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-mu-g/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 > 0.25) for any of the conditions. At comparable PVA values the norepinephrine group showed an increase of MVo2 compared with the prenorepinephrine baseline state (P < 0.01), and the verapamil group showed a reduction of MVo2 compared with the preverapamil baseline state (P < 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.