Effect of acute exposure to 3,660 m altitude on orthostatic responses and  tolerance

Blaber, Andrew P.; Hartley, Tim; Pretorius, P. J.

doi:10.1152/japplphysiol.00749.2002

Cited by 33 publications

(39 citation statements)

References 54 publications

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“…Nevertheless, a few results on the interactive eVects of chemoreXex and baroreXex control on muscle sympathetic nerve activity that have been reported by now (Somers et al 1991), speak in favour of our conclusions. And third, syncope is a multifactor event (Blaber et al 2003), thus investigating factors that aVect BRS at high altitude will provide only a limited, yet indispensable insight into the associated physiological mechanisms.…”

Section: Discussionmentioning

confidence: 99%

Baroreflex sensitivity in acute hypoxia and carbohydrate loading

Klemenc¹,

Golja

2011

Eur J Appl Physiol

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Hypoxia decreases baroreflex sensitivity (BRS) and can be a sufficient cause for syncope in healthy individuals. Carbohydrate loading enhances efferent sympathetic activity, which affects cardiac contractility, heart rate and vascular resistance, the main determinants of blood pressure. Thus, in both normoxia and hypoxia, carbohydrate loading may be more than simply metabolically beneficial, as it may affect blood pressure regulation. We hypothesised that carbohydrate loading will, in both normoxia and hypoxia, alter the regulation of blood pressure, as reflected in a change in baroreflex sensitivity. Fourteen subjects participated in two experiments, composed of a 15-min normoxic period, after which the subjects ingested water or an equal amount of water with carbohydrates. A 30-min rest period was then followed by a 10-min second normoxic and a 30-min hypoxic period. Blood pressure and heart rate were monitored continuously during the experiment to determine BRS. Despite an increased sympathetic activation, reflected in increased heart rate (P < 0.001) BRS was lower (P < 0.01) after carbohydrate loading, as compared to the water experiment, in both normoxic [23.7 (12.4) versus 28.8 (13.8) ms/mmHg] and hypoxic [16.8 (11.0) versus 24.3 (12.3) ms/mmHg] phases of the present study. As BRS was decreased in acute hypoxic exposure, the results confirm that hypoxia interferes with blood pressure regulation. However, although oral carbohydrate loading induced sympathoexcitation, it did not improve blood pressure regulation in hypoxia, as evident from the BRS data. Baroreflex effects of other forms of carbohydrate loading, not causing postprandial blood shifts to digestive system, should therefore be investigated.

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Section: Discussionmentioning

confidence: 99%

Baroreflex sensitivity in acute hypoxia and carbohydrate loading

Klemenc¹,

Golja

2011

Eur J Appl Physiol

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“…Conversely, acute exposure to 15% O 2 does not cause any change in BP response, cardiac autonomic activity and vascular physical characteristics as subjects rested in a supine position and during physical exertions (i.e., sitting up and the Valsalva maneuver). Impaired baroreXex has been associated with reduced orthostatic tolerance during exposure to high altitudes (Blaber et al 2003;Sagawa et al 1993). However, the Wndings are conXicting regarding the eVect of hypoxia on carotid baroreXex control of HR in humans.…”

Section: Discussionmentioning

confidence: 99%

Systemic hypoxia affects cardiac autonomic activity and vascular hemodynamic control modulated by physical stimulation

Huang

Wong

2009

Eur J Appl Physiol

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This study investigates how various hypoxic interventions affect cardiac autonomic activity and hemodynamic control during posture change and the Valsalva maneuver. Ten healthy sedentary men exposed to 12, 15 and 21% O(2) for 1 h in a normobaric hypoxia chamber in a random order. Before and after various O(2) concentrations were administered, subjects performed the sit-up test and Valsalva maneuver, respectively. An impedance plethysmography was utilized to measure blood pressure (BP) and vascular hemodynamics, whereas spectral analysis of heart rate variability (HRV) was performed to determine cardiac autonomic activity. Analytical results can be summarized as follows: while the patient rests in a supine position, exposure to 12% O(2) reduces the ratio of lower to upper extremity systolic BP, which is accompanied by (1) suppressed arterial reactive hyperemia and increased venous flow resistance, as well as (2) decreased total power and high frequency (HF) and increased low frequency (LF) and the ratio of LF to HF. Moreover, the hypoxia-induced changes of time and frequency domains in HRV at resting supine disappear following the sit-up test, whereas this hypoxic exposure attenuates the BP and heart rate responses to the Valsalva maneuver. Conversely, resting and physical stimuli-mediated HRV and vascular hemodynamic values are unaltered by both 15 and 21% O(2) exposures. We conclude that acute hypoxic exposure affects cardiovascular autonomic functions, with reactions determined by the intervening O(2) concentrations. Moreover, the BP and cardiac autonomic responses to 12% O(2), but not 15% O(2), exposure are depressed while performing posture change and the Valsalva maneuver.

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“…Dagegen blieb einer Studie von d'Este zufolge der mittlere systolische Blutdruck von normotensiven Probanden in 2.572 m Höhe unverändert, während bei Patienten mit mäßiggradigem unbehandeltem Hypertonus ein geringer Blutdruckanstieg verzeichnet wurde [15]. Andererseits können durch akute Hypoxieexposition auch bei Gesunden Synkopen provoziert werden wie Expositionsstudien unter simulierten Höhenbedingungen zeigten sowie auch neurologische Störungen wie zerebrale Anfälle, Doppelbilder, Skotome und transitorisch ischämische Attacken auftreten [16][17][18][19]. Nach Untersuchungen von Roach sind Menschen auch im fortgeschrittenen Alter und mit präexistenten chronischen Erkrankungen, wie z.…”

Section: Blutdruckverhalten Und Koronares Risikounclassified

Aspects and necessity of moderate-altitude research

Domej

Schwaberger

Guger

et al. 2005

Wien Med Wochenschr

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Alpinism in all its variations is a leading factor in tourism. Within a few decades, alpine sports, even at high altitudes, have become available to a wide range of people. Now, more people than ever before are hiking, trekking, climbing and skiing at moderate and high altitudes. Annually, 40 million people spend time in the Alps and 100 million visit high altitudes worldwide. However, alpine excursions may entail health problems and many aspects of impaired adaptation to altitude remain unstudied. High-altitude research has mainly been associated with expeditions, with moderate altitudes receiving far less attention, though most tourism takes place at that level. The overwhelming numbers of alpine tourists mean that there is urgent need for high- and moderate-altitude medical research, which would also be within the realm of political responsibility in mountainous countries. Research in mountain medicine and dissemination of relevant findings can show how to improve and conserve performance in healthy individuals and could point the way toward new, safe approaches in the rehabilitation of patients with chronic diseases. It is imperative that mountain medicine continues to develop on a scientific basis.

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Effect of acute exposure to 3,660 m altitude on orthostatic responses and tolerance

Cited by 33 publications

References 54 publications

Baroreflex sensitivity in acute hypoxia and carbohydrate loading

Baroreflex sensitivity in acute hypoxia and carbohydrate loading

Systemic hypoxia affects cardiac autonomic activity and vascular hemodynamic control modulated by physical stimulation

Aspects and necessity of moderate-altitude research

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