In The Air - Be Aware! 

Part I

Effects of air temperature and strong scents in patients with asthma and asthma-like symptoms

Eva Millqvist
MD, PhD

This is a reduced version of my doctoral thesis from 1996. It is written in the main for persons with a medical education of some kind. The principal focus is on exercise-induced asthma and asthma-like symptoms induced by chemical irritants. During the following five years several new studies have been performed which have enhanced our knowledge in these fields. Some of this new research is presented in: In The Air - Be Aware, Part II.

The aims of the thesis were to:

- study the occurrence and severity of asthmatic symptoms induced by a cold climate,

- study whether a heat-and moisture-exchanging material could prevent cold-induced asthma,

-  develop a  cosmetically acceptable face mask, preventing
cold-induced asthma,

- determine how air of different temperatures in the nose influences the lower airways in asthmatic patients,

- develop and evaluate a scent-provocation test in patients with asthma-like symptoms and chemical sensitivity.  

Background
Patients with asthma or asthma-like symptoms often report acute or increased breathing problems on exposure to cold air, physical exercise and chemical irritants. Clinically, the association between cold weather, exercise and asthma is well known, but it has not been systematically studied. Cold-induced asthma symptoms is prevented mainly by medication rather than by altering the temperature of the inspired air. In patients with asthma provocations with cold air are used to assess hyperreactivity, but a temperature-dependent relation between the upper and lower airways is not proven. It is also well known, but not well documented, that strong scents may induce airway symptoms in patients having asthma and other conditions. However, no standardised test is available for scent provocation in such patients.  

Methods
A questionnaire was used to analyse the occurrence and severity of asthmatic symptoms in a cold winter climate. The preventive effect of breathing through a material with heat-and moisture-exchanging properties was analysed in asthmatic patients, during exercise in a cold chamber. A cellulose-fabric face mask was developed from this material. The changes in lung function after nasal provocations with air of different temperatures were studied in asthmatic patients who were sensitive to cold. In patients not having asthma, but who reported airway symptoms from chemical agents, the symptoms induced by provocations with perfume were analysed with an inhalation provocation model. The patients used a nose clip and could not feel any smell.

Results
Most of the asthmatic patients complained of greater difficulty when breathing in cold weather, whereas only a few of the healthy controls reported such symptoms. Breathing through a cellulose-fabric face mask exchanging heat and moisture prevented exercise-induced asthma in cold air. In asthmatic patients, provocations with cold air in the nose reduced the lung function, but provocations with warm air had the opposite effect. In patients with asthma-like symptoms and reporting sensitivity to strong scents, placebo-controlled provocations with perfume caused symptoms in the airways.

Conclusions
Cold-induced asthma is an important problem that can be abolished by breathing through a heat-and moisture-exchanging material. The lower airways are influenced by the nasal air temperature, indicating the presence of a naso-bronchial reflex and this may be of great clinical importance. In some subjects who do not have asthma, symptoms resembling asthma and suggestive of hyperreactivity were detected in a scent-provocation test with perfume. Such symptoms do not derive from the olfactory system.

Table of contents   
- Abstract
- List of publications
- Introduction - Airway physiology 
- Bronchial hyperreactivity and cold-sensitivity
- Aims
- Material and Methods
- Results
- Discussion
- Concluding remarks
- References
- Paper I
- Paper II
- Paper III
- Paper IV
- Paper V