Circulatory and Respiratory Adaptation, during Long‐Term, Non‐Steady State Exercise, in the Sitting Position1

Abstract Ekelund, L. G. and A. Holmgren. Circulatory and respiratory adaptation during lone‐term, non‐steady state exercise in the sitting position . Acta physiol. scand. 1964. 62 . 240–255. — Circulatory and respiratory changes during long‐term, non‐steady state exercise in the sitting position was studied with heart catheterization technique in six healthy young men with average training. The work load was chosen individually to increase the heart rate to about 140–150 beats per minute after 10 min work and to 170–180 beats per min after 60 min work. The circulatory changes during these experimental conditions were characterized by continuously falling systemic arterial blood pressure, constant cardiac output, and increasing heart rate, indicating a continuously fallinn stroke volume. The blood volume was lower during exercise than at rest in the supine position but remained unchanged between 10 and 50 min work. The acid‐base status was characterized as a compensated metabolic acidosis, which remained essentially constant throughout the test. The respiratory response was characterized by a successively increasing total ventilation, a moderate increase in alveolar ventilation and a marked increase in dead‐space ventilation. The increase in total ventilation was effectuated by an increase of both the respiratory rate and the tidal volume. The overall ventilation‐perfusion relationship showed a slight continuous increase. Both circulatory and respiratory changes may be explained in the light of a gravitational shift in the distribution of the blood volume.