|MEDICAL EDUCATION TEACHING NOTE
|Year : 2017 | Volume
| Issue : 2 | Page : 105-108
Students' responses under “negative pressure” to respiratory questions at the 15th physiology quiz international event: 100 medical school teams from 22 countries
Hwee-Ming Cheng, See-Ziau Hoe
Department of Physiology, Faculty of Medicine, University of Malaya, Kuala Lumpur 50603, Malaysia
|Date of Submission||28-Sep-2017|
|Date of Acceptance||24-Oct-2017|
|Date of Web Publication||15-Dec-2017|
Prof. Hwee-Ming Cheng
Department of Physiology, Faculty of Medicine, University of Malaya, Kuala Lumpur 50603
Source of Support: None, Conflict of Interest: None
The annual Inter-medical School Physiology Quiz (IMSPQ) reached a milestone in August 2017 with the participation of 100 university medical schools at the 15th IMSPQ. A total of 440 students from 22 countries competed. The written test on day 1 shortlisted 48 of the 100 teams for the 2nd day oral quiz stimulating sessions, conducted before a live audience. The IMSPQ provides a unique sample of international students, taught under a diverse spectrum of medical curriculums, designed to meet the university and national priorities of the countries. The written test, taken by all 440 students, is a challenging 75-min paper with 100 physiology statements covering all organ systems. Certainty in students' answers was targeted by a true/false response, with no marks for unattempted questions but with a negative mark on incorrect answers. The insights from an analysis of responses to the lung physiology, including cardiorespiratory mechanism, are helpful and enlightening for Physiology teachers. They show common areas of difficulty and imprecise understanding. This brief teaching note will describe and give some comments on the students' respiratory responses under pressure of negative marking.
Keywords: Education, physiology quiz, respiratory system
|How to cite this article:|
Cheng HM, Hoe SZ. Students' responses under “negative pressure” to respiratory questions at the 15th physiology quiz international event: 100 medical school teams from 22 countries. BLDE Univ J Health Sci 2017;2:105-8
|How to cite this URL:|
Cheng HM, Hoe SZ. Students' responses under “negative pressure” to respiratory questions at the 15th physiology quiz international event: 100 medical school teams from 22 countries. BLDE Univ J Health Sci [serial online] 2017 [cited 2020 Aug 13];2:105-8. Available from: http://www.bldeujournalhs.in/text.asp?2017/2/2/105/220944
| Right, Wrong, Blank Responses|| |
The Inter-medical School Physiology Quiz (IMSPQ) birthed in 2003 has grown into a global event in Physiology education. The IMSPQ is a rich resource for both students and teachers in learning and teaching essential concepts in Physiology. This paper provides valuable insights from the 15th IMSPQ. There were 15 respiratory questions, designed to test not merely factual recall but also a good understanding and grasp of Physiology. [Table 1] shows how the 440 students responded, grouped into right, wrong, and no responses.
|Table 1: Responses of 440 students to true/false respiratory questions at the 15th Inter-medical School Physiology Quiz, 2017|
Click here to view
The percentage of correct answers to the 15 true/false sentences ranged from 38% to 81%. For the incorrect responses, the range was 9% to 40%. How careful did the students attempt the questions under negative penalty marking? The blank responses showed 5% to 40%, with most questions being left answered by around 20% of the students.
| Uncertainty and Misconceptions|| |
The most unanswered question (Question 14; 40%) was on the quantitative comparison between the water vapor pressure and the partial pressure of carbon dioxide (PCO2) in the anatomical dead space (ADS). There are several facts that needed to answer this question correctly. The actual value of the water vapor pressure at body temperature is not really necessary to remember. The air in the “dead” conducting airways of the lungs will be the unaltered, inspired air. The PCO2 in this normal dead space is then close to 0 mmHg. Thus, the water vapor pressure (the value is 47 mmHg whether the student knows it or not!) cannot be lower than the 0 mmHg for PCO2.
The other most left unanswered question (33%) (Question 13) is on the quantitative aspects of oxygen (O2) extraction at the microcirculation. The previous dead space and this tissue space questions do highlight that students generally shy away from quantitative aspects of physiology. We should teach and direct our students' learning to focus on units and quantity, and they will enhance their conceptualization of physiology. At rest, the normal extraction of O2 only reduces the Hb–O2 saturation by 25% from about 100% to 75% in venous blood. Thus, the term deoxygenated blood is not synonymous with O2-depleted venous blood. Since Hb–O2 represents the bulk of the blood O2 content, the O2 content is also deceased by the same measure of ~25%.
The most attempted question (5% blank) (Question 2) was on the ventilation/perfusion (V/Q) ratio of the upright lungs. About three-quarter (~75%) of the students responded correctly. There is no way to ascertain if the students merely memorize that the V/Q ratio increases from the base to the apex of the upright lungs. One way to discover this is to ask three true/false questions – how the alveolar ventilation change, how the pulmonary perfusion change, and the comparative degree of change in ventilation or perfusion, from base to apex of the upright lungs. The students who answer correctly all the three questions would have the right understanding and are unlikely to have made a correct guess.
Misconceptions could be reflected by the high number of wrong answers, although most students answered those questions. The confidence in their answers is then misplaced since there is still some misunderstanding. The sentence with a low blank (11%) but showed a considerable wrong response (35%) (Question 10) was on the expected partial pressure changes in carbon monoxide (CO) poisoning and anemia. In both cases, the partial pressure of O2 (PO2) would be unchanged. The essential concept is that the PO2 is only contributed by dissolved O2 in the plasma of blood. The total hemoglobin-binding capacity for O2 is reduced in CO toxicity and in a reduced hematocrit in dietary-associated anemia. However, the dissolved component of the total O2 content is unaffected. The arterial blood PO2 is dependent on the alveolar air PO2 which is normal if the lung function is not affected.
The other question with a 40% wrong response (Question 15) is on the pressure changes during normal breathing. The respiratory cycle, normal negative-pressure breathing, requires a mechanistic appreciation of the changes in intrapleural (Pip) and intra-alveolar pressures. Airflow does not occur at the end of inspiration (or beginning of expiration) when the atmospheric pressure and the intra-alveolar pressure equalize. At this point in the respiratory cycle, the alveolar air pressure relative to atmospheric pressure is 0 mmHg. The definition of transpulmonary pressure (Ppt) (assuming the students know it) is the transmural pressure across the alveolar wall. The Ppt is then equal to Pip (0 minus Ppt).
| Ventilated Answers|| |
For 7 of the 15 respiratory questions, <60% of the 440 students answered correctly. There is presumably significant negative pressure in attempting these respiratory questions. In the Inter-medical School Physiology Quiz (IMSPQ), prizes are given for the top 10 individual scores. For the best 48 teams who will advance to the oral quiz, the average team score will be computed. There is then a good competitive pressure to answer carefully. The analysis of the IMSPQ responses reflects the knowledge base of these selected students, chosen to represent their medical schools. Common uncertainties and misconceptions observed are thus precious insights that can help us discern and better our Physiology teaching.
Four of the seven questions have been commented on above. We can learn from the negative feedback of the students' responses to the other three questions. The alveolar ventilation question (Question 9) had a 57% correct response. The “wasted” ventilation of the normal ADS is the product of the breathing frequency (Freq) and the ADS. Similarly, the alveolar ventilation is the product of the Freq and the alveolar exchange space. All students would have memorized the equation: (Tidal volume – ADS) × Freq to give alveolar ventilation. The question was asked in a slightly different conceptual way, and perhaps, this accounts for the less than expected correct responses.
A related “dead space” question with 53% correct answers (Question 11) was on the comparison between the alveolar and expired PO2. The word “expired” sometimes gives the impression that it is O2-depleted air. However, the expired tidal volume is a mixture of alveolar air and O2-rich ADS air, the latter being unexchanged inspired air from the previous breath. Thus, the alveolar air PO2 (103 mmHg) is less than the expired air PO2 (between 103 and 160 mmHg of inspired air).
The same reasoning will show that the “expired” air PCO2 is lower than alveolar PCO2 (40 mmHg), diluted by the ADS CO2-deficient air.
The question on compensation for V/Q mismatch (Question 12) scored a 49% correct responses. The compensatory hypoxic pulmonary vasoconstriction for a hypoventilated alveolar region (low V/Q) (Question 4) had a higher (66%) correct answers. The physiologic compensation for relatively hyperventilated alveoli (high V/Q) is generally less familiar for students. The decreased PCO2 in these alveoli produces the compensated constriction of bronchial smooth muscle of the supplying airways to improve the V/Q balance.
| “self-Directed” Learning in Respiration|| |
We tell our students that Respiratory Physiology is one area that they can image and imagine when learning the system. Literally, “self-directed” learning can be effectively used to enhance the grasp of respiration mechanisms., For example,
- The student can familiarize the various lung volumes and capacities by performing a maximal expiration to reach the residual volume or a maximal inspiration to reach the total lung capacity
- While at rest and a hand on her chest, the student can work through mentally the various pressures that are involved in negative-pressure breathing, namely, intrapleural, intra-alveolar, transpulmonary, and atmospheric pressures
- The student can voluntarily hold her breath and think about the changing alveolar CO2/O2 partial pressures
- The student can hyperventilate and review the diffusive changes at the alveolar–capillary membrane and how the arterial PCO2 is reduced with the development of respiratory alkalosis 
- While hyperventilating, the student can conceptualize why the increased ventilation is not the major contributor to the increased rate of O2 delivery to the cells (the higher cardiac output is the primary determinant)
- The student can jump on the spot in her room and think about all the multiple sensory inputs that maintain the increased alveolar ventilation during exercise.
We hope the above insights from the 15th IMSPQ will be helpful for those who teach Respiratory Physiology. Take a deep breath and be inspired to continue your worthy calling as a physiology educator.
| References|| |
Cheng HM, Hoe SZ. Update on the growth of the international intermedical school physiology quiz. Adv Physiol Educ 2016;40:198-9.
Cheng HM. Physiology Question-Based Learning: Cardio, Respiratory and Renal Systems. London: Springer International Publishing Switzerland; 2015.
Cheng HM, Chan YY. Respiratory Physiology: Figure-based Instruction. Singapore: Cengage Learning Asia; 2008.
Cheng HM. Thinking Through Physiology. Kuala Lumpur: Pearson Malaysia; 2012.
Mah KK, Cheng HM. Learning and Teaching Tools for Basic and Clinical Respiratory Physiology. London: Springer International Publishing Switzerland; 2015.