= Minute ventilation
{title2=$\dot V_E$}
\b[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,
$$
\dot V_E=f\,\overline V_T.
$$
It measures gross ventilation, distinct from the portion renewing gas in effectively exchanging alveolar regions.<Pulmonary Function Testing by Warren M. Gold and Laura L. Koth>[Minute Ventilation and Alveolar Ventilation]{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 $1.5\times60/15=6$ 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> is
$$
\dot V_A=\frac{\sum_{i=1}^N(V_{T,i}-V_D)}{T}.
$$
For 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.
Back to article page
