Ventilation and circulation

Question 1

A 23 year old male patient is scheduled for a pulmonary exam. His mass is 70 kg and has a tidal volume of 500 ml. What approximate amount of the tidal volume contributes to gas exchange?

Answer 1

350 cc

Question 2

A 19 year old patient presents with a midaxillary chest wound to the left side. Their blood pressure is 140/100 while their SaO2 is <90. You suspect a collapsed lung. What change in lung pressure occurs as a consequence of the breaking the airtight seal of the pleural cavity?

Answer 2

The intrapleural pressure (Pip) is zero

The correct answer is C, Pip = zero. A chest would will cause air to enter the intrapleural space and normalize the pressure with the atmosphere which we regard as zero. This will cause the Ptp and Palv to go to zero. The chestwall force expanding the lungs will be lost and the lungs will collapse. Without the negative pressure of Pip the chest wall will pull away from the lungs and the force it exerts on the lungs will decrease below normal.

Question 3

Ventilation effort (work) ______ when alveolar surface tension increases

Answer 3

Ventilation effort increases - additional muscle action will be required

Question 4

The compliance of the respiratory system changes with lung volume. Close to which lung volume has the respiratory system it’s greatest compliance?

Answer 4

FRC

Question 5

For a person at rest, what supplies the force for expiration?

Answer 5

The elastic recoil of the lung

The elastic recoil of the lungs drives passive expiration. The internal intercostals and abdominal muscles are involved in active expiration. The external intercostals are concerned with inhalation. The patient likely has COPD for which exhalation through pursed lips and a slow RR are adaptations to the increased compliance of the lungs which causes small airway collapse at higher RR.

Question 6

Which lung volume cannot be measured directly by spirometry?

Answer 6

Residual volume

Residual volume cannot be directly measured by spirometry but the others can. You would want to know what the residual volume is so as to determine functional residual capacity. FRC will increase with COPD as residual volume increases (i.e. the FEV1/FVC will decrease). With asthma RV will not change and return to normal with proper treatment.

Question 7

You have a 12 year old patient who is having an acute asthma attack. Why is the child struggling to ventilate their lungs?

Answer 7

An increase in airway resistance

Question 8

A patient explains that breathing slow and deep is easier for them than taking normal breaths and respiration rate. Why does this reduce the work of breathing?

Answer 8

Deep breathing utilizes the ability of radial traction to expand the airways to overcome airway resistance

Question 9

A 62 year old man with a history of hypertension presents to the emergency department following a laboratory accident where a nitrogen gas cylinder leaked nitrogen gas into a confined space, diluting the oxygen content of the air below 70 mmHg. The man was found unconscious. He is receiving supplemental oxygen and inspiratory crackles are heard in his chest. Regarding the pulmonary circulation which statement is true?

a) Blood flow is highest at lung apex in an upright Pt
b) Hypoxia causes pulmonary vasoconstriction, elevating the pulmonary BP
c) Pulmonary pressures are much lower than systemic, and pulmonary vascular resistance is higher
d) Right ventricular output is normally greater than left ventricular output

Answer 9

b) Hypoxia causes pulmonary vasoconstriction, elevating the pulmonary BP

Hypoxia causes vasoconstriction. Pulmonary resistance is much lower than systemic resistance. Right and left ventricular output have to match. Blood supply is greater at the base than the apex of the lung. The nitrogen gas lead reduced the partial pressure of O2 in the lab causing hypoxic vasoconstriction. Because of an existing compromise in the vascular system (hypertension) the patient also developed pulmonary edema.

Question 10

Answer 10

D) Decreases pulmonary vascular resistance, improving oxygenation

Question 11

Answer 11

C. Decreased (more positive) transpulmonary pressure, decreased chest wall compliance

Question 12

Answer 12

A

Question 13

Answer 13

B

Extrathoracic obstruction causes a diminished expiratory curve on the P-V loop

Question 14

Answer 14

C. Enhanced ventilation-perfusion (V/Q) matching by shifting perfusion to ventilated dorsal lung zones

Question 15

Mr Haldane, age 68, is admitted to the hospital with dyspnea. He has a history of COPD. ABG results indicate PaO2 = 58 mmHg, PaCO2 = 60 mmHg and pH 7.4. A nurse has just begun to administer supplemental oxygen (FiO2 = 0.4). If a new ABG test was quickly performed after starting supplemental O2, how do you expect the PaCO2 level to have changed?

Answer 15

PaCO₂ will be increased

In the Haldane effect O2 will force CO2 off hemoglobin. This will cause and increase in PaCO2 until the CO2 can be expelled from the lungs. This would take several ventilation cycles as each tidal volume represents approximately 13% of the end-inspiration lung volume (0.7TV + ERV + RV)

Question 16

An emphysema patient with no history of elevated BMI explains to you that since they adopted the carnivore/paleo diet and eat nothing but meat they feel less out of breath. Why might this be the case?

Answer 16

A high fat diet has a decrease Respiratory Quotient, R, and will generate less CO2 and increase PAo2.

The value of R decrease with the proportion of fat consumed. This will reduce PvCO2 which will reduce PACO2. According to the Alveolar Gas Equation a decrease in PACO2 will increase the PAO2 which will increase the PaO2 and cause the patient to feel less dyspneic. O2 demand is linked to body mass, not diet composition. Sudden weight loss will decrease O2 demand but will not change lung volumes unless the patient was morbidly obese.