Transplacental infection with Japanese encephalitis virus

During a widespread epidemic of Japanese encephalitis, five pregnant women affected by the illness were observed. The diagnosis of Japanese encephalitis virus (JEV) infection was established on the basis of clinical presentation, rising titers of hemagglutination-inhibiting antibody, and the presence of specific IgM antibodies. Two women aborted, two were delivered of apparently normal children, and the fate of one case is not known. From brain, liver, and placental tissues of one of the aborted fetuses, JEV was isolated. This appears to be the first report of human transplacental infection with JEV.

Mechanism of 3' to 5' exonuclease associated with phage T5-induced DNA polymerase: processiveness and template specificity

T5-induced DNA polymerase has an associated 3' to 5' exonuclease activity. Both single-stranded and duplex DNA are hydrolyzed by this enzyme in a quasi-processive manner. This is indicated by the results of polymer-challenge experiments utilizing product analysis techniques. Due to the quasi-processive mode of hydrolysis, the kinetics of label release from the 3'-terminally labeled oligonucleotide substrates, annealed to complementary homopolymers, show an initial high rate of hydrolysis. In the case of both single-stranded and duplex DNA substrates, hydrolysis seems to continue, at best, up to the point where the enzyme is five or six nucleotides away from the 5-end. The enzyme carries out mismatch repair, as evidenced by experiments with primer molecules containing improper base residues at the 3'-OH terminus. Control experiments with complementary base residues at the 3'-end indicate that extensive removal of terminal residue takes place in the presence of dNTP's only when such residues are "improper" in the Watson-Crick sense.

Amniotic fluid lipids in sickle cell disease

Amniotic fluid of sickle cell disease patients past the thirty-seventh week of pregnancy contained 63.4%, 71.7%, and 48.6% less total lipids, total nonpolar lipids, and total phospholipids, respectively, as compared with amniotic fluid of normal patients. No remarkable variation in the composition of nonpolar lipids was noticed between the two groups. However, the phospholipid composition was significantly varied. For example, the percentage amounts of choline glycerophospholipids (lecithin) was low and the percentage amounts of other phospholipids was high in sickle cell pregnancy as compared with normal pregnancy. Furthermore, increased levels of polyunsaturated fatty acids and fluorescent lipid pigments were found in amniotic fluids of sickle cell patients.

Ventricular wall thickness: a predictor of response to vasodilators in cardiomyopathy

The effect of chronic adjunctive vasodilator therapy was assessed in 14 symptomatic patients with idiopathic cardiomyopathy. Thirteen of the 14 patients improved by one or more in the New York Heart Association functional class, one remained unchanged. Three became asymptomatic (class I). Noninvasive and invasive (hemodynamic) parameters before and after vasodilators were assessed. The echocardiographic findings of septal and posterior wall thickness of 1.2 cm or greater were the best predictors of good response in our patients who subsequently became asymptomatic.

The effects of acute focal cerebral ischemia on digoxin toxicity and pharmacokinetics

24 h after ligation of the left middle cerebral artery in cats (sham operation in the control group), a constant intravenous infusion of digoxin was begun and continued to toxicity (ventricular rhythm) and death. We found that the lethal dose of digoxin was significantly less in the stroke group than in the control group, but the lethal plasma digoxin concentration was significantly greater in the stroke group than in the control group. In a subsequent study, we demonstrated that ischemic stroke caused a significant prolongation in the elimination half-life of digoxin and an increase in the volume of distribution. The mean plasma clearance of the stroke group was approximately three fourths of that of the control group. We concluded that the decreased tolerance to digoxin after ischemic stroke was due to the prolonged half-life and decreased clearance of digoxin.

Echocardiographic diagnosis of a right ventricular metastatic tumor

Clinical and echocardiographic studies were done in a patient with a secondary right ventricular tumor. Stationary cardiac tumors produce differential diagnostic problems not associated with mobile cardiac tumors. In spite of limitations of specificity, positive diagnostic features do exist. This report emphasizes the usefulness as well as technical difficulties in assessing the presence of a secondary right ventricular tumor echocardiographically.

Comparative study of red cell enzymes in Mirpur (a Portuguese-descendant community) and a neighbouring Hindu population of Gopalchak

Five enzyme systems (ACP1, PGM1, MDH, LDH and EsD) have been studied in Mirpur and Gopalchak. The allele PGM13 is present in polymorphic frequency in Mirpur. In respect of ACP1 and PGM1 loci, these two populations differ significantly.

Superoxide dismutase, glutathione peroxidase, catalase and lipid peroxidation of normal and sickled erythrocytes

Sickled erythrocytes showed reduced glutathione peroxidase and catalase activities in comparison to normal erythrocytes. In addition, increased levels of superoxide dismutase and 'peroxidation potential' as well as fluorescent lipid pigments and malonaldehyde suggestive of membrane lipid peroxidation were found in sickled erythrocytes. Finally, sickled erythrocytes showed membrane 'bound' Heinz bodies as well as reduced membrane lipids and unsaturated fatty acids. From these observations, it is suggested that membrane lipid peroxidation occurs in sickled cells.

Microlymphatic surgery in management of lymphoedema of the upper limb

Microlymphatic surgery is a recent addition to the range of surgical procedures for lymphoedema. Lymphaticovenous anastomosis is the most direct approach to the basic cause of obstructive lymphoedema bypassing the obstruction of the axilla or groin. With increased experience the overall results have improved and, in selective cases, segmental reduction is carried out either at the same operation or at a later date. Microlymphatic surgery in conjunction with segmental reduction of the upper arm is aesthetically and functionally most acceptable. The most significant effect of lymphaticovenous anastomosis in relieving the lymphoedema of the upper limb is over the dorsum of the hand and lower forearm. At least two, or more if possible, lymphaticovenous anastomoses are required for effectiveness of the procedure. Besides subjective and objective improvement in the lymphoedema there is significant reduction in frequency of cellulitis following lymphaticovenous anastomoses. The technique, along with the results and follow-up over 5 years is presented.

Improving results in orbital hypertelorism correction

Between 1971 and 1977, 40 patients with orbital hypertelorism were operated on by the craniofacial team in Toronto. Results have improved as a result of this experience. Tomography in two planes has revealed four types of medial orbital wall deformity. Cephalographs proved inadequate to understand this three-dimensional problem. Mobilization of the orbits and their correct realignment, with removal of the precise amount of interorbital bone, are only preliminary steps in producing good results. Different techniques for reattachment of the medial canthal ligament, correct orientation of the lateral canthus, changes in methods of nasal excision, and the elimination of other facial or eyelid scars are helping to produce more normal looking patients. Simultaneous major intraoral procedures have been the greatest source of complications. Limitation of this surgery to one team has given sufficient experience to enable a diminution in morbidity and a halving in blood loss and time taken for the operation.

Processiveness of DNA polymerases. A comparative study using a simple procedure

In this communication, we describe a simple procedure for analyzing the processiveness of DNA polymerases in general. By choosing conditions for which the number of incorporations per available primer is less than 1, we have reduced the probability of a primer molecule being utilized by the enzyme more than once. The primer-template used was poly(dA)300:oligo(dT)10, and the product was isolated by oligo(dT)-cellulose chromatography. The number of dTMP residues added per association was determined from the [3H]dThd + [3'-3H]dTMP/[3H]dThd ratio of the product after its digestion by micrococcal nuclease and spleen phosphodiesterase. Using this procedure, we have found that Escherichia coli DNA polymerase I, T4 DNA polymerase, and calf thymus alpha- and beta-DNA polymerase are "quasi-processive." Most of these enzymes add on the average approximately 10 to 15 nucleotides before dissociating from the template. T5 DNA polymerase, on the other hand, is processive, i.e. it continues to replicate a given template until it is very close to the 5' end of the template. With "nicked DNA-like" poly(dA):oligo(dT), the processiveness of E. coli DNA polymerase I is increased 2- to 2.5-fold. The significance of this increase in determining the "patch size" during DNA repair is discussed.

Geriatric medicine: model for computer-oriented research analysis

It is important to have accurate information derived from basic data about geriatric patients, not only for clinical management but to anticipate changes in the demand for services and the taking of preventive action. A model is presented for computer-oriented analysis. The collection of data is designed to cover the specific physical, physiologic and social needs of the patients both in the hospital and in the community. It must also support effective action about these needs which involve not only usage of existing facilities but the planning of preventive measures and adjustment of the provision for care. In addition, it must support clinical research when necessary. Geriatric records have specific problems, not only those of the patient's identity and clinical data but also the maintenance of psychologic and social information so that the requirements for long-term care can be assessed. This type of record facilitates comparison between groups of patients and allows measurement of inter-hospital performance relating to medical care and the planning of social programs in the community. Such records furnish the background of a more detailed statistical analysis for indicating the direction of national policy. By this means the prevalence of medical, psychologic and social demand can be studied and various preventive actions taken, including the monitoring of geriatric facilities.

Chronic inflammatory bowel disease in Asian immigrants

Chronic inflammatory bowel disease occurs sporadically among the immigrant Asian population in Britain, but information about the incidence and clinical features is lacking. We therefore report our experience of 13 patients seen in a gastrointestinal unit in Birmingham over the past 12 years.

Composition of lipids of bovine optic nerve

Lipids from bovine optic nerve were analyzed. The total content of 16.5% by weight included 27.2% nonpolar lipids, 26.1% glycolipids, and 46.7% phospholipids by weight. Free cholesterol was the major component of the nonpolar lipid fraction. The cerebrosides, 73.5% of total glycolipids, were separated by thin layer chromatography (TLC) into two bands (upper and lower) that were present in equal proportion. Cerebroside sulfates comprised about 27.5% of total glycolipids. Gangliosides were also detected in the glycolipid fraction. In order of predominance, choline glycerophospholipids, ethanolamine glycerophospholipids, ethanolamine plasmalogens, serine glycerophospholipids, sphingomyelins, and inositol glycerophospholipids were the major phospholipids. Palmitoyl (16:0), stearoyl (18:0), and oleoyl (18:1) groups were the major acyl groups in all neutral and phospholipid classes. However, ethanolamine glycerophospholipids, serine glycerophospholipids, and inositol glycerophospholipids contained a large percentage of 22:6 (docosahexaenoyl) group. The major alk-1-enyl groups of the plasmalogens were 16:0, 18:0, and 18:1. Steroyl (18:0), lignoceroyl (24:0), and nervonoyl (24:1) were the major acyl groups in all sphingolipids. Lower cerebroside band and cerebroside sulfates contained large amount of hydroxylignoceroyl (cerebronoyl) and hydroxynervonoyl groups.

Placental enzyme polymorphism among Maharashtrians: alkaline phosphatase and lactate dehydrogenase

The distribution of placental alkaline phosphatase and lactate dehydrogenase types in 635 placentas from various endogamous groups of Maharashtra have been studied by starch gel electrophoresis. In the case of alkaline phosphatase, 6 common phenotypes and 6 rare phenotypes (F2I1, S1S2, S2S3, I1S2, F1S2, F1I2) are encountered. The highest frequency of Pls1 allele (0.7394) and lowest frequency of Pli1 allele (0.0246) have been found in the Nava-Budha. 6 cases of Cal-1 and 5 cases of Cal-2 types of LDH variants have been observed in the total samples, and Muslims possess the highest frequency of Cal-1 types (3.64%). Population groups are compared with respect to Pl alleles.

The effects of aminoethyl phosphonic acid on hepatic microsomal drug metabolism and ultrastructure of normal and cholesterol fed rats

The effects of parenteral administration of aminoethyl phosphonic acid (AEP) on the liver microsomal drug metabolism and ultrastructure were studied in normal and 1% cholesterol-fed albino rats. AEP administration to rats fed a stock-diet resulted in decreased demethylation of aminopyrine with a concomitant fall in cytochrome P-450 level. Aniline hydroxylation remained unaltered. AEP injection to cholesterol-fed rats, caused marked reduction in both aminopyrine demethylation and aniline hydroxylation, with a significant increase in cytochrome P-450 level. AEP injection to both control and cholesterol-fed animals produced a modest increase in Bilirubin UDP-glucuronyl transferase. RNA:DNA ratio showed remarkable elevation in rats fed the cholesterol diet with AEP injection. AEP injection caused an atypical smooth endoplasmic reticulum and a marked loss of nuclear euchromatin. Effect of AEP was more pronounced in rats receiving the cholesterol-diet. AEP administration thus induces structural and drug metabolic enzyme alteration in liver.

Management of lost finger tips in children

A trial was run in the Hand Unit of the Royal Victoria Infirmary, Newcastle upon Tyne, involving sixty consecutive children who has sustained finger tip injuries with tissue loss over a period of three years. The three forms of treatment used in different groups of children were split skin grafting, local flap repair, and a conservative method, with twenty children in each group. The results are compared from both functional and cosmetic points of view and the results analysed.

The effects of aflatoxin B1 on rat fetal lung lipids

The administration of aflatoxin B1 to rats on days 17 and 19 of pregnancy caused increased synthesis of the total lipids and the fatty acids, and decreased synthesis of the phosphatidyl choline in 21-day-old fetal lung. Aflatoxin B1 caused toxicity in the fetal lung as evidenced by the excessive accumulation of the lamellar bodies and the osmiophilic spheroids in the type II cells and the alveolar lumen, respectively. The rearrangement of the lamellar form to the continuous sheet-like tubular myelin form was reduced in the alveolar lumen of the treated lung.

Serological and biochemical investigations among five endogamous groups of Delhi, India

Phenotype and gene frequencies for four blood group systems (ABO, MN, Rh and P) and haptoglobin among five endogamous groups of Delhi, India, are reported. All the systems are polymorphic in all the population groups. The average heterozygosity per locus in high (in the range 48-52 per cent) for all the groups. The extent of genic variability among the groups in terms of net codon differences per locus has been studied; the heterogeneity within the groups is large as compared to the between-group heterogeneity. There is no definite clustering of the of the groups with respect to their biological rank.

Mechanism of T5-induced DNA polymerase. I. Replication of short primer templates

Bacteriophage T5-induced DNA polymerase shows an initial phase of rapid synthesis, followed by a slower steady rate for much longer periods, with short DNA primer-templates (400 to 600 nucleotides long), in vitro. On extrapolating the line of steady rate back to 0 min, an intercept is obtained on the ordinate. With large DNA primer-templates, such as denatured T5 DNA (average chain length approximately 50,000 bases), the rate of synthesis remains constant and is equal to the initial rate obtained with short primer-templates. The zero time intercept was proportional to the amount of enzyme used and independent of temperature. Polymer challenge experiments indicate that the initial phase of rapid synthesis can be attributed to the processive mode of synthesis by T5 DNA polymerase. After synthesizing a stretch of DNA processively for about 200 nucleotide residues, the enzyme apparently forms a "dead-end complex" with the primer-templates used and must dissociate from the primer-template in order to resume synthesis. The average size of the product made processively, during various phase of synthesis, remains invariant and is in good agreement with the size of the zero time intercept per enzyme molecule.

Mechanism of T5-induced DNA polymerase. II. Characterization of the dead-end complex

We have shown that bacteriophage T5-induced DNA polymerase replicates short primer-templates (400 to 600 nucleotides long) at a rapid rate initially, followed by a slower rate sustained for much longer periods (Das, S. K., and Fujimura, R. K. (1977) J. Biol. Chem. 252, 8700-8707). In order to explain the slower steady rate and the results of polymer-challenge experiments, we conjectured the presence of a "dead-end complex" formed by the enzyme with the primer-template at the end of the primer elongation process. In this communication we present evidence which indicates that the presumed complex shows a first order kinetics of decay with a half-life of 3.5 min at 37 degrees. Energies of activation for the steady phase of synthesis and the decay of the dead-end complex were both found to be about 23 kcal/mol. This indicates that the dissociation of the aforesaid complex might be the rate-limiting step during the steady phase of synthesis. Correlation between the salt-induced reduction in the half-life of the complex and the increase in the steady rate of synthesis is in agreement with the above mentioned possibility.

Lipolytic enzymes of Trichophyton rubrum

Trichophyton rubrum cells contain lipase, phospholipases A and B and acyl CoA lysolecithin acyl transferase activities. This dermatophyte excretes lipase and phospholipase A into the growth medium when cultivated in Sabouraud's broth. Extracellular lipase has optimum activity at pH 8.0 whereas the intracellular lipase is maximally active at pH 8.0 whereas the intracellular lipase is maximally active at pH 7.0. The optimum pH of phospholipase A and B activities which are localized in 15000 g sedimentable cell fragments are 7.0 and 6.0 respectively. Supernatant obtained after removal of 1,005,000 g sedimentable fragments from cell extract contains acyl CoA lysolecithin acyl transferase which requires ATP, CoA, Mg2+ and an unsaturated fatty acid for its activity.

Effect of undecanoic acid on germination of microconidia of wild and undecanoic acid resistance mutant of Trichophyton rubrum

Effects of undecanoic acid (UDA) on germination of microconidia and elongation of germ tubes in UDA sensitive (udas) wild type Trichophyton rubrum and UDA resistant (udar) mutant derived from it, were studied. UDA inhibited conidial germination of udas and udar strains at 30 microgram/ml and 120 microgram/ml respectively which were minimum inhibitory concentrations of UDA for these two strains. When spores from both udas and udar were germinated in presence of subinhibitory concentration of UDA, germ tube growth was short. The elongation of germ tubes of spores pregerminated in absence of UDA was also inhibited by dose of UDA not sufficient to inhitib germination.

Phospholipid turnover in Trichophyton rubrum

Phospholipid synthesis, interconversion and breakdown in T. rubrum were followed by radioactive tracer. Synthesis and catabolism of phosphatidyl ethanolamine and phosphatidyl serine are most rapid; phosphatidyl choline and phosphatidyl inositol are metabolised rather slowly. Catabolism of phosphatidyl ethanolamine and phosphatidyl serine are uniform and their conversions to phosphatidyl choline and phosphatidyl inositol are suspected.

Corrugation of the skull in Paget's disease of bone

Paget's disease of bone has been known for about 100 years and the usual deformities of bone, e.g. bowed tibia, large head, are well described in medical text books. However, there does not appear to have been a description of corrugation of the skull as a recognized deformity in Paget's disease. Three cases are now described to illustrate this deformity as an unusual but valuable sign in this disease.

Synthesis and antihypertensive activity of some imidazoindole derivatives

The synthesis of pyridino[1,2-a]imidazo[5,4-b]indole (1) and thiazolo[3,2-a-a]imidazo[5,4-b-a]indole (2) has been achieved by phosphite reduction of 3-nitroso-6-phenylimidazo[1,2-a]pyridine and 5-nitroso-6-phenylimidazo[2,1-bb]thiazole. Compound 1 has shown strong antihypertensive activity in spontaneously hypertensive rats while compound 2 showed similar bioactivity both in spontaneously hypertensive rats and in normotensive dogs. A tricyclic amino derivative, 3-amino-2-phenylimidazo[1,2-a]pyridine, which has structural resemblance to compound 1, showed no hypotensive activity.

Effects of dietary fats on the fatty acid composition of enamel and dentinal lipids of rabbit molars

The effect of dietary fats such as butter, lard, cottonseed oil, and hydrogenated cottonseed oil on the fatty acid composition of enamel and dentin lipids of rabbit molars was studied. The enamel and dentin of molars of all of the rabbits contained a variety of fatty acids, palmitic, stearic, oliec, linoleic, and eicosapentaenoic being the major ones. Enamal lipids were more unsaturated than dentinal lipids in all of the groups. A significant difference was noticed in the fatty acid composition of both the enamel and dentin between these four groups of rabbits. Linoleic acid content was highest in both the enamel and dentin lipids of rabbits fed cottonseed oil. There was no marked difference in the saturated-unsaturated fatty acid ratio in both the enamel and dentin among rabbits fed cottonseed oil, lard, and butter. It is concluded that tooth lipids are responsive to diets and are in direct equilibrium with dietary components.

In search of complications in carpal tunnel decompression

A series of 170 hands in 152 cases of carpal tunnel decompression presented from the Hand Unit of the Royal Victoria Infirmary, Newcastle-upon-Tyne. Special emphasis is laid on unsatisfactory results of the surgical procedure and their remedy.

Exonuclease associated with bacteriophage T5-Induced DNA polymerase

T-5-induced DNA polymerase has been shown to possess a 3' leads to 5'-exonucleolytic activity. The exonuclease acts on both native and denatured DNA, but the apparent rate of degradation of denatured DNA is about five times faster than that for native DNA. The enzyme appears to act only on 3'-OH ends and produces mainly 5'-dNMP's. Like polymerase activity, exonuclease activity shows a pH optimum around 8.6. Mg2+, dithiothreitol, and N-ethylmaleimide had identical effects on both the activities. Nicked DNA was almost totally protected from exonuclease action under synthetic conditions, i.e., in the presence of 4dNTP's. Denatured DNA was partly degraded in the early phase of incubation with 4dNTP's, presumably due to unhybridized tails at the 3'-OH primer ends. However, the exonuclease activity was operative in both cases under synthetic conditions, as evidenced by template-dependent conversion of [3H]dTTP to [3H]dTMP.

A rationale for the treatment of metastatic neuroblastoma

In developing a chemotherapeutic program for children with disseminated neuroblastoma, we established three human neuroblastoma lines in cell culture to study the effects of dibutyryl cyclic AMP, papaverine, 5-trifluoromethyl-2'-deoxyuridine, and cyclophosphamide on cell growth, biochemical behavior, and morphology. Based upon our studies, a clinical treatment program was designed. We have treated 15 patients with disseminated neuroblastoma and have established the optimum dose range and sequence of these drugs. Early results were promising; plans for continuation of clinical and experimental studies were discussed.

Surface and lamina propria lipids of bovine gingiva

In terms of both quality and quantity, the surface lipids are noticeably different from the lamina propria lipids. The surface lipids are mainly structural in nature (cholesterol, cholesterol esters, and phospholipids), whereas the lamina propria lipids are mostly of storage types (triglycerides). The surface lipids are also more unsaturated, whereas the lamina propria lipids are more saturated. Even though gingiva is histologically similar to skin, bovine gingival surface lipids are different from the bovine skin surface lipids. Further studies are needed to investigate the importance of surface lipids in regulating the various physiologic functions of gingiva.

The size of the human omentum and methods of lengthening it for transplantation

The size of the omentum is variable and can only be predicted within the standard deviations. However, the lower limits of its size have now been ascertained over a large series and it is clear that it could be lengthened sufficiently to reach the vault of skull, mid-leg or mid-forearm levels in all cases. Of course, to do so will decrease its width. An alternative to pedicle transfer is to use the whole omentum as a free transplant by vascular anastomosis.

Study on the composition of bovine gingival lipids

The lipids in bovine gingival tissue were characterized qualitatively and quantitatively. The total lipid content was 2.35% on wet weight. The total nonpolar lipids and total polar lipids were 70.69 and 29.31% of the total lipids, respectively. Cholesterol esters, free fatty acids, and triglycerides were the major nonpolar lipids. Polar lipids were predominantly phosphatidyl choline, phosphatidyl ethanolamine, and sphingomyelin. Traces of glycolipids, lysophosphatidyl choline, phosphatidyl inositol, phosphatidyl serine, and prostaglandins were present. Oleic, palmitic, and stearic acids were found to be the major fatty acids in all lipid classes. Cholesterol esters, total polar lipids, and free fatty acids were more unsaturated than glycerides. Linolenic and arachidonic acid contents were highest in cholesterol esters and total polar lipids.

Detection of prostaglandins in bovine gingival tissue

It has been characterized earlier that bovine gingival lipids contain a fairly high level of arachidonic acid, a potential precursor of prostaglandin biosynthesis. The purpose of the present study was to investigate whether prostaglandins are natural components of bovine gingival tissues. Qualitative analysis of the lipid extract by a combination of thin-layer chromatography on plain and silver nitrate-impregnated silical gel plates and ultraviolet absorption spectroscopy strongly indicate the presence of PGE1, PGE2, and PGF2. There was also an indication for the occurrence of other prostaglandins, such as PGB, PGE3, PGF1, and PGF3.

Postmyocardial infarction (Dressler's) syndrome: report of a case with immunological and viral studies

A case of PMIX with immunologic and viral studies obtained prior, during, and after a typical exacerbation are reported. Immunologic studies indicated the presence of humoral antiheart autoantibodies, and an increase in the number and proportion of lymphocytes containing surface IgG immunoglobulin during acute activity. Viral studies were negative. Previously reported immunologic and viral data, as well as etiology and pathogenesis of PMIS are discussed.

Pulmonary function study in old age

A study was carried out in 100 patients aged between 70 and 90 years to investigate pathological and respiratory function changes in old age. Vitalograph and peak flow meter measurements were made, but blood gas analysis was only carried out in 6 patients in view of the technical difficulties. Analysis of the results showed that there was a definite, moderate, restrictive type of defect in pulmonary function in almost all the patients, in those with generalized senile changes as well as in those with a pathological condition. Blood gas analysis showed a minimum degree of alteration in oxygen tension and saturation with normal carbon dioxide tension.