Pulmonary+Mechanics

=Gas Laws= >> P is absolute Pressure >> V is the volume >> n is the number of moles of gas >> R is the ideal gas constant >> T is the absolute temperature
 * Ideal Gas Law, P*V=n*R*T

>> special case of ideal gas law where number of moles, temperature constant >> Applicable to most physiological gas exchange
 * Boyle's Law, P1 * V1 = P2 * V2

>> The total pressure of a mixture of gasses is equal to the sum of the partial pressures of the components of the mixture >> usually, FIO2, or the fraction of inspired oxygen, is 21%.
 * Dalton's Law of Partial Pressure PT = PN2 + PO2 + PCO2 + PX

=Respiratory Anatomy=
 * Branching Structure maximizes surface area
 * Volume of lungs ~4L
 * Sphere of this volume has surface area 0.01m^2
 * Lungs have Surface area ~70 m^2
 * 300 million alveoli
 * each 300 microns diameter

Alveoli Factoids
>* at rest, 0.75s >* during exercise, 0.25s
 * 300 million alveoli
 * Average diameter 380 microns
 * total area 70 square meters
 * Membrane thickness 0.35-2.5 microns
 * Capillary length 10 microns
 * Capilary volume 70-140 ml
 * Blood Transit Time:

=Ventilation=
 * Air enters due to pressure gradients
 * Flow is related to driving pressure gradient
 * Flow is inversely proportional to resistance

Inspiratory Muscles
>* Innervated by phrenic nerve of C3-C5 >* innervation from spinal cord >* Includes scalene, sternocleidomastoid, etc >* innervation off cervical cord
 * Diaphragm
 * External intercostals
 * Accessory Muscles

Ventilatory Volumes
>* Vt, volme of gas exhaled per breath. >* Typically 500 ml >* Volume exhaled per minute. >* VE = Vt * f >* f is minute ventilation rate. >* VD, >* typically 150ml >* no gas exchange occurs here >* Va = Vt - VD x f >* Volume of fresh gas entering lung and available for gas exchange. >* Estimation of alveolar ventilation: >>* Essentially all CO2 in air comes from alveolar gas >>* Dead pace air contains no CO2 >>* Va may be estimated by measuring CO2 >>* Va = total CO2 exhaled / CO2 content >>* Va = VCO2/PCO2 * f
 * Tidal volume
 * Exhaled Minute volume
 * Anatomic dead space
 * Alveolar Ventilation

Bulk Flow & Diffusion
>* Diffusion becomes more important than bulk flow
 * cross sectional area increases with each division
 * velocity becomes very small at bronchiole

>* diffusion is directly proportional to surface area >* diffusion is directly proportional to concentration gradient >>* Concentration gradient is proportional to partial pressures >* Diffusion = Diffusion Constant * Area * Conc Gradient / Thickness
 * Fick's Law of diffusion

>* Poiselle's Law >>* V=P * pi * r^4 / 8 n l >>* Thus, radius is often driving force >>>* Radius influenced by irritaiton, sympathetic, parasympathetic tone
 * Bulk Flow

=Pulmonary Pressure-Volume Curves=

Lung Volumes
>* TLC, volume of gas when lungs full
 * Total Lung Capacity

>* VC, volume f gas to take lungs from max exhalation to max inhalation >*
 * Vital Capacity

Gravitational Effects on Pleural Pressures
=Pulmonary Circulation= =Starling's Forces=