What is a primary physiological cause for JVD during exhalation in obstructive lung disease?

The primary physiological cause for jugular vein distention (JVD) during exhalation in obstructive lung disease is increased intrathoracic pressure. In obstructive lung diseases, such as asthma or chronic obstructive pulmonary disease (COPD), the ability to exhale forcefully is often compromised due to airway obstruction. When a patient exhales, the intrathoracic pressure rises, which can impede venous return to the heart by compressing the superior vena cava.

This increased pressure can lead to a visible distention of the jugular veins, as blood has a harder time returning to the right atrium of the heart when the thoracic pressure is elevated. Consequently, JVD becomes apparent when the intrathoracic pressure increases during the act of exhalation, particularly in patients with obstructive lung disease who may already have compromised cardiovascular status.

Other options may suggest various underlying mechanisms, but they do not directly explain the relation of intrathoracic pressure changes during the breathing process in obstructive lung disease as well as increased intrathoracic pressure does.