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Biomedical subjects

R D Page

Publications and source records attributed to R D Page.

At least 37 records · Page 2Linked to original sources
PubMed1998

A different tempo of mitochondrial DNA evolution in birds and their parasitic lice.

A phylogeny for the lice (Insecta: Phthiraptera: genus Dennyus) parasitic on swiftlets (Aves: Collocalliinae) was constructed based on mitochondrial cytochrome b DNA sequences. This phylogeny is congruent with previous phenetic analyses of morphometric data for the lice. Comparison with a previously obtained phylogeny for the hosts indicates some degree of cospeciation. These cospeciation events are used to compare relative rates of evolution in the birds and their lice for the same segment of the cytochrome b gene. Cytochrome b is evolving two to three times more rapidly in lice than in birds, and louse cytochrome b is highly divergent compared to that of most other insects. Although generation time has been suggested as an explanation for the disparity in evolutionary rates between lice and their hosts, we suggest that the small effective population sizes of lice coupled with founder events occurring during transmission to new host individuals may be an important factor.

Amino Acid Sequence↗
PubMed1998

GeneTree: comparing gene and species phylogenies using reconciled trees.

SUMMARY: GeneTree is a program for comparing gene and species trees using reconciled trees. The program can compute the cost of embedding a gene tree within a species tree, visually display the location and number of gene duplications and losses, and search for optimal species trees. AVAILABILITY: The program is free and is available at ((http://taxonomy.zoology.gla.ac. uk/rod/genetree/genetree.html)).

Algorithms↗
PubMed1998

Comparison of the effects of sevoflurane and isoflurane on arterial oxygenation during one lung ventilation.

We have compared the effects of sevoflurane and isoflurane on arterial oxygenation, heart rate and mean arterial pressure during one lung anaesthesia in a prospective, crossover study. We studied 28 patients undergoing oesophagogastrectomy, allocated alternatively to one of two groups. Patients in group I/S (n = 14) received 1 MAC (1.1%) of isoflurane in oxygen from induction until the end of 30 min of open chest one lung ventilation (OLV) in the lateral position. This was followed by 1 MAC (2.1%) of sevoflurane in oxygen for the next 30 min of OLV. Patients in group S/I (n = 14) received the two anaesthetic agents in the reverse order. We found no significant difference in arterial oxygenation, heart rate or mean arterial pressure between the two potent inhalation agents. In the subgroup of patients with pulmonary artery catheters (n = 12), we found a significant increase (P < 0.05) in derived shunt during sevoflurane anaesthesia. There was no significant difference in mixed venous saturation and cardiac output. We conclude that during one lung ventilation, the choice between sevoflurane and isoflurane did not significantly influence arterial oxygenation.

Aged↗
PubMed1998

Bullectomy for chronic obstructive pulmonary disease.

Chronic obstructive pulmonary disease is a progressive, disabling condition which leads to poor quality of life and limited survival. Over the years, a variety of surgical procedures have been used to achieve symptomatic improvement in selected patients. This article gives a historical account of these interventions and looks at current surgical options, both for primary treatment and management of complications.

Dyspnea↗
PubMed1997

From gene to organismal phylogeny: reconciled trees and the gene tree/species tree problem.

The processes of gene duplication, loss, and lineage sorting can result in incongruence between the phylogenies of genes and those of species. This incongruence complicates the task of inferring the latter from the former. We describe the use of reconciled trees to reconstruct the history of a gene tree with respect to a species tree. Reconciled trees allow the history of the gene tree to be visualized and also quantify the relationship between the two trees. The cost of a reconciled tree is the total number of duplications and gene losses required to reconcile a gene tree with its species tree. We describe the use of heuristic searches to find the species tree which yields the reconciled tree with the lowest cost. This method can be used to infer species trees from one or more gene trees.

Animals↗
PubMed1996

Does behavior reflect phylogeny in swiftlets (Aves: Apodidae)? A test using cytochrome b mitochondrial DNA sequences.

Swiftlets are small insectivorous birds, many of which nest in caves and are known to echolocate. Due to a lack of distinguishing morphological characters, the taxonomy of swiftlets is primarily based on the presence or absence of echolocating ability, together with nest characters. To test the reliability of these behavioral characters, we constructed an independent phylogeny using cytochrome b mitochondrial DNA sequences from swiftlets and their relatives. This phylogeny is broadly consistent with the higher classification of swifts but does not support the monophyly of swiftlets. Echolocating swiftlets (Aerodramus) and the nonecholocating "giant swiftlet" (Hydrochous gigas) group together, but the remaining nonecholocating swiftlets belonging to Collocalia are not sister taxa to these swiftlets. While echolocation may be a synapomorphy of Aerodramus (perhaps secondarily lost in Hydrochous), no character of Aerodramus nests showed a statistically significant fit to the molecular phylogeny, indicating that nest characters are not phylogenetically reliable in this group.

Animals↗
PubMed1996

Lice and cospeciation: a response to Barker.

"The student who intends working on the Mallophaga should take warning that he will be tried almost beyond endurance by the paradoxes and complexities which beset his subject but he will also find, in the dual and inter-related aspect of insect and bird, an infinite fascination." (Rothschild & Clay, 1952: pp. 156-157). The study of host louse coevolution will benefit greatly from the phylogenetic perspective offered by recent advantages in molecular systematics. However, in order to make best use of phylogenies we need to appreciate the complexities of the possible relations between host and parasite phylogeny. At the same time, the very complexity of louse-host systems has a potentially useful consequence; the presence of multiple lineages of lice on the same hosts allow for replicated tests of coevolutionary hypotheses. For example, if a number of louse clades infest the same host clade but some lice show more cospeciation than others, we might ask whether there are features of louse biology that correlate with this difference in host tracking fidelity. It may further be possible to ascertain the relative importance of these features in ecological time through controlled transfer experiments. By beginning to appreciate "the paradoxes and complexities" of host-louse evolution, lice may offer us not only "infinite fascination" but also a chance to address important questions in coevolution.

Animals↗
PubMed1996

Stapler design and strictures at the esophagogastric anastomosis.

An apparent reduction in the rate of benign anastomotic stricture after stapled esophagogastrectomy prompted us to review the results obtained with different stapling devices since 1988. We present a retrospective review of 125 consecutive patients undergoing esophageal resection for malignancy with stapled intrathoracic anastomoses. Benign anastomotic stricture was deemed present when a patient required endoscopic dilatation to treat postoperative dysphagia. We found no difference in risk factors not related to stapler size (tumor histologic characteristics, adjuvant therapy) between patients with stricture and patients without stricture. Event-free survival was compared for different stapler diameters as well as for different stapler designs. We found that staplers of smaller diameter were associated with significantly more strictures (p < 0.005). In a comparison of different designs of 25 mm stapler, the newer CDH device (Ethicon Ltd., Edinburgh, United Kingdom) was associated with a similar stricture rate to that associated with other designs (ILP [Ethicon] and EEA [Autosuture Company Division, United States Surgical Corp., Norwalk, Conn.]). For a given stapler diameter, it appears that different stapler designs have no effect on stricture rate.

Anastomosis, Surgical↗
PubMed1995

Molecular phylogenies and host-parasite cospeciation: gophers and lice as a model system.

Recent methodological advances permit a rigorous comparison of phylogenetic trees for hosts and their parasites to determine the extent to which these groups have cospeciated through evolutionary time. In cases where significant levels of cospeciation are indicated, comparison of amounts of evolutionary change that have accumulated along analogous branches in the host and parasite trees provides a direct assessment of relative rates of evolution in the two groups. For such a comparison to be meaningful, the features compared in the hosts and parasites should be genetically based, evolutionarily homologous, and should evolve in a roughly time-dependent fashion within each group. Nucleotide sequences encoding homologous genes in hosts and parasites are an ideal source of data for comparative studies of evolutionary rates. Recent studies of pocket gophers and their lice are used to illustrate the variety of questions that can be addressed through phylogenetic study of host-parasite systems.

Animals↗
PubMed1995

Continuous warm versus intermittent cold blood cardioplegia for coronary bypass surgery in patients with left ventricular dysfunction.

Between October 1991 and March 1994, 108 consecutive patients with moderate to severe left ventricular dysfunction underwent non-emergency isolated coronary artery surgery under the care of one surgeon (A.R.). They were prospectively randomised to receiving either intermittent cold (Group 1-50 patients) or continuous warm (Group 2-58 patients) blood cardioplegia for myocardial protection. There were no significant differences in clinical outcome between the two groups, as judged by operative mortality, rates of perioperative myocardial infarction, the serum CKMB isoenzyme level at 2 and 18 h after operation, need for circulatory support, postoperative neurological deficit, or duration of hospital stay. Group 2 patients required significantly more potassium (68 vs 29 mmol, P < 0.001) to maintain diastolic arrest and also had higher serum potassium levels after removal of the cross-clamp (P < 0.001). However, sinus rhythm returned spontaneously with greater frequency (91.2% vs 45.8%, P < 0.001) in Group 2 patients. In conclusion this report suggests that retrograde continuous warm blood cardioplegia provides comparable myocardial protection to that achieved with retrograde intermittent cold blood cardioplegia in patients with moderate to severe left ventricular dysfunction undergoing isolated coronary artery surgery.

Aged↗
PubMed1995

Evidence that continuous normothermic blood cardioplegia offers better myocardial protection than intermittent hypothermic cardioplegia.

OBJECTIVES: To compare transmyocardial ischaemia and oxidative stress, as well as non-infarction myocardial injury, in patients randomised to intermittent hypothermic cardioplegia or continuous normothermic blood-potassium cardioplegia. DESIGN: Prospective randomised trial. SETTING: Tertiary cardiac referral centre. METHODS: 24 patients undergoing elective coronary artery bypass surgery were randomised to hypothermic (13 patients, mean (SEM) age 59.5 (2.6) years) or normothermic (11 patients, mean (SEM) age 59.7 (3.3) years) cardioplegia. Transmyocardial oxidative stress and ischaemia were assessed by the difference in plasma concentrations of oxidised glutathione and lactate respectively, from samples taken simultaneously from the coronary sinus and aortic root. Blood samples were taken just before cross clamp application and at intervals up to 15 min after cross clamp release. Non-infarction myocardial injury was assessed by measurement of creatine kinase MB isoenzyme activity from peripheral venous blood taken 2 and 18 h after surgery. RESULTS: Intermittent hypothermic cardioplegia resulted in a significant increase in transmyocardial ischaemia (P < 0.001) and oxidative stress (P < 0.001). Evidence of significantly increased myocyte damage was also present (P < 0.01). No significant corresponding changes were present with normothermic cardioplegia. CONCLUSIONS: Normothermic blood cardioplegia seems to avoid significant changes in myocardial ischaemic status and consequent oxidative stress. This study provides direct evidence that normothermic cardioplegia offers enhanced myocardial protection compared with that of hypothermic cardioplegia. Certain subsets of patients may derive more benefit from normothermic cardioplegia, although it is unclear whether this would be the case for all patients.

Cardiopulmonary Bypass↗
PubMed1994

A prospective randomised study of continuous warm versus intermittent cold blood cardioplegia for coronary artery surgery: preliminary report.

Between October 1991 and March 1993, 281 consecutive patients underwent non-emergency isolated coronary artery surgery under the care of one surgeon (A.R.). They were prospectively randomised to receive either intermittent cold (Group I-144 patients) or continuous warm (Group II-137 patients) blood cardioplegia for myocardial protection. There were no significant differences in clinical outcome between the two groups, as judged by operative mortality, rates of peri-operative myocardial infarction, blood loss, need for circulatory support, post-operative neurological deficit, or duration of intensive care or hospital stay. However, sinus rhythm returned spontaneously with greater frequency (91.2% vs 45.8%, P < 0.001) in Group II patients. There was greater transmyocardial oxidative stress in Group I patients, as evidenced by a significant rise in oxidised glutathione in coronary sinus blood on myocardial reperfusion. Also, the serum CKMb isoenzyme level 2 h post-operatively was significantly raised in Group I patients, although this difference had disappeared by the day after surgery. In conclusion this preliminary report suggests that continuous warm blood cardioplegia provides comparable myocardial protection to that achieved with standard hypothermic techniques in patients undergoing coronary artery surgery.

Coronary Angiography↗
PubMed1994

Central and peripheral limitations to upright exercise in untrained cardiac transplant recipients.

BACKGROUND: Functional capacity and quality of life are subjectively improved after cardiac transplantation. However, the objective improvement in exercise tolerance after transplantation has been disappointing. The extent to which allograft diastolic dysfunction contributes to this exercise intolerance has not been defined. METHODS AND RESULTS: Thirty cardiac transplant recipients between 3 and 16 months after transplantation and 30 age-matched normal control subjects underwent maximal symptom-limited graded upright bicycle exercise testing with simultaneous radionuclide angiography, invasive hemodynamic monitoring, and breath-by-breath gas analysis. Mean blood pressure was higher in the transplant group at supine rest (112.1 versus 97.7 mm Hg), normalized with upright posture, and became lower than normal at peak exercise (121.1 versus 133.2 mm Hg). Systolic function as measured by ejection fraction was normal in both groups. However, the cardiac transplant recipients had significantly lower exercise tolerance, achieving a mean maximal work rate of 390 kilopond-meters per minute (kpm/min), compared with 825 kpm/min in the normal subjects. Peak oxygen consumption was 12.3 mL.min-1.kg-1 in the transplant group, 46% lower than the normal group's value of 22.9 mL.min-1.kg-1. The transplant patients had a resting tachycardia (94 beats per minute) and a 79% reduction in exercise heart rate reserve compared with normal. Despite this chronotropic incompetence, stroke index response to exercise was consistently lower after transplantation, accounting for a 41% reduction in cardiac index at maximal exercise. The lower stroke index was accompanied by a 32% lower end-diastolic volume index at rest and a 14% lower end-diastolic volume index at peak exercise. Despite the smaller ventricular volumes after transplantation, pulmonary capillary wedge pressure was 35% higher than normal at supine rest and 50% higher at maximal exercise. Right atrial and mean pulmonary arterial pressures were similarly elevated. The ratio of pulmonary capillary wedge pressure to end-diastolic volume index was significantly higher during the postural change and exercise, suggesting allograft diastolic dysfunction. Arteriovenous oxygen difference was similar between groups at rest and with submaximal exercise but was 24% lower at maximal exercise in the transplant group, suggesting an abnormality in peripheral oxygen uptake or utilization. CONCLUSIONS: Exercise tolerance is severely limited during the first 16 months after cardiac transplantation despite preservation of allograft left ventricular systolic function. This intolerance is due to an inadequate cardiac index response from a combination of chronotropic incompetence and diastolic dysfunction limiting the appropriate compensatory use of the Starling mechanism. In addition, there is a peripheral abnormality in oxygen transport or utilization that may partially reflect the effects of deconditioning.

Adult↗