HLB - mechanics of breathing, pressures and work

what is the normal resting breath range

between 12 to 18 breaths per minute

what is minute ventillation

the volume of air entering the lungs each minute

what is daltons law

when two or more gases, that do not react, are in a container, their total pressure is the sum of their partial pressures

what is boyles law

at a fixed temperature, pressure is directly proportional to 1/volume

what is charles’ law

at a constant pressure, the volume is directly proportional to temperature

what is henrys law

the number of molecules in a gas that dissolve in a liquid is equal to its solubility

is inspiration an active or passive process

inspiration is an active process

pressure in which two places are equal at the end of inspiration

pressure in the mouth and alveoli

where are the scalene muscles inserted

into the first two ribs

what do the scalene muscles do during contraction

raise the upper ribs and push the sternum forward

what diameter does the bucket handle motion increase

the transverse diameter of the thoracic cavity

what type of inspiration are accessory muscles involved in

forced inspiration

give three examples of accessory muscles

sternomastoid, serratus anterior, and pectoral muscles

where are the sternomastoid muscles located

the upper neck

where are the serratus anterior muscles located

the lateral wall of the thorax

when is ventilation largely diaphragmatic

at rest

is expiration an active or passive process

expiration is a passive process

expiration causes a rise in which two pressures

intrapleural pressure and alveolar pressure

contraction of the abdominal muscles is required in which type of expiration

forced expiration

what two processes involves forced expiration

coughing or sneezing

what can intrapleural pressure rise up to in forced expiration

8kPA

what pressure determines if air will enter the lungs

intra-alveolar/ intra-pulmonary pressure

which is lower intrapleural pressure, or atmospheric pressure

intrapleural pressure

why is intrapleural pressure lower than atmospheric pressure

due to the recoil of the chest and lungs

what does Ptp stand for

the transmural pulmonary pressure

what is the transpulmonary pressure

a distending pressure exerted by the chest on the pleural space

what is the Ptp transferred to and why

the alveoli, to increase their volume and lower their pressure/ generate airflow inwards

during quiet breathing is Ptp positive or negative

Ptp is always positive during quiet breathing

what does Ppl stand for

intrapleural pressure

during quiet breathing is Ppl positive or negative

intrapleural pressure is always negative during quiet breathing

what is Palv

intrapulmonary/ alveolar pressure

what occurs to Palv during quiet breathing

it moves from slightly negative to slightly positive

which is higher during quiet breathing, Palv or Ppl

Palv

what is the value of Palv at the ends of inspiration and expiration and why

zero, so that there is no airflow

what is Ptp equal and opposite to in the lungs

the elastic recoil

what does FRC stand for

functional residual capacity

what is FRC

the volume of air left in the lungs at the end of a normal breath

at FRCwhat does the outward recoil of the chest balance with

the inwards recoil of the lungs

what is the volume of air determined by at FRC

the elastic properties of the lungs and chest wall

what are three things FRC is affected by

lung disease, emphysema, pulmonary fibrosis

what effect does pulmonary fibrosis have on FRC and how

it decreases FRC as the lungs are stiff and small, so elastic recoil is increased

what affect does emphysema have on FRC and how

it increases FRC as it causes a loss in alveolar tissue, so decreases elastic recoil

what is impedance

the frictional airway resistance and elastic resistance to the stretching of the lung and chest wall

what does CL stand for

lung compliance

what is lung compliance

the ability of the lungs to stretch and recoil during ventilation

what is lung compliance measured in

change in lung volume, per unit change in distending pressure

what does P stand for

distending pressure

what is distending pressure

the pressure difference across the lung

what is distending pressure equal to

the alveolar intrapleural pressure

what is hysteresis

the difference between an inspiratory curve and expiratory curve on a graph of volume against transmural pressure

on a graph of volume against transmural pressure, how can the static lung compliance be worked out

it is the steepest gradient, just above the FRC

what is a static pressure volume loop

a graph of volume against transmural pressure, with both an inspiratory and expiratory curve

what is dynamic compliance

the change in lung volume per change in pressure, during active breathing

what does the area of a dynamic loop measure

the work done against airway resistance

in what type of lungs does dynamic compliance differ to static compliance

in stiff lungs

does interstitial fibrosis cause an increase or decrease in compliance

interstitial fibrosis causes a decrease in compliance

why does interstitial compliance cause a decrease in compliance

the alveolar walls are more stiff due to scarring/ fibrosis

is airflow laminar or turbulent during quiet breathing

laminar

how do gas particles move in laminar breathing

gas particles move parallel to the walls of the bronchi, where center gas particles move faster than outer ones, creating a cone shaped front

when does turbulent airflow occur

at higher linear velocities/ during exercise

where does turbulent flow occur

in wide airways and near branch points

what does RAW stand for

airway resistance

what causes airway resistances

friction between air and mucosa

how is RAW calculated

pressure between the alveoli and mouth, divided by the flow rate

what are the two things RAW is inversely proportional to

the 4th power of the radius, and the viscosity of the fluid

what does poiseuiles’s equation mean in relation to RAW

halving the radius increases the resistance by 16 times

which part of the respiratory system causes the most RAW

nose, pharynx and trachea

what does the parasympathetic nerve supply affect in terms of factors affecting RAW

the bronchomotor tone

what do beta adrenergic receptors cause in the lungs

relaxation of the bronchial smooth muscle and epithelium

what does nitric acid cause in the lungs

bronchodilation

what is the affect of acute asthma on RAW

it increases it

why does acute asthma increase RAW

it causes bronchoconstriction, mucosal oedema, mucus hypersecretion and mucus plugging

does COPD increase or decrease RAW

COPD increases RAW

why does COPD increase RAW

due to bronchoconstriction and chronic mucosal hypertrophy

what are surface tension factors caused by

air fluid interface in the alveoli

what do cohesive forces do in relation to surface tension

shrink bubbles/ alveolus down due to tension

what is LaPlace’s law

pressure to keep the alveolus open equates to twice the surface tension, over the radius of the alveoli

what is atelectasis

when alveoli and small airways are inherently unstable and collapse during expiration

what is surfactant

a mixture of phospholipids

what produces surfactant

type 2 pneumocytes

where is surfactant found

floating on the surface of alveolar fluid

how does surfactant lower surface tension

hydrophilic and hydrophobic ends repel each other, interfering with liquid molecule attraction

why is the reduction of surface tension important

it increases compliance, promotes alveolar stability, prevents alveolar collapse, reduces hydrostatic pressure in tissue

why does hydrostatic pressure in tissues outside the capillaries need to be managed

to keep the lungs dry, otherwise fluid can be sucked into the alveoli from the capillaries