Ophthalmologists
10 years of experience
Video profile
Accepting new patients
West University
Austin Retina Assoc
801 W 38th St
Ste 200
Austin, TX 78705
512-451-0103
Locations and availability (11)

Education ?

Medical School Score Rankings
University of Alabama at Birmingham (2000)
  • Currently 4 of 4 apples
Top 25%

Awards & Distinctions ?

Awards  
Patients' Choice Award (2011 - 2013)
Compassionate Doctor Recognition (2013)
Top 10 Doctor - Metro Area (2014)
Greater Austin
Ophthalmologist
Associations
American Society of Retina Specialists
American Board of Ophthalmology
American Academy of Ophthalmology

Affiliations ?

Dr. Nixon is affiliated with 19 hospitals.

Hospital Affilations

Score

Rankings

  • Seton Medical Center
    1201 W 38th St, Austin, TX 78705
    • Currently 4 of 4 crosses
    Top 25%
  • Seton Northwest Hospital
    11113 Research Blvd, Austin, TX 78759
    • Currently 3 of 4 crosses
    Top 50%
  • Daughters of Charity Children's Austin
    601 E 15th St, Austin, TX 78701
    • Currently 3 of 4 crosses
    Top 50%
  • Daughters of Charity Seton Edgar B Davis
    130 Hays St, Luling, TX 78648
    • Currently 2 of 4 crosses
  • Daughters of Charity Seton Highland Lake
    PO Box 1219, Burnet, TX 78611
    • Currently 1 of 4 crosses
  • San Angelo Community Medical Center
    3501 Knickerbocker Rd, San Angelo, TX 76904
    • Currently 1 of 4 crosses
  • Callahan Eye Foundation Hospital
  • Seton Southwest Healthcare Center
    7900 FM 1826, Austin, TX 78737
  • Seton Medical Center Williamson
    201 Seton Pkwy, Round Rock, TX 78665
  • Seton Highland Lakes Hospital
    3201 S Water St, Burnet, TX 78611
  • Seton Shoal Creek Hospital
    3501 Mills Ave, Austin, TX 78731
  • Shannon Medical Center - Memorial Campus
    120 E Harris Ave, San Angelo, TX 76903
  • Northwest Hills Surgical Hospital
  • Brackenridge Hospital
    601 E 15th St, Austin, TX 78701
  • Shannon Medical Center
  • Northwest Hills
  • Medical Park Towers
  • Cooper Green-Mercy Hospital
  • Seton Edgar B. Davis
    130 Hays St, Luling, TX 78648
  • Publications & Research

    Dr. Nixon has contributed to 31 publications.
    Title Branch Retinal Artery Occlusion: Visual Prognosis.
    Date September 2008
    Journal American Journal of Ophthalmology
    Excerpt

    PURPOSE: To evaluate the visual prognosis in eyes with branch retinal artery occlusion (BRAO). DESIGN: Retrospective, observational, consecutive case series. METHODS: Retrospective medical record review of 52 consecutive eyes of 52 patients with BRAO seen at two vitreoretinal practices in Birmingham, Alabama. Only eyes with decreased central macular perfusion on fluorescein angiography (FA) were included. Eyes with anterior segment or optic nerve disease, lack of retinal whitening or a delay in arterial filling on FA, central retinal artery occlusion, and cilioretinal artery occlusion were excluded. The main outcome measure was presenting best-corrected visual acuity (BCVA) and its relationship to final BCVA. RESULTS: On presentation, 54% of eyes with BRAO had BCVA of 20/40 or better. At the mean 14-month visit, 60% of all eyes had visual acuity (VA) of 20/40 or better. VAs of 20/40 or better were retained by 89% of eyes with baseline BCVA of 20/40 or better. Only 14% of eyes with 20/100 or worse BCVA improved to 20/40 or better. Neither visible emboli (P > or = .244) nor the region of macular involvement (P = .142) were significant with respect to visual improvement. CONCLUSIONS: Visual prognosis after BRAO seems to be correlated to presenting VA. Eyes with initial VA of 20/40 or better usually remained at 20/40 or better. Individuals with poor VA of 20/100 or worse generally did not show the significant improvement reported in previous studies.

    Title Follow-up of a Randomized, Placebo-controlled Trial of Dexamethasone to Decrease the Duration of Ventilator Dependency in Very Low Birth Weight Infants: Neurodevelopmental Outcomes at 4 to 11 Years of Age.
    Date November 2007
    Journal Pediatrics
    Excerpt

    OBJECTIVE: High doses of dexamethasone reduce the risk of chronic lung disease among premature infants but may increase the risk of developmental impairments. The objective of this study was to compare developmental outcomes beyond infancy for children who, as neonates, participated in a randomized trial of dexamethasone. PATIENTS AND METHODS: One hundred eighteen children with birth weights <1500 g were randomly assigned at 15 to 25 days of life to a 42-day tapering course of dexamethasone or placebo. All 95 survivors were assessed by using standardized measures of developmental outcome at least once at or beyond 1 year of age, and 84 were examined at 4 to 11 years. For this follow-up study, the outcome of primary interest was death or major neurodevelopmental impairment, which was defined as cerebral palsy, cognitive impairment, or blindness. RESULTS: On the basis of each child's most recent follow-up, the rates of major neurodevelopmental impairments were 40% for the dexamethasone group and 20% for the placebo group. The higher impairment rate for the dexamethasone group was mainly attributed to a higher prevalence of cerebral palsy. Rates of the composite outcome of death or major neurodevelopmental impairment were 47% and 41%, respectively. CONCLUSION: A 42-day tapering course of dexamethasone, which was shown previously to decrease the risk of chronic lung disease in very low birth weight infants, does not increase the risk of the composite outcome of death or major neurodevelopmental impairment.

    Title Trans-luminal Nd:yag Laser Embolysis for Branch Retinal Artery Occlusion.
    Date July 2007
    Journal Retina (philadelphia, Pa.)
    Excerpt

    PURPOSE: To evaluate the clinical efficacy of transluminal YAG laser embolysis (TYE) for patients with severe vision loss secondary to a newly diagnosed branch retinal artery occlusion (BRAO) with visible emboli. METHODS: Five eyes of five patients with acute, severe vision loss secondary to a branch retinal artery occlusion with visible emboli and retinal whitening were prospectively examined, enrolled, and underwent visual acuity testing, ophthalmic examination, color photography, and fluorescein angiography. Each patient was offered TYE and the potential risks of the treatment were explained. Follow-up examinations were undertaken post-procedure day 1 and subsequent follow-up depended on the clinical course. RESULTS: In our five patients baseline best-corrected visual acuity (BCVA) was found to be 5/400, count fingers at 3 feet, count fingers at 5 feet, 20/800, and 20/200. All five of our patients showed improvement in BCVA 1 day after TYE. Fluorescein angiography showed immediate and dramatic restoration in flow past the obstructed arteriole in all patients. Patient 2 developed subretinal hemorrhage, which after vitrectomy and associated procedures the acuity improved to 20/25 at 22 days after the TYE. Final BCVA was 20/30, 20/25, 20/40, 20/30, and 20/40. CONCLUSION: TYE is a treatment modality to be considered in patients with BRAO who present acutely with severe vision loss and a visible embolus. The risks of TYE must be weighed against the possibility of severe and permanent loss of vision secondary to BRAO.

    Title Follow-up Study of a Randomized Controlled Trial of Postnatal Dexamethasone Therapy in Very Low Birth Weight Infants: Effects on Pulmonary Outcomes at Age 8 to 11 Years.
    Date April 2007
    Journal The Journal of Pediatrics
    Excerpt

    OBJECTIVE: To determine whether postnatal dexamethasone (DEX) exposure affects pulmonary outcomes at school age in children born with very low birth weight (VLBW). STUDY DESIGN: Follow-up study of 68 VLBW children who participated in a randomized controlled trial of postnatal DEX. Pulmonary function was assessed by spirometry. Current asthma status was obtained from a parent. RESULTS: Sixty-eight percent of the placebo group had below-normal forced expiratory volume in 1 second (FEV1), compared with 40% of the DEX group (chi2 = 4.84; P = .03), with trends for lower forced vital capacity (FVC) and FEV1 values in the placebo group. Fifty percent of the placebo group and 34% of DEX group had below normal FEV1/FVC (chi2 =1.59; P =.21). Parent-reported prevalence of asthma did not differ between groups. Logistic regression analysis suggested that the positive effects of DEX on pulmonary function at follow-up were mediated in part by shortened exposure to mechanical ventilation. CONCLUSIONS: Postnatal DEX exposure was associated with higher expiratory flow with no adverse effects on pulmonary outcomes at school age. The prevalences of asthma and impaired pulmonary function underscore the influence of neonatal illness on health at school age, and stress the importance of repeated follow-up examinations of these children.

    Title Intravitreal Injection of Bevacizumab (avastin) As Adjunctive Treatment of Proliferative Diabetic Retinopathy.
    Date October 2006
    Journal American Journal of Ophthalmology
    Excerpt

    PURPOSE: To report the use of intravitreal bevacizumab (Avastin) as an adjunctive treatment for proliferative diabetic retinopathy (PDR). DESIGN: Retrospective case review. METHODS: Institutional review board approval to review patient data was obtained for this retrospective study. Three patients underwent intravitreal injection of bevacizumab as part of their treatment for PDR after informed consent was signed. Each patient also underwent fundus photographs before the bevacizumab injection and then one to three weeks after. RESULTS: All three patients showed complete regression of their neovascularization elsewhere (NVE) and neovascularization of the disk (NVD) between one and three weeks after injection. CONCLUSIONS: The speed and degree of neovascular regression after the injection of intravitreal bevacizumab may make this procedure an important adjunctive treatment in the management of selected cases with severe PDR.

    Title Follow-up of a Randomized, Placebo-controlled Trial of Postnatal Dexamethasone: Blood Pressure and Anthropometric Measurements at School Age.
    Date October 2006
    Journal Pediatrics
    Excerpt

    OBJECTIVE: The purpose of this work was to evaluate the effects of a 42-day tapering course of dexamethasone on blood pressure and anthropometric measurements in school-age children who were born with very low birth weight. METHODS: Sixty-eight children, who as neonates participated in a randomized placebo-controlled trial of a 42-day tapering course of dexamethasone (n = 38, dexamethasone; n = 30, placebo) to facilitate weaning from the ventilator, were seen at a median of 9 years of age. Participants underwent measurements of systolic blood pressure, diastolic blood pressure, mid-arm circumference, triceps skinfold thickness, height, and weight. Mann-Whitney U tests were used to compare groups, and Spearman coefficients were used to examine correlations between variables. RESULTS: Comparing dexamethasone- and placebo-treated children, we found no differences in systolic blood pressure, mid-arm circumference, triceps skinfold thickness, height, weight, or body mass index. Twenty-nine percent of all subjects had systolic blood pressure and/or diastolic blood pressure > or = 90th percentile for age and gender. Thirty percent of all subjects had body mass index > or = 85th percentile for age and gender. CONCLUSIONS: In a group of preterm very low birth-weight infants at high risk for chronic lung disease, we found no effects of dexamethasone on blood pressure or anthropometric measurements at 8 to 11 years of age. Of concern is that a high proportion in this sample had blood pressure > or = 90th percentile and/or body mass index > or = 85th percentile.

    Title Clinical Stress Testing in the Pediatric Age Group: a Statement from the American Heart Association Council on Cardiovascular Disease in the Young, Committee on Atherosclerosis, Hypertension, and Obesity in Youth.
    Date May 2006
    Journal Circulation
    Excerpt

    This statement is an updated report of the American Heart Association's previous publications on exercise in children. In this statement, exercise laboratory requirements for environment, equipment, staffing, and procedures are presented. Indications and contraindications to stress testing are discussed, as are types of testing protocols and the use of pharmacological stress protocols. Current stress laboratory practices are reviewed on the basis of a survey of pediatric cardiology training programs.

    Title Visual Hallucinations from Age-related Macular Degeneration.
    Date March 2006
    Journal The American Journal of Medicine
    Title Evidence Based Physical Activity for School-age Youth.
    Date July 2005
    Journal The Journal of Pediatrics
    Excerpt

    OBJECTIVES: To review the effects of physical activity on health and behavior outcomes and develop evidence-based recommendations for physical activity in youth. STUDY DESIGN: A systematic literature review identified 850 articles; additional papers were identified by the expert panelists. Articles in the identified outcome areas were reviewed, evaluated and summarized by an expert panelist. The strength of the evidence, conclusions, key issues, and gaps in the evidence were abstracted in a standardized format and presented and discussed by panelists and organizational representatives. RESULTS: Most intervention studies used supervised programs of moderate to vigorous physical activity of 30 to 45 minutes duration 3 to 5 days per week. The panel believed that a greater amount of physical activity would be necessary to achieve similar beneficial effects on health and behavioral outcomes in ordinary daily circumstances (typically intermittent and unsupervised activity). CONCLUSION: School-age youth should participate daily in 60 minutes or more of moderate to vigorous physical activity that is developmentally appropriate, enjoyable, and involves a variety of activities.

    Title Strength Vs Aerobic Training in Children with Cystic Fibrosis: a Randomized Controlled Trial.
    Date December 2004
    Journal Chest
    Excerpt

    STUDY OBJECTIVE: Exercise has the potential to improve the ability of a patient with cystic fibrosis (CF) to cope with the physical demands of everyday life, and may improve prognosis. The purpose of this study was to compare the effects of a home-based, semi-supervised, upper-body strength-training regimen with a similarly structured aerobic training regimen. DESIGN: Data were collected during a 1-year randomized clinical trial. SETTING: Counselors conducted in-home visits with the participants once per week for the first 8 weeks followed by monthly visits for the remainder of the study. PATIENTS: Sixty-seven patients with CF, aged 8 to 18 years, participated in the trial. INTERVENTION: Participants in both exercise conditions were encouraged to exercise at least three times per week for 1 year. Each child in the aerobic group was given a stair-stepping machine, and each child in the upper-body strength training group was given an upper-body-only weight-resistance machine. MEASURES AND RESULTS: Aerobic fitness, pulmonary function, quality of life, and strength were measured at baseline, at 6 months, and at 12 months. Strength training increased the maximum weight lifted for biceps curls significantly more than aerobic training (p < 0.02). However, this differential did not remain significant after control for increase in height. Both training procedures were associated with increased strength (p < 0.002) and physical work capacity (PWC) [p < 0.033]. CONCLUSIONS: We concluded that strength and aerobic training may increase upper-body strength, and that both types of training may increase PWC for children with CF. Future trials should be conducted with no-training control subjects and larger samples to increase statistical power.

    Title Habitual Physical Activity in Children and Adolescents with Cystic Fibrosis.
    Date April 2001
    Journal Medicine and Science in Sports and Exercise
    Excerpt

    PURPOSE: This study was conducted to: 1) measure total physical activity levels, including the intensities of the various types of activities, in children and adolescents with CF compared with non-CF healthy control subjects; and 2) determine whether vigorous activity level was related to aerobic fitness and disease status in patients with CF. METHODS: Thirty patients with CF (18 male, 12 female) and 30 control subjects (17 male, 13 female), 7-17 yr old, participated in this study. Habitual physical activity was measured using Kriska's Modifiable Activity Questionnaire (MAQ) and the past year's average of total hours, MET-hours, and vigorous (VIG) hours (>6 METs) of activity per week were determined. Aerobic fitness was determined from peak oxygen uptake (VO2peak) obtained via maximal exercise testing on a cycle ergometer. Standard spirometry was used to measure pulmonary function. Body mass index (BMI) was determined from height and weight measurements. RESULTS: The CF and control groups were similar in age and gender distribution, but the patients were smaller (BMI, 98 vs 112% of predicted) and less aerobically fit (36.5 vs 41.4 mL x kg(-1) x min(-1)). Total and MET-hours of physical activity did not differ between groups; however, the CF group participated in significantly fewer hours of vigorous activities than the control group (2 vs 3.7 h x wk(-1)). In patients with worse lung disease, VIG-h x wk(-1) were significantly related to VO2peak (r = 0.83). CONCLUSION: These results suggest that children with CF engage in less vigorous physical activities than their healthy non-CF peers, despite having good lung function. In view of the progressive nature of the disease, and the association between aerobic fitness and vigorous activity, patients should be encouraged to engage in more vigorous activities that promote aerobic fitness and may ultimately have an impact on survival.

    Title Quality of Life in Pediatric Heart, Heart-lung, and Lung Transplant Recipients.
    Date March 2001
    Journal International Journal of Sports Medicine
    Excerpt

    Few studies have assessed quality of life in pediatric heart and/or lung transplant recipients, and have varied by the tool used, the design employed, and the time of assessment from transplant. The results also varied including normal to abnormal "psychologic adjustment", diminishing problem behavior at home following transplantation, as well as improvements and no change in quality of life using tools designed specifically for the objective assessment of quality of life. This area of study is in its infancy and thus future studies should: 1) design and utilize standard tools (both global and disease-specific) that have documented validity and reliability in pediatric transplant recipients; 2) examine changes in quality of life longitudinally, and 3) identify predictors of quality of life and potential treatments that can help improve quality of life in pediatric transplant recipients.

    Title Airway Complications Following Pediatric Lung and Heart-lung Transplantation.
    Date September 2000
    Journal American Journal of Respiratory and Critical Care Medicine
    Excerpt

    Obstruction at the airway anastomosis is a recognized complication of adult heart-lung transplantation (HLT) and lung transplantation (LT). Data for pediatric transplantation have been scarce. We reviewed our experience in pediatric HLT and LT to determine the frequency of airway complications and to document the therapeutic modalities used for their treatment. Fifty-three patients (median age: 13.8 yr; range: 1.3 to 28.2 yr) underwent HLT (n = 25), SLT (n = 3), DLT (n = 25), or repeat DLT (n = 3) and survived for more than 72 h. Major anastomotic airway complications requiring intervention affected one of the 25 HLT (4%) and seven of the 28 LT (SLT + DLT) patients (25%) (p = 0.05). Four patients with granulation tissue occluding the airway were treated with forceps resection, laser ablation, or balloon dilatation. Three patients with fibrotic strictures received silicone stents, laser ablation, or balloon dilatation. Two patients with bronchomalacia or diffuse stricture below the anastomosis underwent metal stent placement. Five of seven patients who were treated for anastomotic complications had satisfactory relief of airway obstruction. As compared with previously studied adults, pediatric heart-lung transplant recipients had the same or a lower frequency, and pediatric lung transplant recipients had a higher frequency of major anastomotic airway complications. A variety of treatment modalities were necessary to achieve adequate relief of airway obstruction.

    Title Comparison of Flutter Device and Chest Physical Therapy in the Treatment of Cystic Fibrosis Pulmonary Exacerbation.
    Date November 1999
    Journal Pediatric Pulmonology
    Excerpt

    Chest physiotherapy (CPT) is recommended for the clearance of bronchial secretions in the management of patients with cystic fibrosis (CF). The Flutter valve (Scandipharm, Birmingham, AL) has been introduced as an alternative method to CPT for airway mucus clearance. The objective of this study was to compare the short-term effects of CPT and the Flutter valve on pulmonary function and exercise tolerance in patients with cystic fibrosis. Twenty-three patients, 5 to 21 years of age, were randomized to receive one of two interventions: CPT or the Flutter valve, upon admission to the hospital for a 2-week treatment of pulmonary exacerbation. Pulmonary function testing (PFTs) and the 6-min walk test were performed on admission, day 7, and day 14 of hospitalization. Data analysis indicated no significant differences between the two groups on admission. Both groups showed improvement in pulmonary function test results, but the Flutter group had a higher mean forced vital capacity (FVC) and forced expiratory volume in 1 sec (FEV(1)) compared to the CPT group after 1 week of intervention. Both groups continued to improve during the 2-week intervention, with no significant difference in FVC or FEV(1) between groups by the end of 2 weeks. Mean forced expiratory flow rate between 25-75% of vital capacity (FEF(25-75)), 6-min walk distance, and resting arterial oxyhemoglobin saturation (SaO(2)) showed little change by day 7, but improved significantly (P< 0.05) by day 14 of hospitalization in both groups, with no significant difference between groups. This study demonstrated that patients using the Flutter device had better pulmonary function after 1 week of therapy and similar improvement in pulmonary function and exercise tolerance compared to CPT after 2 weeks of therapy, suggesting that Flutter valve therapy is an acceptable alternative to standard CPT during in-hospital care of patients with CF.

    Title Physical Activity Epidemiology Applied to Children and Adolescents.
    Date October 1998
    Journal Exercise and Sport Sciences Reviews
    Excerpt

    Physical activity epidemiology is central to establishing the importance of physical activity to public health. However, epidemiologic research applied to children and adolescents is still in its infancy. For example, in the studies we reviewed, many instances could be found where samples were inadequately described or where response rates and completion rates suggest that the final sample may no longer be representative of the population of interest. Many studies also had incomplete statistical adjustment for confounding influences. The need for epidemiologic research was clearly demonstrated where initially beneficial findings were negated by such adjustment. Hence, physical activity epidemiologists can play a considerable role. Their research will be the basis for expanding policy and promotional efforts to educate children and adolescents on the benefits of physical activity and the skills needed to be active, thereby helping them to build a foundation for a lifetime of physical activity.

    Title Effects of Anaerobic Exercise on the Immune System in Eight- to Seventeen-year-old Trained and Untrained Boys.
    Date January 1997
    Journal The Journal of Pediatrics
    Excerpt

    OBJECTIVES: To determine the immunologic response to a brief bout of intense exercise in children and to determine the effects of prolonged activity and maturation level of the subjects on this response. STUDY DESIGN: We determined counts of leukocytes and their subsets, counts of lymphocytes and their subsets, and natural killer (NK) cell activity and cell number before and 3 and 60 minutes after a Wingate anaerobic test (WAnT) in 16 male swimmers (9 to 17 years of age) and 17 male nonswimmers (9 to 17 years of age). Subjects were also categorized by pubertal status based on Tanner staging and by level of physical activity. The Student t test and analysis of variance were used to determine statistical significance, with values expressed as mean +/- SEM. RESULTS: Three minutes after the WAnT, all children had increases in leukocytes (28%), lymphocytes (43%), and NK cells (395%) (p < 0.01). Swimmers had less baseline NK cell activity (54 +/- 6 cytolytic units) than nonswimmers (87 +/- 10 cytolytic units) after the WAnT (p < 0.01), although both groups showed an increase to similar levels of NK activity 3 minutes after exercise. Pubertal effects on these responses were not significant. CONCLUSIONS: Our results demonstrate transient leukocytosis, lymphocytosis, and increases in NK cell number and activity in 8- to 17-year-old boys after a brief bout of intense exercise. Formal athletic training appears to be associated with a lower baseline NK cell activity, and yet such activity is still within the normal range for this age group. Further investigations are necessary to determine the impact of such training on overall health and the ability to fight infection.

    Title Factors Limiting Anaerobic Performance in Adolescent Males with Cystic Fibrosis.
    Date December 1996
    Journal Medicine and Science in Sports and Exercise
    Excerpt

    Forty-one adolescent males (11.1-18.3 yr) with cystic fibrosis (CF) and 37 healthy adolescent males (11.1-17.9 yr) performed a Wingate Anaerobic Test (WAnT). The group with CF was subdivided by sexual maturity, nutritional status, and degree of airway obstruction. The subjects with CF had lower absolute power outputs than the healthy controls [mean power in Watts (mean +/- SD): 350.2 +/- 135.9 vs 424.5 +/- 120.4, P < 0.001; peak power: 525.2 +/- 178.4 vs 665.9 +/- 191.3, P < 0.001). When absolute power was corrected for lean body mass, the subjects with CF had lower power outputs than the healthy controls (mean power in W.kg-1: 8.9 +/- 1.7 vs 9.6 +/- 0.9, P < 0.05; peak power: 13.4 +/- 2.1 vs 15.0 +/- 1.6, P < 0.05). The subgroup with CF with a higher body mass index (BMI > 17.5 kg.m-2) had higher peak and mean power output than subjects with CF with a lower BMI in both absolute power and when power was expressed per lean body mass. When sexual maturation was considered, subjects with CF with salivary testosterone greater than 4.0 ng.dl-1 had a higher mean and peak power in both absolute terms and relative to lean body mass than subjects with CF with salivary testosterone less than 4.0 ng.dl-1. Multiple regression analysis indicated that the nutritional factor accounted for 70%-80% of the variability in power output in the subjects with CF, while testosterone accounted for 10% of the variability. Pulmonary function was not a significant independent correlate of anaerobic power. Our results suggest that nutritional status, and to a lesser extent maturational factors, may play a more important role than pulmonary function in determining anaerobic fitness in male adolescents with CF.

    Title A Six-minute Walk Test for Assessing Exercise Tolerance in Severely Ill Children.
    Date October 1996
    Journal The Journal of Pediatrics
    Excerpt

    OBJECTIVES: The primary objective of this study was to compare exercise tolerance, heart rate, and oxyhemoglobin saturation (Sao2) between a traditional progressive maximal exercise test and a self-paced, 6-minute walk test in severely ill children. STUDY DESIGN: Seventeen patients (9 to 19 years of age) performed a progressive maximal exercise test on a cycle ergometer and a self-paced, 6-minute walk test as part of the evaluation for possible heart, lung, or combined heart and lung transplantation. Physical work capacity and peak oxygen uptake were measured during the progressive cycle test. The walk test was performed in a hospital corridor, with patients trying to cover as much distance as possible in 6 minutes at their own pace. Oxyhemoglobin saturation and heart rate were monitored continuously by pulse oximetry and compared between the two tests. RESULTS: The distance walked in 6 minutes correlated with peak oxygen uptake (r = 0.70, p < 0.01) and physical work capacity (r = 0.64, p < 0.005). The minimum (Min) Sao2 on the bike test correlated significantly with Min Sao2 on the walk test (r = 0.82, p < 0.001), with 11 of 17 patients having a lower Min Sao2 on the walk test than the bike test (mean Min Sao2, 84% and 86%, respectively). The peak heart rate did not correlate significantly between the bike and walk tests (r = 0.25), although significantly lower (p < 0.01) values were observed on the walk (148 beats/min) than bike (169 beats/min) test. CONCLUSIONS: The results suggest that the 6-minute self-paced walk test may provide an alternative method for assessing functional capacity in severely ill children, and that Sao2 measured during progressive exercise testing on a cycle ergometer may not reflect the degree of oxyhemoglobin desaturation during self-paced walking in some patients with severe cardiopulmonary disease.

    Title Role of Exercise in the Evaluation and Management of Pulmonary Disease in Children and Youth.
    Date September 1996
    Journal Medicine and Science in Sports and Exercise
    Excerpt

    Asthma is the most common chronic pulmonary disorder affecting children in the U.S. Cystic fibrosis is the most common life-shortening inherited disease affecting white populations. With both disorders, children may have impaired exercise tolerance and abnormal cardiopulmonary responses to exercise. Exercise testing can aid in the diagnosis of exercise-induced asthma, and in determining prognosis in cystic fibrosis. Children with asthma and cystic fibrosis have been shown to benefit from exercise training, mainly through improved aerobic fitness and cardiopulmonary efficiency. In summary, exercise plays a valuable role in the evaluation and management of children with asthma and cystic fibrosis.

    Title Exercise Testing in Pediatric Heart, Heart-lung, and Lung Transplant Recipients.
    Date June 1995
    Journal Chest
    Excerpt

    Cardiorespiratory responses to progressive exercise were examined in 38 children who had undergone heart (n = 16), heart-lung (n = 13), or double-lung (n = 9) transplantation, and in 41 healthy controls. The four groups were similar in age, but the control subjects and heart transplant recipients were significantly larger than the heart-lung and lung recipients as assessed by body mass index (BMI). Time since transplant was significantly longer in the heart (601 days) compared with heart-lung (146 days) and lung (125 days) transplant groups. Physical work capacity and peak oxygen uptake were significantly reduced (43 to 64% of predicted) in the three transplant groups compared with the control group. Peak heart rate (percent predicted) was significantly higher in the control subjects (94%) compared with the heart (66%), heart-lung (70%), and lung (77%) transplant recipients. Peak minute ventilation was significantly higher in the control (72.9 L/min) and heart transplant (51.0 L/min) groups than the heart-lung (37.4 L/min) and lung (41.3 L/min) transplant groups. The control group had a higher peak tidal volume than the three transplant groups, and a higher peak respiratory rate than the lung transplant recipients. Correlational analysis revealed that physical work capacity (PWC) was significantly related to heart rate at peak exercise (HRpeak) and minute ventilation at peak exercise (VE-peak) in the heart transplant recipients, BMI, VEpeak, and FEV1 in the heart-lung transplant recipients, and BMI, HRpeak, VEpeak, FEV1, and number of days posttransplant in the lung transplant recipients. In addition to these variables, physical deconditioning and factors related to pharmacotherapy, infection, and rejection may also contribute to the decreased PWC observed in the transplant recipients.

    Title Accuracy of Three Pulse Oximeters During Exercise and Hypoxemia in Patients with Cystic Fibrosis.
    Date November 1993
    Journal Chest
    Excerpt

    To evaluate the reliability of noninvasive oximeters during exercise in patients with cystic fibrosis (CF), we studied 9 patients during exercise tests, using 3 devices (Hewlett-Packard 47201A, Biox-Ohmeda 3700, Nellcor 100), comparing oximetry readings with arterial blood co-oximetry. Fifty samples from preexercise, exercise, and recovery were collected; and paired measurements were analyzed for bias (arterial blood gas SaO2--noninvasive SaO2) and precision (1 SD of the bias). Values were available for the Hewlett-Packard and the Biox-Ohmeda at all 50 collection times. The Nellcor failed to read on four occasions, all during exercise. The accuracy of the Biox-Ohmeda readings was significantly worse during exercise than rest, while the Nellcor and the Hewlett-Packard performance did not differ significantly between exercise and rest. During hypoxemia (SaO2 < 90 percent as determined by co-oximetry on arterial blood), the Biox-Ohmeda and Nellcor consistently overestimated saturation, with mean bias of -6.1 percent and -3.0 percent, respectively. The Hewlett-Packard was more reliable and valid during hypoxemia, with a mean bias of -1.0 percent. The Nellcor read significantly more accurately in the six patients with severe digital clubbing than in the three patients with mild digital clubbing. It is important to be aware of possible limitations of noninvasive oximeters before accepting them as accurate.

    Title The Prognostic Value of Exercise Testing in Patients with Cystic Fibrosis.
    Date December 1992
    Journal The New England Journal of Medicine
    Excerpt

    BACKGROUND. Previous studies have shown female sex, impaired pulmonary function, older age, malnutrition, and colonization of the respiratory tract with Pseudomonas cepacia to be associated with a poor prognosis in patients with cystic fibrosis. We sought to determine the prognostic value of exercise testing in addition to the other prognostic factors. METHODS. A total of 109 patients with cystic fibrosis, 7 to 35 years old, underwent pulmonary-function and exercise testing in the late 1970s. They were followed for eight years to determine the factors associated with subsequent mortality. Survival rates were calculated with standard life-table methods. Cox proportional-hazards regression models were used to determine crude relative risks of mortality and relative risks adjusted for age, sex, body-mass index, forced expiratory volume in one second (FEV1) end-tidal partial pressure of carbon dioxide (PCO2) at peak exercise, and oxygen consumption at peak exercise (VO2 peak). RESULTS. Patients with the highest levels of aerobic fitness (VO2 peak, > or = 82 percent of predicted) had a survival rate of 83 percent at eight years, as compared with rates of 51 percent and 28 percent for patients with middle (VO2 peak, 59 to 81 percent of predicted) and lowest (VO2 peak, < or = 58 percent of predicted) levels of fitness, respectively. After adjustment for other risk factors, patients with higher levels of aerobic fitness were more than three times as likely to survive than patients with lower levels of fitness. Colonization with P. cepacia was associated with a risk of dying that was increased fivefold. Age, sex, body-mass index, FEV1, and end-tidal PCO2 at peak exercise were not independently correlated with mortality. CONCLUSIONS. Higher levels of aerobic fitness in patients with cystic fibrosis are associated with a significantly lower risk of dying. Although better aerobic fitness may simply be a marker for less severe illness, measurement of VO2 peak appears to be valuable for predicting prognosis. Further research is warranted to determine whether improving aerobic fitness through exercise programs will result in a better prognosis.

    Title Abatement of Exertional Perceptions Following Dynamic Exercise: Physiological Mediators.
    Date April 1992
    Journal Medicine and Science in Sports and Exercise
    Excerpt

    Perceptual and physiological congruity was examined during recovery from high-intensity dynamic exercise. Nine males (24.8 +/- 0.6 yr; VO2max; 52.3 +/- 1.5 ml.kg-1.min-1) undertook in random order four maximal treadmill protocols. Treadmill speed was held constant (5.3 km.h-1) while grade was incremented by 2, 4, 6, or 8% every 3 min for protocols A, B, C, and D, respectively. Ratings of perceived exertion (RPErec; Borg 15-point scale), ventilation (VE), respiratory rate (RR), oxygen uptake (VO2), and heart rate (HR) were measured preexercise and during each min of a 12-min supine postexercise period that immediately followed treadmill testing. Ratings were obtained for the peripheral perceptual signal arising from the legs (RPErec-L), the respiratory-metabolic signal from the chest (RPErec-C), and the overall body signal (RPErec-O). Blood pH was measured preexercise and during min 1, 6, and 12 of recovery. RPErec-L and RPErec-O were lower (P less than 0.05) and blood pH higher (p less than 0.05) following protocol A than D at all recovery time points. RPErec-C, VE, and RR were lower (P less than 0.05) for protocol A than D at all recovery time points. Differences among protocols were not noted for VO2 or HR at any recovery time point. The decay in signal strength for both RPErec-L and RPErec-O following high-intensity exercise reflected the abatement of metabolic acidosis. RPErec-O was influenced by the abatement of pulmonary ventilation during the postexercise period.

    Title Exercise Performance and Breathing Patterns in Cystic Fibrosis: Male-female Differences and Influence of Resting Pulmonary Function.
    Date June 1991
    Journal Pediatric Pulmonology
    Excerpt

    Despite improved prognosis for patients with cystic fibrosis (CF), they continue to suffer from progressive decline in pulmonary function and exercise tolerance. Beyond puberty, female patients have greater loss of pulmonary function and higher mortality than males, yet no one has studied male-female differences in exercise tolerance among patients. We therefore compared the responses to progressive exercise in 58 male and 52 female patients with CF and analyzed the influence of resting pulmonary function and gender on these responses and on breathing patterns during exercise. Within each of three pulmonary function groups (group 1: FEV1 greater than or equal to 65% predicted; group 2: FEV1 = 50-64% predicted; and group 3: FEV1 less than 50% predicted), female patients had lower exercise tolerance than males. This was reflected in the overall group for each gender: males' peak work load was 130 +/- 64 W, females' 111 +/- 32 W (P = 0.04); males' peak oxygen consumption, 36.9 +/- 11.4 mL/kg/min and females', 31.0 +/- 7.4 mL/kg/min (P = 0.0006). There was no interactive effect between gender and pulmonary function. Neither respiratory rate nor tidal volume differed between sexes. Male and female patients, irrespective of disease severity, employed similar proportions of their ventilatory capacity at exhaustion; group mean minute ventilation to maximum voluntary ventilation ratio ranged from 62.9 to 78.3%, with no apparent relationship to disease severity.

    Title Quality of Well-being Before and After Antibiotic Treatment of Pulmonary Exacerbation in Patients with Cystic Fibrosis.
    Date December 1990
    Journal Chest
    Excerpt

    General quality of life has only recently been measured with an objective tool in patients with cystic fibrosis (CF), and there have been no reported attempts to document changes in patients' overall well-being over time, as patients deteriorate or respond to intervention. We applied the Quality of Well-Being scale (QWB) in 28 patients with CF before and after a two-week course of oral ciprofloxacin used to treat pulmonary exacerbations. There were significant correlations between changes in QWB and various pulmonary function test results; QWB vs FEV1: r = 0.4, p less than 0.03; QWB vs FVC: r = 0.5, p less than 0.01; and QWB vs SaO2: r = 0.4, p less than 0.05. Thus, the QWB can track changes in general well-being in CF patients over a brief time and detect changes associated with pulmonary exacerbation and its treatment.

    Title Oxygen Supplementation During Exercise in Cystic Fibrosis.
    Date November 1990
    Journal The American Review of Respiratory Disease
    Excerpt

    Fourteen female and 22 male patients with cystic fibrosis (CF), 8 to 29 yr of age, performed two progressive exercise tests to exhaustion on a cycle ergometer, breathing normoxic air (21% O2) for one test, and hyperoxic air (30% O2) for the other test. The order of gas administration was randomized. Minute ventilation (VE), oxygen uptake (VO2), end-tidal CO2 tension (PETCO2), work rate, oxyhemoglobin saturation (SAO2), and heart rate (HR) were measured throughout the tests. The SaO2 of 11 patients at peak exercise was 90% or less ("Low Sat" group). The SaO2 of 23 patients remained above 90% throughout the exercise ("High Sat" group). Hyperoxic air minimized desaturation during exercise in the Low Sat group to 2 +/- 2% compared to a decrease of 10 +/- 5% with normoxic air. The decrease in saturation was not significant for the High Sat group (1 +/- 1% for both 21% and 30% O2). Peak work rate and VO2 did not differ significantly between normoxic and hyperoxic conditions. However, VE and HR at peak exercise tended to be lower, and PETCO2 was higher during peak exercise with 30% O2 than 21% O2 for both groups. During submaximal exercise, O2 desaturation was diminished and HR was significantly lower with supplemental O2, specifically in the Low Sat group. VE was significantly lower for both groups during submaximal exercise with hyperoxic air. The results suggest that O2 supplementation minimizes O2 desaturation and enables patients with CF to exercise with reduced ventilatory and cardiovascular work.

    Title Impact of Physical Fitness and Glycemic Control on in Vivo Insulin Action in Adolescents with Iddm.
    Date March 1990
    Journal Diabetes Care
    Excerpt

    The relationship of in vivo insulin-mediated glucose utilization to the state of physical fitness and the degree of glycemic control was examined in 27 adolescents with insulin-dependent diabetes mellitus (IDDM) compared with 10 nondiabetic adolescent control subjects. In vivo total-body insulin-mediated glucose metabolism was evaluated by the hyperinsulinemic-euglycemic clamp. Physical fitness was assessed by maximal oxygen consumption (VO2 max) during cycle ergometry. Patients and control subjects had similar levels of VO2 max (34.9 +/- 8.6 vs. 38.6 +/- 9.9 ml.kg-1.min-1, P = 0.3). Patients had lower total-body insulin-mediated glucose metabolism compared with control subjects (33.9 +/- 14.3 vs. 63.8 +/- 17.2 mumol.kg-1.min-1, P = 0.0002). Among the patients, females had lower total-body insulin-mediated glucose metabolism compared with males (24.2 +/- 2.8 vs. 40.7 +/- 3.4 mumol.kg-1.min-1, P less than 0.001); however, this difference disappeared after correcting for sex differences in fitness levels. Insulin-mediated glucose metabolism correlated with VO2 max in patients and control subjects (r = 0.83, r = 0.81, P less than 0.05). The regression of total-body insulin-mediated glucose metabolism on VO2 max for patients was -2.84 +/- 0.255 VO2 max and for control subjects was 7.12 +/- 0.143 VO2 max, indicating that for similar degrees of physical fitness patients have lower total body insulin-mediated glucose metabolism levels than control subjects. In patients, total-body insulin-mediated glucose metabolism correlated with the degree of glycemic control as assessed by the level of glycosylated hemoglobin (r = -0.63, P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

    Title Exercise Testing in Children.
    Date March 1989
    Journal Pediatric Pulmonology
    Title The Quality of Well-being in Cystic Fibrosis.
    Date March 1989
    Journal Chest
    Excerpt

    Traditional outcome measures in CF include PFTs, exercise tests, and several scoring systems that depend on pulmonary status and are largely subjective. The Quality of Well-being scale (QWB) is a widely used tool for measuring quality of life by three subscales: mobility, physical activity, and social activity, with points assigned within each subscale. The QWB has been shown to be valid in patients with COPD. We administered the QWB scale to 44 patients with CF, aged 7 to 36 years, and examined the relationship between QWB and PFTs, and in 15 patients the QWB vs exercise performance (peak VO2) on a progressive cycle ergometer test. QWB was significantly correlated with each variable examined: QWB vs FEV1, r = 0.5518 (p less than .0001); QWB vs FEF25-75%, r = 0.4793 (p less than .001); QWB vs PEFR, r = 0.4018 (p less than .01); QWB vs peak VO2, r = 0.5778 (p less than .01). The QWB scale is an objective measure that is significantly correlated with measures of performance and pulmonary function in CF. The relationship is not one of identity; further, the QWB is broad based and takes into account general well-being, not just pulmonary health, adding an important dimension to the care of patients with CF.

    Title Effect of Simulated Altitude Erythrocythemia in Women on Hemoglobin Flow Rate During Exercise.
    Date July 1988
    Journal Journal of Applied Physiology (bethesda, Md. : 1985)
    Excerpt

    The effect of simulated altitude erythrocythemia on hemoglobin flow rate and maximal O2 uptake (VO2max) was determined for nine women sea-level residents. Test conditions included normoxia and normobaric hypoxia (16% O2-84% N2). Cycle tests were performed under normoxia (T1-N) and hypoxia (T1-H) at prereinfusion control and under hypoxia 48 h after a placebo infusion (T2-H) and 48 h after autologous infusion of 334 ml of erythrocytes (T3-H). Hematocrit (38.1-44.9%) and hemoglobin concentration (12.7-14.7 g.dl-1) increased from control to postreinfusion. At peak exercise, VO2max decreased from T1-N (2.40 l.min-1) to T1-H (2.15 l.min-1) then increased at T3-H (2.37 l.min-1). Maximal arterial-mixed venous O2 difference decreased from T1-N to T1-H and increased at T3-H. Cardiac output (Q), stroke volume, heart rate, and total peripheral resistance during maximal exercise were unchanged from T1-N through T3-H. Hemoglobin flow rate (Hb flow) at maximum did not change from T1-N to T1-H but increased at T3-H. When compared with submaximal values for T1-N, VO2 was unchanged at T1-H and T3-H; Q increased at T1-H and decreased at T3-H; arterial-mixed venous O2 difference decreased at T1-H and increased at T3-H; Hb flow did not change at T1-N but increased at T3-H. For young women, simulated altitude erythrocythemia increased peak Hb flow and decreased physiological altitude (227.8 m) but did not affect maximum cardiac output (Qmax).

    Title Hemoglobin Concentration and Aerobic Work Capacity in Women Following Induced Erythrocythemia.
    Date October 1984
    Journal Journal of Applied Physiology: Respiratory, Environmental and Exercise Physiology
    Excerpt

    The effect of induced erythrocythemia on hemoglobin concentration ([Hb]) and aerobic work capacity was determined for nine women. Cycle tests were performed at prereinfusion (T1), 2 days after a placebo infusion (T2), 2 days postreinfusion of 334 ml of red blood cells (T3), 8 days postreinfusion (T4), and 14 days postreinfusion (T5). T1 and T2 responses did not differ, negating a placebo effect. [Hb] increased from 12.7 g X dl at T1 to 14.7 g X dl at T3 and then remained constant at T4 and T5. Hematocrit increased from 38.1% at T1 to 44.9% at T3 and then remained constant at T4 and T5. Submaximal O2 uptake (VO2) and stroke volume (SV) did not change from T1 through T5. Submaximal cardiac output (Q) and heart rate (HR) decreased from T1 to T3 and then remained constant at T4 and T5. Arteriovenous O2 difference increased from T1 to T3 and then remained constant at T4 and T5. Maximal VO2 was greater at T3 (2.65 l X min-1), T4 (2.66 l X min-1), and T5 (2.60 l X min-1) than at T1 (2.41 l X min-1). Physical work capacity was greater at T3 (10,740 kg X m), T4 (10,980 kg X m), and T5 (10,380 kg X m) than at T1 (8,747 kg X m). Maximal values for Q, HR, and SV were unchanged from T1 through T5. At maximum, arteriovenous O2 difference and Hb flow rate increased from T1 to T3 and then remained constant at T4 and T5. The greater postreinfusion [Hb] improved O2 transport capacity and appeared to regulate circulatory responses.


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