Purpose: Congenital heart disease (CHD) is the most common live birth defect and a proportion of these patients have chronic hypoxia. Chronic hypoxia leads to secondary erythrocytosis resulting in microvascular dysfunction and increased thrombosis risk. The conjunctival microcirculation is easily accessible for imaging and quantitative assessment. It has not previously been studied in adult CHD patients with cyanosis (CCHD).
Methods: We assessed the conjunctival microcirculation and compared CCHD patients and matched healthy controls to determine if there were differences in measured microcirculatory parameters. We acquired images using an iPhone 6s and slit-lamp biomicroscope. Parameters measured included diameter, axial velocity, wall shear rate and blood volume flow. The axial velocity was estimated by applying the 1D+T continuous wavelet transform (CWT). Results are for all vessels as they were not sub-classified into arterioles or venules.
Results: 11 CCHD patients and 14 healthy controls were recruited to the study. CCHD patients were markedly more hypoxic compared to the healthy controls (84% vs 98%, p= 0.001). A total of 736 vessels (292 vs 444) were suitable for analysis. Mean microvessel diameter (D) did not significantly differ between the CCHD patients and controls (20.4 ±2.7μm vs 20.2 ±2.6μm, p=0.86). Axial velocity (Va) was lower in the CCHD patients (0.47 ±0.06mm/s vs 0.53 ±0.05mm/s, p=0.03). Blood volume flow (Q) was lower for CCHD patients (121 ±30pl/s vs 145 ±50pl/s, p=0.65) with the greatest differences observed in vessels >22μm diameter (216 ±121pl/s vs 258 ±154pl/s, p=0.001). Wall shear rate (WSR) was significantly lower for the CCHD group (153 ±27s-1 vs 174 ±22s-1, p=0.04).
Conclusions: This iPhone and slit-lamp combination assessment of conjunctival vessels found lower axial velocity, wall shear rate and in the largest vessel group, lower blood volume flow in chronically hypoxic patients with congenital heart disease. With further study this assessment method may have utility in the evaluation of patients with chronic hypoxia.
- 1D + T continuous wavelet transform (CWT)
- Axial velocity estimation
- Conjunctival microcirculation
- Cyanotic congenital heart disease
- Microvascular physiology