Oxygen as indicator of lung disease

Importance of energy

Making our organs to work implies the transformation of energy from different instances. Each organ require a provition of nutrients to accomplish its functions. The most visible function is seen in muscles. Muscular actions are designed to help in life with almost every activity. Our muscles take a big part of nutrients and transform them into energy and subsequent physical actions.

Oxygen: a combustible

For the transformation of nutrients at celular muscular level, the combustible “gas” is Oxygen. It is brought to that level bound to Iron in Hemoglobin (Hb) of the red blood cells. Oxygen binds to iron in Hb at lungs where blood is exposed to oxygen. In the lungs, the thin barrier between blood and air is amazingly wide to allow this fuction.

Lung illness and oxygen change

Respiratory diseases affecting the surface for exchange will have an eventual impact in the take over of oxygen from atmospheric air. Acute and chronic conditions will (depending on their severity) reduce the healthy surface for exchange. The good news is that most of acute conditions will reverse or let minimal sequelae. Chronic conditions like extensive scaring, wide destruction of alveolar walls will manifest oxygen reduction in blood at some point of the course of the disease.

Reduced oxygen

Preserving the surface available for a healthy gas exchange provides with an adequate field for physical activities. Exercise requires, not only a healthy lung but also some physical (progressive training). Curiously, lung reserve for gas exchange is big and delay clinical manifestations of reduced blood oxygen (also called hypoxemia). When hypoxemia occurs something severe and serious may be happening and physical activities will be affected.

COPD and reduced oxygen

COPD is characterized by progressive destruction of alveolar walls as well as persistent bronchoconstriction that impedes air of leaving the alveoli. Under these circumstances oxygenated air can not reach the surface that allow access to blood and the surface that can be reached it’s already reduced.

What we can expect from COPD effects at some point of the disease development is hypoxemia. COPD patients with advanced disease will have their physical activities impacted due to hypoxemia especially when the energy requirements are increased (exercise).

Oxygen reduction in other lung diseases: a few examples

These effects may be seen during some asthma crisis. In a set of pulmonary disease called interstitial lung diseases the gas exchange surface is severely affected. In some cases of pneumonia the infectio may lead to pus accumulation in air spaces limiting air access into the lungs.

From Oxygen to where?

Oxygen measurement may be required in many respiratory symptoms assessments. If oxygen is reduced it may be necessary to consider levels of other gases like CO2 as well as levels of acidity. This is for having a more complete profile of the gas exchange and the responses of the body due to this effect.

The relevance of FEV1 measurement in COPD

 

FEV₁ is a key value to be known by smokers and COPD patients in order to assess the severity of the disease. FEV₁ means Forced Expiratory Volume in the First Second of a full forced exhalation after a full inhalation. It is obtained during the spirometry and represents the amount of air that leaves the lung when all the effort is put into exhalation. After the first second of a full exhalation there’s no much more opportunity to exhale additional amounts of air from the lungs.

 

How to get the FEV₁ value

 

It’s like blowing the candles in a birthday cake: the last ones require other inhalation to get turned off.

 

Although during the spirometry there’re no candles, the patient needs to exhale until he/she can not anymore and not breathing in. If there’s an interruption during FEV₁ measurement, this value will not be real and the interpretation will be wrong.

 

To obtain a FEV₁ value the continuous exhalation effort should last 6 seconds at least, when there’s no more flow from the lungs to the spirometer.

 

How different is FEV₁ value between COPD and asthma

 

FEV₁ gives a good estimate of obstruction in COPD and Asthma. In COPD, doesn’t revert so much. In most cases of asthma, it reverts when there aren’t any symptoms.

 

Everybody has a FEV₁ that modifies itself with aging. It increases until middle adulthood and starts to decrease 30 mL every year. In susceptible smokers, the rate of decrease of the FEV₁ is 60 mL every year which means that it is accelerated.

 

What’s the importance of FEV₁ value in research?

 

Dr. Robert Wise from John Hopkins University School of Medicine, Baltimore, Maryland, USA has been an advocate of the  FEV₁ relevance as a key value in the assessment of COPD (Am J of Med 2006:119;S4-S11).  This value represents the focus of investigations when evaluating the efficacy of approaches for the management of COPD.

 

Several years ago, in a famous, standard, reference publication Charles Fletcher and Richard Peto (Brit Med J, 1977:1:1645-1648) provided with data focused on FEV₁ change. Fletcher and Peto found that FEV₁ falls over time in London working men and this decline is accentuated in susceptible smokers. They also found that smoking cessation is the most effective measure to slow the acceleration toward the normal trend (particularly in those who stop smoking before 45 years old).

 

How the FEV₁value defines COPD severity

 

COPD stages are based on FEV₁ values and on how much it represents of the predicted value for gender, race, age, weigh, and height. For instance:

 

• Mild COPD exists when FEV₁ is 80% or more of predicted
• Moderate COPD exists when FEV₁ is 50% or more but less than 80% of predicted
• Severe COPD exists when FEV₁ is 30% or more but less than 50% of predicted
• Very severe COPD exists when FEV₁ is less than 30% of predicted or less than 50% of predicted with chronic respiratory failure (very low oxygen in blood and high levels of carbon dioxide)

 

Then… should we know the FEV₁ value in case of COPD?

 

Then, it’s good to know the FEV₁ to have a clear idea of the severity and change of the disease. This value is only obtained through spirometry and supports appropriate decisions for right measures to avoid rapid decline.

 

Remember: the most effective action to have a normal FEV₁ change during lifetime is quitting smoking as soon as possible.

 

Why spirometry?

Assessing lung function is a particular task. Lung functions are pending on many variables like integrity of the constituents tissues, viability of the airways, effective wrapping system, strenght of the individual body, gender, height, weigh…

Facilitating lung evaluation

However, in terms of lung function it tends to be restricted to the patency of airways. If airways are open, lungs will receive oxygen and the respiration itself is eased. Although the airways in some lung diseases are working appropriately, the tissues beyond may be damaged and lung function will be altered anyway.

What’s spirometry for?

Spirometry is a tool that helps to determine if airways are patent or not, and if lungs have enough elasticity or space to hold air enough to catch oxygen and release carbon dioxide.

With spirometry, the physician may give numeric values to the respiratory exam. Spirometry allows to get objective measurements as the sphygmomanometer provides us with real numbers on blood pressure and electrocardiogram shows the rythm of the heart.

Comparing spirometry with other methods in other diseases

With spirometry there is an almost good picture of lung volumes managed by a patient as well as flows through the airways. The big difference of spirometry when compared to sphygmomanometry or electrocardiography is that the former requires patient effort: an active participation. It requires pre-training, repetitions, and good will to get a good maneuver.

Spirometry and its 2 key values

Spirometry records several values related to the air expelled during a forced expiration. The first key value is the maximal amount of air the patient can exhale; it is called Forced Vital Capacity. The second value will be the amount of that air exhaled during the first second in the Forced Vital Capacity maneuver: Forced Expiratory Volumen in second 1. The importance of this value rely on the maximal effort to expell air which is easy at the begining.

Force Vital Capacity (FVC) may be diminished as an alternative to the normal. When it occurs it talks about restrictions in space. The FVC may be reduced due to a tigh (rigid) lung, a hard wrapping system, fluid around the lungs, thoracic deformities or pain.

Forced expiratory volumen in the first second (FEV₁) may be reduced due to changes and reductions in the caliber of the airways like in COPD, asthma, bronchiectasis.

Obstructive – Restrictive – Mixed

When the ratio FEV₁/FVC is reduced is the same to say: from the air exhaled from lungs forcedly, a small amount is released during the first second (which is not normal). This reduction allows pulmonologists to clasify the abnormality as Obstructive. When it is increased and most probably due to a reduced FVC, the category is Restrictive. And there are mixed patterns too.

Asthma and COPD

When the obstruction is reversible after administration of bronchodilators, it’s more likely a diagnosis of asthma. When the obstruction is always present with a partial response of bronchodilators, it’s more likely COPD (chronic obstructive pulmonary disease) although in some asthmatics it may be hard to revert the obstruction with bronchodilators either.

Can you ask for a spirometry?

Although these are not all the values obtainable from a spirometry, they are key to address a diagnosis. Spirometry with the resultant spirogram is fundamental to assess or confirm most of the respiratory diseases related to breathlessness. Smokers should encourage their physicians to get a spirometry as well as they want to know the blood pressure values.

In a near future…

When patients feel more empowered into the management of their health, particularly the respiratory patients, they will want to know the FEV₁ and FEV₁/FVC values to understand what’s happening inside their bodies. Perhaps, in a near future, a patient will remember that their FEV₁/FVC was 0.7  while their FEV₁ was 65% of the predicted value to help their physician adressing decision process.

Percussion of the Thorax during physical exam: some comments

An empty thorax?

Percussion of the thorax is a maneuver used by physicians to assess part of the integrity of lungs: their emptiness. As the lungs should be filled with air enough to be ventilated and proceed with the local gas exchange.

Lungs are like a huge sponge with a big difference from the typical ones: their dividing walls are full of blood and their spaces are full of air. The amount of air inside lungs is a big one: around 5 liters. Imagine 5 bottles of 1 liter each one inside the thorax and containing only air.

Just touching with two fingers

When percussion is performed hitting the tip of one middle finger on dorsal side of last joint in the other middle finger there is no special sound but some dullness. However, if the second finger is put over the thorax (not in the cardiac area) the sound is like the one on an empty box, similar to a drum, or the body of a guitar.

Some lung divisions

Lungs are composed by lobules (like having more than 2 sponges together). The right lung has 3 sponges together and the left has 2 and small one to give some space to the heart. The right has a big almost pyramidal that goes from the base of the thorax toward the whole back. Over its front there are the two other lobules: one bottom and other top. Here it was described right lung’s lobules: lower, middle, and upper.

For the purpose of this explanation, let’s avoid the left lung description.

Sonority vs dullness

The percussion of the thorax is normally sonorous (resonant). However, it’s not like an empty stomach but with some muffling (due to local blood circulation).

Some variety may be heard according to individuals. The resonance may be softer in an obese person than in the skinny. The expert will find normal sonority in each normal patient.

Changes in the back of right side of the thorax implies changes in the right lower lobe. In the front but bottom, percussion explores middle lobe while in the top front, it talks about upper right lobe.

Obvious changes of percussion in COPD

In COPD, the trapped air tend to increase the sonority of the thorax. It also happens in the symptomatic asthmatic as well as in other different circumstances. However, percussion of thorax is made with the purpose of looking for dullness like in pneumonia (when areas of the lung are filled with pus), pleural effusion (when the space between lung and rib cage is filled with more liquid that necessary to allow the breathing movement).

Granularities of COPD percussion

When a COPD patient has more emphysema than chronic bronchitis, the sonority by percussion is increased. It is also increased when the emphysema has led to creation of big bubbles called bullae. Its localized pattern may lead to clues about the severity of emphysema in precise areas.

A fact on percussion of the thorax

Percussion is a very helpful maneuver during physical exam of symptomatic respiratory patients. It completes the auscultation when it is abnormal. Not all patients will be explored with percussion but some of them may require this type of assessment when it’s necessary to confirm the excess presence of air, or a condition associated with dullness.

Don’t expect your general practitioner to do percussion in a routine manner. It’s just a confirmatory maneuver.

Facts on our defense mechanism and COPD

After smoking, what?

There are cells in mucosal surfaces responsible for initiating the response when injure starts. They behave like gossip reporters when something wrong happens. When there is exposure to antigens, for instance, these cells engulf the substance an run away to present most of the constituents of the original antigen to the army of natural defenders.

A network of alarms

These cells have been originally called Langerhan Cells. According to Tsoumakidou M and cols. ( Am J Resp Crit Care Med 2008. 177:1180-1186) this group of cells are the Dendritic Cells. Dendritic Cells include three subsets: type 1 myeloid, type 2 myeloid, and plasmocitoid. Their origin is not at the lungs, however it is still under debate.

The migratory informers/spies

Those cells are relocated to the lungs by the circulating blood. Once in the lungs, dendritic cells settle down and wait for signals of danger like fish in submarine caves.

Thy are activated when find an antigen, which is engulfed and immediately drained from the area where it was caught. Dendritic Cells migrate to the lymph nodes and during the new relocation the mature expresing in their surface new markers like their uniform abandoning their camouflage and carrying some amounts of antigen.

Once in the lymph nodes, dendritic cells may induce tolerance or T-cell and B-cell responses which depends on how harmfull the antigen is.

Cigarette smoking and Dendritic Cells

How much are our gossip journalists (officially dendritic cells) involved in the reaction to cigarette smoke has not been clarified completely.

In the article by Tsoumakidou, they present a list of effects due to cigarette smoke on dendritic cells. Some studies have demosntrated that exposure to nicotine, cigarette smoke extract, as well as to lung secretions alter their functionality leading to a disarray in the orchestra conducting function.

Other studies have shown that dendritic cell’s function is also altered in experimental mice models of emphysema.

Hypothesis Tsoumakidou of dendritic cells involvement in COPD

Then, the hypothesis of Tsoumakidou is that the long term exposure of dendritic cells to cigarette smoke may be related to the disorder seen in patients with COPD. This situation is manifested through repeated exacerbations, as well as local infections, and the exaggerated inflammatory response seen in this “progressive chronic disease“.

Cigarette Smoking doesn’t help in this life

Although there’s more light in the understansding of COPD, there’s no doubt on the complexity of the cellular environment of this condition and how cigarette smoke really doesn’t help to make it better.