The Effects of Caffeine on Ventilation and Pulmonary Function During Exercise - Caffeine: Chemistry, Analysis, Function and Effects - page 348

N Caffeine stimulates both the central and peripheral chemoreceptors, which
control ventilatory drive.
N In large doses (.6mgkg 21 body weight), caffeine results in significant
increases in submaximal and maximal exercise ventilation.

N

The increases in exercise ventilation with caffeine may be useful in
increasing alveolar oxygen partial pressure and arterial oxygen saturation.

d n 0 t 2 n g | 7

N

However, during heavy exercise, the increased work of breathing may cause
blood flow to be redirected from the locomotor to the ventilatory muscles
via a sympathetic ''metaboreflex'' response, negatively affecting exercise
performance.

N

Caffeine also demonstrates immunomodulatory, anti-inflammatory, and
bronchoprotective effects that contribute to its efficacy as a prophylactic
antiasthma drug.

N

In three studies conducted to date examining the efficacy of caffeine
ingestion on exercise induced bronchoconstriction, pulmonary function
after exercise was significantly improved to levels measured before exercise.

Key Facts of Ventilatory Control During Exercise

N The primary purpose of ventilation during exercise is to regulate arterial
carbon dioxide content, with arterial oxygen content being a secondary
factor.
N Arterial CO 2 content is sensed by both the central chemoreceptors located
in the medulla of the brain and the peripheral chemoreceptors located in a)
the carotid bodies within the carotid arteries in the neck region, and b) the
aortic

arch. Arterial O 2 content is sensed solely by the peripheral

chemoreceptors.

N

The central and peripheral chemoreceptors are normally sensitive to
changes in baseline levels, and send a continuous signal to the respiratory
musculature which is modulated based on changes in chemical stimuli.

N

The airways and lung wall contain mechanoreceptors, which send an
afferent signal in response to various stimuli, such as stretch (hyperinfla-
tion).

N

Ventilation is also affected by temperature (with an increase in temperature
resulting in an increase in ventilation).

N

Ventilation can be regulated during exercise by modulating either tidal
volume (the depth of the breath) or breathing frequency (the number of
breaths per minute) or both.

N

As exercise progresses from rest through low and moderate workloads,
minute ventilation is increased primarily by increasing tidal volume, with
modest increases in breathing frequency.

N

As exercise approaches heavy or maximal levels, minute ventilation is
increased

primarily by increasing breathing frequency, with modest

increases in tidal volume.