Secondary ventilatory response to exercise: modification by agents which alter CBF

¹ Department of Medicine and Heart Research Center, Indiana University School of Medicine, Indianapolis, Indiana

Ventilation increases at the onset of exercise. Another abrupt increase, the secondary ventilatory response, occurs later. This study gives further observations on the secondary ventilatory response and its modification by O₂ breathing and other agents which alter cerebral blood flow. The secondary ventilatory response is similar to the response which follows release of arterial tourniquets inflated on the thighs, which is delayed in time of onset by O₂ breathing and infusion of aminophylline and NH₄Cl and accelerated by CO₂ breathing and NaHCO₃ infusion. This suggested that the respiratory center response may, to some extent, be dependent upon cerebral blood flow. The onset of the secondary ventilatory response was delayed by 100% O₂ breathing. Infusion of NH₄Cl significantly delayed the onset of the secondary rise and NaHCO₃ tended to make it come sooner. The timing of the secondary ventilatory response, then, was changed by substances which alter cerebral blood flow. It is suggested that the secondary ventilatory response may be due to a blood-borne substance released from working muscles.

Submitted on January 10, 1964