Bright light affects alertness and performance rhythms during a 24-h constant routine.

The aim of the present study was to assess the stimulating effects of bright light (BL) on subjective and objective alertness. Eight subjects were exposed to either bright light or dim light (DL) during a 24-h constant routine (0900-0900). Bright light failed to modify either the 24-h course or the level of body temperature.

MIBG scintigraphic assessment of cardiac adrenergic activity in response to altitude hypoxia.

High altitude hypoxia induces a decrease in the cardiac chronotropic function at maximal exercise or in response to isoproterenol infusion, suggesting an alteration in the cardiac sympathetic activation. Iodine-123 metaiodobenzylguanidine [( 123I]MIBG) was used to map scintigraphically the cardiac sympathetic neuronal function in six male subjects (aged 32 +/- 7 yr) after an exposure to high altitude that created hypoxic conditions. Results obtained just after return to sea level (RSL) were compared with the normal values obtained after 2 or 3 mo of normoxia (N).

Reversal of hypoxia-induced decrease in human cardiac response to isoproterenol infusion.

A decrease in heart rate response to isoproterenol (IP) infusion has been previously described in humans exposed to acute (2-3 days) or chronic (21 days) exposure to altitude hypoxia (J. Appl. Physiol.

[Cardiac response to hypoxia and susceptibility to mountain sickness].

Exercising in high altitude is impeded during the first days of exposure to altitude hypoxia by the symptoms of Acute Mountain Sickness (AMS). Susceptibility to AMS is independent of endurance training and determined by the sensitivity of carotid chemoreceptors to hypoxemia and induced hyperventilation and tachycardia. Cardiac response to hypoxia is not as well known as ventilatory response, especially at exercise.

Effect of beta-adrenoceptor blockade on renin-aldosterone and alpha-ANF during exercise at altitude.

The renin-aldosterone system may be depressed in subjects exercising at high altitude, thereby preventing excessive angiotensin I (ANG I) and aldosterone levels, which could favor the onset of acute mountain sickness. The role of beta-adrenoceptors in hormonal responses to hypoxia was investigated in 12 subjects treated with a nonselective beta-blocker, pindolol. The subjects performed a standardized maximal bicycle ergometer exercise with (P) and without (C) acute pindolol treatment (15 mg/day) at sea level, as well as during a 5-day period at high altitude (4,350 m, barometric pressure 450 mmHg).