Section of Measurement in Medicine
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demiological study on 1400 men. Tape cassette Conclusions records were obtained both with air and He-02 Flow can be accurately derived using a spirometer mixture. The digital display reading of FEV1 and with an output on magnetic tape of the increments FVC was noted by the operator and this agreed of volume every 10 ms. The computing techniques within 10 ml with the volumes calculated later involved are simple. The accuracy and effective from the tape, provided that identical criteria were response time of the method can be improved by used for the start and end of a breath. No loss of decreasing the minimum volume increment and pulses on the tape occurred even after many increasing the sampling rate respectively. There is, replays. however, no evidence that for routine flow-volume During this study a visual display for monitoring recordings such improvement is necessary. purposes was produced by electronic differen- REFERENCES tiation of the volume signal from the poten- McDermott M, Bevan M M, James P J & McDermott T J tiometer and the flow-volume curve displayed on a (1976) Bulletin europen de physiopathologie respiratoire 12, 110lIlP fast X-Y plotter. Physical Laboratory The flow at 500% FVC which was calculated National (1957) Modem Computing Methods. NPL Notes on Applied from the tape records was approximately 100% Science No. 16 lower than that obtained from the X-Y plotter trace. This was caused by the differentiator design which introduced a frequency-dependent time de- Dr A Pack and Mrs Rosemary McCusker lay of flow with respect to volume, equivalent to (Centrefor Respiratory Investigation, about 25 ms at 50 % FVC. Royal Infirmary, Glasgow, G4 OSE) Redesign of the differentiator reduced the delay and made the tape and differentiator flows at the Application of Computers to Automation same volume much more similar. This illustrates of Pulmonary Function Tests the difficulties of estimating flow at specific fractions of the vital capacity when small time delays Computer systems are employed more widely in can be introduced either by electronic circuits or by biochemistry and haematology laboratories than mechanical recorders. in pulmonary function laboratories. In the former the need for a computer system is determined by Comparison of Flow-time Curves from the Tape the large number of tests performed. The main with those using a Pneumotachograph needs for computerization in the pulmonary funcIn a laboratory study of 6 normal subjects flow- tion laboratory are related to the amount of data time curves were obtained using three techniques: processing required for certain individual tests and (1) the flow-volume spirometer and tape cassette to the implementation of quality control prorecords; (2) the spirometer and electronic differen- cedures. The application of computers in pultiator to record flow with respect to time on a monary function laboratories will be considered in Mingograph jet pen recorder with a flat frequency four main areas: systems for epidemiological response up to 600 Hz; (3) a Lilly type pneumo- work, systems for on-line testing, systems for tachograph with a 10 cm diameter gauze to meas- control of the test procedure, and a complete ure flow and a Mingograph recorder. The peak system for a pulmonary function laboratory. flow using the pneumotachograph was taken as the In epidemiological studies the need for comhighest flow lasting at least 10 ms. In the pneumo- puterization is related to the large number of tests tachograph records the rise time to maximum flow performed. Many systems in use involve only data took about 50 ms longer than with both other logging equipment with subsequent analysis of the methods. data on the laboratory computer system. With Using the tape records the flow calculated from such systems, problems of a technical nature in the the mean of the highest three consecutive volume performance of the test are translated as problems increments minus 0.33 1/s (the maximum digital- for computer staff attempting to analyse imperfect ization and computation error) gave peak flows up data. There is a need for such systems to have to 18 % higher than those obtained with the immediate data processing capability: this could pneumotachograph; whereas the highest flow cal- be achieved using microprocessor technology. culated from a mean of 10 volume increments Many laboratories employ small computer sys(m = 5), which is an average over 100 ims, gave tems for the on-line performance of certain tests, results similar to the pneumotachograph peak usually related to the research interest of the flow. laboratory. Whilst it may achieve the initial objecThis suggests that the pneumotachograph re- tives of the laboratory, this approach has limisponse time is not as fast as had been assumed. It is tations. The computer system is used inefficiently. difficult to see how the spirometer method could Much of the time is spent in data logging, usually overestimate the flow. at relatively low data rates. With small computer
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systems there are problems in attempting to carry out further development work, while using the computer system for on-line testing. On-line techniques are employed particularly when there is a requirement for analysis of continuously measured data, e.g. breath-by-breath studies of gas exchange (Beaver et al. 1973). The performance of such tests is virtually impossible without computational facilities. On-line systems can also be used for control of the test procedure. Such techniques can allow more sophisticated control of experiments than is possible by manual methods. An example of this is the technique of dynamic end-tidal forcing (Swanson & Bellville 1974). This enables the experimenter to obtain changes in alveolar gas concentrations of the required form, e.g. sinusoidal changes. The system for processing data from routine tests of pulmonary function in this laboratory is a batch-processing system. Data from the tests which are performed are entered by technical staff onto specially designed work sheets. Data are put in to the computer system on paper tape. All input items are checked by the programme as being within a range which has been defined and is appropriate to that specific measurement. This checking procedure detects transcription errors and errors in data preparation. The calculation programme is organized in an overlay structure with separate programmes for each logical group of tests. The system produces two types of report: one for return to the referring physician, and one for laboratory purposes. The computer system adds an interpretative comment to the report. Important by-products of the system are work reports, which are produced weekly, and archival files for research purposes. The system will also produce results for patients who have been tested previously, in a form suitable for transfer to other laboratories. The need for transfer of patients' results should increase as routine pulmonary function testing is applied more widely. The main defects of this system are the need for preparation of data and the relative loss of job satisfaction for technical staff, since there is not an immediate end-product. This may accentuate the problem of quality control in a laboratory which is carrying out a large number of tests. A possible solution to this problem is to introduce a limited data processing capability for each type of laboratory test. Such a solution is now feasible at relatively low cost, using microprocessor technology. It is possible to incorporate in the microprocessor criteria by which it is decided whether the data obtained are acceptable. This will perhaps provide a solution to the difficult problem of implementing quality control in pulmonary function laboratories.
REFERENCES Beaver W L, Wasserman K & Whipp B J (1973) Journal ofApplied Physiology 34, 128-32 Swanson G D & Belhivlle J W (1974) Journal ofApplied Physiology 36,
480-87
Dr Pack in answer to Dr D C S Hutchison said that the staff of the laboratory comprised seven technicians, and one member of the medical staff who was whole-time in the laboratory on a rotational basis; they saw on average 70 patients per week. Mr P K Morgan said that most laboratories acquired their equipment over a period of years; it was quite practicable to add some microprocessing, storage and display equipment and to feed the semiprocessed data to a central computer. The programming could often be done by the technician himself, though this was becoming more difficult. In answer to Dr J E Cotes, Mr Morgan said that the microprocessors might cost anything between £5 and £800. Mr C Derrett added that the microprocessor was normally preprogrammed, though not necessarily so.
Dr Michael Sudlow (Department of Medicine, University of Edinburgh, The Medical School, Edinburgh, EH8 9AG)
Body Plethysmography
The characteristics of pressure, flow and volume plethysmography were described. All are techniques for the measurement of changes in the volume of air in the lungs where these are significantly different from the changes in volume recorded at the mouth. A volume displacement plethysmograph with pressure compensation to improve the frequency response has been developed and linked to a PDP 11-40 computer, on-line, for the monitoring and measurement of lung volumes, forced expiratory manoeuvres (flow volume curves) and dynamic and static lung compliance. Volume is determined with a wedge spirometer connected directly to the plethysmograph, output is taken from a displacement transducer attached to the spirometer hinge. Flow at the mouth is recorded by a Fleish pneumotachograph and pressure transducer. Plethysmograph pressure, mouth pressure and cesophageal pressure are monitored using straingauge transducers with appropriate sensitivities, and in the case of cesophageal pressure low volume displacement. After amplification all the signals are fed into the computer through matched 15 Hz filters. The spirometer and plethysmograph pressure signals are mixed before filtering to improve the frequency response of the volume signal. Preset electrical calibrations are used for flow and pressure signals.
171
demiological study on 1400 men. Tape cassette Conclusions records were obtained both with air and He-02 Flow can be accurately derived using a spirometer mixture. The digital display reading of FEV1 and with an output on magnetic tape of the increments FVC was noted by the operator and this agreed of volume every 10 ms. The computing techniques within 10 ml with the volumes calculated later involved are simple. The accuracy and effective from the tape, provided that identical criteria were response time of the method can be improved by used for the start and end of a breath. No loss of decreasing the minimum volume increment and pulses on the tape occurred even after many increasing the sampling rate respectively. There is, replays. however, no evidence that for routine flow-volume During this study a visual display for monitoring recordings such improvement is necessary. purposes was produced by electronic differen- REFERENCES tiation of the volume signal from the poten- McDermott M, Bevan M M, James P J & McDermott T J tiometer and the flow-volume curve displayed on a (1976) Bulletin europen de physiopathologie respiratoire 12, 110lIlP fast X-Y plotter. Physical Laboratory The flow at 500% FVC which was calculated National (1957) Modem Computing Methods. NPL Notes on Applied from the tape records was approximately 100% Science No. 16 lower than that obtained from the X-Y plotter trace. This was caused by the differentiator design which introduced a frequency-dependent time de- Dr A Pack and Mrs Rosemary McCusker lay of flow with respect to volume, equivalent to (Centrefor Respiratory Investigation, about 25 ms at 50 % FVC. Royal Infirmary, Glasgow, G4 OSE) Redesign of the differentiator reduced the delay and made the tape and differentiator flows at the Application of Computers to Automation same volume much more similar. This illustrates of Pulmonary Function Tests the difficulties of estimating flow at specific fractions of the vital capacity when small time delays Computer systems are employed more widely in can be introduced either by electronic circuits or by biochemistry and haematology laboratories than mechanical recorders. in pulmonary function laboratories. In the former the need for a computer system is determined by Comparison of Flow-time Curves from the Tape the large number of tests performed. The main with those using a Pneumotachograph needs for computerization in the pulmonary funcIn a laboratory study of 6 normal subjects flow- tion laboratory are related to the amount of data time curves were obtained using three techniques: processing required for certain individual tests and (1) the flow-volume spirometer and tape cassette to the implementation of quality control prorecords; (2) the spirometer and electronic differen- cedures. The application of computers in pultiator to record flow with respect to time on a monary function laboratories will be considered in Mingograph jet pen recorder with a flat frequency four main areas: systems for epidemiological response up to 600 Hz; (3) a Lilly type pneumo- work, systems for on-line testing, systems for tachograph with a 10 cm diameter gauze to meas- control of the test procedure, and a complete ure flow and a Mingograph recorder. The peak system for a pulmonary function laboratory. flow using the pneumotachograph was taken as the In epidemiological studies the need for comhighest flow lasting at least 10 ms. In the pneumo- puterization is related to the large number of tests tachograph records the rise time to maximum flow performed. Many systems in use involve only data took about 50 ms longer than with both other logging equipment with subsequent analysis of the methods. data on the laboratory computer system. With Using the tape records the flow calculated from such systems, problems of a technical nature in the the mean of the highest three consecutive volume performance of the test are translated as problems increments minus 0.33 1/s (the maximum digital- for computer staff attempting to analyse imperfect ization and computation error) gave peak flows up data. There is a need for such systems to have to 18 % higher than those obtained with the immediate data processing capability: this could pneumotachograph; whereas the highest flow cal- be achieved using microprocessor technology. culated from a mean of 10 volume increments Many laboratories employ small computer sys(m = 5), which is an average over 100 ims, gave tems for the on-line performance of certain tests, results similar to the pneumotachograph peak usually related to the research interest of the flow. laboratory. Whilst it may achieve the initial objecThis suggests that the pneumotachograph re- tives of the laboratory, this approach has limisponse time is not as fast as had been assumed. It is tations. The computer system is used inefficiently. difficult to see how the spirometer method could Much of the time is spent in data logging, usually overestimate the flow. at relatively low data rates. With small computer
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Proc. roy. Soc. Med. Volume 70 March 1977
systems there are problems in attempting to carry out further development work, while using the computer system for on-line testing. On-line techniques are employed particularly when there is a requirement for analysis of continuously measured data, e.g. breath-by-breath studies of gas exchange (Beaver et al. 1973). The performance of such tests is virtually impossible without computational facilities. On-line systems can also be used for control of the test procedure. Such techniques can allow more sophisticated control of experiments than is possible by manual methods. An example of this is the technique of dynamic end-tidal forcing (Swanson & Bellville 1974). This enables the experimenter to obtain changes in alveolar gas concentrations of the required form, e.g. sinusoidal changes. The system for processing data from routine tests of pulmonary function in this laboratory is a batch-processing system. Data from the tests which are performed are entered by technical staff onto specially designed work sheets. Data are put in to the computer system on paper tape. All input items are checked by the programme as being within a range which has been defined and is appropriate to that specific measurement. This checking procedure detects transcription errors and errors in data preparation. The calculation programme is organized in an overlay structure with separate programmes for each logical group of tests. The system produces two types of report: one for return to the referring physician, and one for laboratory purposes. The computer system adds an interpretative comment to the report. Important by-products of the system are work reports, which are produced weekly, and archival files for research purposes. The system will also produce results for patients who have been tested previously, in a form suitable for transfer to other laboratories. The need for transfer of patients' results should increase as routine pulmonary function testing is applied more widely. The main defects of this system are the need for preparation of data and the relative loss of job satisfaction for technical staff, since there is not an immediate end-product. This may accentuate the problem of quality control in a laboratory which is carrying out a large number of tests. A possible solution to this problem is to introduce a limited data processing capability for each type of laboratory test. Such a solution is now feasible at relatively low cost, using microprocessor technology. It is possible to incorporate in the microprocessor criteria by which it is decided whether the data obtained are acceptable. This will perhaps provide a solution to the difficult problem of implementing quality control in pulmonary function laboratories.
REFERENCES Beaver W L, Wasserman K & Whipp B J (1973) Journal ofApplied Physiology 34, 128-32 Swanson G D & Belhivlle J W (1974) Journal ofApplied Physiology 36,
480-87
Dr Pack in answer to Dr D C S Hutchison said that the staff of the laboratory comprised seven technicians, and one member of the medical staff who was whole-time in the laboratory on a rotational basis; they saw on average 70 patients per week. Mr P K Morgan said that most laboratories acquired their equipment over a period of years; it was quite practicable to add some microprocessing, storage and display equipment and to feed the semiprocessed data to a central computer. The programming could often be done by the technician himself, though this was becoming more difficult. In answer to Dr J E Cotes, Mr Morgan said that the microprocessors might cost anything between £5 and £800. Mr C Derrett added that the microprocessor was normally preprogrammed, though not necessarily so.
Dr Michael Sudlow (Department of Medicine, University of Edinburgh, The Medical School, Edinburgh, EH8 9AG)
Body Plethysmography
The characteristics of pressure, flow and volume plethysmography were described. All are techniques for the measurement of changes in the volume of air in the lungs where these are significantly different from the changes in volume recorded at the mouth. A volume displacement plethysmograph with pressure compensation to improve the frequency response has been developed and linked to a PDP 11-40 computer, on-line, for the monitoring and measurement of lung volumes, forced expiratory manoeuvres (flow volume curves) and dynamic and static lung compliance. Volume is determined with a wedge spirometer connected directly to the plethysmograph, output is taken from a displacement transducer attached to the spirometer hinge. Flow at the mouth is recorded by a Fleish pneumotachograph and pressure transducer. Plethysmograph pressure, mouth pressure and cesophageal pressure are monitored using straingauge transducers with appropriate sensitivities, and in the case of cesophageal pressure low volume displacement. After amplification all the signals are fed into the computer through matched 15 Hz filters. The spirometer and plethysmograph pressure signals are mixed before filtering to improve the frequency response of the volume signal. Preset electrical calibrations are used for flow and pressure signals.
