Michael Weis Bentzon

24-h ambulatory blood pressure in 352 normal Danish subjects, related to age and gender

UNLABELLED The study was conducted to determine age and sex stratified normal values for 24-h ambulatory blood pressure. A sample of 352 healthy subjects (all white) were randomly selected from the community register and stratified by sex and age groups in decades from 20 to 79 years of age. Persons with a history of hypertension, cerebral apoplexy, diabetes, myocardial or renal disease, and who were taking blood pressure-influencing medication were excluded. Ambulatory blood pressure was recorded over 24 h, with measurements taken every 15 min from 07:00 to 22:59, and every 30 min from 23:00 to 6:59. Systolic blood pressure increased only slightly with age and was significantly higher in men than in women. The diastolic blood pressure increased only slightly with age in both sexes until the 50 to 59 years age group and declined thereafter. The diastolic blood pressure was not different for the two sexes. Both systolic and diastolic blood pressure were approximately 15% lower during the night regardless of age or sex. Ambulatory blood pressure during the daytime was on an average of 5 mm Hg lower than office blood pressure, but the mean difference between the two measurements increased with age. The variability of the difference also increased with age. IN CONCLUSION Normal values for ambulatory blood pressure are presented in a randomly selected age- and gender-stratified population. Differences between office blood pressure and ambulatory blood pressure increased with age suggesting that the previously observed higher blood pressure seen in the elderly partly might be explained by a greater impact of white coat hypertension in older people.

Catheter-related Staphylococcus aureus infections

Among 3394 patients with Staphylococcus aureus bacteraemia from the years 1986-89, 88 patients were found whose intravenous catheter and blood grew organisms of the same phage type. Strains of phage type 95 were more frequent among the patients with confirmed catheter-related bacteraemia than among other bacteraemia cases. Strains with particular phage-type patterns occurring with increasing frequency in Denmark during recent years also occurred with significantly higher frequencies among the confirmed catheter-related bacteraemias. No major differences in antibiotic resistance were observed. Patients with catheter-related bacteraemia had, in spite of a higher frequency of underlying diseases, a lower mortality compared with other bacteraemia patients, and endocarditis occurred less frequently (2% vs. 6%). Among 201 S. aureus isolates from catheters in 1988 only strains of group I occurred with increased frequency. The possible role of catheters as selection pressure on the S. aureus population is discussed.

Enzymuria in neonates receiving continuous intravenous infusion of gentamicin.

Urinary excretion of the tubular enzymes NAG and AAP was investigated during gentamicin treatment of 105 newborn infants. The values found for NAG and AAP show a significant positive correlation. The urinary excretion of NAG was on the average 92% higher during gentamicin treatment as compared with non‐treatment periods in the same newborn infant (33 infants). The same tendency applied to AAP. Newborn infants receiving continuous intravenous infusion of gentamicin were not found to be at greater risk of nephrotoxicity than those receiving intermittent gentamicin treatment, using NAG and AAP as an index of nephrotoxicity. The changes in NAG and AAP within treatment periods were studied. During gentamicin treatment an insignificant average increase in the urinary excretion of NAG occurred, whereas a significant decrease was found during non‐treatment periods. A significant negative correlation was found between urinary excretion of NAG and birth weight/gestational age. The long‐term effect of the higher excretion of NAG and AAP in newborn and adult patients during aminoglycoside treatment is unknown.

Resistance to dicloxacillin, methicillin and oxacillin in methicillin-susceptible and methicillin-resistant Staphylococcus aureus detected by dilution and diffusion methods.

A total of 54 Staphylococcus aureus strains of varying methicillin resistance were investigated for their resistance to methicillin, oxacillin and dicloxacillin by different diffusion tests. Inhibition zones were measured around locally prepared paperdiscs with 10 μg methicillin, 5 and 10 μg oxacillin, 5 and 10 μg dicloxacillin, PDM paperdiscs with 10 μg methicillin or oxacillin and Neo‐sensitabs tablets with methicillin or oxacillin. All diffusion tests were performed both with Mueller‐Hinton agar and Danish Blood agar as well as at 37 °C and 30 °C and read after overnight incubation. Differences in zone diameter under different conditions were found to be independent of the susceptibility level of the strains. Seventeen of the strains were detected as methicillin‐resistant (MRSA) by two methods including high inoculum and prolonged incubation at 30 °C. The minimum inhibitory concentration (MIC) of the 54 strains was determined by a plate dilution method at 30 °C and 37 °C. A 10 μg locally prepared methicillin disc detected all MRSA strains with no false reactions either at 37 °C or 30 °C on Mueller‐Hinton agar. Investigations with oxacillin discs had to be performed at 30 °C or with a 5 μg disc in order to detect correctly. PDM paperdiscs gave reactions identical to the corresponding locally prepared discs. Methicillin Neo‐sensitabs detected all MRSA strains but also included a few susceptible strains among the resistant ones. Addition of blood increased the number of not‐detected MRSA strains. All 17 MRSA strains were susceptible to dicloxacillin by the dilution method, and the disc diffusion test showed similar results. Dicloxacillin discs therefore did not detect the presence of MRSA strains. The implications of replacement of the methicillin/oxacillin disc by a dicloxacillin disc are discussed.

Isolated systolic hypertension in an elderly Danish population. Prevalence and daytime ambulatory blood pressure

Isolated systolic hypertension (ISH) is a major risk factor for cardiovascular complications. Nevertheless, data on the prevalence in a representative population do not seem to be available. The prevalence of ISH and the white coat effect was thus studied in a cross‐sectional survey of 2806 inhabitants aged 70–80 years. In untreated subjects, the prevalence of ISH was 17.4% (95% CI 14.9–20.2) in women and 13.5% (95% CI 11.3–15.9) in men using clinic blood pressure at first visit. The prevalence increased significantly with age. The prevalence was reduced to 10.4% when using the average of all‐visits clinic blood pressures. By a simulation model, it was demonstrated that his reduction mainly resulted from a regression towards the mean. Average all‐visits clinic blood pressure was 172.6 ±10.4/81.1±6.0 mmHg. Less than one‐third of those with all‐visit ISH had sustained ISH. Identifying subjects with sustained ISH requires measurements in more than three visits.

Relation between enzyme-linked immunosorbent assay and radioimmunoassay for detection of antibodies to the capsular polysaccharide of Haemophilus influenzae type b

The measurement of antibodies to the capsular polysaccharide (PRP) of Haemophilus influenzae type b (Hib) is important because vaccines inducing such antibodies are now available. We developed and evaluated an enzyme‐linked immunosorbent assay (ELISA) for detection of these antibodies based on direct coating of the plates with tyraminated PRP. The assay fulfilled the requirements for parallel line assays; it was sensitive, specific, and reproducible with a coefficient of variation between days of 19%. Results from the ELISA were compared with results from radioimmunoassay and a correlation coefficient of 0.93 was found. Results obtained by the two methods were proportional and the relation was independent of the antibody level. The relation between them was also unaffected by the contribution of different antibody isotypes, indicating that these were measured to the same extent by both methods. ELISA employing direct coating of the plates with tyraminated PRP represents a useful alternative for detection of antibodies when studying immunogenicity of Hib vaccines.

A subdivision of strains of Staphylococcus aureus in the 94,96 complex by means of experimental phages

In order to facilitate epidemiological investigations a subdivision of Staphylococcus aureus strains belonging to the 94,96 complex by means of two experimental phages, 16 and 47A, was performed. These phages were selected from the nine experimental phages initially examined because they gave the greatest discrimination. On the basis of reactions with these two phages, 2199 isolates which reacted with phages 94 and 96, and 773 isolates which reacted with phage 96 alone, were each subdivided into two major and two minor groups. Strains with different phage patterns were in a few cases (2/64) isolated from the same deep body site in a patient, and lysogenisation experiments suggested that differences in phage patterns were determined by the presence of prophages. Strains with the phage patterns 94/96 and 96 were found to be unevenly distributed throughout Denmark. This regional distribution suggested that particular strains might predominate in some areas. The extended phage patterns with the experimental phages did not give any retrospectively useful epidemiological information. It is proposed that in future phages 16 and 47A be used for specific investigations into the sources and relatedness of strains involved in small incidents.