The response of the surface electrocardiogram to inspiration

The waveshape of the electrocardiogram (ECG), as is well known, varies with respiration. This effect was noted from the early days of clinical electrocardiography (1) and has generally been ascribed to changes in the position of the heart. Although it has mostly been regarded as "noise", it is generated by a process and may contain information on the process. This paper presents two hypotheses: firstly that the change of the ECG with a held-inspiration can be separated into a step and a transient component and secondly that the transient component reflects the time course of changes of the right and left ventricular end-diastolic volumes during the maneuver.