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ABSTRACT: The frequency content of the first second of the maximum forced expiratory manoeuvre (MFEM) was measured to determine if the currently accepted frequency limit of 20 Hz for MFEM is adequate for recording peak expiratory flow (PEF). The frequency response of a Fleisch pneumotachograph (PT) was measured and used to record MFEM from 24 patients attending a lung-function laboratory and 26 normal volunteers. The first 1.024 s of the signal recorded at 1,000 Hz for that blow with maximum PEF, underwent fast Fourier transformation using a triangular window function, applied after 0.75 s to reduce flow linearly to zero. All the frequencies above a set limit were removed, followed by inverse transformation to reconstitute the blow. The limits for this frequency cut-off were progressively varied from 100 Hz down to 15 Hz, with the resulting PEF being compared with the PEF from the reconstituted blow with no frequency reduction. The average+/-SD age for the group was 47+/-18 yrs and the average PEF was 450+/-187 L x min(-1), which, when expressed as a standardized residual, was 0.1+/-2.1, with a range from -4.5-3.9 indicating a good spread around normal values. Average rise time to PEF was 83+/-38 ms and dwell time >90% PEF was 45+/-25 ms. Cut-off >20 Hz reduced the mean PEF of the group by 8.5 L x min(-1) (95% confidence limit 5.5-11.4 L x min(-1)), whereas cut-off >30 Hz reduced mean PEF by 4.4 L x min(-1) (2.6-6.2). In the present study subjects, 30 Hz was on the 95th percentile of frequencies for defining the upper limit for 98% of the power spectrum for the first second of the blow. It has been shown that there are frequencies >20 Hz that contribute to peak expiratory flow enough to influence readings made using conventional hand-held peak expiratory flow meters, such as the mini-Wright. Devices used for recording flow from a maximum forced expiratory manoeuvre should therefore have an adequate frequency response of up to 30 Hz.
European Respiratory Journal 03/2002; 19(3):530-3. · 5.89 Impact Factor
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ABSTRACT: Goiter is a common condition and can cause upper airway obstruction (UAO), which may be difficult to detect. We have studied maximal expiratory and inspiratory flow volume loops using a neural network to see if this offers a better way to identify patients with UAO. The flow-volume loops from 155 patients with goiter were assessed by a human expert and sorted into those with and without UAO. The reliability of this assessment was judged by using two observers who repeated the sorting 8 wk apart. A set of 46 patients with loops suggesting UAO and a set of 51 patients with normal flow loops were taken from these 155, and the loops from a further 50 subjects with airflow limitation caused by chronic obstructive pulmonary disease were used for training and testing the neural network. Novel and standard indices were derived from the loops and used by the neural network. The kappa score for agreement between each of the observers and the original classification were 0.5 and 0.46, respectively, with the agreement between the observers at each reading of 0.58 and 0.68. The neural network found that a combination of four novel scores for flatness of the expiratory loop, the moment ratio, and the FEV1/PEF ratio was best at identifying UAO with a kappa score of 0.81, a sensitivity of 88%, specificity of 94% and an accuracy of 92%. We conclude that a neural network using only six indices taken from the expiratory limb of a flow-volume loop was better than human experts at identifying flow loops with UAO.
American Journal of Respiratory and Critical Care Medicine 07/1998; 157(6 Pt 1):1885-91. · 11.08 Impact Factor
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ABSTRACT: Corticosteroid inhaler therapy using a spacer device is commonly used as an important part of asthma management. Increasingly, generic corticosteroid inhalers are being used with spacer devices. We have therefore tested whether these generic inhalers yield equivalence in dose when compared to the established inhalers. We measured the in vitro output, discharged into a Volumatic spacer from beclomethasone dipropionate inhalers (250 micrograms.puff-1) made by three manufacturers, Allen & Hanburys, 3M and Baker Norton. The output from 20 of each type of inhaler was sampled, in random order, by a computer driven pump system. Beclomethasone was absorbed onto a coded filter, which was analysed independently for drug content. The output per puff differed significantly between the inhalers of each manufacturer, with a 36% difference between the highest output from the Allen & Hanburys device and the lowest output device. We conclude that there are important differences in output from these inhalers when used with a spacer, and that substitution of one device with another will not necessarily give equivalent therapy to the patient.
European Respiratory Journal 11/1995; 8(10):1637-8. · 5.89 Impact Factor
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ABSTRACT: We have studied the temperature of expired air during a maximal forced expiratory manoeuvre, because this has not previously been fully investigated and it will influence how flow and volume recording devices should be calibrated and used. Temperature was recorded with a fine thermocouple, the response time of which was determined at various gas velocities and for which a correction was made. Recordings during maximal forced expiratory manoeuvres were made on 12 normal subjects and 12 subjects with chronic airflow limitation. The thermocouple was placed in the mouthpiece, so that it was at the level of the lips during a blow. In the normal subjects, the effect of differing inhalation protocols was also determined. In the normal subjects, the mean temperature was 33.6 degrees C at peak expiratory flow (PEF), and 34.4 degrees C at 75% forced vital capacity (FVC), but fell to 33.4 degrees C at FVC. In the subjects with chronic airflow limitation, the temperature was constant at 35.0 degrees C from PEF up to 50% FVC, being significantly higher than in the normals, and fell to 33.5 degrees C at FVC. Expired air temperature up to 50% FVC was significantly negatively correlated with absolute PEF, forced expiratory volume in one second (FEV1) and FVC. In the normals, a slow inhalation through the nose raised the expired temperature by almost 1 degree C throughout the blow, whereas inhaling air at 6 degrees C did not affect expired air temperature. The expired air temperature can vary by up to 3 degrees C between individual subjects, and it is influenced by the route of inhalation and the inspired volume.(ABSTRACT TRUNCATED AT 250 WORDS)
European Respiratory Journal 12/1993; 6(10):1556-62. · 5.89 Impact Factor
