THE RESPIRATORY AND CIRCULATORY RESPONSE OF NORMAL MAN TO INHALATION OF 7.6 AND 10.4 PER CENT CO2 WITH A COMPARISON OF THE MAXIMAL VENTILATION PRODUCED BY SEVERE MUSCULAR EXERCISE, INHALATION OF CO2 AND MAXIMAL VOLUNTARY HYPERVENTILATION

Abstract

The respiratory and circulatory responses of normal young [male] [male] to inhalation of 7.6 and 10.4% CO2 were measured. When 7.6% CO2 in O2 was inhaled (42 subjects) the avg. minute volume of respiration increased to a maximum of 51.5 l./min. (range 24-102), pulse rate increased by 16.7 beats/min. and blood pressure rose 30.8 mm. Hg systolic and 22.2 mm. Hg diastolic. When 10.4% CO2 in O2 was inhaled (31 subjects) the avg. maximal minute vol. rose to 76.3 l./min. (range 40-130), pulse rate increased 15.6 beats/min. and blood pressure rose 33.4 mm. Hg systolic and 25.0 mm. Hg diastolic. When the CO2 inhalation was stopped, respiration and systolic blood pressure returned slowly to normal; diastolic blood pressure fell abruptly upon removal of the mask, often to lower than control figures. A comparison was made in 19 subjects of the maximal ventilation produced by a, inhalation of 7.6% CO2 b, inhalation of 10.4% CO2 c, exhausting muscular exercise; and d, maximal voluntary hyperventilation. The avg. figures were 48.9, 71.4, 109.6 and 166 l./min., respectively. The reasons for the failure of the body to respond with greater hyperpnea to high concns. of CO2 and severe muscular exercise are discussed. Data bearing upon the following are included: 1, the times for which 7.6 and 10.4% CO2 are tolerated by healthy men; 2, the symptoms produced by these concns.; and 3, the degree of hyperpnea at which dyspnea was noted by normal subjects.