Objective: To evaluate the effect of dead space (VD) loading on ventilation and respiratory muscle function, test a novel measurement of oxygen consumption of respiratory muscle, and analyze the effect of oxygen consumption of respiratory muscle on exercise performance. Methods: 26 patients with moderate chronic obstructive pulmonary disease (COPD) and 29 age-matched healthy control subjects underwent 30 W or 55 W constant work (CW) exercise in standard protocol and under 300 ml (46 cm in length) dead space loading. Pulmonary function test (PLT) was measured pre and post exercise both in the dead space loading and unloading. Results: Added 300 ml VD did not significantly affect FVC, FEV1, and FEV1/FVC in both COPD and the healthy at rest or after CW exercise.The values of FVC, FEV1, and FEV1/FVC with VD loading in COPD were (3.03 ± 0.15) L, (1.95 ± 0.09) L, and (0.65±0.03), respectively; after 55 W CW exercise, those values were (3.03 ±0.18) L, (2.00 ±0.13) L, and (0.66 ± 0.03), re-spectively (P ＞0.05). Minute ventilation (VE) and oxygen uptake (VO2) significantly went up with VD loading and dropped down with unloading at rest and during exercise in every subject. An average of VO2 increased from (266.3 ± 11.5) ml/min to (460.6 ±44.5) ml/min (at rest), (548.9 ± 35.8) ml/min to (751.4 ± 28.0) ml/min (30 W exercise), and (1004.0 ± 56.3) ml/min to (1276.1 ± 50.2) ml/min (55 W exercise) in COPD (P ＜0.001). The enhancement of VO2 under VD loading (△VO2) was not significantly different between COPD and the control at rest or during lower intensity CW (30 W) exercise. However, △VO2 was significantly higher in COPD than in the control during moderate intensity CW (55 W) exercise [(272.0 ± 23.5) ml/min vs (193.9 ± 18.5) ml/min, P =0.02]. Conclusions: Lengthening respiratory tube to 46 cm (300 ml dead space) combined with moderate constant work exercise does not worsen the airflow obstructive in COPD, or result in respiratory muscle fatigue both in COPD and the healthy. The enhancement of VO2 under VD loading can be considered as oxygen consumption of respiratory muscle working for increased ventilation. An advantage of oxygen consumption in respiratory muscle during moderate intensity exercise in COPD implicates that maintaining the balance of oxygen supplying to both respiratory and limb muscles might be the key point to perform moderate to heavy exercise.%目的评价死腔负荷对通气功能和呼吸肌的影响,测试呼吸肌氧耗的检测方法,探讨呼吸肌氧耗在慢性阻塞性肺疾病(COPD)运动耐力下降中的作用.方法 36例中度COPD患者和29例年龄相近健康对照者在300ml呼吸管路死腔(46 cm长)负荷下,完成30W或55W恒定功率运动试验,并在死腔负荷下检测运动前后肺功能和运动中分钟通气量(VE)和摄氧量(VO2).结果无论COPD或健康对照组,在静息状态或运动后,增加300ml死腔对FVC,FEV和FEV1/FVC无显著影响.COPD组静息死腔负荷下FVC,FEV1和FEV1/FVC分别为(3.03±0.15)L,(1.95±0.09)L,和0.65±0.03,55 W运动后上述指标分别为(3.03±0.18)L,(2.00±0.13)L和0.66±0.03,(P＞0.05).每1例受试个体,无论静息或运动中,附加死腔均导致VE和VO2在原有基础上显著增加,卸除死腔后VE和VO2回落.附加死腔负荷后不同代谢状态下,VO2由(266.3±11.5)ml/min增至(460.6±44.5)ml/min(静息),(548.9±35.8)ml/min至(751.4±28.0)ml/min(30W运动),及(1004.0±56.3)ml/min至(1276.1±50.2)ml/min(55W运动)(P＜0.001).死腔负荷下VO2的增加量(△VO2)在静息和低强度(30W运动)时,COPD组和健康对照组之间无显著差异.在中等强度(55W)运动时,COPD组△VO2显著高于对照组[(272.0±23.5)ml/min与(193.9±18.5)ml/min,P=0.02].结论呼吸管路加长46 cm(300ml死腔),伴随中等强度运动未导致COPD气流阻塞的进一步加重,也未出现呼吸肌疲劳征象.在其它试验条件不变的情况下,增加呼吸管路死腔,VO2的增加量应为呼吸肌克服死腔负荷的氧耗量.COPD呼吸肌具有氧耗优势,呼吸肌与肢体运动肌摄氧比例不平衡,可能是导致COPD运动耐力下降的因素之一.
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