The influence of hyperosmolality on left ventricular contractile state: Disparate effects of nonionic and ionic solutions

Traditional concepts hold that hyperosmolality is a major factor in the myocardial depressant effects of contrast materials. In order to test this hypothesis, the authors studied the effects of intracoronary injections of glucose, mannitol, and sodium chloride solutions varying in osmolality from 300-1800 mOsm in nine anesthetized mongrel dogs instrumented with left ventricular (LV) pressure catheters and intramyocardial ultrasonic segment crystals. The effects of hyperosmolal solutions were studied in the normal state, during beta adrenergic blockade with propranolol, and during systemic hypoxemia. In three dogs, coronary sinus effluent was sampled to determine the changes in the osmolality of the coronary circulation after injection of small amounts of hyperosmolal solutions. Injection of 5 cc of 1800 mOsm solutions of glucose caused the maximum increases in peak (dP/dt) (P < 0.01), dP/dt at an LV pressure of 50 mmHg (dP/dt)50 (P < 0.01), and velocity of contraction (dD/dt) (P < 0.01) compared with controls. The 1800 mOsm solutions of mannitol produced maximum increases in peak (dP/dt) (P < 0.01), (dP/dt)50 (P < 0.01), and (dD/dt) (P < 0.01). Lower osmolality solutions of glucose or mannitol produced smaller increases in myocardial contractile state. Injection of 900 mOsm solutions of sodium chloride caused drastic decreases in LV pressure (P < 0.01), peak (dP/dt) (P < 0.01), (dP/dt)50 (P < 0.01), and (dD/dt) (P < 0.01). In both the normal state and after beta adrenergic blockade there was no significant difference in the magnitude of the response to glucose, mannitol, or sodium chloride. During hypoxemia, the positive inotropic effect of mannitol was greatly attenuated, while the responses to glucose and sodium chloride were unchanged compared with the normal state. Thus, nonionic (molecular) and ionic (dissociating) hyperosmolal solutions have divergent influences on myocardial contraction. Nonionic, hyperosmolal solutions cause a positive, rather than a negative, inotropic effect. These findings imply that excess sodium Na+ is the major factor causing the negative inotropic action of contrast media, and that hyperosmolality per se has no role in this regard.