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Pursed Lip Breathing - Part 2
by Mark W. Mangus, Sr. BSRC, RRT, RPFT, FAARC
While resources describing techniques of performing the PLB maneuver can be found, I want to add my difference of opinion with many of those standardized explanations and to caution folks that ALL of the fancy maneuvers others recommend as being part of “correctly” doing PLB that are applied to the INSPIRATORY phase of breathing are mostly superfluous and do NOTHING to enhance the basic action and result of PLB – to aid in exhalation of a greater amount of air than would be if PLB were not used. PLB is beneficial ONLY as an EXPIRATORY maneuver and has NOTHING to do with inspiration or much, if anything, to do with the inspiratory phase. Most recommend, even admonish PLB users to ‘breathe in through their nose’. All manner of what might ‘seem’ logical and helpful reasons and advantages to doing so are given in the various explanations. Though the reasons may sound plausible and valid, they have little or no real ‘science’ to support them.
They say it filters, warms and humidifies the air. They say it helps slow your rate of breathing by increasing the length of inhalation. Some say that if you inhale through an open mouth that you are decreasing or even negating the benefit of PLB. To those claims I offer the following facts and considerations.....
The nose does not so efficiently filter incoming air that it makes much difference when we look at the ‘cleanliness’ of the air when it reaches a certain point within your lungs. Those who think it does ignore the role of the mucus blanket in the bronchial tubes which is responsible for cleaning, warming and humidifying perhaps 80 % and more of the air as it passes through them into the depths of the lungs. Nor does it add all that much heat or moisture/humidity to the air when we look at it at along various points in the lungs. Indeed, within the lungs, there is a point at which the air is as clean as it will ever be; warmed to body temperature and humidified to 100 % of what it can carry, regardless of by what route it was brought into the lungs. That point is called the iso-thermal layer. The isothermal layer moves up and down between a few generations of bronchial tubes according to the temperature of the air coming in AND in relation to the dilation of the blood vessels around those bronchial tubes as demand for increasing or decreasing heat and moisture exchange changes with incoming air temperature and the humidity it already contains. This mechanism is so efficient as to allow one to jog or run with great increase in ventilation on a freezing day without freezing their lungs or the iso-thermal layer having to move significantly from its normal position within the lungs. It is true that lung disease decreases your tolerance to these kinds of temperature changes, and it is understandable in view of the loss of conducting airways and consequently the mechanisms that perform those functions of warming and moistening the incoming air.
Next, breathing in through the nose is touted as a means to slow one’s rate of breathing. Not only is this a BAD means to accomplish what is efficiently done by EXHALING through pursed lips, but it potentially steals time away from the advantageous duration of exhalation by slowing down the respiratory rate TOO MUCH. And, when you consider activity level and how PLB must change to accommodate the necessarily increased demand for ventilation, messing with “inspiratory time” AND the increasing discomfort encountered when trying to force inspiration through the nose, which, since being a significantly narrower pathway than an open mouth, imposes increasingly excessive resistance to air movement, IN or OUT, really makes using the technique difficult, if not impossible to continue with any measure of effectiveness.
Oxygen by Nasal Cannula
and Pursed Lip Breathing
Some say that by breathing in through your mouth when you use oxygen by nasal cannula that you get less oxygen than by forcing yourself to breathing in through your nose. This is true only to a point, in that breathing in slowly ALWAYS causes more oxygen to be inhaled when it is delivered by constant (continuous) flow devices. But, when you are in the throes of activity/ambulation/exercise, you MUST breathe in faster to keep up with CO2 clearance at whatever level of effectiveness you can manage. AND, with very effective PLB, you will better allow yourself to bring in more oxygen if you don’t already increase flow or are not using a conserving device that delivers what oxygen you receive at a much higher flow rate than any equivalent of continuous flow. As well, some argue that breathing in through the mouth necessarily allows less oxygen to be inhaled than would be brought in through the nose.
Studies have shown little to no difference in how much oxygen is delivered be it by inhaling through the nose or the mouth. And, if you are concerned that you might not get enough oxygen from your cannula during mouth breathing you can either move the prongs into your mouth OR try using a Peterson Straw Mask or even just a mask with two nickel-sized holes cut into it on either side over your cheeks. It will serve as a reservoir of ALL flow to your system so that you don’t lose nearly as much otherwise wasted gas or what cannot be inhaled during exhalation as would happen when using a cannula, alone.
Ultimately, you should breathe IN through whatever pathway is most comfortable and manageable for you under the conditions of the moment that you are using it. If that is through the nose, then fine. If that ends up being through the mouth, then also fine. BUT, you should NOT try to use inhalation through the nose as a means to “slow your breathing down”! I can’t stress this enough! Indeed, too many techniques - - - demonstrated by folks who not only have NORMAL pulmonary function, but, IMO, have no CLUE of the dynamics of breathing and how it feels to have COPD that is severe enough that PLB is of great consequence and benefit - - - inhale at a rate that is unrealistically slowed, not only bringing into question their credibility, but also the usefulness of the technique, itself! If you are shown an unrealistic method, your chances of NOT trying to use it when you can’t make it work the way you were shown are greater! The main points I would keep in mind are that you need to adjust the “durations” of inhalation and exhalation as your respiratory demand increases. BUT, you must strive to maintain relatively the same ratio of inspiratory duration to expiratory duration and, ultimately their ratio. That ratio should target each duration of expiration being three to four times longer than was inspiration that preceded it. With regard to how much force to blow out with, you should adjust that for the moment so that it is neither too much nor too little. Adjust to what feels most effective for the circumstances