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Biomedical subjects

K A Waters

Publications and source records attributed to K A Waters.

31 records · Page 2Linked to original sources
PubMed1996

Overnight growth hormone secretion in achondroplasia: deconvolution analysis, correlation with sleep state, and changes after treatment of obstructive sleep apnea.

The normal profile for overnight GH secretion in achondroplasia has not been previously studied. Factors that have been shown to influence GH secretion include age, obesity, sleep state, and the presence of obstructive sleep apnea (OSA). We assessed GH levels in a group of subjects with achondroplasia, during overnight polysomnography. Nineteen subjects with achondroplasia were studied at 11.3 y of age (median 6.7, range 1.8-30.9). Levels of GH were measured using time-resolved immunofluorometric assay (DELFIA, Pharmacia Biotech Inc.) and analyzed by a deconvolution method. Five subjects were restudied after treatment for OSA. Secretion rates of GH were greater in slow wave (SWS) and rapid eye movement (REM) sleep than in stage one and two (SI-II = light non-REM) sleep (p < 0.01). Total overnight GH secretion decreased with increasing age (r2 = 0.22 p < 0.04). Neither the frequency of arousals, frequency of sleep state transitions nor the severity of OSA correlated with measures of GH secretion. Levels of IGF-I correlated independently with age, body weight (percent ideal), and GH secretion rate (r2 = 0.76, p < 0.001). In a group of five subjects treated for OSA, improved respiratory distress index and reduced sleep state transitions were not associated with significant changes in GH secretion rate by sleep stage; SWS [from 0.62 +/- 0.28 mIU/L/min to 1.02 +/- 0.25 mIU/L/min (NS)] and SI-II sleep [from 0.26 +/- 0.07 mIU/L/min to 0.60 +/- 0.16 mIU/L/min (NS)]. However, in those five subjects, a GH secretion peak during the first 2 h of SWS was initially absent, appearing only after treatment of OSA (1.09 +/- 0.38 mIU/L/min) compared with (2.40 +/- 0.59 mIU/L/min (p = 0.01). A profile of overnight GH secretion is presented for subjects with achondroplasia.

Achondroplasia↗
PubMed1996

Electrocorticographic activity during repeated vs continuous hypoxia in piglets.

To assess the effects on brain activity of repeated vs continuous hypoxia, 16, 10- to 22-day-old piglets were instrumented chronically for electrocortical and arterial pH and gas tension measurements. They inhaled 10% or 6% O2 in N2 for 21 min, either continuously, or during seven, 3 min exposures interrupted by 3 min recovery periods in air, all while behaving naturally within a sealed, temperature controlled, plexiglass box. An isoelectric electrocorticogram (ECoG) and/or seizures, related to the onset of hypoxia, occurred repeatedly in 6 of the 10 exposures to 6% repetitive hypoxia, only twice in 8 exposures to 6% continuous hypoxia, and never in 10% hypoxia. A frequency analysis of the ECoG, excluding all sections exhibiting isoelectric and seizure activity, revealed no changes with 10% hypoxia, but a shift towards the lower bands during both repetitive and continuous 6% hypoxia. The extent of these shifts was greater in records that also displayed isoelectric ECoG and/or seizures. The ECoG spectrum recovered at the end of the hypoxic exposure, but not when isoelectric ECoG and/or seizures coexisted. We conclude that repeated, frequent episodes of hypoxia are more detrimental than a prolonged single event, and may contribute to the occurrence of Sudden Infant Death.

Animals↗
PubMed1996

Cardiorespiratory sleep studies for children can often be performed in the home.

We developed a portable recording system, suitable for unattended use in a patient's home, that quantitates the essential diagnostic elements of pediatric obstructive sleep apnea syndrome (OSAS): obstructive, mixed and central apneas and hyponeas; hemoglobin saturation, sleep vs. wakefulness; body and head positions; snoring: and sleep disturbance. The present paper reviews validation studies and summarizes two recent studies that demonstrate the unique advantages of performing clinical and research cardiorespiratory sleep studies in the child's home. Development of inexpensive, portable records that integrate audiovisual and physiologic information will make such home recordings more widely available.

Humans↗
PubMed1995

Treatment of obstructive sleep apnea in achondroplasia: evaluation of sleep, breathing, and somatosensory-evoked potentials.

The occurrence of obstructive sleep apnea (OSA) is achondroplasia has been linked to brain stem compression. Overnight sleep studies (11 subjects) and somatosensory-evoked potentials (SEP's, 10 subjects) were recorded before and after conventional treatment of OSA in achondroplasia. The two groups were derived from 30 subjects who underwent diagnostic sleep studies and SEPs, including 15 females and 15 males with a median age 6.6 years (range 1.0-47.6) at the time of the first study. In 30 initial studies there was no correlation between severity of OSA and abnormalities on SEP evaluation. Treatment of 17 subjects included adenotonsillectomy (n = 3), weight loss (n = 1), and nasal-mask continuous positive airway pressure (CPAP) (n = 13). Sleep studies in 11 subjects after a delay of 8.8 +/- 2.8 months showed a reduction in respiratory disturbance index (RDI) from 38.4 +/- 6.9 to 6.5 +/- 1.8 events hr(-1) (p < 0.001) and movements/arousals fell from 10.4 +/- 2.2 to 4.8 +/- 0.2 hr(-1) (p < 0.04). Obstructive events were reduced from 33.7 +/- 6.9 to 2.4 +/- 1.0 hr(-1) (p < 0.001). Improvement of respiratory indices was associated with an increased proportion of slow-wave sleep from 25.2 +/- 4.0% to 32.3 +/- 2.4% (p = 0.01), and decrease in stage 1-2 sleep from 59.3 +/- 5.8% to 46.6 +/- 1.9% (p = 0.03). There was no increase in the percentage of REM sleep (15.2 to 21.2%). Repeat SEP studies in 10 subjects, after clinically effective treatment of OSA, showed improvement of SEP score of at least 1 grade, in 5 of 7 (71%) with initially abnormal values. We conclude that treatment of relieve upper airway obstruction improves OSA in achondroplasia, accompanied by changes in sleep structure and, in some cases, improved studies of neurological function.

Achondroplasia↗
PubMed1995

Obstructive sleep apnea: the use of nasal CPAP in 80 children.

This is a retrospective review of children 15 years of age or younger, who underwent overnight sleep studies between 1980 and 1993. All were diagnosed and treated for obstructive sleep apnea (OSA). Overnight studies were performed for OSA in 413 children. One hundred seventy-five (42.4%) children were treated with adenotonsillectomy and 80 (19.4%) with nasal mask continuous positive airway pressure (nCPAP). The proportion of male children was greater than expected in both the entire study group (69%, p < 0.001) and in those treated with nCPAP for OSA (71% p < 0.001). There was no significant difference between the mean age of the children treated with nCPAP (5.7 +/- 0.5 yr) and the entire group studied (5.04 +/- 0.21 yr). A greater proportion of the children who received nCPAP therapy had a congenital syndrome or malformation than in the group with OSA as a whole; 27.7% of children assessed for OSA were affected, and 53% of those children with OSA who received treatment with nCPAP (p < 0.001). Therapy with nCPAP (mean duration 15 +/- 3 mo, mean pressure 7.9 cm H2O) eliminated the signs of OSA in 72 children (90%). Respiratory disturbance index fell from a mean of 27.3 +/- 20.2 to 2.55 +/- 2.74 (p < 0.001). Eight of 32 children who underwent pressure determination studies could not tolerate nCPAP above an upper limit because of hypoventilation or frequent central apneas. Nevertheless, we conclude that nCPAP is an effective and generally well-tolerated therapy for treatment of OSA in infants and children.

Adenoidectomy↗
PubMed1994

Destruction of WiDr multicellular tumor spheroids with the novel thymidylate synthase inhibitor 1843U89 at physiological thymidine concentrations.

The activity of a novel thymidylate synthase inhibitor, 1843U89, against WiDr human colon carcinoma multicellular tumor spheroids was investigated. Continuous exposure of the spheroids to 3 nM 1843U89 for 10 days resulted in spheroid disruption, whereas 100 nM methotrexate (MTX) was required for similar effects. Short-term treatment experiments demonstrated that a 3-day exposure to 100 nM 1843U89 caused spheroid disruption 9 days after drug removal. A 4-day exposure to 10 nM 1843U89 caused spheroid disruption 8 days after drug removal. In contrast, treatment with 10 or 100 nM 1843U89 for 6-48 h or treatment with 1 nM 1843U89 for up to 5 days caused only growth delay. Continuous exposure of spheroids to 30 nM 1843U89 in the presence of 0.05-0.3 microM thymidine was as effective in causing spheroid disruption as treatment in the absence of thymidine, but treatment in the presence of 0.7-3.0 microM thymidine caused partial reversal of spheroid disruption. The results of these experiments suggest that 1843U89 should have potent solid tumor activity in humans but should be less effective in mice due to differences in circulating thymidine levels (0.1 vs 1 microM, respectively).

Antineoplastic Agents↗
PubMed1993

Breathing abnormalities in sleep in achondroplasia.

Overnight sleep studies were performed in 20 subjects with achondroplasia to document further the respiratory abnormalities present in this group. Somatosensory evoked potentials (SEPs) were recorded in 19 of the subjects to screen for the presence of brainstem abnormalities, which are one of the potential aetiological mechanisms. Fifteen children aged 1 to 14 years, and five young adults, aged 20 to 31 years were included. All had upper airway obstruction and 15 (75%) had a pathological apnoea index (greater than five per hour). Other sleep associated respiratory abnormalities, including partial obstruction, central apnoea, and abnormal electromyographic activity of accessory muscles of respiration, also showed a high prevalence. SEPs were abnormal in eight (42%), but there was no correlation between abnormal SEPs and apnoea during sleep, either qualitatively or quantitatively. A high prevalence of both sleep related respiratory abnormalities and abnormal SEPs in young subjects with achondroplasia was demonstrated. However, the sleep related respiratory abnormalities do not always result in significant blood gas disturbances or correlate with abnormal SEPs in this group.

Achondroplasia↗
PubMed1992

Synthesis and biological evaluation of N alpha-(5-deaza-5,6,7,8-tetrahydropteroyl)-L-ornithine.

A novel folic acid analogue, N alpha-(5-deaza-5,6,7,8-tetrahydropteroyl)-L-ornithine, 3, was prepared via a multistep synthetic sequence. The key steps involved the conversion of 5-deazapteroic acid to its N10-formyl derivative followed by catalytic hydrogenation of the pyridine ring and subsequent heating in dilute sodium hydroxide to afford the new 5-deaza-5,6,7,8-tetrahydropteroic acid. After trifluoroacetylation, this compound was coupled to N delta-(tert-butyl-oxycarbonyl)-L-ornithine using conventional peptide bond forming conditions. Deprotection first in base and then in acid gave the title compound. Compound 3 was an effective inhibitor of hog liver folylpolyglutamate synthetase (Kis, estimated = 64 nM), and was shown to retard the formation of polyglutamates of a structurally related folic acid analogue in HCT-8 cells in vitro.

Adenocarcinoma↗
PubMed1992

In vivo antitumor activity and metabolism of a series of 5-deazaacyclotetrahydrofolate (5-DACTHF) analogues.

This study compares the antitumor activity and metabolism of the purine de novo biosynthesis inhibitor 5-deazaacyclotetrahydrofolate and a series of analogues. All compounds have similar IC50 values for inhibition of MCF-7 cell growth, activity of glycineamide ribonucleotide transformylase, and methotrexate uptake by MOLT-4 cells, the latter a measure of cellular uptake potential. Only 5-deazaacyclotetrahydrofolate and the 2'-fluoro and 3'-fluoro analogues demonstrated significant inhibition of colon 38 adenocarcinoma or HCT-116 colon carcinoma growth in vivo. This correlated with the Km of these compounds for folylpolyglutamate synthetase. 5-Deazaacyclotetrahydrofolate and 2'-fluoro-5-deazaacyclotetrahydrofolate which displayed the strongest antitumor activity were detectable in colon 38 tumor tissue 24 hr after dosing and were present nearly exclusively as the polyglutamated species. These results indicate that polyglutamation represents a critical step in the in vivo antitumor activity of these compounds.

Acyltransferases↗
PubMedDate not supplied

Psychological adaptation of nurses post-disaster.

Disasters have the potential to cause major disruptions in lifeline services and family support systems. As caregivers, nurses are required to make difficult choices during national emergencies and may be at risk for experiencing psychological distress following a disaster. This study describes the responses of a group of nurses following Hurricane Hugo, and makes recommendations to minimize the stress placed on nurses working in a time of disaster.

Adaptation, Psychological↗