PEPonline Professionalization of Exercise Physiologyonline An international electronic journal for exercise physiologists ISSN 1099-5862 Vol 5 No 11 November 2002   GRAVITY INVERSION A Teaching Tool for Integrating Critical Thinking and Cardiovascular Physiology Tommy Boone, PhD, MPH, MA, FASEP, EPC Professor and Chair Department of Exercise Physiology The College of St. Scholastica Duluth, MN 55811 “Customers pay only for what is of use to them and gives them value.”  -- Peter Drucker Introduction Not only is “gravity inversion” used to decompress the spine and reduce low back pain [1], it is used to strengthen the abdominal muscles during vertical head-down sit-up exercises [2].  It can also be used to integrate critical thinking and cardiovascular physiology.  For example, what is the answer to the question:  “Aside from aerobic training, can heart rate decrease with an increase in stroke volume?”  Students are likely to think that an increase in stroke volume is always associated with an increase in heart rate.  If stroke volume can increase with a decrease in heart rate, what are the reasons for the physiologic response?  Similarly, “What happens to systolic blood pressure with the transition from standing position to the head-down position?”  Or, the reverse direction, that is, “Does blood pressure increase, decrease, or stay the same with the transition from lying down to sitting up or standing?”  Finding answers to these questions helps to encourage critical thinking?  Nearly every professor works at teaching students and, of course, asking questions is a big part of the process.  But, still, far too many students are allowed to sit and passively receive information [3].  We continue to cling to our traditional system of educating students.  The inertia of the traditional system will change, however.  Students and their parents have come to believe that they are paying for a product, not just an education.  If colleges and universities are to move ahead in the 21st century, the faculty will need to place emphasis on new ideas and new technology that allow for new opportunities.  Our reality check shows that, in an effort to produce knowledge (research), exercise physiologists are dancing a tango with students who need to learn how to think.  If left unchecked, the academic world demonstrates to everyone its inadequate response to current educational concerns.  In this country, if not worldwide, teaching students to think critically is important.  Unfortunately, a look at how exercise physiologists teach exercise physiology courses is a good illustration of little to no change in the rigidity and inflexibility of our thinking about the curriculum.  But change we must, for if we are too busy or too little interested to reform our own profession, then it will be done by others who may further undermine our credibility.  To address this weakness, one recommendation is a paradigm shift from a model of few, if any, hands-on laboratory experiences to one that is transformational.  More undergraduate courses need a laboratory component, and more labs need equipment that is effective in producing physiological data.  As a consequence, why not purchase a gravity inversion apparatus?  It will help students learn.  Students will be able to identify specific physiological responses important to understanding cardiovascular physiology.  In addition to other mandatory pieces of equipment (e.g., metabolic analyzers, heart rate and blood pressure monitors), it is incomprehensible that students will not learn to think differently.  The gravity-facilitated effects on the cardiovascular system are immediate.  Students can determine what happens to the physiology of the body from one body position to the next.  They stand to gain immeasurably from its use.  There is an immediate reinforcement of physiological principles when students are involved simultaneously in the collection of data.  Putting the Idea to Use  Students understand what it means to sit in class and take notes.  Much, if not, most of their education has been essentially a passive experience [3].  When done correctly, the value of a hands-on laboratory experience is that it is an active experience.  However, current thinking suggests that undergraduate students receive less than the desired time in the laboratory setting.  This deficiency is a problem.  Lecture courses need a laboratory component and every exercise physiology laboratory can benefit from having a gravity inversion apparatus to teach critical thinking and cardiovascular physiology.  In order to begin the instructional discourse, the “cognitive process model” of incorporating non-traditional pieces of equipment helps to explain why and how new thinking is valued.  This model is loosely defined by the ten statements that enable faculty to put ideas to use and, therefore, to catapult students into a leadership role in the profession. 1. Rationale for the teaching tool.  For several decades, gravity inversion has been used as a research method to study physiologic responses to simulated weightlessness [4-6].  The findings from these studies have been used to help explain the cardiovascular effects of space flight [7].  For this reason, gravity inversion affords exercise physiologists an important step for elevating the status of the scholarship of teaching.  Its simplicity is a resource that is within the budget of most departments ($500).  Since it is important that faculty improve their teaching skills, the purchase and use of the apparatus should be embraced and even demanded to improve the delivery of academic information.  2. Identification of discordant findings.  Heng and colleagues [8] reported a statistically significant increase in heart rate during gravity inversion (relative to standing) while other researchers have reported a decrease [9,10] or no change in heart rate [11-13].  The cardiac output response to gravity inversion has been reported as increased [11, 14] or decreased [8].  Systolic blood pressure has been reported to decrease [15], increase [16-18] or not change at all during inversion [14].  The point is that the subjects in the different studies responded differently under a variety of circumstances.  The inversion apparatus allows for distinguished effects without long, tedious hours (or months) to realize the physiology of change.  3. We perceive what we expect to perceive.  This statement may seem somewhat trite.  There is a certain truth to the statement though.  It means that we tend to see (or think) what we expect to see (or think).  The unexpected often comes as a surprise, which is often a finding after the data have been treated with statistics.  Of course, what is truly important is that the unexpected is often times the opposite of what students think.  To their surprise, when they see the actual data, they begin to understand and become more responsible for their own thinking.  This is particularly true with respect to the cardiovascular data such as heart rate, stroke volume, cardiac output, systolic blood pressure, systemic vascular resistance, and arteriovenous oxygen difference.  Together they represent the opportunity to build confidence in their abilities to evaluate the effects of stressors and continue to grow in critical reflection.  4. Seeing is believing.  Here, students can be heard saying, “I was wrong.  Blood pressure didn’t change with the different body positions.”  Or, “I can’t believe what we found disagrees with the textbook?”  It is meaningful to not only say to the class that oxygen consumption does not increase or decrease with a change in body position (i.e., as in standing vs. lying down or standing vs. head-down inversion), but to demonstrate it.  Skeptical students may exhibit a pattern of thinking that is less distrustful or defensive, especially when their laboratory work progresses to the point of hands-on communication.  When students learn to find answers for themselves in their own laboratories, it is the beginning of important learning (i.e., seeing is believing).  5. Doing is learning.  What is important is not just sitting in class, but getting involved in the learning process.  To supply data to the students is not enough.  Students must create the data, too.  Then, they must integrate the data with critical reflection and strategy.  One way to do that is with a “research tool” such as the gravity inversion apparatus.  The use of a non-traditional research apparatus helps to define the laboratory experience as a unique opportunity to create a learning environment.  Good teaching requires lectures, discussions, and the performance of all activities that go into teaching.  It also requires an excellence that comes from learning through experience; a journey to knowledge through doing. 6. Excellence requires the right attitude and a radically different view.  In the end, it is not the size of the university that makes the teachers or how well students learn and develop professionally.  It is the size of the teachers!  This should not be misunderstood.  Big is good if big is doing the right thing.  But big is not necessary to do the right thing or to see that the right think is done.  This is true of those that aim at teaching critical thinking by manipulating human physiology.  So far, it seems that most academic exercise physiologists don’t get this point.  This may explain the popularity of research equipment that is used only by the faculty.  Never mind the students or, better yet, leave the “real learning” to the doctorate students.  This raises questions rather than answering questions about the undergraduate degree.  Just think how much better the students would be today had such thinking not become standard practice for the past fifty years.  Attitude is everything.  Each member of the faculty must contribute toward a visionary view, if not, a radical view of the education of exercise physiology students. 7. Just do it.  It is not enough to have a great idea.  There has to be action.  The design of a laboratory-research project is worthless unless students commit to data collection.  To ask, “What can I learn?” or “What can I do to think better?” is to focus on managing subjects and turning attention to a meaningful interaction with the research design and data collection procedures. 8. Converting new ideas into action. It may not appear to be all that difficult or an important contribution to the hands-on activities, but converting new thinking into action isn’t easy.  New data cannot become new ideas without a ruthless effort in thinking and decision making that makes a radical difference. 9. Where can I contribute?  Those who have to ask haven’t been encouraged to think outside of the box.  And yet they have the opportunity to take responsibility in terms of the overall organizational structure of the critical thinking that is woven into the subjects’ responses.  Within a fairly short period of time, one or more students may commit to statistical analysis, another will take blood pressure measurements, and still another will oversee the cardiac output procedures.  Of particular importance is the contribution of individual thinking that is complementary to the overall performance of the team of students. 10. The new exercise physiology is entrepreneurial.  Every research decision in exercise physiology sets the stage for critical reflection with implications for understanding human physiology and communication of lifestyle factors that may impact health and fitness.  But also, contrary to popular belief in the Gold’s Gym jobs, there are “flashes of entrepreneurial thinking” that are real and innovated; thinking that is driven by the need to help others or to simply understand the physiology of a stressor.  Unfortunately, there is little serious talk today about the application of the exercise physiology body of knowledge beyond traditional thinking.  The shift to the new thinking puts exercise physiology in the center of increased job opportunities.  The Decision Steps  After reviewing the 10 statements for putting the idea to use, students are encouraged to write a research report that demonstrates their critical thinking skills.  The report is based on the research purpose(s).  For example, the undergraduate students were asked to answer the following “multifaceted” question: “Does oxygen consumption, cardiac output, heart rate, stroke volume, tissue extraction, systemic vascular resistance, systolic blood pressure, and mean arterial pressure increase, decrease, or stay the same with the transition from standing to horizontal to head-down (45 degrees)?”  Of all the decisions that go into the research effort, none is as important as the decisions regarding: (a) purpose(s), (b) subjects, (c) research design, (d) statistics, (e) findings, and (f) discussion/conclusions.  To take command of the research project is both bold and demanding.  Each decision requires a careful and thoughtful analysis and preparation.  Note that the following brief description of each component of the research effort is consistent with an undergraduate hands-on laboratory “report” only.  The intent is not to reproduce the report but to show some of the content effort on their behalf.  Purpose(s) As an example, the “purpose” of the assignment that was given to my undergraduate students was primarily to integrate critical thinking with several cardiovascular responses to three different body positions (standing, horizontal, and head-down).  The critical thinking that went into the data gathering procedures and the analysis of the relationship of the dependent variables to each other was made possible using the gravity-inversion apparatus.  The secondary purpose of the hands-on laboratory session was to place the students in a situation where they would be responsible for calibration of the Medical Graphics metabolic analyzer and the steps necessary to use the CO2 rebreathing procedure to determine the subjects’ cardiac output.  Following data collection, the data were analyzed for statistical significance.  Students were encouraged to figure out the reasons for the different cardiovascular responses by comparing their findings with a sound contemporary explanation.  This analysis involved content from textbooks and findings from published articles. Subjects Fourteen healthy subjects attended the hands-on laboratory session.  None of the subjects had a prior history of back trauma or lumbar spine complaints.  Most of the subjects were familiar with the gravity-inversion apparatus, having participated as subjects in other labs.  Due to their familiarity with the laboratory equipment and the head-down position, they concentrated on the specifics of the project.  Most of the students worked in “threes” – one student was responsible for the metabolic analyzer, one did heart rate and blood pressure, and one was the subject.  Following data collection, the students shifted responsibility until data were collected for all three students in that group.  The rest of the groups did the same thing as their turn became available.  There were two metabolic/gravity-inversion stations set up for the students. Research Design One student in the group positioned him- or herself in front of the gravity-inversion apparatus facing away from it while remaining in the standing position.  Baseline recordings were done with the subject standing upright for five minutes.  Resting blood pressure and heart rate were measured at the fourth minute while cardiac output was determined at the end of minute 5.  Oxygen consumption was averaged across the five-minute period.  Students had previously worked with the metabolic analyzer and all other equipment for several months in related labs.  At the beginning of the sixth minute, the subject was positioned on the inversion apparatus and rotated to the horizontal position (as in lying down).  The subjects’ arms remained alongside the body on the apparatus for a second, 5-minute period.  The same data were collected in exactly the same manner.  Then, the subject was rotated to the 45-degree head-down position for the final 5 minutes of data collection.  Again, all data were collected as described using the Medical Graphics analyzer, a heart rate monitor, and auscultation of the left brachial artery using a standard sphygmomanometer.  Students used the plateau method to determine cardiac output, using 10% CO2 in a 35% O2 mix.  The students followed the standard steps in performing the CO2 rebreathing procedure.  The analyzer’s software for calculating arterial CO2 (PaCO2) derived from the end-tidal PCO2 (PETCO2), mixed venous PCO2 (PvCO2) derived from the rebreathing procedure, and VCO2.  Otherwise, the students calculated the related cardiovascular responses according to the following formulae: (1) stroke volume was calculated by dividing cardiac output by heart rate; (2) arteriovenous oxygen difference was calculated by dividing oxygen uptake by cardiac output; (3) systemic vascular resistance was calculated by dividing mean arterial pressure by cardiac output; and (4) mean arterial pressure was calculated using the formula: [MAP = DBP + .32(SBP-DBP)]. Statistics Analysis of variance with repeated measures was used to determine significance of change in the cardiovascular responses.  The alpha level was set at 0.05 for statistical significance. Findings Means and standard deviations were computed for all measurements (refer to Table 1).  During the transition from standing to horizontal to head-down, oxygen uptake was unchanged.  Cardiac output and stroke volume were increased during the horizontal position (relative to standing) and increased further during the head-down position (relative to horizontal and standing).  Heart rate decreased during the horizontal and the head-down positions (relative to standing).  Arteriovenous oxygen difference and systemic vascular resistance were decreased during the horizontal position (relative to standing) and decreased further during the head-down position (relative to horizontal and standing).  Systolic blood pressure was increased from during the head-down position (relative to standing and horizontal).  Mean arterial pressure was unchanged. Table 1. Cardiovascular responses during three different body positions, using an ANOVA with repeated measures (M = ± SD). Standing  (A) Horizontal  (B) Head-Down (C) F-Ratio Prob. F VO2 (L/min) .31 ±.08 .32 ±.12 .33 ±.11 .75 .48 Q (L/min)   4.5 ±1.3 A-B A-C 5.4 ±2.2 B-C 6.6 ±2.8 9.2 .0009* HR (beats/min) 80 ±1.8 A-B A-C 69 ±1.7 68 ±1.9 22.9 .0001* SV (ml) 57 ±17 A-B A-C 78 ±33 B-C 98 ±41 14.2 .0001* a-vO2 diff (ml/100 ml) 6.9 ±1.3 A-B A-C 6.2 ±.9 B-C 5.3 ±1.6 7.8 .002* SVR (mmHg/L/min) 19.2 ±2 A-B A-C 17 ±4 B-C 14 ±4 13.6 .0001* SBP (mmHg) 114 ±9 A-C 114 ±9 B-C 115 ±3 .4 .05* MAP (mmHg) 90 ±7 88 ±8 89 ±8 .91 .41 VO2  = oxygen uptake Q  = cardiac output HR  = heart rate SV  = stroke volume a-vO2 diff = arteriovenous oxygen difference SVR  = systemic vascular resistance SBP  = systolic blood pressure MAP  = mean arterial pressure *Significant at 0.05 Discussion/Conclusions Students worked in “threes” at first, then, they came together as a class with a written discussion based on the statistical findings of published work on the physiology of standing and different body positions.  It is not the purpose of this article to extend this point too much further (i.e., taking on a research manuscript form).  The earlier information that characterizes the students’ report is representative of their laboratory effort.  Instead of extending this view, several conclusions will be put forward in a form of a “discovery of information” that encouraged critical reflection and acquisition of new knowledge.  1. For example, a turning point in their lab was the sense that oxygen consumption was not changing with the transition from one body position to the next.  A few students felt, “So what’s the problem?”  In actuality, though, they came to realize that oxygen uptake is unchanged.  The subjects’ need for energy was not altered as a function of whether they were standing, lying down, or in a head-down position.  This surprised the students since an earlier discussion revealed that they believed it would be higher during the standing and head-down positions versus lying down.  With no change in oxygen uptake, the students felt that one side of the VO2 equation (i.e., VO2 = Q x a-vO2 diff) must have increased and one side must have decreased.  As it turns out, that is exactly what happened.  The increase in the central component of the VO2 response was balanced by the decrease in the peripheral component of VO2.  The students found that the extraction of oxygen by all the tissues of the body was decreased.  In other words, the tissues’ need for oxygen was met by the increase in cardiac output. 2. Cardiac output increased when lying down versus standing and during the head-down position versus lying down and standing.  The increased cardiac output is directly related to the reduction in the effects of gravity when in the upright standing position that encourages the pooling of blood in the dependent regions of the lower extremities.  Since the lying down position essentially neutralizes the effect of gravity on the cardiovascular system with regards to a pooling of blood in one primary area, the transition from standing to lying down increased venous return, end-diastolic volume, and therefore stroke volume.  When the subjects were moved from the lying down position to the head-down position, the effect of gravity demonstrated a further increase in venous return with a significant increase in cardiac output.  In other words, students learned that the physiology of standing is exactly the opposite effect of the physiology of being in a head-down position. They also learned that the cardiac output response (and hence, the stroke volume response) was directly a function of the decrease in systemic vascular resistance.  3. Since the subjects’ heart rate decreased from standing to lying down and head-down positions (and yet cardiac output increased), then stroke volume must have increased.  Students found that the stroke volume response was responsible for the cardiac output response.  Stroke volume increased when the subjects assumed the lying down position and increased even further during the head-down position.  4. The final consideration was the significant increase in systolic blood pressure of 1 mmHg that set the stage for a meaningful discussion regarding statistical significance versus practical significance.  Further discussion allowed for an understanding of the pressure receptors in the neck and other structures that are involved in the regulation of blood pressure and heart rate. Final Thoughts First of all, this is not a research paper.  The layout is designed to help the academic exercise physiologists manage the idea of using a gravity-inversion apparatus in the laboratory component of the typical “physiology of exercise” course.  The best one can then hope is that the idea will be put into action.  Of course, the problem of too few labs will not be corrected anytime soon.  The lack of adequate budget focus and of the right departmental policies is, by contrast, the greatest threat to the integrity of our academic programs.  The next questions we must ask are: “Why aren’t we doing whatever is necessary to meet the customers’ needs?  And, while it is never easy, “When are the academic exercise physiologists going to update their body of knowledge with accreditation?”  Perhaps because “being trapped in the manufactured notion of what is exercise physiology” there is the necessity to engage in new thinking.  The risk of doing so is likely to correlate with better jobs for our students who have increased abilities to think critically, who are in position to be leaders in the field, and who are willing to compete for the rights of the profession. 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