Summary:
Purpose: CardioPulmonary Exercise Test (CPET)-derived parameters, VO2peak and VE/VCO2 slope, are established as Chronic Heart Failure (CHF) prognostic factors. We hypothesized that the severity of CHF , as it is expressed with VO2peak and VE/VCO2slope measurements , is associated with deterioration of skeletal muscle microcirculation, as it is assessed by Near InfraRed Spectroscopy (NIRS) in combination with Vascular Occlusion Technique (VOT).
Methods: Twenty-five ambulatory, stable CHF patients (23 males), mean age 57±9.6 years , body mass index 29.2±6.0 Kgr/m2 and EF= 34.2±7.9 %, underwent NIRS in combination with VOT, followed by a CardioPulmonary Exercise Test (CPET). Tissue Oxygen Saturation (StO2) in patients’ thenar muscle was measured by NIRS before, during and after a 3-minute occlusion of the brachial artery. StO2 at baseline, StO2min and StO2max measurements, were recorded . NIRS-derived measurements included Oxygen Consumption Rate (OCR, %/min) and Reperfusion Rate (RR, %/min). All patients concluded their evaluation with a symptom-limited CPET on a cycle-ergometer. Measurements included VO2 at peak exercise (VO2peak) and the slope of the ventilatory equivalent for carbon dioxide output (VE/VCO2 slope). Patients were classified by a) VO2peak=14ml/kgr/min, b) VE/VCO2slope=35, c) VO2peak median=17.6 ml/kgr /min and d) VE/VCO2 slope median=33, into two groups every time, of “mild” and “severe” CHF, and were compared with each other during four consecutive comparisons. Comparisons were made in the field of NIRS-derived and VOT-modified measurements, between groups of “severe” and “mild” CHF, in every single classification.
Results: In Comparison A’ , patients were divided in the “severe” CHF group ( VO2peak≤14 ml/kgr/min) and the “mild”CHF group (with VO2peak>14 ml/kgr/min). Patients with “severe” CHF presented StO2baseline 79.7±3.1% vs 78.2±5.2% ,p=0.642, StO2min 44.3±12% vs 37.8±8%, p=0.137 , StO2max 94±1.8 % vs 92.2±4.9%, p=0.687, OCR 13±2.9 %/min vs 13.1±4.1%/min ,p=0.962 and RR 4.3±1.3%/min vs 4.5±1.3%/min, p=0.616, compared with “mild” CHF group of patients .
In Comparison B’, patients were divided in the “severe” CHF group (VE/VCO2 slope>35) and the “mild”CHF group (with VE/VCO2 slope≤35). Patients with “severe” CHF presented StO2baseline 80.9±4.4% vs 77.5±4.7% ,p=0.037, StO2min 35.9±11.5% vs 41.1±7.8%, p=0.198 , StO2max 92.6±5 % vs 92.7±4.2%, p=0.628, OCR 14.4±5.2 %/min vs 12.5±2.9%/min ,p=0.237 and RR 4.5±1.5%/min vs 4.5±1.2%/min, p=0,892, compared with “mild” CHF group of patients.
In Comparison C’ , patients were divided in the “severe” CHF group ( with VO2peak≤17.6 ml/kgr/min, where 17.6 is the VO2peak median) and the “mild”CHF group (with VO2peak>17.6 ml/kgr/min). Patients with “severe” CHF presented StO2baseline 77.2±5.6 % vs 80±3.5% ,p=0.205, StO2min 41.9±9.2% vs 36.8±8.9%, p=0.174 , StO2max 91.8±4.4 % vs 93.6±4.3%, p=0.137, OCR 12.1±3 %/min vs 14.2±4.3%/min ,p=0.162 and RR 4.1±1%/min vs 4.9±1.5%/min, p=0.133, compared with “mild” CHF group of patients.
In Comparison D’, patients were divided in the “severe” CHF group (VE/VCO2 slope>33, where VE/VCO2slope median=33) and the “mild”CHF group (with VE/VCO2 slope≤33). Patients with “severe” CHF presented StO2baseline 80.7±3.7% vs 76.9±5% ,p=0.018, StO2min 38.3±11.2% vs 40.3±7.7%, p=0.600 , StO2max 92.8±4.2 % vs 92.5±4.7%, p=0.809, OCR 14.1±4.6 %/min vs 12.3±2.9%/min ,p=0.237 and RR 4.3±1.4 vs 4.7±1.2, p=0.572, compared with “mild” CHF group of patients.
In the vast majority of NIRS-derived measurements in our study, there was no statistically significant difference between groups of “severe” and “mild” CHF. The only exception was found in StO2 baseline measurements, when the classification of “severe” and “mild” CHF had been made by VE/VCO2 slope (Classification B’ and D’). Unexpectedly, “severe” CHF patients had significantly higher StO2baseline values (80.9±4.4% vs 77.5±4.7%, p=0.037 in Comparison B’, and 80.7±3.7% vs 76.9±5%, p=0.018 in Comparison D’) compared with “mild” CHF patients. It can be considered , although, that in “Comparison C” (where the classification was made by means of the median value of VO2peak), there is a clear (-but without statistical significance-) trend , for higher measurements of StO2max, OCR and RR in patients with mild CHF, compared to those with severe CHF.
Conclusions: Peripheral muscle microcirculation, as assessed by NIRS and VOT, is (known to be) impaired in CHF patients. We tried to investigate possible association of the NIRS-derived parameters with CHF severity. In the vast majority of NIRS-derived measurements in our study, there was no statistically significant difference between groups of “severe” and “mild” CHF. Unexpectedly, StO2-baseline measurements were found significantly higher in patients with severe CHF compared to patients with mild CHF, when the comparison was made by means of VE/VCO2 slope. Only in the comparison in which the classification was made by means of median value of VO2peak , there was a clear (but not statistically significant) trend for higher measurements of StO2max, OCR and RR in patients with mild CHF.
