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Oxygen must be moved into the lungs where it.......
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Chapter 11 Egans
Gas Exchange and Transport
| Question | Answer |
|---|---|
| Respiration | process of getting O2 into the body for tissue utilization and removal of CO2 into the atmosphere |
| Oxygen must be moved into the lungs where it....... | diffuses into the pulmonary circulation and is transported into the blood to the tissues |
| Carbon dioxide builds up into the tissues because of..... | metabolism |
| Carbon dioxide diffuses into.... | capillary blood before being carried to the lung for exchange with alveolar gasses |
| Gas movement between lungs and tissues occure by? | simple diffusion |
| What is the diffusion gradient for oxygen? | normal atomospheric inspired partial pressure (PIO2) of 159 mm Hg to a low point of 40 mm Hg or less in the capillaries |
| What is the final gradient for oxygen infusion into the cell? How many mm Hg? | intracellular PO2 (5 mm Hg) |
| What is the diffusion gradient for carbon dioxide? | highest in the cells 60 mm Hg and lowest to room air 1 mm Hg |
| What is the difference of the oxygen diffusion gradient compared to the carbon dioxide diffusion gradient. | Oxygen has a cascade gradient moving from atmosphere to Intracellular. Carbon dioxide moves from intracellular to the atmosphere. |
| The carbon dioxide diffusion gradients cascade causes..... | CO2 to move from tissues into the venous blood, which is transported to the lungs and out to the atmosphere |
| Alveolar partial pressure of carbon dioxide (PACO2) | varies directly with the body's production of CO2 and inversely alveolar ventilation |
| What factor is used to convert VCO2 from STPD to BTPS? | 0.863 |
| what is the formula used to convert VCO2 from STPD to BTPS? | PACO2= VCO2 * 0.863 --------------- VA (alveolar ventilation) |
| Normally complex respiratory control mechanisms maintain the PACO2 within a range of? | 35-45mm Hg |
| If carbon dioxide production increase as with exercise or fever what happens to ventilation? | ventilation automatically increases to maintain PACO2 within normal range |
| What is the most important facto in determining the alveolar partial pressure of oxygen (PAO2)? | inspired partial pressure of oxygen (PIO2) |
| Once oxygen is in the lungs it is diluted by what 2 things? | water vapor and carbon dioxide |
| What is the alveolar air equation formula? | PAO2= FIO2*(PB -47)-(PACO2/0.8) |
| According to Dalton's law the partial pressure of alveolar nitrogen must.... | equal the pressure it would exert if it alone were present |
| What is the formula to compute the partial pressure of alveolar nitrogen (PAN2)? | PAN2= PB-(PAO2+PACO2+PH2O) |
| The only partial pressures that change int he alveolus are? Why? | oxygen and carbon dioxide. Because both water vapor tension and PAN2 remain constant. |
| Based on the alveolar air equation if the FIO2 remains constant the the PAO2 will? | vary inversely with PACO2 |
| When a patient is breathing room air what is the sum of the alveolar PO2 and alveolar PCO2? | 140 mm Hg |
| Neural control mechanisms and increased work of breathing prevent decreases in PaCO2 much below? | 15-20mm Hg |
| If patient is breathing room air at sea level the RT should or shouldn't exspect to see a PaO2 any higher that 120 mm Hg during hyperventilation? | should not exspect any higher than 120 mm Hg |
| PO2 values higher than 120 mm Hg indicate? | patient is breathing supplemental oxygen |
| Diffusion | process of gas molecules moving from an area of high partial pressure to low partial pressure |
| In order for oxygen to diffuse into and out of the lung and tissues, O2 and carbon dioxide must move through.... | barriers |
| Alveolar capillary membrane | the barrier to gaseous diffusion in the lung |
| What 3 barriers must be penetrated in order for O2 and CO2 to move btw alveoli and pulmonary capillary blood? | alveolar epithelium, intersitial space, capillary endothelium |
| Fick's first law of Diffusion | the greater the surface area, diffusion constant, and pressure gradient, the more diffusion will occur |
| Diffusion in the normal lung mainly depends on? | gass pressure gradients |
| What must exist in order for gas exchange to occure between the alveoli and pulmonary capillaries? | difference in partial pressures |
| In pulmonary diffusion Alveolar PaO2 averages how many mm Hg? | 100 mm Hg |
| In pulmonary diffusion Mean PaCO2 is approximately how many mm Hg? | 40 mm Hg |
| In pulmonary diffusion PvO2 is how many mm HG? | 40 mm Hg |
| In pulmonary diffusion PvCO2 is how many mm Hg? | 46 mm Hg |
| The pressure gradient for oxygen diffusion into the blood is approximately? | 60 mm Hg |
| Does carbon dioxide diffuse faster or slower across the alveolar-capillary membrane than oxygen? Why? | 20 times faster. Because of its much higher solubility in the plasma. |
| Diffusion time in the lungs depends on? | rate of pulmonary blood flow |
| How long does blood take to flow through the pulmonary capilary? | 0.75 seconds |
| Low concentrations of what are used more commonly to measure diffusing capacity of the lung? | carbon monoxide (0.1%-0.3%) |
| The PaO2 of healthy person breathing at sea level is approximately how much less than the calculated PaO2? | 5-10 mm Hg less |
| 2 factors that account for the 5-10 mm Hg difference in calculated PaO2 are? | 1.right to left shunts in pulmonary and cardiac circulation 2.regional differences in pulmonary ventilation and blood flow |
| What are the 2 anatomilace right to left shunts that exist in a normal human being? | 1.bronchial venous drainage 2.thebsian venous drainage |
| What does a right to left shunt cause poorly oxygenated venous blood to do? | causes it to move directly into the arterial circulation, lowering the oxygen content of the arterial blood. |
| What is the ideal ventilation and perfusion ratio? | 1.0 |
| A high ventilation/perfussion ratio indicates that? Low V/Q? | ventilation is greater than normal, perfusion is less than normal, or both. LOW- ventilation is less than normal, perfusion is greater than normal, or both. |
| In areas with low V/Q the alveolar PO2 is? PCO2 is? | alveolar PO2 lower, PCO2 higher than normal |
| Area with ventilation but no blood flow represent? | dead space |
| Alveolar shunts | V/Q ratio values of zero not normal, distinguished from true anatomical shunts. |
| Regional differences in V/Q ratios in the normal lung are caused by? | gravity and most evident in the upright position |
| Does perfusion increase or decrease farther down the lung? | increases. Bases receive nearly 20 times as much blood flow than the apexes. |
| Does ventilation increase or decrease farther down in the lung bases? | increases. Four times as much ventilation than apexes. |
| V/Q at apexes of lungs | ventilation exceeds blood flow resulting in high V/Q (3.3), high PO2 (132 mm Hg), low PCO2 (32 mm Hg). |
| V/Q at bases of lungs | blod flow increases more than ventilation due to gravity |
| (Oxygen Transport)blood carries O2 in what 2 forms? | 1.dissolved in plasma and erythrocyte fluid. 2. majority is carried in combination with hemeglobin inside the RBC |
| Formula for Dissolve oxygen in blood? | Dissolved oxygen= PO2*0.003 |
| Deoxygenated hemoglobin serves as a what in transport? | important blood buffer for hydrogen ions, important in carbon dioxide transport |
| Oxyhemoglobin | oxygen molecules bind to Hb by way of ferrous iron ion and coverted to it's oxygenated state |
| In whole blood each gram of normal Hb can carry how many ml of oxygen? | 1.34 ml |
| Hb increases the oxygen carrying capacity of the blood by how much? | 70 fold as compared to plasma alone |
| Saturation | measure of proportion of available Hb that is actually carrying oxygen |
| Hb saturation formula | SaO2=[HbO2 / Total Hb]*100 |
| HbO2 curve | relationship btw PaO2 and SaO2 is S shaped |
| How to find the total oxygen content of blood? | total oxygen content of bloo equals the sum of that dissolved and chemically combined with Hb |
| Formula for Total oxygen content of blood | CaO2=(0.003*PO2)+(Hbtot*1.34*SO2) |
| What is the normal CaO2 concentration? | 16-20 ml/dl |
| What is the difference between the arterial and venous oxygen contents? | 5 ml/dl |
| C(a-v)O2 | arteriovenous oxygen contents difference. Amount of O2 given up by every 100mL of blood on each pass through thet tissues |
| Fick equation | The C(a-v)O2 combined with total-body oxygen to calculate cardiac output |
| Normal range for cardiac output | 4-8L/min in adult |
| According to Ficks equation if the O2 consumption remains constant a decrease in cardiac ouput will do what to the arteriovenous oxygen contents difference? | increase the C(a-v)o2 |
| According to ficks equation if the cardiac output rises and oxygen consumption reamins constant what will happen to the arteriovenous oxygen contents difference? | C(a-v)O2 will decrease |
| What are some factors other than HbO2 curve that affect oxygen unloading and loading? | blood pH, body temp, erythrocyte concentration of certain organic phosphates, variations in the structure of Hb, chemical combinations of Hb with substances other than O2 |
| Bohr effect.....What does it do? | impact of changes in blood pH on Hb affinity for O2. It alters the position of the HbO2 dissociation curve. |
| A low pH shifts a curve to the? | right |
| A high pH shifts a curve to the? | left |
| When blood ph drops and shifts the curve to the right the Hb saturation for a given PO2... | falls |
| As blood pH rises and the curve shifts to the left Hb saturation for a given PO2... | rises |
| As blood in the tissue picks up CO2, pH falls and the HbO2 curve shifts to the? Does it increase or decrease the affinity of Hb for oxygen? | right. decreasing the affinity of Hb for O2. |
| With a lower of the affinity of Hb for O2 Hb readily gives up what to the tissues? | O2 |
| Venous blood returns to the lungs and the pH does what? This shifts the curve to the? Does this increase or decrease the affinity of Hb for oxygen? | Increases. left. Increasing the affinity of Hb for O2 and enhancing its uptake from the alveoli. |
| A drop in body temperature shifts the HbO2 cureve to the? | left, increasing Hb affinity for O2. |
| As body temperture rises the curve shifts to the? | right, affinity of Hb for O2 decreases. |
| At the tissues, temperature changes are directly related to? | metabolic rate |
| Organic phosphate 2,3-diphosphoglcerate | found in abundance in the RBC's and forms a loose chemical bond with the globin chains of deoxygenated Hb. |
| 2,3-DPG does what to the molecule in it's deoxygenated state? | It stablilizes the molecule and reuces it's affinity for oxygen |
| What would happen if we didn't have 2,3-DPG? | Hb affinity for O2 would be so great that normal O2 unloading would be immpossible |
| Increased 2,3 DPG concentrations shift the HbO2 curve to the? Promoting what? | right. Oxygen unloading |
| Low 2,3-DPG concentrations shift the curve to the? And does what to the Hb affinity for O2? | left. Increasing the Hb affinity of O2 |
| Alkalosis, chronic hypoxemia, and anemia all increase or decrease 2,3-DPG concentrations? | increase and promote oxygen unloading |
| Acidosis does what to 2,3-DPG? | lowers the level of DPG and a greater affinity of Hb for O2. |
| What happens to DPG in banked blood? | It decreases in concentration over time and after a week of storage there is less than 1/3 of the normal value of DPG. This shifts the HbO2 curve to the left decreasing availability of oxygen to the tissues. |
| What happens with large transfusions of banked blood that is more that a few days old? | It impairs oxygen delivery even in the presence of a normal PO2 |
| When do structural abnormalities of hemoglobins occur? | when the amino acid swquence in the molecule's polypeptide chains varies from normal. |
| What percent of the circulating hemoglobin are abnormal in a healthy individual? | 15-40% |
| Sickle Cell hemoglobin? | abnormal hemoglobin that is less soluable and causes the hemoglobin to become suceptible to polymerization and precipitation when deoxygenated |
| What events cause the hb to crystalize and the RBC to become hardened and curved like a sickle? | dehydration, hypoxia, acidosis |
| Patients with sickle cell are prone to? | vaso-occlusive disease and anemia. |
| Acute chest syndrome? Symptoms? | most common cause of death in patients with sickle cell anemia. Symptoms:acute chest pain, cough, dyspnea, infiltrate on the CXR and develops progressive anemia and hypoxemia |
| Methemoglobin | abnormal form of the molecule where the heme-complex normal ferrous iron ion loses an electron and oxidizes to its ferric state. |
| What happens in the ferric state of methemoglobin? | iron ion cannot combine with oxygen |
| What happens as a result of the iron ion not being able to combine with oxygen in the ferric state of methemoglobin? | a special form of anemia results called methhemoglobinemia |
| What is the most common cause of methemoglobinemia? | therapeutic use of medications containg nitrogen. Nitric oxide, nitroglycerine, lidocaine |
| What color is the blood of a patient who has methemoglobin? | brown, slate-gray skin coloration |
| How do we confirm that a patient has methemoglobin? | spectrophotometry |
| How is methemoglobin treated? | reducing agents such as methylene blue or absorbic acid when the blood level exceeds app. 40% |
| Carboxyhemoglobin | Hb with carbon monoxide |
| Hemeglobins affinity for carbon monoxide is how much more greter than it is for oxygen. | 200 times greater |
| The combination of carbonmonoxide shifts the HbO2 curve to the? | left. Impeding oxygen delivery to the tissues |
| What is the treatment for carbon monoxide poisoning? | giving the patient as muxh oxygen as possible because oxygen reduces the half-life of carboxyhemoglobin. Sometimes a hyperbaric chamber is used |
| Fetal Hemoglobin | blood having a high proportion of an Hb varian during fetal life and for up to 1 year after birth |
| Fetal hemoglobin causes a shift to the? | left. HbF has a greater affinity for oxygen than does normal adult Hb |
| What does the leftward shift of fetal hemoglobin aid in doing? | aids oxygen loading at the placenta |
| The PO2 values to the fetus in utero are high or low? | low |
| What happens after birth with the Fetal hemoglobin? | this enhanced oxygen affinity is less advantageous after birth. Over the first year of life HbF is gradually replaced with normal Hb. |
| P50 | partial pressure of oxygen at which the Hb is 50% saturated, standardized to a pH of 7.40 |
| What is a normal P50? | 26.6 mm Hg |
| Conditions that cause an decrease in Hb affinity for oxygen cause a shift to the? | right. |
| Conditions with an increase in affinity cause a shift to the? What happens to P50? | left. P50 decreases to lower than normal |
| How much carbon dioxide is carried in the blood? | 45-55 ml/dl |
| In what three forms is carbon dioxide carried in the blood? | dissolved in physical solution, chemically combined with protein, ionized as bicarbonate |
| Dissolved carbon dioxide plays an important role in? How much is released at the lungs? | transport. 8% |
| Carbon dioxide hasa the capacity to chemically cobine with free amino groups of protein molecules forming a? | carbamino compound |
| what is carbaminohemoglobin? what percentage does it transport? | A compound of carbon dioxide and hemoglobin, which is one of the forms in which carbon dioxide exists in the blood. 12% of the total carbon dioxide. |
| Approximately what percent of the blood carbon dioxide is transported as bicarbonate? | 80% |
| Hydrolysis | chemical process in which a molecule is cleaved into two parts by the addition of a molecule of water |
| What does the hydrolysis of CO2 form? | carbonic acid |
| What enzyme enhances the hydrolysis reaction? | carbonic anhydrase |
| Where does the majority of hydrolysis occur? | RBC |
| What happens when hydrolysis of carbon dioxide continues for a while? | Bicarbonate begins to accumulate in teh RBC |
| How is equilibrium obtained when bicarbonate accumulates in the RBC? | by the chloride shift |
| Chloride shift | The movement of chloride ions from the plasma into red blood cells as a result of the transfer of carbon dioxide from tissues to the plasma, a process that serves to maintain blood pH. |
| Haldane effect | influence of oxyhemoglobin saturation on CO2 dissociation |
| What is the Haldane effect a result of? | changes in the affinity of Hb for CO2 as a result of its buffering of Hydrogen ions |
| A high SaO2 decreases or increases the blood's capacity to hold carbon dioxide? Does this help in loading or unloading this gas at the lungs? | Decreases. unloading |
| What is the formula for oxygen delivery? | DO2=CaO2*Qt |
| Hypoxia | when oxygen delivery falls short of cellular needs |
| In what three ways will hypoxia occur? | If the arterial blood O2 content is decreased, if cardiac output or perfusion is decreased, or if abnormal cellular function prevents proper uptake of O2 |
| When does hypoxemia occur? | when partial pressure of O2 in the arterial blood (PaO2) is decreased to lower than normal. |
| What things might a decreased PaO2 be caused by? | low ambient PO2, hypoventilation, impaired diffusion, V/Q imbalances, right to left anatomical or physiological shunting, aging, altitude |
| What is the approximate PaO2 at the age of 60? | 85 mm Hg |
| Mountain sickness | traveling to high altitudes which decreases the PaO2 causing hypoxia |
| Alveolar PO2 varies directly or indirectly with alveolar PCO2? | indirectly |
| Even when alveolar PO2 is normal disorders of the alveolar capillary membrane may limit diffuion of oxygen into the pulmonary bed thereby lowering the? Diseases that do this are? | PaO2. Interstitual edema, Pulmonary fibrosis |
| What is the most common cause of hypoxemia in patients with lung disease? | Ventilation perfusion imbalances |
| What happens when ventilation is greater than perfusion? | there is wasted ventilation, alveolar dead space |
| What happens when ventilation is less than perfusion? | ventilation perfusion ratio is low and blood leaves the lungs with abnormally low oxygen content |
| What does ventilation perfusion imbalances usually occur in lung disease? Why? | both excess wated ventilation and poor oxygentation. Because the imbalance impairs O2 exchange and PaO2 is reduced |
| What does a ventilation perfusion imbalance of 0 represent? | there is blood flow but no ventilation and is equivalent to a right to left anatomical shunt |
| To differentiat between hypoxemia caused by a V/Q imbalance and hypoxemia caused by shunting what do you do? | If the O2 is more than 50% and the PaO2 is less than 50% significant shunting is present. otherwise it is a V/Q imbalance |
| Formula for estimating the expected PaO2 in older adults | Expected PaO2=100.1-(0.323*Age in years) |
| For the arterial oxygen content to be adequate there also must be? | enough normal Hb in the blood |
| Can hypoxia occur if the Hb is low even when the PaO2 is normal? Why? | Yes. Because of low oxygen content in the arterial blood |
| What are the 2 hemoglobin deficiencies? | absolute, relative |
| What is absolute hemoglobin deficiency? | occurs when Hb concentration is lower than normal due to a low blood Hb concentration by either loss from hemorrhage or inadequate erythropoesis. |
| What is relative Hb deficiency? | caused by either displacement of O2 from normal Hb or prescence of abnormal Hb variants. |
| What can a low Hb content do to the oxygen carrying capacity of the blood? | seriously impair the oxygen carrying capacity of the blood |
| Hypoxia can still occur when the CaO2 is normal if? | blood flow is reduced |
| What are the 2 types of reduced blood flow? | circulatory failure(shock), local reduction in perfusion(ishemia) |
| What happens with prolonged shock? | causes irreversible damage to the central nervous system and eventual cardiovascular collapse |
| What 3 things can result from ishemia? | anaerobic metabolism, metabolic acidosis, eventual death of tissue |
| Dysoxia | form of hypoxia in which cellular uptake of O2 is abnormally decreased |
| What is an example of dysoxia? | cyanide poisoning. It disrupts intracellular system preventing cellular use of oxygen |
| Dysoxia also may occur when... | tissue oxygen consumption becomes dependent on O2 delivery |
| What leads to lactic acid accumulation and metabolic acidosis? | tissue extraction reaches a maximum and decreases delivery of O2 resulting in a oxygen debt due to oxygen demand exceeding oxygen delivery |
| In sepsis and ARDS oxygen debt may occur at normal levels of? | oxygen delivery |
| Any disorder that lowers alveolar ventilation relative to metabolic need impairs? | carbon dioxide removal |
| What does impaired CO2 removal by the lungs cause? | hypercapnia and respiratory acidosis |
| When does a decrease in alveolar ventilation occur? | minute ventilation is inadequate, dead space ventilation per minute increases, or a ventilation perfusion imbalance exists |
| Inadequate minute ventilation is caused by? | decreased tidal volume |
| Inadequate minute ventilation occurs in what types of conditions? | restrictive conditions: atelectasis, neuromuscular disorders, or conditions that impede thoracic expansion (kyphoscoliosis) |
| A decrease in RR is less common but may be present with respiratory center depression as in? | drug overdose |
| An increased dead space ventilation is caused by either? | rapid shallow breathing, or increased physiologic dead space (V/Q 0) |
| What does increased dead space ventilation cause? | the proportion of wasted deadspace increases and lowers alveolar ventilation and impairs CO2 removal |
| IN theory V/Q imbalance should cause a rise in PACO2. However many patients who are hypoxemic because of a V/Q imbalance have a low or normal PaCO2. What does this suggest? | V/Q imbalances have a greater effect on oxygenation than on carbon dioxide removal. |
| To compensate for high PCO2 values with V/Q imbalances what must happen? | patients minute ventilation must increase |
| Patients who can increase their minute ventilation with V/Q imbalance then to have? | normal or low PaCO2 combined with hypoxemia |
| Patients with an V/Q imbalance who cannot increase their minute ventilation are? when does this occur? | hypercapnic. This occurs only when V/Q imbalance is severe and chronic like with COPD |
| When a patient is hypercapnic what must happen for them to maintain a normal PaCO2? | they must sustain a higher than normal minute ventilation |
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