The effects of induced hypoxia on the cardiovascular system in dogs poisoned with tetanus toxin.

Tetanus toxicity was induced in dogs by injecting the toxin subcutaneously in the groin. On developing generalised toxic symptoms, these dogs were characterised by signs of increased sympathetic discharge to the cardiovascular system as evidenced by high basal values of blood pressure, heart rate and LV dP/dt max. Mild to moderate hypoxia induced by ventilation with 10% O2 in N2 had no appreciable effect on the cardiovascular variables. However, moderate to severe hypoxia induced by ventilation with 7% O2 in N2 further increased the sympathetic discharge to the heart and blood vessels resulting in increases in heart rate, LV dP/dt max and blood pressure. These responses were abolished by adrenergic blockers. The responses in the tetanus dogs were identical to those seen in dogs without tetanus toxicity. Atropine or moderate lactic acidaemia did not alter the responses to hypoxia. Beta-adrenergic blockers appear to be useful drugs in the control of tetanus patients who show evidence of increased sympathetic activity or who develop hypoxaemia.