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Biomedical subjects

D M Denison

Publications and source records attributed to D M Denison.

At least 55 records · Page 3Linked to original sources
PubMed1981

Comparison of intravenous and inhaled terbutaline in the treatment of asthma.

In a double-blind crossover controlled study, intravenous (IV) or nebulized terbutaline was given to eight patients with moderately severe asthma on two separate days. Four incremental doses of terbutaline were given by each route to establish a maximal effect. Both routes of administration produced significant increases increases in FEV1, FVC, PEFR, MEF50% single-breath TLC, and effective pulmonary blood flow. A decrease in slope of alveolar argon plateau was observed with both routes, but helium responsiveness showed variable changes with no significant or consistent effect seen. There was no significant difference between responses to incremental doses and maximal response apart from pulse rate, which rose during IV treatment. These results showed that the IV route had no advantage in terms of effectiveness or site of action over the inhaled route. Since IV treatment can produce systemic side effects, inhaled bronchodilator therapy should be used as the route of choice.

Adult↗
PubMed1980

Single-exhalation method for study of lobar and segmental lung function by mass spectrometry in man.

A single-exhalation method, based on a modification of the conventional single-breath technique, was applied to study lung function in normal subjects during fiberoptic bronchoscopy. After a single inspiration of a test gas mixture (1% He, 1% C2H2, 0.07% C18O in air), the test gas concentrations were continuously monitored during subsequent slow exhalation, using a respiratory mass spectrometer that sampled either at the lips (Whole-lung test) or, through the bronchoscope, at various sites within the bronchial tree (Regional test). Changes in concentrations of the test gases with time allowed estimation of alveolar ventilation (Va), blood flow (Q), and diffusing capacity (DLCO), per unit accessible lung volume (Va). In the Whole-lung test, both DLCO and Q agreed closely with values obtained in the same subject by a rebreathing method. No differences were observed between the upright and the lateral decubitus positions. In teh Regional test, VA/VA, DLCO/VA and Q/VA were larger in the dependent than in the upper lung, when sampling was from the main bronchi in the lateral decubitus positions. Sampling from lobar bronchi in the upright position revealed an increase from top to bottom in VA/VA, DLCO/CA and Q/VA, this being most marked for Q. These results are compatible with the regional variations that have been shown by radioactive techniques and have been attributed to gravitational forces. The method appears to be suitable for the study of lobar and segmental lung function in patients with lung disease.

Bronchoscopy↗
PubMed1980

Applications of respiratory mass spectrometry to intensive care.

A monitoring and research system based on a respiratory mass spectrometer controlled by a microprocessor has been installed in a paediatric intensive care unit. It provides an opportunity to study up to twelve patients simultaneously at distances up to 30 m from the instrument, can operate for prolonged periods without intervention, and includes a routine for regular calibration checks. There is an automatic sensitivity control which compensates for minor variations in probe patency or in water vapour pressure. Information derived from the system can be displayed centrally or at the bedside and data can be conserved for up to 24 hours; past events can be recalled and displayed for either the previous hour or previous 24 hours. The system can be used to measure respired gas tensions, metabolic gas exchange, lung volume, pulmonary blood flow and pulmonary tissue volume. The clinical value and limitations of the system are discussed.

Carbon Dioxide↗
PubMed1980

Radiographic, scintigraphic, and gas-dilution estimates of individual lung and lobar volumes in man.

We describe a method of separately determining the volumes of the right and left lungs from conventional chest radiographs and of determining the volumes of individual lobes and pathological spaces, whenever their boundaries are visible radiologically or can be displayed scintigraphically--for example, during fibreoptic bronchoscopy. Scintigrams of individual lungs, lobes, and segments are obtained by deflecting a stream of air marked with 81m krypton down the suction channel of the bronchoscope into the appropriate bronchus during inspiration, followed by a breath-hold during which the image is recorded with a gamma camera. Both radiographic and scintigraphic methods have been validated by comparison with argon dilution estimates of individual lung and lobar volumes also obtained at bronchoscopy, and results for the three methods in normal subjects are presented. Used in conjunction with bronchoscopic soluble gas uptake studies, these volume measurements permit precise estimation of effective perfusion, tissue and water volume, and gas transfer at lobar and segmental level. Individual lung and lobar volumes can be used to quantify lung and lobar collapse and compression, mediastinal shift, regional ventilation and gas trapping, and phrenic paresis.

Adult↗
PubMed1979

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↗
PubMed1979

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↗
PubMed1979

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↗
PubMed1979

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↗