Noninvasive Optical Characterization of Muscle Blood Flow, Oxygenation, and Metabolism in Women With Fibromyalgia

Yu Shang; Katelyn Gurley; Brock Symons; Douglas Long; Ratchakrit Srikuea; Leslie J Crofford; Charlotte A Peterson; Guoqiang Yu

Disclosures

Arthritis Res Ther. 2012;14(6) 

In This Article

Results

During the familiarization MVIC test, the CAR was found to be very high and was not different between the subjects with FM and healthy controls (0.99 ± 0.01 vs. 0.99 ± 0.02, P = 0.90), indicating that both groups exerted full effort to perform the MVICs. There were no differences between the two groups in age, height, weight, BMI, IPAQ, or baseline MVIC (Table 1). Overall, the subjects lost an average of 28.9% strength after exercise, and there was no significant difference (P > 0.05) between groups in the percentage of strength loss. However, subjects with FM reported significantly more fatigue and pain during exercise (P < 0.001) compared to healthy controls (Table 1), according to the VAS.

Among the thirty-seven subjects (twenty-three healthy controls and fourteen subjects with FM), five subjects (three healthy controls and two subjects with FM) did not have oxygenation measurements due to NIRS oximeter instrument failure. Thus, all subjects were included for relative blood flow (rBF) analysis, whereas only 32 subjects (20 healthy controls and 12 subjects with FM) were included for analysis of blood oxygenation/oxygen metabolism. None of the baseline hemodynamic/metabolic variables were correlated with subject demographic data (age, height, weight, BMI), IPAQ, or baseline MVIC.

Hemodynamic/Metabolic Changes Following Leg Fatiguing Exercise

Figure 1 ([HbO2], [Hb], THC, StO2) and Figure 2 (rBF, rOEF, rVO2) illustrate hemodynamic and metabolic responses in the knee extensor muscle of a subject with FM (Figure 1a, Figure 2a) and a healthy control (Figure 1b, Figure 2b) throughout fatiguing exercise. Subjects with FM and healthy controls had similar hemodynamic and metabolic response patterns. During exercise, rBF increased to meet the increase in oxygen demand (rVO2). The increased blood flow brought a greater volume of blood to the exercising muscles, thus elevating THC. Oxygen consumption in an exercising muscle resulted in an increase in [Hb] and decreases in [HbO2] and StO2. Once the exercise was stopped, all variables recovered towards their baseline values, which was mainly due to the rapidly decreased oxygen demand post-exercise. Notice that because muscle fiber motion artifacts during exercise affected optical measures, data were averaged over 6 seconds immediately following exercise (see the arrows in Figure 1 and Figure 2) to represent hemodynamic/metabolic responses during exercise.

Figure 1.

Illustrative thigh muscle oxygenation responses throughout fatiguing exercise in (a) a subject with fibromyalgia (FM) and (b) a healthy control. The oxygenation responses include oxy- and deoxyhemoglobin concentration ([HbO2] and [Hb]), total hemoglobin concentration (THC) and oxygen saturation (StO2), all presented in absolute values. The first two vertical lines indicate the beginning and the end of fatiguing exercise respectively, and the last four vertical lines indicate the time points 3, 6, 9 and 12 minutes after exercise. The arrow indicates the time points immediately post-exercise (over 6 seconds). Note that the muscle motion artifacts during exercise and during maximal voluntary isometric contraction (MVIC) tests at time points 3, 6, 9 and 12 minute post-exercise may contaminate optical measurements, as seen from the peaks in the figure.

Figure 2.

Illustrative relative blood flow (rBF), oxygen extraction fraction (rOEF) and oxygen consumption rate (rVO2) throughout fatiguing exercise in (a) a subject with firbromyalgia (FM) and (b) a healthy control, all presented in percentage relative to baseline (%). The first two vertical lines indicate the beginning and the end of fatiguing exercise respectively, and the last four vertical lines indicate the time points 3, 6, 9 and 12 minutes after exercise. The arrow indicates the time points immediately post-exercise (over 6 seconds). Note that the muscle motion artifacts during exercise and during maximal voluntary isometric contraction (MVIC) tests at time points 3, 6, 9 and 12 minute post-exercise may contaminate optical measurements, as seen from the peaks in the figure.

The averaged percentage changes during exercise are shown by group in Figure 3. On average, subjects with FM tended to have smaller changes (assigned baseline to be 100%) in all measured variables during exercise than healthy controls, although most of the differences between the two groups were not significant. The increases in rBF and rVO2 during exercise were much larger than those in r[HbO2], r[Hb], rTHC, rStO2 and rOEF, leading to relatively larger variations (error bars) in rBF and rVO2. The rOEF during exercise was significantly less in subjects with FM compared to healthy controls (99.7 ± 2.6 vs. 107.4 ± 2.0; P = 0.03). No significant differences in any hemodynamic/metabolic variables were found between the two groups at time points 3, 6, 9 and 12 minutes after exercise (data not shown).

Figure 3.

Six-second average data immediately after fatiguing exercise (see the arrows in Figure 1 and Figure 2) as a measure of exercise-induced hemodynamic responses. All parameters were normalized/divided to their baselines (%), resulting in relative change of oxy- and deoxyhemoglobin concentration(r[HbO2] and r[Hb]), total hemoglobin concentration (rTHC), oxygen saturation (rStO2), blood flow (rBF), oxygen extraction fraction (rOEF) and oxygen consumption rate (rVO2). The Student's t-test was used to compare the average rBF (nHC = 23, nFM = 14), r[HbO2], r[Hb], rTHC, rStO2, rOEF and rVO2 (nHC = 20, nFM = 12) in subjects with fibromyalgia (FM) and healthy controls (HC) immediately after fatiguing exercise. *P < 0.05.

Recovery Half-time Following Leg Fatiguing Exercise

Figure 4 illustrates hemodynamic recovery response of a subject with FM (Figure 4a) and a healthy control (Figure 4b) following the fatiguing exercise. Although large individual variation existed, subjects with FM and healthy controls showed similar hemodynamic recovery patterns; rBF and Δ[Hb] decreased, whereas Δ[HbO2] increased following the fatiguing exercise. The recovery half-time of rBF was shorter than oxygenation recovery for both the FM and control groups. On average (Figure 5), subjects with FM demonstrated a longer recovery half-time (s) than healthy controls in Δ[HbO2] (53.0 ± 5.1 vs. 40.7 ± 3.0; P = 0.03) and Δ[Hb] (47.1 ± 3.4 vs. 34.1 ± 2.8; P = 0.007), but not in rBF (15.9 ± 1.2 vs. 15.3 ± 0.8; P = 0.69). Notice that due to large inter-subject variations, the differences observed in some of the recovery times (for example, Δ[HbO2]) between individuals (Figure 4) may not agree with those between groups (Figure 5).

Figure 4.

Illustrative recovery half-times of relative blood flow (rBF), change in oxyhemoglobin concentration (Δ[HbO2]) and change in deoxyhemoglobin concentration (Δ[Hb]) following fatiguing exercise in (a) a subject with fibromyalgia (FM) and (b) a healthy control. The vertical solid lines indicate the ending of exercise. The horizontal dashed and dotted lines indicate the maximal and half-maximal recovery values of hemodynamic variables, respectively. The vertical dotted lines indicate the recovery half-times.

Figure 5.

Average recovery half-times of relative blood flow (rBF) (nHC = 23, nFM = 14), change in oxyhemoglobin concentration (Δ[HbO2]) and change in deoxyhemoglobin concentration (Δ[Hb]) (nHC = 20, nFM = 12) in subjects with fibromyalgia (FM) and healthy controls (HC) following fatiguing exercise. The Student's t-test was used to compare the half-times between FM and healthy subjects. *P < 0.05.

Recovery Half-time Following Arm Cuff Occlusion

Figure 6 illustrates hemodynamic recovery responses of a subject with FM (Figure 6a) and a healthy control (Figure 6b) following arm cuff occlusion. Similar to the fatiguing exercise, healthy controls showed a similar hemodynamic recovery pattern to FM subjects. Following the release of the cuff, rBF and Δ[HbO2] increased, whereas Δ[Hb] decreased. The recovery half-time of rBF was shorter than oxygenation recovery for both groups. However, the recovery times of Δ[HbO2] and Δ[Hb] following cuff occlusion differed significantly between the two groups (Figure 7); FM demonstrated a longer recovery half-time (s) than healthy controls in Δ[HbO2] (19.4 ± 2.3 vs. 12.2 ± 0.9; P = 0.002) and Δ[Hb] (20.4 ± 1.8 vs. 16.3 ± 1.1; P = 0.04), but not in rBF (7.5 ± 0.3 vs. 7.6 ± 0.2; P = 0.86). These results mirror the data for fatiguing exercise.

Figure 6.

Illustrative recovery half-times of relative blood flow (rBF), change in oxyhemoglobin concentration (Δ[HbO2]) and change in deoxyhemoglobin concentration (Δ[Hb]) following arm cuff occlusion in (a) a subject with fibromyalgia (FM) and (b) a healthy control. The two solid vertical lines indicate the beginning and ending of cuff occlusion. The horizontal dashed and dotted lines indicate the maximal and half-maximal recovery values of hemodynamic variables, respectively. The vertical dotted lines indicate the recovery half-times.

Figure 7.

Average recovery half-times of relative blood flow (rBF) (nHC = 23, nFM = 14), change in oxyhemoglobin concentration (Δ[HbO2]) and change in deoxyhemoglobin concentration (Δ[Hb]) (nHC = 20, nFM = 12) in subjects with fibromyalgia (FM) and healthy controls (HC) following arm cuff occlusion. The Student's t-test was used to compare the half-times between FM and healthy subjects. *P < 0.05; **P < 0.005.

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