Respiratory Rate and Tidal Wave Volume

Respiratory Rate and Tidal Volume [pic]

The total amount of air moved in and out of the lungs each minute (pulmonary ventilation) depends upon 2 factors: size of each breath (tidal volume) and number of breaths/minute (respiratory rate). For example, suppose your tidal volume is 500 mL (0.5 liters) and you breathe 15 times/minute. Your pulmonary ventilation = 15 breaths/min x 0.5 L/breath = 7.5 L/min.

Pulmonary Ventilation = (Respiratory rate; breaths per minute) x Pulmonary Ventilation Remember that some of the lung air is dead space and does not exchange gases and that only air in the alveoli exchanges gases with the blood. Air in the pharynx, larynx, trachea, bronchi and bronchioles does not exchange gases. The air to the alveoli = tidal volume - dead space. An average human adult at rest has a tidal volume of around 0.5 L and a dead space of around 0.15 liters (~30% of TV). This means that the fresh air to the alveoli is around 0.35 L (~70% of TV).

Total alveolar Ventilation = (Respiratory rate) x (TV - dead space)

Consider a group of patients with the same pulmonary ventilation:
|Patient |Tidal Volume |Respiratory Rate |Pulmonary Ventilation |Dead Space |Alveolar Ventilation |
|1 |1000ml | |6000mL/min |150mL | |
|2 |500ml | |6000mL/min |150mL | |
|3 |300ml | |6000mL/min |150mL | |
|4 |200ml | |6000mL/min |150mL | |
|5 |150ml |