Respiratory Physiology - Physiology MCQ ACEM, Top Exam Questions & Answers, Rated A+

Respiratory Physiology - Physiology MCQ ACEM, Top Exam Questions & Answers, Rated A+ Which of the following statements regarding gaseous perfusion and diffusion properties is CORRECT? 1. Passive diffusion is described by Fowler's law 2. Perfusion limited refers to a gas that is very soluble in the blood 3. Carbon monoxide is diffusion limited 4. Oxygen is only perfusion limited 3. Carbon monoxide is diffusion limited Diffusion through tissues is described by Fick's law (there is no Fowler's law) . This states that the rate of transfer of a gas through a sheet of tissues is proportional to the tissue area and the difference in gas partial pressure between the two sides, and inversely proportional to the tissue thickness. CO is used for measurements because its uptake is diffusion limited (i.e. it is not dependent on the amount of blood available but rather only on the diffusion properties of the blood-gas barrier). It does not form a partial pressure in the blood due to its extremely high solubility in blood (no appreciable back pressure develops). NO is very insoluble in blood and quickly forms a partial pressure (back pressure). It is therefore perfusion limited as the amount taken up by the blood depends entirely on the amount of available blood flow and not at all on the diffusion properties of the blood-gas barrier. Osub2/sub time course lies between CO and NO. Depending on certain circumstance, Osub2/sub can be perfusion limited (normal) or diffusion limited (abnormal), e.g. due to thickening of the blood-gas barrier). The haemoglobin dissociation curve moves to the right under which of the following circumstances? 1. Alkalosis 2. Low temperature 3. Raised CO2 4. Decrease in 2,3 DPG 3. Raised COsub2/sub Factors shifting Hb dissociation curve to the right: - rise in temperature - decrease in the pH - increase in 2,3 DPG (an end product of RBC metabolism) - rising pCOsub2/sub (Memory aide) an exercising muscle is iacidic/i, ihypercarbic/i and ihot/i, and it benefits from an increased unloading of Osub2/sub from its capillaries, i.e. right shift. This is known as the Bohr Effect: a decrease in blood pH or an increase in blood pCOsub2/sub will result in Hb proteins releasing their loads of oxygen (right shift) and a decrease in COsub2/sub or increase in pH will result in Hb picking up more oxygen (left shift). Regarding the lungs, which of the following statements is CORRECT? 1. Perfusion is greatest at the base 2. Ventilation/perfusion (VQ) quotient is directly proportional to gas exchange 3. Ventilation/perfusion (VQ) quotient is inversely proportional to gas exchange 4. Ventilation is greatest in middle zone