Pulmonary Function Tests

Pulmonary function tests Pulmonary volume and capacity § Capacity is more than one volume § In pictures chart is given from spirometer which represent different respiratory volumes and capacity § The average of Tidal volume is 500 ml Factors affect of average (gender-age) different parameters that decrease or increase tidal volume § Tidal volume is the volume of gas inspired or expired in an unforced respiratory cycle (at rest). § Same volume of gas inspired will be expired but different compositions of gases, more CO2 expired and more O2 inspired § Inspiratory reserve volume (IRV) is the volume of air above the tidal volume (during stress more than 500ml). § Inspiratory reserve volume, is the maximum volume of gas than can be inspired during forced breathing in addition to tidal volume. § Expiratory reserve volume is beyond and after tidal volume (during stress) § Expiratory reserve volume is the maximum volume of gas than can be expired during forced breathing in addition to tidal volume. § Even after forced expiration, there is a specific volume of gas left in the lungs called residual volume(1100ml-1200ml from air) § residual volume The volume of gas remaining in the lungs after a maximum expiration § The amount of gas remaining in the lungs after a normal tidal expiration is called functional residual capacity. (Sum volume/sum of expiratory reserve volume+ residual volume) it’s about 2.5 L § The importance of residual volume is to facilitate next respiration since we keep our lungs inflated. § blood flow is continuous, during systole and diastole ,in respiratory system, air flow is not continuous ,it’s intermittent there is only air flow during inspiration and then leaves during expiration and so the importance of residual volume is that there is always air for gas exchange, if all the air left the lungs during expiration there will be no gas exchange when the blood reaches the lungs. So, it keeps the exchange of gases between the lungs and the blood a continuous process. § Total lung capacity (TLC)=6000ml § We can inspire more than expire due to the presence of more inspiratory muscles than expiratory , also limitations in expiration process and limitation in chest skeleton as it favors inspiration . than expiration § Vital capacity is the maximum air that can be expired forcefully after force inspiration . § Vital capacity is the is the maximum amount of gas than can be expired after a maximum insp. Partial pressure of O2 and partial pressure of CO2 Ø Partial pressure of O2 in Alveoli (alveolar air )=105 Ø partial pressure of O2 in the atmosphere is 159mmHg/why??! v Partial pressure in the atmosphere(ATM) is 760mmHg, and the percent of O2 in the air is 21% so 21/100 *760= 159mmHg. v In the alveoli the PO2 decreased to 105 why??? Because during the entry of oxygen it will pass through the conducting zone which works to repletion air And part of O2 move to blood thereby causing the air present in the alveoli to have a greater amount of water vapor than atmospheric air and thus less PO2, also some of the O2 diffused in the blood. v Why there was a decrease in PO2 from the alveoli to the oxygenated blood?? Because of bronchial veins, these veins transport deoxygenated blood from the respiratory system to the left side of the heart, as a result it will decrease pO2 oxygenated blood in the left side of the heart so PO2 is will decrease from 105 to 100. v why PCO2 didn’t change as result of mixing blood in left part of heart with bronchial veins blood ??! Ø Memorize the PO2 and PCO2 numbers in the alveoli/oxyg blood (systemic blood)/tissues/deoxg blood (venous blood). Ø In the venous blood there is 40mmHg oxygen so this means in deoxygenated blood there is oxygen. Transport O2 —> 1.5 %dissolved in plasma 98.5% as Hb-O2(on Fe+2 ) CO ‫ﺑﯾﻧﺎﻓس اﻻﻛﺳﺟﯾن‬ Transport CO2 —> 7% dissolved in plasma 23% as Hb-CO2(on amino acids) 70% as HCO3 The oxygen binds to the iron (Fe2+) in the hemoglobin, while carbon dioxide binds to the amino acid group in the hemoglobin and so it does not compete the O2 on binding. Carbon monoxide could compete the oxygen on binding to iron on hemoglobin, and has 200 times the affinity of O2 to iron. Moreover, CO binds irreversibly it does not unload from the hemoglobin, while the oxygen binds reversibly (loading and unloading) depending on its concentration. For example, the blood in pulmonary capillaries has low O2 conc. so there will be loading of O2 from the lungs to the blood. While in the tissues there is low O2 conc. in the tissues so there will be unloading from the blood to the tissues. However, CO does not unload.