Search PubMed⌕ Search

Biomedical subjects

J A Davis

Publications and source records attributed to J A Davis.

At least 145 records · Page 8Linked to original sources
PubMed1990

Accurate prediction of VO2max in cycle ergometry.

Numerous equations exist for predicting VO2max from the duration (an analog of maximal work rate, Wmax) of a treadmill graded exercise test (GXT). Since a similar equation for cycle ergometry (CE) was not available, we saw the need to develop such an equation, hypothesizing that CE VO2max could be accurately predicted due to its more direct relationship with W. Thus, healthy, sedentary males (N = 115) and females (N = 116), aged 20-70 yr, were given a 15 W.min-1 CE GXT. The following multiple linear regression equations which predict VO2max (ml.min-1) from the independent variables of Wmax (W), body weight (kg), and age (yr) were derived from our subjects: Males: Y = 10.51 (W) + 6.35 (kg) - 10.49 (yr) + 519.3 ml.min-1; R = 0.939, SEE = 212 ml.min-1. Females: Y = 9.39 (W) + 7.7 (kg) - 5.88 (yr) + 136.7 ml.min-1; R = 0.932, SEE = 147 ml.min-1 Using the 95% confidence limits as examples of worst case errors, our equations predict VO2max to within 10% of its true value. Internal (double cross-validation) and external cross-validation analyses yielded r values ranging between 0.920 and 0.950 for the male and female regression equations. These results indicate that use of the equations generated in this study for a 15 W.min-1 CE GXT provides accurate estimates of VO2max.

Adult↗
PubMed1990

Aeromonas, acclimation, and penicillin as complications when leeches are applied to skin flaps in rabbits.

The medicinal leech, Hirudo medicinalis, has been recognized by plastic surgeons for its ability to reduce congestion and improve blood flow in grafted skin flaps by withdrawing excess blood. The leech's ability to digest blood is due to the presence of Aeromonas hydrophila in the gut of the leech. In this report we describe the occurrence of Aeromonas hydrophila septicaemia in rabbits used in a study to evaluate the efficacy of the medicinal leech on abdominal skin flap survival. In New Zealand White rabbits, twin 5 x 10 cm abdominal skin flaps were prepared and the epigastric vein was ligated to produce a model of venous congested skin. After 12 hours, a leech was applied to one of the congested abdominal flaps and skin survivability was assessed and compared with the unleeched flap. Five rabbits died acutely approximately 24 hours post-operatively. Gross necropsy, bacteriology and histopathology findings indicated that A. hydrophila was the causative agent of the septicaemia-toxaemia syndrome with an associated pneumonia and typhlitis. Review of the management and the experimental surgery protocol suggested that the two major disposing factors of Aeromonas septicaemia in these rabbits were stress and excessive prophylactic administration of penicillin.

Aeromonas↗
PubMed1989

Cardiac catheterisation by the Judkins technique as an outpatient procedure.

OBJECTIVE: To assess the safety and cost benefit of left heart catheterisation by a modified Judkins technique performed as a day patient procedure. DESIGN: Review study of case notes of consecutive patients examined by the procedure over three years (January 1984 to December 1986). SETTING: Outpatient referrals in a regional cardiac centre within a district general hospital. PATIENTS: Nine hundred patients aged 18-76 (mean 54) selected at a previous clinic as suitable for the procedure. MAIN RESULTS: Eight hundred and fifty patients (94.4%) were discharged home on the day of the procedure. Forty others (4.4%) could not be discharged owing to complications during or just after the procedure. Of these patients, two died (0.2%), six suffered a myocardial infarction (0.7%), and two had major vascular complications. The remaining 30 patients were admitted because of chest pain without infarction (10 cases), minor vascular incidents (six), haemorrhage at the puncture site (five), arrhythmia (four), pulmonary oedema (three), and contrast reaction (two). Ten patients were admitted for either urgent coronary artery bypass grafting or social reasons. CONCLUSIONS: Cardiac catheterisation is safe as an outpatient procedure in most cases. Beds are spared and roughly 35,000 pounds is saved for every 500 procedures performed.

Adolescent↗
PubMed1989

Breathing-valve encumbrance and arterial blood gas and acid-base status in exercise in man.

It has been suggested that the mouth-piece-breathing valve assemblies commonly used in laboratory investigations of ventilatory control may influence regulation of arterial blood gas and acid-base status during exercise. To examine this hypothesis, 10 healthy males each underwent two incremental cycle-ergometer tests (15 W min-1) to the limit of tolerance: one was conducted free of breathing apparatus; the other utilized a mouth-piece (with noseclip) connected to a low-resistance turbine volume sensor. The order was randomly assigned and tests were separated by a 2 h recovery. Blood sampled from an indwelling brachial artery catheter at rest and every 30 W during exercise was analyzed for PCO2, PO2, pH and HCO-3. Maximum power was not different between the two tests. Furthermore, no systematic effect of the assembly could be discerned on PaCO2, PaO2 or pHa over the entire range of power. We therefore conclude that although ventilation and its pattern may be affected by laboratory breathing apparatus, such encumbrance (if of low resistance and dead space) does not influence blood gas and acid-base regulation during exercise.

Acid-Base Equilibrium↗
PubMed1989

Ventilatory control of the 'isocapnic buffering' region in rapidly-incremental exercise.

During incremental exercise PCO2 does not fall for several work rates ('isocapnic buffering') above the anaerobic threshold (theta an). We explored this apparent lack of compensatory hyperventilation in 24 normal subjects who underwent incremental cycling (15 W/min) to exhaustion. Ventilation, pulmonary gas exchange, and end-tidal gas tensions were computed breath-by-breath. In 10 subjects, arterial blood was sampled every 2 min throughout the test. Our findings confirmed the 'isocapnic' supra-theta an region, but it consistently followed a progressive increase of PETCO2 in the sub-theta an region. A similar pattern was evident for PaCO2. The leveling-out of PETCO2 and PaCO2 was a result of breathing frequency increasing at theta an, thereby shortening expiratory time, i.e., progressively truncating the continued increase in the alveolar PCO2 slope. Consequently 'isocapnic buffering' during incremental exercise does not reflect PCO2 which continues to be regulated at a constant sub-theta an value. Rather it reflects a ventilatory response to the metabolic acidosis which levels a systematically-rising phase of PETCO2 and PaCO2, largely through a change in breathing pattern. Respiratory compensation, as reflected by a declining PETCO2 and PaCO2, does not occur typically for a subsequent 2 or more minutes.

Acid-Base Equilibrium↗
PubMed1989

A new transmissible viral hepatitis of marmosets and tamarins.

Callitrichid hepatitis (CH) is a newly recognized, acute, fatal, epizootic disease of New World primates in the family Callitrichidae. Since 1980, 12 outbreaks of CH have occurred in US zoos, involving several callitrichid species including the endangered golden lion tamarin (Leontopithecus rosalia). CH was experimentally transmitted to common marmosets via a bacteria-free filtrate of liver from a naturally infected tamarin. All three inoculated marmosets developed an acute fatal disease with the characteristic clinical and histopathologic findings of CH. Human hepatotropic viruses that can infect the livers of callitrichids were not detected serologically in any of the experimentally infected marmosets. Enveloped viruslike particles 85-105 nm in diameter were observed in the rough endoplasmic reticulum and Golgi complex of hepatocytes from both naturally infected and experimentally inoculated animals. An immunoblot assay was developed using sera from tamarins exposed to natural outbreaks of CH and liver extracts from experimentally infected or control marmosets. A new CH-specific antigen was detected in the livers of naturally infected and experimentally inoculated marmosets but not controls. These results suggest that the etiologic agent of callitrichid hepatitis is a new primate hepatitis virus.

Animals↗
PubMed1989

Hysteroscopic endometrial ablation with the neodymium-YAG laser.

Over the past 3 years a series of patients referred to the gynaecological department at Stobhill Hospital with menorrhagia have been treated, as an alternative to hysterectomy, by endometrial ablation with the neodymium-YAG laser. The results in the first 25 patients with a follow-up of over 6 months are presented. The overall success rate was only 52%, but by increasing the power output of the laser energy used to 80 W the rate of success increased to 83%. Of the 25 patients 13 were selected for laser treatment because hysterectomy was considered unsuitable on account of obesity or medical and surgical conditions; the other 12 wanted to avoid a hysterectomy. The technique and its problems are discussed.

Adult↗
PubMed1989

Comparison of disposable diapers with fluff absorbent and fluff plus absorbent polymers: effects on skin hydration, skin pH, and diaper dermatitis.

Diaper dermatitis results from the action of a number of physical and chemical factors on the skin. While its etiology is complex, there is agreement that prolonged contact between wet diapers and the skin leading to excessive hydration of the stratum corneum and reduced barrier function is a primary factor. Recent research also indicates that pH elevation resulting from ammonia production increases the probability of skin damage due to fecal enzyme activity. New diapers containing absorbent polymers blended with cellulose fluff in the absorbent core have been developed. The absorbent polymer binds fluids and controls pH in the diaper environment. To assess the effectiveness of these diapers, a clinical study was conducted with approximately 150 infants over 15 weeks, using fluff diapers and absorbent polymer diapers. The results clearly showed that the diapers with absorbent polymer provide a better skin environment than those with fluff only with respect to lower skin wetness and pH control (instrumental measurements). In addition, the clinicians' grades indicated a directional reduction in diaper rash severity.

Body Water↗
PubMed1989

Early diet in preterm babies and developmental status in infancy.

Few data from randomised prospective studies address whether early diet influences later neurodevelopment in man. As part of a larger multicentre trial, 502 low birthweight infants were assigned randomly, for a median of 30 days, to receive a preterm formula or unfortified donor breast milk as sole diets or as supplements to their mothers' expressed milk. Surviving infants were assessed at nine months after their expected date of delivery without knowledge of their feeding regimen. The mean developmental quotient was 0.25 standard deviations lower in those fed donor breast milk rather than preterm formula. In infants fed their mother's expressed milk, however, the disadvantage of receiving banked milk compared with preterm formula as a supplement, was greater when the supplement was over half the total intake, and approached five points, representing 0.5 standard deviations for developmental quotient. Infants fed donor breast milk were at particular disadvantage following fetal growth retardation, with developmental quotients 5.3 points lower. We suggest that the diet used for low birthweight babies over a brief, but perhaps critical, postnatal period has developmental consequences that persist into infancy; infants who are small for gestational age are especially vulnerable to suboptimal postnatal nutrition.

Child Development↗
PubMed1989

Alterations of cytosolic calcium in LLC-PK1 cells induced by vasopressin and exogenous purines.

The regulation of cytosolic calcium in LLC-PK1 cells by various agonists was characterized. Arginine vasopressin (AVP, 100 nM) rapidly increased cytosolic calcium (Caf) measured with fura-2 from a basal level of 65 +/- 5 to 516 +/- 102 nM followed by a return to a plateau level of 128 +/- 18 nM. Similar responses to 100 nM lysine vasopressin were seen. AVP also increased adenosine 3',5'-cyclic monophosphate (cAMP) as previously documented for these cells. A V2-selective AVP analogue increased cAMP without affecting Caf, whereas two V1-receptor antagonists prevented the Caf response to AVP without altering the cAMP response. Increasing cellular cAMP with forskolin, cholera toxin, or stable cAMP analogues did not affect Caf or the response of Caf to AVP. Both adenosine and ATP produced large Caf transients at concentrations of 1-10 microM in both calcium-containing media and after acute chelation of medium Ca with ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA). The A1-selective adenosine analogue, (R-phenyl-isopropyl)-adenosine, and the A2-selective analogue, 5'-(N-ethyl)-carboxamido-adenosine, both produced Caf responses similar to adenosine. The Caf responses to adenosine and its analogues but not to ATP were blocked by the adenosine receptor antagonist, 8-cyclopentyl-1,3-dipropylxanthine. Islet-activating protein, pertussis toxin, inhibited the Caf response to adenosine and enhanced the cAMP response to AVP. Responses to all agonists were demonstrable in greater than 80% of single cells studied by microfluorometry, and individual cells responded to multiple agonists. These studies indicate that the Caf and cAMP responses to AVP in the LLC-PK1 cell line involve separate receptors, and they document the presence in this cell line of at least two types of receptors for exogenous purines.

Arginine Vasopressin↗
PubMed1989

Mutational analysis of a lactogenic hormone reveals a role for lactogen-specific amino acid residues in receptor binding and mitogenic activity.

Mutant forms of mouse placental lactogen-II (PL-II) have been generated to assess the role of specific amino acid residues and protein regions in binding to the PRL receptor and in mitogenic activity. Conversion of any of three lactogen-specific residues significantly reduced both of these hormone functions; mutation of the two other lactogen-specific amino acids revealed only minimal effects unless these changes were coupled with a second mutation. Deletions within the PL-II protein all resulted in a complete loss of function, but switching regions between PL-II and proliferin, another member of the prolactin family in the mouse, did yield a chimeric protein with some PRL-like activity. This activity was increased substantially by conversion of one amino acid residue in the proliferin region to the corresponding lactogen-specific residue. The locations of the amino acids that have been found to affect hormone function are predicted to be closely apposed in the folded protein, suggesting that this region may be the site of interaction of this lactogenic hormone with the PRL receptor.

Amino Acid Sequence↗
PubMed1989

Expression of multiple forms of the prolactin receptor in mouse liver.

We have characterized the PRL receptor (PRL-R) present in mouse liver by purification, cross-linking, and immunological analysis of the protein, and by the isolation of PRL-R cDNA clones. Analysis of the cDNA clones indicates that the liver receptor is actually a family of proteins. Two of these proteins are predicted to be synthesized as precursors of 303 and 292 amino acids, with common signal sequences, extracellular domains, and transmembrane domains; a portion of their cytoplasmic domains are also identical, but these proteins differ markedly in the terminal region of this domain. A third PRL-R protein is predicted to be a truncated form and may be secreted. These multiple PRL-R mRNAs appear to be encoded by at least two genes, with the sequence variation for the two full-length proteins likely due to alternative RNA splicing. These results suggest that the varied actions of PRL may involve multiple receptors that are part of distinct signal transduction pathways.

Amino Acid Sequence↗
PubMed1989

A mutant lactogenic hormone binds, but does not activate, the prolactin receptor.

We have generated mutations in mouse placental lactogen II, a hormone in the PRL/GH family that binds to the PRL receptor, to investigate the role of the conserved cysteine residues in hormone function. Disruption of the small C-terminal disulfide loop did not significantly alter hormone activity. Substitution of serine for cysteine-51, which prevents formation of the large disulfide loop, results in a protein equivalent to placental lactogen II in receptor-binding activity; however, this mutant protein is not mitogenic in an assay for lactogenic hormones. These results indicate that PRL receptor occupancy and activation are distinct events.

Animals↗