Single crystal Er3+ : YAG fibers with tailored refractive index profiles.

Erbium-doped yttrium aluminum garnet (Er3+:YAG) rods were inserted inside undoped tubes and grown into single-crystal fibers of a diameter of 300 µm using the laser-heated pedestal growth technique. Growth at various rates resulted in radially graded distributions of Er3+ dopant ions, as observed using laser-induced fluorescence imaging. Profiles of the refractive index were measured using cross-sectional reflectometry in a microscope. Dopant distributions and the corresponding index profiles were compared with thermal diffusion theory to determine the inter-diffusion coefficient of Y3+ and Er3+ ions at 2000°C, yielding an estimated value of D=(9.10±0.8)×10-11 m2/s. This work constitutes a step toward controlled growth of fibers with high thermal conductivities, low Brillouin gain, and waveguiding properties required for high-power optical amplifier and laser applications.

Oronasal distribution of ventilation at different ages.

The route of breathing, oral or nasal, is a determinant of the doses of inhaled pollutants delivered to target sites in the upper and lower respiratory tracts. We measured partitioning of ventilation, using a divided oronasal mask during a submaximal exercise test, in 37 male and female subjects who ranged in age from 7 to 72 y. The following four patterns of breathing were evident during exercise: (1) nasal only (13.5%), nasal shifting to oronasal (40.5%), oronasal only (40.5%), and oral only (5.4%). Children (i.e., 7-16 y of age) displayed more variability than adults with respect to their patterns of ventilation with exercise. Young adults (i.e., 17-30 y of age) who initially breathed nasally with exercise switched to oral ventilation at a lower percentage of the previously measured maximum ventilation (10.8%) than older subjects (31.8%). The partitioning of ventilation between the nasal and oral routes follows complex patterns that cannot be predicted readily by the age, gender, or nasal airway resistance of the subject.

Cross-training between cycling and running in untrained females.

OBJECTIVE: The purpose of the study was to evaluate the cross-training response between running and cycling in untrained females. EXPERIMENTAL DESIGN: The following study involved a pretest, post-test, 3 x 3 factorial design. SETTING: Training (4 days-week-1, 10 weeks, 70-80% heart rate reserve) occurred at the Center for Exercise and Applied Human Physiology. Exercise testing occurred at the Veterans Hospital, Exercise Laboratory. PATIENTS AND PARTICIPANTS: Subjects included healthy, untrained females aged 18-25 years, (N = 18). INTERVENTION: Subjects were assigned to one of three (n = 6) training groups (run = R, cycle = C, both run and cycle = RC) matched on pre-training CE VO2max results. MEASURES: Graded treadmill run (TR) and cycle ergometer (CE) tests were performed on each subject to determine a mode specific VO2max and the lactate threshold (LT). Graded arm ergometer (AE) was performed to determine VO2max and heart rate and blood lactate at 20 and 40 Watts (W). Testing occurred prior to (0T), after 5 (5T) and after 10 weeks of training (10T). Body fat testing (hydrodensitometry at residual lung volume) was performed at 0T and 10T. RESULTS: TR and CE VO2max as well as TR and CE VO2 at the LT improved throughout the 10 weeks, regardless of training group. Although there were no changes in VO2max or blood lactate levels during AE, submaximal heart rates were significantly reduced over the 10 weeks, regardless of training group. CONCLUSIONS: These results indicate that the aerobic benefits of either run, cycle or combined run and cycle training are similar in untrained females. The LT and AE heart rate data demonstrate that improvements in VOmax due to ten weeks of training are a result of pronounced peripheral and moderate central adaptations.

Pre-exercise glycerol hydration improves cycling endurance time.

The effects of glycerol ingestion (GEH) on hydration and subsequent cycle ergometer submaximal load exercise were examined in well conditioned subjects. We hypothesized that GEH would reduce physiologic strain and increase endurance. The purpose of Study I (n = 11) was to determine if pre-exercise GEH (1.2 gm/kg glycerol in 26 ml/kg solution) compared to pre-exercise placebo hydration (PH) (26 ml/kg of aspartame flavored water) lowered heart rate (HR), lowered rectal temperature (Tc), and prolonged endurance time (ET) during submaximal load cycle ergometry. The purpose of Study II (n = 7) was to determine if the same pre-exercise regimen followed by carbohydrate oral replacement solution (ORS) during exercise also lowered HR, Tc, and prolonged ET. Both studies were double-blind, randomized, crossover trials, performed at an ambient temperature of 23.5-24.5 degrees C, and humidity of 25-27%. Mean HR was lower by 2.8 +/- 0.4 beats/min (p = 0.05) after GEH in Study I and by 4.4 +/- 1.1 beats/min (p = 0.01) in Study II. Endurance time was prolonged after GEH in Study I (93.8 +/- 14 min vs. 77.4 +/- 9 min, p = 0.049) and in Study II (123.4 +/- 17 min vs. 99.0 +/- 11 min, p = 0.03). Rectal temperature did not differ between hydration regimens in both Study I and Study II. Thus, pre-exercise glycerol-enhanced hyperhydration lowers HR and prolongs ET even when combined with ORS during exercise. The regimens tested in this study could potentially be adapted for endurance activities.

Hemodynamic effects of nasal and face mask continuous positive airway pressure.

Studies of the hemodynamic effects of nasal continuous positive airway pressure (n-CPAP) in normal subjects have had conflicting results. The largest study (n = 19) found no effect of up to 15 cm H2O on heart rate (HR), cardiac stroke volume (SV), or cardiac index. We hypothesized that n-CPAP, by increasing intrathoracic pressure, should decrease SV and cardiac output (CO) in a dose-dependent fashion in normal subjects. We also hypothesized that mouth position, i.e., open or closed, could affect intrathoracic pressure and thus SV and CO. Six normal subjects were tested with four levels of CPAP (5, 10, 15, and 20 cm H2O) under three mask conditions-face mask and nasal mask with the mouth open (mo) or with the mouth closed (mc). Noninvasive pulsed Doppler measurements of SV and HR were made under each condition. N-CPAP (mc) and face mask CPAP (f-CPAP) resulted in significant dose-dependent decreases of SV-24 +/- 5 ml (21%) and 33 +/- 5 ml (28%), respectively--from baseline to 20 cm H2O (p < 0.05). HR were unchanged and CO significantly decreased with n-CPAP(mc) and with f-CPAP, 1.6 +/- 0.38 L/min (23%) and 2.29 +/- 0.54 L/min (31%), respectively, from baseline to 20 cm H2O (p < 0.05). Esophageal pressure measurements verified increasing intrathoracic pressure with increasing levels of f-CPAP and n-CPAP (mc) but not with n-CPAP (mo). In conclusion, n-CPAP (mc) and f-CPAP resulted in significant and similar dose-dependent decreases in SV and CO.

Hyperoxic training increases work capacity after maximal training at moderate altitude.

High-intensity training may be difficult to sustain due to limitations in systemic oxygen transport, particularly at high altitudes. The purpose of this study was to examine the effects of a high-intensity training protocol using hyperoxic gas breathing in athletes "maximally trained" at an altitude of 1,600 m. Five subjects underwent progressive cycle training until they reached a plateau of aerobic capacity, maximal workload, and endurance time at 85 percent maximal workload. Significant decreases (2 to 6 percent) in arterial oxygen saturation were found after the 85 percent maximal workload tests. Training intensity was then increased to 95 percent maximal workload while the subjects breathed a gas mixture containing at least 70 percent oxygen. After 6 weeks of hyperoxic training, exercise parameters were compared with the plateau values obtained during the baseline training period. Total time during maximal cycle testing increased from 19.1 to 19.6 min (p = 0.015), heart rate at 85 percent maximal workload decreased from 168 to 163 bpm (p = 0.047), and endurance time at 85 percent maximal workload increased from 6.2 to 8.2 min (p = 0.012). There was a trend toward improvement of maximal workload. We conclude that hyperoxic training increases work capacity after attainment of "maximal training" at moderate altitude.

A comparison of the effects of nifedipine and verapamil on exercise performance in patients with mild to moderate hypertension.

Twenty-four patients completed a double-blind, randomized clinical trial comparing the effects of nifedipine GITS (N) and verapamil SR (V) on blood pressure (BP) control and exercise performance. After a 2-week placebo phase, all subjects had measurements of VO2max, maximal workload, and endurance time. They were then randomized to either N (30 to 90 mg/day) or V (240 to 480 mg/day) and retested when BPs had stabilized. At rest, N lowered systolic (S) BP by 12 mm Hg (P = .02 compared to baseline) and diastolic (D) BP by 11 mm Hg (P = .001). V lowered SBP by 8 mm Hg (P = .013) and DBP by 11 mm Hg (P = .002). Neither drug affected resting heart rate. V significantly decreased resting epinephrine (P = .05) and there was a tendency for V to reduce norepinephrine (P = .07) and dopamine (P = .08). N tended to increase plasma renin activity (P = .07). During graded cycle ergometry N, compared with placebo, significantly lowered DBP at all exercise levels (P = .011), but had no significant effect on heart rate (HR), SBP, or heart rate pressure product (HRPP). Pulse pressure (PP) was significantly increased (P = .045), which was most noticeable at high exercise levels. Compared with placebo, V caused a marked reduction of exercise HR (P < .001), which was more pronounced at high levels, SBP (P = .004), DBP (P = .004), mean arterial pressure (MAP) (P = .001), and HRPP (P < .001).(ABSTRACT TRUNCATED AT 250 WORDS)

Efficacy and safety of clarithromycin compared to cefixime as outpatient treatment of lower respiratory tract infections.

BACKGROUND: Clarithromycin is a new acid-stable, 14-membered macrolide active against many of the organisms responsible for lower respiratory tract infections. It has been administered to over 5,000 patients worldwide and has been shown to be a safe and effective treatment for acute bacterial exacerbations of chronic bronchitis and bacterial pneumonia when given twice daily (250 to 500 mg). Cefixime is an amino-thiazolyl cephalosporin with an extended spectrum of antibacterial activity inhibiting beta-lactamase-producing respiratory pathogens. It has a long half-life, allowing once-daily administration. METHODS: This randomized, double-blind multicenter study compared clarithromycin and cefixime as treatment for patients with community-acquired lower respiratory tract infections (n = 213). Patients had bacterial pneumonia (clarithromycin, 19 percent; cefixime, 21 percent) or acute bacterial exacerbation of chronic bronchitis or asthmatic bronchitis (clarithromycin, 81 percent; cefixime, 79 percent). Patients received 500 mg of clarithromycin twice daily (n = 103) or 400 mg of cefixime once daily (n = 110) for 7 to 14 days. RESULTS: Clinical cure or improvement occurred in 86 percent of the clarithromycin-treated patients and 88 percent of the cefixime-treated patients. When only patients with identified infections with Haemophilus influenzae, Moraxella catarrhalis, or Streptococcus pneumoniae were considered, clinical success rates were 97 percent for clarithromycin and 96 percent for cefixime; the rate of bacteriologic eradication was 91 percent for clarithromycin and 90 percent for cefixime. Adverse events occurred in 29 percent of the clarithromycin-treated patients and 23 percent of the cefixime-treated patients. CONCLUSIONS: This study demonstrates that clarithromycin and cefixime are effective treatments for pneumonia and acute bacterial exacerbations of bronchitis of mild to moderate severity caused by the most common infecting organisms.

Sources of variability in posterior rhinomanometry.

Sources of variability in nasal airway resistance measured by posterior rhinomanometry were studied in 5 subjects tested on 5 different days and 56 subjects tested on 2 different days. On each day, a questionnaire on upper airway health and nasal symptoms was completed. The mean individual difference in nasal airway resistance between the 2 test days in the group of 56 subjects was 5.3% (SD 52.7%). Between-subject variability accounted for 74.9% and 72.5% of the total variability in the group of 5 and the group of 56 subjects, respectively. For the 5 subjects, by accounting for a change in upper airway symptoms or upper respiratory tract infection that occurred over the 5 test days, there was a significant decrease in the between-subject variability. The difference in sources of variation due to a change in upper airway symptoms was not seen in the group of 56 subjects. We conclude that the largest source of variability in nasal airway resistance is due to between-subject differences.

Evaluation of the relationship between heart rate and ventilation for epidemiologic studies.

Estimation of pulmonary exposure and dose in air pollution epidemiology has been impaired by the lack of methods for directly measuring ventilation in ambulatory subjects. Heart-rate monitoring offers an approach to estimate ventilation by using ventilation-on-heart-rate (VE-HR) regressions established during exercise testing to estimate ventilation in the field. Conventional methods and protocols for testing were used to evaluate the relationship between VE and HR during three tasks: (1) exercising on a cycle ergometer, (2) lifting, and (3) vacuuming. The relationship between VE and HR was curvilinear and was best fit with linear regression models, using a natural log transformation of VE. Considerable interindividual variability in slopes and intercepts was observed across all types of exercise tests. The variability about the fitted regression lines for individual subjects was minimal; for example, individual R2 values for the maximum exercise test on 15 men ranged from 0.90 to 0.99 (mean = 0.97). The regression slopes established during upper-body exercise were greater by approximately 30%, relative to those derived in lower-body exercise (paired t test, p < .001). However, VE-HR regression slopes derived from tests in which progressively increasing workloads were used were comparable to those obtained during variable and nonprogressive protocols. These findings indicate that predictive accuracy is maximized by deriving VE-HR regressions for individual subjects and for both lower- and upper-body activities.

Assessment of heart rate as a predictor of ventilation.

The rate of ventilation and route of breathing (i.e., nasal versus oronasal) are potential determinants of pollutant doses to target sites in the lung. However, the lack of accurate methods for ambulatory measurement of ventilation has hindered estimation of exposure and dose in freely ranging individuals, complicating the interpretation of the relationships among exposure, dose, and response in epidemiological studies. The goal of this project was to develop and validate a method of monitoring ventilation for large-scale epidemiologic investigations. We estimated ventilation for individual subjects from ambulatory heart rate monitoring, using the relationship between ventilation and heart rate that had been obtained during exercise testing. Fifty-eight subjects participated in the study, which included healthy adults and children, and subjects with lung and heart disease. Subjects performed cycle exercise and tasks involving lifting and vacuuming. Work loads of progressive and variable order were used in the testing. Conventional methods were used to measure heart rate and total ventilation, and a sampling mask was developed to measure the partitioning of breathing between oral and nasal routes. The minute ventilation-heart rate relation was evaluated under steady-state and varying work loads. In a second phase, subjects wore wristwatch monitors that recorded their heart rates, minute by minute, throughout the day. Subjects recorded activities, locations, and levels of exertion. Two 16-hour monitoring periods were obtained from each subject. The laboratory findings documented considerable intersubject variability in the minute ventilation-heart rate relation with a two- to five-fold range in the coefficients describing the change in ventilation relative to heart rate. This variation implies that individual testing is required to derive accurate predictive equations. Minute ventilation-heart rate regressions for the maximal progressive exercise test and for the test with a nonprogressive submaximal work load sequence were comparable, indicating that varying the sequence of work loads does not substantially affect the minute ventilation-to-heart rate ratio. During upper body work (e.g., lifting), the minute ventilation-to-heart rate ratio was one-third greater than during lower body exercise. Diverse patterns of partitioning breathing between oral and nasal routes were observed with increasing oral ventilation in most subjects as work load increased. In the field, heart rate and activity patterns were monitored successfully in adults and children with low rates of instrument failure and noncompliance.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of acid-base status on acute hypoxic pulmonary vasoconstriction and gas exchange.

To investigate the relationship between hypoxic pulmonary vasoconstriction and respiratory and metabolic acidosis and respiratory alkalosis, the pulmonary gas exchange and pulmonary hemodynamic responses were measured in anesthetized, paralyzed, and mechanically ventilated dogs in two sets of experiments (series A, n = 6; series B, n = 10). The animals were treated with acute hypoxia, CO2 inhalation, hyperventilation, and dinitrophenol in various combinations. Multiple regression analysis indicated that mean pulmonary arterial pressure (Ppa) was significantly correlated with end-tidal PO2, mixed venous PO2, and the mean pulmonary capillary pH (average of arterial and mixed venous pH) as independent variables [series A: r = +0.999, standard error of estimate (SEE) = 0.4 mmHg; series B: r = +0.98, SEE = 1.4 mmHg]. Similar analyses of mean values published by other authors from an acute study on humans with exercise at sea level and simulated altitudes of 10,000 and 15,000 ft also indicated a good relationship (n = 14, r = +0.98, SEE = 2.1 mmHg). The mean data (n = 19) obtained in Operation Everest II at various exercise loads and simulated altitudes gave a correlation of r = +0.87, SEE = 6.1 mmHg. These empirical analyses suggest that variations in the rise of Ppa with hypoxia can be accounted for in vivo by the superimposed acid-base status. Furthermore, ventilation-perfusion inhomogeneity, as estimated in the dogs from end-tidal and arterial O2 and CO2 differences and assuming no true shunt or diffusion impairment, was highly correlated with Ppa and mean pulmonary capillary pH (r = +0.999 in series A, r = +0.77 in series B). The human data from the above studies also showed significant correlations between Ppa and directly measured ventilation-perfusion (standard deviation of perfusion obtained from inert gas measurements). These observations indicate that the beneficial effects of hyperventilation during hypoxia may be related to the marked alkalosis that serves to reduce Ppa and improve pulmonary gas exchange efficiency.

Neutrophil responses to intravascular pneumococcal sonicate.

Leukopenia and pulmonary leukostasis are prominent features in patients succumbing to pneumococcal (PNC) infections. We examined mechanisms involved in recruitment of polymorphonuclear neutrophils (PMNs) into pulmonary capillaries and alveolae after PNC sonicate injection. We showed that by 15 min postinjection, PMN chemotactic activity was found in bronchoalveolar lavage (BAL) fluids and increased with time until the end point of the study at 90 min. Accompanying the increased chemotactic activity in BAL fluids was a decrease in circulating PMNs more pronounced in the femoral artery (FA) than the pulmonary artery (PA). Superoxide anion (O2-) production by peripheral PMNs was depressed following PNC sonicate injection, and comparison of FA and PA showed that FA PMNs produced less O2- than PA PMNs. PA PMNs also showed enhanced random migration when compared to the depressed random migration of FA PMNs. This study demonstrated that an intravascular challenge of PNC sonicate was associated with increased chemotactic activity for PMNs in BAL fluid. Fewer PMNs and altered PMN function resulted from passage through the pulmonary microvasculature after PNC sonicate injection.

A multivariate model for the prediction of relapse after outpatient treatment of decompensated chronic obstructive pulmonary disease.

PURPOSE: To develop and validate a multivariate model for predicting relapses after treatment of decompensated chronic obstructive pulmonary disease in an emergency department. METHODS: A 5-year survey was conducted, including training and validation periods. Stepwise logistic regression was used to develop a multivariate predictive model using clinical data obtained at the time of each visit. A relapse was defined as an unscheduled return to the emergency department within 48 hours. SITE: The study was conducted in the emergency department of the Albuquerque (New Mexico) Veterans Affairs Medical Center. SUBJECTS: The subjects were 289 patients with documented chronic obstructive pulmonary disease. MEASUREMENTS AND MAIN RESULTS: During the first 3 years, there were 705 visits in which the patient was treated and released from the emergency department. Relapse occurred 82 times (11.6%). Logistic regression showed that the following variables had an effect on the risk of relapse: the relapse rate for previous visits, a previous visit within 7 days, long-term home oxygen therapy, the number of doses of nebulized bronchodilators, the administration of aminophylline, and the use of antibiotics and prednisone at the time of discharge from the emergency department. During the next 2 years, the 48-hour relapse rate was 9.9% (47 of 476 discharges). When the model was fitted to these data, all of the original variables contributed to the prediction of relapse except antibiotic use and long-term home oxygen therapy. The logistic model was used to categorize each visit during the validation phase. The relapse rate for "high-risk" visits was significantly higher than that for "low-risk" visits (18.4% vs 6.1%). The method identified 57.4% of visits that ended in relapse at 48 hours. CONCLUSIONS: A multivariate model can be used to identify patients with a poor prognosis after the outpatient treatment of decompensated chronic obstructive pulmonary disease.

A multivariate model for predicting hospital admissions for patients with decompensated chronic obstructive pulmonary disease.

PURPOSE: To develop a method for predicting hospital admissions for patients with decompensated chronic obstructive pulmonary disease treated in an emergency department. METHODS: A 4-year survey including training and validation periods was conducted. Stepwise logistic regression was used to develop a multivariate model using information from the patient's previous visits and results of baseline pulmonary function tests. MEASUREMENTS AND MAIN RESULTS: During the first 2 years, there were 693 visits to the emergency department for decompensated chronic obstructive pulmonary disease. The patient was admitted to the hospital on 210 occasions (30.3%). Logistic regression showed that the probability of admission was related to the following: the admission and relapse rates for previous visits, the proportion of previous discharges from the emergency department in which "conservative therapy" was given, the highest baseline post-bronchodilator forced expiratory volume in 1 second within 3 years of entry, and the highest baseline pre-bronchodilator forced expiratory volume in 1 second-vital capacity ratio. A relapse was defined as an unscheduled return to the emergency department within 48 hours. "Conservative therapy" was any treatment regimen that did not include parenteral medications. During the next 2 years, the model was validated with patients not previously treated at this medical center. Seventy-six (28.3%) of 269 episodes resulted in hospital admission. The logistic model was used to categorize each visit during the validation phase. "High-risk" visits had calculated probabilities of admission greater than .208, while "low-risk" visits had values that were less. The admission rate for 98 low-risk visits (8.2%) was much lower than the rate for 171 high-risk visits (39.8%). CONCLUSIONS: A multivariate model can be used to identify patients with decompensated chronic obstructive pulmonary disease who are unlikely to need hospitalization. This model could be used to select episodes of decompensated chronic obstructive pulmonary disease for treatment at home.

Cardiopulmonary responses to acute hypoxia, head-down tilt and fluid loading in anesthetized dogs.

The separate and combined acute effects of hypoxia (HY-11% O2), head-down tilt (HD-30 degrees) and fluid loading (FL-1.0 L saline) on hemodynamics and pulmonary gas exchange were determined in 17 anesthetized, mechanically ventilated dogs. Both during HY and normoxia (NO), the total respiratory compliance was decreased by HD, attributable to pulmonary vascular congestion. The reductions in compliance were twice as great with FL, indicating pulmonary interstitial edema, which was supported by histological observation of lung tissue. Pressure-flow relationships in the pulmonary circulation indicated that superimposing HD on HY doubled the increase in vascular resistance due to HY alone, while in the systemic circulation the resistance was returned to below NO by HD. A significant positive correlation between the changes in blood volume and pulmonary artery pressure for experimental transitions suggests that a shift in blood volume from systemic to pulmonary circulations and changes in total blood volume probably contributed substantially to these apparent changes in resistance. Pulmonary gas exchange efficiency, whether expressed in terms of shunt or ventilation/perfusion distribution from arterial-end-tidal PCO2 and PO2 differences, showed a significant inverse relationship with pulmonary driving pressure for the experimental conditions imposed. No clear synergistic effects of HY on HD were evident in contributing to pulmonary edema when superimposed prior to FL, but after FL this risk must be considered.

Treatment of decompensated chronic obstructive pulmonary disease in the emergency department--correlation between clinical features and prognosis.

STUDY OBJECTIVE: Patients with decompensated chronic obstructive pulmonary disease (COPD) are at high risk of relapse after treatment in an emergency department. The purpose of this study was to determine if the risk of relapse correlates with the clinical features of the disease. PATIENTS: Three hundred fifty-two patients with documented COPD who were treated for dyspnea in the ED of the Albuquerque Veterans Administration Medical Center over a three-year period. METHODS: We reviewed the clinical features and pulmonary function tests of the patients, who were considered to have COPD if the baseline prebronchodilator one-second forced expiratory volume (FEV1) was less than 80% predicted, and less than 80% of the forced vital capacity and inhaled bronchodilators failed to increase the FEV1 to levels of more than 80% predicted. Visits for pneumonia, pneumothorax, pleural effusion, or pulmonary emboli were excluded. A relapse was defined as an unscheduled revisit to the ED within 14 days of initial treatment. Data were entered into a microcomputer data base and analyzed by a commercial statistical package. RESULTS: Of 877 visits in which the patient was treated and released from the ED, 281 (32.0%) resulted in relapse and were considered unsuccessful Compared with successful visits, unsuccessful visits were characterized by a shorter duration of dyspnea (P = .002), a lower entry FEV1 (P = .027), a lower discharge FEV1 (P = .040), a greater number of treatments with nebulized bronchodilators (P = .009), more frequent use of parenteral adrenergic drugs (P = .006), and less frequent use of oral prednisone on discharge (P = .016). Patients with one or more relapse visits during the study period (relapsers) differed from nonrelapsers in several respects. Relapsers had a greater bronchodilator response on baseline FEV1 than nonrelapsers (P = .047). Nevertheless, relapsers required more bronchodilator treatments in the ED (P less than .001); were treated more frequently with parenteral adrenergic drugs (P less than .001), IV glucocorticoids (P less than .001), and oral prednisone (P less than .001); and recovered less of their baseline FEV1 (P less than .014). CONCLUSION: Bronchodilator response on baseline pulmonary function testing appears to identify patients with COPD who have a poor prognosis after emergency treatment. Their poor response to intensive bronchodilator treatment suggests that loss of bronchodilator response may be involved in the pathogenesis of respiratory decompensation.

The effect of aging on submaximal exercise performance and recovery.

The upward drift of gas exchange variables during 70% maximal exercise and recovery half-times in aged and young subjects of equivalent age-predicted aerobic capacity was measured. In the aged subjects, upward drift of VE, VO2, and HR was reduced compared with the young group. The recovery of VE, VCO2, and VO2 was slowed in the aged. However, at 10 minutes post-exercise, VCO2, VO2, and HR had returned to similar relative values for both groups; in the young subjects VE remained elevated at the end of recovery. The reduced upward drift of gas exchange variables and HR during exercise in aged subjects is consistent with an attenuated response of glycogenolysis and lactate production to adrenergic stimulation and/or to selective loss of type II skeletal muscle fibers. The slowed recovery of VE, VCO2, and VO2 in elderly persons is consistent with age-related reduced CO2 chemosensitivity, delaying elimination of the exercise-induced CO2 load.

Aminophylline in the outpatient management of decompensated chronic obstructive pulmonary disease.

The objective of this study was to determine if IV aminophylline reduces the risk of relapse after treatment of decompensated COPD in an ED. Forty-six visits in which IV aminophylline was given (T visits) were compared with an equal number of visits in which it was withheld (N visits) with respect to pretreatment serum theophylline level, number of treatments with nebulized bronchodilators and use of parenteral beta-adrenergic drugs, IV corticosteroids and prednisone. The difference in 48-h relapse rates for T and N visits was examined by McNemar's test. No differences were found between T and N visits with respect to vital signs, pretreatment FEV1, arterial blood gas values, hematocrit level or blood leukocyte count. The 48-h relapse rate for T visits (22.2 percent) was significantly higher than for N visits (6.7 percent; p = 0.035). Aminophylline does not appear to be beneficial for outpatients with decompensated COPD and may be harmful.

Rate-adaptive cardiac pacing in children using a minute ventilation biosensor.

Chronotropic integrity is required for a normal cardiac output response to exercise. We evaluated a rate-adaptive ventricular demand pacemaker (Telectronics, META-MV) which uses minute ventilation as the sensed physiological variable for adjusting pacing rate, in seven young patients with a mean age of 11.4 years. All patients had clinically significant bradycardia related to complete heart block (n = 4) or sinus node dysfunction (n = 3). For the entire group, paced heart rates increased from 70 +/- 10 beats/min to 151 +/- 19 beats/min with exercise testing. The onset of rate adaptation took less than 30 seconds. Changes in paced rate were linearly related to workload, VO2 (5.9 to 20.7 mL/min/kg) and minute ventilation (8-65 L/min). The decline in pacing rate after exercise was related directly to the gradual decrease in minute ventilation and VO2. Our data show that minute ventilation closely and accurately reflects the metabolic demands of varying workloads in children and can be used to achieve physiological, rate-adaptive pacing.