What is the relationship between Orthopnea and RV function ?
June 15, 2025 by dr s venkatesan
Paroxysmal nocturnal dyspnea and orthopnea are cardinal symptoms of heart failure. The difference between the two has been extensively discussed and debated in medical literature. The key difference is in the time lag that occurs in PND , while orthopnea occur immediately. However, we never looked into PND & Orthopnea with reference LV, RV or biventricular failure.
The fact that Orthopnea occur immediately, raises many critical queries.
It is presumed that the increase in venous return in a recumbent posture immediately causes lung congestion and stimulates pulmonary receptors (J or non-J?) which results in dyspnea. The fact that orthopnea is relieved by sitting posture demands still more explanation. Is it volume-dependent lung congestion, or volume and stretch-dependent RV mechanic receptor stimulation? (or both) I think it is difficult to answer that question.
We get some indirect clues in bed side, by experience. In many patients with Chronic RV dysfunction , orthopnea seems to be less, making it likely pulmonary origin. At the same time, if RV dysfunction is new or acute, it is the raised RVEDP, that is responsible.
Now , we have a problem . Is orthopnea related (more )to RV or LV dysfunction ?
It can have complex inter dependent relationship. In fact, the degree of pulmonary hypertension, the septal push (Reverse Bernheimer effect ) can further confound. Severe RV dysfunction alters the V:Q ratio of lungs, and a also a mismatch between RV vs LV stroke volume.
Final message
The origin of Orthopnea is determined by the status of both RV and LV function. They can either congest or decongest the lung. Realize, in a severely dysfunctional biventricular failure, it is the fine balance between them that keeps the lung dry or wet.
The importance of RV mechanoreceptors and their pathways to dyspnea centers are less understood. While the mechanism of orthopnea is intertwined between the functions of the two ventricles, PND is fairly specific for acute elevation of LVEDP and resultant alveolar interstitial edema. Mind you , orthopnea can occur with totally dry lungs, if its origin is from RV, while it is a rarity in patients with PND.
Post-amble
Time lagged Orthopnea : A proposal for new clinical entity.
We have also seen patients with RV dysfunction mimic PND when they develop dyspnea say 15 to 30 minutes after lying down. Fellows should go back in time and try to re-look and analyze gaps in our understanding of cardinal symptoms.
A small study is easily possible about the incidence of PND and orthopnea in patients with cardiac failure with reference to right and left ventricular function.
