The carbon dioxide balance‐sheets of the body: their determination in normal subjects and in cases of congenital heart disease*

Some factors affecting the open‐circuit determination of maximum breathing capacity

“…of arterial blood. In earlier experiments (Shephard, 1954), an increase in C02 content of 27 ml. produced a pH change of 0-02 unit, so that in the present case an average pH change of 0-05 units might be expected, and towards the end of the 15 sec period pulmonary venous blood might show a pH rise of as much as 010 -units.…”

“…The significance of the carbon dioxide loss can be examined using calculations developed in some earlier balance-sheet studies (Shephard, 1954(Shephard, ,1955. The metabolic cost of hyperventilation is relatively small, and is not immediately apparent owing to a lag imposed by the circulation time; thus the factor most likely to affect the body output of CO2 during the first 15 sec of vigorous hyperventilation is an increase of cardiac output.…”

“…The metabolic cost of hyperventilation is relatively small, and is not immediately apparent owing to a lag imposed by the circulation time; thus the factor most likely to affect the body output of CO2 during the first 15 sec of vigorous hyperventilation is an increase of cardiac output. It has been estimated (Shephard, 1954) that increase of ventilation to three times the resting level gives rise to a 15 % increase of cardiac output. Assuming that mechanical disturbances of the circulation are proportional to the severity of hyperventilation (the relative changes of pulse rate support this view), then a ventilation of twenty times the resting level should give rise to a 100% increase in cardiac output, and an associated clearance of up to 270 ml.…”