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 (MV̇O₂) 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 μg/min delivery rate of norepinephrine, MV̇O₂ (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, MV̇O₂ 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 MV̇O₂ compared with the prenorepinephrine baseline state (P < 0.01), and the verapamil group showed a reduction of MV̇O₂ compared with the preverapamil baseline state (P < 0.05). We conclude that the MV̇O₂ 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.