Fisiopatolog
a del Aparato Respiratorio

Respiratory Anatomy and Lung Volumes

The respiratory system includes upper and lower structures such as the Seno frontal, Fosas nasales, Tr
quea, and Alv
olo. Inspiratory effort is primarily driven by the Diafragma, Escalenos, and Esternocleidomastoideos, while forced expiration involves the Intercostales internos and M
sculos abdominales. Lung volumes include a Tidal volume of $500\,mL$, an Inspiratory reserve volume of $3000\,mL$, and a Residual volume of $1200\,mL$, contributing to a Functional residual capacity of $2300\,mL$ and a total lung capacity of around $5800\,mL$.

Pulmonary Physiology and Gas Exchange

Gas exchange is facilitated by Neumocito tipo I cells, while Neumocito tipo II cells synthesize surfactant to reduce surface tension. Alveolar oxygen pressure ($P_{O_{2}}$) is typically $104\,mmHg$, with capillary blood entering at $40\,mmHg$ and reaching equilibrium at the venous end. The oxygen-hemoglobin dissociation curve shifts right (decreased affinity) with increased temperature, $\uparrow PCO_{2}$, $\uparrow 2,3-DPG$, and decreased $pH$. Control of respiration depends on peripheral chemoreceptors in Cuerpos carotideos and a
rtico responding to $\downarrow pO_{2}$ and $\uparrow pCO_{2}$, and central chemoreceptors responding to concentration changes of $H^{+}$ and $pCO_{2}$.

Gasometry and Acid-Base Balance

Arterial blood gas values typically maintain a $pH$ between $7.35-7,45$, $pCO_{2}$ between $35-45\,mmHg$, and $HCO_{3}^{-}$ between $21-26\,mmol/L$. The Henderson-Hasselbalch equation is utilized to calculate the precision of the solution: $pH = 6.1 + \log\left(\frac{HCO_{3}^{-}}{0.03 \times PCO_{2}}\right)$. Primary imbalances include Metabolic Acidosis (low $HCO_{3}^{-}$, low $pH$), Respiratory Acidosis (high $pCO_{2}$, low $pH$), Metabolic Alkalosis (high $HCO_{3}^{-}$, high $pH$), and Respiratory Alkalosis (low $pCO_{2}$, high $pH$).

Obstructive Pulmonary Pathologies

Chronic Obstructive Pulmonary Disease (EPOC) is characterized by persistent reduction in airflow, often associated with a diagnosis criteria of $FEV_1/FVC < 0.7$. Enfisema involves the destruction of distal air spaces and loss of elastic fibers, leading to "Pink Puffers (Soplador Rosado)" who present with dyspnea but normal oxygenation initially. Chronic Bronchitis involves hipersecreci
n de moco and is identified by permanent cough, often leading to "Blue Bloaters (Cian
tico Abotargado)." Asma is a chronic inflammation involving mastocytes and eosin
filos, causing reversible bronchoconstriction and airway remodeling over time. Fibrosis Qu
stica is a hereditary disease involving a mutated $CFTR$ channel that blocks chloride flow and causes thick mucus accumulation.

Restrictive and Infectious Pathologies

Restrictive diseases such as Fibrosis Pulmonar Idiop
tica and Neumoconiosis (caused by dust inhalation like coal or silica) decrease lung volumes, characterized by $FVC < 80\%$. Sarcoidosis involves granulomas histiocitarios and hiliary lymph node inflammation. Neumon
a, the leading infant mortality cause globally, results in alveolar fluid and pus, caused by agents such as Streptococcus pneumoniae or SARS-Cov2. Tuberculosis, caused by Mycobacterium tuberculosis, leads to the formation of granulomas with cells of Langhans and central necrosis caseosa, diagnosed via tinci
n de Zhiel-Nielsen.

Vascular, Pleural, and Mediastinal Disorders

Hipertesi
n Pulmonar (HTP) occurs when resistance increases ($RVP > 25\,mmHg$), leading to right ventricular dysfunction and cor pulmonale. Edema Agudo de Pulm
n involves fluid accumulation exceeding $500\,mL$ in the extravascular space, often due to Heart Failure. S
ndrome de Distress Respiratorio Agudo (SDRA) is a severe condition with $30-60\%$ mortality caused by damaged alveolo-capillary membranes and protein-rich edema. Pleural pathologies include Derrame Pleural (classified into transudative < $3\,g$ protein or exudative > $3\,g$ protein), Atelectasias (lung collapse), and Neumot
rax, where a Tension Pneumothorax is a clinical emergency characterized by progressive intrapleural pressure increases.

Questions & Clinical Discussion

Discussion focuses on several complex cases including a 63-year-old male with oclui
n de DA and respiratory failure, as well as a 78-year-old male post-triple bypass who developed enfisema subcut
neo and difficulty breathing after a mediastinal drain was removed. Analysis of a 59-year-old patient with persistent cough and diarrhea led to a diagnosis of severe pneumonia with a high sepsis risk based on a Procalcitonina (PCT) value of $2.99\,ng/mL$. Another significant case involved a 67-year-old smoker with sudden dyspnea and a resulting diagnosis of Carcinoma Epidermoide, illustrating the link between smoking, hiliar masses, and airway obstruction. One patient presenting with cyanosis and a $pO_{2}$ of $31\,mmHg$ was found to have methemoglobinemia ($MetaHb > 30.0\%$) after ingesting Tadalafilo (Cialis) from the black market, which highlights the risk of chemical-induced hemoglobin changes.