Cardiovascular effects of 8 h of isocapnic hypoxia with and without beta-blockade in humans

Clar, Christine; Dorrington, Keith L.; Fatemian, Marzieh; Robbins, Peter A.

doi:10.1017/s095806700002008x

Cited by 2 publications

(2 citation statements)

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“…Sustained hypoxia of 8 h duration induced a rise in HR under subsequent euoxic conditions and a rise in the sensitivity of HR to acute hypoxia that was similar to that reported in previous studies (Clar et al 2000; Clar et al 2001). Much of this was abrogated with the acute infusion of trimetaphan in Protocol T, consistent with the previous report that much of the change in HR following sustained hypoxia arises through alterations in parasympathetic function (Clar et al 2001).…”

Section: Discussionsupporting

confidence: 88%

“…As there was no euoxia control protocol in the study design, in theory it is possible that there is a significant ‘time of day’ effect incorporated within the acclimatization effect. In practice we have conducted a considerable number of other studies involving 8 h exposures to hypoxia, which have included euoxia control protocols, and in none of these controls have we found a significant time of day effect (Howard & Robbins, 1995; Tansley et al 1997; Fatemian & Robbins, 1998; Clar et al 1999, 2000; Ren et al 2000).…”

Section: Discussionmentioning

confidence: 99%

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Lack of involvement of the autonomic nervous system in early ventilatory and pulmonary vascular acclimatization to hypoxia in humans

Smith

Balanos

et al. 2007

The Journal of Physiology

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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.

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Section: Discussionsupporting

confidence: 88%