Ventilatory response to hypoxia in intact cats living at 3,850 m

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Abstract
The question whether the ventilatory response to hypoxia is blunted in intact cats living at high altitude is not settled. In the present work the ventilatory responses to acute hypoxia of intact anesthetized cats native to 3850 m were compared with those studied at sea level. The cats weighed between 1.79-3.5 kg and were approximately 1-6 yr old. Both the high-altitude and sea-level cats responded to acute hypoxia. However, in high-altitude cats the response to acute hypoxia began below PETO2 of 55 Torr to which they were acclimatized. In the sea-level cats the response was found around 90 Torr. Thus a greater intensity of alveolar hypoxia was needed in the high-altitude than in the sea-level cats to produce a similar ventilatory effect. An acute normoxia did not cause a sustained decrease of ventilation in high-altitude cats. Bilateral section of sinus nerves which impaired carotid chemoreflex abolished the responses to acute hypoxia in both groups. Thus an hypoxic carotid chemoreflex driving ventilation was intact in cats at 3850 m, although it was less than normal at sea level. This modification, however, was less than that observed in adult humans native to high altitude. Since lifelong hypoxia of 1-6 yr in the cats at 3850 m did not particularly blunt the ventilatory response to acute hypoxia it may be concluded that it takes a longer duration of chronic mild hypoxia to develop the characteristic fully.

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