Respiratory Volumes and Capacities

Varied animals have different lung capacities dependent on their activity level. Cheetahs, for example, have acquired a substantially larger lung capacity than humans to provide all of their muscles with oxygen, enabling them to sprint at a high rate of speed. Elephants’ great size necessitates a high lung capacity, as does their requirement for oxygen in proportion to their size.

Genetics, gender, and height all have a role in the size of the human lungs. The maximum capacity of an ordinary lung is almost six litres of air. However, this is seldom the case. Lung volume and lung capacity are two expressions used to describe how much air is in the lungs. Volume refers to the quantity of air required to perform a single action (such as inhalation or exhalation), while capacity refers to the total amount of air required to do many actions (for example, how much can be inhaled from the end of a maximal exhalation).

Respiratory Volumes

The tidal volume, expiratory reserve volume, inspiratory reserve volume, and residual volume of the lung may be split into four parts. The quantity of air that is inhaled and exhaled in a typical breath is referred to as the tidal volume (TV). Half a litre is about the same as a 20-ounce bottle of soda, so this amount is not excessive. An extra quantity of air that may be expelled following a regular expiration is known as the expiratory reserve volume (ERV). It’s the extra air you have in reserve to exhale if you need to. A regular inhalation is followed by an extra quantity of air that may be breathed, known as the inspiratory reserve volume (IRV). Expiratory reserve volume leaves a residual volume (RV) of air in the lungs. After a maximum exhales, there is always some air remaining in the lungs. The lung tissues would clump together if there was no residual volume left in the lungs. The amount of effort required to re-inflate the lung may be too much for the body to handle. As a result, the lungs are never completely depleted of air. Additionally, residual volume is crucial in minimising substantial variations in respiratory gas levels (O2 and CO2). The only lung capacity that cannot be readily quantified is the residual volume since it is difficult to empty the lung of air. However, there’s no way to quantify the exact amount of this thing.

Spirometry is a method for determining the volume of the lungs. If you want to know how much air you can pull out of your lung in a certain amount of time (typically one second), spirometry is your best tool (FEV1). Besides that, the total quantity of air that can be compelled expelled (FVC) is measured. Lung illnesses such as asthma, emphysema, and fibrosis are all diagnosed using the FEV1/FVC ratio. An abnormally high FEV1/FVC ratio indicates a patient with lung fibrosis, which is characterised by stiffness and inability to flex. Most of the lung capacity is exhaled rapidly by patients who are under anaesthesia. Low FEV1/FVC ratios, on the other hand, are indicative of asthmatic lung resistance. Because the patient’s lungs are full, it is difficult for him or her to expel the air. The maximum volume of exhalation takes a long time to achieve. A tough time breathing is likely to occur in both cases. 

Respiratory Capacities

Two or more volumes are used to assess respiratory capacity. It is the greatest quantity of air that can be breathed or expelled during a respiratory cycle that is measured by the vital capacity (VC). Expiratory reserve volume, tidal volume, and inspiratory reserve volume are added together to get this value. IC is the maximum quantity of air that may be breathed after a typical expiration has finished. Therefore, the tidal volume and the inspiratory reserve volume make up the total volume. Expiratory reserve volume and residual volume are also included in the FRC. After a typical expiration, the FRC measures the quantity of more air that can be breathed. To put it another way, total lung capacity (TLC) is a measure of how much air the lungs can contain. The total of the residual volume, expiratory reserve volume, tidal volume, and inspiratory reserve volume. 

Measurements of respiratory volumes and capacities

• Spirometry 

Tidal volume, inspiratory reserve volume, and expiratory reserve volume may all be measured using simple spirometry. There’s no way to tell whether there’s any leftover volume, however. Height, age, and gender are all included in the measurements, but the most significant effect on a person’s abilities comes from their height.

• Process

The individual breathes via a water-based closed circuit. It’s an oxygen-filled chamber, and when the occupants inhale, gas builds up and shrinks the circuit. Every time the circuit is ventilated, the weight above the chamber rises and falls about the volume of the circuit. An ink pen is used to keep track of the volume that has been inspired or extinguished over time.

• Helium dilution

The total lung capacity may be assessed by the use of helium dilution. Only if the lungs are unobstructed can they be considered accurate. As only ventilated lung volumes are measured, helium may not be able to reach all parts of the lung during ventilation, resulting in an underestimation.

• Process

The individual inhales a gas with a known concentration of helium after a silent expiration (an inert gas). To reduce the concentration of helium, they hold their breath for 10 seconds. Measurement of helium content is then carried out following exhalation. The amount of air that can be vented is determined by the helium’s dilution.

• Nitrogen washout

 Serial/anatomical dead space in the airways up to and including the terminal bronchioles may be calculated using this approach (usually 150mL).

• Process

Breathing pure oxygen and then exhaling via a nitrogen-monitoring valve is the procedure that takes place. To begin, the expelled air is pure oxygen, which represents the amount of dead space since the exhaled air never made it to the alveoli and was subjected to gaseous exchange. 

When nitrogen-rich air from the dead space reaches the valve, it is expelled in a combination with alveolar air, increasing the nitrogen concentration recorded. Only alveolar air may be exhaled, and the nitrogen levels will mirror those of alveolar air once a few breaths have been taken. Lungs’ anatomical dead space volumes may be calculated using nitrogen levels recorded over time.

Conclusion 

To better understand lung volumes, it’s helpful to think of the lungs’ overall volume as a collection of different capabilities. To evaluate the lungs’ mechanical state, its musculature, airway resistance, and the efficacy of gas exchange at the alveolar membrane, several tools are used. In addition, these tests are often inexpensive, non-invasive, and straightforward.