Unilateral Left Heart Failure
In the discussions thus far, we have considered failure of the heart as a whole. Yet, in a large number of patients, especially those with early acute failure, left-sided failure predominates over right-sided failure, and in rare instances, the right side fails without significant failure of the left side. Therefore, we need especially to discuss the special features of unilateral heart failure.
When the left side of the heart fails without con-comitant failure of the right side, blood continues to be pumped into the lungs with usual right heart vigor, whereas it is not pumped adequately out of the lungs by the left heart into the systemic circulation. As a result, the mean pulmonary filling pressure rises because of shift of large volumes of blood from the sys-temic circulation into the pulmonary circulation.
As the volume of blood in the lungs increases, the pulmonary capillary pressure increases, and if this rises above a value approximately equal to the colloid osmotic pressure of the plasma, about 28 mm Hg, fluid begins to filter out of the capillaries into the lung inter-stitial spaces and alveoli, resulting in pulmonary edema.
Thus, among the most important problems of left heart failure are pulmonary vascular congestion and pulmonary edema. In severe, acute left heart failure,pulmonary edema occasionally occurs so rapidly that it can cause death by suffocation in 20 to 30 minutes.
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