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At least 991 records · Page 55Linked to original sources
PubMed1995

[Sources of error in measuring reference values].

For the solution of many problems it is essential to separate the reaction to a stimulus from the spontaneous circadian rhythm of the variable. But disturbing masking effects evoked by the actual activity level and after effects of earlier activities (masking effects) may obstruct such separations. Several protocols have been already described to reduce masking effects. They differ mainly in the quantity of the standardized activity. Those, which try to avoid masking due to sleep, have to use higher levels of activity to keep the subjects awake. Experimental comparisons of masking effects due to activity and due to sleep as well as to sleep deficits clarify that sleep is a less potent masking agent as often expected and may be allowed in routines designed to reduce masking effects. Masking effects due to sleep deficits and moderate activities are commonly underestimated and should be avoided as far as possible in such routines. Besides the circadian changes of reagibility, the extent of masking effects (even on body temperature) questions the usage of baseline measurements. Sleep can be investigated under reduced masking effects.

Bias↗
PubMed1978

[Environmentally dependent erythrocyte membrane permeability as a source of error in the determination of hematocrit].

The volume of human red blood cells (RBC) was evaluated by means of the centrifugation method (hematocrit) and 131-J-labelled human serum albumin, respectively. Both of the methods yielded an identical volume of about 107 micron3 of the single RBC, provided the evaluation was performed in autologous plasma. Contrary to the 131-J-albumin method the results of which were found independent of various pretreatments of RBC, the centrifugation hematocrits of RBC previously washed with PBS and resuspended in PBS or saline protein media resulted in a mean cell volume of about 86 micron3. The decrease of the cell volume was associated with an efflux of K+ ions. If the RBC are centrifuged at 800 g instead of 15000 g, their volume will remain unchanged. The assessment of cytodeformability has shown, that RBC in PBS by loss of cell volume could enter a 2.3 micron micropipette completely. RBC in plasma, though traversing a 2.9 micron micropipette were incapable of entering a 2.3 micron channel completely. With pressures ranging from 300 to 350 mm H2O the processes of these cells undergo microspherulation.

Cell Membrane Permeability↗
PubMed1994

Sensitivity of HER-2/neu antibodies in archival tissue samples: potential source of error in immunohistochemical studies of oncogene expression.

HER-2/neu oncogene amplification and overexpression of breast cancer tissue has been correlated with poor prognosis in women with both node-positive and node-negative disease. However, several studies have not confirmed this association. Review of these studies reveals the presence of considerable methodological variability including differences in study size, follow-up time, techniques and reagents. The majority of papers with clinical follow-up information are immunohistochemical studies using archival, paraffin-embedded breast cancers, and a variety of HER-2/neu antibodies have been used in these studies. Very little information, however, is available about the ability of the antibodies to detect overexpression following tissue processing for paraffin-embedding. Therefore, a series of antibodies, reported in the literature or commercially available, were evaluated to assess their sensitivity and specificity as immunohistochemical reagents. Paraffin-embedded samples of 187 breast cancers, previously characterized as frozen specimens for HER-2/neu amplification by Southern blot and for overexpression by Northern blot, Western blot, and immunohistochemistry, were used. Two multitumor paraffin-embedded tissue blocks were prepared from the previously analyzed breast cancers as a panel of cases to test a series of previously studied and/or commercially available anti-HER-2/neu antibodies. Immunohistochemical staining results obtained with 7 polyclonal and 21 monoclonal antibodies in sections from paraffin-embedded blocks of these breast cancers were compared. The ability of these antibodies to detect overexpression was extremely variable, providing an important explantation for the variable overexpression rate reported in the literature.

Antibodies↗
PubMed1994

[Sonography of the infant hip. Sources of error, progress and current clinical relevance].

Effective prevention of late dysplastic dislocation of the hip (DDH) has become a reality since reliable diagnosis has been possible at an early stage by means of the original sonographic method according to Graf. A correct sonographic diagnosis must be instantly followed by adequate, biomechanically rational, and consistent therapeutic management and long-term follow-up. The results of a strictly comparative follow-up study emphasize the enormous progress in the quality of therapeutic results gained when routine sonographic newborn hip "screening" is performed directly in the maternity wards: successful anatomical healing with conservative treatment is regularly obtained without femoral head necrosis, without surgery and without late DDH, and costs less when sonographic assessment is done within the first days of life. For this reason, the Austrian government has included sonographic neonatal hip screening in its general health prevention program-and also reimbursed the cost of this preventive procedure-since 1992.

Austria↗
PubMed1993

Haemothorax--a source of error in emergency central vein cannulation.

Central venous cannulation is often performed in patients with penetrating wounds of the chest as an aid to diagnosis, and is sometimes also used as a volume infusion resuscitation line in an emergency. The traditional signs of successful central venous cannulation--free aspiration of blood from the exploring needle and inserted cannula, free infusion flow and backflow of blood when the set is lowered below the patient--may all give a false impression of correct placement if there is a significant haemothorax on the same side. Two cases are described where the cannula was sited in a pleural cavity which contained blood, leading to inadequate resuscitation of the patient. The authors recommend that, where possible, peripheral lines or saphenous cutdown be used for volume resuscitation and that central venous cannulation in the emergency situation be performed on the side of the uninjured hemithorax, especially if the operator is inexperienced.

Accidents, Traffic↗
PubMed1993

[Phlebography of the leg veins. Study quality and sources of error].

In a retrospective study, 198 contrast venographies were evaluated by two blinded observers for quality of opacification of the venous system and quality of documentation. There was good correlation between the two observers in 91% of the cases. They found an adequate contrast quality in 183 cases (92.4%), while in 15 cases (7.6%) incomplete contrast was found in some parts of the calf or pelvic veins. Most venograms (195, or 98.5%) were adequately documented. In conclusion, contrast venography is an excellent method for evaluation of the venous system, if performed adequately. Nevertheless, there is room for improvement of both technique and documentation.

Adolescent↗
PubMed1993

Fundamental sources of error and spectral broadening in Doppler ultrasound signals.

Analysis of the signals, spectra and error bounds for Doppler ultrasound signals is challenging and involves numerous concepts in signal analysis, probability, acoustics, and fluid mechanics. Nonetheless, the results of this analysis must be accessible to both engineers and clinicians who work with ultrasound technology. The engineer who designs, builds, or maintains equipment must know whether specific artifacts are fundamental or can be eliminated. The clinician must be able to interpret whether specific signal features accurately represent the flow field or result from limitations of Doppler ultrasound. This article reviews recent advances in both conceptual and numerical models of the Doppler ultrasound process, and relates these advances to practical aspects such as spectral broadening, velocity estimation error, and data analysis error. It then reviews recent innovations in system implementation and signal analysis which are indicative of the future potential of Doppler ultrasound instrumentation.

Artifacts↗
PubMedDate not supplied

Quality control of gamma counters. I. Experimental evaluation of sources of error.

Errors of counting rate as large as 2 percent may occur through variations in instrumental parameters during the measurement of I-125 activity using a gamma counter. Much larger errors result from failure to maintain constant sample geometry; in particular, the slope of calibration curves depends on sample volume.

Quality Control↗