Effect of hypertonic mannitol infusion during prolonged coronary occlusion.

Previous studies investigating the effect of hypertonic mannitol infusion during coronary occlusion have yielded conflicting results. The present study investigated the effect of hypertonic mannitol infusion on regional myocardial blood flow (microsphere technique), a metabolic index of ischaemic severity (myocardial PCO2 (PmCO2] and myocardial water accumulation during a 2 h anterior descending coronary artery (LAD) occlusion in open chest anaesthetised dogs. In seven dogs studied without mannitol intervention, LAD ligation resulted in an initial fall in regional blood flow to 25% of control flow followed by no significant change thereafter. Myocardial PCO2 distal to the ligation rose to a peak of 34.0 +/- 4.4 kPa (256 +/- 89) (mean +/- SEM). At the completion of the 2 h ischaemia period, myocardial water content was 8.4% greater in ischaemic than non-ischaemic tissue (3.87 +/- 0.11 and 3.57 +/- 0.03 g X g-1 dry weight respectively). In seven additional dogs, mannitol infusion begun 12 min following occlusion resulted in an increase in plasma osmolarity from 304 +/- 5 to 346 +/- 8 mosmol X litre-1, but failed to influence regional flow, PmCO2, or water accumulation in the ischaemic tissue. The inability of mannitol to favourably influence the severity of myocardial ischaemia during prolonged coronary occlusion may be due to its inability to prevent myocardial cell swelling in this model.