Atmospheric remote sensing to detect effects of temperature inversions on sputum cell counts in airway diseases☆
Introduction
There is accumulating evidence to suggest that air pollution is a risk factor in the development and exacerbation of lung diseases (e.g. Pope and Dockery, 2006). Geography and meteorology play critical roles in the dilution and dispersion of air pollution from source locations, through vertical mixing and horizontal transport. Vertical mixing is facilitated by upward motion of warm air near the surface, to cold air above. In cases where this temperature profile is reversed and warm air lies above colder air at the surface, vertical motion is restricted (Oke, 1987). This sets up a temperature inversion, which is characterised by stable atmospheric conditions, and results in the accumulation of air pollution. Horizontal wind speeds are also reduced, limiting transport of pollutants downwind. The resulting poor air quality may lead to increased hospitalization or premature death in susceptible populations (Holzworth, 1972, Abdul-Wahab et al., 2005, Laskin, 2006, Malek et al., 2004, Carder et al., 2008, Palmieri et al., 2008).
The subjects of this study reside in the Hamilton Census Metropolitan Area (Fig. 1), an urban area affected by emissions from industry and traffic, and frequent temperature inversions. The development of inversions is driven by the city’s topography, its location on the shores of Lake Ontario and regional meteorology. The Niagara Escarpment is a 90 m high scarp, which divides the study area into an upper plateau and a lower near-shore strip (Fig.1). It promotes the development of advective inversions, which are formed when cold air from the lake flows under warm air from the plateau. Radiation inversions are most common at nighttime and develop when the Earth’s surface loses heat rapidly through thermal radiation, causing the temperature of the air above the ground to become warmer than at the surface. They are most likely to occur on clear, cloudless nights. Regional high pressure systems create subsidence inversions which may last for several days. Daytime inversions occur most often in the spring (37%) and winter (36%) and less frequently in the fall (17%) and summer (10%). While daytime inversions are not as frequent as night-time inversions (Wallace and Kanaroglou, 2009a, Wallace and Kanaroglou, 2009b), the exposure impact is higher, since most people are attending to daily activities during the daylight hours. In addition, many daytime inversions follow a previous night-time inversion, leading to prolonged build-up of pollution. Recent studies highlight a distinct increase in concentrations of pollution during temperature inversions in Hamilton (Wallace and Kanaroglou, 2009a, Wallace and Kanaroglou, 2009b). We investigate whether there is an association between airway inflammation and the occurrence of temperature inversions over the region.
Airway inflammation and bronchitis can be reliably assessed using quantitative cell counts in sputum (Pizzichini et al., 1996). Associations between air pollution and cell counts have been identified in the literature. Nobutomo (1978) observed higher neutrophil counts in sputum of persons who lived in polluted environments, and also determined that the inflammatory response preceded the appearance of symptoms. Dragonieri et al. (2006) identified increased neutrophils, as a percent of the total cell counts, in sputum of traffic policemen, and Fireman et al. (2004) made similar observations in firefighters exposed to the World Trade Center disaster. Bosson et al. (2008) and Graff et al., (2009) reported increased neutrophils in bronchial fluids from healthy patients exposed to particulate matter, in controlled studies, and Wallace et al. (2010) have identified increased risk of neutrophilic bronchitis in subjects living close to major highways. Wardlaw et al. (2005) proposed that exposure to air pollution promotes neutrophilic airway inflammation, as opposed to allergen exposure, which promotes eosinophilic inflammation. A neutrophilic subtype of asthma has been defined in predominantly older persons with severe asthma (Green et al., 2007, Fahy, 2009) and other studies have indicated increased neutrophils in severe (Foley and Hamid, 2007, Chung, 2009, Monteseirín, 2009) or even mild asthma (Li et al., 2006). Zhang et al. (2009) have demonstrated neutrophil increases in asthma subjects exposed to particulate matter and McCreanor et al. (2007) reported increases in biomarkers of neutrophilic inflammation in mild to moderately asmathic patients exposed to traffic-related pollution. Neutrophils are also elevated in patients with chronic obstructive pulmonary disease (COPD) (Stockley, 2002, Quint and Wedzicha, 2007, Barnes, 2008) and in COPD patients exposed to air pollution (Ling and van Eeden, 2009).
The alveolar macrophage is the primary cell in the lungs responsible for uptake and clearance of micro-organisms and environmental particles (Brain, 1986, Lehnert, 1992). The development and progression of COPD is not only believed to be strongly associated with smoking, but also with particulate matter and other air pollutants (Nilsen et al., 1984, Goldsmith et al., 1997, MacNee and Donaldson, 2000, Lahiri et al., 2000, Ädelroth et al., 2006, Larsson et al., 2007, Geiser et al., 2008, Ling and van Eeden, 2009). Macrophage phagocytosis may also be compromised by air pollution (Soukup and Becker, 2001, Zhou and Kobzik, 2007) leading to inflammation and possible exacerbation and progression of COPD (Chung and Adcock, 2008, Geiser et al., 2008). A preponderance of macrophages may also injure the host and enhance the exacerbation of the lung disease (Brain, 1986).
The objective of this study is to investigate whether the occurrence of temperature inversions, and the accompanying increases in air pollution, is associated with changes in quantitative cell counts obtained from sputum samples. The subjects are patients who attended the Firestone Institute for Respiratory Health, an outpatient clinic in Hamilton, Ontario. Temperature inversions were identified using vertical temperature profiles from the Atmospheric Infrared Sounder, an atmospheric sensor developed for climate studies. This instrument resides on the Aqua spacecraft, which was launched by the National Aeronautics and Space Administration in 2002, and orbits the Earth at an altitude of 705 km (NASA, 2009). We also discuss the effects of seasonality on the cell counts. Seasonality influences concentrations of some pollutants as well as the frequency of temperature inversions, and we have identified seasonal variations in total cell counts.
One of the unique aspects of this study is the use of atmospheric satellite data in a respiratory health study, which to our knowledge, has not previously been done. Currently, the satellite data are our best resource for identifying inversions, which encompass the extent of the study area. The nearest radiosonde station is located in Buffalo, New York, 100 km SE of the study area and may not be representative of conditions in Hamilton.
Section snippets
Patient data
The design was a retrospective survey of Hamilton residents with airway diseases, who attended the Firestone Institute for Respiratory Health between January 2004 and December 2006. Initial visits were based on referrals from family physicians, and subsequent visits were either pre-set appointments or made upon request of a patient with worsening symptoms. At each visit, spontaneous or induced sputum was collected. Sputum induction and examination for neutrophils, eosinophils, macrophages,
Summary descriptive statistics
Table 1 summarizes essential characteristics of the subjects. Patients’ ages ranged from 10 to 95 years, with an average of 55 years (standard deviation 17 years). Asthma patients were, on average, younger than COPD or the other group of patients. Women comprised 57% of all subjects. Less than half the subjects with COPD and a quarter of subjects with asthma were smokers. The subjects had moderate severity of disease as indicated by a median daily use of corticosteroids of 800–1000 μg of the
Discussion
The results of this study have shown that the occurrence of an inversion on the day of sputum collection was a statistically significant factor in increased percent neutrophils for the stable group of subjects, and increased percent macrophages in the exacerbated group. When categorized by respiratory disease, we observed that the increases in total count and percent neutrophils in the stable group appear to be influenced to some extent by patients with asthma. The results of our study are
Acknowledgement
We thank Liesel D'silva, MD and John Brannan, PhD for help with tabulation of the sputum data and Chris Allen, MB, for creating the database.
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Cited by (0)
- ☆
Approval from the Research Ethics Board (REB), McMaster University, is not necessary to collect sputum, as this was a routine clinically indicated test. REB approved using the information stored in a database for the purpose of this study.