Document Detail

Phrenic long-term facilitation is robust to hypercapnia and hypocapnia but not hyperventilatory hypotension under PEEP.
MedLine Citation:
PMID:  17331813     Owner:  NLM     Status:  MEDLINE    
Phrenic long-term facilitation (LTF) has been extensively studied in anesthetized animals under well-defined physiological conditions but the factors underlying its possible manifestation under clinically relevant conditions are not well understood. Here, we examine the stability of LTF in the face of hypercapnic or hypocapnic challenges in anesthetized, paralyzed and mechanically ventilated rats. Sixty minutes after induction of phrenic LTF by intermittent hypoxia the animal was exposed to one of four conditions for 5 min with or without positive end-expiratory pressure (PEEP, 3-4 cmH(2)O): hypocapnic apnea, hypocapnia (5 Torr below resting level), 5% CO(2) and 10% CO(2). LTF at 60 min post-intermittent hypoxia was approximately 39% above baseline. Following the above CO(2) tests, LTF almost invariably returned to the corresponding pre-test level after recovery for 20 min. The only exception was the combination of hypocapnic apnea and PEEP, which resulted in a marked decrease in mean arterial pressure (to 38-55mmHg) during test and a subsequent paradoxical sustained attenuation of LTF (to approximately 8% above baseline) even after mean arterial pressure had fully recovered. The results suggest that LTF, once developed, is highly robust to changes in CO(2) levels and is attenuated only after severe hypotension secondary to excessive hyperventilation under PEEP.
Michelle McGuire; Shawna M MacDonald; Gang Song; Chi-Sang Poon
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Publication Detail:
Type:  Journal Article; Research Support, N.I.H., Extramural     Date:  2007-02-03
Journal Detail:
Title:  Respiratory physiology & neurobiology     Volume:  158     ISSN:  1569-9048     ISO Abbreviation:  Respir Physiol Neurobiol     Publication Date:  2007 Aug 
Date Detail:
Created Date:  2007-06-25     Completed Date:  2007-09-18     Revised Date:  2013-06-06    
Medline Journal Info:
Nlm Unique ID:  101140022     Medline TA:  Respir Physiol Neurobiol     Country:  Netherlands    
Other Details:
Languages:  eng     Pagination:  107-11     Citation Subset:  IM    
Harvard-MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology, Bldg. 56-046, 77 Massachusetts Avenue, Cambridge, MA 02139, USA.
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MeSH Terms
Anoxia / physiopathology,  therapy
Disease Models, Animal
Hypercapnia / physiopathology*
Hyperventilation / etiology,  physiopathology*
Hypocapnia / physiopathology*
Hypotension / physiopathology*
Long-Term Potentiation / physiology*
Phrenic Nerve / physiopathology*
Positive-Pressure Respiration*
Sleep Apnea Syndromes / physiopathology,  therapy
Grant Support
Comment In:
Respir Physiol Neurobiol. 2007 Aug 15;158(1):112-3   [PMID:  17412653 ]

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