sampling scheme. DESIGN: Students in the selected classes were requested to complete an anonymous questionnaire, under the supervision of trained interviewers. Univariate and multivariate statistical analyses of potential risk factors were performed. SETTING: Intermediate schools in Riyadh, Saudi Arabia. MAIN OUTCOME MEASURES: Association between current smoking and socio-demographic variables, history of smoking, age of smoking initiation, smoking behaviour among family members, knowledge of the harmful effects of smoking, and whether smoking is allowed in the presence of relatives and acquaintances. RESULTS: The prevalence of current smokers was 13.2% overall, ranging from 3.2% in those 12-13 years old to 31.1% in those aged 18-19. Some of the variables (nationality, father's education, and smoking allowed in the presence of parents or teachers) found to be associated with current smoking in a univariate analysis were no longer significantly associated with smoking in the multivariate analysis. By multivariate analysis, knowledge of the harmful effects of smoking, age, smoking allowed in the presence of friends or brothers, and previous smoking were statistically significant determinants of current smoking. CONCLUSIONS: Current health education activities against smoking should be continued and extended to the young population to further reduce the prevalence of smoking and its health consequences. Religious antipathy toward smoking should be emphasised in any local anti-smoking campaigns.

Adolescent↗

PubMedDate not supplied

Use of sentinel node lymphoscintigraphy in malignant melanoma.

Lymphoscintigraphy is a sensitive, inexpensive, relatively noninvasive method of identifying lymphatic drainage patterns and sentinel lymph nodes in patients with malignant melanoma. Lymphoscintigraphy with filtered technetium-99m sulfur colloid allows prompt visualization of the lymphatic system, produces high-quality images, and delivers a low radiation dose to the patient. In addition, good regional lymph node retention is seen with filtered Tc-99m sulfur colloid, improving the success rate of intraoperative gamma probe localization. In combination with surgical localization, lymphoscintigraphy allows preoperative and intraoperative identification of the sentinel node in patients with intermediate thickness melanomatous lesions, obviating radical lymph node dissection in most patients and possibly prolonging their survival. Variables such as tumor location, type and preparation of radiopharmaceutical, injection technique, imaging technique, and prior surgical intervention influence the efficacy of lymphoscintigraphy. Nevertheless, lymphoscintigraphy is recommended as a cost-effective preoperative procedure in all patients planning to undergo elective lymph node dissection. Because of the unpredictability of lymphatic drainage, preoperative scintigraphic findings may lead to changes in surgical management.

Animals↗

PubMed1983

X-ray microanalysis of uremic nephrocalcinosis.

The nature of uremic nephrocalcinosis was studied by means of X-ray microanalysis in 5/6 nephrectomized rats. The data show that calcified deposits in the renal parenchyma of uremic rats contained substantial amounts of calcium, magnesium, aluminum and silicon. Since calcificates did not reveal a uniform composition they were arbitrarily divided into 3 categories: 'high-calcium' with Mg:Al:Si: Ca molar ratios 7:3:8:37; 'low-calcium' particles were characterized by Fe:Mg:Al:Ca:Si molar ratios 7:3:5:6:13; while 'intermediate-calcium' particles showed Al:Mg:Si:Ca molar ratios equivalent to 2:4:6:7. The variability of calcified deposits in the renal parenchyma of 5/6 nephrectomized rats might be due to different sources, different environmental conditions along the nephron and different stages of calcification process. It is suggested that aluminum and silicon content of deposits may be of value in further characterization of uremic nephrocalcinosis.

Aluminum↗

PubMed1985

Nitrogen washout during tidal breathing with superimposed high-frequency chest wall oscillation.

In order to assess the efficacy of high-frequency chest wall oscillation (HFCWO) superimposed on tidal ventilation, multiple-breath nitrogen washout curves were obtained in 7 normal seated subjects. To maintain a regular breathing pattern throughout the study, the subjects breathed synchronously with a Harvard ventilator set at a constant tidal volume and frequency for each subject during a trial period. Washout curves were obtained during 3 different maneuvers performed in random order. Series A was the control condition with no superimposed HFCWO. In Series B and C, HFCWO at 5 Hz was superimposed on the regulated tidal breathing; the magnitude of the oscillatory tidal volume measured at the airway opening was 20 ml for Series B and 40 ml for Series C. The nitrogen washout was clearly faster in Series C than in Series A for each subject. In Series B, there was an interindividual variability, with a washout rate either equal to that in Maneuver A or in Maneuver C, or intermediate between the two. When these washout curves were analyzed in terms of a simple monocompartment model, the time constant of the washout was found to decrease by 16 +/- 11% in Series B, and 25 +/- 7% in Series C compared with that in Series A. In this group of normal subjects, the correction of any inhomogeneity in the distribution of the ventilation is unlikely to explain these results because of the close fit of all washout curves to a monoexponential model. It is postulated that during inspiration HFCWO enhances gas mixing in the lung periphery and that during expiration it improves gas mixing in the airways.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗