This is a 58 y/o Scottish woman with dyspnea on exertion. This had been progressive initially but is now unchanged. No chest pain, no F/C/NS/cough/hemoptysis.
Unremarkable SHx and FHx.
ROS only positive for DOE and occasional rare dry cough.
Exam: overweight woman in NAD. Weight: 163 lb with height: 62 in (BMI:29.8). Normal HEENT, clear lungs, S1/S2 RRR, benign abdomen.
Spiro: FVC 106% and FEV1 103%, TLC 102% (no air trapping) and normal DLCO. Methacholine challenge showed some reduction in FVC and FEV1 at 25mg but not reaching significance.
Clear CxR.
Here are the highlights of her CPET. What do you think?
Pt stopped due to dyspnea. VO2 max: 1.025 (57%) with VO2/kg/min of 13.8 (52%). AT: 0.692 (predicted >.715, 39% of VO2max). HR: 137 (85%) with O2 pulse 7.5 (89%) and HR reserve 24 (<15).
VEmax: 47.8 (72%) and Vt at peak: 1.128L (169%), RR: 40 (<50) with breathing reserve 9%.
Vd/Vt: o.50 at rest and 0.29 at peak (0.30 and 0.18). RQ at peak was 0.94 (1.1-1.3).
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Well, she reached her AT early but her dead VD/VT went down and she didn't reach maximum HR, so I would say that a cardiac or pulmonary origin are not the cause. Her normal DLCO might make a pulmonary vascular etiology less lilely too. As far as I recall, deconditioning does not result in a low predicted AT. So perhaps the DOE, as suggested by this CPET, is due to obesity.
What do you think of her low respiratory reserve with that high Vt at peak?
You mentioned her ethnicity; could the percent predicted for the VT be inaccurate, or am I barking up the wrong tree?
If the VT is really that high, and the pulmonary reserve is, as you pointed out, almost maxed-out, this may also represent air-trapping. I would expect the dead space to also increase if this were truly air-trapping. Nonetheless, this info, along with her normal DLCO might suggest exercise-induced asthma. Do you have a post-CPET FEV1?
If this diagnosis is correct, what do you make of the negative methacholine challenge?
Actually her surface echo was pretty unremarkable (I forgot to mention that on the initial Hx).
I was more impressed by the relatively low respiratory reserve at peak exercise at a fairly low VO2 (9% reserve). My concerns were similar to Jennings'. Her FEV1 and FVC both dropped efter exercise and her FEV1 at peak was 63% of predicted (down from her normal baseline). I was a bit puzzled since she did have a normal methacholine challenge... still we elected to start her on aggressive bronchodilator therapy and set her up with pulmonary rehab.
Actually, if this is exercise-induced asthma I think sometimes the methacholine challenge test can be negative (as in your patient). Although not incredibly practical, one could challenge with cold air...
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