Murdoch - Respiratory Flashcards
A patient with severe diabetic ketoacidosis is found to be hyperventilating. What stimulus for this increased respiration will be directly driving the central chemoreceptors, and where are these central chemoreceptors located?
= d. Increased H+ concentration in CSF, directly detected by central chemoreceptors located in the medulla oblongata
The patient has a severe metabolic acidosis. Central chemoreceptors are located in the medulla oblongata, and respond to changes in H+ concentration within the CSF. They would respond indirectly to increased carbon dioxide partial pressures, via the resulting increase in H+ concentration in the CSF, but in a hyperventilating patient, carbon dioxide partial pressure is likely to be low. Although H+ ions do not easily cross the blood brain barrier, enough do cross in severe acidosis to stimulate the very sensitive chemoreceptors to cause an early response in this severe metabolic acidosis. A hyperventilating patient is likely to have a low carbon dioxide, so this will not be the source of the respiratory drive. Central chemoreceptors do not respond to low oxygen partial pressures.
A patient has a genetically determined selective deficiency of Immunoglobin A (IgA). Although many of those affected appear symptomatic, what is the major reason for an increased susceptibility to respiratory infections in some of these patients?
A patient is found to have a lung disease characterised histologically by Type II pneumocyte hyperplasia, hyaline membranes, and an increased number of mononuclear cells within the alveolar septa. Chest x-ray reveals a distribution bilaterally in the lower lung fields. What is the best classification of this disease?
= e. Interstitial pneumonia
Hyaline membranes (fibrin lining the alveoli), type II cell hyperplasia, and an interstitial inflammatory infiltrate are features typical of interstitial/atypical pneumonia. A lobar pneumonia has abundant alveolar exudate, with consolidation spreading across lung segments. It is often unilateral. A bronchopneumonia typically has patchy areas of consolidation, often affecting multiple lobes, with suppurative inflammation in bronchi, bronchioles and closely related alveoli.
Some lung diseases can be restricted to various compartments within the lower respiratory tract. The images below show a fresh lung in both inflated (right) and uninflated (left) conditions. What is the anatomical name given to the inflated region in this example?
- a. One terminal bronchiole
- b. One whole lung
- c. One pulmonary lobe
- d. One bronchopulmonary segment
- e. One pulmonary acinus
= d. One bronchopulmonary segment
The pictures confirm that the inflated region is only a portion of a larger structure (lobe). This rules out a whole lung and a whole lobe. An acinus is the region distal to a terminal bronchiole (too small for the region in this image). The well-demarcated, sub-lobar portion is a bronchopulmonary segment. These are supplied by tertiary bronchi, of which there are 8-10 for each lung. Secondary bronchi supply lobes (3 for right side, two for left), and the two primary bronchi each supply an entire lung. Several lung diseases can be restricted to bronchopulmonary segments, and these segments are able to be isolated surgically, enabling sublobar resection.
Examine the photomicrograph below. What is the name given to this disease and what effect, if any, is it likely to have on airway resistance?
- a. Bulla - increased airway resistance on inspiration
- b. Bleb - no effect, but may progress to pneumothorax
- c. Centrilobular emphysema - increased airway resistance on expiration
- d. Interstitial fibrosis - no change in airway resistance
- e. Pneumothorax - symptoms will depend on size of lesion
= c. Centrilobular emphysema - increased airway resistance on expiration
The increased size of air spaces seen here results from breakdown of alveolar walls. This is typical of emphysema. You can see that it is close to the terminal bronchiole, making it a centrilobular emphysema. The elastic alveolar walls normally attach to small airways and provide radial traction to assist in keeping airways open, especially during the raised intrathoracic pressure of expiration. This is why emphysema causes obstructive respiratory disease, with problems during expiration. Trapped air resulting from collapsed airways during expiration will also reduce the volume of air expired, and so may reduce expiratory volume. The destruction of gas exchange area, along with associated alveolar capillaries, reduces both perfusion and gas exchange area.
Examine the flow-volume loop below obtained by spirometry, and indicate whether the patient has obstructive or restrictive disease and which phase of breathing is affected. The dotted line is a reference trace from predicted normal values. The solid thick line is the trace obtained from the patient.
- a. Restrictive disease on expiration
- b. Obstructive disease on expiration
- c. Restrictive disease on inspiration
- d. Obstructive disease on inspiration
- e. Restrictive and obstructive disease, during both inspiration and expiration
= b. Obstructive disease on expiration
Flow rate is on the vertical axis, with expiration above and inspiration below the y axis. Volume is on the y-axis. Obstruction reduces flow rates. A reduced flow rate above the y-axis is a reduced expiratory flow rate. The expiratory curve typically bows inwards towards the y-axis in expiratory obstruction. A restrictive lung disease would reduce volume, and so the value on the y-axis would be reduced (not seen in this instance, which indicates there is no volume restriction).
Define the terms Ghon Focus, Ghon Complex and Ranke Complex.
Ghon focus – a primary peripheral lesion in the lung parenchyma, (often subpleural, or around interlobar fissures) formed from localised coalescing TB granulomas. Often asymptomatic /dormant.
Ghon complex – the combination of the Ghon focus and an affected hilar lymph node.
Ranke complex – The characteristic radiographic appearance arising from dystrophic calcification of the Ghon focus and the associated ipsilateral hilar lymph node.
Explain how emphysema affects airway resistance, including the mechanism by which airway resistance is affected.
The alveoli form an elastic network attached to the conducting airways, and the resulting radial traction maintains airway diameter, especially during expiration. Emphysema involves the destruction of these alveolar walls, resulting in reduced radial forces on the airways. The airways will be more prone to collapse during expiration (high intrathoracic pressure tending to collapse airways), rather than during inspiration (when low intrathoracic pressure will tend to keep airways open), causing increased resistance on expiration (and air trapping from airway collapse).
What is meant by a ventilation-perfusion mismatch? Support your explanation with an example which would cause lowered partial pressure of oxygen in blood leaving the lung.
Gas exchange requires the pulmonary parenchyma to be both ventilated (enabling oxygen partial pressures to be high enough within alveoli, and to prevent carbon dioxide building up within alveoli) as well as perfused by blood, so that the blood gases may equilibrate with the ventilated alveolus. A mismatch occurs when either ventilation is reduced, such as by an obstruction to the airway, or when a ventilated area of parenchyma is not well perfused (e.g. by reduced blood supply). An example would be if an airway obstruction such as chronic bronchitis caused poor ventilation of the associated parenchyma, in the face of adequate vascular perfusion. The blood leaving this area would be poorly oxygenated.
What is Chronic Bronchitis?
What is COPD?
5 Causes of Hypoxemia?
