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[Generation and prediction of hypoxemia in patients with chronic obstructive pulmonary disease].

OBJECTIVE
To study the pathogenesis of nocturnal hypoxemia in patients with chronic obstructive pulmonary disease (COPD).


METHOD
Daytime pulmonary functions, arterial blood gases and nocturnal oxygen level were measured in 30 patients and compared with those of 8 normal subjects.


RESULTS
The nocturnal oxygen level significantly decreased in patients with COPD compared with that in normal subjects, especially during rapid eye movement (REM) period. The decreased extents of nocturnal mean oxyhemoglobin saturation (MSaO2) and nocturnal minimum oxyhemoglobin saturation (MmSaO2) were also very high in COPD (P < 0.05). From the distribution of oxyhemoglobin, the percentage of the time that oxyhemoglobin saturation (SaO2) < 80% and < 90% during sleep (T80, T90) in patients were found higher than those in normal subjects (P < 0.05). The sleep time in which SaO2 below 90 percent obviously increased in COPD patients. The correlative analysis indicated that daytime SaO2 and FEV1% were related to the nocturnal mean oxyhemoglobin saturation (r = 0.79, 0.54). So predictive formula of nocturnal oxyhemoglobin level was derived as follows: MSaO2(%) = 1.03 x SaO2(%) + 0.19 x FEV1%(%) - 14.35(r = 0.83). Daytime SaO2 and PaCO2 were also found concerned with nocturnal oxygen distribution: T80(%) = -2.64 x SaO2(%) + 6.98 x PaCO2(kPa) + 211.31(r = 0.78), T90(%) = -4.49 x SaO2(%) + 437.18(r = 0.62).


CONCLUSION
It was observered that hypoxemia became worse in patients with COPD than in normal subjects during sleep. The level and the distribution of nocturnal oxygen could be predicted by daytime SaO2 and PaCO2. All these indicated that nocturnal oxygen therapy could be useful to improve the outcome of the COPD patients.