Respiratory Physiology Study Guide Flashcards
ventilation
breathing (inspiration and expiration), the mechanical process of breathing
- dependent on volume changes in thoracic cavity
- volume changes -> pressure changes -> flow of gasses to equalize pressure
atmospheric pressure
The pressure exerted by the gasses / air surrounding the body (at sea level atm is 760mmHg or 1 atm)
(-) respiratory pressure - lower than atm
(+) respiratory pressure - higher than atm
(0) respiratory pressure = atm
intrapulmonary pressure
(Ppul): the pressure within the alveoli
- Rises/falls with the phases of breathing – always equalizes with atmospheric pressure
- gets lower with inhale
Intrapleural Pressure
the pressure in the pleural cavity
- Rises/falls with the phases of breathing –always about 4mmHg less than Ppul
relationship between intrapulmonary and intrapleural pressure
Pip is always negative relative to Ppul
- Any condition that equalizes Pip with Ppul or atmospheric pressure will cause lung collapse
Transpulmonary Pressure
the difference between Ppul and Pip
The pressure that keeps the air spaces of the lungs open and prevents lung collapse!
how parietal and visceral pleurae are attached to each other
presence of pleural fluid causes strong adhesive force between pleurae
transpulmonary pressure is greatest when ….
the lungs are larger in size
atelectasis
“lung collapse”
- when a bronchiole becomes plugged
- associated alveoli collapse
- often extension of pneumonia
pnuemothorax
“air thorax”
- presence of air in the pleural cavity
- reversed by drawing air out via a chest tube
- lung will reinflate
boyles law
relationship between pressure and volume of gas - at constant temp, pressure is inversely related to volume (gasses always fill their container)
- p1v1=p2v2
inspiratory muscles
diaphragm and external intercostals
nerve that delivers impulses for contraction from brain’s respiratory centers
phrenic nerve
volume and pressure during inspiration
- diaphragm + external intercostals contract
- height and diameter of thoracic cavity increase
- lungs stretch, intrapulmonary volume increases, Ppul decreases
- air rushes into lungs
- Ppul equalizes to Patm
volume and pressure during expiration
- inspiratory muscles relax - rib cage descends, lungs recoil
- thoracic + intrapulmonary volumes decrease
- Ppul rises
- when Ppul > Patm, air flows out
2 muscles used for forced expiration
transerve abdominis and obliques contract (internal intercostals are also involved)
3 accessory inspiratory muscles involved in forced inspiration
scalenes, SCM (sternocleidomastoid), pectoralis minor
equation + relationship between air flow, airway resistance, and change in pressure
F = ΔP/R
- airway resistance (R): friction or drag encountered in the respiratory passageways
- small change in P can create large changes in air flow (2mmHg or less during quiet breathing)
- flow (f) varies inversely with resistance (r)
- R is determined by diameters of conducting tubes (highest resistance is in medium bronchioles, because the really small ones have diffusion)
- increased resistance = decreased flow
- increased change in pressure = increased flow
bronchodilator
relax muscles in lungs and widen airways/bronchioles
branch of ANS responsible for bronchoconstriction
parasympathetic nervous system
epinephrine
bronchodilator
surface tension
attracts liquid molecules to each other, resists any force that attempts to increase the liquid’s surface area
- water has a high surface tension, so its always working to keep alveoli at their smallest sice
surfactant
detergent-like complex of lipids and proteins produced by type II alveolar cells
- reduces surface tension and discourages alveolar collapse - less energy is required to expand the lungs
when surfactant is made during development
24-28 weeks (done by 35 weeks)
lung compliance
measure of the change in lung volume that occurs with a given change in transpulmonary pressure (higher compliance = lungs that are easier to expand)
- determined by distensibility of lung tissue and alveolar surface tension
factors that reduce lung compliance
fibrosis, reduced amount of surfactant, decreased flexibility of the thoracic cage
tidal volume (TV)
air inspired with normal, quiet breathing (500 mL)
inspiratory reserve volume IRV
air inspired beyond TV (3100 mL)
expiratory reserve volume (ERV)
air expired beyond TV (1200 mL)
residual volume RV
air that remains in the lungs after ERV (1200 mL)
minimal volumes MV
small amount of air that remains in the lungs - even if the chest is opened
Anatomical Dead Space
air that remains in the passageways and does not contribute to gas exchange; ~150mL
Alveolar (Physiologic) Dead Space
air in non-functional alveoli
Total Dead Space
the sum of non-useful volumes – anatomical + alveolar dead space
Obstructive Pulmonary Diseases
diseases of increased airway resistance
- TLC, FRC, RV may increase
Restrictive Disorders
diseases of reduced lung capacity due to fibrosis/disease
- VC, TLC, FRC, RV may decline
inspiratory capacity IC
tv + irv 3600mL
functional residual capacity FRC
rv + erv 2400mL
vital capacity VC
irv + itv + erv 4800mL
total lung capacity TLC
sum of all lung volumes 6000mL
Forced Expiratory Volume (FEV)
determines the amount of air expelled during specific time intervals of the FVC test
FEV1
the amount of air exhaled during the 1st second – typically, about 80%
alveolar ventilation
amount of air flowing in/out of the alveoli per unit of time
- AVR (mL/min) = frequency (breaths/min) x TV – dead space (mL/breath)
- more effective measurement than minute ventilation because dead space is taken into account
- rapid, shallow breathing decreases AVR
Daltons law
- how gas behaves when it is part of a mixture of gases
- The total pressure exerted by a mixture of gases equals the sums of the pressures exerted by each gas individually
- The partial pressure of each gas is proportional to its percentage in the mixture
- Example: O2 makes up 21% of the atmosphere. It has a partial pressure (PO2) of 159mmHg
21% x 760mmHg = 159mmHg
henrys law
how gasses move in and out of solutions
- Each gas will dissolve into a liquid in proportion to its partial pressure
- The greater the concentration of a particular gas, the more and the faster that gas will go into solution
- The direction and amount of movement of a gas are determined by its partial pressure in the 2 phases
- Additional Factors:
Solubility - CO2 is 20x more soluble in H2O than O2
Temperature - as a liquid’s temperature rises, solubility decreases
partial pressure gradient for O2 in the lungs
Venous Blood PO2 = 40mmHg
Alveolar PO2 = 104mmHg
- oxygen is driven into blood as it moves down a steep pressure gradient
- blood can flow 3x faster and still be well-oxygenated
partial pressure of CO2 in the lungs
Venous Blood PCO2 = 45 mmHg
Alveolar PCO2 = 40 mmHg
- diffuses down a less steep pressure gradient than oxygen
- more soluble than oxygen despite diffusing across in equal amounts
ventilation
amount of gas reaching the alveoli
- Changes in PCO2 control ventilation by changing bronchiole diameter
- Where alveolar CO2 is high, bronchioles dilate for faster CO2 removal
- Where alveolar CO2 is low, bronchioles constrict
- Striving for efficient CO2 removal!
Perfusion
amount of blood reaching the alveoli
- Changes in PO2 control perfusion by changing arteriolar diameter
- Where alveolar O2 is high, arterioles dilate to stimulate O2 pickup
- Where alveolar O2 is low, arterioles constrict to divert blood elsewhere
- Striving for efficient O2 pickup!
exchange of O2 and CO2 between blood and body tissues (internal respiration)
- PO2 of tissues < PO2 of blood
O2 is driven into the tissues - PCO2 of tissues > PCO2 of blood
CO2 is driven into blood
efficient coupling of ventilation and perfusion in the lungs
they must be well matched for efficient gas exchange