Normal Values and Concentrations (Respiratory System)

The Normal Pleural pressure at the begining of inspiration is about - 5 cm of water.

During Normal inspiration ,Expansion of the chest cage pulls outward on the lungs with greater force and creates more negative pressure, to an average of about - 7.5 cm of water.

Alveolar pressure is the pressure of the air inside the lung alveoli.

During Normal inspiration, Alveolar pressure decreases to about -1 cm of water.

Compliance of the Lungs:

The total compliance of both lungs together in the normal adult human being averages about 200ml of air per cm of water transpulmonary pressure.

That is, everytime the transpulmonary pressure increases 1 cm of water, the Lung volume after 10 to 20 seconds, will expand 200mls.

During normal quiet respiration, only 3 to 5 percent of the total energy expended by the body is required for pulmonary ventilation.But during heavy exercise,the amount of energy required can increase as much as 50-fold,especially if the person has any degree of increased airway resistance or decreased pulmonary compliance.

Pulmonary Volumes and Capacities:

(Vt)Tidal volume= 500 ml

(IRV)Inspiratory reserve volume = 3000 ml

(ERV)Expiratory reserve volume = 1100ml

(RV)Residual volume = 1200ml

Inspiratory capacity (IC) = IRV(Inspiratory reserve volume) + Vt (Tidal Volume)=3000ml + 500ml = 3500ml

VC= IRV + Vt + ERV

VC= IC + ERV

TLC= VC + RV

TLC IC + FRC

FRC= ERV + RV

RV= FRC - ERV

TLC= FRC + IC

The Normal respiratory rate is about 12 breaths per minute.

Therefore, the minute respiratory volume averages about 6L/min.

A person can live for a short period with a minute respiratory volume as low as 1.5L/min and a respiratory rate of only 2 -4 breathes per minute.

The Normal Dead space air in a young adult man is about 150 mls.This increases slightly with age.

Interrelations Between Interstitial Fluid pressure and Other Pressure in the Lung:

Forces tending to cause movement of fluid outward from the capillaries and into the pulmonary interstitium:

Capillary pressure 7mmHg

Interstital fluid colloid osmotic pressure 14mmHg

Negative interstital fluid pressure 8mmHg

TOTAL OUTWARD FORCE = 29mmHg

Forces tending to cause absorption of fluid into the capillaries:

Plasma colloid osmotic pressure 28mmHg

TOTAL INWARD FORCE = 28mmHg

MEAN FILTRATION PRESSURE:

TOTAL OUTWARD FORCE = 29mmHg - TOTAL INWARD FORCE = 28mmHg = +1

Alveoli consists of :

1) type I alveolar cells (95%), thin

2) type II alveolar cells (5%), secrete surfactant.

3) macrophages (dust cells), defense

Pleura :

The parietal and visceral pleura, are separated by 10–24 µm between the two surfaces.

This space is usually filled with a very small amount of fluid 7 – 10 ml. However, large amounts upto 4–5 litres in an adult of fluid can accumulate in the pleural space under pathological conditions.