The Kussmaul sign describes an abnormal rise or absence of a fall in jugular venous pressure with negative pressure inspiration. It is typically quantified as a less than 5 mm Hg fall in inspiratory right atrial pressure. It is classically associated with constrictive pericarditis, but can be seen in conditions associated with restricted right-sided filling including tricuspid stenosis and RV dysfunction.

Some controversy exists as to whether Kussmaul sign can be present in cardiac tamponade. If defined solely as a pathologic rise in jugular venous pressure with negative pressure inspiration, then Kussmaul sign cannot be present in cardiac tamponade unless there is concurrent constriction from an abnormal pericardium, pericardial clot, or adhesions. The difference between cardiac tamponade (assuming free-flowing intrapericardial fluid) and constrictive physiology is the influence of intrathoracic pressure on the intracardiac filling pressures. In constrictive pericarditis, changes in intrathoracic pressure are not well transmitted through the abnormally thickened pericardium. This effectively disassociates the cardiac chamber pressures from intrathoracic pressure changes. The RA and RV, invested within a constrictive pericardium, have abnormally high filling pressures with little to no respirophasic variation. During the rapid filling phase of diastole, right atrial and RV pressures equalize rapidly as they encounter pericardial constraint, and venous return from the inferior vena cava (IVC) and superior vena cava (SVC) compete for entry into the high-pressure RA. Because IVC inflow is favored over that from the SVC due to augmentation by transdiaphragmatic pressure, jugular venous pressure rises due to constricted SVC inflow. This causes the characteristic, paradoxical rise in jugular venous pressure of the Kussmaul sign.

In cardiac tamponade, respiratory changes in intrathoracic pressure are transmitted to the intrapericardial fluid. Right atrial and RV pressures fall together with intrathoracic pressure during spontaneous inspiration despite the presence of cardiac tamponade, thereby augmenting the gradient for venous return from both the SVC and IVC. This results in a fall in jugular venous pressure with inspiration.

References

• Johnson SK, Naidu RK, Ostopowicz RC, et al. Adolf Kussmaul: distinguished clinician and medical pioneer. Clin Med Res. 2009;7:107-112.
• Talreja DR, Nishimura RA, Oh JK, et al. Constrictive pericarditis in the modern era: novel criteria for diagnosis in the cardiac catheterization laboratory. J Am Coll Cardiol. 2008;51:315-319.