Respiratory Physiology and Spirometry

Inspiration

in

expiration

out

Boyles Law

Volume and pressure are inverse

Atmospheric pressure (PAtm)

760 pressure at sea level

Intrapulmonary pressure (Ppul)

760 Pressure in alveoli

Intrapleural pressure (Pip)

-4 mmhg pressure in pleural cavity 756

Transpulmonary pressure (Ptp)

pressure difference between intrapleural and intrapulmonary pressures = 4mmhg

Insipiration mechanics

Diaphragm and intercostal muscles contract + Thoracic cavity volume increases AIR IN

Mechanic of expiration

Diaphragm and intercostal muscles relax + Thoracic cavity decreases volume AIR FLOWS OUT

Spirometer

Tool used to measure patient’s respiratory volumes

Tidal volume

air moved into and out of lung in quiet respiration

Inspiratory reserve volume (IRV)

amount of air that can be forcibly inhaled

Expiratory reserve volume (ERV)

amount of air that can be forcibly exhaled

Residual volume (RV)

amount of air that remains in lungs

Inspiratory capacity

TV + IRV

Functional residual capacity (FRC)

RV + ERV

Vital capacity (VC)

TV + IRV + ERV

Total lung capacity (TLC)

TV + IRV + ERV + RV (sum of all lung volumes)

Obstructive pulmonary disease

airway resistance (bronchitis) TLC, FRC, RV increase because of hyperinflation of lungs

Restrictive pulmonary disease

reduced TLC due to disease (tuberculosis) or exposure to environmental agents (fibrosis) VC, TLC, FRC, and RV decline cus lung cant expand

Influences for O2 and CO2 across respiratory membranes

• partial pressure

• thickness and surface area of the respiratory membrane

• alveolar ventilation with pulmonary blood perfusion

Steep partial pressure gradients for O2 between blood and lungs

venous blood PO2= 40 mmhg

alveolar PO2= 104 mmHg

Partial pressure gradient for CO2 is less steep

Venous blood PCO2= 45 mmhg

Alveolar PCO2= 40 mmHg

Perfusion: blood flow reaching alveoli

PO2 controls perfusion by changing arteriolar diameter

Ventilation: amount of gas reaching alveoli

PCO2 controls ventilation by changing bronchiolar diameter

Molecular O2 is transported in the blood in two ways

1. 2% dissolved in plasma

2. 98% bound to hemoglobin (Hb) in RBCs

Hemoglobin structure

four polypetide chains with an iron heme group + can transport 4 O2 molecules

Carbon Dioxide transport

1. 7-10% dissolved in plasma as PCO2

2. 20% bound to globin in hemoglobin = carbaminohemoglobin

3. 70% transport as bicarbonate ion in plasma ( CO2 + water = carbonic acid break apart into bicarbonate)

Obstructive diseaseFEV/FEV1

• FEV1 decreased

• FEV1/FVC ratio decreased

restrictive FEV/FEV1

• FEV1 normal or slightly decreased

• FVC decreased

• FEV1/FVC normal or increased

Obstructive disease (x3) air cant leave

• asthma

• chronic bronchitis

• emphysema

restrictive disease *lung wont expand

• pulmonary fibrosis

• tuberculosis

• chest wall disease