Swallow et al evaluated survival for patients with chronic obstructive pulmonary disease (COPD) based on the quadriceps maximal voluntary contraction force (QMVC). This can help to identify a group of patients who may benefit from more aggressive management. The authors are from the Royal Brompton Hospital in London.
Factors associated with increased mortality:
(1) age in years
(2) quadriceps maximal voluntary contraction force divided by body mass index (BMI)
(3) GOLD class 3 or 4
The measurement of quadriceps contraction is described on page 116. The quadriceps muscle of the dominant leg performed isometric contractions with the knee flexed to 90 degrees. The values are expressed in kilograms and the highest of 3 attempts was recorded. The mean QMVC was 32 kilogrrams with the standard deviation 11.5.
QMVC divided by BMI in percent =
= (QMVC in kilograms) / (BMI in kg per square meter) * 100%
A ratio < 120% was associated with worse transplant-free survival at 4 years. Survival for patients with a normal vs reduced ratio tracked together for the first 2 years but diverge afterwards.
Graphs not shown in the paper was survival for each GOLD class vs the QMVC-to-BMI ratio. The survival shown in Figure 3 (survival by GOLD class) looks similar to Figure 2 (survival by quadriceps strength), raising the possibility that there is a link between the two measures. Also not shown is the Z score for QMVC for age; the number of standard deviations below normal would be interesting to compare to survival. Finally there is no mention of how the QMVC changed over time.
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