10-24-2011, 07:20 AM
DD.............
Progressive exertional dyspnea in a heavy smoker suggests chronic bronchitis/emphysema (COPD). The right ventricular dilatation and elevated central venous pressure indicate secondary cor pulmonale. A high central venous pressure raises the hydrostatic pressure in capillary bed venules, thereby increasing net plasma filtration, especially in dependent tissues. If there is a compensator increase in tissue lymphatic drainage to counteract the interstitial fluid increase, edema does not develop. Only when the venous pressure and net capillary filtration have risen sufficiently to overwhelm the resorptive capacity of tissue lymphatics does edema appear.
(Choice A) While an increase in plasma oncotic pressure would oppose edema formation, this does not occur in COPD.
(Choice B) The interstitial fluid pressure is increased in edema.
(Choice C) A decrease in capillary permeability (filtration coefficient) would oppose edema formation, but patients with chronic bronchitis are not known to have decreased capillary permeability.
(Choice E) A decrease in circulating aldosterone could decrease intravascular volumes and pressures, counteracting edema formation. However, patients with cor pulmonale tend to have elevated levels of aldosterone in response to the low cardiac output.
Progressive exertional dyspnea in a heavy smoker suggests chronic bronchitis/emphysema (COPD). The right ventricular dilatation and elevated central venous pressure indicate secondary cor pulmonale. A high central venous pressure raises the hydrostatic pressure in capillary bed venules, thereby increasing net plasma filtration, especially in dependent tissues. If there is a compensator increase in tissue lymphatic drainage to counteract the interstitial fluid increase, edema does not develop. Only when the venous pressure and net capillary filtration have risen sufficiently to overwhelm the resorptive capacity of tissue lymphatics does edema appear.
(Choice A) While an increase in plasma oncotic pressure would oppose edema formation, this does not occur in COPD.
(Choice B) The interstitial fluid pressure is increased in edema.
(Choice C) A decrease in capillary permeability (filtration coefficient) would oppose edema formation, but patients with chronic bronchitis are not known to have decreased capillary permeability.
(Choice E) A decrease in circulating aldosterone could decrease intravascular volumes and pressures, counteracting edema formation. However, patients with cor pulmonale tend to have elevated levels of aldosterone in response to the low cardiac output.