研究討論與結論

心率變異性受到竇房结上交感與副交感神經功能所影響，亦可以反應自主神經系統的變 化；然而，由於不同研究的環境、流程、及病患對於心跳與呼吸等生理訊息的差異，會 使得不同研究結果的解釋出現不完全一致的情形 (Gootman PM, 1991) 。因此較大規模的 研究以建立可以廣泛為其他學者所依循的常態分佈模式是有必要的，不論 Massin 等學 者於 1997 年(210 例 3 天大至 14 歲)或是 Mehta 等學者於 2002 年(96 例 3 天內的新生兒) 發表的研究均在建立正常新生兒或是兒童的正常值範圍，所得到的結論發現 mean RR interval 與年齡對所有心率變異性的參數(SDNN, LF, HF, LF/HF)呈現正相關(一次方或二 次方)；如此，隨著年齡增加而 mean RR interval 亦增加(即心跳速率下降)，乃是副交感 神經功能逐漸成熟，交感神經功能影響逐漸下降的結果，我們可以應用這些訊息在臨床 上做為評估許多會影響到心臟自主神經功能疾病(如：DM, CHF 等)之新工具(Akinci A, 1993; Casolo GC, 1991)。

在胎兒時期，心率變異性亦被用來評估胎兒健康的指標之一。雖然胎兒時期的心肺功能 與出生後正常人類之心血管功能並非完全相同；但是，早產兒出生後的前幾天內心搏輸 出量主要來自心跳速率的影響及自發性呼吸為不規則型態(Rigatto H, 1972)，可以說明此 一時期早產兒的心血管系統與胎兒相似。因此，我們可以預期早產兒與尚未出生而有相 同週數的胎兒有著相同程度的自主神經系統功能發展；如果我們可以由早產兒的心率變 異性得到某些發現，此一結果亦可以反應在相同週數胎兒身上(Zhuravlev YE, 2002)。

Katona 等三位學者(Katona PG, 1980)於 1980 年的研究指出：不論於睡眠週期中的任何時 段，早產兒與足月兒於出生後4~10 週時 Mean RR Interval 均最小，而在安靜睡眠時早產 兒的Mean RR Interval 明顯比足月兒小。Eiselt 等多位學者(Eiselt M, 1993)，發表另外一 篇有關於 12 例接近足月兒的早產兒於達到足月階段(即 37-41 週)時與 16 例正常足月兒 做比較的研究發現：不論新生兒處於活動或是安靜睡眠時，接近足月的早產兒於達到足 月階段與足月新生兒心率變異性之比較，其 Mean RR Interval 較短(p<0.001)；1982 年 Assali 等多位學者的著作(Fetal and Newborn Cardiovascular Physiology, pp 47-92)指出：交 感神經系統的發育及功能的成熟較副交感神經系統來得早(尤其是接近足月之早產兒)； (p=0.003)；當再進一步以出生週數區分時，發現小於 33 週的早產兒其 Mean RR interval 亦明顯小於大(或等)於 33 週的早產兒(p=0.002)；此外，由 SDNN 之 mean 與 standard deviation 分別為 32.56 ± 13.36ms 與 21.13±16.96ms (p=0.006)發現，我們亦可以推論足月 兒的心率穩定度亦較早產兒來得好。

Smith 等三位學者(Smith SL, 2004)，以 16 例極低體重早產兒(有使用氣管內管與呼吸器) 分析指出，發現不論早產兒處於活動抑或是安靜睡眠時，頻域中的各項參數(LF, HF)均 無明顯差異存在；Eiselt 等學者，以接近足月的早產兒於達到足月階段與足月新生兒心 率變異性之比較則發現，不同的頻域參數指標(LF, HF 等)均較低(p<0.001)；Chatow 等學 者，則以早產兒、足月兒、到達足月的早產兒分組研究發現，隨著週數的增加LF/HF 的 值會逐漸下降，而且早產兒的平均LF/HF 值也明顯高於足月兒；此一現象，似乎與成人 的心率變異性一致。然而，本研究卻發現早產兒的 LF/HF 值比足月兒來得低(4.454±3.17 vs. 7.225±5.69, p=0.042)；1997 年，Goto 等學者(Goto M, 1997)以 3 歲到 15 歲的兒童分 析研究指出，LF, HF 與 LF/HF 的值由 3 歲到 6 歲階段會出現逐漸變大(p<0.01 與 p<0.05)

之後則不明顯，實際的原因仍未明朗，但作者的推論指出：對於健康的兒童其心跳速率

因此，我們以本研究與Mazursky等學者 (Mazursky JE, 1998)及Chung等多位學者(Chung DY, 2001)的研究結論分別來說明此一現象：(1)以 28 例受孕週數為 28~32 週的正常早產

而使平均動脈壓會回昇；以往的學者研究(Montano N, 1994)指出：此時的心跳加速乃是 交感神經功能增強及副交感神經(迷走神經)功能減弱的結果→使竇房结加速→使得心跳 降；由於早產兒與相同週數的胎兒有類似的心率變異性(Zhuravlev YE, 2002)，因此可以 推測早產兒出生後到足月的階段，其LF/HF值應會增加。而本研究比較早產兒與足月兒 之心率變異性時發現與此結論有相似之結果；因此，我們推論由於早產兒的自主神經功

能比起足月兒不成熟，此一逐漸成熟的過程將使心率變異性中LF/HF值逐漸上升；而對 於自主神經功能已經成熟的成人或大約成熟階段的較大兒童而言，其LF/HF值的變異性 將不明顯，其關鍵之因素為研究時對象是否處於自主神經功能正在逐漸發育成熟的階 段。

第二節 未來發展方向

(1) 利用心率變異性的特性，已出生早產兒與尚未出生而有相同週數的胎兒有著相同程 度的自主神經系統功能發展；而由早產兒的心率變異性所得之結果，亦可以反應在 相同週數胎兒身上。因此，收集更多的案例建立早產兒心率變異性的常態分佈情形 的資料庫，以可攜式 Holter ECG 紀錄器紀錄懷孕婦女之腹中胎兒的短時間心率變異 性，並連接電腦做即時分析比較相同週數早產兒之資料，以進一步分析預測胎兒之 自主神經發育情況，可以做為婦產科醫師產前檢查監測時的輔助工具。

(2) 嬰兒猝死症(Sudden Infant Death Syndrome—SIDS)是嬰兒時期造成死亡的重要原因之 一，許多的研究顯示其原因可能與趴睡姿、嬰兒週邊環境、男嬰等等有關，但實際 因素仍不是很清楚—可能是嬰兒呼吸道受到阻礙造成窒息、也可能是因為出現致死 性心律不整等；但不論是何種原因引起，嬰兒死亡前其心率一定會發生變化，現今 臨床實務上不可能每個新生兒均隨時用心電圖監視器來監測其心率變化，如果能有 一套完整的系統於短時間內分析出每個出生後新生兒的心率變異性，再配合已建立 的資料庫，篩檢出高危險群以進一步監測，也許將可做為後續研究發展預測及預防 嬰兒猝死症的基礎。

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