A Multivariable Index for Grading Exercise Gas Exchange Severity in Patients with Pulmonary Arterial Hypertension and Heart Failure

Patients with pulmonary arterial hypertension (PAH) and heart failure (HF) display many abnormalities in respiratory gas exchange. These abnormalities are accentuated with exercise and track with disease severity. However, use of gas exchange measures in day-to-day clinical practice is limited by several issues, including the large number of variables available and difficulty in data interpretation. Moreover, maximal exercise testing has limitations in clinical populations due to their complexity, patient anxiety and variability in protocols and cost. Therefore, a multivariable gas exchange index (MVI) that integrates key gas exchange variables obtained during submaximal exercise into a severity score that ranges from normal to severe-very-severe is proposed. To demonstrate the usefulness of this index, we applied this to 2 groups (PAH, n = 42 and HF, n = 47) as well as to age matched healthy controls (n = 25). We demonstrate that this score tracks WHO classification and right ventricular systolic pressure in PAH (r = 0.53 and 0.73, P ≤ 0.01) and NYHA and cardiac index in HF (r = 0.49 and 0.74, P ≤ 0.01). This index demonstrates a stronger relationship than any single gas exchange variable alone. In conclusion, MVI obtained from light, submaximal exercise gas exchange is a useful approach to simplify data interpretation in PAH and HF populations

Use of Noninvasive Gas Exchange to Track pulmonary Vascular Responses to exercise in Heart Failure

We determined whether a non-invasive gas exchange based estimate of pulmonary vascular (PV) capacitance [PV CAP = stroke volume (SV) x pulmonary arterial pressure (Ppa)] (GX CAP ) tracked the PV response to exercise in heart-failure (HF) patients. Pulmonary wedge pressure (Ppw), Ppa, PV resistance (PVR), and gas exchange were measured simultaneously during cycle exercise in 42 HF patients undergoing right-heart catheterization. During exercise, P ET CO 2 and V E /VCO 2 were related to each other ( r = -0.93, P < 0.01) and similarly related to mean Ppa (mPpa) ( r = -0.39 and 0.36; P < 0.05); P ET CO 2 was subsequently used as a metric of mPpa. Oxygen pulse (O 2 pulse) tracked the SV response to exercise (r = 0.91, P < 0.01). Thus, GX CAP was calculated as O 2 pulse x P ET CO 2 . During exercise, invasively determined PV CAP and non-invasive GX CAP were related (r = 0.86, P < 0.01), and GX CAP correlated with mPpa and PVR (r = -0.46 and -0.54; P < 0.01). In conclusion, noninvasive gas exchange measures may represent a simple way to track the PV response to exercise in HF

Clinical feasibility of exercise-based A-V interval optimization for cardiac resynchronization: a pilot study

BACKGROUND: One-third of eligible patients fail to respond to cardiac resynchronization therapy (CRT). Current methods to optimize the atrio-ventricular (A-V) interval are performed at rest, which may limit its efficacy during daily activities. We hypothesized that low-intensity cardiopulmonary exercise testing (CPX) could identify the most favorable physiologic combination of specific gas exchange parameters reflecting pulmonary blood flow or cardiac output, stroke volume, and left atrial pressure to guide determination of the optimal A-V interval. METHODS: We assessed relative feasibility of determining the optimal A-V interval by three methods in 17 patients who underwent optimization of CRT: (1) resting echocardiographic optimization (the Ritter method), (2) resting electrical optimization (intrinsic A-V interval and QRS duration), and (3) during low-intensity, steady-state CPX. Five sequential, incremental A-V intervals were programmed in each method. Assessment of cardiopulmonary stability and potential influence on the CPX-based method were assessed. RESULTS: CPX and determination of a physiological optimal A-V interval was successfully completed in 94.1% of patients, slightly higher than the resting echo-based approach (88.2%). There was a wide variation in the optimal A-V delay determined by each method. There was no observed cardiopulmonary instability or impact of the implant procedure that affected determination of the CPX-based optimized A-V interval. CONCLUSIONS: Determining optimized A-V intervals by CPX is feasible. Proposed mechanisms explaining this finding and long-term impact require further study