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Early studies on the toxicity of certain hydrocarbons, especially anaesthetics, showed that they could render the mammalian heart abnormally reactive or sensitive to adrenaline (epinephrine) resulting in cardiac arrhythmias. 1,1,1,2-tetrafluoroethane (HFC 134a) has been investigated for this effect in beagle dogs and no effect concentrations demonstrated at 40000ppm and 50000ppm in two studies. HFC 134a has a low narcotic potential being able to induce anaesthesia at only very high concentrations.

Additional information

Male Beagle dogs were exposed to nominal HFC-134a concentrations of 50,000, 75,000 or 100,000 ppm (208,000, 313,000, 417,000 mg/m3) and given a bolus injection of 8 µl/kgbw epinephrine. Two of 10 dogs exposed to 75,000 ppm and 2 of 4 dogs exposed to 100,000 ppm exhibited a marked response (multiple extrasystoles). One dog exposed to 100,000 ppm developed ventricular fibrillation and cardiac arrest. None of the 10 dogs exposed to 50,000 ppm HFC-134a exhibited a cardiac sensitisation response (Mullin 1979).

In another study in Beagle dogs, the cardiac sensitisation potential of HFC-134a was evaluated at concentrations of 40,000, 80,000, 160,000 or 320,000 ppm (167,000, 334,000, 667,000, 1,330,000 mg/m3) until equilibrium concentrations in the blood were established (approximately after 5 minutes of exposure). At that time, the dogs were given an intravenous injection of adrenaline (8 µg/kg) and monitored for cardiac arrhythmias. Three of 10 dogs exposed to 80,000 ppm developed cardiac arrhythmias, as did 4 out of 10 dogs exposed to 160,000 ppm and 3 out of 4 dogs exposured to 320,000 ppm. Concentrations of 40,000 ppm HFC-134a were tolerated without any signs of cardiac arrhythmias. The reference compound in this study, CFC-12 (dichlorodifluoroethane), showed a comparable cardiac senstisation potential (Hardy et al 1991). HFC 134a has a low narcotic potential being able to induce anaesthesia at only very high concentrations (> 500000ppm) (Shulman & Sandove, 1967).