Investigation of heart rate variability in a dog with upper respiratory tract obstruction

An eight-year-old bull mastiff presented with respiratory obstruction caused by a tumour dorsolateral to the larynx. Removal of the tumour was attempted but the dog died. A novel noninvasive measurement of heart rate variability and cardiac parasympathetic activity, recorded real-time from an electrocardiograph signal, was used to investigate cardiac rhythm in the dog. A simultaneous record of heart rate and cardiac parasympathetic activity showed severe sinus arrhythmia caused by the parasympathetic tone, in which the inspiratory heart rate exceeded 140 beats per minute (bpm) and the expiratory heart rate fell to below 60 bpm. The extent of respiratory modulation of the cardiac parasympathetic activity (vagal tone) has not been reported before using this technique on-line in a conscious, freely-behaving and spontaneously breathing animal. Non-invasive measurements of cardiac parasympathetic tone show great potential for the assessment of animals with systemic and cardiac disease including cardiac failure.