ASTHMA AND POLLUTION

 

   

A. Taytard

 

Service of the Respiratory Diseases

 

Hospital of Haut-Lévêque

 

Teaching hospital of Bordeaux

 

 

 The quality of the inhaled air makes the essence of the  morbidity and the respiratory mortality of cause. 

 

 The ambient air represents approximately 10 m  3 broken down per day.  One divides it into  air

 

 INDOOR        house (13 to 15 H), work (8 H), car (1 to  2h)

 

 OUTDOOR     cities and campaigns (1 to 2  H). 

 

 Each one of these types of air has its particular aérocontaminants  (in kind and in concentration) likely to involve

                         - lesions of the mechanisms of defence of the breathing  apparatus

                         - a bronchopulmonary disease. 

 

Asthma is the clinical expression of a hyper bronchial  reactivity, i.e. a capacity exaggerated bronchi to react to an aggression.  The attack of asthma  thus requires the meeting of one aérocontaminant attacker and a  hyper-reactive bronchus, and all kinds of aérocontaminants  are likely to start it.  The bond between pollution and  asthma thus comes immediately to mind with, in practice, two questions :

 ?    can the atmospheric pollutants increase the risk to  develop a respiratory disease? 

 ?    can the atmospheric pollutants they even  maintain to worsen a preexistent respiratory disease? 

 

 Some opening remarks must be made before trying to answer  these questions. 

 I / One measure out in practice only some markers of a  complex system  

 2 / the peaks are short, recognizable, but their impact with the long  course is badly known

 3 / daily usual pollution is weak, off accident, but its  impact with the long course is badly known

 4 / the individual risk appears weak, but knowledge on an  individual scale is rare

 5 / the collective impact is significant by the number of  people likely to be reached. 

    We thus passed

 ?         from significant exposures (professional, accidental) producing  diseases clinically and almost immediately  observable, to weak exposures whose consequences visible are only projected on a population scale,

 ?         from a search for individual prevention to the search of a  reduction of risk for the whole of a population. 

The evaluation of the risk is done in 4 stages

 1.  Identification of the pollutant to be accused:  One establishes a  first preliminary bond from cause to effect, between  the exposure to a product and certain noxious effects on health;  one  uses for that the epidemiologic investigations, animal toxicity and  the data of in vitro toxicity; 

 

 2.  Evaluation of the relation "amount-answer":  It is the description  of the quantitative relation which exists between the exposure to a  product and the type, the incidence or the severity  of the result observed, one uses for that the animal experimentation,  human data derived from accidental exposures ,  professional, or controlled in experimental condition; 

 

 3.  Evaluation of the exposure:  It is the identification and the  characterization of the exposed populations, and the determination of  the amplitude and the exposure time;   it depends on the demographic data and the monitoring  of errvironment   

 

4.  Characterization of the risk:  One integrates here the  results of the 3 preceding stages to produce an estimate of the  possibility that a harmful effect on health occurs, and the frequency  and the severity with which the result can be awaited in the  population under certain conditions. 

 The markers of the effect of the air pollution on the  breathing apparatus are numerous

 1 / cardiorespiratory excess of mortality

 2 / Rise of the consumption of care (visits, urgencies,  hospitalizations)

 3 / Exacerbations of asthma (visits, drugs, DP) 

 4 / Increase in the other respiratory diseases

 51 Augmentation in the respiratory symptoms

 6 / Fall of the respiratory function (spirometry, DP,  resistances)

 7 / Increase in the bronchial reactivity

 8 / Bronchopulmonary inflammation (cells, mediators) 

 9 / Deterioration of pulmonary morphology

 10/Alteration of the systems of defense (clearance  muco-ciliaire, macrophagic function, immunizing answer)

 11/Cellular injuries

 

 The impact of pollution on asthma is done under 2 conditions

    * into acute and chronicle

    * at the laboratory and in the population

 

1 /          AT THE LABORATORY

 

 Advantages  : The subjects, homogeneous, are well  defined and the experimenter controls the exposure, the symptoms, the  physiological and biological variables. 

 

 Limits  : The external validation of these results  poses problem insofar as one uses single pollutants or simple mixtures  during acute or subacute tests, which do not answer the chronicity of a  complex environment.  In addition their cost  limit their use. 

 

 Interests :  One can characterize the effects of a  specific pollutant and make assumptions on the mechanisms of action. 

 

 2 /         IN EPIDEMIOLOGY

 

 Advantages :  The epidemiology  makes it possible to study the relation exposition/effects on health in  the general population and the populations with risk.  They are there  real subjects put throught a real exposure. 

 

 Limits  : These studies do not make it possible to  really control neither the exposure to the pollutant nor the Co-factors;  however there is myriade of inhaled pollutants each day and in each  type of environment.  In addition one practically does not have  individual data.  Lastly, the risk of skew is major. 

 

Taking into account all these remarks, one can retain the  following results: 

 there is not formal proof, today, that the  atmospheric pollutants increase there prévalence of asthma.  They can, on the other hand, increase  mortality and morbidity by it in usual living conditions. 

 

 1 /   in the short run

 An exposure to ozone causes a fall of the VEMS  and an increase in the bronchial reactivity but there are 10 to 20% of nonresponders and a phenomenon of  tolerance appears  at the end of 3 to 5 days. 

 

 2 /   in the medium term

 The recourse for asthma to the emergency services is significantly  associated

  - with the PM10  the previous day  for the subjects of less than 65 years,

  - on the level of exposure to ozone and S0 2  for the children. 

 *  There is a relation between the increase in the concentrations of  ozone and S0 2 in the atmosphere and

  - reduction in the ventilatory function measured by the peak  output,

  - appearance of respiratory symptoms, the catch of bronchi dilatings ,

 and for levels of pollution lower than nuns WHO 

 

       At the asthmatic severe ones, the PM 2,5  increase the scores of asthma. 

 ?   In the asthmatic children, there is a significant relation  between the level of particles PM 10  and

      - reduction in the peak output,

      - increase in the prévalence of the  respiratory syrnptômes,

      - medicamentous consumption. 

 

 One can conclude from it that

 ?   the harmful effect of certain components  of pollution is now established, including for relatively low levels  of pollution and without real  effects of threshold

 ?   the atmospheric pollutants are likely to have an  additive harmful effect, even synergic   

 

 To improve the situation one can wish

 ?   an improvement of the quality of the air, but the  definition of the thresholds is not field of the scientific expertise, 

 ?   an alarm,  prediction, and monitoring system,

 

 ?   councils adapted to the populations with risk, but which do  not marginalize them,

 

 ?   an effort of research taking in account individual  measurements. 

 

 ?          And without forgetting the interior pollution  which is that in which one bathes during 90% of our life .

 

 

 

 

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