Peak Flow Meters and CO2
Mark Mangus, RRT EFFORTS Board
Mark Mangus RRT, BSRC, is a member of the Medical Board of EFFORTS (the online support group, Emphysema Foundation For Our Right To Survive, www.emphysema.net) who generously donates his time to answer members’ questions.
Jack from EFFORTS recently asked Mark about peak flow meters and how accurate they are.
A peak flow meter measures your highest expiratory flow rate when you forcefully exhale in a “huff or fast blast.” Accuracy of peak flow is strictly dependent upon patient effort and performance. People with COPD have low flow rates which do not significantly change across a wide spectrum of conditions. If your peak flow reading is less than 200 liters per minute, a peak flow meter is not recommended. Those with asthma have great changes in peak flow rates.
When used daily, a drop in peak flow readings, alerts the user to an impending asthma attack so they may take action quickly.
There is absolutely no evidence that the same holds true for a COPD exacerbation. Asthma is of an acute nature and COPD is not. The swelling in the airways of those with asthma occurs hours before the onset of an attack. That inflammation is what invokes significant changes in peak flow long before the full blown attack occurs. Changes in the airways of those with COPD do not occur as immediately or as severely as they do with asthma. Peak flow is always low and changes a relatively small amount from steady state to full blown exacerbation. You should be very careful when using peak flow as part of your COPD management regimen. The more severe your COPD, the less weight you should place on it.
Alan B was wondering if he could train himself to deep breathe in order to increase oxygen levels and clear carbon dioxide (CO2) from his lungs.
The reason we breathe in and out is solely to eliminate CO2. Your breathing efforts should not be aimed at thoughts of oxygenation as much as at CO2 reduction. Oxygenation is a passive function of breathing and will take care of itself as long as you breathe effectively to reduce CO2. While it is always good to stop and take a few deep breaths, cleansing breaths as they might be referred to in yoga and relaxation techniques, that is something you can do only periodically and for a relatively short duration. If you think you can reduce CO2 retention or somehow train yourself to do other than the natural method of smaller volumes during quiet breathing, I have seen no evidence that such a thing can be done. You can lower your CO2 by taking deliberate deep breaths while resting over a period of time. It will lower the CO2 only during the time you are being deliberate about your breathing. You will revert back to your smaller volume breathing pattern as soon as you stop thinking about it. That is the nature of the beast. Also, when you sleep, you cannot be deliberate about your breathing pattern.
The kidneys compensate for the change in CO2 by retaining bicarbonate to ‘buffer’ the system and maintain a normal pH. These are metabolic changes over which you have no deliberate control. When pH is normal, a must for physiologic stability, it does not matter how diseased and dysfunctional the lungs may be. CO2 is not a concern to the body, overall. The reason folks become CO2 retainers is because the kidneys have done their job to maintain a normal pH and let CO2 do what it will. I’ve said it before and I’ll continue to say it: “People obsess over CO2 – over which they have no control, in deference to the consequential parameter; the pH!”