Suppose you ask a doctor to define expiratory reserve volume (ERV). In that case, they might go along these lines. “The lungs expel the extra amount of air which is often follow by a normal tidal volume expiration.”

Let’s make it more straightforward for you.

Imagine yourself sitting in a usual posture and generally breathing as you do. This is when you are not overexerting yourself with any external activity. The amount of air you inhale while sitting usually is your tidal volume.

Once you breathe out, you will exhale more than you inhaled. The volume you have expired after a conventional breath (let’s suppose in case of blowing up a balloon) will be your expiratory reserve volume.

This reserve volume can be tape into when you overexert yourself or perform the exercise, and eventually, your tidal volume will increase.

To conclude, your ERV measures the amount of surplus air. It is above your normal breath and is usually exhale when you breathe out forcefully.

The normal value for ERV is almost 1100 ml in males and 800 ml in females. The ERV formula can be used to **calculate expiratory reserve volume**. The formula for ERV is “VC = TV+IRV+ERV” or “ERV= VC-TV-IRV”

## Respiratory Volumes

Respiratory volumes measure air inspired, expired and stocked in your lungs. Besides that, some other books are included in ventilatory pulmonary function tests. They can help diagnose various pulmonary pathologies. Following are the important respiratory volumes.

**Tidal Volume****Inspiratory Reserve Volume****Expiratory Reserve Volume****Residual Volume**

## Tidal Volume

It is defined as “the volume that infiltrates and leaves with each separate breath, from a comprehensive quiet inspiration to a normal quiet expiration”. Its average volume is 0.5L.

### Variations in Tidal Volume:

It changes with the breathing pattern. For instance – tidal volume increases with deep breaths and decreases with shallow breaths. It is also drastically increase during pregnancy.

### Formula for Tidal volume:

To calculate tidal volume, this formula is applicable.

“Tidal volume = alveolar space + dead space”

## Inspiratory Reserve Volume

It is defined as “the surplus amount of volume that can be inhaled above the normal limit of tidal volume, from normal quiet inspiration to maximum inspiration”. Its average volume is 2.5L

### Variations in Inspiratory Reserve Volume:

It is highly dependable on muscle strength, lung compliance, elastic recoil of lungs and the terminal point of tidal volume.

### Formula for Inspiratory Reserve Volume:

To calculate inspiratory reserve volume, this formula can be used.

“IRV= IC-TV”

## Expiratory Reserve Volume

It is define as “the extra volume that can be exhaled below the normal limits of tidal volume, from normal quiet expiration to maximum expiration”. Its average volume is 1.5L.

### Variations in Expiratory Reserve Volume:

Expiratory reserve volume also depends on muscular capacity, strength, and decreased airway resistance. It is also relatively low during pregnancy or gestational period, obesity and in patients suffering from bronchial or tracheal obstruction.

### Formula for Expiratory Reserve Volume:

If you are wondering how to calculate expiratory reserve volume, here is the ERV formula

ERV= VC-TV-IRV

## Residual Volume or Reserve Volume

It is define as “the volume is left behind in the lung after maximum expiration”. Its average volume is 1.5L.

### Notes for Residual or Reserve Volume:

Residual volume cannot be determine by the spirometry method.

### Formula for Residual Volume:

To calculate residual volume, this formula can be used.

RV = FRC−ERV, or RV = TLC−IVC.

## Respiratory Capacities

Pulmonary or respiratory capacities are made up of more than one lung volume. They are constant since they do not vary with the physiological breathing pattern. Following are the crucial-to-know lung capacities.

**Vital Capacity****Inspiratory Capacity****Functional Residual Capacity****Total Lung Capacity**

## Vital Capacity

Vital capacity is also known as force vital capacity. It is define as “the volume that can expire after complete inspiration that is a maximum inspiration to maximum expiration”. Its average volume is 4.5L.

### Variations in Vital Capacity:

Vital capacity changes with any pathology. It demands proper lung compliance, muscle power and decreased airway resistance in order to stay normal.

### Formula for Vital Capacity:

This formula can calculate vital capacity

VC= IRV+TV+ERV

## Inspiratory Capacity

It is define as “the amount of air from quiet expiration to maximum inspiration”. Its average volume is 3L.

### Formula for Inspiratory Capacity:

This formula can calculate inspiratory capacity.

IC= TV+IRV

### Variations in Inspiratory Capacity:

There are no noted variations in inspiratory capacity with changing breathing patterns.

## Functional Residual Capacity

It is define as “the volume that is left behind in the lungs after brief quiet expiration. Its average volume is 3L.

### Formula for Functional Residual Capacity:

This formula can calculate functional residual capacity

FRC= ERV+RV

### Variations in Functional Residual Capacity:

Functional residual capacity can be largely influence by height, gender, posture, and variations in lung compliance. Amongst all of them, height affects it the most.

## Total Lung Capacity

It is define as “the volume that is left behind in the lungs after brief quiet inspiration. . Its average volume is 6L.

### Formula for Total Lung Capacity:

The following mentioned formula can calculate total Lung Capacity.

TLC = RV+IVC or TLC = FRC+IC

## Respiratory Spaces:

There are two known respiratory spaces:

**Anatomical/ Serial/ Dead space****Alveolar/ Distributive/ Dead space**

### Anatomical/ Serial/ Dead space:

It is define as “the amount of air that hardly infiltrates the alveoli and never takes part in the process of respiration. It encompasses the amount of air in the upper and lower respiratory tract all the way to the terminal bronchioles.

### Alveolar/ Distributive/ Dead space:

It is define as “the amount of air that enters the alveoli but even then doesn’t partake in the process of respiration. This can depict the alveoli that are ventilate but not perfused, for instance, in the case of pulmonary embolus.

## How Can We Measure Respiratory Volumes?

If your medical provider notices some indications of chronic lung conditions. They will use spirometry to see how properly your lungs are functioning. It is an important tool for the diagnosis of chronic lung diseases such as;

**Asthma****Chronic bronchitis****Emphysema****COPD (Chronic obstructive pulmonary disease)****Restrictive pulmonary diseases (Pulmonary fibrosis)****Cystic fibrosis**

Once the diagnosis of the lung disease has been formulate successfully, physicians use spirometry to keep monitoring the progress. The post-treatment phase can also be monitor to check whether breathing problems have been successfully treat.

## Everyone has the same lung capacity – Yes or No?

Lung capacity differs from person to person. It is dependable on both their morphological and genetic makeup. You might have higher lung capacity if you have the following traits;

**Tall height****Resides at a higher peak****Adequate fitness**

You might have a relatively smaller lung capacity if you have the following traits;

**Short height****Resides at a lower altitude****Overweight**

### Wrap up;

This blog covers all the important and basic lung volumes and capacities and how to measure them. Moreover, it focuses on the expiratory reserve volume’s formula and how to calculate expiratory reserve volume. In simpler terms, it is the amount of surplus that is exhale out above normal limits during forceful breathing or in overexertion conditions – for instance- exercise.

ERV is measure by spirometry and can be a diagnostic tool for restrictive pulmonary diseases and obstructive lung diseases. If you are suffering from any lung disorder, you can visit our lung and sleep center in Michigan and can avail reliable consultation from our physicians.