Understanding the basics of the cardiovascular system (hemodynamics in the case of this thread) is important to having a more thorough knowledge of how the body acutely and chronically responds to exercise/physical activity as well as the direct and indirect implications that has on health, fitness, and sport performance. However, few people outside of a clinical or research setting will: 1) need to know accurate values for variables like cardiac output and stroke volume and 2) have the equipment/resources to be able to determine such values. As a point of clarification, the only way to "measure" stroke volume, cardiac output, ejection fraction, and oxygen consumption is to actually go in there (i.e. the heart or its vessels) with catheters and directly collect the data (volumes, concentrations, etc.). Even cardiologists who need to know things like stroke volume and ejection fraction usually do it noninvasively with an echocardiogram and "eyeball" these variables based on changes in various cardiac dimensions and blood flow velocities. Many of them are, however, very good at this and their "eyeball" estimations might as well be measurements. I got to see this on a daily basis when I worked in a research division of a cardiology clinic as I was going through my doctorate program. Oxygen consumption (i.e. VO2) is also estimated (not "measured") using a metabolic collection and analyzer system that is based on something called indirect calorimetry. Yes, the inspired and expired gases are collected and analyzed for gas concentrations and flow volumes but the end piece of data (i.e. VO2) is still just an estimate based on physiology and hemodynamics that are beyond the scope of this discussion. That is not to say those estimations can't be very accurate, it simply means the term "measure" is not correct. It might sound like semantics, but it is important to know the difference. Long story made slightly longer: know the formulae, understand the relationships of the various components of each formula to one another, be able to talk about what it all means to your particular scenario (e.g. exercising client, clinical patient, elite athlete, etc.) and don't worry about having to know (or determine) indices like stroke volume and cardiac output.
Joe Warpeha
Assistant Professor of Exercise Physiology
Director, Exercise Physiology Laboratories
College of St. Scholastica
|