Monthly Archives: May 2017

The effects of anemia on exercise

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Last week I was reviewing the exercise test results from a patient that appeared to have a relatively straightforward cardiovascular limitation when I noticed the patient also had severe anemia (Hgb = 7.1). Once that fact came up it was no longer clear the patient actually had a cardiac limitation at all.

First the results:

Rest: %Predicted: AT: %Predicted: Max: %Predicted:
VO2 (LPM): 0.33 13% 0.73 28% 1.45 56%
VO2 (ml/kg/min): 5.0 11.0 21.6
VCO2 (LPM) 0.26 0.63 1.81
RER: 0.73 0.83 1.24
SaO2: 98% 97% 97%
PetCO2: 35.2 38.6 31.8
Ve/VO2: 34 26 43
Ve/VCO2: 47 31 35
Ve (LPM): 11.6 8% 19.2 13% 62.9 44%
Vt (L): 0.78 1.29 2.19
RR: 15 15 29
HR (BPM): 61 35% 92 52% 152 85%
BP (mmHg): 92/62 102/64
O2 Pulse (ml/beat): 5.8 39% 8.2 55% 9.8 66%

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Is there such a thing as a normal decrease when the FEV1 isn’t normal?

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I’ve mentioned before that my lab’s database goes back to 1990, so we now have 27 years of test results available for trending. At least a couple times a week we have a patient who was last seen 10 or even 20 years ago. When I review their results I try to see if there has been any significant change from their last tests. Since the last tests are often quite some time in the past the changes in an absolute sense are often noticeably large. The question then becomes whether or not these changes are normal.

Although the ATS/ERS, NIOSH and ACOEM standards for spirometry address changes over time they don’t specifically discuss changes over a decade or longer. Instead, without indicating a time period (other than saying a year or more), the concensus is that a change greater than 15% in age-adjusted FVC or FEV1 is likely to be significant. A change in absolute values greater than:

Or if the current FEV1 is less than:

Then the change is likely significant.

This sounds fairly reasonable and although we could quibble about the importance of how quickly or slowly this age-adjusted 15% change occurs and how well it applies when the patient’s latest age is beyond the reference equation’s study population (we have a fair number of 90+ year old patients nowadays) or when it’s across a developmental threshold (adolescent to adult), it’s still a good starting point.

I’ve been more or less following these rules for the last several years, when the results for a patient whose last test was 18 years ago came across my desk. The FEV1 from the current spirometry was 71% of predicted and the FEV1 from 18 years ago was 70% of predicted. Strictly speaking the absolute change was about -15% (the FEV1 was 2.06 L in 1999 and 1.76 L in 2017, a 0.30 L change) but when adjusted for the change in age, that’s only 40% what a significant change would need to be:

Given that the FEV1 percent predicted from both the older and newer test were essentially identical I automatically started to type “The change in FEV1 is normal for the change in age” when it suddenly occurred to me that neither FEV1 was normal in the first place so how could I be sure the change be normal?

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What does an inverse I:E Ratio during exercise mean?

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Inspiration and expiration usually take different lengths of time, with inspiration almost always being shorter than exhalation. This is due to both to the physiology of breathing and to the pathophysiology of disease processes. During incremental exercise testing there are usually patterns to the way that inspiratory and expiratory times change and these are occasionally diagnostic.

When I started in this field the relationship between inspiratory and expiratory time was usually expressed as the I:E ratio, which was most often written as something like 1:1.2. One of my medical directors pointed out to me that when talking about I:E ratio it was difficult to determine what you meant if you said it was increasing or decreasing. For this reason I started reporting the I:E ratio as the E/I ratio so that instead of 1:1.2 it’s just 1.2.

Somewhere along the way however, for exercise testing at least, the most common way of expressing the I:E ratio seems to have morphed primarily into Ti/TTot (which is the Inspiratory Time/Total Inspiratory and Expiratory Time ratio), less commonly as Ti/Te and almost never as I:E. Even so, I still prefer the E/I ratio approach, partly because I’m used to it but mostly because it emphasizes the expiratory time component. For example:

Ti/TTot: Ti/Te: E/I:
0.50 1.00 1.0
0.48 0.91 1.1
0.45 0.83 1.2
0.43 0.77 1.3
0.42 0.71 1.4
0.40 0.66 1.5
0.38 0.63 1.6
0.37 0.59 1.7
0.36 0.56 1.8
0.34 0.53 1.9
0.33 0.50 2.0

Anyway, at rest most subjects breathe with an E/I ratio somewhere between 1.2 and 1.5 (Ti/TTot 0.45 – 0.40). During exercise the E/I ratio usually decreases more or less steadily and usually reaches 1.0 (Ti/TTot 0.50) at or near peak exercise. When a subject has airway obstruction the E/I ratio often doesn’t decrease and in those with severe airway obstruction it often increases instead. E/I ratios above 2.0 aren’t all that uncommon in subjects with COPD. Occasionally a subject with normal baseline spirometry (i.e. a normal FEV1/FVC ratio) has an elevated and/or increasing E/I ratio throughout testing and this is a clue that they probably have some degree of airway obstruction that’s not otherwise evident, and possibly even EIA if it increases at peak exercise.

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2017 ERS Methacholine Challenge Standards

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After a couple years of waiting for the new methacholine standards to be released “any day now”, they were finally published in this month’s issue of the European Respiratory Journal. The standard is an open access article and can be downloaded by anyone.

The length of time taken to develop the standard was acknowledged and although active ATS participation was withdrawn because the original timeline was not met, for the most part the original ATS participants continued with the task group and the standard has been officially endorsed by the ATS.

The biggest difference between the 1999 standards and those from 2017 is the change from PC20 (provocative concentration causing a 20% decline in FEV) to PD20 (the provocative dose causing a 20% decline in FEV1) as the primary endpoint and this alone will make a difference in how methacholine challenges are performed and calculated.

The 1999 standard included both tidal volume and dosimeter protocols. The dosimeter protocol consisted of 5 breaths to TLC. The 2017 standards state that a dosimeter may be used but that this is primarily to make counting breaths and calculating the cumulative dose easier and that inhalations to TLC are specifically contraindicated due to “the bronchodilating or bronchoprotective effect of a maximal inspiratory manoeuvre with a breathhold at TLC”.

Other differences include:

  • The 1999 standard had both absolute and relative contraindications. There are only contraindications in the 2017 standard.
  • Absolute contraindications in the 1999 standards included an FEV1 < 50% of predicted (or < 1.0 L, age group unspecified) and for the 2017 standard it is an FEV1 < 60% of predicted (or 1.5 L, adults) which were relative contraindications in 1999.

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