Around 300 million people worldwide have asthma and around 874 billion adults have a systolic blood pressure of over 140mmHg. Among these numbers, there is a subset of patients who have both these conditions. Studies show that people with asthma are more likely to develop hypertension. People having both asthma and hypertension have more severe form of asthma, greater reduction in lung function and compromised cardiovascular function. Moreover, medications for asthma can aggravate hypertension and vice versa; this makes managing hypertension in asthmatics more challenging and puts our doctors in a soup.
How are hypertension and asthma linked?
Systemic inflammation forms a fundamental part of the pathophysiology of asthma as well as hypertension. A large cross sectional study shows that middle aged asthmatics with lower FEV1 are at greater risk of hypertension. Moreover, high levels of C reactive protein, a systemic inflammatory marker, was associated with both hypertension and low FEV1.
Genetic factors, age, nervous system dysfunction may predispose an asthmatic individual to hypertension. Obesity brought about by a faulty lifestyle also contribute to systemic inflammation. Interleukin 6 released by adipose tissue is implicated in the development of both asthma and hypertension. Stress is another factor that contributes to both. Environmental factors such as pollutants, viruses, allergens trigger innate and adaptive immune responses which contribute to smooth muscle remodelling- a factor central to both asthma and hypertension.
How is hypertension managed in patients with asthma?
Drug therapy is recommended for patients having stage 1 hypertension (130-139/ 80-89) with cardiovascular risk factor and all patients with stage 2 hypertension (>140/>90mmHg). Before we delve into the choice of antihypertensive for asthmatic patients, the physicians must know that degree of blood pressure reduction rather than selection of antihypertensive medication is a more important determinant of patient outcomes.
Low dose thiazides can be given alone or in combination with other drugs in asthmatic patients. However, there is a risk hypokalemia of taking thiazides with high dose beta 2 agonists. Adding glucocorticoid or theophylline may aggravate this risk. If thiazides are used, serum potassium should be regularly monitored, especially in older patients.
ACE inhibitors are usually safe in patients with asthma. However, in few patients ACE inhibitor related cough has been reported. There is some evidence which also tells us that ACE inhibitor is associated with increase in asthma severity in some patients with hypertension. Though, ACE inhibitors is one of the most widely used class of drug for hypertension, physicians must be alert while prescribing it to patients with asthma.
ARBS are the most preferred drug in asthmatic patients who have hypertension. Studies show that severe asthma exacerbations are related to increased levels of circulating angiotensin II and renin. ARBs also seem to target the mechanisms which cause cough or airway hyper-responsiveness; these are favored in patients who are not able to take ACE inhibitors.
Calcium channel blocker:
Theoretically, calcium channel blockers decrease smooth muscle contraction and reduce bronchoconstriction related to triggers like cold, exercise and allergies. However, in clinical practice, calcium channel blockers do not seem to have any effect on asthma outcomes.
Care must be taken while prescribing beta blockers for patients with asthma due to its concerns of causing bronchoconstriction. Beta blockers must not be given as monotherapy. It should be considered only if the patient has conditions like arrhythmias, congestive heart failure and myocardial infarction. Even among beta blockers, non- selective beta blockers are more harmful for asthmatic patients. Asthma exacerbations have also been reported in patients treated with eyedrops containing non selective beta blockers for glaucoma.
Treating asthma in patients with hypertension:
Systemic glucocorticoids and short acting beta agonists, which are commonly employed for asthma, may affect blood pressure control and increase cardiovascular risk too. Thus, adjusting of the dosage of such medications is important for achieving target blood pressure levels.
Managing other factors:
Obstructive sleep apnea (OSA): OSA is linked with hypertension and the inflammatory processes involved in OSA is associated with asthma and CVD too. Treatment of OSA have been found to reduce inflammatory markers associated with hypertension.
Obesity: For every 5% increase in weight, there is 20-30% increase in the risk of hypertension. Weight loss can decrease 1 mm Hg of BP for every kg lost and also reduces cardiovascular morbidity. Weight loss has a significant impact in asthma outcomes. Thus, losing weight can be very useful for patients with asthma and hypertension.
Lifestyle factors: High salt, high calorie intake (from sources other than fruits and veggies) and reduced physical activity can contribute both to asthma and hypertension. Changes in diet, restricted salt intake and increased physical activity can each potentially reduce blood pressure by 1-4 mmHg. Stress is also linked to both hypertension and asthma; thus, stress reduction techniques like mindfulness meditation and transcendental meditation can be useful too.
Patients having asthma and hypertension are difficult to manage from a pharmacotherapy aspect. However, along with drug therapy, a physician should manage comorbid conditions like obesity and OSA and teach patients about lifestyle measures that can reduce blood pressure like reducing salt intake, increased physical activity, following healthy diet and reducing stress.