Week 1 Formative Quiz Questions Flashcards
Nitrous oxide is a safe sedative to use on most individuals as it blunts only the peripheral chemoreceptor activity.
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.
A pneumothorax (air in the pleural cavity) disrupts the relationship between the visceral pleural membrane and the lungs
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.
The functional unit of the lung is the pulmonary alveolus.
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.
The functional residual capacity can be directly measured with a spirometer.
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.
Under normal circumstances, there is poor correlation between the best-ventilated and best-perfused parts of the lung.
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
Alveolar ventilation volume is more than pulmonary ventilation volume.
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!
At the onset of inspiration, action potential frequency in the phrenic motoneurones decreases.
False. The phrenic nerve innervates the diaphragm, the main muscle of inspiration, so activity would increase during inspiration.
The phrenic nerve takes its origin from the T3, T4 and T5 spinal nerves.
False. The phrenic nerve takes it origins from the C4, C4 and C5 spinal nerves
The term shunt describes the passage of blood through the lungs where the opportunity for gas exchange does not occur.
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
Increases in carbon dioxide in the blood enhance the oxygen binding power of haemoglobin.
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.
The peripheral chemoreceptors in the carotid bodies and the aortic bodies are entirely responsible for stimulation of ventilation by hypoxia.
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).
Central chemoreceptors respond to changes in H+ concentration.
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
Regarding airways and breathing: Expiration at rest is essentially a passive process.
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.
A pneumothorax (air in the pleural cavity) resulting from a penetrating injury to the thoracic wall will cause intrapleural pressure to becomes less negative.
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.
The right lung is divided by a fissure into the upper and lower lobes.
False. The right lung is divided by two fissures (horizontal and oblique) into three lobes (superior, middle and inferior).
The peripheral chemoreceptors will stimulate increased ventilation in anaemia
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.
The haemoglobin-O2 saturation curve will be shifted downward in an anaemia with normal lung function.
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.
Peripheral chemoreceptors mediate the hypocapnia (low PCO2) that occurs at high altitude.
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.
An increase in body temperature favours the off-loading of oxygen from haemoglobin.
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).
The haemoglobin-O2 saturation curve is moved to the left by a decrease in body temperature..
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.
Lung compliance is defined as the magnitude of the change in lung volume produced by a given change in transpulmonary pressure.
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).
Carbon dioxide is carried on the haemoglobin molecule as carboxyhaemoglobin.
False. The term “carboxyhaemoglobin” describes carbon monoxide binding to haemoglobin – your carboxyhaemoglobin levels should be neglible!
Regarding airways and breathing: gas exchange takes place in the bronchi.
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.
The saturation of haemoglobin decreases as blood passes through the tissues because of an increase in pH.
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.