Carotid baroreflex control of heart rate during acute exposure to simulated altitudes of 3,800 m and 4,300 m

Abstract

To examine the baroreflex response in humans during acute high-altitude exposure, the carotid baroreflex cardiac responsiveness was studied using a neck chamber in seven unacclimatized male subjects. Measurements were made in a high-altitude chamber on separate days at sea level and during 1-h exposure at two different altitudes of 3,800 m [partial pressure of oxygen in inspired air (Pi O2 ) = 90 mmHg] and 4,300 m (Pi O2 = 82 mmHg). R-R intervals were plotted against neck chamber pressures, and the baroreceptor response was analyzed by applying a four-parameter sigmoidal logistic function. The baroreceptor response curve shifted downward in either altitude, reflecting a tachycardic response at high altitude, and the magnitude of the shift was greater at 4,300 m than at 3,800 m. There was no change in the sigmoidal parameters at 3,800 m compared with sea level except for a reduction ( P < 0.05) of the minimum R-R interval. At 4,300 m the maximal R-R range, slope coefficient, minimum R-R interval, and maximal gain of the curve decreased significantly ( P < 0.05) compared with sea level values, whereas the centering point of the curve remained unchanged. These results suggest that hypoxia (Pi O2 = 82 mmHg) reduces the sensitivity of carotid baroreflex cardiac response.

Influence of exercise training on cardiac baroreflex sensitivity in patients with COPD

“…In the present study, cardiac echocardiography performed during the routine follow-up of such patients demonstrated normal pulmonary arterial pressures. Alternatively, systemic hypoxia is known to alter BRS in healthy subjects due to induced hyperventilation and chemoreceptor loop activation [25,26]. In COPD patients, the effect of relative hypoxia has also been demonstrated recently, by increased BRS after short-term oxygen supplementation [7].…”

Physical activity at moderate and high altitudes. Cardiovascular and respiratory morbidit

“…Sagawa et al 17 examined the baroreflex response of 7 nonacclimatized men at sea level and at the first hour of exposure to altitudes between 3,800 and 4,300m, in a hypobaric chamber. The results were in accordance with a significant reduction (p<0.05) in the sensitivity of the carotid baroreflex cardiac response.…”

“…At high altitudes and during sleep, some healthy individuals have a periodical respiratory pattern, also called CheyneStokes respiration 17,21,26 . Combined with this variation, there are cyclic changes in the cardiac rhythm and HR 19 .…”

“…It is usually self-limited and rarely leads to death. Symptoms appear between 4 and 8 hours after arrival at the altitude 35 , and the most characteristic ones are the following: headache, nausea, insomnia, anorexia, and dyspnea 17,26,38 . Despite the individual tolerance to hypobaric hypoxia, the best way to prevent AMS is to ascend slowly 19,26,38,44 .…”

“…Controlled studies have shown that acetazolamide reduces the incidence and severity of MAS 17,46,47 . Being an inhibitor of carbonic anhydrase, it facilitates the excretion of urinary bicarbonate, promoting reduction of the respiratory alkalosis and, therefore, increasing the respiratory drive with reduction of the nocturnal hypoxemia 19,26,38,47 .…”