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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↗
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↗
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↗
Measurement of abdominal wall compliance in normal subjects and tetraplegic patients.
On inspiration descent of the diaphragm is opposed by the passive properties of the abdominal wall, the tone of its muscles, and the inertia of the abdominal contents. As a result, intra-abdominal pressure rises and promotes rib cage expansion. In patients with high spinal injury the diaphragm is the most important muscle of inspiration and abdominal wall displacement is more evident than in normal subjects. Abdominal wall compliance has been measured by relating gastric pressure to abdominal wall displacement, which was determined by means of an optical contour mapping system. Six normal subjects and six tetraplegic patients were studied in the supine posture, during passive expiration from total lung capacity to functional residual capacity. Over this lung volume range the normal subjects partitioned an average of 31% of expired volume to the abdominal compartment, while the corresponding average figure in the patients was 77% of expired volume. Since the range of gastric pressure was similar in the two groups, it is concluded that abdominal wall compliance is greater in tetraplegic patients. This high compliance could have a detrimental effect on lower rib cage expansion.
Abdominal Muscles↗
The measurement of metabolic gas exchange and minute volume by mass spectrometry alone.
Metabolic gas exchange and respired minute volume were measured on 37 occasions in 9 normal adults on exercise and at rest, using the concentration of an injected gas, argon, as a measure of flow. These measurements were compared with simultaneous Douglas bag collections in which volumes were determined with a dry gas meter. The two types of measurements agreed within +/- 5%. It was concluded that this technique, designed for the remote monitoring of unconscious patients was suitable for a wide variety of clinical and experimental situations.
Argon↗
The uses of long sampling probes in respiratory mass spectrometry.
We have compared the results of gas analysis by respiratory mass spectrometry using long (30m) sampling probes with those obtained using conventional short (1.3m) probes, examining both static gas mixtures and respired gas at the mouth during manoeuvres designed to make the concentrations of inspired marker gases change in a complex way within a breath. The experiments showed that no important errors were introduced by using the long probes, both for estimates of gas tensions and for derived physiological variables. A slight reduction in signal for a water-soluble component was noted when sampling a moist gas mixture with a long probe, but again this was of no practical significance. Ways in which the use of long sampling probes increase the versatility of the respiratory mass spectrometer are discussed. In essence they enable a greater range of subjects to be studied, they allow simultaneous events to be examined sequentially and they permit a single instrument to be shared between several patients or laboratories.
Argon↗
Estimation of lung volumes from chest radiographs using shape information.
The cross-sectional shapes of the chest and its contained structures have been assessed in post-mortem anatomical sections and from computerised tomographic scans in living subjects. These shapes are described by simple equations that can be used to increase the accuracy of measuring lung volumes from chest radiographs. Radiographic estimates of total lung capacity, using the equations, were compared with plethysmographic and single-breath helium dilution measurements in 35 normal subjects. The postures commonly used for taking chest radiographs were found, on average, to decrease total lung capacity (TLC) and to increase residual volume by about 200 ml when compared with the sitting positions used for the other two measurements (studies made in 18 of the subjects). After correction for this effect, the radiographic estimates of TLC, which measure the displacement volume of the lung, exceeded the plethysmographic estimates of contained gas volume by a mean of 720 ml, which was taken as the volume of tissue, blood, and water in the lungs. The single-breath dilution estimates of TLC fell short of the plethysmographic values by a mean of 480 ml, taken as the volume of contained gas that was inaccessible to helium in 10 seconds. The tomographic studies suggested that the radiographic technique of measuring lung displacement volumes has an accuracy of +/- 210 ml. The method is rapid and simple to use and has intra- and inter-observer variabilities of less than 1% and less than 5% respectively.
Helium↗
Methods of studying lobar and segmental function of the lung in man.
Making the decision whether a patient with chest disease can undergo lung surgery may be easier if the anatomical extent of the disease and the functional effects of resection can be estimated. Although information can be gained by non-invasive physiological studies of lung function of a routine kind, these cannot define the anatomical extent of the disease or distinguish the relative influence of affected and unaffected parts as estimates of lung function. Whole lung ventilation and perfusion scans provide immediate topographic information but have limited resolution and anatomical accuracy, particularly when the architecture of the lung is disturbed by disease. Bronchoscopy gives direct visual information about the more central airways but little or none about the function of the areas they serve. This paper gives brief descriptions of a series of procedures which could help in assessing the feasibility of lung surgery. The size, shape and volumes of individual lungs and lobes can be estimated from plain chest radiographs. Corresponding information about individual segments, and about lobes not delineated by normal X-ray, can be obtained using radio-active krypton 81m and a gamma camera during otherwise routine fibreoptic bronchscopy segments can be determined by simple single-breath manoeuvres at bronchoscopy using a respiratory mass spectrometer. The radio-isotope and spectrometric tests can be obtained in the same breath. The spectrometric tests can be recorded from more than one part of the lung within the same breath. All of the procedures give information in terms of anatomical units of interest to the surgeon.
Adult↗
Cold air test: a simplified standard method for airway reactivity.
A simple and standardized test has been developed to measure airway responsiveness to cold dry air. This consists of stepwise increases in ventilation of dry subfreezing air at 10, 20, 40 and 60% of predicted indirect maximum breathing capacity (IMBC). For each step, the inhalation time was 3 min. The optimal time between the steps was 5 min. Exposure ceased when either a fall in forced expiratory volume in one second (FEV1) of more than 20% of baseline occurred or when there was no response after breathing cold air at 60% predicted IMBC. Moderate isocapnic hyperventilation with cold air beyond 3 min induced no further bronchoconstriction. Varying the interval (0, 2 and 5 min) between the steps produced no significant differences in test results. Changing the pattern of breathing had no effect on airway responsiveness, provided that the patient maintained a constant minute-ventilation. This implies that it is not necessary to monitor the rate and depth of respiration continuously in order to achieve a given minute-ventilation, making the technique simpler. In addition, a "CO2 requirement graph" has been constructed at different levels of ventilation. This allows the inspired CO2 concentration to be preset, eliminating the need for elaborate equipment and monitoring of end-tidal CO2 to keep the subject isocapnic during hyperventilation.
Adult↗