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Biomedical subjects

D M Denison

Publications and source records attributed to D M Denison.

At least 37 records · Page 2Linked to original sources
PubMed1986

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↗
PubMed1986

Use of different magnification factors to calculate radiological lung volumes.

In previous papers from this laboratory, Pierce et al described a method of measuring lung volumes from routine chest radiographs. The images on the film are magnified, and this was taken into account in their calculations. Their findings have recently been confirmed by Rodenstein et al. It is important to measure magnification accurately because errors in linear dimensions are cubed when volume is calculated. This paper describes two simple methods of improving the accuracy of the calculation of magnification.

Humans↗
PubMed1986

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↗
PubMed1986

Estimation of regional gas and tissue volumes of the lung in supine man using computed tomography.

This study was intended to discover how well computed tomography could recover the volume and weight of lung like foams in a body like shell, and then how well it could recover the volume and weight of the lungs in supine man. Model thoraces were made with various loaves of bread submerged in water. Computed tomography scans recovered the volume of the model lungs (true volume range 250-12,500 ml) within +0.2 (SD 68) ml and their weights (true range 72-3125 g) within +30 (78) g. Scans also recovered successive injections of 50 ml of water, within +/- 5 ml. Scans in 12 healthy supine men recovered their vital capacities, total lung capacities (TLC), and predicted tissue volumes with comparable accuracy. At total lung capacity the mean tissue volume of single lungs was 431 (64) ml and at residual volume (RV) it was 427 (63) ml. Tissue volume was then used to match inspiratory and expiratory slices and calculate regional ventilation. Throughout the mid 90% of lung the RV/TLC ratio was fairly constant--mean 21% (5%). New methods of presenting such regional data graphically and automatically are also described.

Adult↗
PubMed1985

Contribution of the rib cage to breathing in tetraplegia.

In tetraplegia there is often paradoxical inward motion of the rib cage during inspiration. The volume of this negative contribution is difficult to estimate but can be obtained by optical mapping. The partitioning of ventilation between the rib cage and abdomen in six normal subjects, 10 stable tetraplegic patients, and one tetraplegic patient at intervals during rehabilitation has been studied by this technique. In normal subjects the tidal volume and the vital capacity were the sum of positive contributions from the rib cage and abdomen. In stable tetraplegic subjects with similar neurological levels, the rib cage contribution varied widely but the total chest wall displacement could not be predicted from the vital capacity. In the patient studied sequentially rib cage paradox reversed with time after injury, and this was associated with an absolute increase in vital capacity and an improvement in the action of the diaphragm.

Adolescent↗
PubMed1984

Analysis of an optical mapping technique for lung function studies.

An optical technique for lung function measurement studies is described and analysed. Procedures which permit the reconstruction of three dimensional data concerning the thoraco-abdominal wall are developed and methods for calculating volumes, surface areas and cross-sections are outlined.

Humans↗
PubMed1984

Pulmonary vascular resistance in children with congenital heart disease.

Pulmonary and systemic blood flow and pulmonary vascular resistance were measured in 21 children with congenital heart disease. Blood flow was calculated by the direct Fick method, using measurements of metabolic gas exchange obtained by remote respiratory mass spectrometry. The observations showed that the administration of oxygen caused an appreciable fall in pulmonary vascular resistance in 16 of the 21 children studied and that this fall would not have been appreciated from a study of pulmonary arterial pressure alone as it was masked by a corresponding rise in blood flow. In 10 of 14 children, in whom superior vena caval blood was also sampled, the rise in flow was largely due to an increase in intracardiac left to right shunt. It was accompanied by widening of the alveolar-arterial oxygen gradient, perhaps due to imperfect gas equilibration within the lung.

Blood Circulation↗
PubMed1984

An optical method of studying the shape and movement of the chest wall in recumbent patients.

A method of optical mapping has been developed that allows the shape and motion of the chest wall to be studied in recumbent patients. It uses a single camera at a fixed viewpoint to determine the three dimensional coordinates of the visible surface of the body, and hence to measure the volume and shape of the visible segment. Measurements on different test objects (volumes 228-7807 ml) in different positions suggest a reproducibility of volume measurement of +/- 26 ml (SD) and a maximum volume error of 150 ml. Studies of computed tomography scans in inspiration and expiration show that it should be possible to capture 97% of respiratory motion by this method. The mean difference between optical and spirometric measurements of expired volume in six subjects was 0.25 (SD 0.2) 1. Within subject systematic errors of up to 10% were noted. The mean deviation about the regression line of optically measured expired volume on spirometric expired volume varied from 68 to 243 ml in the six subjects (mean 131 (SD 92) ml). To examine the potential of the optical technique, for rapid data acquisition it was used to construct a 24 point flow volume loop from a normal subject.

Anthropometry↗
PubMed1984

Optical mapping of the thoracoabdominal wall.

An optical technique has been developed for mapping the size and shape of the thoracoabdominal wall and the change in its shape with breathing. A fixed pattern composed of stripes of light is projected on to both sides of the trunk. These stripes become distorted when viewed from in front and behind, forming contours over the trunk surface. The contours are photographed and then encoded digitally. The digital information can be used to compute automatically the volume of the trunk, the position of any point on its surface, and its cross sectional shape at any level. The technique has been tested on rigid objects (a globe, a cone, and two dummy torsos) that can be measured precisely. With this optical technique linear dimensions can be calculated to within 0.5 mm, cross sectional area to within 5%, and volume to within 1.6-3.7%. These results suggest that this non-invasive technique measures the shape and volume of complex three dimensional surfaces with sufficient accuracy to be tried in clinical practice.

Abdominal Muscles↗
PubMed1983

Response of pulmonary circulation to oral pirbuterol in chronic airflow obstruction.

The effects of the oral beta agonist pirbuterol on pulmonary haemodynamics and gas exchange were studied in nine patients with severe irreversible airflow obstruction and moderate arterial hypoxaemia. After administration of 15 mg pirbuterol pulmonary vascular resistance fell by 19% but cardiac output rose by 24%, so that pulmonary arterial pressure showed no significant change. Systemic arterial oxygen pressure fell by 7%, limiting the rise in oxygen delivery to 21%. All changes were significant at the 2% level. These results show that pirbuterol dilates the pulmonary bed at the cost of a slight worsening of gas exchange, which is compensated by an independent rise in blood flow.

Adrenergic beta-Agonists↗
PubMed1983

Pulmonary effects in man of oral prizidilol hydrochloride (SK&F 92657), a new antihypertensive agent.

The effects on heart rate, blood pressure and pulmonary function of single oral doses of prizidilol hydrochloride (400 mg SK&F 92657) and propranolol (40 mg) were compared with placebo in nine healthy volunteers, in a double blind crossover study. Prizidilol had no effect on heart rate while propranolol caused a significant reduction compared with placebo. Diastolic blood pressure was lowered to the same extent by both prizidilol and propranolol. Propranolol significantly reduced the forced expiratory volume in 1 second (FEV1), forced vital capacity (FVC) and the maximal expiratory flow at 50% vital capacity (MEF 50). Prizidilol had no effect on flow-volume loop parameters. Effective pulmonary blood flow was not altered by propranolol, but it was significantly increased by prizidilol. Oral prizidilol exerts its hypotensive effect by vasodilatation without reflex tachycardia. It does not cause airways obstruction in healthy subjects.

Adrenergic beta-Antagonists↗
PubMed1983

Neutrophil chemotactic factor in exercise- and hyperventilation-induced asthma.

Elevated levels of the mast-cell-associated serum neutrophil chemotactic factor (NCF) and an increase in blood basophil counts were observed in 6 atopic asthmatics during exercise-induced asthma (EIA). These changes were not found when the same degree of airways obstruction was elicited in the same subjects by isocapnic hyperventilation (ISH) with cold air. The NCF was unlikely to be related to the basophilia alone, because asthmatics without EIA who underwent the same exercise task, produced a similar basophilia but significantly less NCF. These findings suggest that mast-cell-associated (as opposed to basophil-associated) mediators of hypersensitivity are detectable in the bloodstream during the bronchoconstriction induced by exercise, but not by ISH.

Adolescent↗
PubMed1982

Direct recordings of the temperatures in the tracheobronchial tree in normal man.

In an effect to determine how far inspired air could penetrate into the respiratory tract before being brought to body conditions, we measured the temperature in the airways of the anterior basilar segment of the right lower lobe in five normal subjects while they breathed air at subfreezing and ambient conditions. During quiet breathing, most of the heating of the incoming gas took place in the upper airways as expected. However, as the thermal burden was increased by rapid inspirations, frigid air, and hyperventilation, the temperature of the distal airways progressively fell and the point at which the incoming air reached body conditions moved deep into the periphery of the lung. These findings demonstrate that heat and water transfer is not localized to one region, but rather is a continuous process that begins the moment the air enters the body and involves as much of the respiratory tract as necessary to complete the task.

Adult↗