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Biomedical subjects

P McConville

Publications and source records attributed to P McConville.

10 recordsLinked to original sources
PubMed2005

Temporal dynamics of inotropic, chronotropic, and metabolic responses during beta1- and beta2-AR stimulation in the isolated, perfused rat heart.

During the beta-adrenergic receptor (beta-AR)-mediated stress response in the heart, the relations between functional responses and metabolism are ill defined, with the distinction between beta1- and beta2-AR subtypes creating further complexity. Specific outstanding questions include the temporal relation between inotropic and chronotropic responses and their metabolic correlates. We sought to elucidate the relative magnitudes and temporal dynamics of the response to beta1- and beta2-AR stimulation and the energy expenditure and bioenergetic state related to these responses in the isolated perfused rat heart. Inotropic [left ventricular developed pressure (LVDP) and dP/dt], chronotropic [heart rate (HR)], and metabolic responses were measured during beta1- (n = 9; agonist: norepinephrine) and beta2- (n = 9; agonist: zinterol) AR stimulation. Myocardial oxygen consumption (MVO2) was measured using fiber-optic oximetry, and high-energy phosphate levels and intracellular pH were measured using 31P NMR spectroscopy. A multiple-dose protocol was used, with near-maximal beta-AR stimulation at the highest doses. In both beta1 and beta2 groups, there were dose-dependent increases in LVDP, dP/dt, HR, and MVO2. The inotropic response showed more rapid onset, washout, and variation during dose than did the chronotropic response and was closely correlated with MVO2. This suggests that the myocardial bioenergetic state is more closely related to the inotropic response than to the chronotropic response. In addition, beta1-AR stimulation resulted in a greater magnitude and rate of onset of inotropic and MVO2 responses than did beta2-AR stimulation during maximal stimulation. However, a similar decrease in intracellular energy charge was seen in the two groups, consistent with a greater rate of oxidative phosphorylation during beta1- than during beta2-AR stimulation.

Adrenergic beta-Agonists↗
PubMed2005

Psychiatric characteristics of frequent attenders at accident and emergency: a case register comparison with non frequent attenders.

BACKGROUND AND AIMS: Patients attending Accident and Emergency (A&E) on a frequent basis consume a large amount of NHS resources and often frustrate health workers employed in the service. This audit aimed to identify the personal and psychiatric characteristics of these patients and highlight areas where intervention may be helpful. METHODS AND RESULTS: Patients presenting to A &E more than 20 times in four years were comparison to non-frequent attenders using case register information. The study demonstrates that frequent attenders are well known to psychiatric services, but are not engaged in ongoing contact. This is not due to a difference in attendance rate between frequent attenders and controls but may represent reluctance for follow up either on the part of the patient or the psychiatrist. CONCLUSIONS: These patients have a combination of physical, psychiatric and social pathologies and the services to address these needs does not seem to currently exist but should be considered.

Adult↗
PubMed2001

The lever-coil: a simple, inexpensive sensor for respiratory and cardiac motion in MRI experiments.

Thoracic and abdominal magnetic resonance imaging studies generally require some type of compensation for respiratory and cardiac motions in order to yield artifact-free images with good signal-to-noise ratio. Most techniques for respiratory compensation require the use of a non-NMR sensing device to monitor the subject's chest motion, while cardiac motion compensation generally requires the use of ECG leads within the magnet. An inductive pickup coil placed on the subject's chest is perhaps the simplest and least expensive means of monitoring respiration in a MR scanner. However, due to inductive coupling between the pickup coil, radio frequency resonator and gradient set, this arrangement often results in both NMR and respiratory signal artifacts and can also present a burn hazard to the subject depending on the placement and orientation of the pickup coil. Moreover, the presence of a pickup coil on the chest can degrade local magnetic field homogeneity and thus degrade image quality. Similar problems arise when ECG leads must be connected to the subject for cardiac monitoring and gating. To preserve the benefits of the simple pickup coil while circumventing these limitations, a "lever-coil" sensor is presented in which a pickup coil is mechanically coupled to the subject but is not located within the resonator or gradient coil. This results in much lower mutual inductance between the pickup coil and the resonator or gradients. The optimization of the geometry of the apparatus is discussed and lever-coil signal traces are shown which demonstrate the sensor's ability to simultaneously detect both respiratory and cardiac motion in mice. Finally, respiratory-gated and cardiac-triggered spin echo images of the rat abdomen and mouse heart are presented to demonstrate the utility of the lever-coil sensor.

Animals↗
PubMed2001

Diffusion limited evaporation rates in hydrogel contact lenses.

PURPOSE: To systematically measure evaporative water loss for a range of commercial hydrogel contact lens types, correlate the results with measured water self-diffusion coefficients and determine the best way to present and quantify the in vitro evaporation data. METHODS: Evaporative water loss was measured gravimetrically for the four commercial contact lens types: Acuvue (powers: -0.50 D, -0.75 D), Newvues (powers: -0.50 D, -0.75 D, -1.00 D), CIBAsoft (powers: -0.50 D, -0.75 D, -1.00 D) and SeeQuence 2 (power: -0.75 D), with water contents of 60%, 55%, 38%, and 38%, respectively. Water proton self-diffusion coefficients were measured for these materials using standard nuclear magnetic resonance (NMR) pulsed field gradient techniques. RESULTS: The initial rate of evaporation was linear for 5-10 minutes then decreased in all cases. No significant differences were observed in this initial rate between the lenses studied. However, the evaporative rate decreased more slowly with time for the higher water content lenses. The diffusion coefficients were found to be highly dependent on the equilibrium water content, regardless of material composition. CONCLUSIONS: The most effective way to present/quantify this type of evaporative data is to plot the time-course of the mass evaporation rate. We have found that the decrease in evaporative rate with time is a diffusion-limited effect whereby lenses with higher water content can maintain a higher rate of diffusion of water (to the evaporative surface) due to the presence of higher proportions of mobile water molecules. The NMR diffusion data corroborate these findings.

Contact Lenses, Hydrophilic↗
PubMed2000

Test liquids for quantitative MRI measurements of self-diffusion coefficient in vivo.

A range of liquids suitable as quality control test objects for measuring the accuracy of clinical MRI diffusion sequences (both apparent diffusion coefficient and tensor) has been identified and characterized. The self-diffusion coefficients for 15 liquids (3 cyclic alkanes: cyclohexane to cyclooctane, 9 n-alkanes: n-octane to n-hexadecane, and 3 n-alcohols: ethanol to 1-propanol were measured at 15-30 degrees C using an NMR spectrometer. Values at 22 degrees C range from 0.36 to 2.2 10(-9) m(2)s(-1). Typical 95% confidence limits are +/-2%. Temperature coefficients are 1.7-3.2% degrees C. T1 and T2 values at 1.5 T and proton density are given. n-tridecane has a diffusion coefficient close to that of normal white matter. The longer n-alkanes may be useful T2 standards. Measurements from a spin-echo MRI sequence agreed to within 2%.

Alcohols↗
PubMed2000

The reliability of case register diagnoses: a birth cohort analysis.

BACKGROUND: Few studies assess the reliability of case register diagnoses, despite their widespread use in psychiatric research. This study investigates case register diagnostic reliability in comparison to casenote derived diagnoses in a birth cohort. METHODS: Diagnostic information from the case register and casenotes of 449 individuals was extracted. The incident and lifetime register diagnoses were compared with those derived from the casenotes. RESULTS: Inter-rater reliability was good (kappa = 0.71). Agreement between casenote and incident register diagnosis was moderate (kappa = 0.52), as was agreement between casenote and register lifetime diagnosis (kappa = 0.58). Case register diagnoses were insufficiently accurate to stand alone. Case register diagnoses for organic disorder, schizophrenia, alcoholism, learning disability, personality disorder and transient or no psychiatric disorder were reliable enough for the case register to act as a useful screening instrument. The case register was not acceptable, even as a screening instrument, for the diagnoses of neurotic or affective disorders. CONCLUSIONS: Studies relying only on case register diagnoses may be flawed if diagnoses are not independently verified. National statistics derived from case register data, especially for neurosis and affective disorder, may be unreliable.

Cohort Studies↗
PubMed1997

Limitations of in vitro contact lens dehydration/rehydration data in predicting on-eye dehydration.

PURPOSE: The purpose of this study was to use in vitro dehydration and rehydration data to model the predicted hydration changes that may occur as a soft contact lens loses and gains water on the eye between blinks. METHODS: Using a recent in vitro data set for four lens materials dehydrated and rehydrated in saline, we derived a mathematical model to describe dehydration and rehydration time courses. The model further combined the dehydration and rehydration data iteratively, as a function of blink frequency, and pre-lens break-up time. RESULTS: The model showed that reduced break-up times or decreased blink frequencies significantly affected dehydration rates and steady state dehydration for lenses of a variety of water contents. However, the model did not agree with the commonly accepted clinical belief that high water content lens materials dehydrate more than low water content materials. DISCUSSION: The discrepancy of the model with historical observations may be accounted for by one or more of the following factors, which were not accounted for in the present model: 1) temperature dependent dehydration (as a lens is taken from a room temperature vial and warmed when placed on the eye); 2) the colloid osmotic pressure, ionicity, pH, and chemical potential of tears (compared to saline); and 3) dehydration by other non-evaporative mechanisms.

Blinking↗
PubMed1991

Implanted 3He, 4He, and Xe in further studies of diamonds from Western Australia.

In measurements of the noble gases in additional samples of diamonds from the Argyle and Ellendale lamproites in Western Australia we have failed to encounter any neon-rich stones such as showed solar-like isotopic compositions in earlier work. No neon was detected above the relatively high blank levels in our glass apparatus. White and brown diamonds showed no differences in noble gas content, nor did samples segregated by the color of long-wave UF fluorescence. The rare gas patterns in the 1.2 Ga Argyle pipe are largely consistent with implanted 3He, 4He, and fissiogenic Xe from U/Th in the matrix rock in which the diamonds have been stored for so long. These implanted species are absent in diamonds from the much younger (approximately 20 Ma) Ellendale pipe. We give implantation formulae for several models of inhomogeneously distributed U/Th. Differences in 3He content between pipe and alluvial Argyle samples are consistent with expected cosmogenic production in the latter. An expanded data base for helium and carbon isotopic data on the same samples supports a negative [4He]-delta 13C correlation seen earlier in work from our group, but if the Argyle samples, which contain light carbon, are corrected for implanted 4He, the correlation is considerably weakened. We no longer see an earlier 3He/4He-delta 13C correlation.

Carbon Isotopes↗