Sandek K, Bratel T, Lagerstrand L, Rosell H
Department of Medicine, Karolinska Institutet at Huddinge University Hospital, Stockholm, Sweden.
Respir Med. 2002 Nov;96(11):934-43. doi: 10.1053/rmed.2002.1371.
The development of the high-resolution computed tomography (HRCT) has improved the ability to detect and quantify emphysema in various groups of patients with chronic airflow obstruction (COPD). Significant correlations have previously been found between indices of air flow obstruction, hyperinflation, reduced diffusing capacity for carbon monoxide (DLCO), and the extent of emphysema (emph.%) assessed by HRCT. However, the relationship between emph.% and ventilation-perfusion (V(A)/Q) inequality in COPD is unknown. Twenty COPD patients with a mean forced expiratory volume in 1 s (FEV1) of 38.2 (+/- 15.5)% in percent of predicted value (%P), a mean PaO2 value of 9.6 (+/- 1.3) kPa, and a mean diffusing capacity of 43.6 (+/- 23.0)%P, were subjected to measurements by the multiple elimination inert gas technique (MIGET). The extent of emphysema was determined by HRCT at both full inspiration, emph.I(%) and at full expiration, emph.E(%), with a cut-off limit of -910 Hounsfield Units (HU) using the "Density Mask" method. The ventilation directed towards high V(A)/Q areas was 73 (+/- 10.2)% and the mean ventilation (V-mean) was elevated about three times compared to normal. The mean emph.(I)% and emph.(E) was 45.6 (+/- 16.9) and 32.7 (+/- 190)%, respectively. Significant correlations were shown between the emphysema extent and several lung function parameters, but no correlation was found between the emphysema extent and the V(A)/Q relationships or the blood gas values. Reduced DLCO%P correlated with less high V(A)/Q ventilation (r=0.73, P < 0.05) for the subgroup of COPD patients with DLCO(%P) less than 50% (n=12).
In COPD patients, suffering from moderate to severe emphysema without severe blood gas impairment, no correlation was shown between the extent of emphysema, as assessed by HRCT, and the severity of ventilation-perfusion inequality. A substantial collateral ventilation in severe emphysema may be a mechanism that prevents a deterioration in V(A)/Q relationships and in blood gas levels.
高分辨率计算机断层扫描（HRCT）的发展提高了在各类慢性气流阻塞（COPD）患者中检测和量化肺气肿的能力。此前已发现气流阻塞指数、肺过度充气、一氧化碳弥散量降低（DLCO）与通过HRCT评估的肺气肿程度（肺气肿%）之间存在显著相关性。然而，COPD患者中肺气肿%与通气-灌注（V(A)/Q）失衡之间的关系尚不清楚。对20例COPD患者进行了多重消除惰性气体技术（MIGET）测量，这些患者的1秒用力呼气量（FEV1）平均为预测值的38.2（±15.5）%，平均动脉血氧分压（PaO2）值为9.6（±1.3）kPa，平均弥散量为预测值的43.6（±23.0）%。通过HRCT在深吸气时确定肺气肿程度，即肺气肿I（%），在深呼气时确定肺气肿程度，即肺气肿E（%），使用“密度掩模”方法，截断值为-910亨氏单位（HU）。流向高V(A)/Q区域的通气量为73（±10.2）%，平均通气量（V-均值）比正常情况升高约三倍。平均肺气肿I（%）和肺气肿E（%）分别为45.6（±16.9）%和32.7（±19.0）%。肺气肿程度与几个肺功能参数之间存在显著相关性，但肺气肿程度与V(A)/Q关系或血气值之间未发现相关性。对于DLCO（%P）小于50%（n = 12）的COPD患者亚组，DLCO%P降低与高V(A)/Q通气减少相关（r = 0.73，P < 0.05）。
在患有中度至重度肺气肿且无严重血气损害的COPD患者中，通过HRCT评估的肺气肿程度与通气-灌注失衡的严重程度之间未显示相关性。重度肺气肿中大量的侧支通气可能是防止V(A)/Q关系和血气水平恶化的一种机制。
