Cath Lab Digest - October 2007 - (Page 41)

OCTOBER 2007 ASK THE CLINICAL INSTRUCTOR 41 Ask the Clinical Instructor A Q&A column for those new to the cath lab Questions are answered by: Todd Ginapp, EMT-P, RCIS, FSICP Todd is the Cardiology Manager for Memorial Hermann Southeast in Houston, Texas. He also teaches an online RCIS Review course for Spokane Community College, in Spokane, Washington, and regularly presents with RCIS Review Courses. Figure 2. Figure 3. “There seems to be some confusion about how respirations affect intracardiac pressures and how to properly read them.” — Anonymous email to tginapp@rcisreview.com Y es, it is important to understand how breathing affects pressure waveforms to obtain the most accurate readings. To do this, we have to revisit the basic mechanics of normal respiration. it might seem this way, it is not what happens. Respirations are based upon pressures inside and outside of the chest. When pressures on the inside of the chest are less than the pressures outside of the chest, air moves into the chest. The reverse is also true. When pressures on the inside of the chest are higher than the pressures on the outside of the chest, air is pushed out of the chest. We can simulate the mechanics in the chest with the bell jar. Let’s bring out an experiment that you should remember from junior high or high school. Hopefully, you recall the “bell jar” (Figure 1) experiment, used to demonstrate how our lungs work. Simply, this is a large glass dome with some small balloons inside and a large piece of rubber attached to the bottom. The large piece of rubber also has a knob on it that you can hold. In this experiment, we think of the dome as the chest, the small balloons as the lungs and the large piece of rubber as the diaphragm. Figure 4. Figure 5. Figure 4. INSPIRATION: Diaphragm contracts and moves down. Pressures decrease because of more space in the chest. Figure 5. EXPIRATION: Diaphragm relaxes and returns to normal position. Pressures increase because of less space in the chest. Basically, if we push up on the rubber piece in Figure 2 (diaphragm) we create a positive pressure within Most people will think that they the dome (chest) because we have “suck” air in for respirations. While reduced the space that the air in the dome (chest) is occupying, and essentially Figure 1. The Bell Jar Experiment it is compressed. If there is an opening to the outside environment (trachea and mouth), then the pressures must equalize and air moves out of the balloons (lungs) to the outside environment until the pressures are equalized. An analogy would be a can of soda that has been agitated a little. Pressure builds up in the can, and when you pop open the top, the pressure rushes out of the can until the pressure inside and outside the can are equalized. As we noted, the opposite is true as well. If you pull down on the rubber piece in Figure 2 (diaphragm) you create a negative pressure within the dome (chest) because we have increased the space that the air in the dome (chest) is occupying. If there is the opening to the outside environment (trachea and mouth), then the pressures must equalize and air is pulled into the balloons (lungs) from the outside environment until the pressures are equalized. An analogy would be the jar of pickles sealed with a vacuum. When you turn the lid, you hear a ‘pop’ and air rushes into the jar until the pressures inside and outside are equal. Let’s apply this to the chest instead of to a bell jar. If you place your hands on your abdomen during inspiration, you should be able to feel that your diaphragm moves caudal and your chest expands (Figure 4). This creates the negative pressure in the chest that is transmitted to the lungs and allows air to rush in to equalize with the outside. Contracting the diaphragm applies negative intrathoracic pressure to the lungs, causing inspiration. It also applies this negative pressure to the right atrium, causing increased venous return from the abdomen (Figure 6). During expiration (Figure 5), you should be able to feel your diaphragm move cranial, which in turn creates the positive pressure in the lungs allowing air to be expelled. Expiration is passive, because the

Table of Contents Feed for the Digital Edition of Cath Lab Digest - October 2007

Saints Medical Center Fibromuscular Dysplasia in Children and Adolescents Cerebral Vascular Accident Following a Pulmonary Embolism: Search for the Hidden Patent Foramen Ovale Contents Clinical Editor’s Corner Meetings Calendar CEU Education Center Radiation Tracking in the Cardiac Catheterization Lab Letter to the Editor Carotid Stenting: An update Release from Stent-jail: Beneficial Snow-Plowing? Patient Management Guidelines Searching for a Cardiovascular Position? Tips for Creating a ‘Stand-Out’ Resume Long-Term Implications of Short-Term Closure Decisions – The Evolution to Vascular Access Management and the Boomerang Catalyst System The Ten-Minute Interview with… Angie Bowles, RN, CCRN CMS Issues Final FY 2008 IPPS Rule ACVP• Membership Page Experience with a New Workhorse Guidewire Ask the Clinical Instructor: Q&A for Those New to Cath Lab A Glimpse of the Future of Clinical Education: Boston Scientific’s SimSuite Bus Visits Carnegie Institute 2007 Educational Fair Held at the Washington Hospital Center Research Update: Original Contribution Abstracts from The Journal of Invasive Cardiology What Do You Think? A Virtual Cath Lab Viewer (VCL): The Development of an Online 3D C-arm Simulator and Coronary Anatomy Viewer Clinical & Industry News Cost-Effectiveness of the Radial versus Femoral Artery Approach to Diagnostic Cardiac Catheterization

Cath Lab Digest - October 2007

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