Introduction
The amount of air that fills the lungs at different stages of the respiratory cycle is divided into four volumes and four capacities. The lung capacities include total lung capacity, inspiratory capacity, vital capacity, and functional residual capacity. The lung volumes are residual volume, tidal volume, inspiratory reserve volume, and expiratory reserve volume. Vital capacity is the maximum volume of air that can be breathed out following maximum inspiration.
What Is Vital Capacity?
Vital capacity (VC) is the maximum amount of air that can be breathed out after the complete filling of the lungs following maximum inhalation. It is usually between three and five liters in normal individuals. It is the sum of tidal volume (V), inspiratory reserve volume (IRV), and expiratory reserve volume (ERV). It is calculated as VC = V+IRV+ERV.
Tidal volume is the volume of air that moves in or out of the lungs during the respiratory cycle. Inspiratory reserve volume is the extra volume of air that can be inhaled with maximum effort after reaching the end of a normal, quiet inhalation. Expiratory reserve volume is the extra volume of air that can be exhaled with maximum effort after reaching the end of a normal, quiet exhalation.
It can be measured as slow vital capacity (SVC), inspiratory vital capacity (IVC), or forced vital capacity (FVC). Inspiratory vital capacity is the volume of air that can be inspired after a normal, quiet expiration. Forced vital capacity is the maximum volume of air that can be forcibly exhaled after fully inhaling. The forced vital capacity is similar to vital capacity, but it is measured during maximum exhalation with speed and effort.
Why Is Vital Capacity Important?
The lungs cannot expand fully if the vital capacity is severely decreased. This is an indicator of restrictive lung disease. If the vital capacity is normal, but the lungs are not functioning properly, it is an indication of obstructive lung disease. The lungs are clogged, or the airways are blocked in obstructive lung disease.
Pulmonary function tests are performed to diagnose respiratory diseases. It helps to quantify the functional impairment and monitor the treatment and progression of the disease. The measurement of lung capacities and lung volumes is critical in pulmonary function tests.
The vital capacity of the lungs helps in the diagnosis of underlying lung disease. It also helps in differentiating various causes of the disease. The vital capacity is normal or slightly reduced in obstructive lung diseases like asthma, emphysema, and bronchitis. The vital capacity is decreased in restrictive lung diseases like idiopathic pulmonary fibrosis. The vital capacity measurements do not change in pregnancy due to the increased circumference of the rib cage.
The vital capacity measurement also helps to identify the severity of the involvement of respiratory muscles in neuromuscular diseases. It plays a role in making treatment decisions for diseases like myasthenia crisis and Guillain-Barre syndrome.
What Are the Factors Affecting Vital Capacity?
The vital capacity is related to factors like airway and vascular resistance, oxygen reserve, work of breathing, compliance, closing capacity, and V/Q (ventilation-perfusion ratio) mismatch. The vital capacity depends on factors like age, sex, position, height, weight, and body mass. The residual volume (RV) and the functional residual capacity (FRC) increase with age, which decreases the vital capacity. The vital capacity increases with an increase in the height of an individual. The vital capacity is maximum in the sitting and supine positions. The vital capacity decreases with an increase in body mass index (BMI).
Why Is Vital Capacity Essential for a Healthy Living?
The vital capacity allows the intake of a maximum volume of fresh air and gets rid of the foul air in a single stroke of respiration. It increases the gaseous exchange between the tissues of the body and improves the amount of energy available for the functioning of the human body. An increase in vital capacity increases the oxygen transport to the muscles. Daily breathing exercises increase vital capacity.
What Are the Conditions That Alter the Vital Capacity?
Vital capacity reduces in weak cough, atelectasis, hypoxemia, and an accumulation of oropharyngeal secretions. Obstructive diseases like asthma are associated with the narrowing of airways, which makes it hard to get air out of the lungs. This causes a decrease in vital capacity. Emphysema destroys the lung tissue and results in the loss of elastic recoil of the tissues. The vital capacity decreases in emphysema. In fibrosis, the lungs become stiff and make it difficult for oxygen to pass through the alveoli in the lungs. Vital capacity is reduced in fibrosis due to the stiffening of the lung tissues. Low vital capacity is seen in comorbid conditions like obesity, cardiovascular diseases, and metabolic syndrome. Low vital capacity indicates the presence of lung diseases. Increased vital capacity is essential for healthy living.
Vital capacity can be increased by practicing deep breathing exercises regularly. Regular exercise improves overall function. Aerobic exercise like walking, biking, or swimming improves vital capacity and lung and heart function. An increase in vital lung capacity increases oxygen availability to the body. A decrease in vital capacity causes breathing difficulties and shortness of breath.
How Is Vital Capacity Measured?
A wet or regular spirometer is used to measure the vital capacity. A spirometer is a device with a mouthpiece that is hooked up to a small electronic machine. It is also used to measure the forced vital capacity. Forced vital capacity is measured to distinguish obstructive diseases like asthma and chronic obstructive pulmonary disease (COPD), which makes it difficult to exhale air, and restrictive diseases like fibrosis and sarcoidosis, which causes difficulty in inhaling air.
Conclusion
Vital capacity is the maximum volume of air that can be breathed out after the complete filling of the lungs following maximum inhalation. It is essential for the diagnosis of underlying lung diseases. Vital capacity is significant because it improves oxygen availability to the body tissues. Regular exercises and aerobic activities increase vital capacity due to increased oxygen intake and increased lung usage during exercise. An increase in vital capacity improves overall lung function.
