Inspiratory reserve volume represents the air that a patient can take in after normal inspiration during forced breathing. Together with expiratory reserve volume and respiratory volume, inspiratory reserve volume gives vital capacity. Lung volumes are measured in spirometry.
What is the inspiratory reserve volume?
Inspiratory reserve volume refers to inspiration and corresponds to the volume of space in the lungs that can be additionally occupied by air after physiological inspiration by forced breathing. Human respiration is characterized by different volumes. As such, the individual spatial contents of the lungs are referred to, which are occupied by the respiratory air during respiration. Lung volumes are mainly divided into those of inspiration and expiration. Inspiration is the inhalation. Expiration refers to breathing out. Lung capacities must be distinguished from lung volumes. They correspond to a combination of different lung volumes. The main volumes of the lungs are expiratory reserve volume, residual volume and inspiratory reserve volume. The respiratory time volume, on the other hand, is the product of the respiratory volume and the respiratory rate. The inspiratory reserve volume refers to inhalation and corresponds to the volume of space that can be additionally occupied by air after physiological inspiration by forced breathing. In a healthy adult, the inspiratory and expiratory reserve volumes average about three liters. The measurement of lung volumes is the subject of pneumology. Most lung volumes in this medical field can be determined by spirometry.
Function and task
Active breathing in humans takes place through the lungs. Their alveoli are primarily responsible for gas exchange. CO is carried out of the organism during pulmonary respiration via diffusion processes in the alveoli. Oxygen is taken up from the respiratory air by the alveoli and transported to the individual tissues of the body via the blood as a transport medium. Every tissue in the body is dependent on oxygen. Internal cellular processes cannot take place without oxygen, so that the body tissues and with them the organs die in the event of an insufficient supply of oxygen. As part of pulmonary respiration, the individual volumes of the lungs ensure that sufficient respiratory air can be taken in for the ideal supply of oxygen to the body tissues. The respiratory volume is expanded to about three liters during ventilation. These three liters provide the reserve volume or supplementary air. The inspiratory lung volume accounts for about 1.5 liters of this. The remaining 1.5 liters is accounted for by the expiratory reserve volume. When the physiological breathing air is added to the supplementary air, the maximum air supply is about 3.5 liters. This is the maximum amount of air a person can take in during a single breath. The maximum amount of breathable air in a single breath is also referred to as vital capacity. After expiration, about 1.5 liters of respiratory air remain in the lungs and airways in the form of the residual volume. If the vital capacity and the residual volume are added together, this results in the total capacity. The respiratory time volume, in turn, corresponds to the volume of air that a person can inhale and exhale within a specified period of time. It corresponds to multiplying the respiratory rate by the respiratory volume and is around 7.5 liters per minute at rest. The respiratory reserve volume or minute limit, on the other hand, corresponds to the volume of breath that can be ventilated per minute at maximum respiratory volume and averages between 120 and 170 liters for a healthy adult. The vital capacity can be calculated from the inspiratory reserve volume and the expiratory reserve volume with the aid of the respiratory volume.
Diseases and medical conditions
Expiratory reserve volume and inspiratory reserve volume, as single values of vital capacity, help pulmonologists determine and differentiate between obstructive and restrictive lung diseases. Obstructive lung diseases are characterized by narrowed airways and are present, for example, in diseases such as asthma or COPD. In restrictive lung diseases, the lungs and chest have limited expansion.This is the case, for example, in pulmonary fibrosis, fluid accumulation in the context of pleural effusion or diaphragmatic paresis. Vital capacity as the product of respiratory volume and expiratory and inspiratory reserve volume may help the pulmonologist to classify symptoms as obstruction or restriction. For example, vital capacity is always decreased in the context of restriction. In the case of obstruction, this is not necessarily the case. In most cases, the measurement of the individual volumes takes place within the framework of spirometry, i.e. by means of a spirometer. The patient is given a mouthpiece that is connected to the measuring spirometer. The patient breathes in and out through the mouthpiece, following the doctor’s breathing instructions. These instructions should be followed as accurately as possible to ensure reliable results. Incorrect readings can promote misdiagnosis and result in incorrect therapeutic approaches.
