LV oxygen consumption and pressure-volume area: role of norepinephrine and verapamil

The effect of norepinephrine or verapamil on the relationship of left ventricular (LV) myocardial oxygen consumption (MVO2) and systolic pressure-volume area (PVA) was investigated in hearts within the never-opened thorax of dogs with blocked baroreceptor reflex. LV chamber volumes and myocardial blood flow were measured using a fast computed tomography scanner. At 10 micrograms/min delivery rate of norepinephrine, MVO2 (mJ.g-1.cycle-1) equals (2.30 +/- 0.48) PVA + (20.60 +/- 4.24) (n = 11; 1 mJ.g-1.cycle-1 is equivalent to 0.563 ml O2.100 g-1.min-1 at 112 beats/min). With verapamil infusion, MVO2 equals (2.57 +/- 1.33)PVA + (10.73 +/- 3.16) (n = 17). The regression slopes did not differ (P greater than 0.25) for any of the conditions. At comparable PVA values the norepinephrine group showed an increase of MVO2 compared with the prenorephrine baseline state (P less than 0.01), and the verapamil group showed a reduction of MVO2 compared with the preverapamil baseline state (P less than 0.05). We conclude that the MVO2 to LVPVA relationship in the in situ heart, within the never-opened thorax, conveys that the oxygen-wasting effect of catecholamines is quantifiable using the shift in this relationship.