Forearm skeletal muscle oxygen utilization assessed by NIRS was significantly lower in patients with pulmonary hypertension compared to those without (P=0.02).
Cross-Sectional (n=23)
Does NIRS-derived skeletal muscle oxygen utilization differ in patients with pulmonary hypertension compared to controls?
NIRS-derived skeletal muscle oxygen utilization is reduced in patients with pulmonary hypertension and correlates with functional class and DLCO, suggesting peripheral muscle dysfunction contributes to exercise limitation.
p-value: p=0.02
Abstract Rationale Exercise intolerance in pulmonary hypertension (PH) is traditionally attributed to cardiopulmonary limitations. However, peripheral skeletal muscle dysfunction may also contribute to exercise intolerance in PH patients. Near infrared spectroscopy (NIRS) offers a non-invasive method to assess skeletal muscle oxygen utilization (VO2skm). Prior studies suggest reduced leg VO2skm in lung diseases such as COPD. While atrophy from reduced physical activity may lower VO2skm, disruptions of cellular energy metabolism could also contribute. We hypothesized that NIRS-derived VO2skm is reduced in patients with PH compared to controls and is associated with functional impairment. We evaluated this hypothesis using forearm NIRS measures reasoning the arm may be less prone to disuse atrophy in cardiopulmonary disease. Methods We enrolled adults undergoing right heart catheterization for PH evaluation and healthy controls. Participants were categorized as healthy controls, chronic lung disease without PH (CLD-NoPH), chronic lung disease with PH (CLD-PH), or other forms of PH. NIRS measures of the forearm skeletal muscle oxygen metabolism were obtained at rest through an arterial cuff occlusion method. Association between NIRS-derived VO2skm and clinical/hemodynamic variables were assessed by t-tests and Pearson correlation. Association with functional classification was evaluated using ordinal regression. All patients had normal resting SpO2 measurements during NIRS (with or without oxygen supplementation). Results Twenty-three participants completed NIRS assessment: 5 controls, 8 CLD-NoPH, 6 CLD-PH, and 4 with other PH types. The cohort was 61% female with median age 61 years. VO2skm measurements were obtained in all participants except one (technical failure). VO2skm was significantly lower in those with compared to without PH (P = 0.02) and CLD-PH patients had lower VO2skm than controls (P = 0.03, Figure). There was no correlation between VO2skm and spirometry measures or pulmonary hemodynamics. A positive correlation was noted between VO2skm and DLCO (r = 0.53, P = 0.035) and a trend toward correlation with cardiac index (r = 0.41, P = 0.117). Ordinal regression revealed statistically significant associations between VO2skm and WHO Functional Class (FC) with threshold effects at the FC 1-2 transition and 3-4 transition, suggesting that VO2skm differences are most pronounced at these functional transition points. Conclusions NIRS assessment of VO2skm is feasible and well-tolerated in patients with PH. Patients with PH demonstrate reduced VO2skm compared to controls, with correlations to DLCO and symptoms but not hemodynamics or spirometric parameters. These findings suggest skeletal muscle dysfunction contributes to exercise limitation in PH independent of cardiopulmonary physiology and may implicate impaired peripheral oxygen utilization. This abstract is funded by: NIH, VHA
Trammell et al. (Fri,) conducted a cross-sectional in Pulmonary hypertension and chronic lung disease (n=23). Near infrared spectroscopy (NIRS) of forearm skeletal muscle vs. Healthy controls and patients without pulmonary hypertension was evaluated on Skeletal muscle oxygen utilization (VO2skm) (p=0.02). Forearm skeletal muscle oxygen utilization assessed by NIRS was significantly lower in patients with pulmonary hypertension compared to those without (P=0.02).