Biphasic
Ventilatory Response to Hypoxia in Unanesthetized
Rats
H. MAXOVÁ, M. VÍZEK
Institute
of Pathological Physiology, Second Faculty of
Medicine, Charles University, and Center for
Experimental Cardiovascular Research, Prague,
Czech Republic
Received
November 30, 1999
Accepted April 20, 2000
Summary
To
determine the role of postinspiratory inspiratory
activity of the diaphragm in the biphasic
ventilatory response to hypoxia in unanesthetized
rats, we examined diaphragmatic activity at its
peak (DI), at the end of expiration (DE), and
ventilation in adult unanesthetized rats during
poikilocapnic hypoxia (10 % O2) sustained for 20
min. Hypoxia induced an initial increase in
ventilation followed by a consistent decline.
Tidal volume (VT), frequency of breathing (fR),
DI and DE at first increased, then VT and DE
decreased, while fR and DI remained enhanced.
Phasic activation of the diaphragm (DI - DE)
increased significantly at 10, 15 and 20 min of
hypoxia. These results indicate that 1) the
ventilatory response of unanesthetized rats to
sustained hypoxia has a typical biphasic
character and 2) the increased end-expiratory
activity of the diaphragm limits its phasic
inspiratory activation, but this increase cannot
explain the secondary decline in tidal volume and
ventilation.
Key
words
Ventilation
· Biphasic response to hypoxia · Diaphragmatic
activity · Pattern of breathing
Reprint
requests
H.
Maxová, Institute of Pathological Physiology,
Second Medical Faculty, Charles University,
Plzeňská 221, 150 00 Prague 5, Czech Republic,
fax: 420 2 5721 0995, e-mail: martin.vizek@lfmotol.cuni.cz
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