Effect of respiration on echocardiographic ventricular dimensions and relationship to the second heart sound

The effects of normal respiration on echocardiographic right and left ventricular dimensions were studied in 8 normal subjects (group 1) and in 10 patients with ventricular volume overload due to anaemia (group 2). Right ventricular internal diameter (RVID) increased on inspiration in both groups of patients (group 1, 0.3 +/- 0.1 cm; group 2, 0.6 +/- 0.4 cm), while left ventricular internal diameter (LVID) decreased (group 1, 0.3 +/- 0.2 cm; group 2, 0.4 +/- 0.3 cm). The changes in echocardiographic diameter were related to the duration of electromechanical systole and to the changes in the splitting of the second heart sound; there was a linear relationship between RVID and Q--P2 (P less than 0.001) and A2--P2 (P less than 0.001). Echocardiographic measurements of cardiac chamber size should take into account the changes which occur during respiration.