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Category Archives: Pulmonary Medicine

Ventilation-Perfusion Relationships

26-Sep-16

Gas exchange between the alveoli and the pulmonary capillary blood occurs by diffusion. Diffusion of oxygen and carbon dioxide occurs passively, according to their concentration differences across the alveolar-capillary barrier. These concentration differences must be maintained by ventilation of the alveoli and persusion of the pulmonary capillaries. Alveolar ventilation brings oxygen into the lung and […]

Pressure-Volume Relationships in the Respiratory System

15-Sep-16

The relationship between changes in the pressure distending the alveoli and (transmural pressure) changes in the lung volume is important to understand because it dictates how easily the lung inflates with each breath. The alveolar-distending pressure is often referred to as the transpulmonary pressure. Strictly speaking, the transpulmonary pressure is equal to the pressure in the […]

Mechanism of Pulmonary Edema

13-Sep-16

Pulmonary edema is the extravascular accumulation of fluid in the lung. This pathologic condition may be caused by one or more physiologic abnormalities, but the result is inevitably impaired gas transfer. As the edema fluid builds up, first in the interstitium and later in alveoli, diffusion of gases – particularly oxygen – decreases. The capillary […]

[Respiration][Circulation] Blood Flow to the Lung – General and Pulmonary Vascular Resistance

11-Sep-16

The lung receives blood flow via both the bronchial circulation and the pulmonary circulation. Bronchial blood flow constitutes a very small portion of the output of the left ventricle and supplies part of the tracheobronchial tree with systemic arterial blood. Pulmonary blood flow (PBF) constitutes the entire output of the right venticle and supplies the […]

Effects of Pressure Outside the Heart on Cardiac Output

09-Sep-16

In the figure cited and the preceding dicussions in thread "Pathophysiology of the Circulation" at http://www.tomhsiung.com/wordpress/2016/08/pathophysiology-of-the-circulation/, values of Pms and Pra were expressed relative to atmospheric pressure. However, the transmural pressure of the right atrium exceeds the Pra by the subatmospheric value (about -4 mm Hg) of the Ppl surrounding the heart. Consider the effect of […]