Changes in QRS complex in dogs with normal and exaggerated tidal volumes

The influence of normal and exaggerated ventilation on the QRS was studied in 10 dogs. Peak-to-peak amplitudes of QRS in 4 circumferential unipolar and 2 limb lead ECG were obtained during eupnea and during hyperinflation produced by intermittent positive pressure ventilation or negative extrathoracic pressure. Marked changes were not observed in any lead during eupnea. During hyperinflation to a transpulmonary pressure of 10 mm of Hg (whether by intermittent positive pressure ventilation or negative extrathoracic pressure), voltages decreased in leads I, V10, rV3, and aVF and were variable in leads V3 and V5. Radiography revealed that during the hyperinflation the heart was displaced to the nondependent side of the thorax further from the dependent electrodes and that the heart became generally smaller. Changes in voltage could be attributed to alterations in relationships between the heart and electrodes on the torso surface or to changes in volume conductor properties of the heart and torso.