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Biomedical subjects

A H Kendrick

Publications and source records attributed to A H Kendrick.

At least 19 recordsLinked to original sources
PubMed1998

The effect of physiologic and mechanical aging on the performance of peak flowmeters.

PURPOSE: To investigate the effects of physiologic and mechanical aging on peak flowmeters. MATERIALS AND METHODS: Eight each of MiniWright (MW; Clement Clark; Harlow, UK), Personal-Best (PB; HealthScan Products; Cedar Grove, NJ), Vitalograph (V; Vitalograph Ltd; Buckingham, UK), and Breath-Taker (BT; Medical Development Australia; Melbourne, Australia) peak flowmeters were assessed for accuracy and repeatability before and after aging using a computer-driven syringe to deliver peak flows from 100 to 700 L/min. Four of each type of flowmeter were physiologically aged by normal subjects performing up to six peak flows daily for 1 year. The remaining four of each flowmeter were mechanically aged using an accelerated aging device to deliver 2,000 exponential waveforms with a peak flow of 600 L/min over a period of 3 h. RESULTS: The V and BT flowmeters were linear and accurate over the range 100 to 700 L/min, while the PB overread at high flows. The MW was alinear throughout. The SD of the difference between readings before and after aging ranged from 8.6 to 40.6 L/min (mean, 9.2). Comparing the slopes of the relationship of actual against reference peak expiratory flow (PEF) showed that 16 flowmeters--5 BTs, 6 MWs, 4 PBs, and 1 V had no significant change in slope after aging. Mechanical aging caused a consistent underreading in PEF at high flow rates. Physiologic aging showed a more variable pattern both within and between flowmeter types. The MW was the most affected by physiologic aging, producing overestimates of PEF by as much as 100 L/min at 500 L/min. CONCLUSIONS: We conclude that the effects of physiologic and mechanical aging are different, and that while mechanical aging may provide a guide to the effects of aging, studies using physiologic aging would be more appropriate.

Equipment Failure↗
PubMed1997

Staff education.

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Drug Delivery Systems↗
PubMed1996

Comparison of methods of measuring static lung volumes.

The measurement of static lung volumes is important for the accurate diagnosis of lung disorders, and when making volume-dependent measurements, such as airways resistance. There are a variety of methods available. The most accurate method is that of constant volume body plethysmography, which provides an estimate of total lung capacity regardless of the presence of airflow obstruction. Whilst this method may overestimate lung volumes in asthmatics, and is technically more demanding than gas dilution methods, this should be regarded as the principal method for estimating lung volumes. Gas dilution estimates of multi-breath helium or nitrogen dilution or single-breath estimates using the same gases all underestimate total lung capacity in the presence of airflow obstruction. Single-breath methods will underestimate volumes to a greater extent than multi-breath methods. Multi-breath helium dilution is currently regarded as the acceptable alternative to body plethysmography. Estimates of lung volumes from chest radiographs provide an estimate of lung volumes independent of airflow obstruction. They are probably prone to greater variability than body plethysmographic estimates, and it is regarded as unacceptable to expose patients to excess radiation. Other methods being developed include estimates from nuclear magnetic imaging and computed tomography.

Humans↗
PubMed1995

The efficacy of filters used in respiratory function apparatus.

The ability of two low resistance barrier filters (Collins DC-1 and Pall Pf 305) to remove bacteria from expired air was assessed. A specially designed coupling device was used to hold each filter or a disposable plain cardboard mouthpiece a fixed distance (4.5 cm) from a blood agar plate. Volunteers performed maximal forced vital capacity manoeuvres through the assembled apparatus and bacteria impinged on to the agar plate were enumerated. Both filters allowed the transmission of approximately one-third of expired colony forming units. The efficacy of these filters for reducing the likelihood of cross-infection during spirometry is not supported by this study.

Air Microbiology↗
PubMed1995

Comparison of twenty three nebulizer/compressor combinations for domiciliary use.

We have assessed the physical and dynamic characteristics of 23 home jet nebulizer/compressor combinations currently available in the UK and Europe. The combinations were evaluated in terms of pressure-flow characteristics, aerosol mass distribution, volume output, electrical costs, and sound level. In addition, we determined the effect of nebulizer fill volume on aerosol mass distribution and volume output. One nebulizer was used with six different compressors, and four compressors were tested with three different nebulizers. The pressure-flow relationships showed a wide variation between models, as did flow-rate at the nebulizer (range 3.0-8.0 L.min-1). The mean +/- SD volume nebulized after 10 min using an initial fill volume of 2.5 and 5.0 mL was 46 +/- 9 and 34 +/- 12%, respectively. The mass median aerodynamic diameter (MMAD) over a 5 min nebulization ranged 2.6 to 10.2 microns. Nine of the nebulizations produced an MMAD of less than 5 microns at both fill volumes. Changing nebulizer/compressor combinations affected flow rate, MMAD and volume output. Sound levels varied between models. Running costs were low, with all using less than 74 kilowatt hours of energy per year. We conclude that there is a wide variation in performance of nebulizer/compressor combinations for use with nebulized bronchodilators. Correct matching of the nebulizer/compressor is seen to be important to ensure optimum performance.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Inhalation↗
PubMed1995

Sleep apnoea.

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Humans↗
PubMed1994

Correction of the single breath carbon monoxide transfer factor in exercise for variations in alveolar oxygen pressure.

BACKGROUND: Carbon monoxide transfer factor (TLCO) varies inversely with the partial pressure of alveolar oxygen (PAO2). During exercise the PAO2 in the alveolar gas sample bag decreases so the TLCO increases more than would be expected from the effects of exercise alone. The effects of PAO2 on the estimation of TLCO during exercise have been investigated and studies have been performed to determine whether it is appropriate to standardise to a PAO2 of 16 kPa. METHODS: TLCO was estimated at rest and at a single level of exercise in six normal subjects using test gas mixtures of 0.3% carbon monoxide, 14% helium, and oxygen in three different percentages (17%, 21%, and 27%), remainder nitrogen. In three of the subjects an incremental exercise test with estimates of oxygen consumption (VO2) and cardiac frequency (fC) was also performed using a mixture containing 18% oxygen. RESULTS: TLCO decreased as levels of inspired oxygen increased. When standardised to a PAO2 of 16 kPa TLCO became independent of the inspired oxygen concentration. The significance of the curvilinear relations of TLCO and transfer coefficient to VO2 and fC improved. CONCLUSION: The single breath breath holding TLCO should be standardised to a PAO2 of 16 kPa when estimated during exercise.

Adult↗
PubMed1994

Evaluation of a new electronic spirometer: the vitalograph "Escort" spirometer.

BACKGROUND: The "Escort" spirometer is a lightweight, hand held spirometer employing a Fleisch pneumotachograph. Measurements of forced expiratory volume in one second (FEV1), forced vital capacity (FVC), and peak expiratory flow (PEF) are obtained from a single FVC manoeuvre. Results are displayed on a small liquid crystal display, but there is no graphical display. The performance of the Escort spirometer has been compared with that of a wedge bellows spirometer (Vitalograph S model) and a Wright PEF meter. METHODS: One hundred and thirteen subjects performed three FVC manoeuvres on the wedge bellows and Escort spirometers and three PEF manoeuvres on the Wright meter. The best reading for each index was recorded. In 21 of the subjects comparison of a Wright manoeuvre with an FVC manoeuvre on the Escort spirometer was performed, whilst in three subjects the effect of repeated blows was studied. RESULTS: The FEV1 ranged from 0.5 to 5.4 litres, FVC from 1.05 to 6.2 litres, and PEF from 100 to 725 l/min. The mean (SD) difference for the FEV1 was -0.05 (0.15) (95% confidence interval (95% CI) -0.07 to -0.02) litres, for FVC 0.03 (0.28) (95% CI -0.02 to +0.08) litres, and for PEF 1.68 (50.6) (95% CI -7.7 to +11.1) l/min. The differences were positively correlated with the mean reading for PEF and FVC but not for FEV1. The Wright PEF manoeuvre performed on the Escort produced significantly higher PEF readings (mean difference -22.9 litres). There was no significant effect of repeated FVC manoeuvres on any of the indices. CONCLUSIONS: The Escort spirometer compares extremely well with a wedge bellows spirometer for measurement of FEV1 and FVC, whilst yielding results of PEF from an FVC manoeuvre which are comparable to those obtained from a Wright meter. It can be recommended for use as a portable hand held spirometer.

Evaluation Studies as Topic↗
PubMed1993

Accuracy of perception of severity of asthma: patients treated in general practice.

OBJECTIVE: To determine the frequency of poor perception of severity of asthma in general practice. DESIGN: Asthmatic patients recorded their perceived severity of asthma, with a visual analogue score, and a coded measurement of their peak expiratory flow up to four times daily for 14 consecutive days. SETTINGS: 11 general practices in and around Bristol. SUBJECTS: 255 asthmatic patients (139 men and 116 women) aged 17-76 who were recruited by random selection from the general practices' disease registers or when they requested prescriptions for inhaled bronchodilators. MAIN OUTCOME MEASURES: Correlation between visual analogue scores and peak expiratory flow (as a percentage of predicted peak flow). RESULTS: 152 (60%) of the patients showed no significant correlation between visual analogue asthma scores and simultaneous peak flow measurements (p > 0.05) and were termed poor discriminators. The distribution of good and poor discriminators within each general practice was similar (chi 2 = 6.11, df = 10). The two groups were not characterised by differences in the maximum, minimum, or standard deviation of peak expiratory flow or visual analogue score; in age; or in the proportion of men and women in each group. CONCLUSIONS: In general practice a high proportion of asthmatic patients do not reliably detect changes in their lung function. This reinforces the need for careful objective assessment of lung function in the management of asthma.

Adolescent↗
PubMed1993

Standardisation of gas mixtures for estimating carbon monoxide transfer factor.

BACKGROUND: The American Thoracic Society recommends that the inspired concentration used for the estimation of carbon monoxide transfer factor (TLCO) mixture should be 0.25-0.35% carbon monoxide, 10-14% helium, 17-21% oxygen, balance nitrogen. Inspired oxygen influences alveolar oxygen and hence carbon monoxide uptake, such that transfer factor increases by 0.35% per mm Hg decrease in alveolar oxygen. To aid in the standardisation of TLCO either a known inspired oxygen concentration should be used, or TLCO should be corrected to a standard inspired oxygen concentration. The range of gas mixtures used in practice and the implications for cost and accuracy have been investigated. METHODS: A questionnaire was sent to 185 respiratory units in the UK requesting information on (1) the method used to estimate TLCO, (2) the manufacturer of the equipment, (3) the mixture used, (4) whether "medical quality" gas was ordered, and (5) the level of satisfaction with supplier service. RESULTS: Replies were received from 106 units. Most used the single breath breath holding method for which 17 different test mixtures were ordered. One unit also used the single breath exhalation method. Inspired oxygen ranged from 17.94% to 25%, giving a wide variation in alveolar oxygen and hence TLCO. Forty seven units ordered a specific inspired oxygen, the rest ordering "air" as balance. The cost per litre of gas varied greatly, with the mixture 14% helium, 0.28% carbon monoxide, balance air (17.9% oxygen) and 10% helium, 0.28% carbon monoxide, balance air (18.8% oxygen) being cheapest to produce. Ordering a specific inspired oxygen concentration increased the cost. Large cylinders of gas were cheaper for the same mixture. The mixture for the exhalation method was the most expensive. Sixty seven units ordered "medical quality" gas and six assumed this was supplied. Twenty nine (27%) were dissatisfied with their supplier due to (1) poor service, (2) long delivery times, (3) costs, or (4) wrongly labelled cylinders. CONCLUSIONS: It is recommended that two mixtures be available: (a) 14% helium, 0.28% carbon monoxide, balance air for a helium analyser reading up to 15%, and (b) 10% helium, 0.28% carbon monoxide, balance air for lower reading helium analysers. The mixture should be produced under a medical product licence. The advantage of the single exhalation method for routine clinical use needs to be investigated in view of the higher cost of the mixture.

Carbon Monoxide↗
PubMed1993

Normal values and predictive equations for aerodynamic function in British Caucasian subjects.

Many useful objective measurements of air volume and flow may be made with a high degree of validity and reliability using present-day respirometers within a speech clinic. We have studied measures of aerodynamic function in 76 British Caucasian subjects and derived reference equations for mean flow rate (MFR), phonation quotient (PQ), vocal velocity index (VVI), phonation time and the phonation volume/vital capacity ratio. Measures from resting breathing patterns have also been investigated. Age was found to be an important determinant in the reference equations. MFR, PQ and VVI were all greater than previously reported. The equations derived in this study should provide a more appropriate assessment of aerodynamic function than the previously reported normal ranges.

Adult↗
PubMed1993

How do inhaled bronchodilators work?

1. Beta-agonists affect bronchodilation of the airways by their action on the bronchial smooth muscles. 2. Anticholinergic drugs affect bronchodilation of the airways by blocking the effect of acetylcholine and its bronchoconstrictor action. 3. Receptors are protein molecules found in cell membranes; they can selectively bind to messenger molecules and transduce a chemical signal into a response in a target cell.

Acetylcholine↗