RT 3005 CardioPulmonary The Diffusion of Pulmonary Gases

Describe the clinical connection associated with oxygen toxicity

can deveolp within 24 hours in response to high partial pressures of inspired O2 (Po2), and with longer exposure times to inspired oxygen concentrations (FIo2) above 0.50. The higher the inspired Po2 and the longer the exposure, the more likely oxygen toxicity will develop. Oxygen toxicity affects the lungs and the CNS. Pulmonary effects include tracheobronchitis, substernal chest pain, atelectasis, decreased vital capacity, decreased lung compliance, and decreased diffusing capacity. CNS effects include tremors, twitching, convulsions, coma, and death. CNS effects tend to occur only when a Pt is breathing O2 at pressures greater than 1 atm(hyperbaric medicine).

GAY-LUSSAC'S LAW

(P1 / T1 = P2 / T2) If V remains constant, P will vary proportional to T. Example: Container with 50 cmH2O T increased from 275K to 375K. Pressure in the container is increased to 68 cmH2O P2 = P1 x T2 = 50 cmH2O x 375K = 68 cm H2O T1 275K

BOYLE'S LAW

(P1 x V1 = P2 x V2) If T remains constant, P will vary inversely to V. Example: Container with 200 mL P of 10 cm H2O. Volume is reduced 50% New P= 20 cmH2O P2 = P1 x V1 = 10 cmH2O x 200 mL = 20 cmH2O V2 100 mL

CHARLES' LAW

(V1 / T2 = V2 / T2) If P remains constant, V will vary proportional to T. Example: Balloon with 3L T increased from 250K to 300K. Volume is increased to 3.6L V2 = V1 x T2 = 3L x 300K = 3.6L T1 250K

Clinical Application of Fick's Law

*The area (A) component of the law is verified in that a decreased alveolar surface area ( caused by alveolar collapse or alveolar fluid) decreases the ability of O2 to enter the pulmonary capillary blood. *The P1-P2 portion of the law is confirmed in that a decreased alveolar O2 pressure (PAO2 or P1) (caused by high altitudes or alveolar hypoventilation) reduces the diffusion of O2 into the pulmonary capillary blood. *The thickness (T) factor is confirmed in that an increased alveolar tissue thickness (caused by alveolar fibrosis or alveolar edema) reduces the movement of O2 across the alveolar-capillary membrane. certain adverse pulmonary conditions may be improved. When a pt O2 diffusion rate is decreased because of alveolar thickening, the administration of O2 therapy will be beneficial. As the pt FIO2 increases, the pt's alveolar O2 pressure (PAO2 or P1) also increases, causing movement of O2 across the ACM to increase.

Name the nine major structures of the alveolar-capillary membrane through which a gas molecule must diffuse

1. the liquid lining the intra-alveolar membrane 2. the alveolar epithelial cell 3. the basement membrane of the alveolar epithelial cell 4. loose connective tissue (the interstitial space) 5. the basement membrane of the capillary endothelium 6. the capillary endothelium 7. the plasma in the capillary blood 8. the erythrocyte membrane 9. the intracellular fluid in the erythrocyte ntil a hemoglobin molecule is encountered. The thickness of these physical barriers is between 0.36 and 2.5mm. Under normal circumstances, this is a negligible barrier to the diffusion of O2 and CO2.

Partial Pressure of Oxygen in the Alveoli

100 torr

average alveolar O2 tension (PAO2)

100 torr

Partial Pressure of Oxygen in the Atmosphere

159 torr

Alveolar CO2 Pressure (PACO2)

40 torr

average O2 tension (Pvo2)

40 torr

average alveolar CO2 tension (PACO2)

40 torr

absolute humidity

44 mg/L

average CO2 tension (Pvco2)

46 torr

Water Vapor Pressure (PH2O)

47 torr

Describe the clinical connection association with respiratory disorders that decrease the alveolar surface area

A # of respiratory disorders can drastically reduce the alveolar surface area ("A" component in Fick's law). Emphysema breaks down the walls of adjacent alveoli and pulmonary capillaries, the alveoli merge together into large air sacs (bullae). Emphysema destroys both the alveoli and pulmonary capillaries, the alveolar surface area decreases. Increasing the pt's PAO2 (P1) can be helpful with these patients. The alveolar surface area is also reduced in pulmonary disorders associated with excessive tracheobronchial tree secretions or tumors, which block air flow to the alveoli and alveolar collapse(pleural effusion, pneumothorax, or excessive airway secretions).

Water Vapor Pressure

Alveolar gas is 100% humidified @ body temperature. Absolute humidity 44 mg/dL Water vapor P 47 mmHg

Factors that affect Measured DLCO: Hemoglobin concentration

Anemia: Patients with low hemoglobin content have a low CO-carrying capacity and therefore a low DLCO value. Polycythemia: Patients with high hemoglobin content have a high CO-carrying capacity and therefore a high DLCO value.

Factors that affect Measured DLCO: Body size

As a general rule, the DLCO increases with body size. The size of the lungs is directly related to the subject's ideal body size. Thus the larger the subject, the greater the lung size and the higher the DLCO.

Identify the % and partial pressure of the gases that compose the barometric pressure: Argon

Atmospheric PAr = 0.0093 x 760 = 7.068 mm Hg

Identify the % and partial pressure of the gases that compose the barometric pressure: Carbon Dioxide

Atmospheric PCO2 = 0.0003 x 760 = .228 mm Hg

Identify the % and partial pressure of the gases that compose the barometric pressure: Nitrogen

Atmospheric PN2 =0.7808 x 760 = 593.408 mm Hg

Identify the % and partial pressure of the gases that compose the barometric pressure: Oxygen

Atmospheric PO2 = 0.21 x 760 = 159.6 mm Hg

Temp Conversion (F to C)

C = (F - 32) x 5 / 9

Describe the clinical connection associated with pulmonary disorders that increase the alveolar-capillary thickness

Disorders that cause the alveolar-capillary thickness to increase; pulmonary edema, pneumonia, interstitial lung diseases( scleroderma, sarcoidosis,or Goodpasture's syndrome), acute respiratory distress syndrome (ARDS), and respiratory distress syndrome (RDS) in newborn infants. Total transit time for these conditions is 0.75 sec. Treament efforts: Increase the patient's inspired oxygen concentration.

Identify the partial pressure of the gases in the air, alveoli, and blood: Water (PH2O) vapor

Dry Air 0.0 Alveolar Gas 47.0 Arterial Blood 47.0 Venous Blood 47.0

Identify the partial pressure of the gases in the air, alveoli, and blood: Carbon dioxide (Pco)

Dry Air 0.2 Alveolar Gas 40.0 Arterial Blood 40.0 Venous Blood 46.0

Identify the partial pressure of the gases in the air, alveoli, and blood: Oxygen (Po)

Dry Air 159.0 Alveolar Gas 100.0 Arterial Blood 95.0 Venous Blood 40.0

Identify the partial pressure of the gases in the air, alveoli, and blood: Nitrogen (PN)

Dry Air 600.8 Alveolar Gas 573.0 Arterial Blood 573.0 Venous Blood 573.0

SummaryO2 cascade

Dry gas 159 mmHg Conducting airways149 End exp gas 114 Alveolar 101 Arterial blood 97 Mean systemic Capillary pressure 40 Cellular cytoplasm <40 Mitochondria 3-23 Reason for change Addition of water vapor Mixing of deadspace Addition of CO2 Intrapulmonary shunting O2 diffusion into cell O2 diffusion into mitochondria Metabolic rate

Temp Conversion (C to F)

F = [C x 9 / 5] + 32

Describe how the following relate to the diffusion constants in Fick's law: Henry's Law

Gardenhire's slide: Amount of gas that dissolves in a liquid is proportional to the partial P of the gas. Solubility coefficient @ 37°C: O2 = 0.024 ml/mmHg/ml H2O CO2 = 0.59 ml/mmHg/ml H2O 24:1 Textbook: the amount of a gas that dissolves in a liquid at a given temperature is proportional to the partial pressure of the gas. The amount of gas that can be dissolved by 1mL of a given liquid at standard pressure (760mm Hg) and specified temperature is known as the solubility coefficient of the liquid. (see above) Solubility coefficient varies inversely with temperature. If the temp rises the solubility coefficient decreases in value.

Describe the clinical connection associated with hyperbaric oxygen therapy and the clinical application of Henry's Law

Hyperbaric Oxygen Therapy (HBOT) also known as hyperbaric medicine. Is the therapeutic application of oxygen at pressures greater than 1 atm. A patient receiving HBOT is placed in a sealed hyperbaric chamber and exposed to selected oxygen concentration at 1.5 to 3 x above the normal atmospheric pressure (760 mm Hg). Thus, if a patient receives 100% percent O2 at 3 atm, the partial pressure of O2 (PO2) in the chamber would be 2280 mm Hg (3 x 760 = 2280) According to Henry's law the amount of gas that dissolves in a liquid is directly reated to the partial pressure of the gas. The higher the partial pressure of O2 (PO2) in the hyperbaric chamber, the greater the amount of O2 that will be forced into the patient's pulmonary capillary blood. Conditions treated by Hyperbaric Oxygenation: gas embolism, decompression sickness, radiation necrosis, diabetic wounds of the lower extremities, nonhealing skin grafts, crush injuries, acute traumatic ischemias, thermal burns, clostridial gangrene, necrotizing soft-tissue infections (flesh eating bacteria), refactory osteomyelitis, carbon monxide poisoning, and severe blood loss or anemia.

Explain how Dalton's law relates to the partial pressure of atmospheric gases

In addition, the pressure exerted by each gas--its partial pressure--is directly proportional to the percentage of that gas in the gas mixture. The pressure produced by a particular gas is completely unaffected by the presence of another gas. Each gas in a mixture will individually contribute to the total pressure created by the mixture of gases. Ex. if 10 molecules of gas are enclosed in a container, the total pressure may be expressed as 10; if 5 molecules of a different gas are enclosed in another container of equal volume, the total pressure may be expressed as 15.

Factors that affect Measured DLCO: Carboxyhemoglobin

Individuals who already have CO bound to their hemoglobin (smokers or fire fighters overcome by smoke inhalation) generate a "back pressure" to alveolar PCO. This condition decreases the pressure gradient between the alveolar CO and the blood CO, which in turn reduces the DLCO

Temp Conversion (C to K)

K= C + 273

Other Lung Disorders associated with decreased DLCO value

Lung Abnormality hyperinflation and decreased DLCO DLCO and FRC decreased DLCO increased FRC Pulmonary Disorder Emphysema, etc. (COPD) Lung Abnormality hypoinflation and decreased DLCO DLCO and FRC decreased DLCO decreased FRC Pulmonary Disorder restrictive lung disease( e.g. pulmonary edema, chronic interstitial lung disease) Lung Abnormality normal lung volume and decreased DLCO DLCO and FRC decreased DLCO normal FRC Pulmonary Disorder pulmonary embolism

Factors that affect Measured DLCO: Lung volume

The DLCO is directly related to an individuals lung size. Thus greater the subject's lung volume, the greater the DLCO.

Factors that affect Measured DLCO: Age

The DLCO progressively increases between birth and 20 years of age. After age 20, the DLCO decreases as a result of the normal anatomic alterations of the lungs that reduce the overall alveolar-capillary surface area.

IDEAL GAS LAW

PV=nRT P= Pressure V= Volume n= Number of molecules present R= Gas constant (.08) T= Temperature in Kelvin scale If n remains constant: P1xV1 = P2 x V2 T1 T2

Define perfusion limited, and explain how it relates to a gas such as nitrous oxide

Perfusion means that the transfer of gas across the alveolar wall is a function of the amount of blood that flows past the alveoli. N2O relation: When N2O moves across the alveolar wall and into the blood, it does not chemically combine with hemoglobin. The partial pressure of N2O in the blood plasma rises quickly. It is estimated that the partial pressure of N2O will equal that of the alveolar gas when the blood is only albout 1/10 of the way through the alveolar-capillary system (ACS). Once the partial pressures of the N2O in the blood and in the alveolar gas are equal, the diffusion of N2O stops. In order for the diffusion of N2O to resume, additional blood must enter the ACS. The rate of perfusion, determines the amount of diffusion of N2O.

Describe how oxygen can be classified as perfusion or diffusion limited

Perfusion: When O2 diffuses across the alveolar wall and into the blood, it enters the RBCx and combines with Hb--but not with the eagerness as CO. Hb quickly becomes saturated with O2 and once this occurs, O2 in the plasma can no longer enter the RBCs. This causes a partial pressure of O2 in the plasma to increase. Under normal resting conditions, the partial pressure of O2 in the capillary blood = the partial pressure of O2 in the alveolar gas when the blood is about 1/3 of the way through the capillary. Diffusion: When the diffusion properties of the lungs are impaired, however, the partial pressure of O2 in the capillary blood may never = the partial pressure of the O2 in the alveolar gas during the normal alveolar-capillary transit time. Under normal circumstances the diffusion of O2 is perfusion limited, but under certain abnormal pulmonary conditions the transfer of O2 may become diffusion limited. Note: When the patient has either a decreased cardiac output or a decreased hemoglobin level (anemia), the effects of perfusion limitation may become significant.

Factors that affect Measured DLCO: Alveolar PO2 (PAO2)

The DLCO decreases in response to a high PAO2. This is because O2 and CO both compete for the same hemoglobin sites.

Factors that affect Measured DLCO: Exercise

The DLCO increases with exercise. This is most likely because of the increase cardiac output, and capillary recruitment and distention, associated with exercise.

Factors that affect Measured DLCO: Body position

The DLCO is about 15% to 20% greater when the individual is in the supine position, compared with the upright position.

Describe the clinical connection associated with why a decreased DLCO is a classic diagnostic sign of emphysema

The S/S associated with emphysema appear very similar to other COPD. The classic pulmonary function diagnostic test that verifies that a patient has emphysema is a decreased DLCO. This is because of the alveolar-capillary destruction (decreased alveolar surface area) associated with emphysema. Alveolar-capillary destruction is not associated with the other COPD.

Calculate the ideal alveolar gas equation

The alveolar O2 tension (PAO2) PAO2 = [PB-PH2O] FIO2 -PaCO2 (1.25) or PAO2 = [PB-PH2O] FIO2 - PaCO2 / 0.8 PAO2 is the partial pressure of oxygen in the alveoli PB is the barometric pressure PH2O is the partial pressure of water vapor in the alveoli (PH2O = 47 torr) FIO2 is the fractional concentration of inspired oxygen PaCO2 is the partial pressure of arterial carbon dioxide. Ex. If a patient is receiving an FIO2 of 0.30 on a day when the barometric pressure is 755 torr, and if the PaCO2 is 55 torr, then the patient's alveolar oxygen tension (PAO2) is: PAO2 = [PB-PH2O] FIO2 -PaCO2 (1.25) =[755-47] 0.30-55 (1.25) =[708] 0.30- 68.75 =[212.4] - 68.75 = 143.65 IF FIO2 is >= 60% omit 1.25: PAO2 = [PB-PH2O] FiO2 - PaCO2

stroke volume (SV)

The amount of blood pumped by the left ventricle of the heart in one contraction. The stroke volume is not all the blood contained in the left ventricle; normally, only about two-thirds of the blood in the ventricle is expelled with each beat. Together with the heart rate, the stroke volume determines the output of blood by the heart per minute (cardiac output).

Explain how Fick's Law relates to gas diffusion

The law states that the rate of gas transfer across a sheet of tissue is directly proportional to the surface area of the tissue, to the diffusion constants and to the difference in partial pressure of the gas between the two sides of the tissue, and it is inversely proportional to the thickness of the tissue. Vgas~ A * D * (P1 - P2) / T Vgas= the amount of gas that diffuses from one point to another A= surface area D=diffusion is constant (is determined by Henry's and Graham's law) P1-P2 =the difference in partial pressure between two points T= thickness

Describe how oxygen and carbon dioxide normally diffuse across the alveolar-capillary membrane

The venous blood entering the alveolar-capillary system has an average O2 tension (Pvo2) of 40 torr and an average CO2 tension (Pvco2) of 46 torr. As blood passes through the capillary, the average alveolaroxygen tension (PAo2) is about 100 torr, and the average alveolar CO2 tension (PAco2) is about 40 torr. There is an O2 pressure gradient of about 60 torr and a CO2 pressure gradient of about 6 torr. The O2 molecules diffuse across the alveolar-capillary membrane into the blood while at the same time CO2 molecules diffuse out of the capillary blood and into the alveoli. The diffusion of O2 and CO2 will continue until equilibrium. This is usually accomplished in about 0.75 sec. In the presence of pulmonary diseases, the time to achieve oxygen equilibrium in the alveolar-capillary system may not be adequate. Such diseases are pulmonary edema, pneumonia(alveolar consolidation) and interstitial lung diseases.

Define diffusion limited, and explain how it relates to a gas such as carbon monoxide

means that the movement of gas across the alveolar wall is a function of the integrity of the alveolar-capillary membrane itself. Carbon monoxide relation: When CO moves across the alveolar wall and into the blood, it rapidly enters the RBCs and tightly bonds to hemoglobin (CO has an affinity for hemoglobin 210X greater than O2). When gases are in chemical combination with hemoglobin, they no longer exert a partial pressure. Because CO has a strong chemical attraction to hemoglobin, most of the CO enters the RBCs, combines with hemoglobin, and no longer exerts a partial pressure in the blood plasma. There is no appreciable partial pressure of CO in the blood plasma at any time (p1-p2 stays constant) only the diffusion characteristics of the ACM, not the amount of blood flowing through the capillary limit the diffusion of CO.

Differentiate between pressure gradients and diffusion gradients

pressure gradient: the movement of gas from an area of high pressure (high concentration) to an area of low pressure (low concentration). -The primary mechanism responsible for moving air in and out of the lungs during ventilation. -during ventilation always move a bulk volume of gas in the same direction --either in or out of the lungs -each individual gas (N2,O2, CO2, and trace gases) move in the same direction--either in or out of the lungs. gas diffusion: the movement of "individual gas molecules" from an area of high pressure (high concentration) to an area of low pressure (low concentration). -each individual gas (N2,O2,CO2) can continue to move independently from the other gases from a high pressure area to a low pressure area. -These individual gas partial pressure differences are called diffusion gradients. -Kinetic energy is the driving force responsible for diffusion.

Describe how the following relate to the diffusion constants in Fick's law: Graham's Law

states that the rate of diffusion of a gas through a liquid is; 1. directly proportiaonal to the solubility coefficient of the gas 2. indirectly proportional to the square root of the gram-molecular weight (GWM) of the gas. The relative rates of diffusion to O2 (GMW =32) and CO2 (GMW = 44) it can be seen that O2 is the lighter gas, and moves faster than CO2 Diffusion rate for CO2/ Diffusion rate for O2 = SQRT GMW O2 / SQRT GMW CO2 = SQRT 32/ SQRT 44 =5.6/6.6 combining Graham's and Henry's law it can be said that the rates of diffusion of two gases are directly proportional to the ratio of their solubility coefficients, and inversely proportional to the ratio of their gram-molecular weights. Fick's Law can be rewritten as Vgas ~ A * S * (P1 - P2) / SQRT GMW x T

Pressure Gradient vs Gas Diffusion-In reference to the alveoli

the alveoli by means of a pressure gradient, or the alveoli by way of the pulmonary capillary blood flow. each individual gas can move according to its own diffusion gradient. 2 different gases (O2 & CO2) can move (diffuse) in opposite directions based on their individual diffusion gradients. O2 diffuses from the alveoli into the pulmonary capillaries; while at the same time, CO2 diffuses from the pulmonary capillaries into the alveoli. This continues until the partial pressures of O2 and CO2 are in equilibrium.

Describe Dalton's Law--the law of partial pressures

the total pressure exerted by a mixture of gases is equal to the sum of the pressures exerted independently by each gas in the mixture.