Observer variation in spirometry.
The intra-observer and inter-observer variation associated with clinical spirometry was statistically analyzed. The technical errors for the MEFR and MMF measurements were large enough to question their clinical reliability, especially in borderline instances. Measurement differences between two observers, as in this study, are statistically significant. This observation has special meaning for groups engaged in epidemiologic studies. Significant inter-individual variation will diminish the quality of pooled results.
Variability of routine pulmonary function tests1
Hruby, J. and Butler, J. (1975). Thorax, 30, 548-553. Variability of routine pulmonary functon tests. Pulmonary function tests sometimes indicate a progressive deterioration and at other times a 'stepwise' worsening which may be followed by improvement. Interpretation depends on the extent of random or diurnal variations in function. Routine pulmonary function tests (VC, FEV,, FRC, and airway resistance (Raw)) were repeatedly measured in normal subjects, patients with stable irreversible airways obstruction, and patients with stable restrictive disease. In all groups there was a significant (P<0 001) diurnal variation in Raw, with high values in the morning, low values at noon, and rising values in the evening. The midday Raw values were about 80% of the highest daily values. The considerable random and diurnal variability seen in all tests is reflected in the range of high and low values (% of mean individual response) in individuals. The largest variation in an individual between measurements taken at two different times was 81% in Raw (range: 40% above to 41% below the mean). There was less variation in FEV, (29%), FRC (62%), and VC (30%). Thus the finding of a stepwise change in function could reflect its natural variability. When repeated studies are done to assess progress or the effects of therapy on disease, there are many factors, including the time of day at which the tests are performed, which should be standardized as far as possible.
Effects of reservoir volume on performance of pulse tube cooler.
A pulse tube cooler has the advantages of long-life and low-vibration over conventional cryocoolers such as G-M and Stirling coolers because of the absence of moving parts at low temperature. On the other hand, the combination of a reservoir and orifice is indispensable to optimize the performance of pulse tube coolers. In order to make the pulse tube cooler compact for practical applications, the volume of reservoir should be minimized. This paper analyzes the effects of the reservoir volume on the thermodynamic performance of various components in a simple orifice and a double-inlet pulse tube cooler by combining a linearized model with a thermodynamic analysis. Expressions of entropy production for those components are presented. The results show that the reservoir volume has a significant influence on the entropy production in the various components when the reservoir to pulse tube volume ratio is smaller than about 5. The ratio is important to determine the minimum reservoir volume for a pulse tube cooler. Optimum settings for a double-inlet pulse tube cooler are also discussed.