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Biomedical subjects

D S Ward

Publications and source records attributed to D S Ward.

At least 37 records · Page 2Linked to original sources
PubMed1998

Validity of the computer science and applications (CSA) activity monitor in children.

PURPOSE: The purpose of this study was to evaluate the validity of the CSA activity monitor as a measure of children's physical activity using energy expenditure (EE) as a criterion measure. METHODS: Thirty subjects aged 10 to 14 performed three 5-min treadmill bouts at 3, 4, and 6 mph, respectively. While on the treadmill, subjects wore CSA (WAM 7164) activity monitors on the right and left hips. VO2 was monitored continuously by an automated system. EE was determined by multiplying the average VO2 by the caloric equivalent of the mean respiratory exchange ratio. RESULTS: Repeated measures ANOVA indicated that both CSA monitors were sensitive to changes in treadmill speed. Mean activity counts from each CSA unit were not significantly different and the intraclass reliability coefficient for the two CSA units across all speeds was 0.87. Activity counts from both CSA units were strongly correlated with EE (r = 0.86 and 0.87, P < 0.001). An EE prediction equation was developed from 20 randomly selected subjects and cross-validated on the remaining 10. The equation predicted mean EE within 0.01 kcal.min-1. The correlation between actual and predicted values was 0.93 (P < 0.01) and the SEE was 0.93 kcal.min-1. CONCLUSION: These data indicate that the CSA monitor is a valid and reliable tool for quantifying treadmill walking and running in children.

Adolescent↗
PubMed1997

Physical activity and physical fitness in African-American girls with and without obesity.

Lack of physical activity and low levels of physical fitness are thought to be contributing factors to the high prevalence of obesity in African-American girls. To examine this hypothesis, we compared habitual physical activity and physical fitness in 54 African-American girls with obesity and 96 African-American girls without obesity residing in rural South Carolina. Participation in vigorous (> or = 6 METs) (VPA) or moderate and vigorous physical activity (> or = 4 METs) (MVPA) was assessed on three consecutive days using the Previous Day Physical Activity Recall. Cardiorespiratory fitness was assessed using the PWC 170 cycle ergometer test. Upper body strength was determined at two sites via isometric cable tensiometer tests. Relative to their counterparts without obesity, girls with obesity reported significantly fewer 30-minute blocks of VPA (0.90 +/- 0.14 vs. 1.3 +/- 0.14) and MVPA (1.2 +/- 0.18 vs. 1.7 +/- 0.16) (p < 0.01). Within the entire sample, VPA and MVPA were inversely associated with body mass index (r = -0.17 and r = -0.19) and triceps skinfold thickness (r = -0.19 and r = -0.22) (p < 0.05). In the PWC 170 test and isometric strength tests, girls with obesity demonstrated absolute scores that were similar to, or greater than, those of girls without obesity; however, when scores were expressed relative to bodyweight, girls with obesity demonstrated significantly lower values (p < 0.05). The results support the hypothesis that lack of physical activity and low physical fitness are important contributing factors in the development and/or maintenance of obesity in African-American girls.

Black People↗
PubMed1997

Breathing patterns and levels of consciousness in children during administration of nitrous oxide after oral midazolam premedication.

PURPOSE: The combination of midazolam and nitrous oxide is commonly used to achieve sedation and analgesia during pediatric oral procedures, yet there are few, if any, data that illustrate the ventilatory effects of N2O in children, especially when used in combination with additional central nervous system (CNS) depressants. It was hypothesized that the addition of N2O inhalation to oral midazolam premedication would enhance the sedative effects of the midazolam and add analgesia without causing significant respiratory depression. The purpose of this study was to test this hypothesis. MATERIALS AND METHODS: Thirty-four healthy children about to undergo restorative dental treatment under general anesthesia were premedicated with oral midazolam, 0.7 mg/kg, and were then exposed to 40% N2O for 15 minutes after a 5-minute control period. The effect of adding N2O on SpO2, respiratory rate, PETCO2, VT, and VT/TI was examined and the levels of consciousness (conscious vs deep sedation) before and during N2O inhalation were determined. RESULTS: During the course of the study, no child developed hypoxemia (SpO2 < 92%) nor clinically significant upper airway obstruction. Four children who did not develop hypoventilation (defined as PETCO2 > 45 mm Hg) during the control period did so after initiation of N2O. Overall, there were no significant differences in SpO2, PETCO2, VT, or VT/TI between the control and study periods. However, respiratory rates were significantly higher in the first 10 minutes of N2O inhalation when compared with the control period. Before starting N2O administration, 14 children were not clinically sedated, 19 children met the criteria for conscious sedation, and one child met the criteria for deep sedation. At the end of 15 minutes of N2O inhalation, 12 children were not clinically sedated, 17 children met the definition of conscious sedation, three were deeply sedated, and one child had no response to IV insertion, implying a state of general anesthesia. There were no differences in sedation scores between the control and study periods (P = .6). Overall, seven children had an increase in their sedation score while breathing N2O, four had a decrease in their sedation score, and 22 had no change. CONCLUSIONS: The addition of 40% N2O to oral midazolam, 0.7 mg/kg, did not result in clinically meaningful respiratory depression nor upper airway obstruction, but did, in some children, cause an increase in the level of sedation beyond simple conscious sedation.

Adjuvants, Anesthesia↗
PubMed1997

Correlates of physical activity behavior in rural youth.

The purpose of this study was to identify correlates of physical activity behavior in a sample of rural, predominantly African American youth. Three hundred sixty-one fifth-grade students from two rural counties in South Carolina (69% African American, median age = 11 years) completed a questionnaire designed to measure beliefs and social influences regarding physical activity, physical activity self-efficacy, perceived physical activity habits of family members and friends, and access to exercise and fitness equipment at home. After school physical activity and television watching were assessed using the Previous Day Physical Activity Recall (PDPAR). Students were classified as physically active according to a moderate physical activity standard: two or more 30-min blocks at an intensity of 3 METs (metabolic equivalents) or greater, and a vigorous physical activity standard: one or more 30-min blocks at an intensity of 6 METs or greater. According to the moderate physical activity standard, 34.9% of students were classified as low-active. Multivariate analysis revealed age, gender, television watching, and exercise equipment at home to be significant correlates of low activity status. According to the vigorous physical activity standard, 32.1% of the students were classified as low-active. Multivariate analysis revealed age, gender, television watching, and self-efficacy with respect to seeking support for physical activity to be significant correlates of low activity status. In summary, gender and the amount of television watching were found to be the most important correlates of physical activity in rural, predominantly African American youth.

Black or African American↗
PubMed1997

Effects of exercise mode on hematologic adaptations to endurance training in adult females.

BACKGROUND: The subjects were 26 healthy, sedentary adult females with the following characteristics: maximal oxygen consumption (VO2max) = 32.0 +/- 7.2 ml.kg-1.min-1; age = 32 +/- 5 yr; body mass index (BMI) = 23.2 +/- 3.4 kg.m-2 who were randomly assigned to control (CON; N = 8); treadmill training (TM; N = 8); or cycle ergometer training (CY; N = 10) to test the hypothesis that hematologic adaptations to endurance exercise training are specific to mode of exercise. METHODS: Training, conducted 3-5 (3.4 +/- 0.06) d.week-1 at 80% of mode specific VO2max for 12 weeks, was supervised and progressive, with estimated exercise energy expenditure equated across training groups. Plasma volume (PV, T-1824 dilution); calculated total blood (THb) and red cell volumes (RCV); calculated total hemoglobin (THb) and other hematologic variables were measured at baseline and weeks 2, 4, 8 and 12 of training. RESULTS: Across 12 weeks of training, PV was decreased (95% of baseline) in the TM group but increased (106% of baseline) in the CY group (p = 0.06). Similar trends were observed for RCV (p = 0.15) and TBV (p = 0.08). These results are in contrast to reported changes in PV, TBV and RCV in males following training. Hemodilution was observed in both training groups, reflected by decreases (p < 0.05) in hematocrit (Hct), hemoglobin (Hb) and RC count. Mean corpuscular Hb (MCH) and Hb content (MCHC) increased (p < 0.05) with training. These changes, as well as trend toward increased (p = 0.08) mean corpuscular volume (MCV), suggested the probable presence of a RC population with a lower mean age and decreased oxyhemoglobin affinity. The possibility of Type II error cannot be discounted in these trends, which suggest that PV, TBV and RCV may be affected by mode of endurance exercise in females.

Adaptation, Physiological↗
PubMed1996

Levels of consciousness and ventilatory parameters in young children during sedation with oral midazolam and nitrous oxide.

OBJECTIVE: To determine the ventilatory effects and levels of consciousness achieved during sedation with the combination of oral midazolam and inhaled nitrous oxide. DESIGN: Case series. SETTING: Surgical suite. PATIENTS: Twenty-two consecutive children, aged 1 to 3 years, were seen for elective, ambulatory surgery. INTERVENTIONS: Patients were premedicated with oral midazolam hydrochloride, 0.5 mg/kg, and then breathed 4 concentrations of nitrous oxide (N2O) in oxygen (15%, 30%, 45%, and 60%) for 4 minutes at each concentration prior to induction of general anesthesia. MAIN OUTCOME MEASURES: Levels of consciousness (conscious vs deep sedation) and ventilatory parameters: respiratory rate, end-tidal carbon dioxide tension (PETCO2), and oxyhemoglobin saturation (SPO2). Upper airway obstruction was diagnosed by clinical assessment by an experienced pediatric anesthesiologist (R.S.L.) and respiratory impedance plethysmography. RESULTS: During inhalation of N2O, 12 of the 20 children demonstrated a mild degree of ventilatory depression; PETCO2 values were equal to or greater than 45 mm Hg during at least 2 concentrations of N2O studied. There were no significant changes in SPO2 or PETCO2 with increasing concentrations of N2O (P > .05). Respiratory rates tended to be lower during inhalation of 15% N2O than at higher concentrations (P = .05). No child developed upper airway obstruction or hypoxemia (SPO2 < 92%) at any level of N2O inhalation. Sedation scores were significantly higher at 60% N2O than at all other concentrations of N2O (P < .02) At 15% N2O, 12 children were not clinically sedated, 8 children met the American Academy of Pediatrics definition of conscious sedation, and no child met the definition of deep sedation. At 30% N2O, 10 children were not clinically sedated, 9 met the definition of conscious sedation, and 1 child met the definition of deep sedation. At 45% N2O, 9 children were not clinically sedated, 9 met the definition of conscious sedation, and 2 met the definition of deep sedation. At 60% N2O, 6 children were not clinically sedated, 6 met the definition of conscious sedation, 6 met the definition of deep sedation, and 1 child progressed to a deeper level of sedation in that there was no response to a painful stimulus. One child was withdrawn from the study during inhalation of 45% N2O because of emesis. CONCLUSIONS: The combination of oral midazolam, 0.5 mg/kg, and up to 60% inhaled N2O caused mild ventilatory depression in some children and resulted in a progression from conscious to deep sedation beginning at 30% N2O. When using this particular combination of sedatives, practitioners should monitor each child's mental status continuously and adhere to the appropriate published guidelines for the monitoring and management of such patients.

Ambulatory Surgical Procedures↗
PubMed1996

Gender differences in physical activity and determinants of physical activity in rural fifth grade children.

This study determined if gender differences in physical activity could be accounted for by differences in selected social-cognitive determinants of activity behavior. Some 334 fifth grade, predominantly African-American students provided information regarding after-school physical activity and the hypothesized determinants of activity behavior. Boys reported significantly greater participation in vigorous ( > or = 6 METs) and in moderate to vigorous ( > or = 4 METs). Relative to girls, boys demonstrated higher levels of physical fitness, greater self-efficacy in overcoming barriers to physical activity, greater amounts of television watching, and higher levels of participation in community sports and physical activity organizations. When mean physical activity scores for girls and boys were adjusted for the effects of these determinant variables, the significant gender difference in physical activity remained. However, adjustment for self-efficacy in overcoming barriers and community sports reduced the gender gap by 5% and 7%, respectively. In contrast, adjustment for television watching increased the gender gap by about 8%. Results indicated perceived confidence in overcoming barriers to physical activity and participation in community physical activity programs are factors related to the gender difference in physical activity.

Child↗
PubMed1996

Measurement of tissue volume during non-steady state high-intensity muscle contraction.

To investigate the pressures driving water into stimulated muscle, water distribution during and after muscle stimulation was studied in isolated cat muscles perfused by recirculating diluted blood. 51Cr-labeled EDTA (51Cr-EDTA) and Evans blue-labeled albumin were used to determine extracellular volume and plasma volume (PV), respectively. Change in tissue volume was calculated as -PV. Interstitial volume (IFV) was determined from the ratio of interstitial solute (51Cr-EDTA and sodium) mass and interstitial concentration. Interstitial mass was determined by mass balance, and interstitial concentration was determined from solute flux and Fick's Law. One group was stimulated at 4 Hz for 2 min, and a second was stimulated by 80-Hz trains (1 train/s, 0.1 s duration). Four Hertz stimulation increased total tissue volume by approximately 3 ml/100 g and decreased IFV by 1 ml/100 g. Train stimulation increased total tissue volume by 6 ml/100 g and decreased IFV by 4. These data indicate that water moves into cells faster than the simultaneous transcapillary flow, suggesting that intracellular osmoles provide the primary driving pressure in stimulation-induced swelling.

Animals↗
PubMed1996

The use of fiberoptic endoscopy in anesthesia.

The fiberoptic bronchoscope has contributed greatly to the practice of anesthesiology over the past 30 years. It has become an indispensable tool in the approach to the difficult airway, as well as the placement and positioning of double-lumen tubes for thoracic surgery. The equipment, preparation, and methods for using the endoscope in anesthesia, are presented here.

Anesthesia↗
PubMed1995

Open loop control of multiple drug effects in anesthesia.

Current open-loop computer-controlled infusion pumps do not explicitly control the transient adverse side effects of intravenous drugs during anesthesia. We used optimal control principles to synthesize a single-input multiple-output controller that regulates concentrations at the site of desirable drug effect while penalizing excessive side-effect drug concentrations. The cost function incorporates model-based predictions of future effect-site concentrations, and the capability of the anesthesiologist to anticipate upcoming surgical events. The controller was evaluated and then compared with alternative control strategies through computer simulation of a physiologically based pharmacokinetic model for the intravenous drug alfentanil. Multiple-effect control offers an analytic approach to limit the overshoot in adverse side-effect concentrations at the consequence of increasing the time to achieve the desired drug effect.

Alfentanil↗
PubMed1994

Effects of 20% nitrous oxide on the ventilatory response to hypercapnia and sustained isocapnic hypoxia in man.

To examine the effects of a sub-anaesthetic concentration of nitrous oxide on ventilation, we have studied the ventilatory response to carbon dioxide and isocapnic hypoxia (FIN2O 0.2). In five subjects, we performed step decreases in PE'O2 to 6.7 kPa for 15 min and step increases in PE'CO2 (delta PE'CO2 1.5 kPa). The carbon dioxide responses were partitioned into a fast peripheral and slow central component. All control oxygen responses were biphasic: the acute hypoxic response was 7.2 (4.6) litre min-1 and the subsequent decline 4.2 (2.6) litre min-1. With nitrous oxide, the acute hypoxic response was 10.3 (6.7) litre min-1, but was followed by a nonsignificant decline of 3.8 (3.0) litre min-1 because of a progressive increase in breathing frequency in the hypoxic period. None of the variables obtained from the carbon dioxide responses differed between groups. Our data indicate that a sub-anaesthetic concentration of nitrous oxide did not affect the peripheral chemoreflex loop. The hyperventilatory response to prolonged hypoxia was sustained better with nitrous oxide compared with control.

Adult↗
PubMed1994

Effect of a subanesthetic minimum alveolar concentration of isoflurane on two tests of the hypoxic ventilatory response.

BACKGROUND: These experiments were designed to study the effect of 0.1 minimum alveolar concentration isoflurane on the hypoxic ventilatory response as measured by two common methods of hypoxic testing: when normocapnic hypoxia was induced abruptly and when it was induced gradually. We hypothesized that any disparity in results would be due to an isoflurane effect that was manifested differently in the two tests. METHODS: After 20 min for uptake and equilibration of 0.1 minimum alveolar concentration end-tidal isoflurane or carrier gas in hyperoxia, isocapnic hypoxia was induced either abruptly over 60-80 s ("step" test) or gradually over 10 min ("ramp" test), followed by 20 min of isocapnic hypoxia at 45 mmHg end-tidal oxygen. Control of the hypoxic and isocapnic stimuli was accomplished accurately by a computer-controlled dynamic end-tidal forcing system. Eight subjects performed each test in the presence and absence of isoflurane. RESULTS: For both step tests and ramp tests, 0.1 minimum alveolar concentration isoflurane had no effect on minute ventilation during the defined periods of hypoxia. With isoflurane, delta VE45, the acute change in ventilation from hyperoxia to hypoxia, was 97 +/- 20% (mean +/- SEM) of the control response for step tests and 100 +/- 25% of the control response for ramp tests. The step tests produced significantly larger acute hypoxic responses than did the ramp tests, but by the end of 20 min of hypoxia, ventilation was similar for both tests. CONCLUSIONS: Neither method of hypoxic testing demonstrated the level of isoflurane effect reported by others. A comparison of the two methods of hypoxic testing suggests that ramp tests, as commonly performed, do not allow adequate time for full expression of the acute hypoxic ventilatory response. Step tests also better separated the opposing hypoxic effects of carotid body stimulation and central ventilatory depression.

Adult↗
PubMed1994

The hybrid model: a new pharmacokinetic model for computer-controlled infusion pumps.

Classical pharmacokinetic models used in computer-controlled infusion pumps (CCIPs) assume instantaneous mixing of drug in blood; however, the average recirculation time of blood in man is approximately one minute. To investigate the effects of recirculation dynamics on the transient performance of CCIPs, we propose a hybrid physiologically-based pharmacokinetic model for the narcotic alfentanil. A three-compartment model was derived from the response of the hybrid model to a short infusion and used to compute a CCIP infusion targeting 450 micrograms/l. For this infusion, the hybrid model predicts that the arterial plasma concentration will overshoot the target concentration by 39 percent with an average prediction error of 3 percent. The overshoot and average prediction error increase to 100 and 25 percent respectively when using a three-compartment pharmacokinetic model derived from a bolus. The overshoot can be reduced by decreasing the maximum possible infusion rate, or by increasing the zero-order hold infusion interval.

Alfentanil↗
PubMed1994

Effects of anaesthetics and sedatives on the control of breathing.

Most anaesthetics and sedatives affect breathing via several mechanisms, including effects on respiratory drive, wakefulness, and airway patency. Existing information about the effects of anaesthetic drugs on control of breathing has been obtained using techniques which focus on chemical control of breathing (i.e., the response to hypoxia and/or hypercapnia) and only occasionally take these other factors into account. In addition, a single drug is usually studied in isolation, despite the fact that anaesthetists often employ multiple drugs which may cause synergistic ventilatory depression. Finally, the pattern of change in O2/CO2 and the time of measurement of ventilation can influence the results of laboratory tests. For example, the effect of morphine on the CO2 response differs with steady-state versus rebreathing tests and, for the same dose of morphine, as a function of wakefulness. The measured hypoxic ventilatory response depends on the degree of hypercapnia, level of consciousness, and the time elapsed after the induction of hypoxia, since the response is characterized by an acute increase in ventilation followed by a subsequent decline. Unconsciousness induced by anaesthetics and sedatives may cause hypoventilation due to obstruction of the upper airway by either the epiglottis or the soft palate. For these reasons, clinicians should be aware that drugs which cause ventilatory depression in the laboratory may have different (possibly much greater) effects in their patients.

Airway Obstruction↗
PubMed1993

Water uptake in stimulated cat skeletal muscle.

Isolated vasodilated cat hindlimb skeletal muscles were perfused at constant flow and stimulated at 4 Hz for 2-4 min in three studies. Water uptake rates were measured gravimetrically or calculated from venous protein concentration changes. Venous plasma sodium, potassium, chloride, and osmolality were also measured. Maximum water uptake rates averaged 1.8 +/- 0.2 (SE) ml.min-1 x 100 g-1, reaching twice that in some experiments. Water uptake continued after stimulation had ceased. Constant-flow perfusion maintained a constant capillary pressure that was corroborated by measurements of arterial and venous perfusate pressures. Water uptake rate was not influenced by hematocrit but was highly correlated with plasma flow rate. The evidence strongly suggests that small-molecule osmotic pressure was the primary pressure causing the transcapillary water flux. Venous plasma sodium and chloride concentrations increased almost as much as protein (108 and 87% of the protein increase, respectively), as would be expected when water fluxes are driven by small-molecule osmotic pressure. Peak potassium efflux averaged 36 +/- 3 mu eq.min-1 x 100 g-1, but potassium did not contribute significantly to the osmotic gradient.

Animals↗