[Disorders of heart rhythm and ECG changes in experimental apneic states]

Apnoeic events are often accompanied by various disturbances in electric cardiac activity, the character and development as well as mechanism of which remain broadly unknown suggesting both direct metabolic defects as well as neurogenous autonomic influences.

Changes in ECG and heart rate induced by repeated short-lasting inhalation of hypoxic poikilocapnic mixtures (100% N2 and/or 0.5-1% CO2 or 6% CO2 in N2) were analyzed in 17 spontaneously breathing cats anaesthetized with sodium pentobarbitone (40 mg.kg-1i.p.).

N2 inhalation evokes hypoxaemic hyperventilation progressing into apnoea and bradycardia with secondary low-level atrioventricular conduction block and ischaemic changes in ECG. Contrary to this reversible respiratory failure, hypoxaemic hypercapnic hyperventilation and apnoea evoked by inhalation of 6% CO2 in N2 or 100% CO2 were accompanied by very marked additional effects of hypercapnia and acidosis. They appeared earlier and were more severe (high-level AV conduction block and premature contractions) suggesting direct myocardial alteration due to acidosis.

The results provide experimental data for better understanding the dynamics, intensity and development of dysrhythmias and ECG changes occurring in two different types of cardiorespiratory failure in animal experiments as well as in central and obstructive types of sleep apnoea and other apnoeic events in humans. (Fig. 3, Ref. 27.)