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ABSTRACT: Cerebral vascular response via local and reflex adjustments is part of the integrated response to hypoxia and is coupled with changes in systemic vascular resistances that allow a redistribution of blood flow toward the brain. The cerebral vascular response in airmen exposed to simulated high altitude is not clear, thus we sought to investigate this aspect.
Four healthy military airmen were exposed to simulated high altitude in a hypobaric chamber according to a standard training protocol. Blood saturation (SpO2) and blood flow velocity with transcranial Doppler from the left middle cerebral artery (Vm) were continuously recorded. Pulsatility Index (PI), resistance index (RI), and systolic/diastolic ratio (S/D ratio) were computed. Alternate hypoxia-hyperoxia trials for 2 and 1 min, respectively, were used to assess the cerebrovascular response.
Acute hypoxia induced an increase in Vm that promptly recovered when the oxygen supply was restored (mean increase of 5.5% at 18,000 ft and 17.2% at 25,000 ft). Alternate hypoxia-hyperoxia at 25,000 and 18,000 ft elicited changes in both SpO2 and Vm. In hypoxia, PI significantly decreased (mean decrease o" 25.6% at 18,000 ft and 39.5% at 25,000 ft), as did RI (mean decrease of 18.7% at 18,000 ft and 34.4% at 25,000 ft), while S/D ratio increased.
The standard altitude training protocol induced a transient cerebrovascular response. The response was as expected, with hypoxia-induced vasodilation and opposite changes when breathing pure oxygen.
Aviation Space and Environmental Medicine 12/2011; 82(12):1138-42. · 0.88 Impact Factor
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ABSTRACT: In recent years many methods of physical therapy have been proposed for the treatment of benign paroxysmal positional vertigo due to otolithic debris in the horizontal semicircular canal. All these methods have attempted to promote displacement of debris from the canal to the utricle. This paper reports our experiences with maneuvers advocated by Lempert and Vannucchi et al. Eighteen patients suffering from benign paroxysmal positional vertigo of the horizontal canal were evaluated in the present study. All seven patients treated with the Vannucchi maneuvers resolved their vertigos. Ten of the remaining patients were managed with Lempert's maneuver and responded successfully. The physical therapy used failed in only one patient. Current experience has shown that both maneuvers are particularly valid and efficacious.
Archiv für Klinische und Experimentelle Ohren- Nasen- und Kehlkopfheilkunde 02/1997; 254(7):326-8. · 1.29 Impact Factor
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American Journal of Otolaryngology 21(1):65-8. · 0.87 Impact Factor
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ABSTRACT: The aim of the present paper was the investigation of middle-latency responses (MLRs) and steady-state responses (SSRs) during and after a 30-min exposure to hypobaric hypoxia (5182 m above sea level). The test was performed in a hypobaric chamber on 8 male audiologically normal volunteers. The auditory stimulus (500-Hz tone burst), delivered at rates of 10 and 40/s for MLRs and SSRs, respectively, was recalibrated in the hypobaric condition because of the reduced air density. Absolute latencies of waves Na and Pa and their interpeak amplitude were the MLR parameters investigated; for the SSRs, the first positive wave (P1) absolute latency and the interpeak amplitude between P1 and the first negative wave (N1) were considered. The results showed an absence of statistically significant modification of the MLRs. On the contrary, the SSRs showed a significant (p < 0.025) latency increase during hypoxia, with an immediate recovery upon return to ground level. No significant changes of SSR amplitudes were observed. One possible data interpretation is related to the higher stimulation rate adopted for the SSRs; a second possibility could be a different electrogenesis between MLRs and SSRs.
Audiology: official organ of the International Society of Audiology 32(6):356-62.
