Respiratory Flashcards
Poiselles law
Airway inversely proportional to radius to the power of 4
Flow proportional to pressure gradient and radius
Flow inversely proportional to viscosity and length
However many more small airways so overall resistance less in bronchioles
Measured by spirometry
Tidal volume and vital capacity
Measuring residual volume
Helium dilution
Nitrogen washout
Body plethysmography
Measuring dead space
Fowler single breath nitrogen - anatomical dead space
Bohr - physiological art co2 minus expired co2
Compliance
Volume change (L) / pressure change (cmH2O)
Max at mid insp - 200ml/cm h2o
Greater compliance at base
Measured exp
2/3 due to surface tension alveoli, 1/3 elastin and collagen
Hysteresis - different compliance insp and exp
Increased and decreases compliance
Increase - surfactant, age, emphysema
Decrease - oedema, fibrosis, pulmonaru venous hypertension
Pulmonary pressure
15mmhg
Lung metabolises
Surfactant
Synth - pg, histamine
Removes from blood - seratonin, pg, norad, bradykinin, ach
Activates - angiotensin
Po2 and sats
27.5mmhg - 50 %
40 - 75
60 - 90
90 - 98
bohr effect
Decrease o2 affinity of hb when pH falls
(Curve to right)
Causes oxygen dissociation curve to right
Harder for O2 to bind
Increased heat, co2 and 23 dpg
Decreased pH
Haldane effect
Decreased affinity for co2 on hb when oxygen attached
Deoxyhb increased affinity co2 therefore more in venous
Ficks law
Passive Diffusion of gas across membrane dependant on:
Thickness
Area
Pressure gradient
Diffusion constant
Henrys law
Amount of gas dissolved in liquid directly proportional to its partial pressure
CO
Shifts curve to the left
240 x affinity hb than 02
V/Q
Normally 0.8
4/5
Lower at bottom due to more blood flow
Brain breathing centres
Pneumotaxic (inhib) and apneustic in pons
In medulla:
Pre BÖTC pace maker to phrenic
Drg insp
Vrg exp (DIVE)
Chemoreceptors for breathing
Ventral medulla to inc co2 tension and H (H+ most important)
Aortic and cortid bodies same plus hypoxia
Aortic via x to medulla
Carotid via sinus and IX to medulla
Respiratory quotient
Co2 released/ o2 consumed
Carbs 1
Brain 0.97
Fat 0.7
Altitude pO2
0.21(mmhg-47)
Long term changes at altitude
Decreased bicarb (renal excretion)
Low PaCO2
Increased pulm art pressure
Increased alveolar vent
Diffusion vs perfusion limited
Diffusion CO and CO2 unable to fully transfer in time blood flows through
Perfusiom limited O2 and NO saturate within 0.75s
La place law
Pressure = 2*surface tension/radius
In Alveoli pressure reduced when surface tension reduced with surfactant
Age and lung function
Reduced elastic more air trapped - increased compliance, RV and FRC
Air trapping decreased FEV1
Vq mismatch decreased paO2 and decreased total capacity
