睡眠醫學二十二之睡眠窒息與認知問題

大家都認識到睡眠窒息可以破壞睡眠結構，及引致病人不斷覺醒，但大家卻未必知道這兩種現象有可能導致病人認知困難。延醫處理睡眠窒息症本身，可增加以下疾病的風險: 高血壓[1]；心臟病[2]；中風[3]；腎病[4]；糖尿病[5]等。此等新陳代謝及血管疾病亦會轉過來令睡眠窒息惡化，最後大增睡眠窒息症病人的認知困難，甚至令人較年青時就患上認知障礙(老人癡呆)[6]。

何謂認知功能{cognition}?這包括attention[注意力]；memory[記憶力]；executive function[行政能力如策劃、解決難題等等]；visuospatial/constructional abilities[視覺空間能力] 及language [語言能力][7]。現有的証據確認睡眠窒息會削弱病人的注意力、vigilance[警覺性]、長短期記憶力[8,9] 及行政能力[10]，最新研究指連information processing [資訊處理] 也受到影響[11] 。

關於睡眠窒息症如何造成認知困難? 現時有兩派學說: 其中一派覺得睡眠窒息症病人的認知困難是短期及可逆轉的，純粹是由於睡眠不足引致日間嗜睡及專注力不足而矣[12,13,14]；第二派學說卻認為睡眠窒息症會形成病人腦部結構性改變，因而引發認知困難[15,16,17]。若果第一派學說是正確的話，那麼連續正氣壓机[CPAP] 應該不單能改善睡眠窒息症病人的日間嗜睡，亦應能改善病人的認知困難，但事實卻不然[18] 。的確好些睡眠窒息症病人有某些腦部結構性改變[19] ，但另一方面，睡眠窒息症的病情又與認知困難的嚴重性沒有直接關係[20,21] 。亦有人認為睡眠窒息症病人本身多有併存病，尤其是血管疾病，單單這些併存病就已經可以改變病人腦部結構[22]，繼而導致病人行政能力衰退[23]。

但為何這方面的研究常常出現相反的結論呢? 事緣如何量度睡眠窒息症病人日間嗜睡程度[24,25]或睡眠窒息症的病情[26,27]就沒有統一的方案。每一個睡眠窒息症病人都有不同的病因和病理，而不同年紀的睡眠窒息症病人亦可能有不同的病徵[28,29]及其覺醒閾值[Arousal threshold][30,31]。

總括來說，要更多認識睡眠窒息與認知困難的關係[32]，就需要解決多不勝數的科研問題，因此前面的路真是又長又艱難的。

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