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This Article Free via Open Access: OA OA Full Text Full Text (PDF) OA All Versions of this Article: 579/1/215    most recent jphysiol.2006.118190v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Liu, C. Articles by Robbins, P. A. Search for Related Content PubMed PubMed Citation Articles by Liu, C. Articles by Robbins, P. A. Related Collections Respiratory

¹ Department of Physiology, Anatomy and Genetics, University of Oxford, Sherrington Building, Parks Road, Oxford OX1 3PT, UK
² School of Sport and Exercise Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
³ Department of Respiratory Medicine, University of Cambridge, Level 5, Box 157, Addenbrooke's Hospital, Hills Road, Cambridge CB2 2QQ, UK

The activity within the autonomic nervous system may be altered following sustained exposure to hypoxia, and it is possible that this increase in activity underlies the early acclimatization of both ventilation and the pulmonary vasculature to hypoxia. To test this hypothesis, seven individuals were infused with the ganglionic blocker trimetaphan before and after an 8 h exposure to hypoxia. The short half-life of trimetaphan should ensure that the initial infusion does not affect acclimatization to the 8 h hypoxia exposure, and the use of a ganglion blocking agent should inhibit activity within all branches of the autonomic nervous system. During the infusions of trimetaphan, measurements of ventilation and echocardiographic assessments of pulmonary vascular tone (P_max) were made during euoxia and during a short period of isocapnic hypoxia. Subjects were also studied on two control days, when a saline infusion was substituted for trimetaphan. Trimetaphan had no effect on either euoxic ventilation or the sensitivity of ventilation to acute hypoxia. Trimetaphan significantly reduced P_max in euoxia (P < 0.05), but had no significant effect on the sensitivity of P_max to acute hypoxia once changes in cardiac output had been controlled for. The 8 h period of hypoxia elevated euoxic ventilation (P < 0.001) and P_max (P < 0.001) and increased their sensitivities to acute hypoxia (P < 0.001 for both), indicating that significant acclimatization had occurred. Trimetaphan had no effect on the acclimatization response of any of these variables. We conclude that altered autonomic activity following 8 h of hypoxia does not underlie the acclimatization observed in ventilation or pulmonary vascular tone.

(Received 28 July 2006; accepted after revision 28 November 2006; first published online 30 November 2006)
Corresponding author P. A. Robbins: Department of Physiology, Anatomy and Genetics, University of Oxford, Sherrington Building, Parks Road, Oxford OX1 3PT, UK. Email: peter.robbins{at}physiol.ox.ac.uk

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