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1 Laboratorio de Neurobiología, Facultad de Ciencias Biológicas, P. Universidad Católica de Chile
2 Laboratorio de Fisiología Celular, Departamento de Biología, Facultad de Ciencias, Universidad de Chile, Santiago, Chile
The carotid body (CB) chemoreceptors may play an important role in the enhanced hypoxic ventilatory response induced by chronic intermittent hypoxia (CIH). We studied the effects of cyclic hypoxic episodes of short duration on cat cardiorespiratory reflexes, heart rate variability, and CB chemosensory activity. Cats were exposed to cyclic hypoxic episodes (PO2 
75 Torr) repeated during 8 h for 2–4 days. Cats were anaesthetized with sodium pentobarbitone (40 mg kg–1 I.P., followed by 8–12 mg I.V.), and ventilatory and cardiovascular responses to NaCN (0.1–100 µg kg–1 I.V.) and several isocapnic levels of oxygen (PO2 20–740 Torr) were studied. After studying the reflex responses, we recorded the CB chemosensory responses induced by the same stimuli. Results showed that CIH for 4 days selectively enhanced cat CB ventilatory (VT and VI) responses to hypoxia, while responses to NaCN remained largely unchanged. Similarly, basal CB discharges and responses to acute hypoxia (PO2 < 100 Torr) were larger in CIH than in control cats, without modification of the responses to NaCN. Exposure to CIH did not increase basal arterial pressure, heart rate, or their changes induced by acute hypoxia or hyperoxia. However, the spectral analysis of heart rate variability of CIH cats showed a marked increase of the low-/high-frequency ratio and an increase of the power spectral distribution of low frequencies of heart rate variability. Thus, the enhanced CB reactivity to hypoxia may contribute to the augmented ventilatory response to hypoxia, as well as to modified heart rate variability due to early changes in autonomic activity.
(Received 20 July 2004;
accepted after revision 18 August 2004;
first published online 19 August 2004)
Corresponding author R. Iturriaga: Laboratorio de Neurobiología, Facultad de Ciencias Biológicas, P. Universidad Católica of Chile, Casilla 114-D, Santiago 1, Chile. Email: riturria{at}bio.puc.cl
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