This led to the demonstration that relative hypoxemia and hypoventilation at high altitude were associated with a diminished ventilatory response to hypoxia, but the nature and causes of the altered hypoxic response were uncertain. The uniform loss of hypoxic response in individuals born at high altitude or with congenital cyanotic heart disease suggested that this response was not inborn but acquired, although it was unclear whether the critical hypoxic exposure was in the neonatal period or could occur later in life. Subsequent studies showed highly variable hypoxic response in non-native residents of high altitude, which correlated with the duration of high-altitude residence such that longer periods of exposure to high altitude were associated with lower hypoxic ventilatory responses (Fig 2). It was also found that hypoxic ventilatory responses in young children, aged 9 to 10, were comparable to those measured in low-altitude children, suggesting that the attenuated responses observed in native adults likely occurred not in the neonatal period, but more likely after the first decade of life. Taken together, these findings suggest that the ventilatory response to hypoxia may be progressively decreased during long-term exposure to hypoxia, and this may contribute to the variation in hypoxic ventilatory response, in arterial oxygenation, and in erythrocytosis at altitude. buy asthma inhaler
Figure 2. Hypoxic ventilatory responses measured as the shape parameter “A” as a function of duration of high-altitude exposure. Mean and standard error of the mean are shown for natives of low and high altitude. Individual points represent values in high-altitude non-native residents. Responses in non-native residents exhibit greater variation than those in low- or high-altitude natives. The strength of the response varies inversely with the duration of high-alti-tude exposure such that, after 20-25 years of residence, values in non-native subjects approach those measured in natives.
Tags: Chronic obstructive pulmonary disease, Hypercapnia, Hypoxia