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. (Tue,) conducted a other in 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.
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