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The John Rankin Laboratory of Pulmonary Medicine, Department of Preventive Medicine, University of Wisconsin, Madison, Wisconsin 53705-2368
Received 6 June 1996; accepted in final form 28 October 1996.
Smith, Curtis A., Craig A. Harms, Kathleen S. Henderson, and
Jerome A. Dempsey. Ventilatory effects of specific carotid body
hypocapnia and hypoxia in awake dogs. J. Appl.
Physiol. 82(3): 791-798, 1997.
Specific carotid
body (CB) hypocapnia in the
10-Torr (less than eupneic) range
reduced ventilation in the awake and sleeping dog to the same degree as
did CB hyperoxia [CB PO2 (PCBO2);
>500 Torr; C. A. Smith, K. W. Saupe, K. S. Henderson, and J. A. Dempsey. J. Appl. Physiol. 79:
689-699, 1995], suggesting a powerful inhibitory effect of
hypocapnia at the carotid chemosensor over a range of
PCO2 encountered commonly in
physiological hyperpneas. The primary purpose of this study was to
assess the ventilatory effect of CB hypocapnia on the ventilatory
response to concomitant CB hypoxia. The secondary purpose was to assess the relative gains of the CB and central chemoreceptors to hypocapnia. In eight awake female dogs the vascularly isolated CB was perfused with
hypoxic blood (mild,
PCBO2
50 Torr or severe, PCBO2
36 Torr) in a background of normocapnia or hypocapnia (10 Torr less
than eupneic arterial PCO2) in the
perfusate. The systemic (and brain) circulation was normoxic
throughout, and arterial PCO2 was not
controlled (poikilocapnia). With CB hypocapnia, the peak ventilation
(range 19-27 s) in response to hypoxic CB perfusion increased 48%
(mild) and 77% (severe) due to increased tidal volume. When CB
hypocapnia was present, these increases in ventilation were reduced to
21 and 27%, respectively. With systemic hypocapnia, with the isolated
CB maintained normocapnic and hypoxic for >70 s, the steady-state
poikilocapnic ventilatory response (i.e., to systemic hypocapnia alone)
decreased 15% (mild CB hypoxia) and 27% (severe CB hypoxia) from the
peak response, respectively. We conclude that carotid body hypocapnia
can be a major source of inhibitory feedback to respiratory motor
output during the hyperventilatory response to hypoxic carotid body
stimulation.
control of breathing; stimulus interaction; extracorporeal perfusion; chemoreceptors
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