Healthcare and Medicine Reference
In-Depth Information
high altitude truly differs from that at sea level. It is pos-
sible that arterial desaturation induced by high altitude
shifts SaO 2 during sleep to the steeper portion of the dis-
sociation curve and thereby amplifies the influence of ven-
tilatory dysrhythmia on SaO 2 .
Ventilatory and SaO 2 oscillations similar to those
observed by Kryger and colleagues 98 have also been
described at high altitude by Lahiri and colleagues 36 in
Sherpas native to high altitude but not in Sherpas native
to low altitude. The potential contribution of ethnic and/
or genetic differences is suggested by a study comparing
Tibetan and Chinese Han residents of 4000 meters. Sleep
was studied in a hypobaric chamber at simulated altitudes
of 2261 and 5000 meters. At the higher altitude, Tibetans
had more periodic breathing, higher SaO 2 , and better sleep
structure than did the Han subjects. 100
Although decreased hypoxic ventilatory response during
wakefulness has been observed in natives of Leadville 101
and in Sherpas native to high altitude, 102 it is unclear
whether this contributes to respiratory dysrhythmia and
hypoxemia in highlanders during sleep at altitude.
However, improvement in hypoxemia during wakefulness
and sleep in long-term residents at high altitude with use
of the ventilatory stimulant medroxyprogesterone acetate
suggests that decreased ventilatory drive may have a per-
missive role. 98 , 103 Similar findings are reported for acetazol-
amide which over a three week's treatment in residents in
the Andes at 4300 m increased oxygen saturation and
markedly reduced the apnea-hypopnea index during
sleep. 104
Natives and long-term residents of high altitude exhibit
chronic mountain sickness or Monge's disease, a syndrome
of excessive polycythemia with headache, dizziness, breath-
lessness, and sleep disturbance. The pathophysiology of
the syndrome is debated, but likely is induced by increased
hypoxemia reflecting the combined effects of altitude,
decreased ventilatory drive and lung dysfunction. Com-
pared to normal subjects, individuals with chronic moun-
tain sickness exhibit exaggerated hypoxemia during sleep
without an increase in RDI. 104-106 These subjects also
exhibit greater daytime hypoxemia and thus the role of
sleep-associated desaturation remains uncertain.
drase, which likely works by reducing alkalotic ventilatory
inhibition. Recent studies suggest that benzodiazepines
and other hypnotic agents may improve sleep quality
without apparent adverse effects. 107
Clinical Pearl
Sleep at altitude is disturbed by the opposing influ-
ences of hypoxic stimulation and alkalotic inhibition
which lead to periodic breathing and frequent associ-
ated arousals. Effective treatments include correction
of alkalosis with acetazolamide or blunting of hypoxic
stimulation with some benzodiazepines.
1. Moore LG, Harrison GL, McCullough RE, et al. Low acute
hypoxic ventilatory response and hypoxic depression in acute alti-
tude sickness. J Appl Physiol 1986;60:1407-1412.
2. Bisgard GE. Carotid body mechanisms in acclimatization to
hypoxia. Respir Physiol 2000;121:237-246.
3. Joern AT, Shurley JT, Brooks RE, et al. Short-term changes in sleep
patterns on arrival at the South Polar Plateau. Arch Intern Med
4. Reite M, Jackson D, Cahoon RL, et al. Sleep physiology at
high altitude. Electroencephalogr Clin Neurophysiol 1975;38:
5. Goldenberg F, Richalet JP, Onnen I, et al. Sleep apneas and high
altitude newcomers. Int J Sports Med 1992;13:S34-S36.
6. Mizuno K, Asano K, Okudaira N. Sleep and respiration under acute
hypobaric hypoxia. Jpn J Physiol 1993;43:161-175.
7. Normand H, Barragan M, Benoit O, et al. Periodic breathing and
O2 saturation in relation to sleep stages at high altitude. Aviat Space
Environ Med 1990;61:229-235.
8. Wickramasinghe H, Anholm JD. Sleep and breathing at high alti-
tude. Sleep Breath 1999;3:89-102.
9. Miller JC, Horvath SM. Sleep at altitude. Aviat Space Environ Med
10. Anholm JD, Powles AC, Downey RD, et al. Operation Everest II:
arterial oxygen saturation and sleep at extreme simulated altitude.
Am Rev Respir Dis 1992;145:817-826.
11. Bonnet MH. Performance and sleepiness as a function of frequency
and placement of sleep disruption. Psychophysiology 1986;23:
12. Netzer NC, Strohl KP. Sleep and breathing in recreational climbers
at an altitude of 4200 and 6400 meters: observational study of sleep
and patterning of respiration during sleep in a group of recreational
climbers. Sleep Breath 1999;3:75-82.
13. Ohi M, Chin K, Hirai M, et al. Oxygen desaturation following
voluntary hyperventilation in normal subjects. Am J Respir Crit
Care Med 1994;149:731-738.
14. Lovering AT, Fraigne JJ, Dunin-Barkowski WL, et al. Hypocapnia
decreases the amount of rapid eye movement sleep in cats. Sleep
15. Ward M. Periodic respiration. A short historical note. Ann R Coll
Surg Engl 1973;52:330-334.
16. Douglas C, Haldane J, Henderson Y, et al. Physiological observa-
tions made of Pike's Peak, Colorado, with special reference to
adaptation to low barometric pressures. Philosophical Trans R Soc
Lond 1913;203:185-381.
17. Berssenbrugge A, Dempsey J, Iber C, et al. Mechanisms of hypoxia-
induced periodic breathing during sleep in humans. J Physiol
18. Kryger M, McCullough RE, Collins D, et al. Treatment of excessive
polycythemia of high altitude with respiratory stimulant drugs. Am
Rev Respir Dis 1978;117:455-464.
19. Masuyama S, Kohchiyama S, Shinozaki T, et al. Periodic breathing
at high altitude and ventilatory responses to O2 and CO2. Jpn J
Physiol 1989;39:523-535.
20. Sutton JR, Houston CS, Mansell AL, et al. Effect of acetazolamide
on hypoxemia during sleep at high altitude. N Engl J Med 1979;
The sensation of disrupted sleep after ascent to high alti-
tude is associated with frequent awakenings, which in part
probably reflect sleep fragmentation by respiratory dys-
rhythmia typically consisting of monotonously repetitive
periodic breathing. This periodicity is produced by venti-
latory inhibition by hypocapnic alkalosis alternating with
stimulation by hypoxia, which terminates apnea and initi-
ates hyperpnea with consequent hypocapnia, leading to
perpetuation of periodicity. Sleep disruption and periodic
breathing decrease with time at moderate altitude and are
also considerably reduced by pretreatment with acetazol-
amide, which reduces alkalosis. In long-term residents of
high altitude, less-distinctive, undulating respiratory dys-
rhythmias are described, with unstable and decreased arte-
rial oxygenation.
The most common treatment is prophylactic adminis-
tration of acetazolamide, an inhibitor of carbonic anhy-
Search Pocayo ::

Custom Search