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Stellenbosch University Logo. MBChB I Respiratory Lectures 2022 Prof. Faadiel Essop Room 3027, BMRI Email: [email protected] Gas exchange.

A figure shows two examples of gases in solution. The first figure shows oxygen solubility. When the temperature remains constant, the amount of a gas that dissolves in a liquid depends on both the solubility of the gas in the liquid and the partial pressure of the gas. In the initial state, there is no oxygen in the solution. P o 2 = 100 millimeters of mercury in the air and P O 2 = 0 in the water. In the second state, oxygen dissolves and begins to enter the water. In the third state, at equilibrium, P O 2 in the air and water are equal. Low O 2 solubility means concentrations are not equal. P O 2 = 100 millimeters of mercury while O 2 = 5.20 millimoles per liter in the air. In the water, P O 2 = 100 millimeters of mercury while O 2 = 0.15 millimoles per liter. The second figure shows C O solubility. When C O 2 is at equilibrium at the same partial pressure of 100 millimeters of mercury, more C O 2 dissolves. In the air, P C O 2 = 100 millimeters of mercury while C O 2 = 5.20 millimoles per liter. In the water, P C O 2 = 100 millimeters of mercury, while C O 2 = 3.0 millimoles per liter..

Movement of gases is directly proportional to pressure gradient of the gas solubility of the gas in liquid temperature.

Gas entering capillaries first dissolve in the plasma Dissolved gas accounts only for <2% of O 2 in blood Rest (98%) carried by hemoglobin (Hb) molecule Thus, total blood oxygen content = dissolved O 2 + O 2 bound to hemoglobin (HbO 2 ) The Fick equation can be used to estimate oxygen consumption Oxygen consumption (Q O2 ).

Adolph Fick 1829-1901. A figure show mass balance, mass flow, and the Fick equation as follows. Arterial O 2 transport in milliliters O 2 per minute to cellular oxygen consumption or Q O 2 in milliliters O 2 per minute to venous O 2 transport in milliliters O 2 per minute. The following formulas are provided. Mass Balance is arterial O 2 transport minus Q O 2 = venous O 2 transport. This rearranges to arterial O 2 transport minus venous O 2 transport = Q O 2. Mass Flow is O 2 transport = cardiac output or C O in liters of blood per minute times O 2 concentration in milliliters of O 2 per liter of blood. The Fick Equation is to substitute the mass flow equation for O 2 transport in the mass balance equation as follows. Left parenthesis C O times arterial left bracket O 2 right bracket right parenthesis minus left parenthesis C O times venous left bracket O 2 right bracket right parenthesis equals Q O 2. Using algebra such as left parenthesis A B right parenthesis minus left parenthesis A C right parenthesis = A left parenthesis B minus C right parenthesis, is as follows. C O times left parenthesis arterial left bracket O 2 right bracket minus venous left bracket O 2 right bracket right parenthesis = Q O 2..

Stellenbosch University Logo. Mass balance & the Fick equation.

Stellenbosch University Logo. Mass balance & the Fick equation.

Gas entering capillaries first dissolve in the plasma Dissolved gas accounts for <2% of O 2 in blood Fick equation can be used to estimate oxygen consumption Oxygen consumption.

https://www.britannica.com/science/hemoglobin. Hemoglobin is a tetramer – made up of 4 globular protein chains Each chain is centered around a heme group, with an iron atom Each iron atom can (reversibly) bind with one O 2 molecule Such bonding is weak and can easily be broken Thus, each hemoglobin molecule can potentially bind up to 4 O 2 molecules.

The figure shows oxygen transport and notes that more than 98 % of the oxygen in blood is bound to hemoglobin in red blood cells, and less than 2 % is dissolved in plasma. O 2 in the alveoli passes to the arterial blood. O 2 dissolves in the plasma or P O 2 at less than 2 %. In the red blood cell, O 2 plus H B becomes H B O 2 at greater than 98 %. H B O 2 is transported to cells. H B plus O 2, where the 0 2 dissolves in the plasma, transports the cell. O 2 in the cell is used in cellular respiration..

Diagrams A, B, and C show how hemoglobin increases oxygen transport. In diagram A, oxygen transport in blood without hemoglobin is alveolar P O 2 = arterial P O 2. P O 2 = 100 millimeters of mercury in the alveoli. The O 2 is transferred to the arterial plasma where P O 2 = 100 millimeters of mercury. Oxygen dissolves in plasma. O 2 content of plasma = 3 milliliters of O 2 per liter of blood. O 2 content of red blood cells = 0. Total O 2 carrying capacity is 3 milliliters of O 2 per liter of blood. In diagram B, oxygen transport at normal P o 2 in blood with hemoglobin is P o 2 = 100 millimeters of mercury in the alveoli. P o 2 also = 100 millimeters of mercury in the arterial plasma. Red blood cells with hemoglobin are carrying 98 % of their maximum load of oxygen. O 2 content of plasma = 3 milliliters of O 2 per liter of blood. O 2 content of red blood cells = 197 milliliters of O 2 per liter of blood. The total O 2 carrying capacity is 200 milliliters of 0 2 per liter of blood. In diagram C, oxygen transport at reduced P o 2 in blood with hemoglobin is p o 2 = 28 millimeters of mercury in the alveoli. P o 2 also equals 28 millimeters of mercury in the arterial plasma. Red blood cells are carrying 50 % of their maximum load of oxygen. O 2 content of plasma = 0.8 milliliters of 0 2 per liter of blood. O 2 content of red blood cells = 99.5 milliliters of O 2 per liter of blood. The total O 2 carrying capacity is 100.3 milliliters of O 2 per liter of blood..

A concept map lists the binding factors as follows. The amount of oxygen bound to H B depends on Plasma o 2 and the amount of hemoglobin. Plasma o 2 determines the % of saturation of H B times the total number of H B binding sites. The amount of hemoglobin determines the total number of H B binding sites. The total number of H B binding sites is calculated from H B content per R B C times the number of R B C’s..

A figure shows graphs a and b noting the binding properties of adult and fetal hemoglobin. P o 2 in millimeters of mercury is measured on the x axis and hemoglobin saturation in percentage is measured on the Y for both graphs. On graph A, the oxyhemoglobin saturation curve is determined in vitro in the laboratory. The curve is an increasing slope with a resting cell at 40, 75 and the alveoli at 100, 98. On graph B, the maternal and fetal hemoglobin have different oxygen related binding properties. The maternal hemoglobin is a curve that is an increasing slope but it is slightly underneath the increasing fetal hemoglobin curve..

Stellenbosch University Logo. Oxygen-hemoglobin binding curves.

A figure shows graphs a and b noting the binding properties of adult and fetal hemoglobin. P o 2 in millimeters of mercury is measured on the x axis and hemoglobin saturation in percentage is measured on the Y for both graphs. On graph A, the oxyhemoglobin saturation curve is determined in vitro in the laboratory. The curve is an increasing slope with a resting cell at 40, 75 and the alveoli at 100, 98. On graph B, the maternal and fetal hemoglobin have different oxygen related binding properties. The maternal hemoglobin is a curve that is an increasing slope but it is slightly underneath the increasing fetal hemoglobin curve..

A figure shows graphs c, d, e, and f noting the physical factors after hemoglobin’s affinity for oxygen. P o 2 in millimeters of mercury is measured on the x axis and hemoglobin saturation in percentage is measured on the Y for all graphs. On graph C, the effect of P H is shown. Three increasing curves are shown slightly under the previous one. Curve 7.6 crosses at 40, 93. Curve 7.4 crosses at 40, 73. Curve 7.2 crosses at 40, 60. On graph D, the effect of temperature is shown. Three increasing curves are shown slightly under the previous one. Curve 20 degrees Celsius crosses at 40, 100. Curve 37 degrees Celsius crosses at 40, 72. Curve 43 degrees Celsius crosses at 40, 55. On graph E, the effect of P c o 2 is measured. Three increasing curves are shown slightly under the previous one. P c o 2 = 20 millimeters of mercury and crosses at 40, 83. P c o 2 = 40 millimeters of mercury and crosses at 40, 70. P c o 2 = 80 millimeters of mercury and crosses at 40, 50. On graph F, the effect of the metabolic compound 2,3 B P G is shown. With no 2, 3 B P G an increasing curve stops at 30, 90. With normal 2,3 B P G the increasing curve crosses at 40, 72. With added 2,3 B P G the increasing curve crosses at 40, 50. All figures are estimates..

A concept map shown for arterial oxygen notes that the total oxygen content of arterial blood depends on the amount of oxygen dissolved in plasma and bound to hemoglobin. The map reads as follows. Total arterial o 2 content goes down to oxygen dissolves in plasma P o 2 of plasma and oxygen bound to H B. The oxygen dissolves in plasma P o 2 of plasma is influenced by the composition of air, alveolar ventilation, oxygen diffusion between alveoli and blood, and adequate perfusion of alveoli. The alveolar ventilation goes down to rate and depth of breathing, airway resistance, and lung compliance. The oxygen diffusion between alveoli and blood goes down to surface area and diffusion distance. The diffusion distance goes down to membrane thickness and amount of interstitial fluid. Oxygen dissolves in plasma P o 2 of plasma also helps determine the % of saturation of H B which is under oxygen bound to h B. Oxygen bound to H B goes downs to % of saturation of H B times total number of binding sites. The % of saturation of H B is affected by P c o 2, p h, temperature, and 2,3 b p g. The total number of binding sites goes down to h b content per r b c times number of r b c’s..

Excess CO 2 levels must be removed from the body as may trigger serious side-effects hypercapnia causes pH disturbance (acidosis) pH changes can lead to protein denaturation High P CO2 levels can depress central nervous system – confusion, coma and even death.

Excess CO 2 levels must be removed from the body as may trigger serious side-effects hypercapnia causes pH disturbance (acidosis) pH changes can lead to protein denaturation High P CO2 levels can depress central nervous system – confusion, coma and even death.

4. Hemoglobin binds most of H + in red blood cells; i.e. acts as a buffer to help maintain pH.

A figure notes the following measurements for o 2 and c o 2 exchange and transport. Dry air = 760 millimeters of mercury. Under dry air, p o 2 = 160 millimeters of mercury and p c o 2 = 0.25 millimeters of mercury. In the alveoli, p o 2 = 100 millimeters of mercury and p c o 2 = 40 millimeters of mercury. In o 2 transport, h b o 2 is greater than 98 %. Dissolved o 2 is less than 2 % or p o 2. In arterial blood, p o 2 = 100 millimeters of mercury and p c o 2 = 40 millimeters of mercury. In the cells, p o 2 is less than or equal to 40 millimeters of mercury and p c o 2 is greater than or equal to 46 millimeters of mercury. In venous blood, p o 2 is less than or equal to 40 millimeters of mercury and p c o 2 is greater than or equal to 46 millimeters of mercury. In c o 2 transport, h c o 3 negative = 70 %, h b c o 2 = 23 %, and dissolved c o 2 = 7 %..

Respiratory neurons in the medulla control inspiratory and expiratory muscles Neurons in the pons integrate sensory information & interact with medullary neurons to influence ventilation Rhythmic pattern of breathing arises from a neural network of spontaneously discharging neurons Ventilation is subject to continuous modulation by chemoreceptor- and mechanoreceptor-linked reflexes and higher brain centers.

Sherwood, CH13, p482. Stellenbosch University Logo.

A figure is shown with the structure and function of the brain stem controlling ventilation. P R G is pontine respiratory group. D R G is dorsal respiratory group. V R G is ventral respiratory group. N T S is nucleus tractus solitarius. The figure is as follows. The higher brain centers goes to the P R G. This then goes to the both the N T S and V R G. Sensory input from C N 9, 10 which is mechanical and chemosensory is shown going to the N T S. Medullary chemoreceptors monitor c o 2 in the n t s. The pre botzinger complex is listed in the V R G and the exchange to the N T S is the D R G. From the N T S, output is primarily to the diaphragm. From the V R G, output is to expiratory, some inspiratory, pharynx, larynx, and tongue muscles..

Glomus cells in carotid body activated by lower P O2 (or lower pH, higher P CO2 ) Oxygen not usually important factor to regulate ventilation; must fall to levels lower than 60 mmHg By contrast, any condition that lowers pH or enhances P CO2 will activate such cells (to minor extent though) & assist to increase ventilation Thus, such peripheral chemoreceptors respond only to dramatic changes in arterial P O2 , e.g. high altitude, COPD, heart failure.

CO 2 is the most important controller of ventilation via peripheral & central chemoreceptors – elicit robust response Such receptors set the respiratory pace & provide continuous input into the control network The H + produced from the CO 2 -HCO 3 - reaction largely initiates this reflex However, if P CO2 remains elevated for days, ventilation falls back to normal levels as chemoreceptors adapt In some situations (like this), P O2 becomes the primary stimulus (via peripheral chemoreceptors) Here, COPD is a good example – most of the chemical stimulus for ventilation comes from low O 2 sensed by carotid body chemoreceptors.

Stellenbosch University Logo. Central chemoreceptors & P CO2 monitoring.

Sherwood, CH13, p482. Stellenbosch University Logo.

Stellenbosch University Logo. Other factors influencing ventilation control.

Stellenbosch University Logo. MBChB I Respiratory Lectures 2022 Prof. Faadiel Essop Room 3027, BMRI Email: [email protected] Volumes and capacities.

Tendency for alveoli to collapse. Atelectasis: complete or partial collapse of the entire lung or a lobe(s).

airway resistance. slope = compliance; steeper slope = more compliance.

Respiratory mechanics: lung compliance. Stellenbosch University Logo.

Respiratory mechanics: pulmonary function tests. Stellenbosch University Logo.

Respiratory mechanics: pulmonary function tests. Stellenbosch University Logo.

Respiratory mechanics: pulmonary function tests. Stellenbosch University Logo.

Respiratory mechanics: pulmonary function tests. Stellenbosch University Logo.

Respiratory mechanics: pulmonary function tests. Stellenbosch University Logo.

Tidal volume (V T ): volume of air that moves during single inspiration or expiration; average V T = 500 mL during quiet breathing Ventilation rate: normally 12-20 breaths per minute for an adult.

The answer to previous question = NO. Anatomic dead space:.

Gas Exchange | SpringerLink. https://link.springer.com/chapter/10.1007/978-1-4471-4315-4_1.

Thus, although 6 L/min fresh air enters the respiratory system, only 4.2 L actually reaches the alveoli.

Respiratory mechanics: efficacy of ventilation. Stellenbosch University Logo.

Minute ventilation (VE): amount of air entering the lungs per minute VE = ventilation rate × tidal volume Alveolar ventilation (VA): amount of gas per unit of time that reaches the alveoli and becomes involved in gas exchange VA = ventilation rate x (tidal volume − dead space volume) Dead space ventilation (VD): amount of air per unit of time that is not involved in gas exchange, such as the air that remains in the conducting zones VD = ventilation rate x dead space volume.

FEV 1 decreases in both restrictive & obstructive lung diseases.

Respiratory mechanics: spirogram. Stellenbosch University Logo.

Respiratory mechanics: forced vital capacity test.

Table 38-1 Average Pulmonary Volumes and Capacities for a Healthy, Young Adult Man Pulmonary Volumes and Capacities Volumes Tidal volume Inspiratory reserve volume Expiratory volume Residual volume Capacities Inspiratory capacity Functional residual capacity Vital capacity Total lung capacity Normal Values (ml) 3000 1200 3500 5800.

Ratio of ventilation (air getting into alveoli) to perfusion (amount of blood being sent to the lungs).