title: Ventilatory responses to cardiac output changes in patients with pacemakers.
abstract: Cardiac output changes were induced by step changes of heart rate (HR) in six patients with cardiac pacemakers during monitoring of ventilation and gas exchange, breath-by-breath. Mean low HR was 48 beats/min; mean high HR was 82 beats/min. The change of oxygen uptake immediately after the HR change was used as an index of altered cardiac output. After HR increase, oxygen uptake (V02) rose by 34 +/- 20% (SD), and after HR decrease, Vo2 fell by 24 +/- 11%. There was no change in arterial blood pressure. After HR increase, ventilation increased, after a mean delay of 19 +/- 4 s; after HR reduction, ventilation fell, after a mean delay of 29 +/- 7 s. In the period between HR increase and the resulting increase in ventilation, end-tidal PCO2 (PETCO2) rose by 2.6 +/- 2.0 Torr, and in the period between HR decreases and the fall in ventilation, PETCO2 dropped by 2.9 +/- 2.2 Torr. The response time and end-tidal gas tension changes implicate the chemoreceptors in the reflex correction of blood gas disturbances that may result from imbalances between cardiac output and ventilation.
mesh_terms: D000328:Adult; D002302:Cardiac Output; D006339:Heart Rate; D006801:Humans; D008875:Middle Aged; D010138:Pacemaker, Artificial; D012119:Respiration