Respiratory Case Study # 2



Respiratory Case Study # 1 revised 16 November 2014

A 50-year-old man comes to the pulmonary laboratory for evaluation of chronic dyspnea. He has smoked one pack of cigarettes a day for 30 years. He complains of a morning cough that produces lots of mucus (phlegm) and frequent respiratory infections. His arterial blood is analyzed for pH, partial pressure of oxygen (PaO2), partial pressure of carbon dioxide (PaCO2), percentage saturation of hemoglobin with oxygen (Sa O2) and hemoglobin content. The results are shown below. The patient is at sea level and breathing ambient air (21% oxygen).

Your instructor will tell you where you would obtain a sample of arterial blood for blood gas analysis.

Complete the table by adding the values considered normal for each parameter and indicating whether the actual value (level) is normal, high, or low. Consult the Physiological Reference Values handout. Information will be discussed in blocks separated by horizontal lines.

|Parameter | Patient’s value |Normal value |Hi, Lo, Normal |

|pH |7.47 |7.35 – 7.45 | |

|PaCO2 |30 mm Hg | | |

|PaO2 |60 mm Hg |What’s the best number to memorize? | |

|Sa O2 |90% | | |

|Hemoglobin |18.5 g/dl blood |14-18 g/dl blood | |

|Respiratory rate |25 breaths/min | | |

|Tidal volume |400 ml | | |

Conventions: “P” signifies “partial pressure”

“A” signifies “Alveolar”

“a” signifies “arterial” and unless otherwise indicated is systemic arterial.

“S” is “saturation”

Why would a sample of venous blood not be useful to evaluate pulmonary function?

How is is pH related to his PaCO2?

Is this patient’s hemoglobin saturation expected given his PaO2? (Consult the oxyhemoglobin dissociation curve on p. 468 of text)

In what two ways is oxygen transported in the blood?

For each mm Hg PaO2, 0.003 ml of O2 will dissolve in one dl of blood.

Given that our patient has a PaO2 of 60, calculate how much oxygen will be dissolved in the arterial blood of our patient.

Each g of Hb fully saturated with O2 can bind 1.34 ml of O2.

Calculate how much oxygen will be bound to Hb in the arterial blood of our patient.

Hint: What must you do to account for the fact that our patient’s Hb is not 100% saturated?

What is our patient’s total arterial oxygen content?

The normal range for total arterial oxygen content is 16.5-20 ml O2/dl.

Is the patient anemic? Explain your answer.

Diagram the negative feedback that keeps his hemoglobin levels in the normal range.

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What is the formula for minute ventilation? Calculate minute ventilation for our patient and compare this value to what is considered normal for this individual.

What is the formula for alveolar minute ventilation? From the information provided, is it possible to calculate alveolar minute ventilation? Why or why not? (Consult text p. 459 & 461)

What is the definition of hyperventilation? (consult p. 465) Can you discern from the respiratory rate or tidal volume if this person hyperventilating?

Which of the blood gas data indicates that the patient is hyperventilating?

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How is inspired air modified as it passes through the conducting zone?

What is the normal A-a gradient? Why doesn’t PAO2 exactly equal PaO2 in a normal healthy person? (consult p. 464)

Our patient’s PAO2 was determined to be 114 mm Hg. Does this value of PAO2 suggest that the patient is hyperventilating, hypoventilating, or ventilating normally?

Determine our patient’s Alveolar-arterial gradient by subtracting the patient’s measured PaO2 from his calculated PAO2.

In our patient, is there a strong gradient for diffusion of oxygen? Does it appear that O2 is actually diffusing properly from the alveoli into pulmonary capillaries as it should? What should the PaO2 be if PAO2 is 114? )

What does this suggest about the surface area in the lungs of this smoker?

Considering the relative solubilities O2 and CO2 in body fluids, how do you explain the fact that this patient has no problem with CO2 exchange in his lungs?

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Having determined from blood work that the patient has some disturbances in blood gases, the patient next undergoes tests of mechanical lung function.

At this point in lab, we’ll take about 45 minutes to use the Spirometers and PowerLabs to measure several lung volumes and capacities on at least one student at each lab table using the printed instructions placed on each table.

You’ll need to know the definitions of and how to measure:

TV, IRV, ERV, RV, VC, FEV1.0 and record those values for your lab partner.

Complete this table for the person at your lab table:

|TV |IRV |ERV |VC |

|Vital Capacity (VC) |3 L (75% of predicted) | | |

|Forced expiratory volume in 1 second |1.6 L (55% of predicted) | | |

|(FEV-1) | | | |

|Total Lung Capacity |7.8 L (130% of predicted) | | |

|Residual volume |2.8 L (140% of predicted) | | |

Which of these test results suggest that our patient has difficulty exhaling?

How do you explain his poor ability to exhale forcefully? What does this imply about his conducting airways during exhalation?

Recall that he’s smoke a pack of cigarettes daily for the last 30 years. How might his airways have responded to this chronic insult? Would you expect him to produce large volumes of mucus? If so, what effect with this have on air flow during ventilation?

Would his mucociliary escalator be functioning properly? Why or why not?

Does our patient have chronic bronchitis?

Why might he have a higher-than-normal frequency of respiratory infections?

The patient is instructed to exhale through pursed lips. What does this accomplish?

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Given the observation that his chest circumference is only a little larger than typical for his age, how do you explain his very large TLC? Hint: Do you think he has more lung tissue or less lung tissue than normal? Is this related to his larger-than-predicted residual volume?

His lungs hold a very large volume of air with a higher than normal PAO2 (114 mm Hg) but his arterial O2 is only 60 mmHg? What does this imply about the total surface area available for gas exchange?

Alveolar macrophages clean debris inside the alveoli. If you were to obtain a lung biopsy, would you expect to see more or fewer alveolar macrophages than normal? Explain why.

Activated macrophages secrete elastase which digests elastin fibers around the alveoli. How would the loss of elastin affect inhalation?

How would the loss of elastin fibers affect exhalation?

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Given the medical history and the test results, would you diagnose this patient as having emphysema?

Imaging analysis reveals an enlargement of the right ventricle. Explain why and how this condition (called cor pulmonale) develops. Hint: Consider the likely state of his pulmonary vasculature.

Consult the Merck Manual for more information about emphysema.

Specifically

According to the Merck Manual, albuterol and ipratroprium are prescribed to treat stable COPD. How does each of these drugs work to minimize the symptoms?

Corticosteriods are also prescribed. How are they effective in treating COPD?

Patients with this disease are treated with inhalants that contain protease inhibitors. What is the rational for this treatment?

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The patient is instructed on the use of supplemental oxygen. What is the theory underlying this long-term therapy? What is the objective in terms of the A-a gradient?

What is the prognosis for patients who have been diagnosed with this disease?

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