Respiratory time volume is the volume of air at ambient pressure that is inhaled and exhaled per unit time. Technically, it is the flow rate of air through the lungs per unit time, which can be measured directly or calculated as the product of respiratory volume and respiratory rate. Respiratory time volume varies widely, depending on the power demand by the body and on ambient air pressure.
What is respiratory time volume?
Respiratory time volume includes the total volume of air that passes through the lungs per unit time at ambient air pressure. Respiratory time volume includes the total volume of air that passes through the lungs per unit time at ambient air pressure, i.e., inhaled and exhaled. If minutes are chosen as the time reference, the respiratory time volume is also referred to as the respiratory minute volume (AMV). In healthy humans, the size of the respiratory time volume is strongly dependent on the power demand of the body, but also on altitude and temperature. Basically, adaptation to the body’s demand can be achieved by changing the respiratory volume, the volume of a single breath, or by changing the respiratory rate. Usually, both parameters change unconsciously during an adaptation to demand. Normally, the adaptation occurs involuntarily via the autonomic nervous system. At rest, the respiratory minute volume in a healthy adult is about 8 to 10 liters. This value can be increased to three to five times during heavy physical exertion. In well-trained top athletes, it can even increase to fifteen times. The maximum utilization of the respiratory volume at maximum frequency corresponds to the so-called respiratory threshold value. It can be achieved by voluntary, conscious breathing and can be increased within certain limits by training the chest and rib muscles.
Function and task
Respiratory time volume, the flow rate of air through the lungs, is the most important control variable for matching the oxygen supply to the body’s needs. Excessive respiratory time volume, which can be achieved by hyperventilation, results in oxygen oversupply, causing typical symptoms and dangerous to life-threatening conditions. The opposite, hypoxia, which can occur through hypoventilation or too little oxygen in the breath, also causes typical symptoms and life-threatening conditions. In healthy humans, the control of respiratory time volume occurs unconsciously through the respiratory center, a special region in the central nervous system in the medulla oblongata, the medulla oblongata. The respiratory center receives messages about the partial pressure of oxygen (O2) and of carbon dioxide (CO2), as well as about the pH value of the blood, via chemoreceptors located at specific points in the bloodstream. These are the three most important parameters that enable the respiratory center to control the respiratory time volume in such a way that the aforementioned parameters are as constantly as possible within the normal range. However, the control of the respiratory time volume is not the only setting possibility for the body. When there is a strong demand for oxygen from the muscle tissue, the body also responds with an increased cardiac output to support oxygen uptake and carbon dioxide release via increased blood circulation in the capillaries surrounding the alveoli. A special challenge for the control of respiratory minute volume exists not only when there is an extraordinary demand for power, but also when there are unusual environmental conditions such as those encountered at high altitudes. Air pressure decreases with increasing altitude. At 4,810 m above sea level (Mt. Blanc), it is only 53.9% of the air pressure at sea level. This means that for the same breathing time volume, only a little more than half of the oxygen that would be available at sea level is available. During longer stays of several weeks at high altitudes, the body additionally reacts by increasing red blood cells (erythrocytes) in order to support gas exchange at the walls of the capillaries (altitude training).
Diseases and ailments
Involuntary control of respiratory time volume and tuning to oxygen demand within narrow tolerance limits requires that the chemoreceptors involved correctly supply the respiratory center in the medulla oblongata with data on oxygen and carbon dioxide concentrations and blood pH.Another prerequisite for correct control is that the respiratory center sends the appropriate contraction and relaxation commands to the respiratory muscles. Other conditions for regulation of respiratory time volume in accordance with demand are normal airway resistance without ventilatory disturbances and the proper functioning of gas exchange in the capillaries of the alveoli. Of course, the atmospheric environment in terms of oxygen content and ambient pressure must also be within the limits that can still be controlled by the respiratory center in terms of respiratory control. Causes that can lead to temporary or chronic hyperventilation are certain lung diseases or disorders of the respiratory center. The respiratory center can be impaired in its function by a craniocerebral trauma or by a circulatory disturbance of the respiratory center – for example, by a stroke or by severe anxiety or stress situations. Sustained hyperventilation, an increase in respiratory time volume beyond what is required, results in increased exhalation of carbon dioxide. Typically, muscle cramps, dizziness, and anxiety set in. Equally typical are paresthesias such as numbness or false sensations from the skin receptors and paralysis, muscle tremors and muscle pain. The symptoms are triggered by respitatory alkalosis, an increase in pH, which leads to a decrease in calcium ions in the blood (hypocalcemia). The opposite disorder, a decrease in respiratory volume due to hypoventilation, can also have many different causes. The most common trigger factors are obstructive lung diseases such as bronchial asthma or an influence of opioid drugs on the respiratory center or a partial motor failure of the respiratory muscles (paresis). The so-called Pickwick syndrome occurs in cases of pronounced obesity. Excessive fatty tissue in the abdominal and thoracic cavity leads to a diaphragmatic elevation and associated external compression of the lungs. This causes chronic hypoventilation, which leads to hyperacidity of the blood due to increased carbon dioxide concentration.
