The effects of anemia on exercise

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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Fick Cardiac Output

We’ve all run across the Fick equation for cardiac output at one time or another. There are very limited circumstances when we’d ever get to use it but at the same time it’s one of those simple but incredibly profound equations that’s also a foundation of pulmonary physiology.

The Fick equation is:

where:

VO2 = oxygen uptake

CvO2 = mixed venous oxygen content

CaO2 = arterial oxygen content

And what it describes is:

It’s a mass-balance equation that basically says that what goes in must come out, but how do you get from oxygen uptake to cardiac output?
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