Search PubMed⌕ Search

Biomedical subjects

J C Hardy

Publications and source records attributed to J C Hardy.

At least 19 recordsLinked to original sources
PubMed2003

High precision measurement of the superallowed 0+ --> 0+ beta decay of 22Mg.

The half-life, 3.8755(12) s, and superallowed branching ratio, 0.5315(12), for 22Mg beta decay have been measured with high precision. The latter depended on gamma-ray intensities being measured with an HPGe detector calibrated for relative efficiencies to an unprecedented 0.15%. Previous precise measurements of 0+ --> 0+ transitions have been restricted to the nine that populate stable daughter nuclei. No more such cases exist, and any improvement in a critical Cabibbo-Kobayashi-Maskawa unitarity test must depend on precise measurements of more exotic nuclei. With this branching-ratio measurement, we show those to be possible for T(z)=-1 parents. We obtain a corrected Ft value of 3071(9) s, in good agreement with expectations.

Journal Article↗
PubMed2002

Superallowed beta decay of nuclei with a >or= 62: the limiting effect of weak Gamow-Teller branches.

The most precise value of V(ud), which is obtained from superallowed nuclear beta decay, leads to a violation of Cabibbo-Kobayashi-Maskawa unitarity by 2.2sigma. Experiments are underway on two continents to test and improve this result through decay studies of odd-odd N = Z nuclei with A>or=62. We show, in a series of illustrative shell-model calculations, that numerous weak Gamow-Teller branches are expected to compete with the superallowed branch in each of these nuclei. Though the total Gamow-Teller strength is significant, many of the individual branches will be unobservably weak. Thus, new techniques must be developed if reliable ft values are to be obtained with 0.1% precision for the superallowed branches.

Journal Article↗
PubMed2001

Precise half-life measurement for the superallowed 0(+)-->0(+) beta emitter (74)Rb: first results from the new radioactive beam facility (ISAC) at TRIUMF.

Presently, the world data for superallowed beta decay leads to a result in disagreement (at the 98% confidence level) with the predictions of the minimal standard model for the unitarity of the Cabibbo-Kobayashi-Maskawa matrix. Precise data for the superallowed 0(+)-->0(+) beta decay of (74)Rb would provide a critical test of the nucleus-dependent isospin symmetry-breaking corrections that must be calculated for these superallowed Fermi beta decays. The present work reports the first precise measurement of the half-life for (74)Rb ( t(1/2) = 64.761+/-0.031 ms). The data were obtained at the radioactive beam facility (ISAC) at TRIUMF using a beam of approximately 4000 (74)Rb ions s(-1).

Journal Article↗
PubMed2001

Bioisosteres of 9-carboxymethyl-4-oxo-imidazo[1,2-a]indeno-[1,2-e]pyrazin-2-carboxylic acid derivatives. Progress towards selective, potent in vivo AMPA antagonists with longer durations of action.

A novel series of 2- and 9-disubstituted heterocyclic-fused 4-oxo-indeno[1,2-e]pyrazin derivatives was synthesized. One of them, the 9-(1H-tetrazol-5-ylmethyl)-4-oxo-5,10-dihydroimidazo[1,2-a]indeno[1,2-e]pyrazin-2-yl phosphonic acid 4i exhibited a strong and a selective binding affinity for the AMPA receptor (IC50 = 13 nM) and demonstrated potent antagonist activity (IC50 = 6nM) at the ionotropic AMPA receptor. This compound also displayed good anticonvulsant properties against electrically-induced convulsions after ip and iv administration with ED50 values between 0.8 and 1 mg/kg. Furthermore, a strong increase in potency was observed when given iv 3 h before test (ED50 = 3.5 instead of 25.6 mg/kg for the corresponding 9-carboxymethyl-2-carboxylic acid analogue). These data confirmed that there is an advantage in replacing the classical carboxy substituents by their bioisosteres such as tetrazole or phosphonic acid groups.

Animals↗
PubMed2001

Hypoxia augments apnea-induced peripheral vasoconstriction in humans.

Obstructive apnea and voluntary breath holding are associated with transient increases in muscle sympathetic nerve activity (MSNA) and arterial pressure. The contribution of changes in blood flow relative to the contribution of changes in vascular resistance to the apnea-induced transient rise in arterial pressure is unclear. We measured heart rate, mean arterial blood pressure (MAP), MSNA (peroneal microneurography), and femoral artery blood velocity (V(FA), Doppler) in humans during voluntary end-expiratory apnea while they were exposed to room air, hypoxia (10.5% inspiratory fraction of O2), and hyperoxia (100% inspiratory fraction of O2). Changes from baseline of leg blood flow (Q) and vascular resistance (R) were estimated from the following relationships: Q proportional to V(FA), corrected for the heart rate, and R proportional to MAP/Q. During apnea, MSNA rose; this rise in MSNA was followed by a rise in MAP, which peaked a few seconds after resumption of breathing. Responses of MSNA and MAP to apnea were greatest during hypoxia and smallest during hyperoxia (P < 0.05 for both compared with room air breathing). Similarly, apnea was associated with a decrease in Q and an increase in R. The decrease in Q was greatest during hypoxia and smallest during hyperoxia (-25 +/- 3 vs. -6 +/- 4%, P < 0.05), and the increase in R was the greatest during hypoxia and the least during hyperoxia (60 +/- 8 vs. 21 +/- 6%, P < 0.05). Thus voluntary apnea is associated with vasoconstriction, which is in part mediated by the sympathetic nervous system. Because apnea-induced vasoconstriction is most intense during hypoxia and attenuated during hyperoxia, it appears to depend at least in part on stimulation of arterial chemoreceptors.

Adult↗
PubMed2000

Studies on the removal of abnormal prion protein by processes used in the manufacture of human plasma products.

BACKGROUND AND OBJECTIVES: To identify if any process steps used in plasma fractionation may have a capability of removing agents of human transmissible spongiform encephalopathy (TSE). MATERIALS AND METHODS: Sixteen fractionation steps were investigated separately by adding a preparation of hamster adapted scrapie 263K to the starting material at each process step and determining the distribution into resultant fractions of protease-K-resistant (abnormal) prion protein by Western blot analysis. RESULTS: A number of process operations were found to remove abnormal prion protein to the limit of detection of the assay. These were cold ethanol precipitation of fraction IV (log reduction, LR, >/=3.0) and a depth filtration (LR >/=4.9) in the albumin process; cold ethanol fraction I+III precipitation (LR >/=3.7) and a depth filtration (LR >/=2.8) in the immunoglobulin processes and adsorption with DEAE-Toyopearl 650M ion exchanger (LR >/=3.5) in the fibrinogen process. In addition, a substantial degree of removal of abnormal prion protein was observed across DEAE-Toyopearl 650M ion exchange (LR = 3.1) used in the preparation of factor-VIII concentrate; DEAE-cellulose ion exchange (LR = 3.0) and DEAE-sepharose ion exchange (LR = 3.0) used in the preparation of factor-IX concentrates and S-sepharose ion exchange (LR = 2.9) used in the preparation of thrombin. CONCLUSIONS: Plasma fractionation processes used in the manufacture of albumin, immunoglobulins, factor-VIII concentrate, factor-IX concentrates, fibrinogen and thrombin all contain steps which may be capable of removing causative agents of human TSEs.

Animals↗
PubMed1997

Aortic valve replacement in a United States Air Force pilot: case report and literature review.

We report the first case of a United States Air Force pilot returned to flying status after cardiac valve replacement. A 34-yr-old C-130 pilot underwent placement of an aortic valve homograft as a result of an episode of acute bacterial endocarditis on a bicuspid aortic valve. After a period of observation and a careful evaluation, he was returned to flying status in low-G aircraft. While cardiac valve replacement has traditionally been considered disqualifying for military aviation duties, aortic valve homografts have been associated with a lower morbidity and a significantly improved prognosis when compared to the other types of prosthetic heart valves. With careful evaluation and close follow-up, military aviators with aortic valve homografts can be considered for return to flying duties in low-G aircraft.

Acute Disease↗
PubMed1994

Sympathetic nerve activity during prolonged rhythmic forearm exercise.

Exercise is a potent stimulus to activate the sympathetic nervous system. Previous work suggests that metabolite-sensitive muscle afferents are activated near the point of fatigue, and, when activated, they determine the muscle sympathetic nerve activity (MSNA) response to isometric forearm exercise. Yet, studies using a more prolonged rhythmic exercise paradigm suggest that the sympathetic nervous system can be activated in a more graded fashion. The purpose of this study was to determine whether metaboreceptor stimulation would also be responsible for MSNA responses to prolonged rhythmic isotonic forearm exercise. Subjects (n = 16) performed rhythmic isotonic forearm exercise at 25% maximal voluntary contraction for 30 min as we measured MSNA (microneurography). We observed progressive increases in MSNA with a peak increase of 161 units from a baseline value of 180 units. We also performed posthandgrip circulatory arrest (PHG-CA) in nine of these subjects. This maneuver isolates the metaboreceptor contribution to MSNA. During PHG-CA, delta MSNA values were not different from those observed during a freely perfused recovery period (n = 7). We also compared MSNA responses during the rhythmic paradigm with those seen during a static protocol at 40% of maximal voluntary contraction in five subjects. The two types of exercise caused similar increases in MSNA, but only the static paradigm was associated with a sustained MSNA response during PHG-CA. Finally, 31P-nuclear magnetic resonance was used to evaluate muscle metabolic responses during rhythmic and static forearm exercise (n = 6). Static exercise caused muscle acidosis and an increase in H2PO4-, whereas rhythmic exercise had no effect on muscle metabolism.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Sympathetic and blood pressure responses to voluntary apnea are augmented by hypoxemia.

Oscillations of arterial pressure during sleep are the hemodynamic hallmark of the sleep apnea syndrome. The mechanism of these transient pressure elevations is incompletely understood. To investigate the role of the arterial chemoreflex in the neurocirculatory responses to apnea, we measured mean arterial pressure (MAP; Finapres) and muscle sympathetic nerve activity (MSNA; peroneal microneurography) during voluntary end-expiratory apnea during exposure to room air, 10.5% O2 in N2 (hypoxemia), and 100% O2 (hyperoxia) in 11 healthy men. While the men breathed spontaneously, MSNA (in bursts/min) rose during hypoxemia and decreased during hyperoxia and MAP remained unchanged. During room air exposure, apnea led to a rise of 94 +/- 54% in MSNA total amplitude and a rise of 6.5 +/- 2.1 mmHg in MAP. MSNA and MAP increased by 616 +/- 158% and 10.8 +/- 2.4 mmHg, respectively, during hypoxemic apnea of equal duration (time-matched responses) and by 98 +/- 41% and 4.9 +/- 2.0 mmHg, respectively, during hyperoxic apnea (P < 0.05 for hypoxemic vs. hyperoxic apnea for both). Thus, in awake healthy humans, activation of the arterial chemoreflex by hypoxemia appears to contribute importantly to the sympathetic and blood pressure responses to apnea.

Administration, Inhalation↗
PubMed1994

Forearm compression during exercise increases sympathetic nerve traffic.

Previously, we showed that forearm venous congestion augmented muscle sympathetic nerve activity (MSNA) during static exercise. We postulated that venous congestion increased interstitial pressure, sensitizing mechanoreceptor afferents that led to a greater sympathoexcitation during exercise. In this study, we tested the hypothesis that forearm compression (FC) would increase interstitial pressure and selectively stimulate mechanically sensitive afferents. We measured MSNA during 2 min of ischemic static exercise (40% maximal voluntary contraction) and 2 min of posthandgrip circulatory arrest. Exercise was performed again after 5 min of FC induced by inflation of a forearm cuff to 90 mmHg (n = 6) and 110 mmHg (n = 7). FC without exercise had no effect on any of the hemodynamic variables. MSNA and mean arterial blood pressure responses were not augmented when exercise was performed with FC at 90 mmHg. However, static exercise coupled with FC at 110 mmHg did augment the reflex responses to static exercise (changes in MSNA before and after FC were 277 +/- 58 and 503 +/- 82 arbitrary units, respectively, P < 0.02; changes in mean arterial pressure before and after FC were 35 +/- 4 and 41 +/- 5 mmHg, respectively, P < 0.003). These responses were probably not due to greater metaboreceptor stimulation, since posthandgrip circulatory arrest responses were unaffected by FC. We postulate that FC sensitizes mechanoreceptors, leading to greater sympathoexcitation during exercise.

Adult↗
PubMed1991

Predicting poor-communication status in preschool children using risk factors present at birth.

The speech and language status of 662 children between the ages of 30 months and 5 years was determined through the use of parent report information. Twelve of these children were reported by their parents to have been diagnosed as having a speech-language disorder, and 50 of these children were found to be at or below the 10th percentile in language development for children of their age. Information about family background and birth history obtained when these children were born was evaluated with respect to its power to predict speech-language status in these preschool children. A set of risk criteria was found to accurately predict 55% of those children with poor communication skills and 76% of those with normal communication development. This prediction was improved by the addition of data about the child's birth order. These results suggest that programs of preschool identification should consider the inclusion of a registry of children who are at risk for a communication disorder.

Birth Order↗
PubMed1990

A child with signs of developmental apraxia of speech with whom a palatal lift prosthesis was used to manage palatal dysfunction.

A client is described who exhibited a large number of characteristics consistent with developmental apraxia of speech (DAS). The exhibited symptoms included excessive nasal resonance and nasal emission of air due to velopharyngeal port dysfunction, for which successful management was achieved by use of a palatal lift prosthesis. The results of the client's use of the lift, in conjunction with her speech and language remedial programming, is presented.

Apraxias↗
PubMed1990

Retroperitoneal fibrosis in two patients with Parkinson's disease treated with bromocriptine.

Retroperitoneal fibrosis has been observed in two patients with Parkinson's disease treated with bromocriptine. The patients complained of abdominal or lower back pain and presented with various degrees of renal insufficiency, with anuria in one. Laboratory evaluation furthermore showed an increased sedimentation rate and inflammatory anemia. Computerized tomography disclosed marked retroperitoneal thickening, and biopsy was performed in one patient. The symptoms appeared eighteen months and five years after treatment was started, at doses of 20 and 22.5 mg of bromocriptine daily. The medication was discontinued in both patients and steroid therapy was initiated, with resolution of all clinical, biological and radiological evidence of disease. This potential but rare complication of a widely prescribed drug warrants monitoring of renal function and sedimentation rate in patients undergoing bromocriptine treatment.

Aged↗
PubMed1990

[Leiomyosarcoma of the scrotum].

Scrotal leiomyosarcoma is a rare tumor which may occur from each muscular structure of the scrotum. A brief review of the literature and the therapeutic possibilities are presented.

Aged↗