Biomedical subjects
Publications and source records attributed to A H Kendrick.
1. When lung function is being measured, it is important that it is accurately interpreted and reported. 2. Clinical history and previously recorded values should be taken into account. 3. When correctly interpreted, measurements can provide useful information to aid diagnosis.
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The performance of a Vitalograph spirometer has been compared with a rolling seal spirometer (Ohio) to determine whether (i) spirometric measurements are normally distributed, (ii) fatigue occurs with repeated attempts, and (iii) how many tests are required. Twenty forced expiratory manoeuvres were performed on both spirometers at minute intervals, on ten normal subjects. To determine how many tests were required, the first five manoeuvres for each subject were analysed using eleven algorithms. The Vitalograph had a smaller volume, a shorter timing duration and a combined inertia and resistance greater than the European standards. The Ohio complied with the standards for volume and timing duration and had a much lower combined inertia and resistance. For each device, the spirometric indices were normally distributed, there were no fatigue effects, and no significant difference between any two algorithms. We conclude that (1) the performance of repeated forced expiratory manoeuvres using the Vitalograph spirometer does not result in fatigue, (2) spirometric indices are normally distributed, (3) estimation of forced expiratory flows between 25-50% of vital capacity from a Vitalograph may not be appropriate, and (4) the best of a number of technically satisfactory attempts, measured at one minute intervals, may be reported.
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The effects of age and sex on the single-breath transfer factor (TLCO) estimated during exercise have been investigated in 80 normal subjects (40 men) divided equally into four groups: 1) 20-29 yrs; 2) 30-39 yrs; 3) 40-49 yrs and 4) 50-59 yrs. Oxygen consumption (VO2), cardiac frequency (fc), TLCO and transfer coefficient (KCO) were estimated at rest and at 25 W increments up to 100 W in women and 150 W in men. Quadratic regression equations were obtained for the relationships of TLCO and KCO to VO2, fc and workload (WL). TLCO and KCO at any WL, VO2 or fc were greatest in group 1 and least in group 4. The rate of decline of TLCO and KCO in men and women at l.min-1 VO2 was 0.063 and 0.031 mmol.min-1.kPa-1.yr-1 and 0.006 and 0.007 mmol.min-1.kPa-1.l-1.yr-1, respectively. Within each sex the curvilinearity of the relationships was similar regardless of age. At any WL, TLCO was greater in men than in women, whilst KCO was greater in women than in men. Sex differences were not abolished by correcting TLCO and KCO for anthropometric indices. We conclude that age and sex have significant effects on TLCO and KCO on exercise.
1. Resting pulmonary blood flow (Q), using the uptake of the soluble inert gas Freon-22 and an indirect estimate of lung tissue volume, has been estimated during breath-holding (Qc) and compared with direct Fick cardiac output (Qf) in 16 patients with various cardiac disorders. 2. The effect of breath-hold time was investigated by comparing Qc estimated using 6 and 10 s of breath-holding in 17 patients. Repeatability was assessed by duplicate measurements of Qc in the patients and in six normal subjects. 3. Qc tended to overestimate Qf, the bias and error being 0.09 l/min and 0.59, respectively. The coefficient of repeatability for Qc in the patients was 0.75 l/min and in the normal subjects was 0.66 l/min. For Qf it was 0.72 l/min. There was no significant difference in Qc measured at the two breath-hold times. 4. The technique is simple to perform, and provides a rapid estimate of Q, monitoring acute and chronic changes in cardiac output in normal subjects and patients with cardiac disease.
Eighteen adult patients presenting with breathlessness associated with bradycardia, and whose breathlessness was diminished or abolished by permanent pacing, were studied at least one month after this procedure in order to examine the relationship between symptoms and exercise performance. All were pacing-dependent at rest and were studied over successive two-weekly periods at set rates of 50, 70 and 90 beats min-1 in a double-blind, balanced and randomized trial. The degree of breathlessness was closely related to exercise capacity judged by 6-min walk testing, effort scores and weekly pedometer distance. Overall results were worse at 50 beats min-1 than the two faster rates. For a given individual, changing of ventricular rate caused parallel alterations in symptoms and performance. The 6-min walking test was a useful guide to disability in these patients, tightly linked to the symptoms of effort and breathlessness, and may be of clinical value in assessing mild heart failure. The pedometer readings were influenced more by the patients' walking habits than by fitness.
The use of assumed values of oxygen consumption has become an accepted practice in the calculation of direct Fick cardiac output. A survey showed that the assumed values in common use were derived from basal metabolic rate studies on normal subjects, a use which may not be valid. We have compared previous assumed values based on basal metabolic rate or cardiac catheterization studies with those obtained by direct measurement in 80 patients (age range 38-78 years) with various cardiac disorders. Comparison of the assumed and directly measured values of indexed oxygen consumption and the cardiac index showed large discrepancies, with over half the values differing by more than +/- 10% and many by more than +/- 25% from the measured value. Assumed values of oxygen consumption should be used with caution when calculating cardiac output during cardiac catheterization procedures, because large errors can result. The equations of LaFarge and Miettinen gave the closest approximation to the measured data and their use is recommended in preference to values predicted from basal metabolic rate studies.
In order to investigate the mechanism of dyspnoea in hyperthyroidism measurements of spirometry, lung volume, transfer factor for carbon monoxide and its subdivisions, maximal respiratory pressures, methacholine challenge, arterial blood gases were made and exercise studies performed on 16 patients before treatment for hyperthyroidism. Methacholine challenge showed that only three of 14 patients increased airway reactivity, which was mild. Maximal pressures which could be generated by the respiratory muscles were reduced in some patients, as was functional residual capacity. Exercise ventilation and breathing frequency were increased and the respiratory exchange ratio was abnormally high. Anaerobic threshold was measured in nine of 15 subjects and was below normal in each case. All but two subjects stopped exercise because of dyspnoea, and the maximum oxygen uptake achieved by the group was 53 per cent (n = 15, range 26-66 per cent) of predicted maximum oxygen consumption. The maximum ventilation averaged only 43 per cent (n = 15, range 16-96 per cent) of the maximal breathing capacity predicted from spirometric tests. Nine patients were studied shortly after being rendered euthyroid by treatment. At rest, only maximal respiratory pressures increased significantly. On exercise, the maximal workload attained and the ventilation achieved increased significantly. Breathing patterns, maximal oxygen consumption, ventilation, anaerobic threshold and cardiac frequency remained unchanged. We conclude that: patients with hyperthyroidism do not generally have increased airway reactivity; when hyperthyroid, respiratory muscles are weak, and improve following treatment; exercise capacity is impaired in hyperthyroid patients probably because of a combination of an inefficiently rapid and shallow breathing pattern, an increase of anaerobic metabolism and discomfort associated with the act of breathing. Although exercise capacity increases and the sensation of dyspnoea may decrease after treatment the pattern of breathing does not immediately return to normal.
The bronchodilator response to cumulative doses of terbutaline administered by metered dose inhaler with and without a conical spacer device and by Acorn nebuliser has been compared in groups of patients with chronic severe and moderately severe asthma. After laboratory studies the patients undertook a randomised domiciliary crossover comparison of bronchodilator response to terbutaline given by metered dose inhaler with and without a spacer device, during which the severity of asthma was assessed by thrice daily recordings of peak expiratory flow (PEF) and symptom score. Improvement in FEV1 produced in the laboratory by the metered dose inhaler with spacer device was significantly greater than by metered dose inhaler alone (p less than 0.001) and similar to that from the nebuliser in both asthmatic groups throughout a range of terbutaline doses. In the domiciliary comparison mean midday and evening PEF rates were significantly higher with the use of the spacer device both in those with severe (p less than 0.01) and in those with moderately severe (p less than 0.05) asthma, and mean morning PEF was significantly higher in the severe group (p less than 0.05). The spacer device also produced a significant improvement in symptom score in both the severe and the moderately severe groups (p less than 0.05). Regular domiciliary use of the spacer device with the metered dose inhaler improves bronchodilator response, particularly in patients with chronic severe asthma, and may be a useful alternative to nebuliser treatment.
This study was designed to standardise a progressive exercise test for the assessment of change in carbon monoxide transfer coefficient (KCO) with exercise and to examine the variation between subjects and the reproducibility within subjects. Normal subjects exercised on a bicycle ergometer while ventilation, heart rate, and expired gas concentrations were recorded continuously. Preliminary studies showed that reduction of the breath hold time to six seconds made measurements of KCO during heavy exercise more comfortable without affecting the result. When KCO was measured immediately after exercise it was lower than when measured during exercise. KCO was measured in 50 normal subjects at rest and at three different work loads maintained for three minutes with a pause of five minutes between each. The relationships between KCO and both oxygen consumption and work load were linear in all subjects but the relationship between KCO and heart rate was distorted by high resting heart rates in some subjects. The mean slope of the relationship between KCO and oxygen consumption (VO2) was steeper in women than in men (mean slopes 0.627 and 0.348 mmol min-1 kPa-1 l-1 per 1 min-1 respectively), and the same was true for the relationship between KCO and work rate. The heart rate rose more steeply in relation to VO2 in women, so that the relationship of KCO to heart rate was similar in men and women (mean slope 0.01 mmol min-1 kPa-1 l-1 per beat min-1). Repeat studies on five occasions in five individuals gave coefficients of variation for the slopes of the relationships between KCO and VO2, work rate, and heart rate of 5-10%.
The transfer factor (diffusing capacity) for carbon monoxide (TLCO) is known to rise with increasing levels of work, but uncertainty remains as to the exact relationship of TLCO and the transfer coefficient (KCO) to oxygen uptake (VO2). We have studied the effects of increasing levels of work on TLCO and KCO in 22 normal male subjects using the single-breath technique and a standardized protocol. Additionally, we have investigated whether young people were different from a middle-age group, the need for carboxyhaemoglobin corrections in current smokers and non-smokers, and the variations of cardiac frequency during breath-holding. Our results show that TLCO and KCO increase in a curvilinear manner up to maximal VO2, a quadratic equation describing the relationship. There was no effect of age up to 50 years. There was no significant increase in the carboxyhaemoglobin levels, and therefore this correction is unnecessary. Cardiac frequency showed no significant variation during the breath-holding manoeuvre, except at rest and at low levels of exercise.