Ventilatory Mechanics Study Documents

‭VENTILATORY MECHANICS.‬ ‭ entilation‬ ‭is‬ ‭a‬ ‭periodic‬ ‭phenomenon‬ ‭which‬ ‭consists‬ ‭of‬ ‭a‬ ‭succession‬ ‭of‬ V ‭inspiration‬ ‭movements‬ ‭during‬ ‭which‬ ‭a‬ ‭volume‬ ‭of‬ ‭air‬ ‭is‬ ‭inspired‬ ‭and‬ ‭expiration‬ ‭phenomena‬ ‭during‬ ‭which‬ ‭a‬ ‭certain‬‭volume‬‭of‬‭air‬‭is‬‭rejected‬‭or‬ ‭expired.‬‭These‬‭are‬‭therefore‬‭processes‬‭which‬‭govern‬‭the‬‭entry‬‭and‬‭exit‬‭of‬ ‭air from the lungs.‬ ‭ as‬ ‭currents‬ ‭are‬ ‭always‬ ‭established‬ ‭from‬ ‭a‬ ‭high‬ ‭pressure‬ ‭zone‬ ‭to‬ ‭a‬ ‭low‬ G ‭pressure‬‭zone.‬‭Any‬‭variation‬‭in‬‭volume‬‭causes‬‭a‬‭variation‬‭in‬‭pressure.‬‭The‬ ‭product: P x V = constant.‬ ‭ he‬ ‭volume‬ ‭of‬ ‭a‬ ‭gas‬ ‭is‬ ‭therefore‬‭inversely‬‭proportional‬‭to‬‭the‬‭pressure‬‭it‬ T ‭experiences.‬ ‭Inspiration: an active phenomenon.‬ I‭ nspiration‬ ‭is‬ ‭an‬ ‭active‬ ‭phenomenon‬ ‭during‬ ‭which‬ ‭thoracic‬ ‭volume‬ ‭increases.‬ ‭On‬ ‭the‬ ‭other‬ ‭hand,‬ ‭alveolar‬ ‭pressure‬ ‭(or‬ ‭lung‬ ‭pressure)‬ ‭decreases.‬ ‭This‬ ‭pressure‬ ‭then‬‭becomes‬‭lower‬‭than‬‭atmospheric‬‭pressure.‬ ‭This‬ ‭phenomenon‬ ‭will‬ ‭therefore‬ ‭allow‬ ‭the‬ ‭entry‬ ‭of‬ ‭the‬ ‭air‬ ‭(around‬ ‭21%‬ ‭oxygen,‬ ‭78%‬ ‭nitrogen‬ ‭and‬ ‭a‬ ‭very‬ ‭small‬ ‭part‬ ‭of‬ ‭CO2)‬ ‭from‬ ‭the‬ ‭mouth‬ ‭towards‬ ‭the‬ ‭alveoli.‬ ‭This‬ ‭phenomenon‬ ‭is‬ ‭said‬ ‭to‬ ‭act‬ ‭according‬ ‭to‬ ‭a‬ ‭pressure‬ ‭gradient‬ ‭(that‬ ‭is‬ ‭to‬‭say‬‭by‬‭the‬‭difference‬‭between‬‭the‬‭pressures‬ ‭inside and outside the lung).‬ ‭ he‬ ‭increase‬ ‭in‬‭lung‬‭volume‬‭occurs‬‭through‬‭contraction‬‭of‬‭the‬‭inspiratory‬ T ‭muscles.‬ ‭These‬ ‭muscles‬ ‭increase‬ ‭the‬ ‭dimension‬ ‭of‬ ‭the‬ ‭rib‬ ‭cage‬ ‭in‬ ‭all‬ ‭directions‬‭(increase‬‭in‬‭diameter‬‭in‬‭the‬‭vertical‬‭direction,‬‭in‬‭the‬‭transverse‬ ‭direction and in the antero-posterior direction).‬ ‭ he‬ ‭main‬ ‭muscle‬ ‭of‬ ‭inspiration‬ ‭is‬ ‭the‬ ‭diaphragm.‬ ‭When‬ ‭inhaling,‬ ‭it‬ ‭will‬ T ‭lower‬ ‭and‬ ‭push‬ ‭the‬ ‭volume‬‭of‬‭the‬‭rib‬‭cage‬‭downward.‬‭It‬‭is‬‭a‬‭flat‬‭muscle,‬ ‭called‬ ‭radiated,‬ ‭which‬ ‭extends‬ ‭between‬ ‭the‬ ‭thorax‬ ‭and‬ ‭the‬ ‭abdomen.‬ ‭It‬ ‭has three beams:‬ ‭⮚‬ ‭A costal bundle: whose fibers originate from the 7th to the 12th rib.‬ ‭⮚‬ ‭A vertebral bundle: which originates from the lumbar vertebrae.‬ ‭⮚‬ ‭A sternal bundle: which originates at the level of the apophysis‬ ‭xiphoid.‬ ‭ his‬ ‭muscle‬ ‭is‬ ‭pierced‬ ‭by‬ ‭orifices‬ ‭which‬ ‭allow‬ ‭vessels‬ ‭including‬ ‭the‬‭aorta‬ T ‭and‬ ‭the‬ ‭vena‬ ‭cava‬ ‭to‬ ‭pass‬ ‭and‬ ‭the‬ ‭esophagus‬ ‭to‬ ‭pass.‬ ‭This‬ ‭muscle‬ ‭is‬ ‭therefore the main inspiration.‬