Pathophysiology

Pathophysiology Chapter 8

Objectives • Cellular Metabolism • Aerobic • Anaerobic • Components necessary for adequate perfusion

Aerobic metabolism. • Cellular respiration – Process through which the cells break down glucose to produce energy (ATP) • Aerobic respiration is cellular respiration in the presence of oxygen • Glycolysis – Process through which glucose is broken down into pyruvic acid molecules • Occurs in the cytosol • Releases small amount of energy (2 moles of ATP) • Process continues in the mitochondria in the presence of oxygen to release more amounts of energy (36 moles of ATP) • By-products produce heat, carbon dioxide, and water

Anaerobic Metabolism • Cellular respiration without oxygen • The pyruvic acid is converted to lactic acid • By-products are lactic acid and 2 moles of ATP • High levels of acid inactivate enzyme function, disrupt cell membranes, and lead to cell death • Sodium/potassium pump failure

The sodium/potassium pump. Energy (ATP) is required to pump sodium molecules out of the cell against the concentration gradient. Potassium then moves with the gradient to flow into thecell. Sodium and potassium are exchanged in a continuous cycle that is necessary for proper cell function. The cycle continues as long as the cells produce energy through aerobic metabolism. When insufficient energy is produced, through anaerobic metabolism, the sodium/potassium pump will fail and cells will die.

Composition of Ambient Air • Perfusion is delivery of oxygen, glucose, and other substances to the cells and elimination of waste products from the cells • Concentration of ambient air – determines the proportion of oxygen molecules that end up in the alveoli for gas exchange • Should be at least 21% • Lower means less oxygen available for metabolism • Increasing concentration of oxygen will; • FiO2 is the fraction of inspired oxygen administered to a patient who is breathing on their own. • FDO2 is a fraction of delivered oxygen administered to a patient by a ventilation device, for a patient that is not able to breath on their own. • Toxic gases • Some displace oxygen and can suffocate • Some disrupt the ability of the blood to carry adequate amounts of oxygen • Some interfere with the cells ability to use oxygen

Patency of Airway • A patent airway is one that is not obstructed • Nasopharynx • Oropharynx and Pharynx • Epiglottis • Larynx • Trachea and Bronchi An obstructed airway can occur at any of these structures.

Respiratory Compromise associated with Mechanics of Ventilation • Boyle’s Law applied to ventilation • An increase in pressure will decrease the volume of gas • A decrease in pressure will increase the volume of gas

Compliance and Airway Resistance • Compliance – Measure of the ability of the chest wall and lungs to stretch, distend, and expand • Airway resistance – The ease of airflow down the conduit of airway structures leading to the alveoli • Pleural space – Any break creates negative pressure, drawing air into the pleural space • Ensure to occlude any open chest wound early in the primary assessment of a patient

Minute ventilation • Minute ventilation – the amount of air moved in and out of the lungs in one minute • Minute ventilation = tidal volume (VT) X frequency of ventilation (f/minute) Adult tidal volume is ~ 500 mL and breathes ~ 12 per minute Minute ventilation = 500 mL X 12/minute Minute ventilation = 6,000 mL or 6 L/minute • Frequency of ventilation is the number of ventilations per minute • A decrease in tidal volume or frequency of ventilations will decrease the minute ventilation • A decrease in the minute ventilation will reduce the amount of air available for gas exchange in the alveoli and lead to cellular hypoxia

Alveolar Ventilation The amount of air moved in and out of the alveoli in one minute Dead air space (VD) consists of anatomical areas in the respiratory tract where air collects during inhalation Alveolar ventilation = (tidal volume – dead air space) X frequency of ventilation/minute Alveolar ventilation = (VT – VD) X f/minute Average adult tidal volume of 500 mL at 12/minute Alveolar ventilation = (500 mL – 150 mL) X 12/minute Alveolar ventilation = 4,200 mL or 4.2 L/minute

Respiration is controlled by the autonomic nervous system. Receptors within the body measure oxygen, carbon dioxide, and hydrogen ions and send signals to the brain to adjust the rate and depth of respiration. • Chemoreceptor’s monitor pH, carbon • dioxide, and oxygen levels in arterial blood • Central are most sensitive to carbon • dioxide and changes in the pH of the CSF • Peripheral are more sensitive to the level • of oxygen in arterial blood • Hypoxic drive is a condition which • hypoxia becomes the stimuli for ventilation • in place of hypercarbia • Lung receptors provide impulses to regulate respiration • Irritant receptors • Stretch receptors • J-receptors • Respiratory centers in the brain stem; • Dorsal respiratory group (DRG) • Ventral respiratory group (VRG) • Apneustic center • Pneumotaxic center

Ventilation/Perfusion Ratio • Ventilation/Perfusion (V/Q) • is the amount of ventilation the • alveoli receive to the amount of • perfusion through the capillaries. • Pressure imbalances • Pressure in alveoli exceeds the • B/P in the capillary bed • Results in poor pulmonary perfusion, • hypoxemia, and cellular hypoxia • Ventilatory disturbances • Less oxygen available to the alveoli • for the amount of blood flowing • through capillaries, less oxygen will be • delivered to the cells. • Can lead to hypoxemia and cellular • hypoxia • To manage focus on improving • ventilation and oxygenation

Perfusion of the pulmonary capillaries is affected by pressure within the alveoli and pressure within the capillaries. • Perfusion disturbances • Adequate oxygenation but not • enough blood due to decreased • blood flow = less oxygen delivered • Can lead to severe cellular hypoxia • To manage, focus on increasing the • blood flow through pulmonary • capillaries, the availability of the • hemoglobin, and the delivery of • oxygen to the cells.

Transport of Oxygen and Carbon Dioxide by the blood • A disturbance by lead to cellular hypoxia and hypercarbia • Cellular hypoxia – lack of oxygen available to the cells • Hypercarbia – Build-up of carbon dioxide in the blood • Oxygen transport • 1.5 to 3% is dissolved in plasma • 97 – 98.5% is transported by attaching to hemoglobin molecules • Hemoglobin – a protein molecule that has four iron sites for oxygen to bind to. • Oxyhemoglobin – an oxygen molecule once it binds with hemoglobin • Deoxyhemoglobin – a hemoglobin molecule without any oxygen attached to it. • Carbon Dioxide transport • 7% dissolved in plasma • 23% is attached to hemoglobin • 70% is in the form of bicarbonate

Alveolar/capillary gas exchange • Gases move from higher concentrations to lower • Oxygen moves from alveoli into capillaries, • carbon dioxide moves from capillary to alveoli • Carbon dioxide rich air is then expelled, • oxygen is carried to the left atrium of the heart, then • throughout the body • Cell/capillary gas exchange • Oxygenated blood from the left ventricle travels through an artery to arterioles to • capillaries • In capillaries, oxygen breaks free of hemoglobin and diffuses out of the plasma to • the cell • In capillaries, carbon dioxide leaves the cell, into the capillary, dissolves, attaches • to hemoglobin, or converts to bicarbonate • Carbon Dioxide rich blood transports back to right atrium, to right ventricle, to lungs

Blood Volume Composition of blood • 45% is cells and protein • 55% is plasma Plasma suspends/carries formed elements in blood • 91% consists of water Remaining is proteins • Albumin • Antibodies • Clotting factors Formed elements include • Red blood cells • White blood cells • Platelets • Distribution of blood • Most is within the venous system • The venous system changes size to respond to changes in blood volume • It supplies the right side of the heart with an adequate volume of blood

Hydrostatic pressure • The force inside the vessel or capillary bed, generated by the contraction of the heart and blood pressure (B/P) • It pushes water out of the capillary, and can promote edema. • Plasma oncotic pressure • Is responsible for keeping fluid inside the vessels • It acts opposite from hydrostatic pressure because it pulls water into the capillary. • A balance must be maintained between the two pressures for equilibrium of fluid balance

Pump function of the Myocardium • Cardiac Output • The amount of blood ejected by the left ventricle in one minute • Cardiac output = heart rate X stroke volume • Heart rate • Number of times the heart contracts in one minute • influenced by the sinoatrial (SA) node along with hormones and automatic nervous system • Sympathetic & Parasympathetic nervous systems control cardiovascular control center in the brain stem • An increase in stimulation by sympathetic nervous system or a decrease in stimulation by the parasympathetic nervous system increases the heart rate • An increase in stimulation by parasympathetic nervous system or a decrease in stimulation from the sympathetic system decreases heart rate

Stroke volume • The volume of blood ejected by the left ventricle with each contraction • Preload is the pressure generated in the left ventricle at the end diastole • Frank Starling’s law of the heart describes that the stretch of the muscle fiber at the end of diastole determines the force available to eject the blood from the ventricle • Afterload is the resistance in the aorta that must be overcome by contraction of the left ventricle to eject blood

Systemic Vascular Resistance • The resistance offered to blood flow through a vessel • Basic measure is the diastolic blood pressure • Chronically elevated diastolic pressure will lead to heart failure • Influenced by the autonomic nervous system • Sympathetic – causes constrict • Parasympathetic - dilation • Systemic Vascular Resistance effect • on Pulse Pressure • An increase in the resistance • increases the diastolic blood pressure • A decrease in the resistance • decreases the diastolic blood pressure • Pulse pressure is the difference • between the systolic and diastolic • blood pressure readings.

Microcirculation is the flow of blood through the smallest blood vessels: arterioles, capillaries, and venules. Precapillary sphincters control the flow of blood through the capillaries. • Arterioles control the • movement of blood into • the capillaries • Metarterioles connect arterioles • and venules • Precapillary sphincters control • movement of blood • Control of blood flow through • capillaries • Local factors • Neural factors • Hormonal factors

Blood Pressure Blood Pressure (B/P) = cardiac output (CO) X systemic vascular resistance (SVR) • An increase in CO or Heart Rate (HR) will increase B/P • A decrease in CO or HR will decrease B/P • An increase in stroke volume or the SVR will increase B/P • A decrease in stroke volume or the SVR will decrease B/P Perfusion of cells is linked to blood pressure • An increase in B/P will increase cellular perfusion • A decrease in B/P will decrease cellular perfusion Regulation of blood pressure by baroreceptors and chemoreceptors • Baroreceptors are stretch-sensitive receptors that detect changes in blood pressure and send impulses to the brain stem to make alterations in B/P • Chemoreceptors monitor the content of oxygen, carbon dioxide, and pH. They then cause the brain stem to trigger changes in the sympathetic nervous system

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Pathophysiology