Cloosterman S G, Hofland I D, van Schayck C P, Folgering H T
Department of General Practice and Social Medicine, University of Nijmegen, The Netherlands.
Thorax. 1998 Sep;53(9):768-74. doi: 10.1136/thx.53.9.768.
Dyspnoea is a common and disabling symptom in patients with cardiopulmonary disease. Unfortunately the mechanisms that produce dyspnoea are still poorly understood. The relationship between dyspnoea and the load on the ventilatory muscles, chemical drive, and ventilatory indices was therefore assessed in patients with obstructive pulmonary disease during an incremental exercise test.
Fifty patients with a wide range of obstructive pulmonary disease (mean forced expiratory volume in one second (FEV1) 66.1 (28.8)% predicted) performed an incremental cycle ergometer test. A subdivision was made between subjects with CO2 retention (delta PaCO2 > or = 0, n = 22) and subjects without CO2 retention (delta PaCO2 < 0, n = 28) during exercise. During the test dyspnoea (Borg score), oesophageal pressures (mechanical load on the ventilatory muscles (time tension index (TTI), blood gas tensions, and minute ventilation were measured. Correlations for changes in mechanical and chemical factors with changes in dyspnoea score were calculated to assess relevant factors. An analysis of covariance was used to examine whether there was a relationship between dyspnoea score and each of these factors and whether this relationship was different between the subgroups with and without CO2 retention. Multiple regression analysis was used to assess the independent effect of each parameter on dyspnoea sensation. Furthermore, the amplitude of pleural pressure swing ((Pi + Pe)act) generated at maximal work load (Ptot, an indication of the load on all respiratory muscles) was calculated. Analysis of covariance was used to assess whether there was a relationship between tidal volume (VT) and Ptot and whether this relationship was different between the groups (slopes are an expression of the length-tension inappropriateness, LTI).
In the total group and the group without CO2 retention a significant correlation between dyspnoea and the increase in the inspiratory time tension index (TTIi) was present. In the group with CO2 retention a significant correlation was seen between dyspnoea and delta PaCO2. The factors delta PaO2, delta VE%MVV and delta (VT/Ti) showed a correlation with a p value of < or = 0.10 both in the total group and in those without CO2 retention. In an analysis of covariance the relationship between dyspnoea score and delta PaCO2 appeared to be significantly different between the two subgroups, being more pronounced in the group with CO2 retention. No other relationships with change in dyspnoea score were found. There was no significant relationship between VT and Ptot in the total group nor in the two subgroups, indicating some length-tension inappropriateness in both groups.
In patients with distinctive pulmonary disease who are normocapnic or hypocapnic the mechanical load (delta TTIi) and length-tension inappropriateness (LTI) on ventilatory muscles seem to be the main determinant of exertional dyspnoea. As soon as hypercapnia occurs, this seems to override all other inputs for dyspnoea.
呼吸困难是心肺疾病患者常见且导致功能障碍的症状。遗憾的是，产生呼吸困难的机制仍未被充分理解。因此，在递增运动试验期间，对阻塞性肺疾病患者的呼吸困难与呼吸肌负荷、化学驱动及通气指标之间的关系进行了评估。
50例患有各种阻塞性肺疾病的患者（预计一秒用力呼气量（FEV1）平均为66.1（28.8）%）进行递增式蹬车试验。运动期间，将受试者分为有二氧化碳潴留组（△PaCO2≥0，n = 22）和无二氧化碳潴留组（△PaCO2＜0，n = 28）。试验期间测量呼吸困难程度（Borg评分）、食管压力（呼吸肌的机械负荷（时间张力指数（TTI））、血气张力及分钟通气量。计算机械和化学因素变化与呼吸困难评分变化之间的相关性，以评估相关因素。采用协方差分析来检验呼吸困难评分与这些因素中的每一个之间是否存在关系，以及这种关系在有和无二氧化碳潴留的亚组之间是否不同。采用多元回归分析来评估每个参数对呼吸困难感觉的独立影响。此外，计算最大工作负荷时产生的胸膜压力摆动幅度（（Pi + Pe）act）（Ptot，所有呼吸肌负荷的一个指标）。采用协方差分析来评估潮气量（VT）与Ptot之间是否存在关系，以及这种关系在两组之间是否不同（斜率表示长度 - 张力不匹配，LTI）。
在整个组和无二氧化碳潴留组中，呼吸困难与吸气时间张力指数（TTIi）的增加之间存在显著相关性。在有二氧化碳潴留组中，呼吸困难与△PaCO2之间存在显著相关性。因素△PaO2、△VE%MVV和△（VT/Ti）在整个组和无二氧化碳潴留组中均显示出p值≤0.10的相关性。在协方差分析中，呼吸困难评分与△PaCO2之间的关系在两个亚组之间似乎有显著差异，在有二氧化碳潴留组中更为明显。未发现与呼吸困难评分变化的其他关系。在整个组以及两个亚组中，VT与Ptot之间均无显著关系，表明两组均存在一定程度的长度 - 张力不匹配。
在正常碳酸血症或低碳酸血症的特异性肺部疾病患者中，呼吸肌的机械负荷（△TTIi）和长度 - 张力不匹配（LTI）似乎是运动性呼吸困难的主要决定因素。一旦发生高碳酸血症，这似乎会凌驾于所有其他导致呼吸困难的因素之上。
