Inhalation of gas mixtures containing different concentrations of
FC 12 by anesthetized and normally oxygenated dogs produces blood levels of
FC 12 which are stable and proportional to the rate of
FC 12 in the mixture. From the arterial concentration of 40 microgram/ml
FC 12 (5 %
FC 12 mixture) and over,
FC 12 alone causes effects proportional to doses: arterial pressure decrease with
tachycardia. At high rates of
FC 12 tachypnoea and slight morphological alterations of the electrocardiogram can be recorded. Arhythmia never occurs under the action of
FC 12 alone even at maximum arterial concentration reached here : 230 microgram/ml (40 %
FC 12 mixture). Recorded disturbances are always reversible. The intravenous perfusion of
epinephrine alone evokes the appearance of premature contractions at the only dose of 5 microgram/kg/mn. The presence of
FC 12 in blood conjoined with
epinephrine induces the inhibition of the hypertensive action of
epinephrine at high concentration and lowers the arhythmogenic threshold. The dog is clearly more sensitive than the rabbit to the arhythmogenic action of
epinephrine and
FC 12. The required rates of
epinephrine and
FC 12 validate the hypothesis of cardiac sensitization by
FC 12 to the arhythmogenic action of circulating
adrenaline to explain the cases of sudden "sniffing" deaths in man.