Respiratory physiology

Question 1

9938 – Sudden elevation of the arterial pCO2 level is associated with
1: raised intracranial pressure
2: respiratory acidosis
3: skin vasodilatation
4: an increased plasma bicarbonate level

Answer 1

TTTT
Ganong, 19th ed, Ch 32, 37 and 39.

Question 2

14616 – Alveolar ventilation
1: is the volume of fresh gas entering alveoli per minute
2: is about 350 ml per breath
3: determines the alveolar PCO2 by means of an inverse relationship
4: is measured with a spirometer

Answer 2

TTTF
Refer to West, Chapter 2, p14

Question 3

12494 – The following acid-base data pH 7.21 PaCO2 20 mmHg HCO3 8 mmol/1 BE -19mmol/1 would be most consistent with
A. lobar atelectasis of the lung
B. starvation
C. septicaemic shock
D. anxiety
E. duodenal ulcer with pyloric obstruction

Answer 3

C
The data pattern suggests a partially compensated metabolic acidosis because the hypocapnia is accompanied by a low pH and low bicarbonate together with a large negative base excess. This is not due to atelectasis of the lung, because the low PaCO2 would not be accompanied by the extreme hypoxaemia needed to produce such a severe metabolic acidosis (A false), nor is it due to anxiety as the pH would be raised in the presence of the hypocapnia (D false). It is not pyloric obstruction (with vomiting) where one would expect acid loss resulting in metabolic alkalosis (E false). Both starvation and septic shock would result in metabolic acidosis, but the former would be mild and compensated with a higher pH and plasma bicarbonate (B false). Therefore this severe acid-base disturbance would be most consistent with the anaerobic metabolism of septic shock (C true).

Question 4

23199 – Respiratory acidosis is associated with
1: elevated arterial PCO2
2: decreased plasma bicarbonate level
3: inadequate ventilation
4: increased arterio-venous oxygen difference

Answer 4

TFTF

Question 5

10119 – The total amount of carbon dioxide in arterial blood exists as follows
1: 60% as bicarbonate in plasma
2: 5% as dissolved carbon dioxide
3: 30% as carbamino haemoglobin
4: 5% as carbonic acid

Answer 5

FTFF
West, 6th ed, Ch 6, Ganong, 19th ed, Ch 35

Question 6

9862 – S: During exercise there is an increase in alveolar pCO2 because R: during exercise venous blood pCO2 increases

Answer 6

S is false and R is true
Ganong, 19th ed, Ch 37

Question 7

24354 – With regard to acid-base status, if the arterial blood pH, pCO2 and bicarbonate are all above their respective reference ranges
1: a primary respiratory alkalosis exists
2: the pattern is consistent with pyloric obstruction
3: a primary respiratory acidosis exists
4: the pattern is consistent with primary hyperaldosteronism

Answer 7

FTFT
Guyton 9th ed. p400 Ganong, 19th Ed, Ch 39 p697-704
ph high - alkalosis
pco2 high - resp compensation
bicab high - metabolic alkalosis
4: retention of Na + loss of H

Question 8

10134 – Peripheral chemoreceptors regulating respiration
1: are located in the carotid bodies
2: represent the only chemoreceptors in man able to produce a hypoxic ventilatory response
3: are not stimulated by anaemia
4: do not produce a significant ventilatory response until the PaO2 is reduced to 50 - 60 mmHg

Answer 8

TTTT
Ganong, 19th ed, Ch 36

Question 9

12602 – S: The measured respiratory quotient (RQ) may rise during severe exercise because R: hyperventilation will result from lactic acidosis

Answer 9

S is true, R is true and a valid explanation of S
The respiratory quotient (RQ) is the ratio of CO2 production to O2 consumption and can be
measured for a tissue, an organ or the body. This question relates to the body RQ. During severe exercise, because of hyperventilation from lactic acidosis and a relative O2 debt, RQ may rise to 2.0. Therefore S and R are true and R is a valid explanation of S.

Question 10

9898 – S: The uptake of CO2 by blood in the tissue capillaries assists the release of oxygen from haemoglobin because R: with the Bohr effect a rise in blood pCO2 shifts the haemoglobin oxygen dissociation curve to the left

Answer 10

S is true and R is false
Ganong, 19th ed, Ch 34
Shifting of the curve to the right

Question 11

10043 – With respect to carbon dioxide uptake by blood in tissue capillaries
1: H+ generated is buffered by deoxyhaemoglobin
2: about 60% of CO2 is carried in carbamino combination with haemoglobin
3: there is a chloride and water shift into red blood cells
4: plasma carbonic anhydrase is required

Answer 11

TFTF
Ganong, 19th ed, Ch 35

Question 12

10033 – Factors determining the alveolar pO2 include the
1: inspired oxygen concentration
2: alveolar ventilation
3: oxygen consumption of the body
4: haemoglobin level in the blood

Answer 12

TTTF
Ganong, 19th ed, Ch 34

Question 13

14601 – Which of the following contribute(s) significantly to the oxygen tension difference between alveolar gas and systemic arterial blood (A-a PO2 diff.) in healthy subjects?
1: rate of diffusion of oxygen across the alveolar-capillary membrane
2: anatomical R to L shunts
3: reaction rate of oxygen combining with haemoglobin
4: low ventilation/perfusion ratio regions of lung

Answer 13

FTFT
Refer to West, 2nd Ed, Ch 5, page 61-68

Question 14

10114 – Arterial hypoxia causes
1: an increased respiratory rate
2: dilatation of coronary arterioles
3: respiratory alkalosis
4: dilatation of renal arterioles

Answer 14

TTTF
Ganong, 19th ed, Ch 36

Question 15

10023 – Accumulation of water in pulmonary alveoli is chiefly prevented by
1: elimination of excess water in the expired air
2: surfactant, which maintains a low surface tension in alveoli
3: capillary permeability to water being negligible in alveolar capillaries
4: a low hydrostatic pressure in alveolar capillaries

Answer 15

FTFT
Ganong, 19th ed, Ch 34

Question 16

9904 – S: The functional residual capacity of the lung cannot be measured by spirometry because R: the functional residual capacity of the lung includes the residual volume which cannot be expelled by respiratory effort

Answer 16

S is true, R is true and a valid explanation of S
Ganong, 19th ed, Ch 33

Question 17

10028 – The functional residual capacity of the lung is decreased
1: in the supine position
2: with chronic obstructive airways disease
3: with term pregnancy
4: with positive end-expiratory pressure

Answer 17

TFTF
Ganong, 19th ed, Ch 34

Question 18

9868 – S: The arterial Po2 is reduced in carbon monoxide poisoning because R: in carbon monoxide poisoning carboxy-haemoglobin (COHb) shifts the haemo-globin-oxygen dissociation curve of the remaining haemoglobin to the left

Answer 18

S is false and R is true
Ganong, 19th ed, Ch 37

Question 19

10124 – The closing volume of the lung
1: is the lung volume when small airway closure begins to occur
2: is usually between the residual volume and functional residual capacity
3: increases with age
4: is increased by small airways disease

Answer 19

TTTT
Ganong, 19th ed, Ch 34

Question 20

14611 – A restrictive defect in ventilatory function occurs with
1: fractured ribs
2: upper abdominal surgery
3: lobar pneumonia
4: old T6 spinal cord injury

Answer 20

TTTT
Refer to West, Ch 10

Question 21

15027 – With regard to respiratory dead space
1: physiological dead space is equal to the sum of anatomical and alveolar dead space
2: alveolar dead space is negligible in health
3: physiological dead space may be estimated by use of the Bohr equation
4: physiological dead space to tidal volume ratio (VD/VT) is normally about 0.3

Answer 21

TTTT
Refer to West, 2nd Ed, Ch 2, page 18-20; Ch 10, page 148-152; Ganong, Ch 34, page 627-628

Question 22

14596 – Oxygen uptake by haemoglobin in lung capillaries
1: varies directly with the blood pH
2: varies inversely with PaCO2
3: is characterised in the fetus by a shift of the dissociation curve to the left compared with that after birth
4: varies inversely with the concentration of 2,3 diphosphoglycerate (2,3-DPG) in the red cell

Answer 22

TTTT
Refer to Ganong 19th Ed, Ch 35, page 636-637.

Question 23

12608 – S: Metabolic acidosis has a greater respiratory stimulating effect than would be suggested by the measured change in blood pH
because R: during metabolic acidosis pCO2 also increases and stimulates respiration

Answer 23

The stimulatory effect on the respiratory centre that results from acidosis is mediated via the CSF. CO2 is more soluble in CSF than H+ and in the CSF is rapidly converted to H2CO3. Therefore, larger rises in blood pH are required to increase the CSF H+ sufficiently to stimulate the respiratory centre (S false). As a consequence of respiratory centre stimulation with resultant hyperventilation, pCO2 levels fall in metabolic acidosis (R false).

Question 24

15037 – Breathing 60% oxygen by face mask would be expected to correct arterial hypoxaemia due to
1: an increase in physiological dead space
2: hypoventilation
3: a small physiological shunt (venous admixture less than 10%)
4: a large physiological shunt (venous admixture more than 10%)

Answer 24

TTTF
Refer to Ganong, 19th Ed, Ch 37, page 562-655

Question 25

14606 – An increase in ventilation results from an increase in the rate of firing of the arterial chemoreceptors in response to
1: an increase in arterial PCO2
2: a reduction in arterial PO2 to 70 mm Hg (9.3 kPa)
3: a reduction in arterial pH
4: chronic anaemia (less than 9.0 gm haemoglobin/dl blood)

Answer 25

TFTF
Refer to Ganong, 19th Ed, Ch 36, page 642 and following
2: no response if PaO2 >50 - 60 mmHg

Question 26

15042 – A healthy young individual hyperventilates leading to a doubling of alveolar ventilation. Immediate effects before the onset of any renal compensatory changes would include
1: a PaCO2 of about 20 mmHg (2.7 kPa)
2: a decrease in plasma bicarbonate level
3: a decrease in intracranial pressure
4: a PaO2 of about 120 mmHg (16 kPa)

Answer 26

TTTT
Refer to Ganong, 19th Ed, Ch 37, page 661; Ch 39, page 700

Question 27

15423 – During the carriage of CO2 from the tissues to the lungs
1: there is an increase in the chloride content of the red blood cells
2: venous plasma bicarbonate increases by 6 mmol/l
3: carbamino compounds are formed both in the plasma and the red blood cell
4: venous blood pH decreases to less than 7.30

Answer 27

TFTF
Refer to Ganong, 19th Ed, Ch 36, page 640 and following

Question 28

15428 – Factors involved in ventilatory control during aerobic exercise include
1: a rise in arterial PCO2
2: afferent feedback from limb movement
3: lactic acidosis
4: an increase in body temperature

Answer 28

FTFT
Refer to West, Ch 8, page 126-127

Question 29

9943 – Pulmonary vascular resistance is
1: increased with a rise in pulmonary arterial pressure
2: approximately 10% of the systemic vascular resistance
3: decreased with an increase in lung volume
4: locally controlled by the oxygen tension in adjacent alveoli

Answer 29

FTFT
West, Ch 4

Question 30

10038 – In the upright lung
1: intrapleural pressure is more negative at the apex than at the base
2: the ventilation/perfusion ratio is greater at the base than at the apex
3: alveolar pO2 is higher at the apex than at the base
4: the apex is more compliant than the base

Answer 30

TFTF
Ganong, 19th ed, Ch 34

Question 31

15032 – Emphysema would be associated with
1: a reduced FEV1/VC ratio
2: an impaired expiratory flow-volume curve
3: a reduced peak expiratory flow rate
4: a reduced functional residual capacity

Answer 31

TTTF
Refer to West, Ch 10; Ganong, 19th Ed, Ch 37, page 658

Question 32

9948 – With normal quiet breathing
1: respiratory work is done mainly to overcome airways resistance
2: expiratory work is accomplished by energy stored in stretched elastic structures
3: elastic work is done only to stretch the elastic fibres in the lung
4: the work of breathing represents less than 5% of the total resting oxygen consumption

Answer 32

FTFT
West, 7th Ed, Chapter 7. Ganong 20th Ed, Chapter 34, p635.
Elastic work is performed by the resp muscles in stretching the elastic tissues of the chest wall and lungs.

Question 33

15418 – With respect to forced expiratory flow volume curves
1: expiratory flow declines with decreasing lung volume
2: maximum expiratory flow rate is independent of effort at mid to low lung volumes
3: features of the curve are due to dynamic airway collapse
4: effective driving pressure for expiration is alveolar minus intrapleural pressure

Answer 33

TTTT
Refer to West, Ch 7, page 107-110

Question 34

15413 – Forces which are acting on the lung at the end of normal expiration include
1: elastic tendency of the thoracic cage to sustain expansion
2: surface tension effects at the alveolus tending to produce collapse
3: elastic tendency of the lung to collapse
4: a negative intrapleural pressure

Answer 34

TTTT

Question 35

7126 – Which of the following would NOT be expected in a 70kg adult
human male at rest?
A. inspiratory reserve volume 3500 ml
B. expiratory reserve volume 1000 ml
C. tidal volume 2000 ml
D. residual volume 1200 ml
E. physiological dead space 150 ml

Answer 35

C
The tidal volume is the amount of air moving into the lungs with each normal inspiration (or out of the lungs with each normal expiration). A normal value of the tidal volume would be 500 ml, not 2000 ml.
The response is false and would not be the expected volume in a 70 kg man; C is thus the correct answer.

Question 36

25855 – The pulse oximeter
1: is unaffected by the level of carboxyhaemoglobin
2: is a useful indicator of PaO2
3: may be inaccurate in hypovolaemia
4: may be used to measure pulse rate
5: measures oxygen saturation, which is independent of arterial pH or hypercapnia

Answer 36

FFTTT

Question 37

25794 – Patients for whom mask oxygen therapy is inadequate
1: are often tachypnoeic
2: show distress, dyspnoea, exhaustion, sweating and confusion
3: may not show low oxygen saturation or low pulse oximetry until at a late stage
4: include those with vital capacity less than 15 ml/kg
5: include those with FEV1 less than 10 mI/kg

Answer 37

TTTTT

Question 38

25782 – An acute fall in lung functional residual capacity (FRC)
1: occurs during post-operative atelectasis
2: is caused by chronic bronchitis with sputum retention
3: occurs following pulmonary embolism
4: results in respiratory failure when PaO2 = 8.3 kPa and PaCO2 = 6.2 kPa
5: should be treated initially by high flow mask oxygen

Answer 38

TTFFT

Question 39

25805 – Arterial blood gases and acid base status
1: give some assessment of respiratory, renal and cardiovascular function
2: assessment by once daily arterial puncture causes greater morbidity than an indwelling arterial line
3: readings consistent with metabolic acidosis could be characterised by pH = 7.15 and HCO3 = 18 mmol/L and negative base excess of 10
4: showing a PaO2 of 120 mmHg (16.0 kPa) indicates good oxygenating ability in a patient breathing 80% oxygen

Answer 39

TFTF

Question 40

18331 – The so-called ‘acute brain syndrome’ as seen in surgical patients after operation is
A. a common component of grieving
B. usually a manifestation of a patient’s inability to cope
C. most importantly due to deprivation of rapid eye movement (REM) sleep
D. commonly a result of the unmasking of a pre-existing depressive illness
E. commonly associated with hypoxia

Answer 40

E
‘Acute brain syndrome’ is a synonym for acute delirium with a confusional state. In the post-operative period this is commonly associated with hypoxia (E); and blood gas measurements are often required to confirm this diagnosis. The other respones are false.

Question 41

25788 – Patients can be weaned from the ventilator
1: when an FIO2 of 40% maintains normal PaO2
2: once the original cause of respiratory failure has been treated successfully
3: more easily while still heavily sedated
4: with a modern ventilator irrespective of nutritional status
5: when CO2 elimination is no longer a problem

Answer 41

TTFFT

Question 42

25740 – Pulse oximetry
A. utilises both plethysmography and light spectroscopy in producing its output
B. is useful in determining the presence of acidosis
C. is fooled by carboxyhaemoglobin into giving an erroneous low reading
D. when giving a reading of SaO2 of 90% equates to a PaO2 of 50mmHg (6.5kPa)
E. is not affected by ambient light

Answer 42

A

Question 43

18322 – In a patient receiving post-operative assisted ventilation with positive end-expiratory pressure (PEEP), the sudden occurrence of hypotension is most likely caused by
A. hypovolaemia
B. acute congestive cardiac failure
C. haemothorax
D. massive atelectasis
E. tension pneumothorax

Answer 43

E
Assisted ventilation with positive end-expiratory pressure (PEEP) is liable to precipitate tension pneumothorax because of the persistently positive intra-pulmonary pressures generated; such a complication would be the first to exclude or verify in the clinical circumstances listed (E).

Question 44

25800 – Concerning routine respiratory management in surgical wards
1: management is better guided by regular radiography than by auscultation
2: chest physiotherapy and nebulized saline therapy should be employed in a highly selective manner
3: management depends on adequate analgesia
4: pulse oximetry assesses all key aspects of ventilatory function

Answer 44

FFTF