Gas Exchange Research Paper

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Blood gas and Acid Base disorders
Gas exchange:
Respiration is the process whereby oxygen is delivered to metabolically active tissues and the carbondioxide produced from the metabolism is subsequently removed. Hypoxemia occurs when there is defective oxygenation of tissues and hypercapnea occurs when ventilation is impaired and respiratory acidosis supervenes.
The amount of oxygen in the blood is determined by the amount of dissolved oxygen, the hemoglobin in the blood and the affinity of the hemoglobin for oxygen. The hemoglobin in blood is only 97% saturated. The arterial blood therefore contains a total of about 19.8ml of oxygen per dL.0.29ml in solution and 19.5ml bound to hemoglobin. In venous blood at rest, hemoglobin is 75% saturated
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Venous blood carries more carbon dioxide than arterial blood. About 11% of the carbon dioxide added to the blood in systemic capillaries is carried to lungs as carbamino-CO2.
Abnormalities of gas exchange and transport
Gas exchange is abnormal when either tissue oxygen delivery or CO2 removal is impaired33.
i. Impaired oxygen delivery: Oxygen delivery tissue is the function of arterial oxygen content times cardiac output. When oxygen delivery is inadequate for cellular needs, hypoxia occurs. ii. Hypoxemia: Occurs when the partial pressure of oxygen in the arterial blood (PaO2) is decreased to less than the predicted normal value based on the age of the patient. iii. Decreased partial pressure of oxygen in arterial blood: Decreased PaO2 may be caused by a low ambient PO2, hypoventilation, impaired diffusion, V/Q mismatches and right to left anatomic or physiologic shunting.
V/Q imbalances are the most common cause of hypoxemia in patients with lung disease33. iv. Hemoglobin differences: For arterial oxygen content to be adequate, there must also be enough normal Hb in the blood. If the blood hemoglobin is low, hypoxia can occur because of low oxygen content in the arterial
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However, if body fails to eliminate the remaining acids, these buffers are soon exhausted, and the pH of body fluids quickly decreases to life threatening levels. By eliminating the carbon dioxide, the lungs can rapidly remove large quantities of fixed acid from the blood. The kidneys also remove fixed acids, but at a slow pace33.

Bronchial Asthma
“Asthma is a heterogeneous disease, characterized by chronic airway inflammation and the diagnosis is usually clinical. It is defined by the history of respiratory symptoms such as wheeze, shortness of breath, chest tightness and cough that vary over time and in intensity, together with variable expiratory airflow limitation.”34
The following features are typical of asthma and, if present, increase the probability that the patient has asthma:34
• More than one symptom (wheeze, shortness of breath, cough, chest tightness), especially in adults
• Symptoms often worse at night or in the early morning
• Symptoms vary over time and in intensity
• Symptoms are triggered by viral infections (colds), exercise, allergen exposure, changes in weather, laughter, or irritants such as car exhaust fumes, smoke or strong

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