Pressure applied: Mechanisms affecting heart-lung interactions and cardiac filling in patients with HFpEF during rest and exercise.

Heart failure with preserved ejection fraction (HFpEF) is characterized by elevated left-ventricular (LV) filling pressures largely owing to diastolic dysfunction and stiffness. The measurement of filling pressure presents unique challenges as cardiac structures live within the context of the thorax. The heart and pulmonary vasculature are therefore subjected to the same changes in external volume as the lung. Here, we review the mechanisms by which LV filling pressure interacts with the thoracic space, with a particular focus on patients with HFpEF during rest and exercise. Specifically, we discuss the means by which intrathoracic volume impacts ventricular filling and function. We outline the interacting compliances within the thoracic cavity which can alter intrathoracic and therefore cardiac filling pressures. We also detail means by which intrathoracic pressure can be modulated by different conditions and body positions, such as supine posture, gravity, and obesity. Throughout, we highlight gaps in the literature as well as perspective towards possible future directions.