Normally there is an inspiratory decrease in JVP. In constrictive pericarditis there is an inspiratory increase in JVP. Kussmaul's sign is also seen in severe right heart failure regardless of aetiology.
It is caused by the inability of the heart to accept the increase in right ventricular volume without a marked increase in the filling pressure.
Adolf Kussmaul (1822-1902) was Professor of Medicine successively at Heidelberg, Enlargen, Freiburg and Strasbourg, and coined the term 'polyarteritis nodosa' (Ber/ Klin Wochnschr 1873; 10: 433).
Kussmaul breathing is deep sighing respiration seen when the arterial pH is Iow.