eMedicineLive

What is bronchoscopic lung volume reduction?
COPD (Chronic Obstructive Pulmonary Disease) is an obstructive airway disease where there is resistance to the outflow of air from the lung. This leads to retention of air within the lungs and the characteristic hyperinflation with expansion of the chest wall. The respiratory muscles including diaphragm are stretched out, limiting their ability to inhale and exhale air as they operate at a disadvantageous length-tension curve.  The residual volume of the lung (air remaining in the lungs after maximum expiration) is increased. Hence during expiration, the thoracic muscles cannot fully relax as the increased residual volume keeps it stretched.

Reducing the lung volume by lung volume reduction surgery (LVRS) was found to relieve dyspnea and improve the quality of life in selected patients. The main reason attributed for the success of LVRS is the remodelling and improvement in the chest wall and respiratory muscle dynamics. LVRS is a major surgery and people with advanced COPD may not tolerate it.

One of the alternatives to LVRS is bronchoscopic lung volume reduction surgery (BLVRS). Bronchoscopic lung volume reduction surgery involves placement of one way valves in the airways leading to lung segments with most advanced COPD. Thus air entry to the worst affected parts of the lungs may be stopped. Theoretically the lung segment which has a one-way value should decrease in size as there is no air entry during inspiration but air exits out during expiration. But complete collapse of the lung segment is not achieved in part due to the collateral ventilation, where air enters the blocked segment from adjacent segment through bypass channels. But the partial collapse of the lung segment or lobe reduces the hyperinflation and decreases the strain on the respiratory muscles resulting in functional improvement in COPD.

How does the endobronchial value work?
The one way value placed during BLVR allows the air to move out during expiration but blocks the flow of air into the lung segment during inspiration. Thus overtime it would reduce the volume of residual air in that segment. This may decrease the overall lung volume and helps in functional improvement in respiratory muscle function.

Why complete collapse of the target segment of lung cannot be achieved by BLVR?
In BLVR one way valve is placed in the airway leading to segment to prevent the inflow of air to that particular segment or lobe. But the presence of collateral ventilation in the lung results in air bypassing the one-way valve block and reaches the targeted segment. Hence only partial collapse is expected after endobronchial valve placement. The collateral ventilation occurs through the inter alveolar pores of kohn, accessory bronchiolar-alveolar pathways and interbronchial connections. It is important to know that the presence of excess collateral ventilation make brochoscopic lung volume reduction less effective. Hence patients with limited collateral ventilation benefit the most from BLVRS.

What are the types of endobronchial valves available?
Two types of valves are available.
1) Zephyr endobronchial valve
2) Emphasys one-way valve

How is the endobronchial valves placed inside the airways?
The target segment is chosen based on the CT scan image and V/Q scan. Usually the worst affected part of the lung is chosen.
1) Regular bronchoscope is introduced into the lung and placed in the target bronchi.
2) The diameter of the bronchi at the target location is measured. Based on the diameter of the bronchi the size of the endobronchial valve is decided. 
3) The valve delivery catheter is introduced through the working channel of the bronchoscope
4) The endobronchial valve is placed in the target bronchi. The self expanding retainer fixes the valve to the bronchial wall.
5) The self expanding tubular mesh prevents the dislodgement of the endobronchial valve during coughing
6) The valve can be removed on a later date if placed in undesirable position or in case of any adverse effect requiring its removal.

Is there any criteria to select patients for BLVR?
The selection criteria for BLVR is similar to that of LVRS.

What are benefits of BLVR in advanced COPD patients?
Studies show improvement in forced expiratory volume in the first second (FEV1), a standard index of lung function. Other benefits noted are improvement in exercise tolerance, decrease in regional volume of lung at the targeted lung segment, less requirement of oxygen, chest wall shape remodelling, symptomatic improvement in breathlessness etc.