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Biomedical subjects

R Fletcher

Publications and source records attributed to R Fletcher.

At least 163 records · Page 9Linked to original sources
PubMed1981

The concept of deadspace with special reference to the single breath test for carbon dioxide.

We present a review and a theoretical analysis of factors determining airway deadspace (VDaw) and alveolar deadspace (VDalv), the two constituents of physiological deadspace (VDphys). VDaw if the volume of gas between the lips and the alveolar/fresh gas interface, the location of which is determined by inspiratory flow pattern and airway geometry. VDalv can be caused by incomplete alveolar gas mixing and associated V/Q mismatching within the terminal respiratory units, temporal V/Q mismatching within units, spatial V/Q mismatching between units, and venous admixture. Most causes of VDphys are influenced by inspiratory flow pattern and the time available for gas diffusion and distribution. Analysis can be made from the single breath test for carbon dioxide (SBT--CO2) which is the plot of fraction of carbon dioxide in expired gas against expired volume. The common causes of VDalv are associated with a sloping SBT-CO2 phase III. Combination of SBT-CO2 with PaCO2 yields VDphys and VDalv. A sloping phase III with a negative arterial-end-tidal PCO2 gradient implies compensation by perfusion for early emptying, overventilated alveoli.

Breath Tests↗
PubMed1981

Malignant hyperthermia syndrome in an anxious patient.

A 30-yr-old patient with fulminant ulcerative colitis was anaesthetized on three occasions, for colectomy and rectal stump removal. The first anaesthesia, with droperidol and fentanyl and pancuronium neuromuscular block, was uneventful. Addition of suxamethonium on the second occasion and use of the original drugs plus nitrous oxide for the third anaesthesia produced symptoms of MH, which was confirmed by muscle biopsy. There was no hyperthermia. The patient's admitted anxiety before the last two operations is believed to have played a role in the genesis of MH.

Adult↗
PubMed1981

Prediction of the physiological dead space/tidal volume ratio during anaesthesia/IPPV from simple pre-operative tests.

It can be shown that the assumption of an arbitrary value for VDphys/VT during IPPV can lead to unacceptable degrees of hypo- or hyperventilation. We investigated 33 adult patients scheduled for major non-thoracic surgery, to see if any simple tests could be used to predict VDphys/VT during anaesthesia/IPPV. Fifteen were smokers and 18 non- or ex-smokers. The tests were spirometry, and the single breath tests for CO2 and for N2 (SBT-CO2: SBT-N2). Patients were ventilated during anaesthesia with a Servo Ventilator 900 B, and SBT-CO2 was recorded from a CO2 Analyzer 930. During anaesthesia/IPPV, smokers had significantly greater VDphys/VT (0.40 +/- 0.10 vs. 0.31 +/- 0.07 [P less than 0.01]), and they had more steeply sloping phase IIIs of SBT-CO2 (P less than 0.01) than non- and ex-smokers. For smokers, VDphys/VT was correlated to age (r = 0.75, P less than 0.01), to the slope of phase III of both SBT-CO2 and SBT-N2, and to the ratio of FEV% to its predicted value. For non- and ex-smokers, only one variable, efficiency, describing the shape of SBT-CO2, was correlated to VDphys/VT (r = 0.53, P less than 0.05). Pre-operative prediction of VDphys/VT based on age, smoking history, and SBT-CO2 can reduce the uncertainty in estimating VDphys/VT and therefore ventilatory requirements. It appears to offer the greatest benefits amongst smokers, who show a large variation in VDphys/VT.

Age Factors↗
PubMed1981

Comparison of nadolol, a new long-acting beta-receptor blocking agent, and placebo in the treatment of stable angina pectoris.

Nadolol, a new nonselective beta 1 and beta 2 adrenergic blocking agent, has a plasma half-life of 17 to 23 hours. We studied 37 volunteers with stable angina pectoris who had five or more episodes of pain per week and who also had a 1 mm or greater ST segment depression 80 msec past the J point during a Bruce protocol treadmill test. An eight-week placebo controlled run-in period preceded double-blind randomization to nadolol administered once per day (17 patients) or identical appearing placebo for four weeks (20 patients), after which an exercise test was done. Diaries for pain episodes and nitroglycerin consumption were kept. Exercise tests were performed 24 hours after the last nadolol or placebo dose. Episodes of pain per week were reduced 59.8 percent after nadolol and 28.2 percent after placebo (P less than .01). Nitroglycerin consumption after nadolol was reduced 66.8 percent while after placebo it was reduced 36.2 percent (P less than .05). Resting and peak heart rates and peak rate-pressure products showed typical reductions due to beta-blockade 24 hours after nadolol compared with stability of these during placebo, all P less than .001. Exercise time after nadolol increased 42.2 percent, which was more than the 14.5 percent increase after placebo (P less than .05). Exercise work after nadolol increased 64.7 percent, greater than the 22 percent increase after placebo (P less than .05). Mean ST segment depression at end of exercise was little changed before and after treatment in both groups, reflecting consistency of effort. Improvement in symptoms and work capacity associated with nadolol significantly exceeded the placebo group responses. Unlike other available agents of this class, a single daily dose of nadolol produced therapeutically effective 24-hour beta-blockade in patients with disabling angina pectoris.

Angina Pectoris↗
PubMed1980

VP-16-213 salvage therapy for refractory germinal neoplasms.

Thirty-three patients with advanced refractory germinal neoplasms were treated with VP-16-213 alone or in combination with cis-platinum, bleomycin, and frequently Adriamycin. All had prior chemotherapy, which in most was extensive. There were 14 complete and 15 partial remissions. Five of the patients with partial remission were rendered disease free by resection of residual tumor. Eleven remain disease free from 6+--23+ months. Toxicity was considerable. One-third were hospitalized for fever and granulocytopenia and four had life-threatening thrombocytopenia. There was one drug-related death. VP-16 is an active drug in germinal neoplasms. It appears to be an important component of "salvage" regimens for refractory patients, but severe toxicity may ensue.

Antineoplastic Agents↗
PubMed1980

I.V. practolol during microlaryngoscopy. Effect on arterial pressure, heart rate, blood glucose and lipolysis.

Twenty-five patients undergoing microlaryngoscopy were anaesthetized with thiopentone and nitrous oxide with suxamethonium as a muscle relaxant. Thirteen received practolol 0.4 mg kg-1 and atropine 1.5 mg i.v. shortly before anaesthesia. During anaesthesia practolol 0.2 mg kg-1 was given. Twelve (control) received atropine 0.5 mg before anaesthesia. Practolol reduced the frequency of tachycardia and arrhythmia. The treatment group had a greater reduction in systolic arterial pressure during induction. The hypertensive response to laryngoscopy was not significantly attenuated by practolol. A weak hyperglycaemic response to microlaryngoscopy was not affected, nor was the plasma concentration of glycerol.

Aged↗
PubMed1980

Clinical studies of gas exchange during ventilatory support--a method using the Siemens-Elema CO2 analyzer.

We describe a new portable infra-red analyses for use with the Siemens-Elema Servo ventilator. The sensor head constitutes a Y-piece connecting the patient to the ventilator tubing, and gives instant carbon dioxide determination. It is based upon simple principles that can be realized with modern techniques, offering for instance freedom from interference by anaesthetic gases, and eliminating the need for calibration. A non-zero inspired carbon dioxide concentration interferes with the measurements. Integration of the carbon dioxide signal with the flow signal from the Servo ventilator yields data about carbon dioxide excretion, and additional calculation yields VD/VT if PaCO2 is known. The accuracy of determination of end-tidal carbon dioxide and carbon dioxide elimination was found to be adequate for research purposes, and that of VD/VT for clinical purposes. The device is considered to be of value in the operating theatre and intensive care unit, for monitoring, as a guide to ventilatory needs, and for the investigation of the magnitude and causes of increased deadspace.

Aged↗
PubMed1980

Coronary disease and anaesthesia.

The anaesthetic care of patients with coronary artery disease can probably be improved. The goal is to maintain a favourable myocardial oxygen supply/demand ratio. This may necessitate the use of beta-blockade and vasodilators, or alternatively perhaps halothane, in order to reduce arterial pressure and heart rate, and thereby reduce myocardial work. Normoventilation and adequate analgesia help to prevent increases in peripheral resistance. Careful ECG monitoring may reveal ischaemia or left ventricular strain, which should be regarded as an indication to reduce myocardial work.

Anesthesia↗
PubMed1980

Trimethoprim interferes with serum methotrexate assay by the competitive protein binding technique.

Administration of Bactrim (a combination of trimethoprim and sulfamethoxazole) to a patient who also was receiving methotrexate caused a significant increase in apparent plasma methotrexate concentrations as determined by competitive protein binding assay with use of dihydrofolate reductase (EC 1.5.1.3) from Lactobacillus casei as the binding protein. This spurious increase was caused by trimethoprim in the patient's plasma. A plasma trimethoprim concentration of 0.1 mg/L inhibited binding of radiolabeled methotrexate to dihydrofolate reductase by 50%. In contrast, radioimmunoassay for methotrexate was not affected by concomitant administration of trimethoprim. The competitive protein binding assay for methotrexate should not be used in patients being treated with Bactrim or Septra (a similar combination). However, the L. casei competitive protein binding assay technique can be used to assay plasma trimethoprim concentrations with sensitivity to 0.02 mg of trimethoprim per liter.

Adult↗
PubMed1979

Evaluation of a CCTV device for partial sight.

Closed circuit TV has proved to be a valuable aid for many patients with partial sight and a new device for magnification of printed material has been developed. This is in the form of a small camera, guided over the page by the subject's hand and incorporating a roller drive for a scanning mechanism. The scanning head fits into the hand easily; it is linked to an electronic TV receiver in the form of a mosaic. Tracking the scanner manually operates a flow of the display to the left, with new material emerging from the right of the screen. The present paper outlines an evaluation of the device under different conditions with patients.

Adolescent↗