Oxygenation
Oxygenation is a critical physiological process that ensures the delivery of oxygen to tissues and the removal of carbon dioxide from the body. Both respiratory and cardiac systems work in harmony to maintain adequate oxygenation, making their proper function essential for overall health.
By the end of this section, you should know about:
- Respiratory Biochemistry
- Factors Influencing Stroke Volume and Cardiac Function
- The Cardiac Conduction System and Its Role in Heart Function
- Respiratory and Cardiac Alterations: Hypoventilation, Hyperventilation, and Hypoxia
- Cardiac Alterations: Conduction, Output, and Ischemia
Let’s take a closer look at them.
Test Your Knowledge
At the end of this section, take a fast and free pop quiz to see how much you know about Oxygenation.
Oxygenation: Respiratory Biochemistry
Respiration refers to the exchange of oxygen and carbon dioxide during cellular activity. Air leaves the atmosphere and enters the lungs, where oxygen exchanges carbon dioxide in the lungs through the lungs. Oxygenation requires airflow, circulation, and diffusion. Ventilation is the movement of air into and out of the lungs, facilitated by changes in pressure. The diaphragm, the main respiratory muscle, creates negative pressure in the lungs to force air into the lungs during respiration.
During perfusion, the cardiovascular system pumps oxygenated blood to the arteries and returns deoxygenated blood to the lungs. Diffusion allows respiratory gases to move along a concentration gradient. The proper functioning of the respiratory system, muscles and nerves, and central nervous system are essential for proper gas exchange.
Work of Breathing
Work of breath (WOB) is the effort required to expand and contract the lungs. Respiration is small and effective in healthy people. Stress, an active process, relies on chemical stimuli, while respiration is passive, dependent on lung dynamics. Certain vasoconstrictors increase the surface area of the lungs and prevent them from collapsing.
Lung diseases such as COPD impair elastic regression, reducing surfactant production, and increasing WOB. Conditions such as atelectasis cause muscle fibers to collapse, impairing the exchange of oxygen and carbon dioxide. Accessory muscles in the neck and chest can help expand lung tone but over time cause fatigue. Decreased lung volume, airway resistance (as seen in asthma), and prolonged use of associated muscles increase energy demands
Lung weight and pulmonary circulation
Lung weight—the number of waves, the number of residuals, and the force required—varies with age, sex, and health. Tidal volume is the air inhaled after normal breathing, and residual volume is the air remaining after forced expiration.
The pulmonary circulation carries blood through the lungs for gas exchange. Deoxygenated blood flows from the right ventricle to the pulmonary arteries and alveoli, where it is oxygenated. This oxygenated blood then returns to the left ventricle for systemic distribution. Normal blood flow depends on the pumping capacity of the right ventricle.
Respiratory Gas Exchange and Transport
Gas exchange takes place in the airways and alveoli. When seen in conditions such as pneumonia or infiltration, the stiffness of the muscle slows dilation and impedes oxygen delivery. In addition, diseases such as emphysema or surgery reduce the surface area available for gas exchange.
Oxygen transport depends on ventilation, blood flow, diffusion, and the ability of hemoglobin to carry oxygen. Hemoglobin binds to oxygen to form oxyhemoglobin, which breaks down and releases oxygen to the tissues. Similarly, carbon dioxide, a metabolic byproduct, is returned to the lungs. They are converted into carbonic acid, break down as ions, and are inhaled during respiration.
Regulation of Respiration
Respiratory regulation ensures adequate oxygen intake and carbon dioxide elimination during physiological processes such as exercise or illness. In the nervous system, the central nervous system controls the rate and rate of respiration, whereas pharmacokinetics depends on changes in blood oxygen, carbon dioxide, and pH levels and Chemoreceptors in the medulla, aorta, and carotid bodies sense these changes and stimulate ventilation to maintain adequate ventilation.
Cardiovascular Physiology
The cardiovascular system pumps oxygenated blood to the lungs and pumps oxygenated blood to the tissues of the body. The right ventricle pumps oxygenated blood to the lungs, while the left ventricle pumps oxygenated blood through the systemic tissues. As the blood circulates, oxygen and nutrients are exchanged for metabolic waste, which is removed by circulation back to the heart.
Myocardial Function and Blood Flow
The pumping activity of the heart ensures that oxygen is delivered to the tissues. In diastole, the ventricles fill and contract in systole, where stroke volume represents the volume of blood fired. Conditions such as bleeding or dehydration reduce blood volume and shock levels. The Frank-Starling law states that the contractile force increases as the coronary arteries dilate, but a diseased heart fails to follow this principle, resulting in heart failure.
Blood flow to the heart is unidirectional due to the action of the quadriceps. During diastole the atrial and ventricular valves open to allow blood to flow into the ventricles, and during systole the crescent valves open to allow blood to flow forward Partial systemic circulation Coronary circulation delivers oxygen and nutrients for the heart muscle, the left coronary artery plays an important role in supporting the left ventricle.
Systemic Circulation
Systemic circulation moves oxygen and nutrients through the tissues and removes waste products through the tissues. Oxygenated blood from the left ventricle flows into the capillaries, branching into capillaries where gas exchange takes place. Deoxygenated blood leaves the arteries, joins the large arteries, and returns to the right side of the heart to return to the lungs.
In summary, the respiratory and cardiovascular systems are intricately interconnected, working together to ensure the supply of oxygen, the exchange of gases, and the elimination of wastes necessary for the maintenance of life and any damage to these processes impairs oxygen delivery, causing important physiological consequences.
Acute Coronary Syndrome (ACS): A range of conditions associated with sudden, reduced blood flow to the heart, including unstable angina and myocardial infarction.
Afterload: The resistance the heart must overcome to pump blood out during systole, often affected by blood pressure and the tone of the vascular system.
Angina Pectoris: Chest pain or discomfort caused by reduced blood flow to the heart muscle, often associated with coronary artery disease.
Apnea: A temporary cessation of breathing, especially during sleep.
Atelectasis: Partial or complete collapse of the lung, often resulting in impaired oxygen exchange.
Bilevel Positive Airway Pressure (BiPAP): A noninvasive ventilation therapy that provides two levels of pressure, one for inhalation and one for exhalation, to assist breathing.
Bronchoscopy: A procedure in which a flexible tube is inserted into the airways to view the lungs and air passages, often used for diagnostic purposes.
Capnography: A monitoring tool that measures the concentration of carbon dioxide in exhaled air, used to assess ventilation and respiratory status.
Oxygenation: Factors Influencing Stroke Volume and Cardiac Function
Stroke volume, which directly affects heart dynamics, influences preload, postload, and myocardial contraction. Preload refers to the volume of blood in the left ventricle at end diastole, also known as end-diastolic volume. According to Starling’s law, the more the ventricular muscle dilates during filling, the stronger the contraction, and the greater the stroke Therapeutically, hemorrhagic conditions decrease preload by decreased circulating blood volume, subsequently reducing stroke volume and cardiac output Increases production.
Left ventricular resistance occurs during postload hemorrhage, and diastolic aortic pressure is a clinical sign. Conditions such as hypertension increase extrinsic metabolism, forcing the heart to work harder and increasing cardiac workload. Myocardial contractility, which measures the contractile capacity of the myocardium, also significantly affects stroke rate. In addition to poor ventricular contractility, which often results from cardiac injury such as acute myocardial infarction (MI), stroke volume and cardiac output decrease, aging myocardium thickens, and ventricular contractility slows and it contracts for a long time, again affecting the overall function of the heart
Cardiac output also plays a role because of the effect of heart rate on diastolic filling time. Persistent tachycardia (greater than 160 beats/min) results in a shorter duration of diastolic filling, reducing stroke volume and ultimately cardiac output Older adults exhibit a slower heart rate in response to stress, . often, it’s not really aging but physical deconditioning. However, exercise remains beneficial for maintaining cardiac function at all ages.
Postural Drainage: A technique used in chest physiotherapy to help clear mucus from the lungs by positioning the body in specific ways.
Preload: The volume of blood in the ventricles before contraction, which affects the stroke volume and cardiac output.
Pursed-lip Breathing: A breathing technique used to slow exhalation and improve oxygenation, often used by patients with chronic obstructive pulmonary disease (COPD).
Stroke Volume: The amount of blood pumped by the heart in one beat.
Surfactant: A substance produced by the lungs that reduces surface tension and helps prevent the alveoli from collapsing.
Tracheostomy: A surgical opening in the neck to create an airway, often used for long-term respiratory support.
Ventilation: The process of moving air in and out of the lungs to facilitate gas exchange.
Ventilator-Associated Pneumonia (VAP): A type of pneumonia that occurs in patients who are on mechanical ventilation for an extended period, typically due to aspiration or infection.
Ventricular Fibrillation: A life-threatening arrhythmia in which the heart’s ventricles quiver rather than contracting effectively, leading to the loss of effective circulation.
Ventricular Tachycardia: A rapid heart rate originating from the ventricles, which can be life-threatening if sustained.
Wheezing: A high-pitched whistling sound during breathing, often heard in conditions like asthma or bronchitis, caused by narrowed airways.
Oxygenation: The Cardiac Conduction System and Its Role in Heart Function
The rhythmic contraction of the heart depends on the cardiovascular system that generates and conducts electrical impulses. The autonomic nervous system influences this system, with excitatory fibers increasing, and visceral fibers slowing. The motor system originates at the sinoatrial (SA) node, over the right natural pacemaker of the heart. Initiate sensations at a resting pace of 60–100 beats per minute. These impulses travel through the atrium to the atrioventricular (AV) node, where the atria are emptied before ventricular delay. The impulse then passes through clusters of His and Purkinje fibers, producing ventricular contraction.
The electrocardiogram (ECG) records the electrical activity of this mechanical system. The P wave indicates atrial depolarization, followed by atrial contraction. The PR interval indicates the time when impulses from the SA node travel through the AV node and ventricles, with a total duration of 0.12–0.2 seconds the posterior QRS complex of the node represents ventricular depolarization, followed by ventricular contraction, whereas the QT interval determines the period of ventricular depolarization and repolarization Changes in the QT interval are associated with electrolyte imbalances and certain medications.
Physiological Factors Affecting Oxygenation
Oxygenation is influenced by ventilation, circulation, and ventilation. Many physiological processes affect these processes, including decreased oxygen saturation, hypovolemia, decreased stimulation oxygen levels, increased metabolic rate and hemoglobin transport of oxygen to tissues species in particular, reducing oxygen delivery in conditions such as anemia or carbon monoxide (CO) poisoning. Low hemoglobin levels in anemia cause fatigue, shortness of breath, tachycardia and weakness, while CO poisoning occurs when hemoglobin is tightly bound to CO, preventing oxygen delivery.
Hypovolemia from shock or excessive dehydration leads to decreased circulation, resulting in tissue oxygen hypoxia. The body compensates by increasing heart rate and muscle contraction to keep the heart working. Decreased oxygen levels caused by airway obstruction, high altitude, or low ventilation also result in decreased oxygen delivery. Furthermore, the elevated metabolic rates observed during influenza, pregnancy, wound healing, or exercise increase oxygen demand. Prolonged atrial fibrillation leads to tissue damage including respiratory muscles and increased carbon dioxide production, thus requiring greater respiratory effort to maintain oxygen levels.
Conditions Affecting Chest Wall Movement and Oxygenation
Any condition in which the chest wall does not move interferes with ventilation and oxygenation. Increased intrauterine pressure during pregnancy, especially in the third trimester, decreases breathing, leading to dyspnea and fatigue obesity also increases lung weight and its chest wall alignment decreases, often leading to obstructive sleep apnea and oxygen deprivation. Obese patients are more likely to develop atelectasis and pneumonia after surgery due to decreased bronchial expansion and residual alveolar fluid.
Musculoskeletal abnormalities such as pectus excavatum, scoliosis, and kyphosis hinder chest wall expansion. Injuries such as chest trauma caused by multiple broken ribs can cause chest wall instability, resulting in abnormal lung tissue and hypoxia during respiration Postoperative incisions and opioids damage the chest wall the movement and breathing again. Neurovascular diseases such as myasthenia gravis and Guillain-Barré syndrome weaken the respiratory muscles, leading to hypoventilation, atelectasis, and hypoxemia as well as neuromuscular changes such as the medulla oblongata or spinal cord injury, disturbance of systems and nerves controlling respiration, decreased lung volume, . and decreased oxygen saturation.
Chronic Diseases and Alterations in Respiratory Functioning
Chronic lung diseases, such as emphysema, severely impair oxygen delivery by altering lung mechanics. Overuse of the accessory muscles and air trapping expose a barrel chest, flattening the chest and hyperextending the chest areas. This distinguishes between hypoxemia and hypercapnia. Overall, diseases affecting ventilation or oxygen delivery cause three major changes in respiratory function: hypoventilation, hyperventilation, and airtightness
Hypoventilation occurs when ventilation is insufficient to meet the body’s oxygen needs or to eliminate sufficient carbon dioxide, causing CO2 to be over-expressed through excess ventilation relative to elevated PaCO2 levels, causing hypocapnia. Hypoxia, a condition of arterial oxygen deficiency, is usually measured by arterial blood gas or pulse oximetry. Prolonged hypoxemia can trigger adaptive mechanisms such as cell proliferation that increases platelet production to improve oxygen transport.
Together, these factors underscore the critical importance of maintaining adequate ventilation, perfusion, and oxygen transport to meet the body’s metabolic demands. Understanding these physiological, developmental, and pathological influences enables better clinical management of conditions impacting oxygenation and cardiac function.
Myocardial Ischemia: Reduced blood flow to the heart muscle, often due to a blockage in the coronary arteries, leading to chest pain (angina).
Nasal Cannula: A device used to deliver oxygen to a patient through two small prongs that sit in the nostrils.
Nebulization: A process of turning liquid medication into a mist to be inhaled into the lungs, often used for respiratory conditions like asthma.
Noninvasive Positive-Pressure Ventilation (NPPV): A type of ventilation support that delivers air pressure to the airways without the need for invasive procedures like endotracheal intubation.
Normal Sinus Rhythm (NSR): The normal rhythm of the heart, characterized by regular heartbeats at a rate of 60–100 beats per minute.
Orthopnea: Difficulty breathing when lying flat, often relieved by sitting or propping up the upper body.
Perfusion: The process of delivering oxygen and nutrients to tissues via the bloodstream.
Pneumothorax: The presence of air in the pleural space, causing lung collapse.
Oxygenation: Respiratory and Cardiac Alterations: Hypoventilation, Hyperventilation, and Hypoxia
Hypoventilation
Hypoventilation occurs when air-ventilation is insufficient to meet the body’s oxygen needs or to eliminate sufficient carbon dioxide, resulting in CO2 storage Atelectasis is alveolar collapse that prevents normal exchange of oxygen and carbon dioxide, because too little air and enables overdose of airborne Oxygen in patients with chronic obstructive pulmonary disease (COPD) can has caused hypo ventilation. These patients rely on low arterial oxygen saturation (PaO2) to stimulate respiration due to insensitive CO2 chemoreceptors. These vessels can be occluded by more oxygen than 1–3 L/min (24%-28%), leading to persistent CO2 retention, respiratory acidification, and, if left untreated, asthma stops Symptoms of hypoventilation include altered mental status, muscle weakness, and cardiac arrhythmias, which, if left uncorrected, lead to dizziness, unconsciousness, and death.
Hyperventilation
Hyperventilation occurs when aerobic CO2 is reduced faster than cellular metabolism. The condition is usually caused by severe anxiety, infection, chemicals, or an acid-base imbalance. For example, fever increases metabolism, increases CO2 production, and stimulates rapid breathing. Drugs can also be used to induce hyperventilation, as in salicylate poisoning or amphetamine use, both of which increase CO2 production. Metabolic acidosis, like diabetic ketoacidosis, provokes hyperventilation as the body tries to compensate by reducing CO2 and carbonic acid levels Clinical symptoms of hypoxia include rapid breathing, shortness of breath shortness of breath, lumps and cramps in the body, light-headedness, confusion in severe cases and loss of consciousness.
Hypoxia
Hypoxia refers to the lack of oxygen in tissues at the cellular level, and is life-threatening if left untreated. This can occur for several reasons: decreased hemoglobin levels through decreased oxygen transport, decreased inspired oxygen levels (such as at high altitudes), deoxygenation a non-degradation (e.g., cyanide poisoning), decreased arterial oxygen delivery (e.g. pneumonia). ), inadequate venous perfusion (e.g., trauma), or poor ventilation (e.g., chest trauma). Early symptoms of hypoxia include nervousness, restlessness, dizziness, and decreased concentration, with increased heart rate and respiration as hypoxia progresses, fatigue and agitation develop, and decreased respiration due to muscles because of the fatigue of the. Blue discoloration of the skin and mucous membranes Cyanosis is a late sign of hypoxia, with central cyanosis indicating severe hypoxemia and peripheral cyanosis indicating hypoxemia.
Oxygenation: Cardiac Alterations: Conduction, Output, and Ischemia
Disturbances in Cardiac Conduction: Conduction disorders occur when electrical stimulation originates outside the sinoatrial (SA) node, causing irregularities. This arrhythmia can be caused by ischemia, valve dysfunction, anxiety, drug toxicity, electrolyte imbalance, or lifestyle factors such as caffeine, alcohol, tobacco use Arrhythmic tachycardia (heart rate >100 bpm); , bradycardia (heart rate <60 bpm), early There is a strong pulse, or block of pulse. Both tachydysrhythmias and brady dysrhythmias result in decreased cardiac output, which impairs diastolic filling or overall heart rate. Atrial fibrillation, which is common in older adults, causes irregular atrial fibrillation due to aggressive atrial fibrillation from multiple sources, while ventricular anomalies arising in the ventricles are life-threatening due to risk a there is sudden cardiac death due to decreased cardiac output.
Decreased myocardial pumping activity alters cardiac output which is a hallmark of heart failure. In left ventricular failure, left ventricular dysfunction reduces cardiac output, leading to fatigue, dizziness, and confusion due to arterial hypoxia thus Blood returns to the pulmonary circulation, causing edema, pulmonary fissures, dyspnea, and paroxysmal nocturia. Conversely, right-sided heart failure, often secondary to pulmonary disease or chronic left-sided failure, causes elevated pulmonary vascular resistance. The right ventricle weakens under increased workload, leading to systemic congestion with clinical signs such as weight gain, distended neck veins, hepatomegaly, splenomegaly, and peripheral edema.
Valvular Dysfunction
Valvular heart disease involves either constriction (hardening of the valves) or regression (failure of the valves to close). Vasoconstriction restricts blood flow, forcing the ventricles to work harder, eventually leading to hypertrophy and possibly heart failure. Recoil causes blood to return to nearby chambers, creating vessels. For example, mitral regurgitation causes blood to flow back into the atria during ventricular contraction, affecting cardiac performance.
Myocardial Ischemia, Angina, and Myocardial Infarction
Myocardial ischemia results from an imbalance between oxygen supply and demand, often leading to angina or myocardial infarction (MI). Angina pectoris presents as chest pain—painful, sharp, or pressure-like—often radiating to the arms, jaw, neck, or back. It usually lasts 3–5 minutes, is triggered by activities that increase oxygen demand, and is relieved by relaxation or vasodilators such as nitroglycerin. In contrast, myocardial infarction or acute myocardial infarction develops as ischemia progresses, causing irreversible myocardial cell death after 20 minutes
M.I. However, women often present with nonspecific symptoms such as fatigue, dyspepsia, dyspnea, and back or jaw pain. Women are at increased risk of dying within one year after a heart attack because of delays in diagnosis and differences in symptom presentation.