Electrocardiographic interpretation of the nasopharyngealresponse in conscious rabbits

The present study was conducted to recognize by part, the cardiovascular events of the nasopharyngeal reflex, through electrocardiographic interpretations. ECG patterns were traced in twelve clinically normal and healthy New Zealand White rabbits of both sexes, weighing between 2-3 kg and aged between 1-3 years with inhalant irritants. Immediately after induction of formaldehyde vapour, the heart rate fell by 69% from a mean of 192 ± 7.310 bpm to 60 ± 1.296 bpm, whereas exposure with cigarette smoke caused a fall in heart rate by 74% from a mean of 205 ± 9.605 bpm to 53 ± 3.065 bpm. With both irritants, P wave becomes smaller and totally disappeared, indicating an increased vagal activity inducing a sinoatrial node arrest. The amplitude of QRS complex also significantly decreased; and so did the duration of P wave and PR interval, presumably due to junctional escape. T wave duration decreased with slow ventricular repolarization. Bradycardia was also evident with increased QT interval. However, there was no change in QRS complex or ventricular depolarization, mediated perhaps via compensatory sympathetic influence on the ventricular myocardium. The study demonstrates that both formaldehyde and cigarette smoke provoked a similar protective response of rabbits against noxious fumes.