2,833 publications from this institution
This prospective, double-blind study used invasive monitoring and echo-Doppler techniques to compare the hemodynamic effects of nebivolol, a new beta 1-selective beta-blocking agent with those of atenolol in patients recovering from coronary artery bypass grafting surgery. Five milligrams nebivolol and 50 mg atenolol equally decreased heart rate (HR) and blood pressure (BP) but, nebivolol, in contrast to atenolol, caused no decrease in stroke index (SI), cardiac index (CI), and right ventricular ejection fraction (RVEF). These differences appeared to be related in part to different peripheral effects of the two agents because nebivolol administration was associated with a reduction in systemic vascular resistance (SVR). After < or = 10 days of treatment, acceleration of aortic flow velocity increased and isovolumic relaxation time decreased with nebivolol but not with atenolol treatment. Both drugs were equally well tolerated. Therefore, nebivolol shares most of its effects with classical beta 1-blockers but is devoid of the potentially harmful effects on cardiac output (CO) and peripheral resistance.
The microcirculation plays a major role in oxygen delivery and organ perfusion, and is largely involved in the pathophysiological alterations of shock states. It has been a focus of research for a long time, but human clinical and physiological studies have been limited by a lack of reliable techniques available at the bedside. Intravital microscopy, although of interest in experimental studies, is not feasible in human studies. Laser Doppler techniques can measure blood flow, but do not take into account the heterogeneity of the microcirculation. Recently, the Orthogonal Polarized Spectral (OPS) imaging technique has enabled the study of the microcirculation in humans. This technique has allowed a better definition of microcirculatory alterations in disease states, defined the role of some medical interventions, and been used to predict outcome. In this text, we briefly describe the techniques available to study the microcirculation and review experimental and human studies in this domain.
In Response: In our article [1], we warned against the risk of mathematical coupling of data when oxygen uptake (VO2) and oxygen delivery (DO2) are calculated from the same values of hemoglobin, arterial oxygen saturation (SaO2), and especially cardiac index. There is generally a good agreement between direct and indirect determinations of VO2[2], but both methods have their limitations. In this study [1] as in others [3,4], we preferred to assess the relationship between cardiac index and oxygen extraction, because this relationship is not subject to mathematical coupling of data [5]. We strongly disagree with Dr. Myles and Dr. McRae when they state that a strong relationship between VO2 and DO2 implies VO2/DO2 dependency. On the contrary, we wrote that the close relationship between VO2 and DO2 should not be interpreted as VO2/DO2 dependency. The demonstration of VO2/DO2 dependency should be based on repeated assessments of VO2 during an acute change in DO2[6]. We claimed that the progressive increased in VO2 reflected the progressive increase in oxygen demand after cardiac surgery, and that changes in cardiac index were adaptive. When the cardiac index response was insufficient, mixed venous oxygen saturation decreased, reflecting an increase in oxygen extraction. Jean-Louis Vincent, MD, PhD Christina Routsi, MD Department of Intensive Care, Cliniques Universitaires de Bruxelles, Hospital Erasme, Brussels, Belgium