41- Rate and rhythm of breathing. Pulmonary and alveolar ventilation.Static lung volumes and capacities and their functional importance. Anatomical and physiological dead space. Estimation of external respiration. Elastic and nonelastic resistance to breathing. Air flow during breathing. The work of breathing.

rate

Rate:

• Rate of breathing (or respiratory rate) is simply how many breaths you take per minute.

• Alveolar ventilation per minute is the volume of fresh air that actually reaches the alveoli and participates in gas exchange each minute.

Alveolar ventilation = (tidal volume – dead space) × respiratory rate

Va= Frequency x (VT – VD)

Va = Volume of alveolar ventilation per minute

Frequency = frequency of respiration per minute

VT= Tidal volume- volume of air inspired or expired per inspiration at rest- 500 ml

VD= physiologic dead space volume

• Eupnoea Normal respiration rate.

• Polypnoea- Rapid respiration rate.

• Beadypnoea -Abnormally slow respiration

• Apnea- Termination of breathing

• Asphyxia- suffocation and lack of oxygen in respired air

Pulmonary and Alveolar ventilation

Pulmonary and Alveolar ventilation

Pulmonary ventilation -inflow and outflow of air between the atmosphere and lung alveoli.

(difference is the alv vent rate = just the rate, the pulm is just the inflow and outflow)

Lungs can expand and contract in 2 ways.

1. Downward and upward movement of the diaphragm to lengthen or shorten the chest cavity.

2. Elevation and depression of the ribs to increase/decrease anteroposterior diameter of the chest cavity

• The main purpose for pulmonary ventilation is to continually renew the air in the gas exchange areas.

• These areas include the alveoli, alveolar sacs, alveolar ducts, and respiratory bronchioles. The rate at which the new air reaches

these areas is called alveolar ventilation.

• Some air inhaled does not reach the gas exchange areas but simply fills the passages where gas exchange does not occur.

• Such as the nose, pharynx, and trachea. This air is called dead space air.

• On expiration, the air in the dead space is expired first, before any air from the alveoli.

• Therefore the dead space is very disadvantageous for removing expiratory gases from the lungs.

ELASTIC AND NON-ELASTIC RESISTANCE

ELASTIC AND NON-ELASTIC RESISTANCE

Work against elastic resistance

- this work is usually generated during inhalation phase - stored as potential energy which is released during exhalation.

Work against non-elastic resistance

- pressure difference is required to overcome the frictional resistance to gas flow due to viscosity (major reason for non-elastic resistance)

- to provide movement of non-elastic components of the airway tissues to make space for pulmonary volume change

work of breathing

Work of breathing

Work of breathing = energy needed to inhale or exhale a breathing gas.

types of work:

1. Elastic work: work required to expand the lungs against the lung and chest elastic forces

2. Resistance work: work required to overcome the viscosity of the lungs and chest wall structures

3. Airway resistance work: work required to overcome airway resistance to movement of air into the lungs.

Compliance of the lungs

change in lung volume per unit change in transpulmonary pressure

• Compliance=ΔVolume / ΔTranspulmonary Pressure

Dependent on:

1. Elastic forces of the lung tissue itself- elastin and collagen fibres

2. Elastic forces caused by surface tension of the fluid that lines the inside walls of the alveoli and other lung spaces.

static lung volumes

Tidal Volume (TV):

Volume of air inhaled or exhaled during a normal breath

Approx. 0.5 L

Inspiratory Reserve Volume (IRV):

Max volume of air that can be inhaled after a normal tidal inhalation

Approx. 3.0 L

Expiratory Reserve Volume (ERV):

Max volume of air that can be exhaled after a normal tidal exhalation (not inhalation)

Approx. 0.7 - 1.0 L

Residual Volume (RV):

Volume of air remaining in the lungs after a maximal exhalation

Approx. 1.2 L

Minute Ventilation (or Minute Volume):

Total volume of air breathed in or out per minute

Calculated as:

Minute Ventilation = Tidal Volume × Respiratory Rate

Typical resting value: 6-8 L/min (e.g., 12-16 breaths/min × 0.5 L)

Inspiratory Capacity (IC):

Volume of air that can be inhaled after a normal exhalation

IC = TV + IRV

Total Lung Capacity (TLC): (I think you meant this instead of “TVC”)

Total volume of air in the lungs after a maximal inhalation

TLC = TV + IRV + ERV + RV

Sometimes estimated using body height and coefficients

Pulmonary capacities

pulmonary capacities are a combination of two or more lung volumes together and are used in

describing events in the pulmonary cycle.

pulm capacity

Pulmonary capacities

pulmonary capacities are a combination of two or more lung volumes together and are used in

describing events in the pulmonary cycle.

The important capacities are:

1. Inspiratory capacity = tidal volume + inspiratory reserve volume(3.5L) begins max vol of air

that can e inhaled forecefully after normal tidal exhalation IC=TV +IRV

volume of air in the lungs after normal tidal exhalation

3. Vital capacity = inspiratory reserve volume + tidal volume + expiratory reserve volume

the max.~4600ml VC=TV+IRV+ERV

volume change that occurs between max inhalation and max exhalation

4. Total lung capacity = vital capacity + residual volume : the max. volume to which the

lungs can be expanded (~5800ml)

Anatomical and physiological dead space

Source of the air that’s inspired does not reach the sides of gas exchange instead this air fills up spaces –

respiratory passages which do not participate in gas exchange. Theses passages include- the nose,

pharynx and trachea.

1. Anatomical dead space: it is the portion of airways which conducts gas to the alveoli but no gas

exchange is possible in these spaces.

2. Alveolar/pulmonary dead space: it is the sum of alveoli which have little or no blood flowing

through their pulmonary capillaries and thus cannot take part in gas exchange. It is very low in

normal healthy persons but can increase in lung diseases.

The total dead space (physiological dead space) =sum of the anatomical dead space plus the alveolar dead space.

External respiration and estimation

• External respiration refers to gas exchange across the respiratory membrane in the lungs between

alveoli and venous blood (deoxygenated blood).

• As venous blood flows through the pulmonary capillaries,

• oxygen diffuses into the blood and carbon dioxide diffuses into the alveolar gas.

• Each gas diffuses down its own partial pressure gradient - that is, from a high to low partial pressure.