Reproducibility of Novel Indices of Reactive Hyperemia Using Laser Speckle Contrast Imaging
Authors: Shirazi Behnia Rezazadeh , Valentine Rudy , Lang James 
Published: April 2020

Post‐occlusive reactive hyperemia (PORH) is an indicator of microvascular function, but lack of standardization and reliability of measurement have limited its use clinically. The purpose of this study was to assess the intra‐ and inter‐day reliability of conventional and novel parameters of PORH using laser speckle contrast imaging (LSCI). Seventeen healthy adults (age = 24±3 years) completed three PORH bouts over two randomly assigned lab visits that were interspaced by 4–14 days. LSCI region of interest was a standardized 10 cm region below the antecubital fossa on the dominant ventral forearm. A 5‐min brachial artery occlusion period induced by inflating an arm cuff to 200 mmHg, preceded a 4‐min hyperemic period. LSCI flux was expressed as cutaneous vascular conductance (CVC; flux/mean arterial pressure). Reliability and reproducibility were assessed using intraclass correlation (ICC) and coefficient of variation (CV). Maximal flow (peak) and area under the curve (AUC) normalized to zero perfusion showed intra‐ and inter‐day reliability of ICC > 0.70. Inter‐day ICC was lower when AUC was expressed as a function of resting flow (ICC=0.50) or biological zero (ICC=0.66). Time to maximal flow (TMF) had lower intra‐day (CV=12%) and inter‐day (CV=18%) reproducibility. When representing velocity (overshoot rate of change, ORC) within defined time ranges (5s, 10s, 15s, and 20s into hyperemia) as a piecewise function, the inter‐day reproducibility was <11%. Thus, depending on data normalization, PORH using LSCI is a reliable method to assess microvascular function. TMF should be interpreted with caution, but an alternative temporal index may be the ORC.Support or Funding InformationThis research did not receive any specific grant from funding agencies in the public, commercial, or non‐profit sectors.Commonly examined post‐occlusive reactive hyperemia parameters are illustrated. Resting flow (RF), maximal flow (MF), time to maximal flow (TMF), amplitude of the MF normalized to RF and BZ (AMPRF and AMPBZ) and 4‐min post cuff‐deflation area under hyperemic curve (4‐min AUC) normalized to zero perfusion are shown. Time = 0 corresponds to cuff deflation. Magnified tracing at the top right shows the hyperemic response 30s post‐cuff deflation.Figure 1
Statistics for the PORH parameters are shown as mean ± SD, ICC, 95% limits of agreement, and coefficient of variation for the three PORH responses (VA, VB1, VB2). ICC values less than 0.5, between 0.5–0.75, between 0.75–0.9, and above 0.9 are classified as having poor, moderate, good, and excellent reliability. CV values less than 10%, between 10–25%, and above 25% are considered having good, moderate, and poor reproducibility.

Descriptive Statistics (CVC)

Reproducibility Statistics (CVC)

Mean ± SD

INTRADAY (VB1 & VB2)

INTERDAY (VA & VB1)

VA

VB1

VB2

ICC (LOA)

CV (%)

ICC (LOA)

CV (%)

RF

0.62 ± 0.17

0.62 ± 0.14

0.60 ± 0.15

0.89 (0.73, 0.96)

6.47

0.89 (0.72, 0.96)

6.72

MF

2.41 ± 0.70

2.32 ± 0.56

2.35 ± 0.73

0.88 (0.70 0.95)

5.13

0.77 (0.48,0.91)

9.49

TMF

19.3 ± 5.68

19.0 ± 6.82

18.9 ± 5.11

0.65 (0.25, 0.86)

11.71

0.52 (0.06, 0.80)

17.75

4‐min AUC

282 ± 88.5

274 ± 70.4

262 ± 67.2

0.93 (0.79, 0.97)

4.88

0.73 (0.39, 0.89)

9.33

PI

300 ± 74.0

282 ± 62.6

285 ± 53.2

0.70 (0.34, 0.88)

10.74

0.51 (0.07, 0.79)

12.65

AMPRF

1.81 ± 0.60

1.71 ±0.46

1.75 ± 0.60

0.85 (0.64, 0.94)

6.65

0.66 (0.28, 0.86)

12.61

AMPBZ

2.18 ± 0.67

2.10 ± 0.51

2.13 ± 0.67

0.86 (0.66, 0.95)

5.53

0.75 (0.45, 0.90)

10.27

AUCRF

134 ± 60.1

125 ± 48.8

117 ± 40

0.88 (0.70, 0.95)

10.63

0.50 (0.04, 0.79)

16.64

AUCBZ

231 ±83.3

219 ± 63.2

207 ± 55.8

0.91 (0.74, 0.97)

6.46

0.66 (0.27, 0.86)

11.97

1‐min AUC

114 ± 34.0

112 ± 30.9

111 ± 32.2

0.94 (0.83, 0.98)

4.83

0.77 (0.47, 0.91)

9.70

AUC index

3.15 ± 0.53

3.06 ± 0.54

3.04 ± 0.39

0.84 (0.62, 0.94)

4.82

0.33 (−0.18, 0.69)

9.35

ORC5

0.37 ± 0.10

0.36 ± 0.10

0.35 ± 0.10

0.89 (0.72, 0.96)

6.95

0.73 (0.4, 0.89)

9.52

ORC10

0.21 ± 0.05

0.20 ± 0.04

0.20 ± 0.06

0.83 (0.58, 0.93)

6.33

0.71 (0.38, 0.89)

8.39

ORC15

0.15 ± 0.04

0.14 ± 0.03

0.15 ± 0.04

0.85 (0.64, 0.94)

5.13

0.74 (0.43, 0.90)

8.65

ORC20

0.11 ± 0.03

0.11 ± 0.03

0.11 ± 0.04

0.87 (0.69, 0.95)

4.83

0.69 (0.34, 0.88)

10.70

ORCMF

0.12 ± 0.05

0.12 ± 0.04

0.12 ± 0.05

0.74 (0.41, 0.90)

15.27

0.22 (−0.31, 0.63)

22.90