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Keywords:

  • Asthma;
  • Exposure control;
  • Temperature-controlled laminar airflow;
  • Cat allergen;
  • Nasal air sampling

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. Funding
  9. References
  10. Supporting Information

Temperature-controlled laminar airflow improves symptoms in atopic asthmatics, but its effects on personal allergen exposure are unknown. We aimed to evaluate its effects on personal cat allergen and particulate exposures in a simulated bedroom environment. Five healthy volunteers lay under an active and an inactive temperature-controlled laminar airflow device for 175 min, in a simulated bedroom containing bedding from a cat owner. Total airborne particles (≥0.5 – ≥10 μm diameter) were quantified with a laser particle counter. Airborne allergen was sampled with Institute of Occupational Medicine filters. Inhaled exposure was sampled with nasal air samplers. Allergen-containing particles were quantified by immunoassay. Treatment reduced total airborne particles (>0.5 μm diameter) by >99% (P < 0.001) and reduced airborne allergen concentration within the breathing zone (ratio of median counts = 30, P = 0.043). Treatment reduced inhaled allergen (ratio of median counts = 7, P = 0.043). Treatment was not associated with a change in airborne allergen concentration outside of the breathing zone (P = 0.160). Temperature-controlled laminar airflow treatment of individuals in an allergen-rich experimental environment results in significant reductions in breathing zone allergenic and non-allergenic particle exposure, and in inhaled cat allergen exposure. These findings may explain the clinical benefits of temperature-controlled laminar airflow.

Practical Implications

The temperature-controlled laminar airflow device significantly reduces total airborne particulate and aeroallergen exposure within the breathing zone, in an allergen-rich environment. The reductions in aeroallergen and total airborne particulates help to explain the clinical benefits seen in asthma sufferers taking part in randomized controlled trials of this device. In this simulated bedroom environment, the magnitude of reduction in breathing zone allergen exposure varied, depending on the precise method and position of sampling. Nasal air sampling is a particularly useful measure of exposure as it occurs at the bedding surface–nasal interface; static low-flow samplers can be placed at precise points within the breathing zone ‘plume’ and allow measurements over a longer sampling period. These differences in exposure can be used to inform the design of field studies of aeroallergen exposure, where only a single mode of measurement of exposure is likely to be practical.

Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. Funding
  9. References
  10. Supporting Information

Exposure to perennial aeroallergens has been shown in both challenge and epidemiological studies to worsen asthma control (Langley et al., 2003; Phipatanakul et al., 2000; Raja et al., 2010). Thus, avoidance of exposure to aeroallergens for sensitized individuals might be expected to produce clinical benefit. House dust-mite allergen is found in mattress and pillow dust reservoirs in the majority of homes in temperate climates (Simpson et al., 2002; Tovey et al., 2008) and is usually rendered airborne only upon disturbance (De Blay et al., 1991). Studies of mite allergen avoidance have commonly used bedding encasement to prevent allergen egress from these reservoirs into the breathing zone, yet have yielded disappointing results (Gøtzsche and Johansen, 2008). Particles containing pet allergens such as cat dander are more easily rendered airborne and are readily transferred between locations. Transfer of cat allergen from homes to schools is sufficient to exacerbate asthma in susceptible children (Almqvist et al., 2001). Pet allergen can be detected in the ambient air and in soft furnishings inside homes without a pet (Custovic et al., 1999; Gore et al., 2006). Avoidance of pet allergens therefore requires a more complex environmental intervention than bedding encasement alone.

Humans spend up to a third of their life in bed, where the personal breathing zone is in close contact with bedding surfaces. Here, inhaled pet allergen exposure is likely to be closely related to the surface concentration of pet allergens (De Lucca et al., 2000) and will be affected by several factors: ambient airborne allergen concentration; disturbance caused by turning in bed; bed clothing allergen load; head position; room ventilation; and the presence of a pet. The temperature difference between the air surrounding an erect human body and the ambient room temperature gives rise to convection current rising up from the body: a ‘human plume’ (Craven and Settles, 2006). When recumbent, these convection currents appear particularly prominent above the head, where they can entrain exhaled breath aerosols and may also therefore entrain other particles from bedding surfaces into the breathing zone (Tang et al., 2009). Allergen reservoir encasement methods such as mattress covers can have only a limited effect on renewable surface allergen levels and will have no effect on the convection current of warm air generated around a recumbent body. This could be one explanation for the lack of efficacy reported in studies of aeroallergen avoidance for patients with established asthma.

Air filtration units are used for allergen avoidance and allow up to 15 room air changes per hour, cleaning air in a non-directional manner. Randomized controlled trials of such units for treating asthmatic patients with pet allergy show no clinical benefit and little effect on airborne cat allergen levels (Kilburn et al., 2001; Van der Heide et al., 1999; Wood et al., 1998). Laminar airflow systems are used to remove airborne microbial particles from operating theater environments. In an uncontrolled study, one bedside device using horizontal laminar airflow was shown to improve rhinitis symptoms and daytime somnolence, although exposures were not measured (Morris et al., 2006). Recently, a device using temperature-controlled laminar airflow (TLA) was shown in a placebo-controlled trial to improve asthma-specific quality of life and airways inflammation (Boyle et al., 2012). This device directly controls nocturnal exposure to aeroallergens by delivering cooled and filtered air from an overhead position above the head of the bed (Figures 1, S1). The cooler, denser air falls and acts counter to the rising convection current, thereby displacing allergen-bearing particles away from the breathing zone down to floor level. We investigated the effects of TLA treatment on personal breathing zone particle and cat allergen exposures in subjects lying recumbent in a cat allergen-rich environment.

image

Figure 1. Experimental chamber. In the breathing zone, the particle counter (A) and IOM sampling head (B) were mounted in parallel, with the sampling ends of the tubing set 8 cm above the forehead. A second particle counter/IOM sampler pair was located peripherally. NAS = nasal air sampler. IOM = Institute of Occupational Medicine air sampler

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Materials and methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. Funding
  9. References
  10. Supporting Information

A room in a clinical research facility at Imperial College London with no air conditioning or through ventilation was used; the dimensions were 2.4 × 2.9 × 3.3 m. A PVC-covered couch was used as a bed, with a mattress, pillow, and sheets from the home of a cat owner. The bedding was visibly clean but had not been recently washed. A TLA device (Airsonett®, Airsonett AB, Sweden) was placed overhead, with a distance of 38 cm between the forehead and the TLA device (Figures 1, S2). The TLA device works as follows: air from the room enters the TLA device and passes through a filter that captures allergens and other particles; the filtered air is cooled to 0.75°C below the ambient room temperature (measured at level of the head) and is supplied at low velocity from the air supply nozzle as a descending plume of air. The clean air zone produced by the TLA device is defined by the volume of an imaginary cylinder below the air supply nozzle, with a diameter of about 60–80 cm and a height of 55 cm. The descending airflow is evenly distributed over the diameter with an airflow rate of at least 120 m3/h (Figure S3).

The different sampling methods used to determine allergen and particle levels are described below. The experimental chamber was sealed during sampling periods. The ambient room temperature was 19°C. Each study volunteer was alone in the chamber and changed their own nasal air samplers. A study monitor sat outside the chamber; the monitor controlled the Institute of Occupational Medicine (IOM) samplers and laser particle counters by a remote switch and also issued instructions on when to change nasal air samplers and on when to make a scheduled body turn.

Presentation of particle count data

While airborne cat allergen exposure is weighted toward particles >5 μm in size, a smaller proportion is airborne on smaller particles (Custovic et al., 1998; De Blay et al., 1991; Luczynska et al., 1990). The nasal air sampler has a much higher collection efficiency for particles >5 μm in size than for particles <5 μm (Graham et al., 2000). To show a clear comparison between the different measures of exposure, we present the graphical form of the total particles exposure data and the results of the analysis on the effects of turning over, for particles in the size category >5 μm. In addition, tabulated, descriptive data for total particles exposure are presented for each of the size categories.

Total airborne particle detection

Laser particle counters were calibrated to 2.83 l/min. Particle counter one (Aerotrak 9306, TSI Inc., Shoreview, MN, USA) was attached to a 30-cm-long antistatic tube (internal diameter 9 mm). The open tip of this tube was suspended from the ceiling, 8 cm above the midpoint of the forehead (Figure 1). Particle counter two (Aerotrak 9303) was placed outside of the immediate breathing zone, 1 m from the subject's head. During the experiment, samples were taken continuously; particle counter one sampled for 60 seconds/sample continuously; particle counter two sampled for 50 s/sample every minute.

Airborne allergen concentration

Two portable low-flow pumps (Reciprotor A/S, Copenhagen, Denmark), calibrated to 2 l/min, were fitted with IOM sampling heads (SKC Ltd, Blandford Forum, UK) containing 0·8 μm pore mixed cellulose ester filter disks (SKC Ltd). These were switched on as the subject got into bed and ran continuously throughout each experimental arm for 160 min, collecting 0·32 m3 of air. They measured cumulative cat allergen exposures above the forehead and peripherally at 1 m away from the personal breathing zone, and were mounted in parallel with the laser particle counters. Cat-allergen-bearing particles were visualized using HALOgen® staining (De Lucca et al., 2000).

Inhaled exposure

Nasal air samplers (NAS, Woolcock Institute of Medical Research, Sydney, Australia) were worn on fourteen occasions during each experimental arm (Figure 2). A 1-minute gap was scheduled before each nasal air sample. This gave time for the nasal air sampler to be inserted or replaced, while the subject mouth-breathed to reduce nasal airflow until the start of sampling. After each change in body position, a five-minute duration nasal air sample was taken, and thereafter, two 15-min duration samples were taken. Each NAS contained a pair of adhesive tapes (Woolcock Institute of Medical Research) onto which inhaled particles impacted and were collected.

image

Figure 2. Schedule of sampling and turns made by volunteers. Nasal air sampling was performed as outlined in the key. S = side position. The time scale is nonlinear

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To verify that the act of manually handling a nasal air sampler in this environment did not cause contamination of the adhesive tapes with cat allergen, two further nasal air samplers were used at the end of each study arm. The volunteer was instructed to mouth breath. Then, over a period of 1 min, the volunteer removed a nasal air sampler from its protective container, offered it up to the nose and then immediately placed it back into its container for processing. Over a subsequent 1-min period, a body turn was made from the back onto the side and a second nasal air sampler was offered up to the nose and then immediately returned to its container for processing.

Participant movements and air sampling schedule

Five healthy adults were recruited from staff members of the Department of Paediatrics, Imperial College, London. Written informed consent was obtained, and the studies were approved by a national research ethics committee. Each participant spent two 175-min sessions in the experimental chamber, one with the device switched off and one with it switched on. Subjects put on clean, antistatic clothing (Fristab ANT, 97% polyester, 3% conductive thread) in an antechamber and then entered the experimental chamber, sealing the door after entry.

On entering the chamber, the volunteer placed the first nasal air sampler into their own nose, and the particle counters were switched on. After 10 min, the TLA device was switched on by the volunteer (active arm only). At 15 min, the IOM samplers were switched on and the subject got into bed. Volunteers were instructed to keep the bedding close to their body up to the neck level. Hands were kept still, above the covers. Body turns were made at precise intervals using a minimum of disruption (Figure 2) and at a frequency chosen to mimic natural sleep (De Koninck et al., 1992). The first scheduled turn was made from recumbency to lying on one side; on subsequent turns, the volunteer alternated their position between these two states.

Nasal air sampler processing

Each pair of adhesive strips was laminated onto 1.0 μm pore polyvinylidene difluoride (PVDF) membrane in a laminar flow cabinet. Laboratory negative-control laminates were made at the same time. Samples were processed as previously described using the HALOgen® protocol (De Lucca et al., 2000). Allergen-bearing particles were visualized by light microscopy (×100) and counted.

Surface allergen detection

At the end of the experiment, surface allergen sampling was performed once using rollers covered with 24 cm2 adhesive tape (Woolcock Institute of Medical Research). A single pass was made with one roller across the width of the mattress (area = 180 cm2). Similarly, separate rolled samples were taken from the duvet (area = 180 cm2) and pillow (area = 150 cm2). Adhesive strips were laminated onto 1.0 μm pore PVDF, and 3 × 1 cm2 pieces per sample were stained for the cat allergen Fel d 1 using the HALOgen® protocol (De Lucca et al., 2000). The median (minimum and maximum) of these three counts is presented.

Statistics

Effect of TLA on total airborne particle counts

Count data were log10-transformed prior to analysis by univariate ANOVA (fixed factor = off/on, covariate = sample sequence). Count data collected throughout the entire experiment were used. Data for the breathing zone and peripheral zone are presented separately.

Airborne allergen concentration

Because of the nature of the airborne allergen concentration data (low numerical value counts), data were square-root-transformed. To determine whether there was a difference in IOM cat allergen counts between TLA treatment and no TLA treatment conditions, transformed data were analyzed by paired T-test. As it is not meaningful to provide a detransformed fold difference from square-root-transformed data, untransformed data were also analyzed by paired samples Wilcoxon signed rank test and a ratio of medians calculated. Data for the breathing zone and peripheral zone are presented separately.

Inhaled exposure

Untransformed nasal air sampler raw counts were summed to give a cumulative measure of exposure across each experimental arm for each volunteer prior to analysis by Wilcoxon signed rank test. In an additional analysis, nasal air sampler counts were adjusted to 15-min sample durations and data were square-root-transformed and then analyzed by ANOVA for repeated measures (Gore et al., 2006).

Effect of turning over on total airborne particle counts

The effect on overhead total particle counts of the subject turning over and the possible confounding effect of the disturbance caused by the subject changing the nasal air sampler were investigated by generalized estimating equations as follows: Count data associated with the disturbance caused by getting into bed were removed, and so data collected between 18 and 172 min were selected. One-minute time periods centered on each turn or sampler change command were identified. An unstructured working correlation matrix was specified, with a normal distribution identity link function, and 100 iterations. Variables were defined as follows: subject variable – volunteer identity; within-subject variable – time; predictors – time (covariate), and a variable indicating a change in position, of nasal air sampler or neither (factor); response variables – log-transformed total particle counts for particles >5 μm in size. The analysis was performed separately for the TLA switched either off or on. Results are expressed as estimated marginal means with confidence intervals (95% CI) for each condition (no change in activity, a change in the nasal air sampler alone, a change in position).

Effect of turning over on inhaled allergen exposure

The effect on nasal cat allergen exposure of the subject turning over was investigated by generalized estimating equations: Only data from when the subject was in bed were used. NAS count data were adjusted to 15-min sampling durations and square-root-transformed. An unstructured working correlation matrix was specified, with a normal distribution identity link function and 100 iterations. Variables were defined as follows: subject variable – volunteer identity; within-subject variable – time; predictors – time (covariate), and a variable indicating sample order with reference to the most recent change in position (factor); response variables – transformed nasal cat allergen counts. The analysis was performed separately for the TLA switched either off or on. Results are expressed as estimated marginal means (95% CI) for each condition.

Spearman's rank correlation coefficient was used for bivariate correlation of nonparametric data. All statistical analyses were performed using SPSS version 15.0 (SPSS Inc, Chicago, IL, USA).

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. Funding
  9. References
  10. Supporting Information

The experimental procedure was well tolerated by the five volunteers, without adverse event. The bedding surface cat-allergen-bearing median (minimum, maximum) particle counts were: pillow, 22/cm2 (17/cm2, 27/cm2); mattress, 61/cm2 (55/cm2, 71/cm2); and duvet, 48/cm2 (33/cm2, 80/cm2).

Breathing zone exposures

Background total airborne particles exposure

Background particle counts were taken in the experimental chamber each minute for 10 min before the start of each experiment, and the mean was calculated. For particles ≥5 μm in size, the minimum mean baseline count was 41 700/m3 and the maximum mean baseline count was 111 750/m3.

Total airborne particles exposure

Temperature-controlled laminar airflow treatment caused significant reductions in total airborne particles of all size categories in the breathing zone. The magnitude of the reduction was >99% in every category (P < 0.001; Table 1, Figure 3).

Table 1. Effect of TLA on total airborne particle counts in the breathing zone
Particle size>0.5 μm>1 μm>5 μm>10 μm
  1. a

    P < 0.001. Particle size ranges are as stated (e.g., >1 μm means all particles greater than 1 micron in size as determined by the laser particle counter).

Geometric mean (95% CI) particle counts/m3
No TLA4.03 × 106 (3.40 × 106, 4.78 × 106)3.36 × 105 (2.65 × 105, 4.25 × 105)9240a (7860, 10 900)996 (836, 1190)
TLA1340 (1130, 1590)13 (10, 16)<2a (<2, <2)<2 (<2, <2)
% Reduction in exposure with TLA cf No TLA (95% CI)>99%a>99%a>99%a>99%a
image

Figure 3. Total airborne particles exposure: Size category >5 μm. The mean of 5 volunteers' particle counts are shown for the breathing zone (left) and peripheral zone (right) positions. Separate lines for the TLA-off and TLA-on conditions are shown. The y-axis is to log10 scale

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Airborne allergen concentration

There was a significant reduction in cat allergen particle counts with TLA treatment, when exposure was measured in the breathing zone by the IOM sampler (T = 3.463, df = 4, P = 0.026). When data were analyzed by Wilcoxon ranked sum test, the median (range) particle counts/m3 were: no TLA treatment, 396 (38, 620); and TLA treatment, 13 (0, 25), P = 0.043. The ratio of median counts (no TLA treatment: TLA treatment) was 30 (Figure 4).

image

Figure 4. Airborne allergen concentration. Each data point represents the particle count per m3 for each individual in each of the TLA-off and TLA-on conditions. Each line represents one subject and connects the data points for that individual taken under each condition. The y-axis is to a square root scale

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Cat allergen particle counts collected in the breathing zone by the IOM sampler were positively correlated with the cumulative sum of an individual's cat allergen particle counts collected by nasal air sampling during the same experimental setting: r = 0.699, P = 0.024.

Inhaled exposure

There was a significant reduction in cumulative NAS counts with TLA treatment. The median (range) of cumulative particle numbers per subject was: no TLA treatment, 73 (11, 96); TLA treatment, 10 (3, 28); P = 0.043; and ratio of medians (no TLA treatment: TLA treatment) = 7. There was also evidence of a reduction in transformed NAS counts with TLA treatment; this did not quite reach statistical significance. Detransformed mean counts (95% CI) per sampler were no TLA treatment 3 (1, 6); and TLA treatment 0 (0, 1); F = 7.65, df = 1, P = 0.051, Figure 5).

image

Figure 5. Inhaled exposure. Each volunteer wore a series of nasal air samplers throughout each experimental sitting to detect inhaled cat allergen. The sample sequence (x-axis) refers to this sequence. Each data point is the detransformed mean of the five volunteers' nasal cat allergen counts at that point in the experiment. Empty and filled circles represent the TLA-off and TLA-on conditions, respectively. Error bars are 95% CI. All sample durations have been corrected to 15 min. The changes in position of the volunteers are annotated. The difference between TLA-off and TLA-on operation: P = 0.051. The y-axis is to a square root scale

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Control counts from NAS taken at the end of each experimental arm revealed no evidence of contamination caused by the act of removing and replacing nasal air samplers (median counts were zero.)

Peripheral zone exposures

Total airborne particles exposure

There was a >80% reduction in total peripheral particle counts with TLA treatment (size categories ≥0.5 μm and >5 μm, P < 0.001. Data for size category >5 μm are shown in Figure 3).

Airborne allergen exposure

There was no significant difference in transformed IOM counts in the peripheral zone with TLA treatment (T = 1.722, df = 4, P = 0.16). When data were then analyzed by Wilcoxon ranked sum test, there was also no significant difference. The median (range) particle counts/m3 were no TLA treatment, 154 (0, 433); TLA treatment, 38 (0, 54); and ratio of medians (no TLA treatment: TLA treatment) = 4.0, P = 0.281 (Figure 4).

Effects of turning over on exposures

Effects of turning over and of inserting NAS on total particles exposure

Turning over in bed significantly increased overhead total airborne particles exposure (size category >5 μm), no matter whether the TLA was switched off or switched on. There was no significant rise in exposure when volunteers changed nasal air samplers over but did not change position (Table 2).

Table 2. Effects of turning over and of inserting NAS on breathing zone total airborne particles exposure (size category >5 μm)
 No change in sampler or positionChange in sampler onlyChange sampler and position
  1. a

    P < 0.001. Statistical comparison was made against the ‘no change’ data. Data are geometric mean (95% CI) particle counts/m3.

TLA Off8988 (5948, 13581)9364 (5985, 14650)19414 (12978, 29043)a
TLA On259 (254, 265)212 (193, 232)a975 (575, 1655)a
Effects of turning over on inhaled exposure

Nasal cat allergen exposures were consistently higher just after a change in position when compared with subsequent nasal air samples (Table 3).

Table 3. Effects of turning over on inhaled cat allergen particles exposure
 First nasal air sample after turningSecond nasal air sample after turningThird nasal air sample after turning
  1. a

    P < 0.005 for mean exposure compared with first sample after turning. Data refer to inhaled cat allergen particle counts and are detransformed mean (95% CI) particle counts per 15-min sample.

TLA Off4 (2, 9)3 (1, 5)1 (1, 1)a
TLA On1 (0, 2)0 (0, 1)a0 (0, 0)a

These results demonstrate that turning over in bed increases both breathing zone total particles exposure and inhaled cat allergen exposure.

Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. Funding
  9. References
  10. Supporting Information

Boyle et al. (2012) recently demonstrated that the TLA device we investigated causes an improvement in asthma-specific quality of life and reduced exhaled nitric oxide in a population of atopic asthmatics. The presumption is that the clinical efficacy of this environmental control measure is related to the efficiency with which aeroallergens are removed from the personal breathing zone. There is, however, no consensus on the magnitude of the reduction in exposure required to lead to clinical benefit, or on the best method for evaluating any change in exposure brought about.

Trials of non-directional air cleaners have shown limited clinical benefit. A number of different methods have been used to evaluate the effects of these cleaners on pet aeroallergen exposure; these studies have shown conflicting results. Wood used a static air sampler to demonstrate a small reduction in home airborne cat allergen (Wood et al., 1998). However, when further aeroallergen concentration data from non-compliant participants were submitted to the Cochrane collaboration, this small reduction was found to be not significant (Kilburn et al., 2001). Conversely, others have used the same sampling methodology to record reductions in ambient pet allergen exposures of up to 90% (Custovic et al., 1998; Green et al., 1999). When nasal air sampling was used, the reduction in cat allergen exposure was only around 60% (Gore et al., 2003). Other studies have used IOM-type samplers placed in fixed positions over long collection periods. Xu used this approach to evaluate the effect of a heating, ventilation and air conditioning unit on airborne particulates, demonstrating reductions in cat and mite exposures of 88% and 44%, respectively; this was accompanied by an improvement in airway peak flow and markers of airway inflammation (Xu et al., 2010). The differences between the results from these various studies will, in part, be due to differences between the air collection devices used (e.g., static samplers; IOM samplers; nasal air samplers) but will also be due to the choice of the location of the sampling head (e.g., fixed position in the same room; lapel-mounted; breathing zone).

Studies of aeroallergen exposure as determined within the breathing zone have recently yielded fresh insights into the relationships between reservoir and personal allergen exposures. For example, De Lucca investigated the distribution of cat- and mite-allergen-bearing particles on items of clothing (De Lucca et al., 2000). She showed that reservoir measures of cat and mite allergen from within clothing fabric correlated with the concentration of allergen on the fabric surface; furthermore, the surface allergen concentration correlated with the number of nasally inhaled allergen particles when the clothing was worn. Wrzeszcz demonstrated that relatively gentle disturbance in the bedroom environment may be enough to render small quantities of mite allergen detectable within the breathing zone (Wrzeszcz et al., 2008). Field data on airborne allergen resuspension rates from domestic settled dust confirm that both cat and mite allergens in settled dust contribute to the detectable airborne allergenic biomass in homes (Raja et al., 2010). Therefore, the breathing zone is a highly sensitive microenvironment where inspired aeroallergen load may be affected by adjacent surfaces, nearby reservoirs and their interactions with an allergen abatement device. Our results confirm that changes in aeroallergen exposure brought about by a new intervention should be studied at this microenvironmental level, with measurements made from within the breathing zone.

We used three methods to assess breathing zone exposure to particles: laser particle counting to measure total airborne particles exposure and IOM sampling with nasal air sampling for cat allergen detection. We found a reduction in nasally inspired cat allergen levels in subjects treated with TLA. Consistent with this, there was a significant reduction in breathing zone cat allergen exposure as measured by IOM sampling. The breathing zone cumulative cat-allergen-bearing particle counts (IOM) were positively correlated with the cumulative sum of the nasal air sampler counts, thereby helping to validate these measurements against each other. Treatment with the TLA device caused a significant reduction in total airborne particles both within and outside the breathing zone.

We found a disparity between the reductions seen in cumulative cat allergen exposure in the breathing zone as determined by IOM sampling from a point just above the forehead, and by nasal air sampling. This may be due to the effects of the close proximity of the nose to the cat allergen-contaminated bedding surface. Another contributory factor may be that subjects were instructed to mouth breath for 1 min while changing nasal air samplers in order that the nasal air sampler collections could start at an exact time point; meanwhile, IOM sampling continued. Furthermore, the NAS has a size cutoff, such that that proportion of cat allergen that is borne on particles in the size category <5 μm would be unlikely to be collected at low resting nasal airflow rates (Graham et al., 2000). The IOM has no such cutoff, with the detection of particles limited merely by the 0.8-μm pore size of the collection membrane and the optical resolution of the immunostaining system. There may also be local factors (e.g., disturbance) that differentially affect the size distribution of particles as they enter the IOM and NAS. Despite these technical factors, a reduction in nasal cat exposure with TLA treatment was demonstrated.

Turning over in bed causes a rise in the number of total airborne particles (size category >5 μm) in the breathing zone as well as a rise in the number of inhaled cat allergen particles, thus demonstrating that studies of this type should take into account participants' movements. While there are still episodes of low aeroallergen exposure generated by personal movement even with TLA treatment, these exposures are transient and the cumulative, total exposures are markedly reduced by this intervention.

We used cat allergen as the test allergen in our study. While we have not directly measured mite allergen exposure, the reduction in particles >10 μm in size in the breathing zone suggests that TLA treatment will also be effective for reducing mite allergen exposure. It would be interesting to confirm this in future work.

With TLA treatment, there were reductions of similar magnitude in cat-allergen-bearing particle levels and total particulates (size categories >0.5 μm and >5 μm) outside of the breathing zone, although the reductions in cat-allergen-bearing particles did not reach significance. It would be interesting to assess the effects of regular TLA treatment on such peripheral zone exposures in homes over longer time periods. It is possible that prolonged use will reduce reservoir levels and have a room air cleaning effect.

The experimental model used in our study does not exactly replicate the conditions for aeroallergen exposure as they occur in the home. In our model, bedding represented the sole source of cat allergen. In domestic dwellings, cats may be present throughout the house, and cat allergen may be found to be dispersed on wall surfaces, in carpets and on other soft furnishings. The experimental chamber was not subject to open ventilation in the manner of a normal domestic dwelling. Volunteers in their own homes will differ in their sleep patterns, in the number and amplitude of movements they are likely to make at night, and in the degree to which they comply with treatment. However, detailed multimodality exposure assessments such as those performed here would not be feasible in the home environment; subsequent comparison between different measures of exposure within the breathing zone would not be possible.

The Airsonett device is used above the head of the person in bed. We don't yet know to what extent the practice of aeroallergen abatement elsewhere might augment the clinical benefits of Airsonett in the bedroom, although such practice seems logical. Obvious locations for abatement are in the rest of the house (pet exclusion, washing of bedding and soft furnishings), or in schools, where peer-to-peer allergen transfer appears to occur via school clothing (Almqvist et al., 2001).

In summary, we found large reductions in personal breathing zone cat allergen and non-allergenic particle exposures with TLA. These reductions may explain the beneficial clinical effects of TLA for treating atopic asthma, while other environmental control measures which do not cause these large reductions in exposure have failed to show clinical benefit.

Funding

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. Funding
  9. References
  10. Supporting Information

The study was funded by Airsonett AB. Robert Boyle and John Warner are supported by a National Institute for Health Research Comprehensive Biomedical Research Centre (BRC) and by the MRC and Asthma UK Centre in Allergic Mechanisms of Asthma. The study was conducted in a clinical research facility supported by Biomedical Research Centre funding from NIHR. The one author affiliated to the sponsor (PS) contributed to study design and practical organization and critically appraised the manuscript.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. Funding
  9. References
  10. Supporting Information
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Supporting Information

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. Funding
  9. References
  10. Supporting Information
FilenameFormatSizeDescription
ina12122-sup-0001-FigureS1.pngPNG image124KFigure S1. Air is slightly cooled by the TLA device. Cooler air is more dense than surrounding air, and thus falls in an inverted plume over the breathing zone (blue arrows), thereby displacing airborne particles traveling into the breathing zone (red arrows) into a more peripheral location. This is a schematic, to aid understanding of the principles of TLA treatment. It does not represent the full complexity of air currents in the home; for example, air entrained into the overhead inverted plume is not shown.
ina12122-sup-0002-FigureS2.jpgimage/jpg359KFigure S2. Experimental set-up. A = nasal air sampler. B = sampling tubing for laser particle counter and IOM sampler.
ina12122-sup-0003-FigureS3.jpgimage/jpg34KFigure S3. The clean zone produced by the TLA device is defined by the volume of an imaginary cylinder below the air supply nozzle, with a diameter of about 60–80 cm and a height of 55 cm.
ina12122-sup-0004-SuppInfo.docxWord document533K 

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