Series en disnea. Parte 2. Análisis de sus mecanismos según pasan los años / Series on dyspnea. Part 2. Analysis of its mechanisms as the years go by

RESUMEN Este artículo está dedicado al análisis detallado de los mecanismos de disnea. Se tra tarán el control químico de la respiración, los reflejos neurales, la mecánica respiratoria, el costo de oxígeno para respirar y la inadecuación entre tensión y longitud de la fibra muscular. En general, las diferentes explicaciones estuvieron asociadas al desarrollo de aparatos y metodologías de estudio de los laboratorios pulmonares. Todas las teorías tuvieron defensores y detractores e, interesantemente, con el desarrollo de sofisticadas técnicas neurofisiológicas y de imágenes funcionales ha sido posible jerarquizar cada uno de los mecanismos. Todas han sobrevivido al paso del tiempo y ninguna puede explicar de manera unicista la disnea en todas las situaciones clínicas, lo cual habla de la naturaleza compleja y multifactorial del fenómeno.

ABSTRACT This article is devoted to a detailed analysis of the mechanisms of dyspnea. Chemical control of respiration, neural reflexes, respiratory mechanics, the cost of oxygen to breathe, and the mismatch between tension and muscle fiber length will be discussed. In general, the different explanations were associated with the development of apparatus and study methodologies in pulmonary laboratories. All the theories had defenders and detractors and, interestingly, with the development of sophisticated neurophysiological techniques and functional imaging it has been possible to prioritize each of the mecha nisms. All have survived the passage of time and none can explain dyspnea in all clinical situations, which speaks of the complex and multifactorial nature of the phenomenon.

Effects of sedation on respiratory mechanic dynamics and oxygen metabolism in patients with mechanical ventlilation / 中华急诊医学杂志

Objective To investigate the effect of sedation on respiratory mechanic dynamics, intrapulmonary shunt fraction,oxygen metabolism in patients with mechanical ventilation.Method Sixty patients with mechanical ventilation were divided randomly into control group and sedation group.Propofal was administered to patients,whose ramsay scores were kept atⅢorⅣlevels,in sedation group while the equal amount of normal saline was given in control group.Mixed venous blood and arterial blood samples were taken for blood gas analysis in both groups before and at 2 hours after administration.Heart rate,blood pressure,breathing rate and airway resistance all were recorded at the same time.Results There were no significant differences in oxygenation index,blood pressure,blood lactic acid,total lung static compliance and intrapulmonary shunt fraction between two groups before and after administration.Heart rate,respiratory rate,oxygen uptake and airway resistance of patients in sedation group were lower than those in control group,and partial pressure of oxygen in mixed venous blood of patients in sedation group were higher than those in control group.These differences were statistically significant.Conclusions Sedation can decrease oxygen uptake and airway resistance of patients with mechanical ventilation.However,no alteration in the oxygenation index,total lung static compliance and intrapulmonic shunt ratio can be observed.