| Abstrakt: |
Chronic intermittent hypoxia (72 episodes/night, 7 nights) increases synaptic efficacy in crossed-spinal synaptic pathways to phrenic motor neurons below a C2 spinal hemisection (C2HS; Fuller et al., J. Neurosci., 2003), although it is not known if intermittent hypoxia improves ventilatory function in C2HS rats. Daily acute intermittent hypoxia (dAIH; 10 episodes/day, 7 days) induces similar respiratory plasticity (Wilkerson and Mitchell, ibid, 2004, 2005). We tested the hypothesis that dAIH reverses ventilatory deficits in rats with C2HS. Rats were exposed to dAIH or an equivalent duration of normoxia beginning one-week post-C2HS, and ventilation, tidal volume and breathing frequency were measured (whole-body plethysmography) during normoxia (21% O2), 5% and 7% CO2 in air, and then 7% CO2 with hypoxia (10% O2; 25 min exposures). In normoxia-treated C2HS rats (n=6), tidal volume and ventilation were decreased at each level of chemoreceptor stimulation whereas breathing frequency was elevated compared to sham-operated rats (n=14; p<0.05). In dAIH-treated C2HS rats (n=6), ventilation and tidal volume were increased versus normoxia-treated C2HS rats (p<0.05), and were no longer different from sham-operated rats (p>0.05). In contrast, breathing frequency remained elevated in dAIH-treated C2HS rats at all levels of chemoreceptor stimulation (p<0.05). These data suggest that dAIH improves the capacity to increase tidal volume and pulmonary ventilation following C2HS, but does not restore normal breathing patterns. Thus, dAIH may be a useful therapeutic approach in the treatment of respiratory insufficiency following cervical spinal injuries. [ABSTRACT FROM AUTHOR] |
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