 Minute ventilation

Minute ventilation, ${\dot{V}}_E$, is the total volume of respiratory gas moved per unit time, conventionally expressed in litres per minute. When breath volumes are represented by mean tidal volume ${\overline{V}}_T$ and respiratory rate $f$ over the same interval,It measures gross ventilation, distinct from the portion renewing gas in effectively exchanging alveolar regions.^[ref]

An original record contains three complete expirations of 0.4, 0.6 and 0.5 L over 15 s. Their total is 1.5 L, giving $1.5\times 60/15=6$ L/min. The rate is 12 breaths/min and the mean tidal volume is 0.5 L, producing the same answer. Variable breath depth is therefore compatible with this identity if both summaries use the same record.

With a fixed effective respiratory dead space $V_D$ per breath, the corresponding model for alveolar ventilation isFor the constructed record and $V_D=0.15$ L, the effective volume is $1.5-3(0.15)=1.05$ L per 15 s, or 4.2 L/min. The remaining 1.8 L/min belongs to the modeled dead-space turnover. This subtraction assumes each included breath exceeds the modeled dead-space volume.

A pneumotachograph can supply signed volumetric flow rate for integration. Integrating only the expiratory phase yields expired volume; integrating a full balanced breath with its sign intact yields approximately zero net volume. A ventilation report must consequently identify the phase, interval and gas-volume conditions rather than interpreting every integral as the same quantity. Gross minute ventilation alone does not establish oxygen uptake, carbon-dioxide removal or their distribution among lung regions.