Cardiopulmonary Exercise Testing to Evaluate Pulmonary AVMs With and Without Airflow Obstruction

Hypoxemia, Dyspnea, and Exercise Tolerance in Patients With Pulmonary Arteriovenous Malformations , With and Without Airflow Obstruction

Pulmonary arteriovenous malformations (PAVMs) are a rare vascular condition affecting the lungs. PAVMs lead to low blood oxygen levels, yet are very well tolerated by patients. This study will examine the exercise capacity of PAVM patients using formal cardiopulmonary exercise tests performed on a stationary bicycle, and whether this is affected by the presence of concurrent airflow obstruction, such as due to asthma.

It is well known that the lung is the site at which oxygen enters the blood stream, diffusing from the alveolar air sacs into the pulmonary capillaries. This newly oxygenated blood is carried to the heart in the pulmonary veins, then passes into the systemic circulation to provide oxygen to the tissues.

Patients with pulmonary arteriovenous malformations (PAVMs) have abnormal vascular connections between pulmonary arteries and pulmonary veins in the lung. Blood flowing through PAVMs therefore bypasses the oxygenation sites in the pulmonary capillaries. Low blood oxygen levels (hypoxemia) is frequent in PAVM patients but breathlessness (dyspnea) is not. The investigators have shown that dyspnea was not a common presenting complaint in a large UK series, and that there is little correlation between severity of dyspnea in PAVM patients, and blood oxygen levels.

In this study the investigators will address the question "Do PAVM patients have lower exercise tolerance if they have concurrent airflow obstruction?" The primary outcome measure will be the total body oxygen consumption in mls/min/kg, at peak exercise (the V[dot]O2 peak (also known as "VO2 max")).

The investigators will address this by first performing standardised cardiopulmonary exercise testing, as used in the clinic and our previous study (11/H0803/9), on age and sex matched patients with PAVMs. 30 will be recruited with airflow obstruction, and 30 without airflow obstruction. Physiological parameters will be compared, to test the null hypothesis that the impact of exercise on PAVM patients' cardiopulmonary systems does not differ according to the presence or absence of airflow obstruction. Cellular and molecular methods will be used to dissect mechanistic pathways.

Inclusion Criteria:

• Ability to provide informed consent
• Pulmonary AVMs no airflow obstruction: Pulmonary AVMs confirmed by CT scan and no evidence or history of airflow obstruction on clinical grounds, or by spirometric evaluations.
• Pulmonary AVMs with airflow obstruction: Pulmonary AVMs confirmed by CT scan and evidence or history of airflow obstruction on clinical grounds, and/or by spirometric evaluations (such as FEV1/VC ratio <80%).

Exclusion Criteria:

• Inability to provide informed consent
• Any known cardiovascular abnormality including a history of syncope (faintness, dizziness, lightheadedness or loss of consciousness due to an abnormality of the cardiovascular system).
• Current respiratory tract infection (eg a cold).
• Pregnancy.
• Claustrophobia or needle phobia