Central nervous system and chemoreceptor factors in control of breathing.

256 20TH ASPEN LUNG CONFERENCE CHEST, 73: 2, FEBRUARY, 1978 SUPPLEMENT Dr. Seceringhau.s: You must know what the HCO is and normalize the data. There really isn’t any difference between the t\V() methods. Proper normalization of the data make the differences go away. In fact, the Pco2 and pH change faster with the steady state method than with the rebreathing method. Dr. Edelinan: Yes, hut one difference that does not go away is that Read’s method is sensitive to changes in brain blood flow, whereas the steady state method is not. This creates the set-up for there to he a real difference in the response curves. While I can, I would like to ask Dr. Dempsey why, if he believes in the Tenney loop, he did not return his subjects to a hyperoxic state rather than a normoxic state. Dr. Dempsey: Normoxia is the more physiologic state. Hyperoxia presents additional unquantifiable complications such as an effect on CO transport and thus, possibly on brain ECF [H+]. Further, the important thing in these “post-hyperventilation” analyses is the abrupt relief of hypoxic conditions; and return to a normoxic state accomplishes this aim in the simplest manner. Dr. Dempsey (in response to a question by Dr. Fitzgeraid) : We believed that in humans and dogs the major controller of CSF [HCO ] in respiratory alkalosis was plasma [HCOJ. Then we did longterm (ie days) hyperventilation while holding plasma [HCO ] near normal and found that CSF [HCO.J decreased in a normal manner. We think, then, that “local” or “CSF-specific” factors-linked to brain Pco2-play a major role in CSF [HCO3-] regulation, at least in chronic hypocapnia. Dr. Kazemi: I think experiments of a few hours’ duration are too short to show the full effect on CSF [H+]. Also, where these 11+ changes take place is impo ant. Dr. Loeschcke’s lab has shown that small 4 ’ . ,es in plasma [HCO ] cause small changes in [HCO3] at the brain surface but these changes in [HCO3] are not reflected immediately in bulk CSF. Dr. Fitzgerald: Do [HCO3-] changes affect CA++ and other important ions in local brain ECF? This question takes us back to Dr. Cameron’s point. Dr. Hornbein: Things are getting more, not less complicated and I guess that’s as it should be. Perhaps we are placing too much emphasis on [11+] as the regulator of V. There are probably other ions and chemical stimulators which should be studied.