What is Respiratory Volume and Capacities?
o During one cycle of respiration, volume of air that is present in the lungs is known as the lung volume and lung capacities. These are measured in different phases of the respiration cycle.
o One respiration cycle is the complete process of inspiration and expiration. During normal inspiration there is usage of diaphragm and other intercoastal muscles, but when a deep breath is to be taken more muscles contribute for the process.
What is Respiratory Volume?
There are four volumes that are administered in the respiratory cycle and discussed below.
o Tidal Volume (TV or VT): It is the amount of air that reaches the lung or moves out of the lung during one cycle of normal breathing. The normal amount for a healthy female is said to 400 mL and for a healthy male is 500 mL
o Residual Volume (RV): After maximum exhalation of air, the amount of air still remaining in the lungs is considered as the residual volume. For an average adult person, the residual volume is about 1100 – 1200 mL
o Expiratory Reserve Volume (ERV): The maximum amount of air that can be released after the exhalation of normal tidal volume is said to Expiratory Reserve Volume. The value observed in an average female is 700 mL and for an average male is 1100 mL.
o Inspiratory Reserve Volume (IRV): The maximum amount that can be inhaled after the inspiration of the tidal volume is said to be the Inspiratory Reserve Volume. For an average adult male, the value is 3300 mL and for an average female is 1900 mL.
How to Measure Respiratory Volume?
The Tidal volume, inspiratory reserve volume, expiratory reserve volume lung volumes can be measured by the spirometry technique.
Significance of Respiratory Volume
This technique is used as pulmonary test or breathing test that can estimates the amount of air taken in and given out of the body. These techniques can understand the values to know about any underlying respiratory disorder with it.
o Inspiratory Capacity (IC): Maximum amount of air that can be inhaled after the tidal volume expiration. It is said as the sum of inspiratory reserve volume and tidal volume. The average value for male is 3800 mL and that of females is 2400 mL
o Vital Capacity (VC): It is the amount of air that be exhaled after the maximum inhalation is called the vital capacity. Sum of expiratory reserve volume with inspiratory reserve volume and tidal volume. The average value for males is 4800 mL and for females is 3100 mL
o Functional Residual Capacity (FRC): The amount of air present in the lungs post passive exhalation is called functional residual capacity. The average value for female is 1800 mL and the average value for the males is 2400 mL
o Total Lung Capacity (TLC): The amount of air in lungs after full inspiration is the Total lung capacity and the average value for females is 4200 mL and the average value males is 6000 mL.
o It is the sum of the inspiratory reserve volume, residual volume with tidal volume and expiratory reserve volume.
Significance of Respiratory Capacity
o The residual volume, the functional residual capacity and total lung capacity is measured by the nitrogen washout, body plethysmography and helium dilution technique.
o Nitrogen Washout: Principle of this method that the person has to breathe oxygen 100% and breathe out in the spirometer and the nitrogen is washed out of the lungs. By this the nitrogen concentration is measured and also helps in calculating the expiratory volume of the lungs. This method helps in calculating functional residual capacity (FRC) by calculating the difference between initial concentration and final exhaled concentration.
o Body Plethysmography: Method that helps to estimate the amount of air that is present in the lungs after deep breath (inhalation) and the amount of air present in lungs after exhalation. It estimates the FRC with the help of Boyle’s law.
o Helium Dilution Technique: This method works for the estimating the lung volumes of a person by using 10% helium with oxygen.
o These lungs volumes and capacities basically understand the amount of air that we breathe in and exhale fall under the range and check the strength of the lungs based on the age and gender and help us know the disorders if found and proceed with the treatment.
Factors Affecting Respiratory Capacity and Respiratory Volume
There are certain factors that affect these volumes and capacities of the lungs;
o People living in different altitudes: People living in higher altitudes than the sea level tend to have higher lung capacity due to the relatively lower partial pressure of the oxygen. As in the sea level the people have more of partial pressure in oxygen the process of the dilution of oxygen is faster therefore the requirement of body is met and the which causes decrease in lung volume when compared with people living in higher altitude.
o Healthy and obese people: The lung capacity is decreased in the people who do not follow a healthy life. The lung capacity to breathe in reduces, but this condition can be improved on some part. Certain environmental conditions also result in the disorders like asthma that affects the lung volumes and capacities.
o Certain lung capacities change during pregnancy. It is observed that the functional residual capacity drops by 18% to the 20%. This is due to compression of the diaphragm by the uterus affecting the decrease in total lung capacity.