Harvard-MIT Division of Health Sciences and Technology HST.542J: Quantitative Physiology: Organ Transport Systems Instructors: Roger Mark and Jose Venegas MASSACHUSETTS INSTITUTE OF TECHNOLOGY Departments of Electrical Engineering, Mechanical Engineering, and the Harvard-MIT Division of Health Sciences and Technology 6.022J/2.792J/BEH.371J/HST.542J: Quantitative Physiology: Organ Transport Systems QUIZ 3 Thursday, April 29, 2004 Name:These are normal values of physiological parameters for a 70 kg person. Rrs (respiratory system R) = 4 mbar·s/l Ccw = 200 ml/mbar Clung = 200 ml/mbar VD (Anatomic) = 150 ml V � O2 = 274 ml/min V � CO2 = 220 ml/min RQ = 0.8 Qs /QT (Shunt fraction) < 0.05 QT (cardiac output) = 5 l/min Patm = 760 mmHg PvCO2 = 46 mmHg PvO2 = 40 mmHg PaCO2 = 40 mmHg PaO2 (at room air) = 100 mmHg (A − a)D O2 ≈ 6-10 mmHg pH = 7.4 cHb = 15 g/100ml-blood Hb O2 Binding capacity = 20.1 ml O2/100ml blood FRC = 2.4 l The normal hemoglobin O2 saturation curve is also included and should be used only when there is no alternative data available. Figure 1: The first two problems are cases that include certain respiratory physiologic abnormalities. You can use the normal values as a reference, or in absence of additional information. 6.022j—2004: Quiz 3 2Problem 1 (Case 1) A patient comes to the emergency ward with shortness of breath and wheezing. He is breath-ing room air at a rate of 30 breaths per minute, and the pulse oximeter shows his arterial blood saturation to be SaO2 = 0.80. Arterial and mixed venous blood samples are taken at arrival and reveal the following values: PvCO2 = 44 mmHg PvO2 = 27 mmHg PaCO2 = 39 mmHg PaO2 (at room air) = 20 mmHg The blood gas data comes with a computer generated caution questioning the validity of the measurements. A. Please identify which of the four blood gas values may have an error and explain your rea-soning. (25%) B. You need to make a best guess to treat the patient with the knowledge available to you; can you find an approximate value of the erroneous blood gas? (25%) C. The patient is given 100% O2 by mask and one hour later his blood gases come back: PvCO2 = 48 mmHg PvO2 = 47 mmHg PaCO2 = 42 mmHg PaO2 = 60 mmHg This time without caution notes. What can you say about the cause of gas exchange impairment in this patient? (50%) Hint, you can ignore the oxygen carrying capacity of plasma in your calculations. 6.022j—2004: Quiz 3 3Problem 2 (Case 2) The same patient eventually develops respiratory failure and is placed on a mechanical ventilator adjusted to parameters matching his tidal breathing: VT = 390 ml f = 30 bpm Tins = 40% Texp = 50% Fi O2 = 0.50 And his blood gases are measured as: PvCO2 = 42 mmHg PvO2 = 45 mmHg PaCO2 = 40 mmHg PaO2 = 275 mmHg V˙O2 = 274 ml/min V˙CO2 = 220 ml/min The ventilator output shows the following screen Figure 2: 6.022j—2004: Quiz 3 4A. Is this patient exhibiting dynamic hyper-inflation, and why or why not? (25%) B. Can you estimate the patient’s respiratory system mechanical parameters: Resistance and Compliance? (25%) C. The attending MD suggests decreasing frequency while keeping the inspiration (insufflation in Germanic English) and exhalation time % unchanged. What frequency and tidal volume would you choose? Assume that the VD physiologic remains unchanged. (50%) (Note: if you decide to use VD anatomic in your calculation, you will lose 25% of the question points.) 6.022j—2004: Quiz 3 5Problem 3 Pulmonary fibrosis is a debilitating disease of the lung characterized by replacement of elastin by collagen and resulting in a decrease of lung compliance. In severe cases, lung transplant is the only option for survival. To maximize organ availability and reduce post-operative mortality, usually unilateral lung transplant is conducted. A. First draw the normal chest wall and lung compliance curves. Then draw changes that result from pulmonary fibrosis (CL reduced by 1/2). Assume that compliances are linear and that the chest wall compliance does not change. What happens with FRC in pulmonary fibrosis? (25%) B. Second, draw the effects of replacing one of the lungs with a normal donor lung. What will be the new FRC after surgery? You can assume that both right and left lungs have equal compliance before surgery. (25%) 6.022j—2004: Quiz 3 6C. How does the amount of pressure required to inspire a similar tidal volume compare between before and after surgery? (25%) D. In what proportions is the tidal volume distributed between both lungs? (25%) 6.022j—2004: Quiz 3