COMPUTER SIMULATION OF RESPIRATORY IMPEDANCE AND FLOW TRANSFER FUNCTIONS DURING HIGH FREQUENCY OSCILLATIONS

The usefulness of measuring respiratory flow in the airway andat the chest wall and of measuring respiratory input impedance(Z) to monitor high frequency ventilation was investigated bycomputer simulation using a monoalveolar 10–co-efficientmodel. The latter included a central airway with its resistance(Rw) and inertance (Iw), a resistive peripheral airway (Rp),a lumped bronchial compliance (Cb), alveolar gas compliance(Cgas), lung tissue with its resistance (Rl) and compliance(Cl), and chest wall resistance (Rw), inertance (Iw) and com-pliance(Cw).Gas flow in the peripheral airway (Vp), shunt flow through Cb(Vb), gas compression flow (lgas) and rate of volume changeof the lung (Vl) and of the chest (Vw) were computed and expressedas a function of gas flow in the central airway (Vc). For normalvalues of the coefficients. Vp/Vc was found to decrease moderatelywith increasing frequency and was still 0.75 at 20Hz. Peripheralairway obstruction (Rp x 5) considerably decreased Vp/Vc particularlyat high frequency. It did not change the relationship betweenthe two measurable flows. Vc and Vw, but increased the effectiveresistance at low frequency and shifted the reactance curveto the right. A reduced lung or chest wall compliance producedlittle change in Vp/Vc and Z except at very low frequencies;however, it decreased the phase lag between Viv and Vc. Finally,an increased airway wall compliance decreased Vp/Vc, but hadlittle effect on Z and Vw/Vc. It is concluded that measuringrespiratory impedance may help in detecting some, but not allof the conditions in which peripheral flow convection is decreasedduring high frequency oscillations.     

Trends in risk factors for vascular disease in Australia

Data from the National Heart Foundation Risk Factor Prevalence Surveys of 1980 and 1983 were analysed to detect national trends in risk factors for vascular disease in Australia. After statistical adjustment for differences in the demographic characteristics of the two populations of survey participants, our results show trends in smoking and blood pressure that are likely to result in a continuing fall in the incidence of vascular disease. There was a fall in the prevalence of current smoking from 32% to 29% but little change in the average daily consumption of cigarettes by current smokers. The prevalence of previously-undetected hypertension fell significantly from 10% to 7%. A small increase occurred in the proportion of all hypertensive patients who were treated and whose blood pressure was controlled, and a decline of 2.0 mmHg (P less than 0.0001) in mean diastolic blood pressures, but no significant change in mean systolic pressures. Mean total plasma cholesterol levels did not change; average levels of plasma triglycerides fell by 0.11 mmol/L (P less than 0.0001); and mean high-density lipoprotein cholesterol levels increased by 0.03 mol/L (P less than 0.0001). All indices of relative body weight increased between 1980 and 1983; mean body mass index rose by 0.23 with associated rises in the prevalence of obesity and of overweight status. The changes in other factors such as use of added salt, the consumption of alcohol, the level of physical activity and adherence to a special diet, all were in the desirable direction, although minor changes in the survey questionnaire might have served to exaggerate the apparent trends.     

Viral hepatitis in the US Navy, 1975-1984

The epidemiology of viral hepatitis in US Navy enlisted personnel was reviewed for the years 1975-1984. Hospital discharge summaries of all active duty enlisted personnel admitted to a US Navy treatment facility were used for the study. From 1975 to 1984, total first hospitalizations for viral hepatitis declined from 128 per 100,000 personnel (95% confidence interval (Cl) 118-139) to 56 per 100,000 personnel (95% Cl 50-63). The highest incidence of acute viral hepatitis (115 per 100,000 personnel) was found in the youngest age groups aged 24 years and less. Risk factors for acute hepatitis included a previous hospitalization with either drug abuse (relative risk = 363) or a sexually transmitted disease (relative risk = 25) listed among the discharge diagnoses. Having a medical job classification was also associated with an increased risk of acute hepatitis. The steep decline in the incidence of viral hepatitis during this 10-year period may have been due to decreasing drug abuse in the US Navy. Immunization of high-risk groups in the US Navy with hepatitis B vaccine could be an effective policy for the prevention of acute viral hepatitis.     

Conformationally restricted analogues of the muscarinic agent N-methyl-N-(1-methyl-4-pyrrolidino-2-butynyl)acetamide

Conformationally restricted analogues of the selective partial muscarinic agonist N-methyl-N-(1-methyl-4-pyrrolidino-2-butynyl)acetamide (BM 5; 2) were synthesized. The compounds were tested for muscarinic and antimuscarinic activity in the isolated guinea pig ileum and in intact mice. They were found to be moderately potent muscarinic antagonists or weak partial agonists. The new compounds were less potent than 2 in inhibiting (-)-[3H]-N-methylscopolamine binding in the rate cerebral cortex. Thus, structural modifications of 2 in which part of the amide moiety has been connected with the methyl group in the butynyl chain to form a five-membered ring decrease affinity and in most cases abolish efficacy.     

Positive end-expiratory pressure and the damaged right ventricle. An experimental open versus closed chest study

Hemodynamic changes after isolated impairment of right ventricular function (produced by increasing afterload by temporary banding of the pulmonary artery) were studied in 22 ventilated pigs during increased levels of positive end-expiratory pressure (4, 8, 12, and 16 cm H2O). In the open chest group, application of positive end-expiratory pressure produced only a slight decrease of cardiac index. After right ventricular damage a decrease of cardiac index of more than 25% occurred only when higher levels of positive end-expiratory pressure were applied. In contrast to the open chest group, the closed chest group showed more distinct cardiovascular responses after positive end-expiratory pressure. In the damaged right ventricle with a positive end-expiratory pressure of 16 cm H2O, right ventricular end-diastolic pressure increased more than 100%. With positive end-expiratory pressure, cardiac index decreased 34% before and 47% after right ventricular damage. We conclude that positive end-expiratory pressure induces a more pronounced decrease in cardiac index if right ventricular function is impaired. During open chest conditions with lower levels of positive end-expiratory pressure, these changes are only small, however, and probably irrelevant. During closed chest conditions, the hemodynamic changes are much more pronounced. High right ventricular end-diastolic pressures resulting from impaired right ventricular contractility as well as from high levels of positive end-expiratory pressure may have an impact on biventricular function and right ventricular coronary driving pressure.     

Nuclease hypersensitivity of the rat cytochrome P450IA1 gene

The bovine pancreatic deoxyribonuclease I (DNAase I) hypersensitivity of the rat cytochrome P450IA1 gene was investigated. A nuclease-hypersensitive region was observed at approximately 3.2 to 5.1 kilobase pairs upstream of exon 1 in adult and fetal rat liver. This region did not necessarily correlate with gene expression following 3-methylcholanthrene induction, although it may determine the potential for inducibility of this gene.     

Pemphigus erythematosus--detection of anti-DNA antibodies

In an 80-year-old woman with pemphigus erythematosus, we demonstrated ANA as well as anti-DNA antibodies in the serum. This finding supports the argument that this skin disorder represents a combination of a disease of the pemphigus group with systemic lupus erythematosus.