Ventilation: The Ventilation: The Mechanics of Mechanics of

BreathingBreathing

Miss UlrichMiss Ulrich

Organs of Organs of the the

RespiratorRespiratory systemy system

Lungs close up…Lungs close up…

Bronchial Bronchial Tree Tree Consisting Consisting of the of the PassagewayPassageways that s that Connect the Connect the Trachea and Trachea and Alveoli Alveoli

Q: Where does gas exchange occur?

BreathingBreathing

The movement of air into and out of The movement of air into and out of the lungs (the lungs (ventilationventilation) results from ) results from a pressure difference between the a pressure difference between the thoracic cavity and the atmosphere. thoracic cavity and the atmosphere.

This pressure difference is created by This pressure difference is created by changing the volume of the thoracic changing the volume of the thoracic cavity. cavity.

Involuntary RespirationInvoluntary Respiration

Involuntary RespirationInvoluntary Respiration.  .  The basic rhythm The basic rhythm of breathing occurs without conscious effort.  of breathing occurs without conscious effort. 

The The inspiratory centerinspiratory center located in the located in the medulla sets the basic rhythm by medulla sets the basic rhythm by automatically initiating inspiration with a two automatically initiating inspiration with a two second burst of nerve impulses to the second burst of nerve impulses to the diaphragm and the external intercostal diaphragm and the external intercostal muscles.   muscles.  

Contraction of the diaphragm Contraction of the diaphragm  and the external and the external intercostal muscles draws air into the lungs. intercostal muscles draws air into the lungs.

The Expiratory CenterThe Expiratory Center.   The expiratory .   The expiratory center is located in the medulla.  This center center is located in the medulla.  This center

functions during forced expiration functions during forced expiration stimulating the internal intercostal and stimulating the internal intercostal and

abdominal muscles to contract.abdominal muscles to contract.

InhalationInhalation During inhalation, the During inhalation, the diaphragmdiaphragm contracts and contracts and flattens and the flattens and the external external intercostal musclesintercostal muscles draw draw the ribs upward and the ribs upward and outward. outward. 

This increase in thoracic This increase in thoracic volume results in a volume results in a decrease in intrapulmonary decrease in intrapulmonary pressure.  pressure. 

Air enters the lungs to Air enters the lungs to stabilize the pressure stabilize the pressure difference between the difference between the external atmosphere and external atmosphere and the internal compartments the internal compartments of the lungs.  of the lungs. 

Normal inhalation is an Normal inhalation is an active processactive process, requiring , requiring muscular workmuscular work.  . 

During During quiet breathing, quiet breathing, intercostalsintercostals maintain the rigidity maintain the rigidity of the chest wall. Otherwise, of the chest wall. Otherwise, reduced intra-thoracic pressure reduced intra-thoracic pressure would cause the chest wall to would cause the chest wall to collapse inwards. collapse inwards.

External IntercostalsExternal Intercostals (on the (on the outside of the ribcase) wrap outside of the ribcase) wrap around from the back of the rib around from the back of the rib almost to the end of the bony almost to the end of the bony part of the rib in front. . They part of the rib in front. . They elevate the ribs. elevate the ribs.

Internal IntercostalsInternal Intercostals in the in the inside of the ribcase) extend inside of the ribcase) extend from the front of the ribs, and from the front of the ribs, and go around back, past the bend go around back, past the bend in the ribs . They depress the in the ribs . They depress the ribs.ribs.

Diaphragm In a healthy adult, the diaphragm is the dominant In a healthy adult, the diaphragm is the dominant

muscle of respiration at rest muscle of respiration at rest The diaphragm is a musculotendinous sheet The diaphragm is a musculotendinous sheet

separating the thorax from the abdomen. It is separating the thorax from the abdomen. It is attached to the thoracic cage under the lower ribs. attached to the thoracic cage under the lower ribs.

ExpirationExpiration Exhalation is normally Exhalation is normally

a passive process.  a passive process.  The diaphragm and The diaphragm and

external intercostal external intercostal musclesmuscles relax relax decreasing the decreasing the volume of the thoracic volume of the thoracic cavity.  cavity. 

This causes the This causes the pressure within the pressure within the lungs to exceed the lungs to exceed the atmospheric atmospheric pressure.  pressure. 

Air is expelled from Air is expelled from the lungs.the lungs.

Forced ExhalationForced Exhalation During a forced exhalation, the During a forced exhalation, the internal internal

intercostal musclesintercostal muscles contract, depressing contract, depressing the rib cage.  the rib cage. 

The The abdominal muscles contractabdominal muscles contract, pushing , pushing the organs in the abdominal cavity against the organs in the abdominal cavity against the diaphragm.  the diaphragm. 

The The thoracic volume decreasesthoracic volume decreases to a level to a level lower than achieved in normal exhalation.  lower than achieved in normal exhalation. 

These muscles are used to counteract the These muscles are used to counteract the effects of obstructive pulmonary disorders.  effects of obstructive pulmonary disorders. 

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ERVERV

These muscles are used during a These muscles are used during a forced exhalation to determine the forced exhalation to determine the expiratory reserve volume (ERV). .

ERV is - the maximum volume of gas ERV is - the maximum volume of gas that can be forcefully exhaled after a that can be forcefully exhaled after a normal exhalation (tidal volume). normal exhalation (tidal volume).

Other Terms of BreathingOther Terms of Breathing The volume of the The volume of the

lungs is divided lungs is divided into four functional into four functional compartments, compartments, lung lung volumesvolumes.  .  Combinations of Combinations of two or more lung two or more lung volumes are called volumes are called a a lung capacitylung capacity. .

Spirograph pattern graphSpirograph pattern graph

TermsTerms tidal volumetidal volume ( ( TVTV ) ) - the volume of gas - the volume of gas

inspired or expired during each normal inspired or expired during each normal (unforced) ventilation cycle (volume of air (unforced) ventilation cycle (volume of air moved into the lungs in a single breath.moved into the lungs in a single breath.

inspiratory reserve volumeinspiratory reserve volume ( ( IRVIRV ) ) -the -the maximum amount of gas that can be maximum amount of gas that can be forcefully inhaled after a normal inhalation. forcefully inhaled after a normal inhalation.

expiratory reserve volumeexpiratory reserve volume ( ( ERVERV ) ) - the - the maximum volume of gas that can be maximum volume of gas that can be forcefully exhaled after a normal forcefully exhaled after a normal exhalation. exhalation.

TermsTerms residual volumeresidual volume ( ( RVRV ) ) - the amount of - the amount of

gas left in the lungs after a maximum gas left in the lungs after a maximum (forced) exhalation. Necessary otherwise (forced) exhalation. Necessary otherwise the lungs would collapse.the lungs would collapse.

total lung capacitytotal lung capacity ( ( TLCTLC ) ) - the amount - the amount of gas in the lungs after a maximum of gas in the lungs after a maximum (forced) inhalation.  (forced) inhalation.  TLCTLC = = IRVIRV + + TVTV + + ERVERV + + RVRV

vital capacity ( VC )vital capacity ( VC ) -the maximum -the maximum volume of gas that can be exhaled by volume of gas that can be exhaled by voluntary effort after a maximum voluntary effort after a maximum inhalation.  VC = IRV + TV + ERVinhalation.  VC = IRV + TV + ERV

TermsTerms

inspiratory capacity ( IC )inspiratory capacity ( IC ) - the - the maximum amount of gas that can maximum amount of gas that can be inhaled after a normal be inhaled after a normal (unforced) exhalation.    IC = IRV + (unforced) exhalation.    IC = IRV + TV TV

functional residual capacity ( FRC )functional residual capacity ( FRC ) - the amount of gas left in the - the amount of gas left in the lungs after a normal (unforced) lungs after a normal (unforced) exhalation.  FRC =  ERV + RVexhalation.  FRC =  ERV + RV