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Etienne Beaule wrote: > > Dear pH, I believe that would depend on your level of narcosis. If > >your chemoreceptors are not be abile to funtion properly (due to, say > >narcosis) then they may not be able to detect that CO2 has risen to a > >point which would normally trigger the ANS. > > I am curious... Is there any research supporting the conclusion that > narcosis can affect the efficacy/function of the peripheral > chemoreceptors? > > I have my doubts on that but sometimes diving physiology can become quite > surprising... 1. The ANS? Respiratory control is a function of the brainstem but _not_ the ANS. Read any physiology book. 2. You're curious, but not curious enough to go to the effort to find out for yourself. Oh well, here goes: The pCO2/ventilation response curve is flattened and shifted to the right by anaesthetic agents and most CNS depressant drugs. Presumably nitrogen narcosis (to which I presume you're referring, although I seem to have missed pH's original submission) would have such an effect. Narcotic effects due to hypercarbia itself don't depress respiration until pCO2 gets well over 100-150 mmHg - unlikely to be a 'primary' factor, but potentially part of a terminal death spiral initiated by some other process. The pCO2/ventilation response is largely due to central chemoreceptors, not peripheral ones (which are oxygen sensitive). The peripheral chemo- receptors _are_ exquisitely sensitive to anaesthetics (incl hyperbaric N2?) which causes loss of ventilatory response to hypoxia. There can be little doubt that central chemoreceptors are also depressed by 'narcotics'. Since you asked for research, try: 1. Knill RL and Clement JL (1982) Variable effects of anaesthetics on the ventilatory response to hypoxaemia in man. Can. Anaesth. Soc. J. 29:93. 2. Knill RL and Gelb AW (1978) Ventilatory responses to hypoxia and hypercapnia during halothane sedation and anesthesia in man. Anesthesiology 49: 244. 3. Derenne J-Ph, Couture J, Iscoe S, et al. (1976) Occlusion pressures in men rebreathing CO2 under methoxyflurane anesthesia. J Appl Physiol 40:805 (yes, really) Obviously these refer to more formal 'anaesthetic substances' than hyperbaric nitrogen: the principles (if not the specifics) are likely to be applicable to respiratory control while diving. Additional factors contributing to hypercarbia during diving will be well known to most readers; I will not enumerate them here. gerards -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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