Increasing resistance from 1.5 to 6 mm Hg sec/ml decreased the volume intercept of the end-systolic pressure-volume relationship from 5.5 to 0.6 ml (P<0.01), without changing its slope.
Do changes in arterial impedance affect the end-systolic pressure-volume relationship in excised canine left ventricles?
In a canine model, the slope of the end-systolic pressure-volume relationship is insensitive to afterload impedance changes, whereas its volume intercept is dependent on resistance and characteristic impedance.
p-value: p=<0.01
To study the end-systolic pressure-volume relationship of left ventricle ejection against physiological afterload, we imposed seven simulated arterial impedances on excised canine left ventricles connected to a newly developed servo-pump system. We set each of the impedance parameters (resistance, capacitance, and characteristic impedance) to 50, 100, and 200% of normal value (resistance: 3 mm Hg sec/ml; capacitance: 0.4 ml/mm Hg; characteristic impedance: 0.2 mm Hg sec/ml), while leaving the other parameters normal. Under a given impedance, the end-systolic pressure-volume relationship was determined by preloading the ventricle at four different end-diastolic volumes. There was no significant change in the slope of the end-systolic pressure-volume relationship with changes in any of the afterloading impedance parameters. However, the volume intercept of the end-systolic pressure-volume relationship decreased significantly with resistance from 5.5 +/- 1.0 (SE) ml at resistance equal to 1.5 mm Hg sec/ml to 0.6 +/- 1.8 ml at resistance equal to 6 mm Hg sec/ml (P less than 0.01). The volume axis intercept also decreased with characteristic impedance, from 5.9 +/- 2.0 ml at a characteristic impedance of 0.1 mm Hg sec/ml to 5.4 +/- 2.1 ml at a characteristic impedance of 0.4 mm Hg sec/ml, (P less than 0.05). We conclude that the slope of the end-systolic pressure-volume relationship is insensitive to a wide range of changes in afterload impedance, but its volume intercept is dependent on resistance and characteristic impedance.
Maughan et al. (1984) studied physiological afterload. simulated arterial impedances vs. normal value was evaluated on slope and volume intercept of the end-systolic pressure-volume relationship (p=<0.01). Increasing resistance from 1.5 to 6 mm Hg sec/ml decreased the volume intercept of the end-systolic pressure-volume relationship from 5.5 to 0.6 ml (P<0.01), without changing its slope.