Question

What is tidal volume?

Answer 1

Tidal volume is the respiratory rate in the lungs. It is the lung volume representing the normal volume of air displaced during normal inhalation and exhalation. Lung capacity can be defined by the residual volume and vital capacity. Tidal volume can be calculated by subtracting IRV from IC.

Complete answer:
Tidal volume of the lungs can be measured by the amount of air inhaled during normal breath. The amount of air entering or leaving the respiratory tract with each breath determines tidal volume. In healthy young human adults, tidal volume is approximately 500 ml per inspiration or 7 ml/kg of body mass. Tidal volume is denoted by VT. It indicates a subdivision of the lung; when tidal volume is precisely measured, as in gas exchange calculation.
VT = IC-IRV, VT = VC-(IRV+ERV), VT=TLC-(IRV+ERV+RV).
The sum of inspiratory reserve volume and tidal volume gives inspiratory capacity. Inspiratory and expiratory reserve volume is the amount of maximal volume of air inhaled and exhaled.
It plays a significant role during mechanical ventilation to ensure adequate ventilation without causing trauma to the lungs. It is measured in milliliters and ventilation volumes are estimated based on a patient’s ideal body mass. Leaks in the breathing circuit or introduction of additional gas affect the measurement of tidal volumes. Lung injuries like ALI/ARDS can be caused by ventilation with large tidal volume. Patients suffering from lung diseases should be given proper ventilation.

Note: Total lung capacity can be determined by the volume in the lungs at maximum inhalation. It can be calculated by the sum of vital capacity and residual volume. Residual volume is the amount of air remaining in the lungs after a maximal exhalation. Vital capacity of the lungs is the volume of air breathed out after the deepest inhalation. The actual volume of the lungs includes the volume of conducting airway.