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Biomedical subjects

G Cumming

Publications and source records attributed to G Cumming.

At least 37 records · Page 2Linked to original sources
PubMed1988

Alveolar carbon monoxide: a comparison of methods of measurement and a study of the effect of change in body posture.

1. We have compared rebreathing, breath-hold and mean alveolar methods of measuring alveolar carbon monoxide (CO), at levels similar to those found in smokers, as a preliminary to using them as indirect measures of carboxyhaemoglobin levels. In the present study alveolar CO levels were raised by rebreathing a 2% CO mixture. 2. Breath-hold CO was measured after breath-hold times of 0-35 s in 5 s increments. Using generalized linear models, the maximum value for breath-hold CO was estimated to occur at 23 s. Breath-hold CO after a 20 and 25 s breath-hold were similar to and significantly greater than those of less than 20 s or greater than 25 s. 3. As expired CO increased, the difference between breath-hold and mean alveolar CO became proportionally larger. On average, breath-hold CO was 24% larger than mean alveolar CO. 4. Rebreathing, breath-hold and mean alveolar CO were compared at four different inspired oxygen concentrations. Expired CO increased significantly with increasing oxygen for all three methods. At end-tidal oxygen levels of less than 25%, breath-hold and rebreathing CO were similar, however, the overall mean difference between the three methods was significant. 5. While rebreathing CO was unaffected by changes in ventilation/perfusion of the lung, induced by change in body posture, both breath-hold and mean alveolar CO showed a significant fall with change from the supine to erect posture.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

Is alveolar carbon monoxide an unreliable index of carboxyhaemoglobin changes during smoking in man?

1. We measured alveolar carbon monoxide (CO) after a 20 s breath-holding period and carboxyhaemoglobin both before and after smoking a cigarette on 500 occasions (101 individuals). The two measurements were closely correlated but there was a marked difference in the change or 'boost' after smoking one cigarette. The mean relative boosts ([post value--pre value]/[pre+post]/2) for alveolar CO and carboxyhaemoglobin were 7.7% and 20.3%, while negative boosts (fall rather than the expected rise) were seen in 103 of 500 and three of 500 occasions respectively. In 140 studies a third alveolar CO reading taken 5 min later was slightly larger, but the difference was insignificant. 2. In seven subjects where the carboxyhaemoglobin level was raised by breathing a 2% CO gas mixture, the alveolar CO and carboxyhaemoglobin boosts were similar (71.7% and 75.2% respectively), and they fell sharply subsequently rather than increasing further as occurred after smoking. 3. We conclude that alveolar CO measurements give a useful estimate of carboxyhaemoglobin level if the subject has not smoked for at least half an hour but that measurements of alveolar CO boost are useless since the act of smoking interferes with alveolar sampling. We postulate that cigarette smoking induces a transient change in pulmonary gas exchange.

Adult↗
PubMed1988

Effect of inhaled methacholine on gas mixing efficiency.

1. Pulmonary function tests, including alveolar mixing efficiency by the single-breath and multi-breath methods, and ventilation scans were performed on 16 volunteer subjects. The tests were repeated after the inhalation of a methacholine aerosol in sufficient dosage to increase airways resistance. 2. After inhalation of methacholine there was a significant fall in mean series dead space of 31 ml (P less than 0.05), and mean multi-breath alveolar mixing efficiency fell from 68% to 36% (P less than 0.001), a fall occurring in all subjects. Mean single-breath alveolar mixing efficiency measured on the first breath of the nitrogen washout fell from 76% to 70%, but this change did not reach statistical significance (0.1 greater than P greater than 0.05). 3. In eight of the subjects, technically adequate lung scans and pulmonary function tests were obtained both before and not more than 30 min after methacholine inhalation. In seven there were obvious visible defects on the ventilation scans, and in five of these the computer-calculated underventilation score became abnormal. 4. Thus inhalation of methacholine causes maldistribution of ventilation, a fall in alveolar mixing efficiency and a fall in series dead space, presumably brought about by bronchoconstriction. The parallel component of this maldistribution of ventilation, as judged by 81mKr ventilation scanning, does not of itself seem to be sufficient to explain the fall in alveolar mixing efficiency, and therefore a degree of diffusion limitation is probably involved as well.

Administration, Inhalation↗
PubMed1988

Acute effect of smoking on rebreathing carbon monoxide, breath-hold carbon monoxide and alveolar oxygen.

1. The rise ('boost') in carboxyhaemoglobin (HbCO) on smoking has been studied with alveolar carbon monoxide measurements before and after smoking a cigarette. We re-examined this in 28 subjects with HbCO values compared with rebreathing carbon monoxide [FACO(Rb)] and breath-hold alveolar carbon monoxide and oxygen concentrations, obtained after a 20 s breath-hold [FACO(Bh) and FAO2(Bh), respectively]. Tests were done in the order FACO(Bh) and FAO2(Bh), FACO(Rb), FACO(Bh) and FAO2(Bh) before and after smoking a single cigarette, with HbCO being measured 1 min before and after smoking. 2. The changes were expressed as the relative boost: (Post value-pre value)/(Pre value + post value)/2 X 100 For HbCO the average value was 23.7%, but the FACO(Rb) boost was only 9.8%. The first post-smoking FACO(Bh) boost was 3.9% (5.0 min after smoking), rising to 8.5% 9.4 min later. 3. The FAO2(Bh) values fell from a mean of 15.4% before smoking to 14.3% (5.0 min after smoking) then recovered to 15.4% 9.4 min later, suggesting a transient effect on pulmonary gas exchange. Correction of the first post-smoke FACO(Bh) data for this effect increased the relative boost to 11.5%. Routine FAO2(Bh) measurements may be useful in further smoking studies. 4. We conclude that none of the alveolar sampling techniques gives a reliable measurement of the acute HbCO changes associated with smoking.

Adult↗
PubMed1988

Lung function in West Sussex firemen: a four year study.

Although firefighting is a hazardous occupation, published evidence of long-term lung damage in firemen is inconsistent. A group of 96 men from the West Sussex Fire Brigade, which covers a simi-rural, semi-urban area, were followed up for between one and four years. They included 31 non-smokers, 40 smokers, and 25 ex-smokers. After four years 12 firemen had been lost to the study. A control group of 69 volunteers, consisting of non-smoking men from various other occupations, were followed up in parallel. Lung function tests, covering a wider range than has been previously used in similar studies, were repeated six monthly for two years and annually for a further two years. The results were expressed in terms of the rate of change with time of the lung function variables. Many of the variables deteriorated in both firemen and controls, but the rate of deterioration was greater in the controls than the firemen for vital capacity, ratio of residual volume to total lung capacity, FEV1, FVC, peak expiratory flow (PEF), flow at 50% and 25% remaining vital capacity (V50 and V25 respectively), and airways resistance (Raw). With respect to PEF, V50, V25, and Raw the control subjects deteriorated more rapidly even than the smokers and ex-smokers among the firemen. Alveolar mixing efficiency (AME), a measure of small airways function, did not change significantly over the study period in any group. Non-smoking firemen had the highest mean value of AME, decreasing through ex-smokers, controls, and smokers. We conclude that these results show no evidence of chronic lung damage in West Sussex firemen; indeed, the firemen as a group show a lower rate of deterioration of lung function with age than do the control subjects. This is attributed to the selection of fit men for the service, continued physical training, and the regular use of breathing apparatus.

Adolescent↗
PubMed1988

Respiratory symptoms in West Sussex firemen.

There are few reports of long term follow up of symptoms in firemen. In a four year study of symptoms in a group of 96 firemen (31 non-smokers, 40 smokers, and 25 ex-smokers) of which 89 remained in the study for its full duration a volunteer control group of 69 male non-smokers from a variety of occupations was also followed up. A history of symptoms and of smoking habits was obtained on entry to the study, then every six months for two years, and annually for a further two years. All those remaining in the study after four years were interviewed and a history of their use of breathing apparatus and of being affected by smoke and fumes was obtained. Symptom frequency was least in control subjects, intermediate in non-smokers and ex-smokers, and most in smokers. Before the study period (history obtained at the first session) smoking increased symptoms 3.9 times and being affected by smoke in the past increased symptoms 2.3 times, compared with non-smokers who had not been affected by smoke. In smokers who had also been affected by smoke symptoms increased by 9.1 times, suggesting a multiplicative effect. During the study period symptom frequency was increased about 4.4 times in smokers and 5.7 times in those who had been affected by smoke at work in the past compared with non-smokers who had not been affected by smoke. In smokers who had also been affected by smoke symptom frequency increased by 7.4 times, the combined effects of the two types of smoker being less than additive. These results suggest that being affected by smoke and fumes at work may be a cause of long term symptoms in firemen. In firemen who are non-smokers and who had not been affected by smoke symptom frequency was similar to that observed in the control subjects. Thus the current routine use of breathing apparatus appears to be effective in preventing long term symptoms.

England↗
PubMed1986

Test of the neurolinguistic programming hypothesis that eye-movements relate to processing imagery.

Bandler and Grinder's hypothesis that eye-movements reflect sensory processing was examined. 28 volunteers first memorized and then recalled visual, auditory, and kinesthetic stimuli. Changes in eye-positions during recall were videotaped and categorized by two raters into positions hypothesized by Bandler and Grinder's model to represent visual, auditory, and kinesthetic recall. Planned contrast analyses suggested that visual stimulus items, when recalled, elicited significantly more upward eye-positions and stares than auditory and kinesthetic items. Auditory and kinesthetic items, however, did not elicit more changes in eye-position hypothesized by the model to represent auditory and kinesthetic recall, respectively.

Adult↗
PubMed1985

Reliable detection of inspiration and expiration by computer.

A new computer assisted method is proposed to distinguish between the inspiratory and expiratory phases of breathing. The method is based on the analysis of both gas flow and CO2-concentration. The algorithm is effective and reliable and is most suitable in critical care patients when an uninterrupted sequence of breaths is to be analysed immediately at the bedside. Marked variations in tidal volume such as are seen in intermittent mandatory ventilation or spontaneous breathing during the phase of weaning from the ventilator, artefacts such as mechanical vibrations of the flow transducer or its connecting tubes do not disturb the analysis.

Computers↗
PubMed1985

Effect of breathing pattern on gas mixing in a model with asymmetrical alveolar ducts.

A model of the pulmonary airways was used to study three single-breath indices of gas mixing, dead space (VD), slope of the alveolar plateau, and alveolar mixing inefficiency (AMI). In the model, discrete elements of airway volume were represented by nodes. Using a finite difference technique the differential equation for simultaneous convection and diffusion was solved for the nodal network. Conducting airways and respiratory bronchioles were modeled symmetrically, but alveolar ducts asymmetrically, permitting interaction between convection and diffusion. VD, alveolar slope, and AMI increased with increasing flow. Similar trends were seen with inspired volume, although slope decreased at high inspired volumes with constant flow. VD was affected most by inspiratory flow and AMI and alveolar slope by expiratory time. VD fell approximately exponentially with time of breath holding. Eight different breathing patterns were compared. They had a small effect on alveolar slope and AMI and a greater effect on VD. The model shows how series and parallel inhomogeneity occur together and interact in asymmetrical systems: the old argument as to which is the more important should be abandoned.

Gases↗
PubMed1985

Accurate measurement of N2 volumes during N2 washout requires dynamic adjustment of delay time.

Measurement of respiratory gas composition by a mass spectrometer lags behind the measurement of gas flow. To obtain specific gas volumes (e.g., the N2 volume) by multiplication and integration of concentration and flow, one has to synchronize flow and concentration signals using the delay time (TD) of the gas analyzer. During the N2 washout, however, gas composition changes and causes alterations of TD. This leads to errors of up to 17 and 70% in the measurement of pulmonary volume and series dead space, respectively, in an ideally mixing physical model of the lung. On the basis of Poiseuille's law and exact measurements of the characteristics of the capillary it is possible to adjust the synchronization, which improves the absolute accuracy considerably.

Animals↗
PubMed1984

Sleep promotion, hospital practice and recovery from illness.

Is sleep especially beneficial in times of illness? Despite the widespread use of hypnotics, the medical position on this question is equivocal, for hospital practices seem rarely designed to encourage maximum sleeping. Sleep promotion is defined as the arrangement of conditions so that patients can achieve as much sleep as possible. It is hypothesised that sleep promotion is of benefit, at least by improving patient well-being, possibly also be hastening healing processes. Some background to the hypothesis and some possible consequences of it are discussed. It is recommended that hospital procedures should be designed to encourage sleeping.

Hospitals↗
PubMed1984

Recognition of abstract and concrete words in a dichotic listening paradigm.

A dichotic listening paradigm was used to examine the hypothesis that whilst concrete nouns can be processed equally well by both right and left hemispheres, the left hemisphere is superior in processing abstract nouns. Although simple main effects of word frequency, ear of presentation, sex of subject and concreteness / abstractness were significant and in the expected directions, further fine-grained analyses using in particular the laterality coefficient showed that only about a third of the subjects showed a clear right ear advantage, and that this was not related to any of the independent variables. There was no evidence supporting differential hemispheric processing of concrete and abstract words and it is suggested that methods of data analysis used in this kind of research need to be carefully examined.

Adolescent↗
PubMed1984

Distribution of dead space volume in the human lung.

The first four breaths from a multi-breath nitrogen wash-out have been analysed in 20 normal subjects by differentiation and data smoothing of phase II of the expired concentrations of nitrogen and carbon dioxide. This procedure yields a distribution curve which is skewed to the right, the mode of which represents the usual value of dead space. The minimum and maximum values were found by excluding 2.5% of data points at each end of the distribution. The values of minimum, mode and maximum in men were 67.6, 147 and 300 ml. For women the values were 55.4, 109 and 235 ml. It is suggested that this distribution reflects the asymmetrical nature of the bronchial tree and comparison with anatomical data suggests that anatomy is the principal determinant of the distribution of dead space. The contribution made by the spread of the stationary interface within individual bronchioles is evident but small.

Adult↗