Pulmonary Ventilation
Alveolar dead space
non-functional alveoli due to collapse, poor perfusion, or obstruction
Exhalation (expiration)
- Breathing out is also due to a pressure difference - To exhale, pressure difference is opposite that of inhalation - pressure in lungs is greater than that of the atmosphere - *Passive exhalation*
Infant Respiratory Distress Syndrome (IRDS)
- Deficiency of surfactant in premature infants - Alveoli collapse due to high surface tension - Treated by using continuous positive air pressure (CPAP) breathing machines - increases pressure of air going into the lungs - and synthetic surfactant until infant begins producing its own
Active exhalation
- Forceful exhalation- ex. Yelling, exercise, or playing a wind instrument - Requires muscles of exhalation - Although Pip is always less than Ppul, Pip can sometimes exceed Patm during forced exhalation such as a cough
*surface tension* of alveolar fluid
- Found at all air-water interfaces - Polar water molecules are more strongly attracted to each other than gas in air > when air tries to fill the alveoli, water on alveoli surface doesn't want to pull away from itself and produces an inward pull resisting expansion - Causes alveoli to assume the smallest possible diameter - Accounts for 2/3 of lung elastic recoil. - If unopposed, this force would cause the alveoli to close w/ each expiration and make our *"Work of Breathing"* insupportable
Inhalation (inspiration)
- Just before each inhalation, pressure inside lungs is equal to atmospheric pressure > 760mmHg - Air flows from high to low pressure - For air to flow into lungs, pressure in alveoli must be less than atmospheric - This decrease in alveoli pressure is accomplished by increasing the volume of lungs thru mechanical coupling to a change in thoracic volume
Nonrespiratory Air Movements
- May modify normal ventilation rhythm/volume - Most result from reflex action, although some are voluntary - Not used for the express purpose of moving air for gas exchange - Ex.- cough, sneeze, crying, laughing, hiccups, yawns
Diaphragm
- Most important muscle for inspiration - Dome-shaped skeletal muscle innervated by phrenic nerve
Passive exhalation
- Normal exhalation during quiet breathing - Called passive b/c no muscular contractions are involved Instead, it results from inward forces: - The elastic recoil of chest wall and lungs - the inward pull of surface tension of alveolar fluid
Intrapulmonary (intra-alveolar) pressure (Ppul)
- Pressure in alveoli - Changes when breathing - Always eventually equalizes w/ Patm
Intrapleural pressure (Pip)
- Pressure in pleural cavity - Changes when breathing - always be negative pressure (<Patm and <Ppul) in order to prevent lung collapse - Plural fluid amount must be kept to a mini - Excess is pumped out by lymphatics - If accumulates > positive Pip pressure > lung collapse
3 steps of respiration
- Pulmonary ventilation - External (pulmonary) respiration - Internal (tissue) respiration
Airway Resistance
- larger diameter = less airway resistance and the greater flow - If bronchioles dilate even a little, resistance drops by a power of 4 > Constriction increases resistance by power of 4
Pressure's role in airway resistance
- lungs expand during inhalation = bronchioles enlarge b/c they're expanding outward in all directions > decreases resistance to flow in to lungs - During exhalation, the increase in pressure compresses bronchioles > increases resistance to flow out of lungs
Surfactant
- mixture of phospholipids and lipoproteins present in alveolar fluid - Reduces alveolar fluid surface tension below surface tension of pure water by blocking some water-to-water interactions - Allows for easier inflation of alveoli and helps prevent alveolar collapse during exhalation
Pulmonary ventilation
- mvmt of air btwn atmosphere and alveoli of lungs - consists of inhalation and exhalation
Obstructive disorders
- pathological condition that narrows, or obstructs, airways - Narrowing of airways greatly increases resistance for inhalation and exhalation > Increased work of breathing - Airways can also become blocked via collapse of bronchioles, alveoli, or build-up of excess mucous
External intercostals
2nd most important muscles of inhalation
Compliance of Lungs
How easily something stretches - High pulmonary compliance = lungs and chest wall are easily expanded - easier for inflation - Low pulmonary compliance = they resist expansion - harder for inflation
- Elasticity- Lungs have a high amount of elastic fibers > Allows for greater stretch and recoil - Surface tension
Lung compliance dependent upon which 2 factors?
anatomical dead space
Only about 70% of tidal volume (air breathed in and out at rest) reaches respiratory zone - other 30% remains in conducting zone - No contribution to gas exchange
- Negative respiratory pressure = less than Patm - Positive respiratory pressure = greater than Patm - Zero respiratory pressure = Patm
Pressure Relationships in the Thoracic Cavity: how are Respiratory pressures (those in cavities used for breathing) described relative to Patm?
- Intrapulmonary (intra-alveolar) pressure (Ppul) - Intrapleural pressure (Pip)
Pressures Involved in Ventilation
we must know the physics of gases
To understand how mechanical coupling btwn lungs, pleural cavities, and chest wall results in breathing...
Pneumothorax
air, or liquid (blood or Interstitial fluid), in pleural cavity - From either wound in parietal or rupture of visceral pleura - Intrapleural pressure goes from -4 to 0 thus eliminating the transpulmonary pressure that keeps a lung open - Inward forces no longer opposed by outward force > lung collapses in on itself - chest wall moves outward b/c its elastic recoil is no longer opposed by coupling to the inward pulling forces of lungs - Treated by removing excess intrapleural air/fluid w/ chest tubes; restores negative pressure => lung re-inflates - b/c lungs are in separate pleural cavities, one may collapse w/o interfering w/ function of other
Boyle's law
applies to containers w/ changeable volume - like our thoracic cage. - states that volume and pressure are inversely related. - Thus if there is a decrease in a container's volume, there will be an increase in pressure w/in. - V ∝ 1/P - P1V1 = P2V2
gas laws
apply equally to gases of atmosphere, gases in our lungs, gases dissolved in blood, and gases diffusing into and out of cells of body
Negative Pip
caused by opposing forces pulling lungs in opposite directions - Inward pull being opposed by outward pull creates a lesser pressure btwn lungs and thoracic wall (Pip) when compared to pressure in lungs (Ppul)
- Nitrogen (N2)- 78% - Oxygen (O2)- 21% - Carbon Dioxide (CO2)- 0.04% - Water Vapor- variable, but on avg ~1%
gas composition of earth's atmosphere
barometer
measures *atmospheric pressure (Patm)* - Baro = pressure or weight - Meter = measure - Air pressure varies greatly depending on the altitude and the temperature
Smooth muscle's role in resistance
regulates diameter of airways - dependent upon parasympathetic and sympathetic interaction
Physiological (total) dead space
sum of anatomical and alveolar dead space
These want lungs to assume the smallest possible size > promote lung collapse 1) *Elastic recoil* of lungs decreases lung size = Imagine the recoil of a slightly stretched rubber band 2) *Surface tension* of alveolar fluid reduces alveolar size = The water lining the alveolar surface in lungs doesn't want to pull apart when they are slightly inflated, or are inflating
what are 2 inward forces of negative Pip?
- surface tension of alveolar fluid - Compliance of lungs - Airway resistance
what are 3 other factors that affect the ease with which we ventilate?
- Sternocleidomastoid- Elevates sternum - Scaline- Elevates first 2 ribs - Pectoralis minor- Elevates ribs 3-5 - Involved in *active inhalation* - These assist in increasing thoracic volume during exercise or deep, forceful inhalations - Do not really contribute quiet breathing
what are accessory muscles of inhalation? what are they involved in?
asthma, bronchitis, chronic obstructive pulmonary disease (COPD), emphysema, cystic fibrosis
what are examples of Obstructive disorders?
mass and weight (5 x 1018 kg, most within 11 km of surface) - The pressure we feel on surface of earth is the weight of gasses in atmosphere - At high altitudes, atmospheric pressure is less; descending to sea level, atmospheric pressure is greater. - Our bodies are adapted to this pressure and it plays a key role in the foundation for many of our systems
what do gases of atmosphere have?
- Lowers the dome > increases the vertical volume of thoracic cavity - The change in volume is transferred to lungs via intrapleural cavity and pressure w/in it => Intrapleural pressure becomes slightly more negative generating a greater outward pull on lungs => causes lungs to expand thus increasing their volume and decreasing pressure at alveoli below that of atmospheric - Air rushes in from higher external atmospheric pressure to lower internal alveoli pressure causing lungs to fill in an effort to equalize the 2 pressures - This is responsible for ~75% of air that enters lungs during *resting (quiet) breathing* - Amount of diaphragm contraction (flattening) correlates to amount of air entering lungs - More flattening => increased volume (thoracic and lungs) => greater pressure difference => increased filling to equalize
what does the contraction do to the diaphragm?
properties of earth's atmosphere to extract O2 necessary for human life
what does the respiratory system depend on?
it flattens - Advanced pregnancy, excessive obesity, and confining abdominal clothing can obstruct diaphragm flattening
what happens during Contraction of diaphragm?
- Exhalation begins when the inspiratory muscles relax - diaphragm relaxes and begins to rise superiorly and regain it's dome shape - external intercostals relax and ribs are depressed This decreases the anteroposterior, vertical, and lateral diameters of thoracic cavity - Decreases lung volume - This causes an increase in alveolar pressure above that of atmospheric - Air flows from high (lungs) to low (external environment) pressure
what happens during passive exhalation?
these muscles elevate ribs increasing anteroposterior and lateral diameters of chest cavity -Increases thoracic volume in addition to that of diaphragm contraction - Responsible for ~25% of air entering lungs during quiet breathing - During inhalation, the ribs move upward and outward like the handle on a bucket
what happens to the external intercostals during contraction?
- Abdominals- Moves inferior ribs downward and compresses abdominal viscera > Forces diaphragm superiorly - Internal intercostals- Pulls ribs inferiorly (downward)
what happens to the muscles during active exhalation?
760 mmHg = 1 atmosphere
what is the air pressure at sea level?
Pulls outward on lungs wanting to enlarge lungs - *Caused by elasticity of chest wall* = This outward pull is coupled to lungs by pressure in sealed intraplerual space
what is the outward force of negative Pip?
changes in pressure at alveoli relative to atmospheric pressure - changes in pressure are due to changes in thoracic volume
what is ventilation/breathing made possible by?
- *Restrictive disorders* restrict lung expansion resulting in a decreased lung volume, an increased work of breathing, and inadequate ventilation that can lead to reduced blood oxygenation - Pulmonary fibrosis- Deposition of scar tissue in the lungs; Scar tissue not very elastic - Deficiency in surfactant - Pulmonary edema (excess fluid in the lungs) - Impedance to expansion- E.g. Ventilatory muscle paralysis, broken ribs, obesity
what things decrease compliance of lungs?
