Role of mixed venous blood Pco2 in respiratory control

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Abstract
The Pco2 of mixed venous blood has been increased abruptly by 5—49 mm Hg, without altering the volume or pressure of blood returning to the right ventricle, by infusion of blood with 550—700 mm Hg Pco2 into the right atrium, and simultaneous withdrawal of equal volumes of blood from the inferior vena cava. Twenty-five such blood exchanges in four anesthetized cats, four anesthetized dogs, and three unanesthetized dogs failed, with one exception, to increase respiratory frequency or tidal volume if PaCOCO2 remained constant; respiration increased only when PaCOCO2 rose. Correlation of ventilatory minute volume with PvCOCO2 was poor (r = 0.296; P > 0.1) but was good with PaCOCO2 (r = 0.608; P < 0.001). Experiments on the innervated and denervated carotid body (dog) demonstrated that chemoreceptors can respond rapidly (0.5 sec) to changes in PaOO2 or PaCOCO2. The absence of demonstrable ventilatory response to increased PvCOCO2 over periods of 0.5–3.0 min in animals in whom increments in PaCOCO2 led promptly to increased ventilation indicates that there are no CO2 receptors in the precapillary pulmonary circulation of importance in the physiological regulation of respiration. Submitted on May 25, 1961