The effect of low-level normobaric hypoxia on orthostatic responses

Caroline Alice Rickards, David G. Newman

Research output: Contribution to journalArticle

16 Citations (Scopus)

Abstract

Background: Altitude-induced hypoxia is believed to decrease tolerance to orthostasis. This preliminary investigation assesses the interaction between low-level normobaric hypoxia and the cardiovascular responses to orthostasis. Hypothesis: We hypothesize that low-level hypoxia at simulated altitudes up to 3350 m adversely affects cardiovascular responses to orthostasis. Methods: Six women and eight men underwent +75° head-up tilt (HUT) at 3 simulated altitudes (115 m (377 ft), 1680 m (5500 ft) and 3350 m (11,000 ft)). Minute ventilation (VE), tidal volume (VT), breathing frequency (f), heart rate (HR), and arterial blood pressure (BP) were measured non-invasively. Ventilatory parameters (VE, VT, and f) were measured during the control period to assess the respiratory response to hypoxia. Cardiovascular variables (HR and BP) during HUT were compared and analyzed by calculating the deviation from control (pre-tilt) values. Results: Respiratory data showed no significant hypoxic ventilatory response. The average HR deviation significantly decreased (p < 0.05) with HUT from 13 ± 2 bpm (115 m) to 9 ± 2 bpm (3350 m). The pattern of mean arterial BP deviation with HUT was similar across the three altitudes (-6.6 ± 2.9 mm Hg at 115 m to -6.8 ± 2.4 mm Hg at 3350 m), with no significant differences. Conclusions: Changes in HR and arterial BP are fundamental aspects of the cardiovascular response to orthostatic stress. Although there were no significant changes in the BP response to orthostasis with hypoxia, the HR changes seen in this study suggest that the ability to modulate HR under orthostatic stress is reduced with exposure to low-level normobaric hypoxia.

Original languageEnglish
Pages (from-to)460-465
Number of pages6
JournalAviation Space and Environmental Medicine
Volume73
Issue number5
StatePublished - 6 May 2002

Fingerprint

Blood pressure
Heart Rate
Dizziness
Arterial Pressure
Head
Tidal Volume
Ventilation
Altitude Sickness
Blood Pressure
Hypoxia
Respiration

Keywords

  • Altitude
  • Cardiovascular
  • Gravity
  • Hypoxia
  • Orthostatic
  • Tilt
  • Tolerance

Cite this

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title = "The effect of low-level normobaric hypoxia on orthostatic responses",
abstract = "Background: Altitude-induced hypoxia is believed to decrease tolerance to orthostasis. This preliminary investigation assesses the interaction between low-level normobaric hypoxia and the cardiovascular responses to orthostasis. Hypothesis: We hypothesize that low-level hypoxia at simulated altitudes up to 3350 m adversely affects cardiovascular responses to orthostasis. Methods: Six women and eight men underwent +75° head-up tilt (HUT) at 3 simulated altitudes (115 m (377 ft), 1680 m (5500 ft) and 3350 m (11,000 ft)). Minute ventilation (VE), tidal volume (VT), breathing frequency (f), heart rate (HR), and arterial blood pressure (BP) were measured non-invasively. Ventilatory parameters (VE, VT, and f) were measured during the control period to assess the respiratory response to hypoxia. Cardiovascular variables (HR and BP) during HUT were compared and analyzed by calculating the deviation from control (pre-tilt) values. Results: Respiratory data showed no significant hypoxic ventilatory response. The average HR deviation significantly decreased (p < 0.05) with HUT from 13 ± 2 bpm (115 m) to 9 ± 2 bpm (3350 m). The pattern of mean arterial BP deviation with HUT was similar across the three altitudes (-6.6 ± 2.9 mm Hg at 115 m to -6.8 ± 2.4 mm Hg at 3350 m), with no significant differences. Conclusions: Changes in HR and arterial BP are fundamental aspects of the cardiovascular response to orthostatic stress. Although there were no significant changes in the BP response to orthostasis with hypoxia, the HR changes seen in this study suggest that the ability to modulate HR under orthostatic stress is reduced with exposure to low-level normobaric hypoxia.",
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The effect of low-level normobaric hypoxia on orthostatic responses. / Rickards, Caroline Alice; Newman, David G.

In: Aviation Space and Environmental Medicine, Vol. 73, No. 5, 06.05.2002, p. 460-465.

Research output: Contribution to journalArticle

TY - JOUR

T1 - The effect of low-level normobaric hypoxia on orthostatic responses

AU - Rickards, Caroline Alice

AU - Newman, David G.

PY - 2002/5/6

Y1 - 2002/5/6

N2 - Background: Altitude-induced hypoxia is believed to decrease tolerance to orthostasis. This preliminary investigation assesses the interaction between low-level normobaric hypoxia and the cardiovascular responses to orthostasis. Hypothesis: We hypothesize that low-level hypoxia at simulated altitudes up to 3350 m adversely affects cardiovascular responses to orthostasis. Methods: Six women and eight men underwent +75° head-up tilt (HUT) at 3 simulated altitudes (115 m (377 ft), 1680 m (5500 ft) and 3350 m (11,000 ft)). Minute ventilation (VE), tidal volume (VT), breathing frequency (f), heart rate (HR), and arterial blood pressure (BP) were measured non-invasively. Ventilatory parameters (VE, VT, and f) were measured during the control period to assess the respiratory response to hypoxia. Cardiovascular variables (HR and BP) during HUT were compared and analyzed by calculating the deviation from control (pre-tilt) values. Results: Respiratory data showed no significant hypoxic ventilatory response. The average HR deviation significantly decreased (p < 0.05) with HUT from 13 ± 2 bpm (115 m) to 9 ± 2 bpm (3350 m). The pattern of mean arterial BP deviation with HUT was similar across the three altitudes (-6.6 ± 2.9 mm Hg at 115 m to -6.8 ± 2.4 mm Hg at 3350 m), with no significant differences. Conclusions: Changes in HR and arterial BP are fundamental aspects of the cardiovascular response to orthostatic stress. Although there were no significant changes in the BP response to orthostasis with hypoxia, the HR changes seen in this study suggest that the ability to modulate HR under orthostatic stress is reduced with exposure to low-level normobaric hypoxia.

AB - Background: Altitude-induced hypoxia is believed to decrease tolerance to orthostasis. This preliminary investigation assesses the interaction between low-level normobaric hypoxia and the cardiovascular responses to orthostasis. Hypothesis: We hypothesize that low-level hypoxia at simulated altitudes up to 3350 m adversely affects cardiovascular responses to orthostasis. Methods: Six women and eight men underwent +75° head-up tilt (HUT) at 3 simulated altitudes (115 m (377 ft), 1680 m (5500 ft) and 3350 m (11,000 ft)). Minute ventilation (VE), tidal volume (VT), breathing frequency (f), heart rate (HR), and arterial blood pressure (BP) were measured non-invasively. Ventilatory parameters (VE, VT, and f) were measured during the control period to assess the respiratory response to hypoxia. Cardiovascular variables (HR and BP) during HUT were compared and analyzed by calculating the deviation from control (pre-tilt) values. Results: Respiratory data showed no significant hypoxic ventilatory response. The average HR deviation significantly decreased (p < 0.05) with HUT from 13 ± 2 bpm (115 m) to 9 ± 2 bpm (3350 m). The pattern of mean arterial BP deviation with HUT was similar across the three altitudes (-6.6 ± 2.9 mm Hg at 115 m to -6.8 ± 2.4 mm Hg at 3350 m), with no significant differences. Conclusions: Changes in HR and arterial BP are fundamental aspects of the cardiovascular response to orthostatic stress. Although there were no significant changes in the BP response to orthostasis with hypoxia, the HR changes seen in this study suggest that the ability to modulate HR under orthostatic stress is reduced with exposure to low-level normobaric hypoxia.

KW - Altitude

KW - Cardiovascular

KW - Gravity

KW - Hypoxia

KW - Orthostatic

KW - Tilt

KW - Tolerance

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M3 - Article

C2 - 12014605

AN - SCOPUS:0036227552

VL - 73

SP - 460

EP - 465

JO - Aviation Space and Environmental Medicine

JF - Aviation Space and Environmental Medicine

SN - 0095-6562

IS - 5

ER -