Search PubMed⌕ Search

Biomedical subjects

K B Saunders

Publications and source records attributed to K B Saunders.

At least 55 records · Page 3Linked to original sources
PubMed1986

Immediate ventilatory response to sudden changes in venous return in humans.

We changed venous return transiently by postural manoeuvres, and by lower body positive pressure, to see what happened simultaneously to ventilation. Cardiac output was measured by a Doppler technique. In seven subjects, after inflation of a pressure suit to 80 and 40 mmHg at 30 deg head-up tilt, both cardiac output and ventilation increased. Ventilation increased rapidly to a peak in the first 5 s, cardiac output more slowly to a steady state in about 20 s, at 80 mmHg inflation. After inflation to 80 mmHg in six subjects at 12.5 deg head-up and 30 deg head-down tilt, cardiac output did not change in the first, and fell in the second case. There were no significant changes in ventilation. On release of pressure there were transient increases in both cardiac output and ventilation, with ventilation lagging behind cardiac output, in contrast to (2) above. In five subjects, elevation of the legs at 30 deg head-up tilt caused a rise in both cardiac output and ventilation, but in two subjects neither occurred. In all seven subjects there was a transient increase in cardiac output and ventilation when the legs were lowered. Ventilation and cardiac output changes were approximately in phase. We were therefore unable to dissociate entirely increasing cardiac output from increasing ventilation. The relation between them was certainly not a simple proportional one.

Adult↗
PubMed1986

Lung function and within-breath changes in resistance in patients who have had a laryngectomy.

We describe the construction of a simple device which may be used to connect a patient with a tracheostomy to standard lung function testing equipment. We compared the lung function of nine patients after laryngectomy with nine patients matched for similar degrees of airflow obstruction, and found that peak flow rate (as per cent predicted) was significantly lower than predicted FEV1 in the patients with tracheostomy. This suggests that the larynx may normally affect production of peak flow. We then compared the change in resistance over the normal tidal volume in the two groups, finding no significant difference, and obtained similar results from paired studies in two patients before and after laryngectomy. We conclude that, while the laryngeal aperture varies during tidal breathing, it plays no major part in the overall resistance changes which occur during a normal breath.

Adult↗
PubMed1985

Validation of a Doppler technique for beat-to-beat measurement of cardiac output.

We have measured aortic flow in the ascending aorta in man with a Bach-Simpson BVM 202 blood velocity meter, and aortic root diameter by M-mode echocardiography, and thus derived beat-to-beat cardiac output (Q). We tested the technique in 21 patients (53 comparisons) with various cardiovascular problems against a thermodilution method, and in four normal subjects at rest and two levels of exercise (50 and 100 W) against a nitrous oxide rebreathing method. We obtained excellent overall correlation in a range of 0.5-10 litres/min (r = 0.98, n = 77, sy,x = 0.48 litre/min), the formula for the least squares regression being: (Q Doppler) = 0.95 (Q Thermodilution/N2O) + 0.11 litre/min. The Doppler signal is sufficiently noise-free to obtain maximum acceleration of flow from the first derivative of velocity.

Adult↗
PubMed1985

Diurnal variation and adaptation of the cough response to citric acid in normal subjects.

The lowest concentrations of citric acid were measured that caused coughing in 10 normal subjects who inhaled successively higher concentrations. Two subjects did not cough at any concentration. In the remaining eight the threshold concentration was significantly higher when measured in the afternoon than it was in the morning (p less than 0.05). The expected diurnal variation in peak expiratory flow rate (PEFR) was found (significant in the whole group--p less than 0.05); but PEFR did not change significantly when measured before and immediately after coughing caused by citric acid inhalations. In a second group of 10 normal subjects two series of citric acid inhalations were given, separated by one hour. The total number of coughs was significantly lower on the second run (p less than 0.05). Thus diurnal variation and adaptation of the cough response must be taken into account when antitussive drugs are tested.

Adaptation, Physiological↗
PubMed1985

Effect of bronchodilators on the cough response to inhaled citric acid in normal and asthmatic subjects.

Coughing was induced in seven normal and eight asthmatic subjects by giving successive inhalations of citric acid aerosols of progressively higher concentration (range 0.5-32%). A baseline cough response was obtained on each of four experimental days, and there was no significant difference between days in this respect. Then the subjects received by inhalation either a bronchodilator (salbutamol 5 mg or ipratropium 1 mg) or placebo, in a paired double blind crossover design. A second citric acid run followed and was used for paired drug-placebo comparisons. In the asthmatic subjects the cough response was diminished by both bronchodilators (p less than 0.05), and the cough threshold was significantly higher after ipratropium but not salbutamol. In normal subjects no significant effects were found. Airways calibre was assessed, by an oscillatory technique that measures the resistance of the respiratory system (Siemens Siregnost FD 5), in four of the seven normal and all eight asthmatic subjects. The mean respiratory resistance was higher in asthmatic than in normal subjects, and fell significantly after both bronchodilators. In normal subjects smaller decreases in respiratory resistance occurred, significant only with salbutamol. The simplest hypothesis which explains the results relates change in cough response to altered neuroreceptor sensitivity associated with rapid changes in bronchial calibre.

Aerosols↗
PubMed1983

How many blows really make an FEV1, FVC, or PEFR?

We have collected peak expiratory flow rates, one-second forced expiratory volumes, and forced vital capacities in sets of 10 or 20 values at one-minute intervals from 30 normal, 49 asthmatic, and 26 bronchitic subjects. Analysis shows that the derivatives are compatible with a normal distribution of the values in the sets, so that the true value is best represented by the arithmetic mean of all valid attempts. One-third of all subjects showed skewness in one or more indices but these were equally divided between positive and negative directions. There is no sign of the dominant negative skewness that would result if the true value was indeed a maximum, which could be approached or equalled but never exceeded. There is no sign that repetition worsens performance. Seventy-two subjects showed no regression in any index and those of the remainder who deteriorated were balanced by equal numbers in all categories who improved. There is a significant tendency for both the highest and the lowest values to occur in the earlier part of any series. Probability theory suggests that this is a statistical phenomenon. The best estimate of the true value of these indices is probably the mean of as many observations as can be conveniently obtained and the data can be treated statistically as if they were a sample from a normally distributed population.

Adolescent↗
PubMed1981

The site of airflow limitation in asthma: the effect of time, acute exacerbations of disease and clinical features.

We have used the helium/oxygen technique to assess the main site of airflow obstruction in patients with asthma. Of 14 out-patients with asthma studied serially (minimum of three observations over 5-12 months) 10 remained either responders or non-responders to helium/oxygen (He/O2) on each occasion tested, despite variations in severity of airflow obstruction. Four out of six patients studied during an acute exacerbation of asthma were initially non-responders to He/O2 but became responders during recovery. The response to He/O2 of these and 15 other patients with asthma was compared with a variety of clinical features. There was a statistically significant decline in flow rate response to He/O2 breathing with increased length of history of asthma, but no differences in smoking history, are, sex or atopic status between the responders and non-responders. This implies a progressive involvement of smaller peripheral airways during the course of the disease. Perhaps more systematic treatment of young asthmatics would prevent this.

Adult↗
PubMed1981

Moment analysis of the flow-time curve after breathing gases of different densities.

In an attempt to improve methods of determining the site of airway narrowing we have tried using a heavier than air gas mixture (SF6/02) in addition to the more widely used lighter than air gas mixture (HE/O2). Response to varying inspired gas density has been assessed by means of change in mean transit time (MTT) as well as by means of change in flow rate at 50% of vital capacity (Vmax50). The possibility that derivatives of second moment analysis of the flow time curve reflect the presence of small airway disease is studied. The reproducibility of response to SF6/O2 breathing was better than that to He/O2 breathing. However there was no correlation between response to these two gas mixtures in either normal subjects or in patients with asthma. The response of MTT to He/O2 breathing correlated with the response to Vmax50 and although no more reproducible, there are theoretical advantages in using MTT as the method of assessment. The derivative of the second moment of the flow-time curve. COV, did not correlate with flow rate response to He/O2 breathing.

Adult↗
PubMed1981

Influence of age on response to ipratropium and salbutamol in asthma.

We studied the differential response to inhaled salbutamol and ipratropium of 29 asthmatic patients, 18 intrinsic, 11 extrinsic, using peak expiratory flow rate (PEFR), forced expiratory volume in one second (FEV1), and forced vital capacity (FVC). Thirty minutes after a theoretically maximally bronchodilating dose of salbutamol (400 microgram) or ipratropium (80 microgram), second doses frequently caused further bronchodilatation. We suspect that second doses may reach bronchi untouched by the first inhalation. Analysis of variance showed a powerful intrinsic versus extrinsic effect, and there were clearly differences between patients in their response to treatment (patient versus drug interaction) but these differences were not removed by dividing the patients into intrinsic and extrinsic groups. Results for the group as a whole favoured salbutamol, but examination of individual results by a pattern-recognition technique showed ipratropium equally effective in eight patients and more effective in three. All patients with a definite predominant salbutamol response were less than 40 years old. The response to salbutamol declined significantly with age, whereas that to ipratropium did not. In general in patients aged less than 40 years salbutamol is the drug of choice. With advancing age, and the apparent decline of beta-adrenergic responsiveness, the initially comparatively small response to ipratropium becomes relatively more important and may predominate. In older patients ipratropium, or continued therapy with both drugs, may be preferable.

Adult↗
PubMed1981

Site of action of ipratropium bromide and clinical and physiological determinants of response in patients with asthma.

It has been suggested that in normal subjects inhaled anticholinergic agents have a preferential dilating effect on large central airways. We therefore studied 21 patients with asthma to see if response to inhaled ipratropium bromide was related to the initial central or peripheral site of major airway narrowing. Fourteen out of 21 patients with asthma increased their Vmax more than 10% after ipratropium but when assessed by air and helium/oxygen (He/O2) flow-volume curves, responders and non-responders to He/O2 breathing were divided equally between those who benefited from the drug, and those who did not. There were no significant differences in percentage improvement in Vmax between initial responders, and initial non-responders to He/O2 breathing. Furthermore the results from air and He/O2 flow-volume curves suggest that, contrary to some previous reports (not in asthmatics), inhaled ipratropium has a generalised action throughout the airways. There were no differences in severity of airflow obstruction, nor in age, sex, smoking history, or atopic status between those who benefited from ipratropium and those who did not. However, those improving after the drug had a significantly longer history of asthma than those who did not.

Adult↗
PubMed1980

Arterial blood gas tensions in acute severe asthma.

We have studied the serial changes in arterial blood gases in fourteen patients with acute severe asthma, all of whom received a standard therapeutic regime and had similar measurements made at identical time intervals under standard conditions. Hypoxaemia on admission was a constant finding, and the arterial oxygen tension often took a week or longer to return to a normal level. Treatment with 60% inspired oxygen provided a safe means of relieving hypoxaemia, provided that blood gases were measured before and during oxygen therapy. Most patients had a normal arterial carbon dioxide tension, which indicated the severity of their illness. Acid-base disturbances, when present, were mild and needed no specific treatment. Age, duration of the acute attack, and severity of airways obstruction were all unrelated to the changes in blood gas tension, and pulse rate was found to be a poor predictor of hypoxaemia in elderly asthmatics. Serial measurements of the arterial blood gases should be made in all patients with acute severe asthma.

Acidosis, Respiratory↗
PubMed1979

Changes in arterial blood gases during and after a period of oxygen breathing in patients with chronic hypercapnic respiratory failure and in patients with asthma.

1. Ten patients with chronic hypercapnic respiratory failure (group 1) and eight patients with asthma (group 2) breathed pure O2 from an MC mask for 60 min. Blood gases were measured during this period and for the subsequent 45 min. 2. In mine of ten patients in group 1 and in all eight patients in group 2 arterial O2 tension (Pa,O2) fell to values lower than had been obtained before O2 was given. 3. These undershoots in Pa,O2 are unrelated to changing CO2 stores or to hypoventilation, and are more likely due to persistence of altered ventilation-perfusion ratios associated with O2 breathing. 4. Magnitude of the undershoots is usually small, and periods of less than 15 min of O2 are unlikely to be harmful.

Adolescent↗
PubMed1979

Effect of an inhaled antihistamine (clemastine) as a bronchodilator and as a maintenance treatment in asthma.

Although intravenous chlorpheniramine can cause bronchodilatation, oral and parenteral antihistamines have not proved useful in treating asthma. Inhaled antihistamines may cause throat irritation, but a recent study of the antihistamine, clemastine, showed it to be an effective bronchodilator without irritant effects. We have extended these studies to determine the site of action of inhaled clemastine and to assess its potential usefulness both as a bronchodilator and as a maintenance treatment. Eleven stable asthmatic patients received inhaled clemastine and placebo and the effect was assessed by serial maximum expiratory flow volume (MEFV) curves breathing air and a helium/oxygen (He/O2) mixture. There was no significant improvement in peak flow rates during air breathing after clemastine and no significant difference between the responses to drug and placebo. Minor but significant changes were seen in some flow measurements on the downslope of the MEFV curve during air and He/O2 breathing, and these are tentatively ascribed to a dilating effect of clemastine on peripheral airways where flow is laminar. Subsequent administration of inhaled isoprenaline showed the patients to be still capable of significant bronchodilatation. The addition of clemastine, from a pressurised aerosol, to the patients' therapeutic regimen for two weeks was no more effective than placebo in controlling airflow obstruction, and did not reduce the need for standard bronchodilators. In our patients clemastine was not a clinically useful bronchodilator either acutely or as a maintenance treatment for asthma.

Adult↗