Aspects on Cardiac Pumping

Sammanfattning: Cardiac pumping physiology is important for understanding the pathophysiology of patients with cardiac disease. MRI gives the opportunity to measure volumes and flow non-invasively with high accuracy and precision. This thesis examines some aspects on cardiac pumping physiology. Study I showed that the total heart volume in humans decreases during systole by ~8 % (range 5-11 %), and anatomically identified the major outer volume variations to occur around the AV-plane with a left-side predominance. Also, a new method for measuring total heart volume variation (THVV) by MRI flow quantification was developed and validated against cine measurements. Study II showed that the THVV is similar in patients before and after cardiac bypass surgery compared to healthy subjects. Furthermore, study II also showed that the movement of the center of volume of the heart during the cardiac cycle, in both healthy individuals and patients, describes a well-defined loop in three-dimensional space with ~2 mm between the extreme points. This loop is called the center of volume variation, COVV. After coronary-bypass surgery, however, intra-individual COVV approximately doubled, possibly related to the paradoxical septal movement following cardiac surgery. Study III showed that longitudinal AV-plane displacement (AVPD) is the primary contributor to left ventricular (LV) pumping, accounting for ~60 % of the stroke volume (SV) in healthy subjects and that this does not differ in athletes or in patients with dilated ventricles. Study IV showed that radial function of the ventricles explains over 80 % of the THVV during the cardiac cycle. The longitudinal component of right ventricular (RV) pumping is ~80 % and the difference compared to the LV is explained by the larger AVPD of the RV. Study V identified and quantified a previously unknown increase in total heart volume before the end of systolic ejection. This total heart volume increase or late ejection filling volume (LEFV) into the atria was ~11 ml or ~18 % of THVV, with no difference between the left and right side of the heart. This volume might be important for understanding the coupling of systolic to diastolic function. Furthermore, the decrease in total heart volume caused by flow from the heart generated by atrial contraction (the atrial wave reversal volume, AWRV) was quantified to be ~7 ml or ~11 % of THVV. Thus, the heart is largest before atrial contraction prior to the end of diastole and smallest before the end of systole. In summary, this thesis has explained the total heart volume variations throughout the cardiac cycle and quantified the contribution of the AV-plane to ventricular pumping.