Effect of slow versus fast desaturation on the ventilatory response to hypoxia

The ventilatory response to progressive hypoxia was studied in 15 healthy adult males by employing two different rates of desaturation. In a slow hypoxic ramp, peripheral oxygen saturation was gradually reduced to 70% over 10-13 min, while in a fast ramp the saturation was reduced over 3-5 min. The ventilatory response to hypoxia was evaluated as the slope of the regression between oxygen desaturation and minute ventilation (l/min/%). There was no significant difference in the slope between the slow and fast ramps. The subjects were further divided into two subgroups; namely high and low responders, according to the value of their slopes. A slope of 0.6 l/min/% was considered the cut-off limit for this classification. In the group of high responders, the hypoxic ventilatory response was significantly higher with the slow ramp than with the fast ramp (p < 0.05). In the low responders, the response was significantly higher with the fast ramp (p < 0.05). We conclude that the hypoxic ventilatory responses are influenced by the rate of desaturation and they appear to be related to the individual sensitivity to hypoxia. These responses are reversed in the low compared with the high responders.