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Clinical Protocols↗
Biomedical subjects
D M Denison
Publications and source records attributed to D M Denison.
Heart-lung transplantation for cystic fibrosis.
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Adult↗
Changes in lung function and pulmonary capillary permeability after cardiopulmonary bypass.
OBJECTIVE: To assess the possibility that changes in lung function following cardiopulmonary bypass are associated with increased pulmonary capillary permeability. DESIGN: A prospective, descriptive study. SETTING: Adult cardiothoracic ICU in a post-graduate teaching hospital. PATIENTS: Ten sequential patients undergoing cardiac surgery requiring cardiopulmonary bypass. MEASUREMENTS: Arterial blood gas tensions, helium dilution end-expiratory lung volume, and carbon monoxide transfer were measured by a rebreathing technique preoperatively and 2 hrs postoperatively. Lung extravascular protein accumulation index was measured by a double-isotope technique 2 hrs postoperatively and in a group of normal controls. RESULTS: Mean +/- SEM alveolar-arterial PO2 gradient increased from 77 +/- 14 torr (10.3 +/- 1.8 kPa) to 138 +/- 24 torr (18.5 +/- 3.2 kPa) (p less than .01). Functional residual capacity decreased by 20.2 +/- 5.6% (p less than .01). Carbon monoxide transfer decreased by 26.7 +/- 5.3% (p less than .01) for the lung as a whole and by 17.9 +/- 3.2% (p less than .01) per liter of accessible gas volume. Protein accumulation index ranged from 0.03 to 3.2 x 10(-3) (median 0.6) postoperatively (median for normal subjects 0.4; p less than .05), although only one patient had a value indicative of clinically important endothelial injury. CONCLUSIONS: Cardiac surgery involving cardiopulmonary bypass results in a deterioration in lung function characterized by a loss of lung volume, a reduction in carbon monoxide transfer, and an increase in the alveolar-arterial PO2 gradient. These changes do not appear to be mediated by an increase in pulmonary endothelial permeability.
Aged↗
Pulmonary function testing in the intensive care unit.
A number of tests of pulmonary function have been successfully developed for use in the intensive care unit. When performed in the ICU on critically ill patients, many of the traditional laboratory-based tests will have different clinical implications than when performed in ambulatory patients, for example vital capacity measurement. Also, the clinical questions posed in the ICU are often different, such that estimates of lung water may be clinically more useful than more traditional measures, such as the flow-volume loop. There is a need for further research to identify the clinical utility of these measurements. As the understanding of ARDS and MOF improves, new therapies may be developed which will require sensitive methods in order that they can be evaluated accurately. Similarly, the potential for new methods of respiratory support such as jet ventilation, extracorporeal techniques and lung transplantation reinforce the need for the pulmonary physician to be able to make an accurate assessment of respiratory function on the intensive care unit.
Extravascular Lung Water↗
Ipratropium bromide: are patients treated with optimal therapy?
A double-blind crossover placebo controlled study was performed on 20 patients with stable chronic asthma, in order to obtain dose response data to ipratropium bromide (40, 80, 200 micrograms) given by metered dose inhaler. The use of the 200 micrograms dose gave a significantly greater peak effect and duration of action than the recommended standard therapeutic dose of 40 micrograms. There were marked individual variations in response to higher doses. Maximum response detected by spirometry occurred within 24 hours of inhalation, thus patients likely to gain clinical benefit are readily identified. The higher dose was well tolerated by most patients and may have clinical application in the treatment of patients who do not respond to the standard dose regime.
Adult↗
Vertical gradients of lung density in supine subjects with fibrosing alveolitis or pulmonary emphysema.
Computed tomography was used to determine the vertical gradient of density in the peripheral lung tissue of 12 patients with histologically proved fibrosing alveolitis and 12 patients with chronic bronchitis and evidence of pulmonary emphysema on the computed tomograms. Measurements were made at total lung capacity and at residual volume and compared with similar measurements from 12 normal subjects reported in a previous study. At residual volume the mean peripheral tissue density in the emphysematous lungs was 0.081 kg/l compared with 0.426 kg/l in the fibrotic lungs and 0.323 kg/l in the normal lungs. The observed densities in the three groups were compared with those in a theoretical model predicting the vertical changes of lung density caused by gravitational effects that would be found in lungs with differing compliance. The emphysematous lungs showed a much greater increase of density with descent down the lung than that predicted for normal lungs, and the results were explicable by an increase in compliance. The fibrotic lungs showed considerably less change in density than expected, implying loss of compliance. It is suggested that local changes of compliance are important determinants of vertical density gradients in diseased lungs.
Adult↗
Lung function testing and AIDS.
Lung function testing on patients with acquired immune deficiency syndrome (AIDS) has been restricted because of the risks of cross infection. We have adapted equipment which is currently used for routine lung function testing with inexpensive disposable components to remove the risk of contamination. Results from the modified equipment were compared with those obtained using conventional equipment on 56 subjects. We found an excellent correlation between compared values for all parameters.
Acquired Immunodeficiency Syndrome↗
Vertical gradients of lung density in healthy supine men.
Computed tomography was used to determine the vertical gradient of physical density in peripheral lung tissue of 12 healthy supine subjects, at total lung capacity and residual volume. At total lung capacity the mean (SD) density of peripheral lung tissue at the level of the mid right atrium was 0.0715 (0.017) g/cm3 and the vertical gradient of density was slight. At residual volume the density of peripheral tissue at the same level was 0.272 (0.067) g/cm3 and the vertical density gradient was curvilinear and more pronounced. Predictions of the gradient at residual volume were made on the basis of the known compliance of the lung and measured effects were attributed to the action of gravity on blood vessel distensibility at total lung capacity. These predictions agreed closely with the actual density gradient measured at residual volume and provide a basis for forecasting the vertical density gradient that would exist in healthy lungs at any degree of inflation. Departure from these gradients would imply local abnormalities of lung compliance, distribution of mechanical stress, or distensibility of vessels.
Humans↗
Effective pulmonary blood flow in normal children at rest.
Effective pulmonary blood flow was measured with a soluble inert gas uptake method (10% argon, 3.5% freon-22, 35% oxygen, balance nitrogen) in 98 apparently healthy children aged 5-14 years. None had any evidence of cardiorespiratory disease and all had normal values for absolute and dynamic lung volumes and transfer factor for carbon monoxide. Values of blood flow measured by a rebreathing method correlated reasonably closely with height, weight, body surface area, and lung volumes, and to a lesser extent with hand and foot size. The mean (SD) effective pulmonary blood flow index was 2.7 (0.31) 1 min-1 m-2. Small children found a single breath method of measuring flow more difficult to perform and the results were more variable.
Adolescent↗
Quantitative features in the computed tomography of healthy lungs.
This study set out to determine whether quantitative features of lung computed tomography scans could be identified that would lead to a tightly defined normal range for use in assessing patients. Fourteen normal subjects with apparently healthy lungs were studied. A technique was developed for rapid and automatic extraction of lung field data from the computed tomography scans. The Hounsfield unit histograms were constructed and, when normalised for predicted lung volumes, shown to be consistent in shape for all the subjects. A three dimensional presentation of the data in the form of a "net plot" was devised, and from this a logarithmic relationship between the area of each lung slice and its mean density was derived (r = 0.9, n = 545, p less than 0.0001). The residual density, calculated as the difference between measured density and density predicted from the relationship with area, was shown to be normally distributed with a mean of 0 and a standard deviation of 25 Hounsfield units (chi 2 test: p less than 0.05). A presentation combining this residual density with the net plot is described.
Adult↗
Diagnosis of pulmonary hypertension from radiographic estimates of pulmonary arterial size.
The reported accuracy of radiographic measurements in predicting pulmonary hypertension is very variable. Measurements of right and left descending pulmonary artery diameter have been reported to provide a correct diagnosis in as many as 98% of patients. A study was carried out to determine the predictive value of measurements made from the chest radiographs of 50 normal subjects and of 27 patients undergoing right heart catheterisation for cardiac or pulmonary vascular disease, taking account of radiographic magnification. After such corrections a right descending pulmonary artery diameter over 16.7 mm or a left descending pulmonary artery diameter of over 16.9 mm distinguished 12 of 23 pulmonary hypertensive subjects, with no false positive results. The diameter was then arbitrarily squared (any differences between patients and control subjects being exaggerated) and the product was divided by either predicted or actual lung volume in an attempt to correct for body size. The new index distinguished 19 of 23 patients with pulmonary hypertension, with one false positive, when the divisor was actual lung volume; when predicted lung volume was used 18 of 23 patients were distinguished, again with one false positive result.
Adult↗
Rebreathing method for the simultaneous measurement of oxygen consumption and effective pulmonary blood flow during exercise.
This paper describes a rebreathing method for the simultaneous measurement of oxygen consumption (VO2) and effective pulmonary blood flow (QP. eff) at rest and during exercise. Subjects rebreathed a test gas consisting of 35% oxygen, 3.5% chlorodifluoromethane (freon-22), and 10% argon in nitrogen for 30 seconds or until the respired oxygen tension fell to below 13.3 kPa. Sixty normal subjects were studied on a motorized treadmill, the Bruce protocol being used. The rebreathing manoeuvre was performed at three minute intervals, and was initially practised sitting down. Measurements were then made with the subjects standing at rest, and subsequently during the last minute of each stage of the Bruce exercise protocol until the subjects were exhausted. Heart rate was recorded from the electrocardiogram. Oxygen uptake plotted against calculated power (watts) showed a discontinuity between resting and exercise values, probably because power output during treadmill exercise is underestimated. The arbitrary addition of 30 watts to the exercise power output abolished this discontinuity. There was good agreement between rebreathing estimates of oxygen consumption and values measured during a second exercise test by the conventional open circuit argon dilution method. Coefficients of variation of oxygen consumption and effective pulmonary blood flow measured by rebreathing were usually less than 10% even during maximal exertion. At rest mean (SD) effective pulmonary blood flow corrected for body surface area was 2.2 (0.46) l/min/m2. Effective pulmonary blood flow rose linearly with oxygen consumption. At rest the arteriovenous oxygen content difference for pulmonary blood (VO2/QP eff) was 9.1 (1.6) ml/dl, rising to a maximum of 16.4 (1.8) ml/dl. The stroke volume index was 27.5 (6.8) ml/m2, rising to a maximum of 46.5 (7.1) ml/m2 during exertion.
Adult↗
The rib cage and abdominal components of respiratory system compliance in tetraplegic patients.
The specific compliance of the chest wall and lungs combined was measured in eight patients with stable tetraplegia. Expiration was impeded with a series of spring-loaded resistances, and end-expiratory pressures plotted against changes in chest wall volume at end-expiration. An optical contour mapping system was used to partition changes in chest wall volume into rib cage and abdominal components. These measurements suggest that the compliance of the whole system is reduced by one third in patients with stable tetraplegia, compared with normal subjects. This may be because of abnormal stiffening of the rib cage.
Abdominal Muscles↗
Computed tomography in diffuse lung disease: improving the image.
Diffuse lung disease is often a difficult clinical and radiographic problem to resolve. Standard computed tomography (CT) techniques are often unhelpful. By combining practical physiological criteria with narrow section CT a protocol has been developed which yields more accurate information and is now the standard method of CT investigation of diffuse lung disease in our department.
Bronchiectasis↗
Effect of long term oxygen treatment at home in children with pulmonary vascular disease.
Inhalation of 100% oxygen by nine children with pulmonary vascular disease increased pulmonary blood flow measured at cardiac catheterisation; there was no significant change in pulmonary artery pressure. Fifteen children with pulmonary vascular disease that was severe enough to preclude corrective cardiac operation were studied to determine the effect of long term oxygen treatment on pulmonary vascular disease. Nine received long term domiciliary oxygen for a minimum of twelve hours a day for up to five years. Though the untreated group closely resembled the treated group their survival was significantly less good. All nine treated children are alive whereas five of the six children who did not receive oxygen have died.
Adolescent↗
Value of computed tomography for selecting patients with bullous lung disease for surgery.
Computed tomography and lung function tests were performed on 43 patients who had evidence on the chest radiograph suggesting bullous emphysema. After computed tomography scan two groups of patients could be identified. Twenty patients had generalised emphysema, which was locally worse in the area of the suspected bulla; and 23 had well defined bullae, which were potentially operable. Results of lung function tests did not distinguish between the two groups. The volume and ventilation of the true bullae were measured by computed tomography and this confirmed that most of them did not contribute to ventilation (residual volume (RV)/total capacity (TLC) bulla = 89% (SD 10%). The patients with true bullae were considered suitable for surgery but only 12 had an operation. All the patients who underwent surgery survived and had a symptomatic improvement, which was accompanied by objective increases in spirometric volumes and by reductions in static lung volumes; there were no improvements in carbon monoxide transfer or blood gas tensions. It is concluded that computed tomography used alone can identify bullae that are amen-able to surgery and can measure their volume and ventilation. The surgical removal of such clearly identified bullae is safe and associated with symptomatic and functional improvement even when the preoperative FEV1 is less than 1 litre. This improvement is likely to be a consequence of reduction in lung volume and may not necessarily be associated with relief of compressed peribullous lung or the removal of dead space.
Forced Expiratory Volume↗
Computed tomography based estimates of regional gas and tissue volume of the lung in supine subjects with chronic airflow limitation or fibrosing alveolitis.
Twelve patients with chronic airflow limitation and 12 patients with a histological diagnosis of fibrosing alveolitis were studied. The calculated mean (SD) tissue volume of a single lung at total lung capacity was 467 (91) ml in the patients with alveolitis, which was 43% (14%) more than predicted for healthy people of the same age, sex, and height. The tissue volume of a single lung at total lung capacity was 436 (82) ml in the patients with chronic airflow limitation, which was 26% (21%) more than predicted. At residual volumes the tissue contents of the fibrotic and the obstructed lungs changed very little (to 407 (84) ml and 433 (84) ml respectively). This allowed tissue volume to be used as a marker of position within the lung, to match inspiratory and expiratory slices and to calculate regional ventilation. In both groups local ventilation was diminished and more variable than in healthy lungs--that is, in the mid 70% of lung volume the local residual volume to total gas volume ratios (RV/TGV) were 32% (10%) in the fibrotic group and 66% (14%) in the group with chronic airflow limitation, compared with 23% (5%) in healthy subjects. As expected, the fibrotic lungs were much denser (0.246 (0.036) g/ml) and the lungs with chronic airflow obstruction were less dense (0.114 (0.026) g/ml) than were healthy lungs (0.126 (0.017) g/ml).
Adult↗
Effect of abdominal binders on breathing in tetraplegic patients.
We studied the effect on breathing of a conventional and a newly designed abdominal binder in seven patients with complete tetraplegia. The indices of respiratory ability used were the transdiaphragmatic pressure on maximal sniff (sniff Pdi), the maximum static inspiratory mouth pressure (PImax), and the vital capacity (VC). These were measured in patients with and without binders, in the supine position, raised up to 70 degrees on a tilt table, and seated upright. When patients were raised from the supine to the 70 degrees tilt and to the seated posture, sniff Pdi and VC decreased. Both binders improved VC in the seated position and at 70 degrees tilt, and sniff Pdi at 70 degrees tilt. The new binder was as effective as but no better than the conventional binder. PImax was too variable to be a valuable index of inspiratory power. These findings support the view that abdominal binders assist breathing in tetraplegic patients who are seated or raised to near vertical positions.
Abdominal Muscles↗