RESPIRATION EXERCISES
RESPIRATION PRACTICAL
1) Confusing terms glossary
This exercise is an extension of Appendix E on Confusing Terms in the No
Frills Generic Skills Guide. Read the introduction there, then scroll down to find the terms which are relevant to the respiratory practical. Below are some from that list, but you should be able to add more from your lectures and textbooks.
Constriction - contraction
Flow
– flux
Renal medulla – medulla of brainstem
Resistance of arterioles - resistance of bronchioles
Vasodilator – bronchodilator
Add your own additional pairs:
Write down your own definitions for the following pairs of terms, and give their units and typical values where appropriate. Consider any mathematical relationships which are relevant. i) total pulmonary ventilation – alveolar ventilation ii) hyperventilation – hypoventilation iii) tidal volume – residual volume iv) end-tidal alveolar gas – dead space gas v) central chemoreceptors – peripheral chemoreceptors
2) Misconception MCQs
Choose the correct option which best completes the statement in the stem.
Q1 Under steady state conditions of metabolism: a) alveolar pCO
2 is directly proportional to alveolar ventilation b) alveolar pO
2 is directly proportional to alveolar ventilation c) alveolar pCO
2 is inversely proportional to alveolar ventilation d) alveolar pO
2 is inversely proportional to alveolar ventilation
Q2 The greatest impact of the diversion of gases into and out of body stores when holding one’s breath is in producing: a) a faster rise in alveolar pO
2 b) a slower fall in alveolar pO
2 c) a faster fall in alveolar pCO
2 d) a slower rise in alveolar pCO
2

[Answers: 1c 2d]
3) Logical fallacies (and how to avoid them)
Explain what is wrong with each of the following statements. a) Alveolar ventilation is proportional to tidal volume, dead space volume and respiratory rate.
Explanation: Alveolar ventilation is equal to (tidal volume – dead space volume) times respiratory rate. Since proportional means that the two variables change together by the same fraction, alveolar ventilation will change proportionally to respiratory rate change, but only to the difference between the two volumes and not each individually. Furthermore, if a simultaneous change in this volume difference were to occur when the rate was changed, then alveolar ventilation would be equal to a product in which no term had been kept constant, and hence would not be proportional to any variable. b) During end-tidal expiration, due to diffusion of oxygen and carbon dioxide down pressure gradients, the pressure in blood equates that of the alveoli, producing an equilibrium.
Explanation: This statement contains a number of common errors. End-tidal expiration should rather be expressed as end-tidal volume in order to make a claim about equality of gas pressures. The pressure in blood must be defined as a particular gas partial pressure (and not hydrostatic or osmotic pressures). Diffusion of oxygen and carbon dioxide down their pressure gradients does produce an equilibrium between alveolar and dissolved blood gas, so that the values for each gas in the two compartments are equal. It is this equality which allows one to use a sample of endtidal gas as a proxy for arterial blood, as the dead space gas has already been exhaled. c) The amounts of pCO
2
and pO
2 are different in different subjects, as these are dependent on age, sex, weight etc.
Explanation: Although one might hypothesize that physical differences between individuals would result in different blood gas levels, counteracting this are the physiological homeostatic mechanisms which maintain pCO
2
and pO
2
at approximately the same values within the normal range, so that metabolism can proceed efficiently. d) Breathing pure oxygen containing a small fraction of carbon dioxide causes all alveolar nitrogen to be replaced within a couple of breaths.
Explanation: As the amount of air remaining in the lungs at the end of a normal expiration (functional residual capacity) is about 2300 ml, and only about 350 ml of new air is brought into the alveoli with each normal inspiration, it obviously requires many more than a couple of breaths to completely replace the alveolar air, including the major nitrogen fraction, with pure oxygen.

4) Sequences which make sense
Rearrange the following 10 concepts relating to ventilatory change into a numbered chronological sequence which shows how one leads to the next (as in a concept map). Indicate by arrows (↑↓) the direction of each change.
1.
Rebreathing own expired air
Alveolar pCO
2
Arterial pCO
2
Alveolar pO
2
Arterial pO
2
Oxyhaemoglobin
Carbaminohaemoglobin
Plasma bicarbonate concentration
Alveolar ventilation rate
Medullary chemoreceptor stimulation
1. Rebreathing own expired air i) ii) iii)
5) The three most important facts
In this exercise you have to make a choice from all the relationships you have covered in the previous exercises, which THREE are the most vital to underpin a hypothesis about alveolar gas composition variation with ventilation pattern. Since it is essential that the hypotheses evolve from what you have written in the Introduction , these would constitute the three most important sentences as they would be the ones from which your hypotheses could then be predicted . i) ii) iii)
Repeat this exercise now for the Discussion , where the THREE relationships are those which best explain how your data have supported your hypotheses.

Extra notes
When answering some of the questions on respiratory activity, the concepts below may be relevant. Consider the pressure gradients creating during a normal respiratory cycle which move the different gases in different directions, how the physical and chemical stores affect the equilibria, and what happens when the gas mixture breathed is not normal air. Remember that voluntary control of ventilation gives different outcomes from involuntary control.
Gaseous equilibria
Gas stores
Breathing higher oxygen concentrations

Concept maps