Asthma is a chronic inflammatory disease characterized by periodic obstruction of the bronchioles. Two key features of asthma are reversible airflow obstruction and bronchial hyperresponsiveness to stimuli. Triggers of airway hyperresponsiveness include respiratory infections, exercise, cold or dry air, atmospheric pollutants, occupational irritants, or specific environmental allergens. other risk factors for asthma include heredity, history of allergies, cigarette smoking, and socioeconomic status.
The overall prevalence of asthma is increasing. In the United States, asthma has a prevalence of approximately 6% and mortality is 1 in 10,000. In the last decade, the death rate from asthma in the United States has increased significantly, with the increase in women being more than twice that observed in men (54% compared to 23%).
In addition to having a higher mortality in females, asthma displaysseveral other differences between genders. The gender differences in asthma begin in childhood in which the prevalence of asthma is higher in boys. This has been attributed to boys having smaller airways in proportion to lung volumes than girls, although it has also been suggested that there is an under diagnosis of asthma in girls. The difference in asthma prevalence between genders reverses sometime during adolescence, when the asthma rate in females actually increases. Lung growth is dysynaptic in girls and their lungs stop growing in the late teens. The lungs of boys, on the other hand, demonstrate isotropic growth and their lungs continue to grow until the age of 20. These differences may be the result of pubertal changes in sex hormones.
In adulthood, asthma is more common in women than in men, and it appears to have a greater impact on quality of life in women. Recent studies have also found that obesity is associated with the development of asthma in women but not in men. This difference is believed to be due to the influence of obesity on levels of female sex hormones. Studies of patients reporting to the emergency department for asthma have found that although men typically have worse lung function as measured by flow spirometry, women are hospitalized more frequently than men and have longer hospital stays. In a longitudinal study of 914 patients with asthma in Kaiser Permanente, researchers found that women reported more symptoms, used more medication, and had greater health care use than men. In general, women tend to experience greater discomfort than men for the same level of airflow obstruction. Reasons for these gender differences are not entirely known but are thought to be multifactorial, including biological, social, and psychological factors.
Two aspects of asthma unique to women are premenstrual asthma and asthma during pregnancy. Premenstrual asthma has been reported in up to 30-40% of women and is associated with a worsening of asthma symptoms prior to and during menstruation. Several mechanisms for premenstrual asthma have been proposed, but the most widely studied is the influence of sex hormones on asthma. Studies demonstrating the relaxant effect of estrogen and progesterone on bronchial smooth muscle, as well as studies showing an improvement in asthma symptoms after estrogen administration, have led researchers to speculate that the premenstrual drop in estrogen levels may be responsible for the worsening of asthma symptoms.
Hormonal influences are also among the proposed mechanisms for the course of asthma in pregnancy. Asthma is a common problem during pregnancy and can have a potentially serious impact on pregnancy outcomes. Recent studies have found that, on average, asthma symptoms during pregnancy worsen in a third of women, improve in another third, and remain the same in the remaining third. Women with severe asthma prior to pregnancy are at greater risk for exacerbations during pregnancy. Furthermore, while symptoms tend to improve during the third trimester, they may worsen postpartum. However, the majority of women return to their prepregnancy asthma state in a few months. Proper management of asthma is essential during pregnancy, as poor control has been associated with increased maternal morbidity and adverse perinatal outcomes. Treatment of asthma during pregnancy is similar to treatment in nonpregnant women and includes the use of inhaled beta agonists, corticosteroids, theophyllines, and antiallergy medications.