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Does simulated apnea elicit respiratory long term facilitation?
Author(s) -
Mahamed Safraaz,
Mitchell Gordon S
Publication year - 2006
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.20.4.a372
Subject(s) - anesthesia , apnea , medicine , hypoxia (environmental) , respiratory system , intermittent hypoxia , phrenic nerve , control of respiration , chemistry , obstructive sleep apnea , oxygen , organic chemistry
Respiratory plasticity following acute intermittent hypoxia may help to prevent apneas and hypopneas during sleep. Long term facilitation (LTF) is a progressive increase in respiratory motor output following acute intermittent hypoxia. LTF is most frequently studied in anesthetized rats following three, 5‐min episodes of isocapnic hypoxia with 5‐min intervals. Since spontaneous apneas are shorter than 5‐min, and result in hypercapnic hypoxia, we determined whether simulated apneas also induce LTF in anesthetized rats. We hypothesized that repetitive 25‐sec pump apneas at 5‐min intervals would elicit LTF in both phrenic and hypoglossal (XII) motor output. Phrenic and XII activity were recorded in anesthetized, vagotomized and ventilated Sprague Dawley rats (Harlan, 217) before and 60‐min after 6, 25‐sec pump apneas, separated by 5‐min of control, hyperoxic conditions (PaO 2 > 200 mmHg). 60‐min after the final pump apnea, LTF was observed in both phrenic (53±7% baseline; n = 6; p < 0.05) and XII activity (53±6% baseline; p < 0.05). Both were significantly greater than time controls (phrenic: 5±7%; and XII: 8±13% baseline; n = 3; p < 0.05). The magnitude of pump‐apnea induced LTF is similar to values observed after 3, 5‐min episodes of isocapnic hypoxia. Thus, 6 25‐sec pump apneas are sufficient to produce a robust respiratory LTF in both phrenic and XII motor output. Although all aspects of a spontaneous apnea were not simulated by this protocol, we speculate that LTF has the potential to play an important role in stabilizing breathing during sleep, minimizing the recurrence of apneas. Such an effect may help explain the evolution of obstructive sleep apnea syndrome as it progresses from tolerable, when LTF mechanisms are sufficient, to intolerable, when LTF is either absent or no longer adequate to prevent further apneas. Supported by NIH HL65383, HL 89209 and CIHR (Canada).