THE EFFECTIVE STIMULUS FOR INCREASED PULMONARY VENTILATION DURING MUSCULAR EXERTION

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Abstract
The increase in pulmonary ventilation was studied in normal men exercising the limbs, first with normal circulation, and then with the circulation cut off by pressure from inflated cuffs. Very light exercise (at a rate of 12 kilogrammeters per min.) of the flexors of the hand during total ischemia of the arms usually resulted in a smaller ventilation than when the arms had normal circulation. Release of the ischemia was followed at once by a marked hyperventilation. In subjects walking uphill on a treadmill (at a rate of 700 kilogram-meters per min. for a 90 kg. subject), total ischemia of both legs resulted in a marked diminution of pulmonary ventilation, even though the nervous pathways were intact, and release of the ischemia was followed at once by a marked hyperventilation, much higher than the value prior to ischemia. These results are interpreted to mean that the chemical stimulus for increased ventilation in exercise of these types is far more important than the reflex. The discrepancies between these results and Harrison''s are perhaps due to the fact that consistent results are found only after the subjects have become well accustomed to the exptl. procedures by several repetitions of the expts., and when exercise of sufficient severity is used so that the changes in ventilation and O2 consumption are relatively large in magnitude.

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