Effects of intermittent hypoxia on pulmonary haemodynamics: animal models versus studies in humans

The aim of this review was to analyse the effects of intermittent hypoxia (IH) on pulmonary haemodynamics, comparing results of animal experiments with results of clinical studies. In animal investigations even short hypoxic exposure, continuously or in short repeated episodes mimicking obstructive sleep apnoea (OSA), leads to pulmonary artery remodelling and to pulmonary hypertension (PH). Results of investigations on effects of nocturnal IH on pulmonary haemodynamics in patients with chronic obstructive pulmonary disease (COPD) are discordant. Earlier studies reported the development of mild PH in subjects desaturating during sleep, while more recent investigations did not confirm those findings. Alveolar IH developing during apnoeic episodes during sleep in OSA patients is a disease-induced model to study its effects on pulmonary haemodynamics. In the majority of studies in OSA patients pulmonary arterial pressure remained within normal values. PH was found in patients with OSA accompanied by COPD and/or extreme obesity. People commuting between lowland and high altitude due to their employment, are also repeatedly exposed to IH. Results of clinical investigations suggest that it did not lead to the development of permanent PH. The mechanisms of discrepancies between effects of intermittent hypoxia in animal models and in humans remain to be studied.