Abstract
The cardiovagal baroreflex is an important physiological reflex that is commonly taught in health-related university physiology courses. This reflex is responsible for the rapid maintenance of blood pressure through dynamic changes in heart rate (HR) and vascular resistance. The use of lower-body negative pressure (LBNP) and lower-body positive pressure (LBPP) can manipulate these stretch sensitive baroreceptors. High performance and relatively inexpensive homemade LBNP and LBPP chambers can be easily constructed providing a valuable tool for both research and teaching purposes. There has been previous documentation of how to build a LBNP chamber; however, the information available usually lacks appropriate construction details, and there is currently no literature on how to build a chamber that can accommodate both LBNP and LBPP. In addition, a recently developed novel LBNP/LBPP chamber positioned on a 360° tilt-table provided the unique utility of superimposing both LBNP/LBPP and body position as independent or combined stressors to alter central blood volume. The primary purposes of this manuscript are to (1) provide step-by-step instructions on how to build a tilt-table LBNP/LBPP chamber, and (2) demonstrate the effectiveness of a tilt-table LBNP/LBPP chamber to facilitate undergraduate and graduate learning in the laboratory by effectively demonstrating the cardiovagal baroreflex.
Highlights
The cardiovagal baroreflex is a bi-directional, pressure/stretch-sensitive, negative feedback response to changes in mean arterial pressure (MAP) mediated by the autonomic nervous system (Mancia et al 1984; Fadel and Raven 2012)
During lower-body positive pressure (LBPP), heart rate (HR), stroke volume (SV), and cardiac output (CO) remained similar throughout the entire protocol; as expected, MAP increased by ∼10 mm Hg
The laboratory demonstrations aided the students’ articulation of the following learning objectives: (1) ability to describe the specific cardiovagal baroreflex-mediated mechanisms that are responsible for the maintenance of blood pressure during lower-body negative pressure (LBNP) and LBPP in supine position; (2) ability to recognize cardiovascular collapse, a potential response when using LBNP, to ensure participant safety; (3) ability to describe the specific cardiovagal baroreflex-mediated mechanisms that are responsible for blood pressure regulation during changes in body position (45° HDT, supine, and 45° head-up tilt (HUT)) at rest; and (4) ability to understand why there are differences in the cardiovascular response to LBNP in different body positions (45° HDT, supine, and 45° HUT)
Summary
The cardiovagal baroreflex is a bi-directional, pressure/stretch-sensitive, negative feedback response to changes in mean arterial pressure (MAP) mediated by the autonomic nervous system (Mancia et al 1984; Fadel and Raven 2012). This reflex is critical for moment-to-moment regulation of heart rate (HR) and vascular resistance in humans and is often a fundamental concept taught in physiology and medical-related courses. The cardiac response can be monitored using recordings of HR and stroke volume (SV), whereas the vascular response can be monitored with measures of muscle sympathetic nervous activity (MSNA), vascular ultrasound, or both These latter techniques, require expensive equipment and trained personnel. Both of these responses simultaneously contribute to the maintenance of MAP, which can be monitored on a beat-by-beat basis
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