FIGURE 4.

Relation between the number of cross-bridges (mass transfer) developed locally in the anterior wall and the rate of pressure development during contractions of the beating rat hearts (upper panel) and myosin spacing (d_1,0) changes in relation to LVV of the hearts (lower panel). In the upper panel, baseline means (open circles) are connected with volume-loading means (solid circles) for individual rat hearts (n = 5). A significant direct relation between mass transfer index and LVP dP/dt_max is presented for the group (thick line y = 0.00029x − 0.153, P < 0.004; dashed lines indicate 95% CI of mean). In the lower panel, the relation between d_1,0 spacing during systole (interval between ED and ES) for baseline (circles) and volume-loading (squares) treatments and LVV is significant (dashed line y = 42.65 − 0.0084x, P < 0.0001), but on average 1 nm less than the maximum d_1,0 recorded shortly after ES in each cycle. Open symbols indicate ED, half-closed ES and closed symbols the average recorded maximum d_1,0 ± SD in all hearts (typically mean of 8–12 consecutive cardiac cycles).