Long and short axis dimensions of the left ventricle change in opposite ways during respiration.

Cardiac output and stroke volume are known to vary with respiration. While right ventricular stroke volume increases on inspiration, left ventricular stroke volume decreases. This is an echocardiographic study of the changes in left ventricular dimensions in 20 healthy subjects. Our results show that the decrease in left ventricular stroke volume on inspiration is a net effect of a decrease in short axis shortening due to a decrease in diastolic diameter by 4.8% (P < 0.001) and an increased motion in the long axis direction expressed as an increase in mitral ring motion by 5.5% (P < 0.001). The findings point to the importance of the interventricular septum for the regulation of stroke volume.