The Effects of Caffeine on Ventilation and Pulmonary Function During Exercise - Caffeine: Chemistry, Analysis, Function and Effects - page 339

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Figure 18.1 Individual hypoxic and hypercapnic ventilatory responses with placebo

and 650 mg caffeine ingestion. C (triangles), control; P (open circles),
placebo; CF (closed circles), caffeine (650 mg). VE, minute ventilation;
PETCO 2 , end tidal carbon dioxide partial pressure; SaO 2 , arterial
oxyhemoglobin saturation. Horizontal bars represent mean values.
* Significantly different from control and placebo, P,0.05. Figure
appears in D'Urzo et al 1990. Reprinted with permission from the
American Physiological Society.

In contrast, how caffeine affects peripheral chemosensitivity in highly trained
athletes appears to be another matter entirely. As a group, highly trained
endurance athletes commonly show blunted ventilatory responsiveness to
hypoxia and hypercapnia (Byrne-Quinn et al 1978). Whether this reduced
ventilatory responsiveness is an adaptive result to chronic endurance training or
is a naturally occurring trait, one which may predispose an individual to success
in endurance exercise activities, is not clear. In any case, data suggest that the
baseline level of ventilatory responsiveness to hypoxia and hypercapnia may
affect the ability of caffeine (and other pharmacological compounds) to augment
peripheral chemosensitivity. For example, work by Chapman and Stager (2008)
studying highly trained endurance athletes suggests that caffeine does not affect
peripheral chemosensitivity in this particular subset of the population. In a
group of eight highly trained, caffeine na¨ve male distance runners, neither the
resting hypoxic or hypercapnic ventilatory responses showed a significant
change after ingestion of 8 mg kg 21 body weight caffeine. All told, it appears
that highly trained endurance athletes are generally insensitive to an increased
gain in peripheral chemosensitivity with caffeine, likely due to the severely
blunted baseline chemoresponsiveness typically seen in this population.

18.2.2 Caffeine and Ventilation During Exercise
In both trained and untrained adults, caffeine has a strong analeptic effect.
Peripheral chemosensitivity effects aside, it has been argued that the primary
focus behind the ventilatory effect of caffeine is the central stimulation of the
respiratory medullary complex. As a result, several studies have demonstrated