The effect of temperature on recording spirograms

Joint Indian Chest Society-National College of Chest Physicians (India) guidelines for spirometry

Although a simple and useful pulmonary function test, spirometry remains underutilized in India. The Indian Chest Society and National College of Chest Physicians (India) jointly supported an expert group to provide recommendations for spirometry in India. Based on a scientific grading of available published evidence, as well as other international recommendations, we propose a consensus statement for planning, performing and interpreting spirometry in a systematic manner across all levels of healthcare in India. We stress the use of standard equipment, and the need for quality control, to optimize testing. Important technical requirements for patient selection, and proper conduct of the vital capacity maneuver, are outlined. A brief algorithm to interpret and report spirometric data using minimal and most important variables is presented. The use of statistically valid lower limits of normality during interpretation is emphasized, and a listing of Indian reference equations is provided for this purpose. Other important issues such as peak expiratory flow, bronchodilator reversibility testing, and technician training are also discussed. We hope that this document will improve use of spirometry in a standardized fashion across diverse settings in India.

Effect of spirometer temperature on FEV1 in a longitudinal epidemiological study

OBJECTIVES

To assess the magnitude of error in pulmonary function measurements introduced by variation in spirometer temperature under field conditions. In a large scale epidemiological study of school children, the influence was investigated of spirometer temperature on forced expiratory volume in 1 second (FEV1) measured with dry rolling seal volumetric spirometers and conventional body temperature, pressure, and saturation (BTPS) corrections.

METHODS

Linear regression analyses were performed on data from 995 test-retest pairs on 851 different children, with 1-110 days between test and retest, and spirometer temperature differences between -13 degrees C and +9 degrees C.

RESULTS

After adjusting for effects of growth (test-retest intervals) and circadian variation (changes in times of testing), differences in standard BTPS corrected FEV1 showed significant (p < 0.05) dependence on differences in spirometer temperature between tests (-0.24%/degree C).

CONCLUSIONS

When spirometer temperatures vary widely, standard BTPS correction does not fully adjust for gas contraction. To improve accuracy of volume measurements in epidemiological studies, additional correction for variation in spirometer temperature should be considered.

Assessment of a new transtelephonic portable spirometer

BACKGROUND

A new portable spirometer, the Spirophone, has been developed that records a subject's blow and can then transmit all the data by telephone to a receiving centre for analysis and comment. Tests of this device were undertaken to determine its accuracy and reliability.

METHODS

The performance of the Spirophone was tested using computer generated wave forms, by delivering blows from calibrated syringes at different flows, and by comparing subjects' blows with those recorded with a commercial spirometer.

RESULTS

Using computer generated wave forms all lung function indices were accurate to within 1% and blows delivered from calibrating syringes were accurate to within 5%. When subjects performed repeated forced vital capacity (FVC) manoeuvres there were no significant differences between lung function indices recorded with the Spirophone and with a commercial spirometer. With the Spirophone and commercial spirometer in series the FVC and forced expiratory volume in one second (FEV1) were within 5% of each other in nine out of 10 healthy subjects.

CONCLUSION

The Spirophone recorded maximal forced expiratory manoeuvres with acceptable accuracy, reliability, and reproducibility, and this system offers the ability to monitor a patient's lung function at a centre remote from the patient.

The accuracy of portable peak flow meters

BACKGROUND

The variability of peak expiratory flow (PEF) is now commonly used in the diagnosis and management of asthma. It is essential for PEF meters to have a linear response in order to obtain an unbiased measurement of PEF variability. As the accuracy and linearity of portable PEF meters have not been rigorously tested in recent years this aspect of their performance has been investigated.

METHODS

The response of several portable PEF meters was tested with absolute standards of flow generated by a computer driven, servo controlled pump and their response was compared with that of a pneumotachograph.

RESULTS

For each device tested the readings were highly repeatable to within the limits of accuracy with which the pointer position can be assessed by eye. The between instrument variation in reading for six identical devices expressed as a 95% confidence limit was, on average across the range of flows, +/- 8.5 l/min for the Mini-Wright, +/- 7.9 l/min for the Vitalograph, and +/- 6.4 l/min for the Ferraris. PEF meters based on the Wright meter all had similar error profiles with overreading of up to 80 l/min in the mid flow range from 300 to 500 l/min. This overreading was greatest for the Mini-Wright and Ferraris devices, and less so for the original Wright and Vitalograph meters. A Micro-Medical Turbine meter was accurate up to 400 l/min and then began to underread by up to 60 l/min at 720 l/min. For the low range devices the Vitalograph device was accurate to within 10 l/min up to 200 l/min, with the Mini-Wright overreading by up to 30 l/min above 150 l/min.

CONCLUSION

Although the Mini-Wright, Ferraris, and Vitalograph meters gave remarkably repeatable results their error profiles for the full range meters will lead to important errors in recording PEF variability. This may lead to incorrect diagnosis and bias in implementing strategies of asthma treatment based on PEF measurement.

Changes in maximum expiratory flow-volume curve configuration after treatment with inhaled corticosteroids

The present study reports the changes in configuration of maximal flow-volume curves after eight weeks' treatment with inhaled corticosteroids in 14 asthmatic patients. The configuration was compared with that seen after bronchodilatation following inhalation of a single dose of ipratropium bromide. After inhaled corticosteroids the shape of the flow-volume curves was less bowed toward the volume axis, whereas the shape of the flow-volume curves after inhalation of ipratropium bromide showed no significant change. A significant correlation was observed between the decrease in blood eosinophil cell count and the straightening of the flow-volume curves, quantitatively expressed as shape factor and slope ratio. It is concluded that these changes in flow-volume curve configuration reflect a decrease in inhomogeneously distributed inflammatory airway narrowing.