Characterising skeletal muscle haemoglobin saturation during exercise using near-infrared spectroscopy in chronic kidney disease

Abstract

Background: Chronic kidney disease (CKD) patients have reduced exercise capacity. Possible contributing factors may include impaired muscle O₂ utilisation through reduced mitochondria number and/or function slowing the restoration of muscle ATP concentrations via oxidative phosphorylation. Using near-infrared spectroscopy (NIRS), we explored changes in skeletal muscle haemoglobin/myoglobin O₂ saturation (SMO₂%) during exercise.

Methods: 24 CKD patients [58.3 (± 16.5) years, eGFR 56.4 (± 22.3) ml/min/1.73 m²] completed the incremental shuttle walk test (ISWT) as a marker of exercise capacity. Using NIRS, SMO₂% was measured continuously before, during, and after (recovery) exercise. Exploratory differences were investigated between exercise capacity tertiles in CKD, and compared with six healthy controls.

Results: We identified two discrete phases; a decline in SMO₂% during incremental exercise, followed by rapid increase upon cessation (recovery). Compared to patients with low exercise capacity [distance walked during ISWT, 269.0 (± 35.9) m], patients with a higher exercise capacity [727.1 (± 38.1) m] took 45% longer to reach their minimum SMO₂% (P = .038) and recovered (half-time recovery) 79% faster (P = .046). Compared to controls, CKD patients took significantly 56% longer to recover (i.e., restore SMO₂% to baseline, full recovery) (P = .014).

Conclusions: Using NIRS, we have determined for the first time in CKD, that favourable SMO₂% kinetics (slower deoxygenation rate, quicker recovery) are associated with greater exercise capacity. These dysfunctional kinetics may indicate reduced mitochondria capacity to perform oxidative phosphorylation-a process essential for carrying out even simple activities of daily living. Accordingly, NIRS may provide a simple, low cost, and non-invasive means to evaluate muscle O₂ kinetics in CKD.

Keywords: Chronic kidney disease; Exercise; Haemoglobin; Near-infrared spectroscopy; Oxygen saturation.

Fig. 1

Relative size and application of BSXInsight NIRS device to lower leg. LED light-emitting diode

Fig. 2

Representative example SMO₂% for example HC and CKD patient during incremental exercise. Data presented as SMO₂% change (as a % of baseline); to reduce noise, data is shown as 20 s average. HC healthy control, CKD chronic kidney disease. Baseline refers to 3 min sitting measure of calf SMO₂% obtained at rest. Phase 1 refers to the incremental shuttle walk test (ISWT); Phase 2 refers to the 3 min recovery period. A = the minimum SMO₂% value; B = time taken to reach the minimum value; C = the absolute and percentage drops in SMO₂% from rest to the minimum exercise value; D = recovery ½ time; E = recovery full time; F = SMO₂% value reached after 3 min recovery; G = % overshoot above baseline; H = end of ISWT for HC; I = end of ISWT for CKD