Respiratory Case Study # 2

Respiratory Case Study # 1 updated 18 November 2013

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. 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).

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

PaO2 60 mm Hg

Sa O2 90%

PaCO2 30 mm Hg Hemoglobin 18g/dl blood 14-18 g/dl blood Respiratory rate 25 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” Is this patient’s hemoglobin saturation expected given his PaO2? (Consult p. 455 of text) ______In what two forms is oxygen transported in the blood?

Using the following information, calculate a) the amount of oxygen dissolved in the blood b) the amount of oxygen bound to hemoglobin c) the total arterial oxygen content

solubility of oxygen in blood = 0.003 ml O2/mmHg PaO2*dL oxygen capacity of Hb = 1.34 ml O2/g Hb

What is the normal total arterial oxygen content?

Is the patient’s total arterial oxygen content in the normal range?

Is the patient anemic?

Diagram the negative feedback loop responsible for keeping his hemoglobin levels elevated. ______From the information provided, is it possible to calculate alveolar minute ventilation? Why or why not? (Consult the textbook for the formula for Alveolar minute ventilation.)

Calculate minute ventilation and compare this value to what is considered normal for this individual.

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? (Consult the textbook for the definition of hyperventilation.) ______Calculate the partial pressure of oxygen in inspired air (PIO2) with the equation PIO2 = FIO2 (barometric pressure – 47mm Hg) where FIO2 is the fraction (expressed as a percentage) of inspired air that is oxygen.

The professor will explain why one must subtract 47mmHg in this calculation.

Calculate the patient’s PAO2 according to the equation

PAO2 = PI O2 - PaCO2 [ FIO2 + (1-FIO2)/RQ] where RQ is the respiratory quotient, which is assumed to be 0.8.

Does the value of PAO2 suggest that the patient is hyperventilating, hypoventilating, or is ventilating normally?

Why is the RQ assumed to be 0.8? What would the RQ be if the diet was only carbohydrates, only fats, only proteins?

What is the normal A-a gradient? Why doesn’t PAO2 exactly equal PaO2 in a normal healthy person? (consult text for discussion of ventilation/perfusion.)

Subtract PaO2 from the calculated PAO2 to determine the Alveolar-arterial gradient in this patient.

Comparing the patient’s A-a gradient to normal values, what does this suggest about gas exchange of oxygen in the patient’s lungs?

Does this patient have problems with CO2 exchange in his lungs?

Why would this patient’s dyspnea worsen if he were to exert himself with any physical activity?

______The patient next undergoes tests of mechanical lung function. The following lung volumes and capacities are measured. Percentages of predicted values based on his height and weight are shown. Any lung volume or capacity between 80% and 120% of predicted is considered in the normal range. Find the normal values by consulting the Physiological Reference handout or Figure 13-18 in your text.)

Parameter Patient’s value Normal value Level Forced vital capacity 3 L (75% of predicted) (FVC) Forced expiratory 1.6 L (55% of predicted) volume in 1 second (FEV-1) Total Lung Capacity 7.8 L (130% of predicted) Residual volume 2.8 L (140% of predicted)

What are the four non-overlapping lung volumes. What is the difference between a lung volume and a capacity? (consult Fig. 13-18.)

What is your conclusion based on the mechanical lung function test results? Can you diagnose (provide a name for) this pulmonary disease? ______The patient is instructed on the use of supplemental oxygen. What is the theory underlying this long-term therapy?

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

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

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