The effects of increasing pulmonary stretch and posture on sinus arrhythmia

1. It is generally accepted that sinus arrhythmia is due to change in vagal tone and that it is only present when vagal tone to the sino-atrial node predominates over sympathetic tone. Arguments persist about the origin of the feed-back information which initiates the arrhythmia, mostly among supporters of stretch receptors in the lungs and thorax (Anrep et al., 1936; Clynes, 1960), and baroreflexes in the blood vessels (Bainbridge, 1920; Davies and Neilson, 1967; Adeoshun, 1976). 2. The literature is scanty about the genesis of sinus arrhythmia. It would be worthwhile to investigate sinus arrhythmia under varying tidal volumes and posture. With this procedure it might be possible to differentiate between the importance of extrathoracic blood vessel stretch receptors and lung stretch receptors in the genesis of the arrhythmia. 3. This study is designed to investigate some of the causal factors involved in the production of sinus arrhythmia.