The total amount of gas you try to inhale and then try to exhale. Vital capacity is the maximum ventilation capacity of a breath, which can reflect the potential ability of respiratory function in a certain sense.
Adult male's vital capacity is about 3500ml, and female's is about 2500ml. Adults have the largest lung capacity, while young people and the elderly have smaller lung capacity.
The better the health, the greater the vital capacity, and lung tissue injuries such as tuberculosis, pulmonary fibrosis, atelectasis or lobectomy may reduce the vital capacity to some extent; Spinal kyphosis, pleural thickening, exudative pleurisy or pneumothorax can also limit lung expansion and reduce vital capacity. Therefore, the obvious decrease of vital capacity is the manifestation of restrictive ventilation disorder.
Because the measurement method of vital capacity is simple and repeatable, it is a common index of health examination. Because the expiratory speed is not limited, it is impossible to find the diseases of respiratory ventilation by measuring vital capacity, so it is ideal to use time vital capacity measurement as the dynamic index of lung function.
Time vital capacity is to exhale at the fastest speed after the maximum inhalation until the end of breathing. At the same time, the expiratory volume at the end of 1, 2 and 3 seconds was recorded respectively. Normal people should exhale 83%, 96% and 99% of their vital capacity respectively. It often takes 5-6 seconds or more for patients with obstructive pulmonary disease to exhale their full vital capacity. In many pathological cases with limited respiratory movement, the vital capacity increases at 1 s, so the whole vital capacity can be called in advance. Therefore, time vital capacity can be used as a reference to distinguish obstructive or restrictive ventilation disorders.