ISSN:
1439-6327
Keywords:
Peripheral chemoreceptors
;
Hypoxic ventilatory response
;
Altitude acclimatization
;
High altitude
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Abstract Hypoxic ventilatory response (HVR) was examined before and after acclimatization to high altitude. Transient hyperoxic switches according to Dejours's technique were used to examine the contribution of HVR to the hyperpnoea of increasing exercise intensities. Ten mountaineers were exposed to hypoxia (oxygen fraction in inspired gas,F 1O2 = 0.11, 79 mmHg) before the expedition and after return from altitude (56 days, 30 days at 4900 m or higher). After 25-min breathing hypoxic gas, the subjects performed a maximal cycle ergometer test (increments 50 W per 5 min). Respired gases and ventilation $$(\dot V_E )$$ were analysed breath-by-breath, partial pressure of oxygen (PO2) and oxygen saturation (SO2) were measured in capillary blood. The HVR was tested by switching two breaths to anF 1O2 of 1.0. The nadir of $$\dot V_E $$ after the switch was measured (decrease in ventilation, D $$\dot V_E $$ ). The HVR was expressed as the D $$\dot V_E $$ at a PO2 of 40 mmHg (D $$\dot V_{E40} $$ ) and the D $$\dot V_E $$ versus decrease ofSO2 (D $$\dot V_E $$ /[100 −SO2]). The HVR estimated by D $$\dot V_{E40} $$ increased from 19.9 to 28.01 · min−1 (median,P = 0.013). The HVR expressed as D $$\dot V_E $$ /(100 −SO2) at rest was no different before and after acclimatization (0.89 and 0.86 l · min−1 · %−1, respectively) and during exercise it did not change before the expedition (0.831 · min−1 %−1). However, D $$\dot V_E $$ /(100 −SO2) increased significantly with exercise intensity after the expedition (1.61 l · min−1 · %−1 at 200 W). The changes of D $$\dot V_E $$ versusSO2 as well as of D $$\dot V_E $$ versus $$\dot V_E $$ were steeper after the expedition than before. In summary, after return from 30 day at high altitude, an increased HVR was observed. The augmentation of HVR was evident at higher exercise intensities and we suggest that this reflects a change in sensitivity of the peripheral chemoreflex loop.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF02425477
Permalink
