Appreciation of Increased Pulmonary Vascular Resistance from the Maximum Desaturation in 2-Chair Test: An Appraisal

The desat max of 2-chair test, claimed to have identified the sildenafil responsiveness in COPD-PH (pulmonary hypertension), should represent high PVR (pulmonary vascular resistance).

Hemodynamically diagnosed PH in CLD (chronic lung disease)-patients were analyzed statistically and divided into two groups on high or low PVR (>2 and ≤2 Wood units) to judge the power of the desat-max of 2-chair test differentiating them. Co-relationship of desat-max was sought with different spirometric, Doppler-echocardiographic, and RHC (right heart catheterization) derived parameters as TPG (trans-pulmonary gradient), PVR, mPAP (mean pulmonary pressure) and PCWP (pulmonary capillary wedge pressure). Further, the specificity and sensitivity of variable desat-max values were calculated and high PVR and a VIP plot was drawn with all available variables to see their impact on PVR compared to desat-max.

We included 57 patients of CLD-PH consisting of COPD (n=26), chronic asthma (n=9), ILD (n=7), and miscellaneous diseases (n=15). When divided on high or low PVR, the two groups (n=39 and 18) stood similar in demographic, spirometric, and Doppler-echocardiography measurements. However, they differed in desat-max (-8.76±4.90 and -3.61±1.94; P<0.0001) and in RHC derived mean-PVR (4.25±2.97 vs 1.20±0.53; P<0.0001), mean-TPG (12.86± 4.84 vs 5.11±2.78; P<0.0001), cardiac output (3.77±1.07 and 4.29±1.15; P=0.02). The calculated best cut-off desat-max (>4.5%) could identify high PVR with 72.22% sensitivity and 79.40% specificity with adjusted odds ratio of 19.55. The desat-max correlated best with RHC-measured PVR (r=0.56) but not with PCWP (r=0.09).

Desat-max of 2-chair test appears indicative of high PVR in CLD-PH. The revelation merits further research.