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Biomedical subjects

S M Ryan

Publications and source records attributed to S M Ryan.

At least 19 recordsLinked to original sources
PubMed1992

Spectral analysis of heart rate dynamics in elderly persons with postprandial hypotension.

Prior studies suggest that postprandial hypotension in elderly persons may be due to defective sympathetic nervous system activation. We examined autonomic control of heart rate (HR) after a meal using spectral analysis of HR data in 13 old (89 +/- 6 years) and 7 young (24 +/- 4 years) subjects. Total spectral power, an index of overall HR variability, was calculated for the frequency band between 0.01 and 0.40 Hz. Relatively low-frequency power, associated with sympathetic nervous system and baroreflex activation, was calculated for the 0.01 to 0.15 Hz band. High-frequency power, representing parasympathetic influences on HR, was calculated for the 0.15 to 0.40 Hz band. Mean arterial blood pressure declined 27 +/- 8 mm Hg by 60 minutes after the meal in elderly subjects, compared with 9 +/- 8 mm Hg in young subjects (p less than or equal to 0.0001, young vs old). The mean change in low-frequency HR power from 30 to 50 minutes after the meal was +19.4 +/- 25.3 U in young subjects versus -0.1 +/- 1.5 U in old subjects (p less than or equal to 0.02). Mean change in total power was also greater in young (19.0 +/- 26.6 U) subjects compared with old subjects (0.0 +/- 1.6 U, p greater than or equal to 0.02). Mean ratio of low:high-frequency power increased 3.1 +/- 3.3 U in young subjects vs 0.5 +/- 2.7 U in old subjects (p less than or equal to 0.01). The increase in low-frequency HR power and in the low:high frequency band ratio in young subjects is consistent with sympathetic activation in the postprandial period.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

A reading-level design study of phonological skills underlying fourth-grade children's word reading difficulties.

A 3-group reading-level design was used to investigate phonological analysis, verbal working memory, and pseudoword reading performance in less skilled fourth-grade readers. Children were given phonological oddity tasks assessing their sensitivity to subsyllabic and phonemic units, together with standardized tests of verbal working memory and pseudoword reading. Less skilled fourth-grade readers performed lower than both chronological age and reading-level controls on the phonological oddity and pseudoword reading tests. Less skilled fourth-grade readers performed at the same level as skilled second-grade readers on a test of verbal working memory. Skilled fourth-grade readers scored higher than both other groups on this test. Correlational analyses were consistent with the view that phonological analysis skills contribute more strongly than verbal working memory skills to children's decoding abilities.

Child↗
PubMed1991

Aging and the complexity of cardiovascular dynamics.

Biomedical signals often vary in a complex and irregular manner. Analysis of variability in such signals generally does not address directly their complexity, and so may miss potentially useful information. We analyze the complexity of heart rate and beat-to-beat blood pressure using two methods motivated by nonlinear dynamics (chaos theory). A comparison of a group of healthy elderly subjects with healthy young adults indicates that the complexity of cardiovascular dynamics is reduced with aging. This suggests that complexity of variability may be a useful physiological marker.

Adult↗
PubMed1991

Nocturnal positive-pressure ventilation via nasal mask in patients with severe chronic obstructive pulmonary disease.

Intermittent positive pressure ventilation administered nocturnally via a nasal mask has been associated with improvements in pulmonary function and symptoms in patients with restrictive ventilatory disorders. We hypothesized that nocturnal nasal ventilation (NNV) would bring about similar improvements in patients with severe chronic obstructive pulmonary disease (COPD). The study used a randomized, crossover design, with subjects undergoing NNV or "standard care" for sequential 3-month periods. Of 23 patients with obstructive lung disease and a FEV1 less than 1 L who were initially enrolled, 4 were excluded because of obstructive sleep apnea prior to randomization. Among the remaining 19 patients, 7 withdrew because of intolerance of the nose mask, 5 were withdrawn because of intercurrent illnesses, and 7 completed both arms of the protocol. These latter 7 patients used the ventilator for an average of 6.7 h/night, and 3 of the 7 had partial relief of dyspnea during ventilator use. However, in comparison with studies performed upon initiation or after the standard care arm of the study, studies performed after 3 months of NNV revealed no improvements in pulmonary function, respiratory muscle strength, gas exchange, exercise endurance, sleep efficiency, quality or oxygenation, or dyspnea ratings. The only improvements observed were in neuropsychological function, possibly related to a placebo effect or another unknown mechanism. Despite the small sample size, our study indicates that NNV is not well tolerated by and brings about minimal improvements in stable outpatients with severe COPD.

Aged↗
PubMed1988

Monoamine neurotransmitters and metabolites during the estrous cycle, pregnancy, and the postpartum period.

A wide variety of behavioral changes in the female rat have been associated with the estrous cycle, pregnancy, and the postpartum period and their accompanying hormonal fluctuations. Since monoamine systems have been implicated in the control of these behaviors, the present study examined the tissue concentrations of norepinephrine (NE), dopamine (DA), and serotonin (5HT) and their primary metabolites dihydroxyphenylglycol (DHPG), 3-methoxy-4-hydroxyphenylglycol (MHPG), 3,4-dihydroxyphenylacetic acid (DOPAC), and 5-hydroxyindoleacetic acid (5HIAA) in the anterior cerebral cortex, hippocampus, and cerebellum during the estrous cycle, late pregnancy, and the early postpartum period. Results show no significant differences in neurotransmitter or metabolite levels during the estrous cycle in any of the three brain regions examined. However, profound differences were observed between samples from late pregnancy, early postpartum, and the estrous cycle. In general, NE and 5HT levels in all three brain regions fell from normal values during late pregnancy and rose in the early postpartum period; levels of their metabolites rose in postpartum samples. Conversely, DA levels were elevated in late pregnancy and depressed in the early postpartum period in anterior cortex, while DOPAC levels were depressed in both late pregnancy and the early postpartum period. The finding of changes in monoamine metabolism associated with pregnancy and its termination could be important in understanding the increased susceptibility to affective illness in women during the postpartum period.

Animals↗
PubMed1988

The estrous cycle and estrogen modulate stress-induced analgesia.

In this article we investigate the impact of estrous cycle, ovariectomy, and estrogen replacement on both opioid and nonopioid stress-induced analgesia. Stage of estrous strongly influenced analgesia. Diestrus females exhibited the typical male pattern produced by the analgesia inducing procedures used--strong nonopioid analgesia following 10-20 tailshocks, and strong opioid analgesia following 80-100 tailshocks. In these experiments the nonopioid analgesia was slightly attenuated during estrus, but the opioid analgesia was markedly reduced. The role of estrogen in producing these changes was studied with estrogen replacement in ovariectomized subjects. Ovariectomy only slightly altered nonopioid analgesia but eliminated opioid analgesia, which suggests that some estrogen might be necessary to maintain the integrity of the system(s) underlying opioid analgesia. Estrogen administration restored opioid analgesia, but further estrogen suppressed opioid analgesia, duplicating the estrus pattern. It did not suppress nonopioid analgesia. Opioid analgesia was enhanced 102 hr after estrogen replacement, thus duplicating the diestrus pattern. Estrogen thus appears to be responsible for the impact of estrous cycle on opioid but not on nonopioid analgesia. These results suggest that ovarian hormones may modulate the impact of stressors on endogenous pain inhibition and other stress-responsive systems.

Animals↗
PubMed1986

Stressor controllability and the pituitary-adrenal system.

Stressor controllability can alter both behavior and pituitary-adrenal activity. Potential mediation of these behavioral effects by differential pituitary-adrenal output requires that the precise conditions that lead to differential behavioral consequences also produce differential pituitary-adrenal activity. Both plasma ACTH and corticosterone levels were measured at various times following escapable and yoked inescapable electric shock conditions known to produce differential behavioral outcomes. The escapable and inescapable shock procedures did not produce a detectable differential effect. Both shock conditions produced equivalent elevation of ACTH and corticosterone. Neither decay rates nor the ACTH and corticosterone response to shock reexposure differed among shocked groups.

Adrenocorticotropic Hormone↗
PubMed1985

Spinal pain suppression mechanisms may differ for phasic and tonic pain.

The dorsolateral funiculus (DLF) spinal pathway has previously been identified as a major pathway involved in descending modulation of pain. While bilateral lesions of the DLF attenuated systemic morphine analgesia as measured by the tail-flick test, they failed to attenuate analgesia as measured by the formalin test. These results suggest that phasic and tonic pain, modeled by the tail-flick and formalin tests, respectively, may utilize different pain suppression mechanisms.

Animals↗
PubMed1984

Librium prevents the analgesia and shuttlebox escape deficit typically observed following inescapable shock.

Administration of a benzodiazepine, chlordiazepoxide (CDP), prior to exposure to inescapable shock prevented both the long-term analgesia and the shuttle-escape deficit typically observed following inescapable shock. If given only prior to testing, CDP had little effect. The protective effects of CDP were determined not to be a result of state dependency or a general facilitatory effect of the drug on escape performance. It is suggested that the induction of anxiety or fear by inescapable shock is critical in mobilizing endogenous changes such as transmitter depletion which are thought to be responsible for the deficits observed.

Analgesia↗
PubMed1984

The formalin test and the opioid nature of stress-induced analgesia.

Exposure to electric shock produces an analgesic reaction (SIA) that is reversed by opiate antagonists ("opioid" SIA) under some conditions but not under other conditions ("nonopioid" SIA). A number of studies using tail-flick to radiant heat as the measure of pain sensitivity have found that a small number of shocks lead to nonopioid SIA, while a large number of shocks produce opioid SIA. In contrast, a small number of shocks have been reported to produce opioid SIA when the Formalin test was used to measure pain reactivity. However, the Formalin test involves administering a chronic pain stimulus (injection of Formalin into the paw) for an extended period before the shocks. Here it is reported that this "preexperimental" stress is sufficient to convert the SIA after a small number of shocks measured by tail-flick to the opioid form.

Afferent Pathways↗
PubMed1983

Coping and immunosuppression: inescapable but not escapable shock suppresses lymphocyte proliferation.

Rats were given series of escapable shocks, identical inescapable shocks, or no shock. The subjects were reexposed to a small amount of shock 24 hours later, after which an in vitro measure of the cellular immune response was examined. Lymphocyte proliferation in response to the mitogens phytohemagglutinin and concanavalin A was suppressed in the inescapable shock group but not in the escapable shock group. This suggests that the controllability of stressors is critical in modulating immune functioning.

Animals↗
PubMed1978

Effect of the dopamine agonist, lergotrile mesylate, on circulating anterior pituitary hormones in man.

The effects of the ergoline derivative, lergotrile mesylate, on the serum levels of PRL, GH, TSH, LH, FSH, cortisol, and blood sugar were studied in six normal males. The effects of lergotrile mesylate on the serum levels of GH and PRL were also studied in eight patients with acromegaly and in two with idiopathic hyperprolactinemia. In the normal subjects, 2 mg oral lergotrile lowered basal PRL levels after 90 min and markedly impaired the PRL response to TRH (200 micrograms iv); the mean peak value +/- SE was 8.3 +/- 1.1 micrograms/liter, compared to the control value of 66.6 /+- 11.3 micrograms/liter. Lergotrile raised serum GH levels in five of the six subjects to peaks of 8-49 micrograms/liter, compared to 2-8 micrograms/liter after placebo. In three subjects, the GH response to lergotrile was attenuated by the prior administration of the dopamine antagonist, metoclopramide (10 mg orally). Lergotrile had no effect on FSH and LH levels under basal conditions or after the gonadotrophin-releasing hormone (GnRH; 100 micrograms iv). Circulating TSH levels were unaltered basally but impaired after TRH. Blood sugar levels were unaltered; serum cortisol was elevated in five of six subjects; there was a brief depression of diastolic blood pressure, but no change in pulse rate. The side effects after lergotrile were variable, with drowsiness as a consistent feature. These actions are similar to those of bromocriptine (an ergot derivative treatment of hyperprolactinemia and acromegaly, to suppress PRL and GH secretion, and in parkinsonism. Therefore, it may be expected that lergotrile could fulfill these clinical uses; however, in the studies comparing the effects of single oral doses of lergotrile (2 mg) and bromocriptine (2.5 mg) on GH and PRL secretion in patients with acromegaly and hyperprolactinemia, lergotrile in the dose used has been found to have an earlier onset and shorter duration of action.

Acromegaly↗
PubMed1975

RNA-dependent DNA-polymerase activity in human milk.

A simple method is described for testing milk specimens from nursing mothers for the presence of RNA-dependent DNA-polymerase activity. Positive results were obtained in five of 137 women (3.6%) without a family history of breast cancer, and in six of 31 women (19.3%) with a family history of breast cancer.

Breast Feeding↗
PubMed1971

Perception.

Explore the source record for details and available documents.

Afterimage↗
PubMed1969

Graduate program in biomedical communication.

The need for harnessing the achievements of communication technology to the burgeoning mass of biomedical information is critical. Recognizing this problem and aware of the short supply of professionals with the skills necessary for the job, a group of leaders from the fields of medicine and communications formed a consortium in 1967 and have developed a twelve month graduate program in biomedical communication. Designed to ground the advanced student in the development and administration of biomedical communication programs, the curriculum focuses on the principles and practice of communication and the development of communications media. Courses are given in the control and communication of information; the printed and spoken word; visual media of photographic arts, television, and motion pictures; computer science; and administration and systems analysis.

Communication↗