Muscles of Inspiration 

• Diaphragm 
• External intercostals

Contraction of Diaphragm

• Displaces abdominal conents to enlarge thoracic cavity
• elevates margins of lower ribs to increase thorax circumference (they extend outwards)

External intercostals

• used for quiet respiration
• contraction of external intercostal muscles elevates anterior end of each rib to raise the rib cage and increase the volume of the thorax

Muscles of Forced Expiration

• When ventilation increases to >40 liters/minute
• abdominal muscles: abdominal muscles contract to increase intra-abdominal pressure and force diaphragm upward
• Internal intercostal muscles: contraction of internal intercostal muscles depresses ribs to decrease the thorax volume

Pleura

• space between the lungs and chest wall 
• pleural fluid
• pleural pressure(subasmospheric, negative)
• transpulmonary pressure=P_alveolus-P_pleural 
• P  is -5 at rest

Elastic Properties of the Lung

• elastin primarily contributes to elasticity
• collagen limits over-xpansion
• these fibers generate elastic recoil
• changing the composition of these fibers(pulm fibrosis or emphysema) will change the elastic recoil...or compliance of the lung

Pneumothorax

• loss of sub-atmospheric pressure in pleural space
• when chest wall is breached, air rushes into the thoracic cavity
• elastic recoil causes chest wall to spring outward and lungs to collapse

Pulmonary Surfactant

• made by type II alveolar cells lining the alveoli-reduces surface tension
• 80% phospholipids, 5% surfactant proteins(SP-A, B, C, D) plus lipids and trace materials
• premature infants often have insufficient surfactant production leading to IRDS

Work of Breathing

• 3-5% of total body energy expenditure(baseline) increases with exercise
• factors impacting energy expenditures: compliance work(overcoming elasticity of lung and chest wall, 65%), tissue resistance work(7.5%), airways resistance(28%)
• The capacity to exchange air with the environment is impated by patholigies to: elasticity of lungs and/or chest wall and airway structure

Pulmonary Volumes

• Tidal Volume: volume of normal breath(500ml)
• inspiratory reserve volume: volume that can be maximally inspired after normal inspiration
• expiratory reserve volume: volume that can be maximally expired after normal expiration
• Residual volume: lung volume at end of maximal experiation

Pulmonary Capacities

• Inspiratory capacity: tidal volume + inspiratory reserve volume
• Functional reserve capicity: residual volume+expiratory reserve volume
• Vital capicity= ERC+tidal volume + inspiratory reserve volume
• total lung capacity= vital capacity+residual volume

Types of Dead Space

• anatomic: conducting airways
• physiologic: nonfunctioning alveoli

Daltons Law of Partial Pressures

• the total pressure exerted by a gas mixtur is equal to the sum of the partial pressure which each gas would exert if it alone occupied the entiere volume
• Pb=PN2+PO2+PCO2+PH2O
• the partial pressure of water is important becuase upper airway efficiently saturates inspired air before it reaches the lungs

Ventilatory Flow Percentages

• FEV1 calculated as amount of air exhaled in 1 second
• divided by the FVC to get a percentage
• obstruction is about 42%, takes longer to expel FVC (Residual volume is high in obstruction)
• restrictive means you dont have a big FVC and you can exhale pretty fast so its around 90%
• restrictive lung diseases: pulmonary fibrosis, muscular dystrophies, obesity

Obstructive Lung Diseases

• bronchoconstriction: Asthma
• Structural Changes in airways: Chronic Bronchitis
• Obstructions within airways: excess bronchial secretions
• tissue destruction: emphysema(loss of elastin)
• obstructive increase lung volumes and airway resistance and decrease pulmonary function tests
• lung compliance increases in emphysema

Airway Smooth muscles

• airways contain smooth muscle down to the respiratory bronchioles
• Neural control: Dilation-sympathetic; Constriction-parasympathetic
• Humoral control: Dilation Blood epi and norepi, constriction-histamine(mast cells)

Dynamic Airway Compression

• effort dependent at the beggining
• majority is effort-independent(increasing effort will not increase expiratory flow)
• curve goes up sharply then follows a curve down

Expiratory Flow

• Cartilage rings hold large airways open
• Palv= Effort+ Lung elastic recoil
• Ppleura=Effort
• Pairway= decrease from alveolus to mouth during flow because of airway resistance
• Airway resistance is inversely related to lung volume

Equal Pressure Point

• location in the lung where the Pairway=Ppleura and airway collapse occurs slightly beyond that point
• part of expiratory flow 

Pulmonary Vasculature

• recieves 100% from right ventricle
• systolic 25mmHg
• Diastolic 0-1mmHg
• very compliant, huge range of how much blood they can hold

Pulmonary Blood Volume

• roughly 0.5 liters
• compliant-act as resevoir
• about 70ml in capillaries
• blood in capillary for 0.3 to 0.8 seconds

Top Lung Zone

• lowest perfusion
• arterial pressure is lower then alveoli
• gets more air then it does blood 
• causes compression on the blood vessel, very little flow

Middle Lung Zone

• pressures in alveoli and artery are pretty much equal
• allows for good flow 

Bottom Lung Zone

• most purfusion
• arterial pressure far exceeds alveolar pressure
• full distension and increase in flow in this zone 

Hypoxic Vasoconstriction

• oxygen <70% (not enough oxygen)
• if this happens then the vasculature constricts
• unique characteristic of pulmonary circulation
• allows blood floow to go to most ventilated alveoli

Extremes of V/Q ratio

• no ventilation has a decreased V/Q ratio (zero/flow)
• normal=0.8, which is set as a standard of 1 on his V/Q scale
• no perfusion has an inceasing V/Q ratio(V/zero)

Rates of Gas transfer Across

Alveolar Membrane

• partial pressure gradients: l
• surface area for diffusion: increase with exercise, decrease with emphysema and atelactasis
• solubility of gases(CO2 20x more soluble then O2
• thickness of alveolar membrane(diffusion distance): pulmonary edema, pulmonary fibrosis, pneumonia

PO2 Gradient in circulation

• areterial end of capillary is PO2 of 95mmHg
• Interstitial space has a PO2 of 40 mm Hg
• the target cell PO2 is usually 23 mmHg
• PO2 in the venous end of the capillary is usually around 40mmHg  
• increasing blood flow causes interstitium PO2 levels to be closer to arterial levels, slowing down delivery
• opposite happens when slowing down blood flow

Diseases effecting Thickness 

• Pneumonia: inflammatory fluid accumulation within alveoli
• Pulmonary Fibrosis: chronic airway irritation replaces lung tissue with fibrous tissue
• Pulmonary Edema: increase in vacular permeability or pulmonary pressure(congestive heart failure), increases interstitial fluid

PCO2 Levels in Circulation

• Arterial end of capillary has PCO2 levels of 40mmHg
• interstial fluid has levels of 45mmHg
• target cell has levels of 46mmHg
• venous end of capillary has levels of 45 mmHg
• if you dont increase blood flow you have large increase in PCO2 in interstitial fluid

Shifting Hb Curve to The Right

• increased hydrogen ion
• increased CO2 (decrease pH levels
• Increased temperature 
• increased BPG 
• a right shift goes right and down and allows O2 to unload at higher PO2 levels

Haldane Effect: Key Points

• at the tissues:
• The low tissue PO2 decreases Hb saturation:HbO2    ->Hb+O2
• this facilitates CO2 binding and transport: Hb+CO2    ->HbCO2
• Bohr Effect can be integrated with this(pH and CO2)

Medullary Respiratory Centers 

• regulate rhythmicity
• activate respiratory muscles
• three regulatory regions: DRG(inspiratory neurons that synapse with motor neurons for inspiration), VRG(insp & Exp neurons active with forced), pre-botzinger(respiratory rhythm generation)

Pontine Respiratory Centers

• located within the pons
• influence the output from medullary respiratory centers
• apneustic center: prolongs inspiration by activating neurons in the pre-botzinger complex(sustained contraction)
• pneumotaxic center: halts inspiration by sending inhibitory signals to the apneustic center and prebotzinger complex

Cortex

• outer layer of brain
• voluntary: modifies respiration for speech, yawing, coughing, or breath holding within certain limits
• respiratory reflexes will over ride voluntary actions

Limbic System and hypothalamus

• regulate emotional responses
• control breathing patterns during emotional states

Arterial Chemoreceptors

(peripheral chemoreceptors)

• detect changes in PaO2, PaCO2 and pH
• primary sensitivity is to changes in PaO2
• located in carotid artery with afferent signals via the glossopharyngeal nerve
• or located in aortic arch with afferent signals via the vagus nerve
• do not regulate minute to minute changes in resp.
• primarily an emergency response to low PO2 (below 60mmHg)

Central Chemoreceptors

• central chemoreceptors regulate minute to minute ventilation
• found w/ in the medulla near the ventral respiratory group
• very sensitive to PCO2 and H+
• of note, blood-brain barrier is relatively impermeable to HCO3 and H+ but is highly permeable to CO2

Pulmonary stretch receptors

• found within the smooth muscle of lung airways
• stretching of the lung induces activation of receptors which send inhibitory signals to the medullary centers
• negative feedback mechanism that prevents over-inflation
• active when tidal volumes are high during max. exercise

Irritant receptors

• found in airway epithelial cells
• noxious gas, dust, and cold air can activate receptors 
• lead to bronchoconstriction and rapid shallow breathing
• this is a protective mechanism limiting exposure
• irritant receptors may play a role in asthma
• activation of receptors can induce sneezing or coughing

Pre-eclampsia

• women becomes hypertensive and shows albumin excretion in urine 
• cause is unkown 
• related to placenta and in extreme cases the placenta is removed

Forces first breath must overcome

• surface tension
• elastic recoil of lungs and chest wall
• tissue resistance
• viscous resistance
• a transpulmonary pressure as high as 60-80 cm H2O may be needed to overcome all the resisting factors