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Biomedical subjects

C W Sargent

Publications and source records attributed to C W Sargent.

15 recordsLinked to original sources
PubMed1993

Ventilatory response to exercise in children with congenital central hypoventilation syndrome.

The role of the central and peripheral chemoreceptors in the hyperpnea of exercise has been controversial. We studied five children, age 6 to 11 yr, with absent hypercapneic and hypoxic ventilatory responses during wakefulness (congenital central hypoventilation syndrome, CCHS). Each child performed an incremental treadmill exercise test. Maximal oxygen consumption (VO2) and minute ventilation (VE) at maximal exercise were lower than but not significantly different from these values in a group of nine normal control children of similar age, height, and weight (VO2/kg, 33.7 +/- 5.0 versus 45.4 +/- 2.9 ml/kg/min, mean +/- SEM, NS; VE 28.3 +/- 7.3 versus 43.8 +/- 3.9 L/min, NS). Oxygen tension and saturation fell and CO2 tension rose significantly at maximal exercise in CCHS but not in control subjects. In contrast to control subjects, CCHS subjects increased VE largely by increasing respiratory frequency (f) rather than tidal volume (VT). In the oldest child, submaximal exercise tests at 50% VO2, with varying pacing rate, showed a significant positive relation between pacing rate and f, but not VT. Thus, VE was higher at the faster pacing rate. Further incremental testing in the two oldest subjects with recording of the pacing rate showed positive linear relations between pacing frequency and breathing frequency and between pacing frequency and VE up to a maximum pacing rate of 48 to 50 paces per 15 s. VE beyond this level varied randomly around the maximum level. We conclude that exercise-induced hyperpnea can occur in the absence of chemoreceptor function. In the CCHS children, limb movement is an important determinant of the ventilatory response to exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

Child↗
PubMed1992

Theophylline does not increase ventilatory responses to hypercapnia or hypoxia.

Theophylline is commonly believed to stimulate central respiratory centers. We studied the effect of oral theophylline therapy on ventilatory responses to hypercapnia and hypoxia during a double-blind placebo-controlled trial with a slow release oral theophylline preparation. We measured hypercapnic and hypoxic ventilatory responses using rebreathing techniques in 15 subjects (21 to 41 yr of age, with normal lung function) on three occasions: baseline, after 4 days of Drug 1, and after 4 days of Drug 2. For subjects receiving theophylline, the mean serum theophylline level was 11.3 + 1.3 (SE) micrograms/ml (range, 5.3 to 22.1). Unpleasant side effects were reported by 11 of the 15 subjects (nausea, jitteriness, and agitation) while receiving theophylline but not while receiving placebo. The mean hypercapnic ventilatory response with placebo was 4.3 +/- 0.9 L/min/mm Hg PACO2 and with theophylline it was 4.5 +/- 0.7 L/min/%SaO2 and with theophylline it was -2.7 +/- 0.4 L/min/%SaO2. Hypoxic responses for each subject were measured at similar PvCO2. There were no significant changes in ventilatory responses with theophylline. We conclude that theophylline use, at a dose sufficient to cause side effects, does not affect chemoreceptor responsiveness.

Adult↗
PubMed1989

Abnormal control of ventilation in adolescents with myelodysplasia.

Infants with myelomeningocele have abnormalities in ventilatory control. To determine whether these persist into later life, we studied 14 patients with myelomeningocele and Arnold-Chiari malformation (age 18.0 +/- 0.8 (SE) years), and compared them with 14 control subjects (age 24.0 +/- 0.9 years). Pulmonary function and ventilatory muscle strength did not differ between patients with myelomeningocele and control subjects. Hypercapnic ventilatory responses were significantly lower in the group with myelomeningocele (1.98 L/min/mm Hg) compared with control values (3.33 L/min/mm Hg; p less than 0.01). Hypoxic ventilatory responses (-1.4 L/min/%oxygen saturation of hemoglobin in arterial blood) were not significantly different from control values (-2.14 L/min/%oxygen saturation). In control subjects the hypercapnic and hypoxic ventilatory responses were highly correlated with each other within subjects (r = 0.84; p less than 0.002) but not in those with myelomeningocele (r = 0.34; not significant). We concluded that adolescents and young adults with myelomeningocele have abnormalities in control of ventilation during sleep and wakefulness. We speculate that the Arnold-Chiari malformation interferes with central chemosensitivity (hypercapnic ventilatory response) and central integration of chemoreceptor output.

Adolescent↗
PubMed1989

Hypoxic and hypercapnic ventilatory responses in awake children with congenital central hypoventilation syndrome.

Congenital central hypoventilation syndrome (CCHS) has been thought to be a disorder of central chemoreceptor responsiveness. Previous studies in CCHS have shown decreased or absent ventilatory responsiveness to both hypercarbia and hypoxia. However, hypoxic responsiveness during wakefulness has not been systematically studied. We studied hypoxic and hypercapnic ventilatory responses during wakefulness in five children with CCHS (6 to 11 yr of age). To measure the hypercapnic response, the children rebreathed a hyperoxic hypercapnic mixture until PaCO2 reached 56 to 69 mm Hg. For the hypoxic response, the children rebreathed a hypoxic gas mixture, at mixed venous PCO2, until SaO2 had fallen to less than 78%. We found that the ventilatory responses to hypercapnia and hypoxia were very variable (linear correlation coefficients ranging from -0.44 to +0.63 for hypercapnic responses and from -0.15 to +0.77 for hypoxic responses), with no significant change from baseline in response to either stimulus. There was no evidence of progressive ventilatory stimulation despite increasing stimulus. Additionally, these children had no subjective sensation of dyspnea or discomfort. This establishes that hypoxic and hypercapnic ventilatory control is absent during wakefulness. Chemoreceptor control (peripheral and central) is, therefore, defective in all states in children with CCHS. We speculate that the defect in CCHS lies in central integration of the central and peripheral chemoreceptor signals.

Child↗
PubMed1988

Growth failure in bronchopulmonary dysplasia: elevated metabolic rates and pulmonary mechanics.

Growth failure is a major problem in infants with bronchopulmonary dysplasia (BPD), but the cause is unknown. We studied 13 infants with BPD but without other medical problems that could contribute to growth failure at 6 months' corrected age. We measured resting oxygen consumption (Vo2), Pao2, airway resistance, specific airway conductance, and dynamic pulmonary compliance (Cdyn) by body plethysmography and growth. Growth failure was defined as height and weight less than the tenth percentile of the Babson growth curves. Vo2 in infants with growth failure and BPD was markedly elevated compared with that in control infants and infants with BPD and normal growth. Vo2 showed an inverse correlation with body weight in infants with BPD but not in control infants. Although Vo2 was inversely related to Cdyn, the total work of breathing only partially explained the increased metabolic demands of the growth failure group. We speculate that growth failure in infants with BPD is partially the result of increased metabolic demands from increased work of breathing but that other mechanisms may act to elevate the metabolic expenditure of these infants.

Airway Resistance↗
PubMed1985

Hypoxic and hypercapneic arousal responses and prediction of subsequent apnea in apnea of infancy.

Hypoxic and hypercapneic arousal responses from quiet sleep were tested in 56 infants with apnea of infancy (one or more episodes of cyanosis, limpness, and apnea requiring vigorous stimulation or resuscitation with no treatable cause; age 6.8 +/- 1.1 [SEM] months). Responses were compared with those of nine control infants ranging from 1 to 25 months of age. To assess hypercapneic arousal, the inspired PCO2 was rapidly increased during quiet sleep to 60 mm Hg or until arousal (restlessness, agitation, eye opening) occurred. All control infants and those with apnea of infancy aroused to hypercapnea, but control infants aroused at a lower inspired PCO2 (inspired PCO2 40.1 +/- 2.6 mm Hg) than those with apnea of infancy (inspired PCO2 46.9 +/- 1.5 mm Hg, P less than .05). To assess hypoxic arousal, the inspired PO2 was rapidly decreased during quiet sleep to 80 mm Hg or until arousal occurred. All control infants aroused to hypoxia (inspired PO2 78.3 +/- 2.1 mm Hg). However, only 38% of those with apnea of infancy aroused (inspired PO2 78.1 +/- 0.8 mm Hg), indicating an abnormality in recognition of hypoxia, or central brainstem response to hypoxia. During the 10.4 +/- 1.2 months of follow-up, there was a high incidence of subsequent apneas (greater than 20 seconds) during sleep at home in 50 apneic infants. Infants with abnormal hypoxic arousal responses had more severe subsequent apneas than those with normal hypoxic arousal responses (P less than .05).

Arousal↗
PubMed1983

Furosemide acutely decreases airways resistance in chronic bronchopulmonary dysplasia.

We studied the effects of furosemide on pulmonary mechanics in 10 infants with bronchopulmonary dysplasia aged 41 +/- 1 (SE) weeks post-conception, gestational age at birth 30 +/- 1 wk, birth weight 1370 +/- 200 gm. Thoracic gas volume, airways resistance, and specific airway conductance were measured in an infant body pressure plethysmograph during quiet breathing. Dynamic pulmonary compliance was measured using an esophageal balloon. Infants with BPD had greater Raw, lower SGaw, and lower Cdyn than did 16 normal control infants. Within one hour after administration of furosemide 1 mg/kg IV to infants with BPD, Raw fell 36 +/- 13%, SGaw increased 84 +/- 22%, and Cdyn increased 54 +/- 13%; TGV did not change. Diuretic treatment of BPD in infants is associated with rapid, short-term improvement in Raw and Cdyn.

Airway Resistance↗
PubMed1983

Developmental pattern of maximal transdiaphragmatic pressure in infants during crying.

Diaphragm strength was measured as maximal transdiaphragmatic pressure (Pdi) during airway occlusion in 38 infants aged 11.6 +/- 0.5 (S.E.) months postconception (mpc), range 8-21 mpc. All infants were asymptomatic at the time of study and required no mechanical ventilatory assistance. Ten infants had previous surgical correction of abdominal wall defects (gastroschisis/omphalocele); 10 infants had previous surgical correction of congenital diaphragmatic hernia; and 18 infants had no thoracic or abdominal surgery. The mean maximal Pdi for all infants was 72 +/- 3 cmH2O. There were no significant differences between the three groups. All infants with a maximal Pdi of less than 60 cmH2O were aged less than 10 mpc. After 13 mpc there was no significant increase in maximal Pdi. Between the ages 8-13 mpc there was a significant positive correlation between maximal Pdi and age postconception (r = 0.87, P less than 0.0005), reflecting a developmental pattern of increasing maximal transdiaphragmatic pressure in infants during crying.

Abdominal Muscles↗
PubMed1982

Diaphragm strength in near-miss sudden infant death syndrome.

Diaphragm muscle strength was measured as maximal transdiaphragmatic pressure during airway occlusion in ten near-miss sudden infant death syndrome infants aged 4.1 +/- 0.6 (SE) months post-term, range 2 to 7 months, and ten control infants aged 4.5 +/- 0.8 months post-term, range 0.8 to 8 months. In the near-miss sudden infant death syndrome group, the mean maximal transdiaphragmatic pressure was 106 +/- 6 cm H2O, range 78 to 132 cm H2O, compared with a mean maximal transdiaphragmatic pressure 86 +/- 4 cm H2O, range 69 to 106 cm H2O, in the control group. Diaphragm strength is normal or increased in near-miss sudden infant death syndrome infants.

Crying↗
PubMed1980

Transcutaneous oxygen monitoring during exercise stress testing.

Transcutaneous oxygen tension (tcPO2) was compared with simultaneous arterial oxygen tension (PaO2) in 3 normal young adults and 4 pediatric lung disease patients at rest and during exercise to assess the usefulness of tcPO2 monitoring during exercise stress testing. At rest, the regression coefficient of tcPO2 on PaO2 was 0.78 +/- 0.03 (SEM) (r = 0.924; P < 0.0005). During exercise, the regression coefficient of tcPO2 on PaO2 was 0.88 +/- 0.02 (r = 0.958; P < 0.0005), indicating that tcPO2 approximates PaO2 equally well at rest and during exercise. After a step change in inspired oxygen concentration (FIO2) from 0.21 to 0.17, there was no significant difference in the tcPO2 time constant at rest (66.2 +/- 8.5 s) and during exercise (73.0 +/- 3.1 s). Neither PaO2 nor tcPO2 fell in normal subjects during graded exercise stress testing. However, in 3 of 4 pediatric lung disease patients, there were decreases in both PaO2 (40.7 +/- 11.6 Hg) and tcPO2 (28.7 +/- 10.0 mm Hg) during 7 exercise stress tests. These results indicate that tcPO2 approximates PaO2 equally well at rest and during exercise.

Adolescent↗
PubMed1978

Zero-base budgeting and the library.

This paper describes the application of zero-base budgeting to libraries and the procedures involved in setting up this type of budget. It describes the "decision packages" necessary when this systmem is employed, as well as how to rank the packages and the problems which are related to the process. Zero-base budgeting involves the entire staff of a library, and the incentive engendered makes for a better and more realistic budget. The paper concludes with the problems which one might encounter in zero-base budgeting and the major benefits of the system.

Budgets↗
PubMed1976

Bounty hunting.

Explore the source record for details and available documents.

Audiovisual Aids↗
PubMed1969

Handling technical reports in the medical library.

One of the most widely neglected sources of information in the medical library is the technical report. Often this bibliographic form is ignored because there is a general lack of information on the part of the librarian concerning its mysteries. In many cases the technical report provides the most recent and current information on a given subject, and to ignore it or wait for its appearance in the published literature could prove costly to a research project. Technical reports have reached flood proportions since World War II, and are issued from many diverse sources. Means of acquiring, processing, and using the tools which abstract and index this literature are discussed.

Cataloging↗
PubMed1968

The current catalog--how current?

NLM's Current Catalog has recently come in for some criticism. To be useful as a tool in acquisition and cataloging, currency in receipt of the Current Catalog is necessary. A survey of 263 titles with 1967 imprints, which were received by the Library of the Medical Sciences, University of New Mexico School of Medicine, was made to determine the correlation between the receipt of these books in the library and their appearance in the Current Catalog.

Catalogs, Library↗