Coast J R, Jensen R A, Cassidy S S, Ramanathan M, Johnson R L
Department of Internal Medicine, University of Texas Health Science Center, Dallas 75235.
J Appl Physiol (1985). 1988 Apr;64(4):1624-8. doi: 10.1152/jappl.1988.64.4.1624.
In this study, noninvasive measurements of cardiac output and O2 consumption were performed to estimate the blood flow to and efficiency of the respiratory muscles that are used in elevated inspiratory work loads. Five subjects were studied for 4.5 min at a respiratory rate of 18 breaths/min and a duty cycle of 0.5. Studies were performed at rest without added respiratory loads and at elevated inspiratory work loads with the use of an inspiratory valve that permitted flow only when a threshold pressure was maintained. Cardiac output and O2 consumption were calculated using a rebreathing technique. Respiratory muscle blood flow and O2 consumption were estimated as the difference between resting and loaded breathing. Work of breathing was calculated by integrating the product of mouth pressure and volume. Increases in cardiac output and O2 consumption in response of 4.5 min loaded breathing averaged 1.84 l/min and 108 ml/min, respectively. No increases were seen in response to 20-s loaded breathing. In a separate series of experiments on four subjects, though, cardiac output increased for the first 2 min then leveled off. These results indicate that the increase in cardiac output was a metabolic effect of the increased work load and was not caused primarily by the influence of the highly negative intrathoracic pressure on venous return. Efficiency of the respiratory muscles during inspiratory threshold loading averaged 5.9%, which was similar to measurements of efficiency of respiratory muscles using whole-body O2 consumption that have been reported previously in humans and in dogs.
在本研究中,进行了心输出量和氧气消耗的无创测量,以估计用于增加吸气工作负荷的呼吸肌的血流量和效率。对5名受试者在呼吸频率为18次/分钟、占空比为0.5的条件下进行了4.5分钟的研究。研究分别在静息状态下(无额外呼吸负荷)以及在增加吸气工作负荷时进行,增加吸气工作负荷时使用了一个吸气阀,该阀仅在维持阈值压力时才允许气流通过。心输出量和氧气消耗采用重复呼吸技术进行计算。呼吸肌血流量和氧气消耗通过静息呼吸与负荷呼吸之间的差值进行估计。呼吸功通过对口腔压力和容积的乘积进行积分来计算。4.5分钟负荷呼吸后的心输出量和氧气消耗增加量平均分别为1.84升/分钟和108毫升/分钟。20秒负荷呼吸后未见增加。然而,在对另外4名受试者进行的另一系列实验中,心输出量在前2分钟增加,然后趋于平稳。这些结果表明,心输出量的增加是工作负荷增加的代谢效应,并非主要由高度负压的胸内压对静脉回流的影响所致。吸气阈值负荷期间呼吸肌的效率平均为5.9%,这与先前在人类和犬类中报道的使用全身氧气消耗来测量呼吸肌效率的结果相似。