Respiratory Pathophysiology

all cells in the body require some type of enery to function cells obtain their enerygy from the process of aerobic respiration aerobic respiration requires oxygen or the default is the anaerobic metabolic pathway the aerobic metabolic pathway also produces carbon dioxide as a by product the respiratory system enables the intake of oxygen and release of CO2

Respiratory Mucosa - lines the upper and lower respiratory tract air normally enters the system via the external nares which opens into the nasal cavity the vestibule is guarded by hair that screen out large particles the nasal mucosa traps particles as well as warms and humidifies incoming air Inspired air passes through the glottis en route to the lungs air passes through vibrating folds of tissue producing sound The larynx surrounds and protects the glottis. cylindrical larynx is composed of three large cartilages (thyroid, cricoid, and epiglottis) The epiglottis projects into the pharynx the trachea extends from the 6th cervical vertebre to the 5th thoracic vertebre. Has "C" shaped cartilages to protect and allow distortion of posterior wall from passing food. The trachea branches within the mediastinum forming the right and left bronchi entering the lung at a point called the hilus The lobes of the lungs are separated by fissures. 3 lobes at right and 2 lobes at left the bronchi branch out forming the bronchial tree. As you go farther down the tree there is less cartilage and more muscle. Branch all the way down to alveoli. Many alveoli are interconnected by alveolar ducts surfactant cells produce an oily seccretion that keeps the alveoli from collapsing

Functions of Resp system Gas exchange - provides an area for gas exchange between air and circulating blood Air in and out - moving air to and from exchange surfaces Protection - protecting respiratory surfaces Defense from pathogens - defending the respiratory system and other tissues from pathogens Vocal communication - voice box Blood volume/ pressure and pH - helping to regulate these

Compliance refers to the extent to which the lungs are able to expand under a given pressure. If compliance is increased then the lungs are very easy to inflate. Conversely, if compliance is decreased then the lungs are hard to inflate. Compliance depends upon the elastic forces of the lung tissue which resists expansion of the lung tissue and wants to collapse lung tissue. These elastic forces are dependent on surface tension of the alveolar walls. Surfactant, which is made by type II alveolar epithelial cells decreases surface tension. Surfactant is made of phospholipids, proteins, and ions (especially Ca+) If surfactant is lost or inadequate, this leads to a decreased compliance and a tendency for alveolar collapse. premature infants can have a lack of surfactant leading to respiratory distress syndrome with low alveolar compliance and increased work to breath. Mucous plugs in the bronchioles may lead to a decreased O2 in the alveoli causing a decreased surfactant production and decreased compliance fibrotic pulmonary changes, fluid in the alveoli or interstitial tissues, or collapsed alvveoli lead to a decreased tissue compliance and requires increased increased work to breath. The normal work of breathing requires only 3-5% of the body's total energy expenditure. Can raise to as high as 50% of the bodys total energy expenditure with circumstances decreased compliance.

The goal of the respiratory system is getting air to the alveoli, the alveolar ducts and the respiratory bronchioles (AKA respiratory lobule). Tidal volume is the amount of gas inspired and expired during normal breathing Alveolar ventilation is defined as "the portion of the tidal volume that reaches the alveoli; during expiration, part of this gas remains in the conducting airways and moves back into the alveoli with the next inspiration" Physiologic dead space is the sum of normal anatomic dead space and alveolar dead space anatomic dead space is the portion of the tidal volume that remians in the conducting airways alveolar dead space is the volume of gas in unperfused alveoli Alveolar ventilation is always the greatest in the dependent areas. Through changing position of your patient ventilation to different areas of the lung will be promoted. If a patient has left sided pneumonia the best benefit would come to the patient by positioning him on the right side.

pulmonary capillary blood flow is lowest in the apices where alveolar pressure is greater than capillary pressure. So ventilation is greater than perfusion. blood flow is greatest at the bases of the lungs where the pressure in the vessels is greater than alveolar pressure so perfusion is greater than ventilation. Blood flow and alveolar ventilation are never perfectly matched. Perfusion (Q) is usually greater than ventilation (V). A normal V/Q ratio is 0.8. If the V/Q ratio is low this means there is not enough ventilation to oxygenate the blood. If the V/Q ratio is high this means blood flow is less than ventilation so ventilation is being wasted.

Respiratory physiology Pulmonary ventilation - movement of air into and out of lungs External respiration - The process by which gases are exchanged between the lungs and the pulmonary vasculature. O2 diffuses from the alveoli into the blood, and CO2 diffuses from the blood to the alveoli. Diffusion is a passive process in which gases move across a membrane from an area of higher to lower concentration. In the lungs the membrane is the alveolar-capillary network Internal respiration - The process by which gases are exchanged between the pulmonary vasculature and the body's tissues. Oxygen from the lungs diffuses from the blood into the body tissue. CO2 diffuses from the tissues into the blood. This blood in then carried back to the right side of the heart for re-oxygenation Hypoxia - reduced oxygenation of cells in tissues Hypoxemia - reduced oxygenation of arterial blood (PaO2). Hypoxemia can lead to tissue hypoxia, however tissue hypoxia has other causes and can occur in light of normal arterial oxygenation (low CO or cyanide poisoning) Cyanosis, a bluish coloring of the skin, caused by an unusually high percentage of deoxygenated hemoglobin in the blood. Deoxygenated hemoglobin is purplish, in contrast to the bright red oxyhemoglobin Anoxia - when O2 supply completely shut off, anoxia and tissue death may result

Pulmonary Ventilation Boyles Law - as pressure of gas decreases it volume expands; as pressure increases its volume decreases. Intrapulmonary pressure drives air exchange - decreased pressure, air in. Diaphragm and external and internal intercostals - used for normal quite breathing Accessory muscles - active during active inspiratory and expiratory movements of forced breathing hyperventilation is defined as increased alveolar ventilation. This leads to a decrease in PaCo2. There are many causes of hyperventilation including hypoxemia, head injury, and anxiety or panic attack. hypoventilation is defined as a decreased alveolar ventilation. This leads to a increased PaCo2. Some common causes of hypovetilation include chest wall restriction, altered neurologic control of breathing, and obstructed airway.

Gas exchange Dalton’s Law - In a mixed gas the individual gases exert a pressure proportional to their abundance in the mixture. Partial pressure - the pressure contributed by a single gas is the partial pressure Alveolar ventilation - the amount of air reaching the alveoli each minute

O2 and CO2 exchange ooccurs at the interface of the alveolus and pulmonary capillaries (respiratory membrane) Diffusion of these gases depends on several factors. Two important factors are the thickness and surface area of the respiratory membrane. Interstitial edema and fibrotic changes cause the respiratory membrane to change in thickness. The surface area of the respiratory membrane becomes smaller with emphysema as alveoli are destroyed. If the surface area is decreased more than 25% then the patient can have diffusion problems and shortness of breath even at rest Blood entering peripheral capillaries delivers oxygen and absorbs CO2 at the tissues Po2 - over the range of O2 pressures normally present in the body, a small change in plasma Po2 will mean a large change in the amount of O2 bound or released. At alveolar Po2 the hemoglobin are almost fully saturatted; at the peripheral tissues it retains a substantial O2 reserve When low plasma Po2 continues for an extended period of time, red blood cells generate more 2,3 (BPG) bisphosphoglycerate, which reduces hemoglobins affinity for oxygen. CO2 production - aerobic metabolism in the peripheral tissues generates CO2. About 7 percent of the CO2 transported in the blood is dissolved in the plasma; 23 percent is bound as carbaminohemoglobin; the rest is converted to cardbonic acid which dissociates into H+ and HCO3-

Control of breathing is influenced by neural and chemical factors. Respiratory centers in the brain consist of three pairs of nuclei in the reticular formation of the pons and medulla. These are primarily in control of involuntary breathing Respiratory rhythmicity center - sets the pace for respiration Apneustic center - causes strong, sustained inspiratory movements Pneumotaxic center - inhibits the apneustic center and the inspiratory center in the medulla The stimulus for breathing is an iincreased CO2 level, a decreased O2 level, or an increased pH level. Chemoreceptor reflexes respond to changes in the Po2 and Pco2 in the blood and CSF

Hypoxemia Decreased PaO2 5 causes Decreased inspired oxygen - suffocation Hypoventilation - COPD, drug overdose, depression of resp center Alveolocapillary diffusion problem - pulm edema, fibrosis V/Q mismatch - pneumonia Shunting - ARDS

Respiratory Failure Caused by inability to transfer O2 or CO2 Results from other diseases and systems affecting lungs Hypoxic respiratory failure PaO2 < 60mmHg w/ FiO2 > 60% Hypercapnic respiratory failure PaCO2 > 45mmHg and acidosis Respiratory system - ARDS, pneumonia Cardiac system - Pulmonary edema Pulmonary system- Pulmonary embolus, lung disease V/Q mismatch COPD, pneumonia, asthma, atelectasis, PE Shunt (Extreme V/Q mismatch) PDA, ARDS, Pulmonary Edema Diffusion limitation ARDS, fibrosis, interstitial lung disease Hypoventilation Lung disease, CNS, chest wall problem Airway/ alveoli obstruction Asthma, emphysema, bronchitis, cystic fibrosis CNS – (Decr. Resp. drive) drugs and brainstem injury Decreased Chest Wall movement Flail chest, fractures, scoliosis, massive obesity Neuromuscular Conditions Cervical cord injury, ALS, Guillian Barre

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