How does an antihistamine work?

A) Hypoxemia:
This is the correct answer. Atelectasis, which is the collapse or incomplete inflation of the lung, can lead to impaired gas exchange and subsequent hypoxemia. As lung volume decreases due to collapse, ventilation-perfusion (V/Q) mismatch occurs, resulting in decreased oxygenation of arterial blood. Hypoxemia is a common finding in individuals with atelectasis and may manifest as decreased oxygen saturation levels on pulse oximetry or arterial blood gas analysis.

B) Apnea:
Apnea, defined as the cessation of breathing, is not typically associated with atelectasis. While atelectasis can contribute to respiratory compromise and may result in respiratory distress, including tachypnea or increased work of breathing, it does not usually lead to complete cessation of breathing.

C) Pleural effusion:
A pleural effusion is the accumulation of fluid in the pleural space surrounding the lungs. While pleural effusion may occur concurrently with atelectasis, it is not an expected finding specifically associated with atelectasis itself. Pleural effusion may cause respiratory symptoms such as dyspnea or chest pain but is not a primary manifestation of atelectasis.

D) Dysphagia:
Dysphagia, or difficulty swallowing, is unrelated to atelectasis. While dysphagia can occur as a result of various conditions affecting the esophagus or neurological control of swallowing, it is not a typical manifestation of atelectasis. Atelectasis primarily affects the lungs and respiratory function rather than swallowing function.

A) By blocking the effects of histamine in the body:
Antihistamines are pharmacological agents that work by antagonizing the effects of histamine, a chemical mediator released by mast cells and basophils in response to allergens or other triggers. Histamine contributes to various allergic symptoms such as itching, sneezing, nasal congestion, and watery eyes. Antihistamines exert their effects by competitively binding to histamine receptors (specifically H1 receptors) on target cells, thereby preventing histamine from binding and exerting its physiological effects. By blocking histamine receptors, antihistamines inhibit the action of histamine, leading to the alleviation of allergy symptoms.

B) By reducing inflammation in the body:
While some medications, such as corticosteroids, exert anti-inflammatory effects by suppressing the immune response and inhibiting the production of inflammatory mediators, antihistamines primarily target histamine receptors and do not directly reduce inflammation. Although histamine release can contribute to inflammation, antihistamines mitigate allergic symptoms primarily by blocking the action of histamine rather than by directly reducing inflammation.

C) By increasing the production of histamine in the body:
This statement is inaccurate. Antihistamines do not increase the production of histamine; instead, they counteract the effects of histamine by blocking its activity at receptor sites. The primary mechanism of action of antihistamines involves blocking histamine receptors to prevent histamine from exerting its physiological effects.

D) By stimulating the immune system:
Antihistamines do not stimulate the immune system. Instead, they act as antagonists to histamine receptors, thereby inhibiting histamine-induced responses. While histamine is involved in immune responses and allergic reactions, antihistamines do not directly modulate immune function or stimulate immune activity. Their primary role is to alleviate allergy symptoms by blocking the effects of histamine."