Water “in” the lungs, also known as Pulmonary Edema
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- Water “in” the lungs, also known as Pulmonary Edema

We’ve all heard someone say that someone had ‘water on‘ or ‘water in‘ the lungs.
But what exactly does that mean?
Should we say ‘on‘ the lungs or ‘in‘ the lungs?
In reality, both situations exist:
• Water 'in' the lungs:
- This refers to the accumulation of fluid inside the lungs, specifically in the lung alveoli, known as pulmonary edema.
• Water 'on' the lungs:
- This refers to the accumulation of fluid in the pleural cavity, the space between the lungs and their outer lining. This condition is called pleural effusion.
The causes are multiple, but water ‘on‘ the lungs can be associated with water ‘in‘ the lungs or can be related to a pulmonary disease. We will revisit this topic later.
Where does this water come from? Normally, there shouldn't be any.
To better understand this, we need to revisit some basic principles.
The Lungs and Respiration
The lungs are where the exchange of oxygen (O2) and carbon dioxide (CO2) occurs.
Rich in carbon dioxide, venous bloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood travels to the lungs to replenish oxygen; this oxygenated bloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood then travels back to the heart, which pumps it to oxygenate the organs of the human body.
The arrival of "used" blood, heavy with carbon dioxide (CO2)
“Used” bloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood arrives at the lungs from the right ventricle via the pulmonary artery.
The pulmonary artery branches into a multitude of small arterioles and capillaries to direct the bloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood throughout the lungs.
Pulmonary Capillaries, Microscopic Vessels
Pulmonary capillaries are the junction points between the pulmonary arteries and veins.
These are microscopic vessels in which bloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood cells pass in single file.
Pulmonary Alveoli, These Small Air Sacs
The lungs are composed of a multitude of small air sacs called alveoli. There are more than 600 million alveoli in the lungs.
An alveolus has a diameter of 0.2 mm and its wall is lined with a very thin layer of cells. Pulmonary capillaries cover the entire surface of the alveoli.
Junction of Alveoli and Pulmonary Capillaries
It is at this microscopic site that respiration truly takes place.
Fluid Exchange at the Capillaries
Capillaries are like perforated drains covered with a thin membrane, which prevents proteinsProteins are fundamental components manufactured by the cells of our body. They play an essential role in many biological functions, acting as hormones, antibodies, and even cholesterol transporters, among others. >> and bloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood cells from exiting while allowing bloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood fluids, the water in the bloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood, to escape or re-enter circulation.
Normally, the balance of what exits and enters is maintained. There is no fluid accumulation in the lung.
But where does this balance between the water that exits the capillaries and the water that returns to them come from?
Fluid Exchange at the Capillaries
Capillaries are like perforated drains covered with a thin membrane, which prevents proteins and blood cells from exiting while allowing blood fluids, the water in the blood, to escape or re-enter circulation.
Normally, the balance of what exits and enters is maintained. There is no fluid accumulation in the lung.
But where does this balance between the water that exits the capillaries and the water that returns to them come from?
Lung Cells Bathe in a Fluid
It is important to know that the alveolar cells must bathe in a fluid to ensure their proper functioning and allow the exchange of oxygen (O2) into the bloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood and carbon dioxide (CO2) into the alveoli, and finally out of the lungs through exhalation.
Factors That Control Water
Two factors influence the entry and exit of water from the capillary. One attempts to keep the water inside, while the other allows it to escape.
-Oncotic Factor
Let’s call the first factor the oncotic pressure. For better understanding, let’s say that the “on” in oncotic means “inside” or within.
The retention of water in the capillary is exerted by the bloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood cells and bloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood proteinsProteins are fundamental components manufactured by the cells of our body. They play an essential role in many biological functions, acting as hormones, antibodies, and even cholesterol transporters, among others. >> that cannot cross the capillary membrane. Therefore, the bloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood cells and proteinsProteins are fundamental components manufactured by the cells of our body. They play an essential role in many biological functions, acting as hormones, antibodies, and even cholesterol transporters, among others. >> remain within this microscopic vessel.
-Osmotic Factor
The second factor that influences the entry and exit of water from the capillaries is osmotic pressure.
The term osmotic comes from the word osmosis, which means the free passage of water to balance the concentrations inside and outside the capillaries.
In this way, the cells bathe, but there is no overflow.
The Consequence of a Loss of Balance
Any alteration in these factors can cause an excess of water in the environment where the cells bathe. This excess water will slow the exchange of oxygen and carbon dioxide, resulting in more pronounced shortness of breath during exertion.
This is the case with anemia, a decrease in hemoglobin that alters the oncotic factor. There is less water retention in the capillary. The resulting shortness of breath is further amplified by a decrease in the number of red bloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood cells, the small vessels that transport oxygen.
The same effect will occur with a decrease in bloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood proteinsProteins are fundamental components manufactured by the cells of our body. They play an essential role in many biological functions, acting as hormones, antibodies, and even cholesterol transporters, among others. >> attributable to certain diseases that reduce their production in the liver. This decrease in bloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood proteinsProteins are fundamental components manufactured by the cells of our body. They play an essential role in many biological functions, acting as hormones, antibodies, and even cholesterol transporters, among others. >> can also be due to other intestinal or renal problems, which cause their loss through stool or urine.
These diseases are usually chronic, meaning they develop gradually.
But What Does the Heart Have to Do with This Balance?
You might say that of the two factors mentioned above, you don’t see the role of the heart in the formation of pulmonary edema.
You are right!
There is a third factor. This factor is related to the bloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood pressure in the capillary.
-Third Factor: Blood Pressure
BloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood pressure is generated by the contraction of the heart to circulate bloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood throughout the body, including the lungs. The normal bloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood pressure in the pulmonary capillaries is below 20 mmHg.
An increase in this pressure will create bloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood congestion in the pulmonary capillaries.
An Ice Jam in the River
Let’s take the example of a river where an ice jam has formed. The water rises in front of this jam. The river overflows its banks and floods the surrounding land.
Water Invades the Surrounding Land
At the pulmonary level, water rises in the “bathtub” of the lung cells. Eventually, its overflow causes water to invade the alveoli.
The presence of excess water between the alveolar cells already deteriorates the exchange of oxygen and carbon dioxide. Shortness of breath appears.
The impact is even more significant when water invades the small air sacs of the lungs, known as the alveoli.
Capillaries are the Nerve Center of Congestion Impacts
Pulmonary capillaries are at the mercy of all heart diseases that cause congestion at their level.
We could mention all the issues related to the aortic and mitral valves, any damage to the left ventricle, not to mention certain arrhythmias that cause the heart to beat too quickly, and many more!
Possible Symptoms
-Shortness of Breath
The symptom of shortness of breath will evolve over time. It is related to the amount of water in the environment where the cells are immersed, and even worse, when there is water in the alveoli.
The same applies to two other symptoms related to this loss of balance in fluid exchange in the pulmonary capillaries.
-Shortness of Breath When Lying Down
Some patients are no longer able to sleep without elevating their heads with several pillows; otherwise, they feel like they are suffocating.
This symptom is called “orthopnea.”
What Happens?
When lying down, the bloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood that was pulled by gravity into the legs is now released and recirculated.
Normally, an individual does not feel any impact from this redistribution.
However, in people with certain heart problems, the weakened pump (heart) struggles to handle this extra volume, leading to an overload on the heart.
This increased volume in the heart’s chambers creates congestion in the left ventricle and atrium, which then affects the capillaries, the nerve center of oxygen (O2) and carbon dioxide (CO2) exchange.
Elevating the thorax by using several pillows reduces the effect of bloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood redistribution from the legs. This helps the person breathe more easily.
An increase in the number of pillows needed to maintain comfort is a sign of worsening cardiac condition and should be mentioned to a doctor.
Shortness of Breath at Night
It is possible that the redistribution of bloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood that was pulled by gravity into the legs occurs more gradually.
In this case, the person lies down without initially experiencing shortness of breath. The shortness of breath may wake them up later in the night.
Sitting on the edge of the bed with feet on the floor or getting up to get some air can relieve the shortness of breath within minutes.
This symptom, known as “paroxysmal nocturnal dyspnea,” should also be reported to the doctor.
Chronic Heart Diseases
Some heart diseases are chronic, and symptoms develop gradually over time or fluctuate. Certain events will be more significant than others. This condition is known as recurrent pulmonary edema.
Acute Pulmonary Edema
Other heart conditions can rapidly cause progressive shortness of breath and can put the individual’s life at risk. The bloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood becomes less oxygenated. Carbon dioxide accumulates. The person feels short of breath. Their breathing becomes difficult or even labored.
It’s like drowning. The person is choking. Anxiety reaches its peak.
Cold sweats appear, and respiratory fatigue sets in. This is called acute pulmonary edema.
It’s a medical emergency – Call 911!
If you experience any worrisome symptoms, consult your doctor.
Water "in" and "on" the Lungs
Now, how can water “in” the lungs also be “on” the lungs, meaning in its lining?
Let’s use another example to illustrate this clearly. Imagine putting a sponge in a glass and adding water; the sponge soaks up the water, and the excess stays at the bottom of the glass.
The congestion of the pulmonary capillaries floods the lung and then floods the lining of the lung.
This flooding gives rise to pleural effusions around both lungs or a pleural effusion if it is on only one side.