Biophysics of breathing. Spirography

                                          Lecture outline

•           Mechanisms of gas exchange between organism and surroundings (respiratory movements –
mechanics of breathing, diffusion and dissolution of gases)

•           Respiratory volumes and capacities

•           Respiratory resistances

•           Respiratory work

•           Spirography

•           Some biophysical aspects of breathing

                                       Respiratory movements

•             These movements are done mainly by intercostal muscles and diaphragm

•             Thoracic breathing (predominant in women) and abdominal breathing (predominant in
men)

                               Diffusion of O[2 ]and CO[2] in plasma

                                           Gas exchnage

                                     Exchange of O[2 ]and CO[2]

                      Changes of negative pleural pressure during respiration

                                Respiratory volumes and capacities

Air in airways – death space - 150 ml

Residual air volume in alveoli - RV - 1 l

Expiration reserve volume -  ERV – 1.5 l

(Resting, tidal) respiratory volume - TV - 0.5 l

Inspiration reserve volume - IRV – 2.5 l



Vital capacity

VC = ERV + TV + IRV

Functional residual capacity

FRC = RV + ERV



Measure of lungs ventilation: minute volume



                        MV = Respiratory volume ×breathing rate [l.min^-1]

                                           Pneumothorax

                                      Respiratory resistances

•            Elastic resistance of lungs and chest is given by tension of elastic fibres in
pulmonary tissue. The surface tension of alveoli has similar effect.

•            Non-elastic resistance of tissues (also tissue viscous resistance). It arises due to
friction of pulmonary tissue, chest, respiratory muscles and organs of abdominal cavity.

•            Flow resistance of airways – complex of resistances caused by air flow  (effect of air
viscosity, incl. turbulences). It increases substantially when the airways are narrowed.

                                         Respiratory work

This work is necessary to overcome all the respiratory resistances:

W = p.DV

p is the difference of intrapulmonary and pleural pressures,

DV is  the breathing volume

                                How to calculate respiratory work?

At rest:

minute volume MV = 7 l

breathing rate BR = 14 min^-1

pressure p = 0.7 kPa

respiratory volume V = 0.5 l (5 x 10^-4 m^3)

work W = 0.35 J – for one inspiration

294 J per 1 hour





                                                                                     At great load:

                                                                                         MV = 200 l

                                                                                      BR 100 min^-1

                                                                                        p = 0,7 kPa

                                                                            V = 2 l (2 x 10^-3 m^3)

                                                                    W = 1.4 J - for one inspiration

                                                                                  8400 J per 1 hour

                         Measurement of respiratory volumes - spirography

                                             Spirogram

                               Some biophysical aspects of breathing

•             Physical properties of lungs and their manifestations in some areas of diagnostics
and therapy:

Ø  The lungs represent the largest contact area with ambient medium

Ø  Many functions of organism can be influenced by rate or depth of breathing (hyperventilation)

Ø  Breathing movements can disturb e.g. X-ray diagnostics

Ø  Lungs have negative contrast in X-ray images

Ø  Physical properties of alveoli are similar to bubbles – lung tissue can be impaired by
cavitation phenomena (risk in ultrasound diagnostics and lithotripsy)