ECG parameters and exposure to carbon ultrafine particles in young healthy subjects.

The mechanisms underlying the association between air pollution and cardiovascular morbidity and mortality are unknown. This study aimed to determine whether controlled exposure to elemental carbon ultrafine particles (UFP) affects electrocardiogram (ECG) parameters describing heart rate variability; repolarization duration, morphology, and variability; and changes in the ST segment. Two separate controlled studies (12 subjects each) were performed using a crossover design, in which each subject was exposed to filtered air and carbon UFP for 2 hours. The first protocol involved 2 exposures to air and 10 microg/m(3) (approximately 2 x 10(6) particles/cm(3), count median diameter approximately 25 nm, geometric standard deviation approximately 1.6), at rest. The second protocol included 3 exposures to air, 10, and 25 microg/m(3) UFP (approximately 7 x 10(6) particles/cm(3)), with repeated exercise. Each subject underwent a continuous digital 12-lead ECG Holter recording to analyze the above ECG parameters. Repeated measures analysis of variance (ANOVA) was used to compare tested parameters between exposures. The observed responses to UFP exposure were small and generally not significant, although there were trends indicating an increase in parasympathetic tone, which is most likely also responsible for trends toward ST elevation, blunted QTc shortening, and increased variability of T-wave complexity after exposure to UFP. Recovery from exercise showed a blunted response of the parasympathetic system after exposure to UFP in comparison to air exposure. In conclusion, transient exposure to 10-25 microg/m(3) ultrafine carbon particles does not cause marked changes in ECG-derived parameters in young healthy subjects. However, trends are observed indicating that some subjects might be susceptible to air pollution, with a response involving autonomic modulation of the heart and repolarization of the ventricular myocardium.

Changes in fluorescence intensity of selected leukocyte surface markers following fixation.

BACKGROUND: Immunophenotyping of blood leukocytes often involves fixation with paraformaldehyde prior to cytometry analysis. However, the influence of cell type and marker specificity on the stability of fluorescence intensity after fixation has not been well studied. METHODS: Human whole blood was stained using a panel of fluorescein isothiocyanate-labeled antibodies to surface markers. Unfixed and fixed samples were analyzed by flow cytometry at 0, 2, 4, 6, 24, 48, and 96 h after staining. Fluorescence measurements were converted to molecules of equivalent soluble fluorochrome for comparison. RESULTS: Fixation caused a significant decrease in both forward and side scatter at 48 h which required gating adjustments to achieve resolution of cell populations. The autofluorescence increased progressively in fixed samples (ninefold at 96 h for monocytes). Variable decreases in marker-associated fluorescence became apparent after correction for autofluorescence. The magnitude of the decrease at 96 h varied with cell type and marker, from 5% for CD32 on monocytes to 39% for CD16 on neutrophils. CONCLUSION: The change in fluorescence intensity following staining and fixation of leukocytes varies with cell type and surface marker. Fluorescence stability should be determined for each cell type and marker used, and the confounding effects of fixation on cell autofluorescence should be considered.

Ultrafine particle deposition in humans during rest and exercise.

Ultrafine particles (diameter < 100 nm) may be important in the health effects of air pollution, in part because of their predicted high respiratory deposition. However, there are few measurements of ultrafine particle deposition during spontaneous breathing. The fractional deposition for the total respiratory tract of ultrafine carbon particles (count median diameter = 26 nm, geometric standard deviation = 1.6) was measured in 12 healthy subjects (6 female, 6 male) at rest (minute ventilation 9.0 +/- 1.3 L/min) using a mouthpiece exposure system. The mean +/- SD fractional deposition was 0.66 +/- 0.11 by particle number and 0.58 +/- 0.13 by particle mass concentration, similar to model predictions. The number deposition fraction increased as particle size decreased, reaching 0.80 +/- 0.09 for the smallest particles (midpoint count median diameter = 8.7 nm). No gender differences were observed. In an additional 7 subjects (2 female, 5 male) alternating rest with moderate exercise (minute ventilation 38.1 +/- 9.5 L/min), the deposition fraction during exercise increased to 0.83 +/- 0.04 and 0.76 +/- 0.06 by particle number and mass concentration, respectively, and reached 0.94 +/- 0.02 for the smallest particles. Experimental deposition data exceeded model predictions during exercise. The total number of deposited particles was more than 4.5-fold higher during exercise than at rest because of the combined increase in deposition fraction and minute ventilation. Fractional deposition of ultrafine particles during mouth breathing is high in healthy subjects, and increases further with exercise.