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Biomedical subjects

T R Martin

Publications and source records attributed to T R Martin.

At least 163 records · Page 9Linked to original sources
PubMed1983

An objective feature extraction technique applied to the Doppler waveforms from the groin: a prospective study.

A group of 80 patients presenting with lower limb ischaemia were classified according to their arteriographic findings. The maximum frequency envelope from the Doppler waveforms obtained from the common femoral artery were retrospectively analysed using a mathematical feature extraction technique, principal component analysis (PCA). Two of the three coefficients uniquely describing each waveform were plotted and classified according to their arteriographic groupings. The best separating planes were then defined. Twenty-eight new patients were subsequently prospectively assessed using the principal components and separating planes defined in the previous study. The results were compared with the arteriographic findings and showed that PCA represents a significant improvement in diagnostic accuracy when compared with other techniques.

Aorta↗
PubMed1982

A study of the effects of glutaraldehyde and formaldehyde on the mechanical behaviour of bovine pericardium.

The inherent variability in the mechanical behavior of bovine pericardium causes difficulties in establishing the effects of treatment procedures used in the manufacture of bioprosthetic cardiac valves. A new experimental technique has been developed in which the specimen acts as its own control, obviating the need to perform large numbers of experiments to obtain statistically significant results. The procedure used is described in detail as is the equipment employed. The technique was used to assess the effect of glutaraldehyde and formaldehyde on the stress/strain response of bovine pericardium. The results show that the fixing process in glutaraldehyde is virtually complete within two hours and causes significant changes in the mechanical behaviour of the tissue. The tissue becomes progressively stiffer as the treatment period is extended, which is especially pronounced at low levels of stress. Formaldehyde storage subsequent to fixing in glutaraldehyde was found to have no effect on the stress/strain response of the bovine pericardium.

Aldehydes↗
PubMed1982

The physical properties of bovine pericardium: a study of the effects of stretching during chemical treatment in glutaraldehyde.

The uniaxial stress/strain response of bovine pericardium up to a stress of 1 N/mm2 was studied. The tissue was chemically modified in 0.5% buffered glutaraldehyde for 24 hours under various conditions of constraint. Four groups were studied: an unrestricted control group, a group held at their original length, a group stretched to a stress of 0.04 N/mm2, and a group stretched to a stress of 0.4 N/mm2 during treatment. Histological examination revealed changes in structural organization of the collagen, which explained the alterations in the stress/strain response. A significant alteration in mechanical properties after glutaraldehyde treatment was observed, with considerable loss of extensibility for the prestretched tissues. A valve made from such a prestretched tissue may be stenotic and possibly subject to early failure.

Aldehydes↗
PubMed1982

In vitro evaluation of prosthetic heart valves: anomalies and limitations.

The in vitro evaluation of fifteen commercially available prosthetic heart valves is described. The group comprised both mechanical and bioprosthetic valves. The experimental studies were carried out in a steady flow circuit which included a flexible valve test section, the geometry of which was modelled on the aortic anatomy. The fluidic performance of the valves was examined over a range of flows and in particular, the phenomenon of "pressure recovery" distal to the valve was studied in depth. A number of theoretical parameters which might be used to define valve performance were evaluated but none was found to be ideal. The conclusions of the study emphasise the limitations of such in vitro testing and the danger of extrapolating such experimental data to the possible valve performance in vivo.

Aortic Valve↗
PubMed1982

Effect of hemodialysis on the pharmacokinetics of theophylline in chronic renal failure.

We studied theophylline elimination in 8 patients with chronic renal failure to determine the effect of hemodialysis on the pharmacokinetics of theophylline. Each subject was studied twice, once on a nondialysis day and again during dialysis. Total body theophylline clearance on the nondialysis day was similar to that reported for patients with normal renal function (57.4 +/- 27.2 ml/kg/h). Hemodialysis accelerated theophylline elimination and shortened serum theophylline half-life in all patients (nondialysis t 1/2 = 7.3 h +/- 2.3 vs. dialysis t 1/2 = 2.7 +/- 0.9 h, p less than 0.01). Dialysis clearance averaged 59.7 +/- 16.4 ml/kg/h with a fraction of drug removed of 0.4 liters in 4 h. Guidelines for theophylline management during hemodialysis are suggested.

Adult↗
PubMed1982

The prognosis of patients with chronic obstructive pulmonary disease after hospitalization for acute respiratory failure.

We followed the course of 36 consecutive patients hospitalized with chronic obstructive pulmonary disease and acute respiratory failure due to exacerbation of chronic bronchitis in order to clarify the prognosis in this common group of patients. All of the patients had spirometric evidence of severe, poorly reversible airflow limitation and all had a similar cause of acute respiratory failure. In addition, all received similar treatment during hospitalization and follow-up. Patients wtih asthma and pneumonia were excluded by clinical, spirometric, and roentgenographic criteria. Hospital survival was 94 percent, and only one patient required intubation. Two-year survival was 72 percent, and none of the patients died during a readmission for acute respiratory failure. This prognosis is much better than commonly recognized and compares favorably to that of stable outpatients with similar degrees of airflow limitation. An episode of acute respiratory failure, triggered by an exacerbation of chronic bronchitis, does not necessarily alter the prognosis of patients with COPD.

Bronchitis↗
PubMed1981

A study of the uniaxial mechanical properties of human dura mater preserved in glycerol.

Heart valve replacements have now been made for some years from human dura mater. While the clinical results have been encouraging there is a considerable lack of information on the mechanical properties of the dura mater and the effects of the glycerol treatment employed. This study revealed that glycerol provided an adequate preserving medium for periods of up to 12 days, with no significant changes in the mechanical properties of dura mater. A wide range in mechanical properties was observed with, for example, the tensile strength varying from 3.28 N/mm2 to 7.86 N/mm2. Although no age-related deterioration in human dura mater could be shown, the results do suggest that dura mater in excess of fifty years of age should be avoided in order to prevent the selection of poor quality material.

Adult↗
PubMed1981

The mechanical properties of human dura mater and the effects of storage media.

Data are presented on the tensile strength and ultimate extensibility of human dura mater. Experiments were performed, prior to, and after, storage in glycerol. The results indicate that storage in glycerol has a small effect on the measured mechanical properties, but this was not statistically significant. In addition, storage in saline after glycerol preservation for up to thirty days was found to have no effect on the mechanical properties of dura mater, as long as the tissue had previously been sterilised and sterility was maintained. However, the considerable variability found in the mechanical properties of human dura prevented this being established beyond doubt. The implications of this variability for tissue selection is discussed.

Adult↗
PubMed1981

A prospective study of the accuracy of Doppler ultrasound in detecting carotid artery disease.

Results are presented from a two year prospective study using a Doppler ultrasound technique for the detection of carotid disease. The patients studied presented with transient cerebral ischaemic attacks or small strokes in the carotid territory. No other form of patient selection was used. Results were compared with those from carotid and arch aortography. 86% of normal vessels and 78% of diseases vessels were correctly classified. It is concluded that this technique offers a safe and accurate screening procedure for the management of patients presenting with transient cerebral ischaemia or small strokes.

Arteriosclerosis↗
PubMed1980

Ultrasound measurements of pulse-wave velocity in the peripheral arteries of diabetic subjects.

1. Pulse-wave velocity in both upper and lower limbs has been measured in a series of diabetic and control subjects. Subjects were studied with a Doppler ultrasound system and a real-time frequency analyser. 2. The subjects comprised three groups: (a) diabetic subjects with peripheral neuropathy (43); (b) non-complicated diabetic subjects (8); (c) non-diabetic control subjects (11). Those diabetic subjects with peripheral neuropathy included 12 with non-infected foot ulcers, nine with healed foot ulcers and 22 who gave no history of foot ulceration. All of the diabetic and control subjects had clinically normal peripheral pulses. 3. In the upper limbs the pulse-wave velocity was similar for all groups. By contrast, in the lower limbs pulse-wave velocity was significantly increased (P less than 0.005) in patients with healed or ulcerated feet compared with controls, non-complicated diabetic subjects or diabetic subjects with peripheral neuropathy alone. 4. It is suggested that the increased pulse-wave velocity results from an underlying, diffuse, atherosclerosis. This is not detectable clinically and was found to predominantly affect the lower limb arteries rather than the upper limb vessels. This may be an important aetiological factor in the development of foot ulcers in these patients.

Adult↗
PubMed1980

A comparison of upper gastrointestinal endoscopy and radiography.

One hundred symptomatic patients were evaluated independently with upper gastrointestinal radiography and fiberoptic endoscopy, and the results were compared. Of the two endoscopists sequentially examining the same patient, one was informed of available clinical and radiographic details and the other was not. Knowledge of the x-ray examination by the informed endoscopist did not improve his accuracy. Each endoscopist made four errors of interpretation. The endoscopic and x-ray findings agreed in 46 of the 100 patients, most often (68%) in esophagus, least often (29%) in the stomach and half the time (45%) in the duodenum. Ulcer craters seen endoscopically were detected radiographically in 36% of patients. We conclude that: 1) knowledge of results of prior upper gastrointestinal radiography did not alter endoscopic results; 2) experienced endoscopists are accurate but make mistakes; and 3) endoscopic findings would have been unaltered had radiography not been performed.

Diagnostic Errors↗
PubMed1980

Developmental study of a lamellar body fraction isolated from human amniotic fluid.

Several properties of a pellet fraction obtained on centrifuging amniotic fluid at 10,000 X g for 20 min were investigated. From these analyses, we defined a developmental profile which appears to describe the maturational process of the fetal lung surfactant system. At 14 to 18 wk gestation, the pellet fraction consisted of membrane-bound vesicles without internal lamellae. The phospholipid composition did not resemble that of surfactant, the major phospholipid being sphingomyelin. This stage, designated as presurfactant, persisted until 30 to 32 wk gestation. After this time, the phospholipid concentration of the pellet fraction increased continuously throughout development, and gradual but continuous changes in phospholipid composition were observed. Lecithin and phosphatidylinositol increased between 30 and 35 wk gestation. Interruption of pregnancies at this stage, termed onset of surfactant synthesis, resulted in 100% incidence of respiratory distress syndrome. From 36 wk gestation to postterm, the pellet fraction contained structures with the characteristic morphology of the lamellar inclusion bodies. The presence of single membrane components in these preparations did not contribute to the phospholipid composition. Early formed lamellar bodies lacked phosphatidylglycerol and had a high content of phosphatidylinositol. Once phosphatidylglycerol appeared in the lamellar body fraction, it continued to increase, accompanied by a decrease in phosphatidylinositol with little change in lecithin. A phosphatidylglycerol value of greater than 1% of the total phospholipids appeared to represent the stage of maturity at which there was no risk of respiratory distress syndrome.

Amniotic Fluid↗
PubMed1980

Controlled clinical trial of methylprednisolone in patients with chronic bronchitis and acute respiratory insufficiency.

To evaluate the role of corticosteroids as treatment for acute exacerbations of chronic obstructive pulmonary disease, we conducted a double-blind, randomized, placebo-controlled trial in 44 consecutive patients with chronic bronchitis and severe airflow obstruction. All were hospitalized with acute respiratory insufficiency from acute bronchitis. Patients with asthma, atopy, or pneumonia were excluded. Treatment consisted of intravenous aminophylline, inhaled isoproterenol, antibiotics, and either methylprednisolone, 0.5 mg/kg of body weight, or placebo every 6 h intravenously for 72 h. Bedside spirometry was done before and after bronchodilator inhalation three times daily. The methylprednisolone-treated group had a greater improvement in both prebronchodilator and postbronchodilator forced expiratory volume in 1 second (P less than 0.001). More patients with large improvements in their prebronchodilator or postbronchodilator flow rates, or both (greater than or equal to 40% by 72 h), received methylprednisolone (P less than 0.01). Methylprednisolone improved airflow more than placebo when added to standard therapy in patients with chronic bronchitis and acute respiratory insufficiency.

Aged↗