Week 1 Formative Quiz Questions

Question 1

Nitrous oxide is a safe sedative to use on most individuals as it blunts only the peripheral chemoreceptor activity.

Answer 1

True. Nitrous oxide is well tolerated in most individuals. In terms of respiratory function it is safe for most individuals as it does not affect central chemoreceptor activity on which most individuals rely. However it does impair peripheral chemoreceptor function. As such it should be used in caution in patients with chronic lung diseases who may be on “hypoxic drive”. Patients with chronic lung disease have had long term exposure to elevated arterial PCO2 due to impaired gas exchange and overtime the central chemoreceptors become desensitised to CO2. In these circumstances the peripheral chemoreceptors take over setting the rhythm of ventilation. Administrating nitrous oxide to these individuals could then knock out the only mechanism they have for monitoring blood gas composition.

Question 2

A pneumothorax (air in the pleural cavity) disrupts the relationship between the visceral pleural membrane and the lungs

Answer 2

False. It disrupts the relationship between the parietal pleural membrane and the visceral pleural membrane. The visceral pleural membrane would remain attached to the lung surface in a pneumothorax.

Question 3

The functional unit of the lung is the pulmonary alveolus.

Answer 3

True. The alveoli are the only point of the respiratory tree where the walls are thin enough to allow gas exchange, and hence they are the only point where functional gas exchange occurs.

Question 4

The functional residual capacity can be directly measured with a spirometer.

Answer 4

False. Spirometry can only measure the volume of air that can be exhaled. As FRC contains residual volume, a volume than cannot be voluntarily exhaled, FRC cannot be directly measured using spirometry.

Question 5

Under normal circumstances, there is poor correlation between the best-ventilated and best-perfused parts of the lung.

Answer 5

False. There is good correlation with ventilation and perfusion – both are greatest at the base of the lung (in the upright position) and both decrease with height. However blood flow declines faster than ventilation so while blood flow exceeds ventilation at the base of the lung, ventilation exceeds blood flow at the apex

Question 6

Alveolar ventilation volume is more than pulmonary ventilation volume.

Answer 6

False. Pulmonary (or minute) ventilation describes the total amount of air breathed in or out per minute (basically tidal volume x respiration rate). Alveolar ventilation accounts for the volume of air that gets stuck in dead space and never reaches the alveoli, so dead space volume must be subtracted from tidal volume before multiplying by respiration rate ((TV-DS) x RR), making alveolar ventilation smaller than pulmonary ventilation i.e. not all the air you breath in reaches the level of the alveoli and participates in gas exchange!

Question 7

At the onset of inspiration, action potential frequency in the phrenic motoneurones decreases.

Answer 7

False. The phrenic nerve innervates the diaphragm, the main muscle of inspiration, so activity would increase during inspiration.

Question 8

The phrenic nerve takes its origin from the T3, T4 and T5 spinal nerves.

Answer 8

False. The phrenic nerve takes it origins from the C4, C4 and C5 spinal nerves

Question 9

The term shunt describes the passage of blood through the lungs where the opportunity for gas exchange does not occur.

Answer 9

True. Shunt describes the situation where blood is effectively “shunted” from one side of the heart to the other without participating in gas exchange in between. It can happen where part of the lung is not being fully ventilated for some reason e.g. tumour, airway obstruction

Question 10

Increases in carbon dioxide in the blood enhance the oxygen binding power of haemoglobin.

Answer 10

False. An increase in the partial pressure of CO2 will shift the oxyhaemoglobin binding curve to the right, meaning that at any given value of PO2 less oxygen is bound to haemoglobin. Basically an increase in PCO2 decreases the affinity of haemoglobin for oxygen. This helps to maintain the delivery of O2 to tissues as metabolic demand (and therefore CO2 production) increases.

Question 11

The peripheral chemoreceptors in the carotid bodies and the aortic bodies are entirely responsible for stimulation of ventilation by hypoxia.

Answer 11

True. Only the peripheral chemoreceptors can detect hypoxia. The central chemoreceptors only respond to hypercapnia (but are much more sensitive to this than the peripheral chemoreceptors are to hypoxia).

Question 12

Central chemoreceptors respond to changes in H+ concentration.

Answer 12

True. Specifically, they respond to changes in H+ concentration in the cerebrospinal fluid (CSF). These H+ are wholly derived from CO2 present in the CSF, which in turn is in equilibrium with CO2 in the plasma so indirectly the central chemoreceptors are responding to increases in CO2 in the plasma. H+ from other metabolic sources cannot cross the blood brain barrier and so do not stimulate the central chemoreceptors

Question 13

Regarding airways and breathing: Expiration at rest is essentially a passive process.

Answer 13

True. During passive expiration, all that happens is your muscles of inspiration (mainly the diaphragm and external intercostal muscles) stop contracting and gently relax to their resting positions, in doing so decreasing the volume of the thoracic cavity and thus increasing pressure which forces the air out.

Question 14

A pneumothorax (air in the pleural cavity) resulting from a penetrating injury to the thoracic wall will cause intrapleural pressure to becomes less negative.

Answer 14

True. Normally intrapleural pressure is negative (i.e. less than atmospheric pressure). In a pneumothorax, penetration of the thoracic wall allows air (at atmospheric pressure) to enter the pleural cavity and thus equalises the pressure between the cavity and the atmosphere. In doing so intrapleural pressure rises to become the same as atmospheric pressure.

Question 15

The right lung is divided by a fissure into the upper and lower lobes.

Answer 15

False. The right lung is divided by two fissures (horizontal and oblique) into three lobes (superior, middle and inferior).

Question 16

The peripheral chemoreceptors will stimulate increased ventilation in anaemia

Answer 16

False. The peripheral chemoreceptors respond to changes in levels of oxygen in solution (PO2) and not the amount of oxygen wrapped up in hemoglobin (where most of the blood oxygen in found). In anaemia the problem is a decrease in oxygen binding capacity of the red blood cells, providing the lungs are healthy the amount of oxygen in solution in the plasma will be normal so the peripheral chemoreceptors will not be activated.

Question 17

The haemoglobin-O2 saturation curve will be shifted downward in an anaemia with normal lung function.

Answer 17

False. The oxyhaemglobin binding curve is unaffected in anaemia. In anaemia the amount of oxygen in solution in the plasma is unaffected (providing the lungs are healthy) and therefore the binding of oxygen to red blood cells is normal. The term anaemia describes a fall in the total oxygen content of the blood but remember 98% of the oxygen in the blood is wrapped up in the haemoglobin in red blood cells, it is not in solution in the plasma. If the lungs are working normally, anaemia therefore comes about due to diminished ability of red blood cells as a whole to carry oxygen for one reason or another e.g. lacking in number, or in oxygen binding sites due to iron deficiency. However the red blood cells that are present in the blood are fully saturated at normal PO2, even if they have fewer binding sites than normal.

Question 18

Peripheral chemoreceptors mediate the hypocapnia (low PCO2) that occurs at high altitude.

Answer 18

True. The lower atmospheric PO2 at altitude means arterial PO2 also falls. This is detected by the peripheral chemoreceptors which stimulate ventilation in an attempt to restore normal PO2. The resulting hyperventilation blows of more CO2 than normal leading to hypocapnia.

Question 19

An increase in body temperature favours the off-loading of oxygen from haemoglobin.

Answer 19

True. Remember the Bohr effect – where increased temperature, increased PCO2 and decreased pH all shift the oxyhaemoglobin binding curve to the right, meaning that for any given value of PO2 less oxygen is bound to haemoglobin (effectively the affinity of haemoglobin for oxygen has decreased).

Question 20

The haemoglobin-O2 saturation curve is moved to the left by a decrease in body temperature..

Answer 20

True. A decrease in body temperature increases the affinity of haemoglobin for oxygen and thus shifts the binding curve to the left. This is one of the reasons hypothermia is so dangerous – at a body temperature of 20oC the haemoglobin remains fully saturated meaning while the blood is jam packed full of oxygen the peripheral tissues cannot access it because the haemoglobin won’t release it.

Question 21

Lung compliance is defined as the magnitude of the change in lung volume produced by a given change in transpulmonary pressure.

Answer 21

True. Compliance describes the change in lung volume for any given change in transpulmonary pressure (sometimes graphs show intrapleural pressure rather than TP but the effect is the same).

Question 22

Carbon dioxide is carried on the haemoglobin molecule as carboxyhaemoglobin.

Answer 22

False. The term “carboxyhaemoglobin” describes carbon monoxide binding to haemoglobin – your carboxyhaemoglobin levels should be neglible!

Question 23

Regarding airways and breathing: gas exchange takes place in the bronchi.

Answer 23

False. The bronchi have walls that are too thick to allow gas exchange to occur. Gas exchange can only take place in the alveoli and the most terminal (distal) parts of the bronchioles.

Question 24

The saturation of haemoglobin decreases as blood passes through the tissues because of an increase in pH.

Answer 24

False. Haemoglobin saturation decreases as blood passes through the tissue because the tissues have a lower partial pressure of oxygen (40mmHg) than is found in the plasma (100mmHg). As such oxygen moves down its partial pressure gradient into the tissues until equilibrium is reached. Alkalosis (a rise in extracellular fluid pH) actually causes haemoglobin to hang onto its oxygen more – it increases the affinity of haemoglobin for oxygen so would increase saturation.

Question 25

Regarding airways and breathing: Forced vital capacity is the maximum amount of gas that can be breathed out of the lungs from full inspiration in one second.

Answer 25

False. FEV1 is the Forced Expired Volume in one second. FVC is the total amount of air that can be forced out of the lungs after a maximum inspiration over any time period. FVC should be the same in volume as Vital Capacity but VC is not necessarily forced, nor the time to exhale measured.

Question 26

A shift of the oxygen dissociation curve of haemoglobin to the right decreases the oxygen content of blood at a given oxygen pressure.

Answer 26

True. A rightward shift means that for any given value of PO2, less oxygen will be bound to haemoglobin than if that shift had not happened – look at the S shaped curve if you don’t believe it!

Question 27

Respiratory acidosis often accompanies severe lung pathology.

Answer 27

True. Most lung pathologies lead to an impairment of gas exchange for one reason or another. This impairment increases CO2 levels in arterial blood. An increase in CO2 leads to an increase in H+ concentration (revise the chemical equation shown in the lectures if you don’t understand why this happens). As the increase in H+ are due to respiratory dysfunction this is called a respiratory acidosis.

Question 28

Tidal volume is the volume of gas that enters or leaves the lung with each cycle of respiration at rest.

Answer 28

True. It is the volume inspired in a relaxed breath at rest, and the same volume is exhaled at rest

Question 29

An increase in 2,3-diphosphoglycerate (DPG) in the red cells will shift the haemoglobin-O2 saturation curve to the right.

Answer 29

True. 2, 3- diphosphoglycerate is produced by red blood cells under stress as may occur during hypoxic conditions (this could be due to e.g. poor ventilation or heart disease). In this case the rise in 2,3-DPG allows more oxygen to be released from the haemoglobin in the periphery by reducing the affinity of haemoglobin for oxygen, and in doing so shifts the curve to the right.

Question 30

Hyperventilation will shift the oxygen dissociation curve of haemoglobin to the right.

Answer 30

False. Hyperventilation will blow off more CO2, thus reducing PCO2. The reduction in PCO2 shifts the oxyhaemoglobin curve to the left. At the same time the loss of CO2 drives the equation describing the relationship between CO2 and hydrogen ions to the left, reducing free H+ concentration and thus increasing pH. An increase in pH, like a decrease in PCO2, also pushes the oxyhaemoglobin binding curve to the left.

Question 31

Patients with chronic lung disease can become wholly reliant on peripheral chemoreceptor activity to maintain their rhythm of ventilation.

Answer 31

True. Some patients with chronic lung disease have had long term exposure to elevated arterial PCO2, due to impaired gas exchange. Overtime the central chemoreceptors, which detect changes in PCO2 and on which healthy individuals rely to set the rhythm of ventilation, become desensitised to CO2. In these circumstances the peripheral chemoreceptors take over setting the rhythm of ventilation. As these chemoreceptors respond to falling oxygen levels, sometimes these individuals are described as being on hypoxic drive. This is clinically important, because giving these people too much supplementary oxygen can therefore dampen their respiratory drive.

Question 32

CO2 in the blood is mainly carried in the form of carbamino compounds.

Answer 32

False. CO2 is mostly (70%) transported in the form of bicarbonate ions. Only 23% is transported in the form of carbamino compounds

Question 33

Alveolar ventilation is defined as the total volume of gas breathed per minute.

Answer 33

False. Alveolar ventilation describes only the volume of gas that reaches the alveoli (and hence is available for gas exchange) per minute. Not all the air we breathe in reaches the alveoli as some gets trapped in dead space and cannot participate in gas exchange.

Question 34

Regarding airways and breathing: Gas exchange at rest is normally complete within a third of the time for which the blood is in the capillaries.

Answer 34

True. Gas exchange is normally complete with 0.25s while contact time of blood with alveoli is 0.75s at rest.

Question 35

Regarding airways and breathing: Vital capacity is the same as Inspiratory Reserve Volume + Functional Residual Capacity.

Answer 35

False: Vital Capacity describes the largest volume of air that can be voluntarily exhaled after a maximum inhalation. Vital Capacity can be described in different ways:

Inspiratory capacity + Expiratory Reserve Volume
Inspiratory Reserve Volume + Tidal Volume + Expiratory Reserve Volume
Functional Residual Capacity includes Residual Volume which cannot be voluntarily exhaled so is not part of Vital Capacity.

Remember, the term “Capacity” describe where two or more “volumes” are added together.

Question 36

The haemoglobin-O2 saturation curve is moved to the left by a rise in pH.

Answer 36

True. Alkalosis increases the affinity of haemoglobin for oxygen and thus shifts the binding curve to the left

Question 37

Regarding airways and breathing: If there are ventilation/perfusion disturbances, the impact is greater on CO2 loss than O2 uptake.

Answer 37

False. CO2 is more water soluble than O2 so can diffuse more readily. For this reason ventilation/perfusion disturbances often affect CO2 levels less than O2.

Question 38

Only 25% of the oxygen carried by haemoglobin is used by the tissues of the body at rest.

Answer 38

True. Red blood cells in systemic arterial blood are almost 100% saturated with oxygen. Red blood cells in systemic venous blood are 75% saturated with oxygen at rest, so only 25% has been extracted by the peripheral tissues.

Question 39

Forced Vital Capacity (FVC) divided by the Forced Expired Volume in one second (FEV1) is a useful clinical measure of lung function.

Answer 39

False. That statement is the wrong way round. A useful clinical measure of lung function is FEV1 divided by FVC (not the other way around). This tells you what proportion of the FVC a patient can exhale in one second.

Question 40

The pulmonary circulation is described as being a low-flow high-pressure system.

Answer 40

False. The pulmonary circulation is described as a high flow, low pressure system. High flow because the entire volume of blood that travels through the rest of the body (systemic circulation) in one minute travels through the lungs (pulmonary circulation) in one minute too. Low pressure because systolic pressure in the pulmonary circulation is around 25mmHg while it is 120mmHg in the systemic circulation.