Case R 3 Respiratory A healthy college student went to Colorado at the end of the school year for a vacation. While there, he drove to the top of Pike's Peak. During his first hour on the peak, he walked about but had to sit down to rest three times. The last time was in the weather station. He glanced at the barometer and saw it read 450 mm Hg. The barometric pressure at sea level is 760 mm Hg, and the pressure decreases with increasing altitude. Each gas in the atmosphere is present as the same fraction of the whole regardless of altitude. On Pike's Peak, each gas has a smaller partial pressure than at sea level. Because inspired PO2 is lower at altitudes higher than sea level, alveolar and arterial PO2 will also be lower. Any change that reduces arterial PO2 (especially to values below about 60 mm Hg) stimulates the peripheral chemoreceptors (carotid and aortic bodies). The resulting reflex increases alveolar ventilation, oxygen delivery to the lungs, and the expiration of carbon dioxide. Other disturbances that lower arterial PO2 also stimulate ventilation via the peripheral chemoreceptors. Predict that changes (increase, decrease, no change) that would have taken place in each of the listed parameters by the time the student entered the weather station compared with the values that he would have had at home (sea level). Next, predict the effects (increase, decrease, no change) of the other listed conditions in an otherwise normal individual at sea level. Consider each listed condition independently of the others. Provide a summary (on the reverse) for each condition. Condition | Alveolar PO2 | Arterial PO2 | Arterial Hb Saturation | Venous Hb Saturation | Tidal Volume | Arterial PCO2 | Arterial pH ---|---|---|---|---|---|---|--- On Pike's Peak | Decrease | Decrease | Decrease | Decrease | increase | decrease | increase Moderate Exercise | No change | No change | No change | Decrease | increase | No Change | No change Pneumonia | increase | decrease | decrease | decrease | increase | -/D/I | -/I/d Partial tracheal obstruction | Decrease | Decrease | Decrease | Decrease | Decrease | increase | Decrease CNS drug depression | Decrease | Decrease | Decrease | Decrease | Decrease | increase | decrease Hb is hemoglobin
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- Ammonia exposure: Arterial hemoglobin saturation would increase due to hyperventilation, arterial pO2 would decrease, and arterial pH would decrease. - Partial tricyclic obstruction: Arterial hemoglobin saturation would decrease, arterial pO2 would decrease, and Show moreβ¦
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Case 20 Dan Hsieh celebrated his graduation from college by joining a mountain climbing expedition in the Swiss Alps. Dan is in excellent physical condition: he runs 3-5 miles daily, and he played intramural soccer, volleyball, and rugby throughout college. At the insistence of his parents, Dan underwent a complete medical examination before the climb, which he passed with flying colors. He was off to the Alps! QUESTIONS 1. Mont Blanc, the highest elevation in the Swiss Alps, is 15,771 feet above sea level. The barometric pressure on Mont Blanc is approximately 420 mm Hg. (The barometric pressure at sea level is 760 mm Hg.) What is the fractional concentration of O2 (FiO2) in atmospheric air on Mont Blanc? What is the partial pressure of oxygen (PO2) of humidified air on Mont Blanc? How does this value of PO2 compare with the PO2 of humidified air at sea level? 2. At his physical examination performed at sea level, Dan's arterial PO2 (PaO2) was 100 mm Hg. If Dan's PaO2 had been measured when he arrived on Mont Blanc, it would have been approximately 50 mm Hg. Why would his PaO2 be decreased at the higher elevation? What was Dan's alveolar PO2 (PAO2) on Mont Blanc? 3. Predict whether each of the following parameters would be increased, decreased, or unchanged on Mont Blanc. Explain why each of the predicted changes would occur. a. Breathing rate b. Percent saturation of hemoglobin c. PO2 at which hemoglobin is 50% saturated (P50) d. Pulmonary artery pressure
Adi S.
Explain the underlying cause of the Korotkoff sounds. Why can these sounds only be detected when the pressure in the cuff is between systolic and diastolic pressure? [4 marks] The sphygmomanometer increases pressure in the cuff surrounding the arm, hence the pressure in the cuff becomes greater than the systolic pressure. This pressure compresses the artery, which prevents blood flow. The pressure decreases when air is released from the cuff and artery compression also decreases. When the pressure is slightly lower than systolic pressure, the artery opens slightly, allowing blood flow. Blood flows through the artery with high velocity as there is a large pressure difference and a small space between openings. High velocity is what causes these audible Korotkoff sounds. When the pressure is further decreased, diastolic pressure is reached and Korotkoff sounds are not heard anymore. The sound can only be heard between systolic and diastolic pressure because compression of the artery by the cuff causes blood to flow in a turbulent and interrupted manner. 2. Which method, auscultation with the cardio-microphone or the oscillometric method using the finger pulse transducer, gives the most accurate measure of systolic arterial pressure? Briefly justify your answer. The auscultation method using the cardio microphone is more accurate at representing systolic arterial pressure. The auscultation method allows to detect systolic pressure accurately at the beginning of Korotkoff sounds, as this is when blood starts to pass through the artery after being compressed. The oscillometric method is not accurate because the pulse of blood flowing through the artery is felt by the transducer. The pulse requires more blood to flow through the artery for oscillations. The oscillation method measures oscillations in the artery wall. It often underrepresents the systolic blood pressure because only 1/3 of blood is ejected. 3. Based on what you have learned from the lectures, what is the immediate effect of a sudden change in posture from lying down to standing up on your stroke volume and why does this happen? How do you expect this change in stroke volume to affect arterial pressure? [4 marks] When there is a sudden change in posture from lying down to standing, gravity tends to pull blood downwards towards the feet. Hence, blood pools in the veins of the feet and lower legs and increases pressure in the feet. As blood pools in the lower limbs, there is less blood circulating back to the heart. The change in volume causes a decline in central pressure, which decreases pressure in the ventricles being filled. There is a decrease in venous return, therefore low stroke volume and cardiac output. When all of that happens, arterial pressure decreases. The change in posture acts as a hemorrhage in the body due to less venous return and thus relies on baroreceptors to bring arterial pressure back to normal. 4. What are the compensatory responses that restore relatively normal arterial pressure when we stand up? [4 marks] Baroreceptors restore arterial pressure to normal when we stand up. These receptors are located in the aortic arch and carotid sinus of the heart and are capable of detecting pressure by the stretch of arterial walls of the heart. The firing rate of these baroreceptors is directly proportional to the arterial pressure, hence a decrease in pressure means decreased firing of baroreceptors. Less firing means more sympathetic activity and less parasympathetic activity. This causes an increase in heart rate, which increases cardiac output. Along with an increase in cardiac output, arterial pressure goes back to the normal range. 5. How did systolic arterial pressure measured using the finger pulse differ with the arm in different positions? Why do you think it differed? Systolic arterial pressure is different in different arm positions because of pressure changes and the force of gravity on the blood flow. Hydrostatic pressure is equal to the pressure produced by cardiac contraction when the arm is level with the heart. Blood pools at the lower part of the body when the arm is lowered. When the arm is above the head, pressure is lower as there is increased resistance in the artery due to gravity. Hence, it can be said that the level of the finger to the heart does affect blood pressure value at fingers, thus fingers must be kept at the level of the heart for accurate results.
Suman K.
Case Study #4 A 65-year-old female who was a lifelong smoker visited her doctor because she was having difficulty breathing. This was nothing new but seemed to be getting worse. It was most difficult to exhale, but it helped if she pursed her lips. After her examination, her doctor prescribed an oxygen tank for her use at home and ordered the following tests: Test Normal Range Patient's Results FVC (Forced Vital Capacity) 2.07 L 1.8 L FEV1.0 (Forced Expiratory Volume in 1 sec) 1.7 L 0.9 L FEV% FEV1.0/FVC 77% 50% MVV (Maximum Voluntary Ventilation) 80-120 L/min 75 L/min FRC (Functional Residual Capacity) 2.4 L 3.0 L ERV (Expiratory Reserve Volume) 1.2 L 0.8 L RV (Residual Volume) 0.5 L 2.2 L Arterial Blood Gas PO2 = 95 mmHg PCO2 = 40 mmHg pH = 7.38-7.42 PO2 = 85 mmHg PCO2 = 46 mmHg pH = 7.39 ECG Mean Electrical Axis Between +110 to -20Β° +130Β° 1. What would be the specific diagnosis for this patient? 2. Which of the following test results above would support this diagnosis? List all that apply. 3. Explain why the RV in this patient has increased. 4. Why is this patient's Arterial Blood Gas measurement abnormal? Is it the increase in PCO2 or the decrease in PO2 that caused the change in her blood pH? Explain. 5. Does her heart have a normal Mean Electrical Axis? If it is abnormal, explain what led to this.
Madhur L.
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