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P K Andersen

Publications and source records attributed to P K Andersen.

At least 73 records · Page 4Linked to original sources
PubMed1997

Estimation of variance in Cox's regression model with shared gamma frailties.

The Cox regression model with a shared frailty factor allows for unobserved heterogeneity or for statistical dependence between the observed survival times. Estimation in this model when the frailties are assumed to follow a gamma distribution is reviewed, and we address the problem of obtaining variance estimates for regression coefficients, frailty parameter, and cumulative baseline hazards using the observed nonparametric information matrix. A number of examples are given comparing this approach with fully parametric inference in models with piecewise constant baseline hazards.

Adult↗
PubMed1996

Relation between treatment efficacy and cumulative dose of alpha interferon in chronic hepatitis B. European Concerted Action on Viral Hepatitis (Eurohep).

BACKGROUND/AIMS: Alpha interferon (IFN) is an established treatment of chronic hepatitis B. The effect has been shown to be dose related, recommended dose regimens being associated with a doubling of the spontaneous, baseline HBeAg to anti-HBe seroconversion rate. However, the efficacy of IFN treatment in relation to the dose of IFN actually received remains to be established. The aim of this study was to estimate the relative efficacy of IFN as a function of the cumulative IFN dose. In addition we determined if and when a patient returns to his baseline chance of seroconversion after stopping IFN therapy. MATERIALS AND METHODS: Individual patient data from 10 clinical controlled trials were available for the present analysis, in all, 746 patients, of whom 491 received IFN and 255 were untreated controls. The data were analyzed performing a time-dependent Cox regression analysis of the relative efficacy of IFN using the cumulative IFN dose administered up to any given time during the observation period and the time after termination of therapy as explanatory variables. RESULTS: In the proposed model, the chance of HBeAg disappearance for a treated patient relative to no therapy was estimated to 2.1 at a cumulative dose of 100 MU and leveled out at about 2.8 at a cumulative dose of 500 MU. The effect of IFN was shown to decay rapidly after discontinuation and after 3 months a patient could be considered to be back to his baseline chance of HBeAg disappearance. These findings show that IFN administered at a dose of 15-30 MU/week should be considered effective (relative efficacy approximately 2) already after 1-2 months of treatment. CONCLUSIONS: The present findings do not lend any support to the concept that IFN treatment becomes less effective when a certain total dose of IFN has been administered or that the treatment effect reaches beyond 3 months after stopping IFN.

Adolescent↗
PubMed1996

Spectral analysis of cyclic fluctuations in haemodynamic parameters in critically ill patients.

In critically ill patients haemodynamic parameters are being routinely monitored. All of the fluctuations in blood pressures cannot be visualised since on most monitors the time window is too short and trend curves do not have a sufficient time resolution. Therefore, frequency analysis was applied to an 800-second window. Systemic artery pressure, central venous pressure and pulmonary artery pressure curves of 6 patients were sampled with a frequency of 40 Hz. The signals were transformed into the frequency domain by the Fast Fourier Transform method. Bispectral analysis was applied to determine the origin of higher frequencies. There were three main frequencies present: heart stroke rate, respiratory frequency and a slow frequency (< 0.05 Hz), which was equal to the used infusion rate (2-10 ml/h) of vaso-active drugs. Continuous infusion of short-acting vaso-active drugs delivered by pulsatile diaphragm pumps to produce slow significant fluctuations in especially the arterial blood pressures (range: 5-40 mmHg). The periodicity of these slow fluctuations is not visualised during routine monitoring, so the observer may misinterpret the cause of changes in blood pressure and make inappropriate clinical decisions. A solution for detection of such slow waves is Fast Fourier Transform combined with bispectral analysis.

Blood Pressure Determination↗
PubMed1995

[Nitrogen oxide inhalation in acute pulmonary failure].

Two cases of adult respiratory distress syndrome (ARDS) treated successfully with nitric oxide (NO) inhalation are described. One patient had severe sepsis and the other had trauma induced ARDS. The slow entry criteria for extracorporeal membrane oxygenation (ECMO) was fulfilled in both cases. NO inhalation substantially improved oxygenation, reduced pulmonary arterial pressure and peak inspiratory pressure. Treatment with NO inhalation was without side effects and easy to administer through the ventilator. Both patients survived without sequelae. We suggest that inhalation with NO should be tried before ECMO treatment is considered in severe ARDS.

Adolescent↗
PubMed1995

Score test of homogeneity for survival data.

If follow-up is made for subjects which are grouped into units, such as familial or spatial units then it may be interesting to test whether the groups are homogeneous (or independent for given explanatory variables). The effect of the groups is modelled as random and we consider a frailty proportional hazards model which allows to adjust for explanatory variables. We derive the score test of homogeneity from the marginal partial likelihood and it turns out to be the sum of a pairwise correlation term of martingale residuals and an overdispersion term. In the particular case where the sizes of the groups are equal to one, this statistic can be used for testing overdispersion. The asymptotic variance of this statistic is derived using counting process arguments. An extension to the case of several strata is given. The resulting test is computationally simple; its use is illustrated using both stimulated and real data. In addition a decomposition of the score statistic is proposed as a sum of a pairwise correlation term and an overdispersion term. The pairwise correlation term can be used for constructing a statistic more robust to departure from the proportional hazard model, and the overdispersion term for constructing a test of fit of the proportional hazard model.

Graft Rejection↗
PubMed1995

Inhalation of nitric oxide as a treatment of pulmonary hypertension in congenital diaphragmatic hernia.

Congenital diaphragmatic hernia (CDH) still has a mortality risk of around 40%. The concomitant pulmonary hypoplasia and the persistent pulmonary hypertension are of major prognostic importance. The use of a selective pulmonary vasodilator may revert this vicious circle that is fatal to many children. Inhalation of nitric oxide (NO) has been suggested as a rational treatment of this condition. The authors report three cases of high-risk infants with CDH where NO was used successfully. It is concluded that hypoxemia in CDH can be treated successfully with NO inhalation when conventional treatment fails, and it may in some cases prove to be an alternative to ECMO.

Administration, Inhalation↗
PubMed1995

Relationship between maternally derived anti-Plasmodium falciparum antibodies and risk of infection and disease in infants living in an area of Liberia, west Africa, in which malaria is highly endemic.

In areas where Plasmodium falciparum is endemic, immunoglobulin G is acquired by the fetus in utero, mainly during the third trimester of pregnancy. The potential protective effect of transferred anti-P. falciparum maternal antibodies was examined in a longitudinal study of 100 infants from birth to 1 year of age. The probability of acquiring a P. falciparum infection and developing an episode of clinical malaria was determined in relation to the P. falciparum-specific antibody level of the infant at birth against P. falciparum schizont antigen or recombinant merozoite surface protein MSP1(19) antigen. The risk of acquiring an episode of clinical malaria increased from birth to 6 months of age, after which it decreased. The overall prevalence of P. falciparum parasitemia was highest (48.9%) in the 6-month-old infants. The age-specific hematocrit value showed the lowest mean value (30.2) from 6 to 9 months, and the spleen rate was the highest (69.8%) at the same age. There was a lower risk of developing an episode of clinical malaria during the first year of life in the infants with high levels of anti-MSP1(19) antibodies at birth. The level of maternally derived overall anti-schizont antigen antibodies did not seem to play a role in the relative risk of developing malaria infection or disease during the first year of life, though the level of specific anti-MSP1(19) antibodies may be associated with protection.

Animals↗
PubMed1995

Observer variation in histological classification of cutaneous malignant melanoma.

To evaluate the variations within and between observers in the interpretation of important histological prognostic factors, a series of 96 melanoma patients was randomly selected from a database of 1691 patients with cutaneous malignant melanoma. The stained sections were examined on two occasions by four experienced pathologists. Analysis by observed agreement and kappa statistics showed maximal tumour thickness to be the best reproducible variable, with ulceration the second best. Regression was the least reproducible, with level of invasion and type of melanoma in the mid range. Intra-observer variation was uniformly less than inter-observer variation for each variable. For tumour thickness a variance component analysis was done to quantify the variability further. The clinician should not base his choice of treatment entirely on the microscopic classification but take into consideration the clinical course and appearance of the tumour.

Analysis of Variance↗
PubMed1995

A nonparametric test for comparing two samples where all observations are either left- or right-censored.

The situation is considered where the status of the individuals under study is assessed only once during their lifetime, and as a consequence the observed time to an event of interest is either left- or right-censored. Nonparametric estimation of the time to event distribution is reviewed and a nonparametric two-sample test is proposed. The performance of the test is illustrated by simulations and by a numerical example.

Analysis of Variance↗
PubMed1994

[Artificial respiration in patients with acute severe asthma. Mode of ventilation and survival].

The purpose of the study was to register the treatment, mode of ventilation and mortality of patients with acute severe asthma treated with intermittent positive pressure ventilation (IPPV) in a Danish intensive care unit (ICU) during a ten-year period. Fifty-seven patients underwent ventilation on 78 occasions. Fifty-three patients were ventilated with controlled hypoventilation and low PEEP, while four patients were treated with high PEEP. One of the 53 patients receiving controlled hypoventilation and two of the four patients who received high PEEP developed a pneumothorax. All the patients were treated with intravenous steroid and infusion of a beta 2-agonist. Eighty-eight point three per cent received an infusion of theophylline whereas only 16.9% were treated with inhalation of a beta 2-agonist. Eight patients already had irreversible brain damage due to cardiac arrest before arrival to the ICU. Seven of these patients died due to brain damage. All the patients who reached the ICU without brain damage survived. After discharge from the hospital increased mortality was observed among these patients. Some of the patients died due to underestimation from doctors as well as patients of the severity of the asthma. Patients with acute severe asthma requiring IPPV should be ventilated with controlled hypoventilation. A high PEEP is associated with an increased risk of barotrauma. Continuing education of doctors and patients is necessary to increase the use of objective airflow measurement.

Acute Disease↗
PubMed1994

[Inhalation therapy with nitric oxide--an evaluation of a dosage system and clinical examples].

In 1987 it was discovered that nitric oxide is a very potent vasodilator and in fact a natural mediator for vasodilatation. The effects of inhalation of nitric oxide on pulmonary vascular resistance were described in 1988 and a new therapeutic possibility for artificially ventilated patients with pulmonary hypertension has arisen. However, the administration of nitric oxide has to be performed with high accuracy and without reaching toxic levels of nitrogendioxide. We have evaluated a system using conventional air and oxygen rotameters for administration of nitric oxide via a ventilator. A comparison of the chemiluminescence technique with a technique based on fuel cells was also performed. With the system it was possible to administer nitric oxide with high accuracy within the range of 10-60 ppm without exceeding values for nitrogendioxide above 0.4 ppm. The analysis of nitric oxide and nitrogendioxide based on electrochemical cells proved to be comparable with the chemiluminescence technique within the same range. Nitric oxide inhalation was used in six patients with severe hypoxia and seemed to have a favorable effect on most of the patients.

Administration, Inhalation↗
PubMed1994

Survival analysis and neural nets.

We consider feed-forward neural nets and their relation to regression models for survival data. We show how the back-propagation algorithm may be used to obtain maximum likelihood estimates in certain standard regression models for survival data, as well as in various generalizations of these. Examples concerning malignant melanoma and post-partum amenorrhoea during lactation are used as illustration. We conclude that although problems with the substantial number of parameters and their interpretation remain, the feed-forward neural network models are flexible extensions to the standard regression models and thereby candidates for use in prediction and exploratory analyses in larger data sets.

Algorithms↗
PubMed1994

[Consequences of incorrect interpretation of vaginal smear tests in a screening program].

A nested case-control study was undertaken in the Maribo County cohort of 27,811 women with negative cervical smears. Fifty-three women who later developed invasive cervical cancer constituted the cases, and five matched controls were selected from the cohort for each case. A total of 633 previous negative smears for the cases and controls were reviewed independently by two pathologists. The review showed misclassification to be frequent in these smears, which were collected in the period 1966-82, and the odds ratio for patients compared with controls for having at least one positive smear was 22.12 (95% CI 7.54-64.94). The study thus shows that more cancer cases could have been prevented by the screening programme were the test to have been more sensitive. The study also shows, however, that the participating women would have to pay a considerable price in the form of unnecessary extra tests if the sensitivity was too high.

Case-Control Studies↗
PubMed1994

The reproducibility of measurement of right ventricular ejection fraction and cardiac output by the thermodilution technique in patients on mechanical ventilation.

Thermodilution determined right ventricular ejection fraction (RVEF) and cardiac output (CO) were measured in 48 critically ill patients requiring mechanical ventilation and inotropic and/or vasoactive drugs. The coefficient of variation on CO and RVEF were calculated from triple determinations. The average coefficient of variation based on 551 triple determinations was 12.6% for RVEF (range 2-51%) and 4.9% for CO (range 0-24%). If a 10% coefficient of variation was chosen as acceptable, 95% of the CO measurements were acceptable. The coefficient of variation on RVEF only fulfilled the 10% criteria in 46% of the measurements, but if the accepted level was raised to a 20% coefficient of variation, 90% of the measurements were acceptable. The measurement of RVEF and CO are used for calculation of e.g. right ventricular end diastolic volume (RVEDV). By applying the average coefficient of variation of RVEF and CO, the accumulated error on calculation of RVEDV was found to be divided by 15%- +20% at worst. Before derived parameters such as RVEDV are interpreted or compared with previously obtained values, the accumulated error should be calculated. To ensure the quality of the measurements, our recommendation is always to calculate the coefficient of variation for each triple determination of RVEF and CO.

Blood Pressure↗
PubMed1993

[Death after earlier deliberate self-poisoning. A 10-year material from an intensive care unit].

In order to describe the survival after deliberate self-poisoning we followed up all patients discharged from an intensive care unit over a ten year period (1979-1988), where admission had been due to deliberate self-poisoning. The acute lethality has been described in a previous publication. Among 1487 patients discharged from the intensive care unit a total of 227 deaths were registered (median observation time: 55 months). According to national lifetables the expected number of deaths was 32. The deaths were classified as natural (44%), suicide (39%), accidental (9%) or other (8%). Among patients who committed suicide there were some significant (p < 0.01) characteristics: the majority of the patients were under 50 years of age, with an observation time of under two years and a history of prior psychiatric illness. The suicide rate was 1.3% per year of observation. We conclude that survivors of deliberate self-poisoning will remain at high risk of dying (especially suicide) in the future, and that useful clinical predictors of fatal outcome have yet to be determined.

Adult↗
PubMed1993

[Monitoring of right ventricular ejection fraction with a modified pulmonary artery catheter].

The thermodilution method for measuring right ventricular ejection fraction (RVEFTD) is described. The reproducibility of RVEFTD measurements was determined in 48 critically ill patients who all needed pharmacological inotropic support and mechanical ventilation. A coefficient of variance of 12.6% on RVEFTD determinations was found. In 46 of 48 patients (96%), the catheter did not need repositioning.

Cardiac Catheterization↗
PubMed1992

Increasing incidence of early onset type 1 (insulin-dependent) diabetes mellitus: a study of Danish male birth cohorts.

To provide information of the incidence trends of Type 1 (insulin-dependent) diabetes mellitus we performed a cohort study of a series of Danish male birth cohorts. All male livebirths in Denmark between 1 January 1949 and 31 December 1964, were investigated regarding the development of Type 1 diabetes during the first 20 years of life using the files of the Danish Conscript Board, supplemented by a search in the Danish National Registry of Deaths. Diagnosis was verified and clinical information obtained from medical records. The material is estimated to be more than 95% complete. A total of 1705 diabetic subjects were identified of whom 23 were not representative of idiopathic Type 1 diabetes. The cumulative rate of Type 1 diabetes development during the first 20 years of life increased from 2.37 to 2.90 per 1000 for the first eight and last eight birth cohorts, respectively. A log-linear analysis of the incidence revealed significantly increasing incidence rates, independent of age effects, with a maximum in the late 1970's. About 75% of the cases presented short duration of symptoms prior to diagnosis, and only very few cases were diagnosed incidentally. Cases were diagnosed relatively less frequently during summer months than during winter months.

Adolescent↗