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Biomedical subjects

D S Ward

Publications and source records attributed to D S Ward.

85 records · Page 5Linked to original sources
PubMed1985

Duration of muscle activity during standing in normally and slowly developing children.

Research in motor control indicates that there are fixed patterns of activity which occur in certain muscle groups involved in standing in adults. The purpose of this study was to assess patterns of duration of muscle activity during quiet standing with and without superimposed arm movement in young children with normal and delayed motor development. Thirty-three children 4, 6, 8 and 10 years of age were screened for level of motor development and classified as either normally or slowly developing. Children performed two tasks: standing and standing with a superimposed 90 degree shoulder abduction movement. Using surface electrodes, EMG activity was monitored in Gastrocnemius, Tibialis Anterior and Erector Spinae muscle groups. The percentage of time activity was present in individual muscle groups was analyzed as a function of age and developmental level. Results indicated that quiet standing in children with delayed motor development was characterized by greater duration of activity in trunk than in leg muscles while in normal children, there was a more equal distribution of muscle activity between the legs and trunk. Both groups of children accommodated superimposed arm movement by increasing the percentage of time Erector Spinae activity was present. Patterns of duration of muscle activity in the legs were, however, different for the two groups of children.

Arm↗
PubMed1984

Stimulation of hypoxic ventilatory drive by droperidol.

Carotid body chemosensitivity is modulated by the neurotransmitter dopamine. Because droperidol has potent dopamine receptor blocking capability, we studied its effects on hypoxic ventilatory response. Droperidol (2.5 mg) was administered intravenously to four volunteers and their hypoxic drive was assessed by a sudden decrease in end-tidal O2 from 106 to 53 torr. End-tidal CO2 was held constant at 41 torr throughout all experiments. Droperidol caused an increase in the slope of the hypoxia-induced ventilatory response from 0.98 +/- 0.23 to 1.87 +/- 0.31 L/min per 1% decrease in saturation (mean +/- SEM, P less than 0.05). A dopamine infusion (3 micrograms X kg-1 X min-1), which depressed hypoxic drive before the administration of droperidol, did not depress the hypoxic drive after droperidol. Droperidol potentiates the hypoxic ventilatory response, presumably by blocking the action of endogenously released dopamine.

Adult↗
PubMed1983

Effect of intravenous dopamine on hypercapnic ventilatory response in humans.

This study assessed the effect of low-dose intravenous dopamine (3 micrograms X kg-1 X min-1) on the hypercapnic ventilatory response in humans. Six normal healthy subjects were studied. By manipulating the inspired carbon dioxide concentration, the end-tidal carbon dioxide tension was raised in a stepwise fashion from 41 to 49 Torr and held at this level for 4 min. The end-tidal CO2 tension was then lowered back to 41 Torr in a stepwise fashion. The end-tidal O2 tension was held constant at 106 Torr throughout the experiment. The ventilatory response to this normoxic hypercapnic stimulus was analyzed by fitting two exponential functions, allowing the response to be separated into slow and fast chemoreflex loops. Each loop is described by a gain, time constant, and time delay. A single eupneic threshold was used for both loops. Nine control experiments and eight experiments performed during dopamine infusion were analyzed. The dopamine infusion caused the fast loop gain to be significantly (P less than 0.05) reduced from 0.64 to 0.19 l X min-1 X Torr-1, while the slow loop gain was unchanged. The fast loop contribution was reduced from 28 to 11% of the total ventilatory response. None of the other model parameters were significantly affected by the dopamine infusion. Exogenously administered dopamine substantially reduces the sensitivity of the fast chemoreflex loop to carbon dioxide.

Adult↗
PubMed1982

Reduction of hypoxic ventilatory drive by dopamine.

To define precisely the effects of dopamine on hypoxic ventilatory drive, two sets of experiments were performed in five healthy subjects. End-tidal CO2 was held constant in all experiments. First, a dopamine infusion (3 microgram/kg/min) was started in subjects already rendered hypoxic, causing an average sustained decrease in ventilation to 60% of the preinfusion ventilation. In the second group of experiments, the ventilatory response of subjects made hypoxic during a dopamine infusion was compared with the hypoxic ventilatory response without the dopamine infusion. Without dopamine, a sudden decrease in end-tidal O2 from 100 to 53 torr caused ventilation to increase from 11.9 to 20.9 L/min (p less than 0.01). During the dopamine infusion, only a statistically insignificant increase in ventilation (9.8 to 12.8 L/min) was seen with the same hypoxic stimulus. Low dose dopamine is a potent depressant of hypoxic ventilatory response.

Adolescent↗
PubMed1981

Anaesthesia for an unusual carcinoid metastasis.

The intra-operative course of a patient found to have a metastatic serotonin-secreting carcinoid tumour in the orbit is reported. No prophylactic or intra-operative therapy was necessary during the administration of enflurane anesthesia. This case demonstrates again the wide spectrum of clinical responses observed among patients with this disease.

Anesthesia, Inhalation↗
PubMed1976

Posthyperventilation isocapnic hyperpnea.

Subjects voluntarily hyperventilated for 10 breaths. A dynamic end-tidal forcing technique manipulated inspired gases to hold end-tidal CO2-O2 tensions at normal values during the voluntary ventilation period and the postvoluntary ventilation recovery period when the subjects returned to spontaneous breathing. Six of the seven subjects studied exhibited a hyperpnea during the recovery period. Although intersubject and intrasubject variations were evident, the average response for 30 experiments in the six subjects was characterized by an initial drop to 32% of the hyperventilation magnitude followed by an exponential-like decrease with a time constant of 22 s. This recovery period response is consistent with theoretical properties of neural network and physical oscillators where there is a persistence in the amplitude response after the removal of the stimulus. Thus, such oscillator properties may govern the respiratory center behavior in man. Furthermore, since isocapnic voluntary ventilation increases cardiac output, the recovery period response may be a consequence of cardiodynamic hyperpnea.

Adult↗
PubMedDate not supplied

Development of questionnaires to measure psychosocial influences on children's physical activity.

BACKGROUND: The purpose of this study was to develop and validate questionnaires used to measure psychosocial determinants of physical activity in preadolescent children. METHODS: Three theory-based questionnaires and a measure of after-school physical activity were administered to 422 fifth-grade students. A cross-validation design was employed for psychometric development of the scales, including factor analysis, reliability, and validation by correlating scale scores with intention to be physically active and after-school physical activity. RESULTS: The Social Influences scale contained a single factor. The Self-Efficacy scale contained three factors: support seeking, barriers, and positive alternatives. The Beliefs scale contained two factors: social outcomes and physical activity outcomes. Reliability coefficients ranged from about 0.50 to 0.78. Significant correlations were obtained between all six scales and intention in the development sample, and between five scales and intention in the validation sample. Significant correlations were obtained between social influence and self-efficacy barriers and physical activity in the development sample, and between social influences and physical activity in the validation sample. CONCLUSIONS: Three scales to measure psychosocial determinants of physical activity were refined for use with rural, predominantly African-American, preadolescent children, and shown to be both reliable and valid. Factor analysis resulted in interpretable subscales that may be used as variables. These preliminary results provide support for using the scales to measure influences on activity in children.

Attitude to Health↗
PubMedDate not supplied

A prospective study of the determinants of physical activity in rural fifth-grade children.

BACKGROUND: Understanding the factors that influence physical activity behavior is important in the design of intervention programs targeted at youth. METHODS: A prospective study design was used to identify the predictors of vigorous physical activity (VPA) (> or = 6 METs) and moderate and vigorous physical activity (MVPA) (> or = 3 METs) among 202 rural, predominantly African-American children. Selected social-cognitive determinants of physical activity were assessed via questionnaire in the fifth grade. Participation in VPA and MVPA was assessed via the previous day physical activity recall 1 year later in the sixth grade. RESULTS: For girls, participation in community sports, self-efficacy in overcoming barriers, enjoyment of school physical education, race (white > black), and perception of mother's activity level (active vs inactive) were significant predictors of VPA. For MVPA, participation in community sports and self-efficacy in overcoming barriers were significant predictors. For boys, self-efficacy in overcoming barriers was the only significant predictor of VPA, while beliefs regarding activity outcomes and participation in community sports were significant predictors of MVPA. CONCLUSION: Social-cognitive constructs such as physical activity self-efficacy, access to community physical activity outlets, and positive beliefs regarding physical activity outcomes are important predictors of future physical activity behavior among rural, predominantly African-American children.

Analysis of Variance↗
PubMedDate not supplied

Upper airway obstruction during midazolam/nitrous oxide sedation in children with enlarged tonsils.

PURPOSE: The purpose of this nonrandomized, case-control study was to examine the incidence and severity of upper airway obstruction (UAO) in children with enlarged tonsils during inhalation of nitrous oxide (N2O). METHODS: Following premedication with oral midazolam, 0.5 mg/kg, measurements were collected during a 3-minute control period followed by 3 minutes of breathing 50% N2O in oxygen. An unblinded anesthesiologist held a facemask over the child's mouth and nose without supporting the head or neck, or attempting to maintain airway patency. Every 20 seconds, the degree of airway obstruction was graded as none, partial, or complete. Twenty-five children presenting for tonsillectomy and 25 controls without enlarged tonsils participated. RESULTS: During 50% N2O inhalation, 14 children (56%) in the tonsillectomy group, and four children (16%) in the control group demonstrated partial UAO. One child in the tonsillectomy group with partial UAO developed hypoxemia (SpO2 72%). One child in the tonsil group developed complete UAO during inhalation of 50% N2O. CONCLUSION: Children who receive sedation with oral midazolam and 50% N2O inhalation may exhibit significant UAO, especially in the presence of enlarged tonsils. Presedation physical exams should evaluate the presence of tonsil size during examination of the mouth and airway.

Administration, Oral↗