Correlation between reversibility of airway obstruction and exhaled nitric oxide levels in children with stable bronchial asthma

Recent trials measuring exhaled nitric oxide (eNO) concentrations have suggested that it may be a useful measure of ongoing airway inflammation in patients with asthma. The purpose of this study was to examine the relationship between eNO levels and baseline as well as postbronchodilator spirometry, a measurement commonly used in the clinical setting to determine the severity of asthma and as a guide to therapeutic decisions. Forty-nine patients between the ages of 5-16 years with physician-diagnosed asthma who attended the pediatric pulmonary clinic for a routine asthma visit with spirometric evaluation were recruited for the study. eNO levels prior to spirometry were obtained before and after receiving inhaled beta(2) agonist. eNO samples were collected in impermeable bags (Tedlar) and assayed within 24 hr by chemiluminescence. Regression analysis was used to assess the relationships between pre- and postbronchodilator eNO and spirometric variables. eNO was also compared in patients receiving and not receiving inhaled corticosteroids (ICS), as well as those whose therapy had been increased after evaluation by a pediatric pulmonologist or allergist. We found no significant difference between the levels of eNO before and after inhalation of beta(2) agonist (P = 0.60 paired t-test). Positive correlation was found between eNO vs. percentage change in FEV(1) (r = 0.35, P = 0.01) and percentage change in FEF(25-75% )(r = 0.29, P = 0.04). A negative correlation was found between prebronchodilator FEV(1) and eNO (r = -0.29, P = 0.03). Patients on ICS had lower mean eNO levels (29.9 vs. 47.6 parts per billion (ppb), P = 0.053) than those not receiving ICS. Patients whose ICS therapy was increased had higher mean eNO levels (47.2 vs. 26.9 ppb, P = 0.018) than those not having ICS therapy increased. We suggest that eNO levels could be a clinically useful measurement of asthma severity and could be used as an adjunct to spirometry to determine appropriate treatment plans. Longitudinal clinical trials are needed to determine if eNO can enhance therapeutic decisions for asthmatic children.

Degradation of histamine solutions used for bronchoprovocation

STUDY OBJECTIVES

To determine optimal storage conditions for histamine diphosphate (HDP) solutions used for bronchoprovocation.

DESIGN

HDP was dissolved in buffered saline solution to concentrations of 0.125 to 16 mg/mL and stored in 3-mL unit dose syringes at different temperatures for varying lengths of time, with and without protection from fluorescent light.

SETTING

Dark freezer (-20 degrees C), dark refrigerator (4 degrees C), and laboratory counter top (20 degrees C) illuminated by fluorescent light (375 foot-candles).

MEASUREMENTS

HDP concentrations were measured after the solutions were prepared and during storage by a high-performance liquid chromatographic assay that differentiates histamine from its break down products.

RESULTS

All dilutions were sterile after preparation and contained 97 to 110% of the labeled amount of HDP. Solutions constantly exposed to fluorescent light (375 foot-candles) and room temperature (20 degrees C) contained only 20 to 37% of the initial concentrations after 7 days. The same dilutions stored at room temperature, but protected from light, contained 83 to 94% of the initial concentrations. Dilutions stored in the dark in a refrigerator (4 degrees C) retained 97% of the initial concentrations after 8 weeks, while dilutions stored in the dark freezer (-20 degrees C) were stable for 12 months.

CONCLUSIONS

Exposure to fluorescent light at room temperature results in degradation of histamine solutions used for bronchoprovocation. Dilutions stored in unit dose syringes and protected from light are stable for at least 8 weeks in the refrigerator and up to 12 months frozen. Once removed from the refrigerator or freezer, the solutions should be used within 6 h or discarded.

Apparent decrease in population clearance of theophylline: implications for dosage

BACKGROUND

Having observed in recent years that the theophylline dose requirements needed to attain peak serum concentrations of 10 to 20 micrograms/ml infrequently reached previously described mean values, we hypothesized that a downward shift in the range of dose requirements had occurred among patients with asthma.

STUDY DESIGN

We examined dosage requirements needed to attain peak serum concentrations of 10 to 20 micrograms/ml in all patients with chronic asthma treated with theophylline by the Pediatric Allergy and Pulmonary Clinic at the University of Iowa from 1990 to 1994 (n = 300) and at the Pediatric Pulmonary Clinic at the University of Florida from 1992 to 1995 (n = 93). We then compared these doses to previous dose requirements from 1978 to 1983 determined in the same manner.

RESULTS

Despite similar mean peak serum concentrations during both time periods (14 micrograms/ml), mean theophylline dosage requirements during the period of this study were approximately 25% lower among all age groups than those previously observed (p < 0.001). There were no significant differences in mean dosage requirements between the Iowa and Florida patients in any age group examined.

CONCLUSIONS

Theophylline dose requirements needed to attain serum concentrations of 10 to 20 micrograms/ml have decreased significantly from those on which current dosing recommendations are based. This suggests a decrease in mean clearance of the population.

Reliability of the Medtrac MDI Chronolog

BACKGROUND

The Medtrac MDI Chronolog is an electronic device for monitoring adherence to metered-dose inhalers. It replaces previous models of the Nebulizer Chronolog and uses a different mechanism of recording actuations.

OBJECTIVE

This study was carried out to determine whether the new model can accurately record and report the date, time, and number of metered-dose inhaler actuations.

METHODS

Four canisters of beclomethasone (Beclovent) were discharged through four Chronologs with fresh batteries at a rate of 1, 2, 4, or 8 times twice daily for 7 days. Four additional canisters were used as controls and discharged simultaneously through the standard actuator. The weight of all canisters and Chronolog battery voltage were measured before and at the end of the 7-day experiment. The data retrieved from the Chronologs were compared with the information recorded manually during each discharge.

RESULTS

The loss in canister weight was consistent for the number of puffs discharged from all four Chronolog units and controls. However, the accuracy of the Chronologs in recording the number of actuations varied between 50% and 100%. The largest amount of data loss occurred with the unit used to discharge 8 puffs and was associated with a dead battery at the end of the 7-day trial. For actuations that were retrievable, the Chronologs accurately recorded the date and time.

CONCLUSIONS

Unexpected battery voltage drain and other mechanical problems that we encountered may cause data loss and the false appearance of missed doses. Thus the units that we tested were not sufficiently reliable to monitor patient adherence.