pulmonary hypertension ( ph ) in adults with sickle cell disease ( scd ) is associated with early mortality 1 , and other complications , including renal insufficiency , leg ulcers , abnormal liver function , systemic hypertension , avascular necrosis , seizures , and cerebrovascular events 2 .
right heart catheterization ( rhc ) is the gold standard to confirm the diagnosis of ph and hemodynamic stratification to determine treatment and followup .
the hemodynamic characteristics of ph , particularly pulmonary artery pressure ( pap ) 3 , and tricuspid regurgitation velocity ( trv ) 1 , have been shown to be independent predictors of mortality in adults with scd .
since scd is a systemic vascular disease 4 , it is likely that scd subjects with ph have alterations in microvascular hemodynamics in multiple organ systems .
previous studies have reported conjunctival microvascular hemodynamics in scd subjects 5 , 6 . however , to the best of our knowledge , there have been no studies evaluating conjunctival microcirculatory hemodynamics in scd subjects with or without ph . in this study , we report the conjunctival and pulmonary hemodynamic properties in scd subjects with and without ph .
prior to subject enrollment , the research study was explained to the subjects , and informed consents were obtained according to the tenets of the declaration of helsinki .
two scd ( ss genotype ) subjects , one with and one without ph , participated in the study .
ten agesimilar africanamerican subjects ( age range : 3268 years ) without scd or history of cerebrovascular , hypertension or ocular diseases participated as healthy control subjects .
systolic and diastolic blood pressures were measured three times at the time of conjunctival imaging , and the averaged values were reported .
imaging of the conjunctival microcirculation was performed with our previously described and validated optical imaging system ( eyeflow ) 6 , 7 , 8 , 9 , 10 , 11 .
briefly , the imaging system comprised of a slit lamp biomicroscope and a digital chargedcoupled device camera , was used to acquire image sequences of red blood cell movement within the conjunctiva microcirculation .
several image sequences were analyzed to provide the measures of diameter ( d ) and axial blood velocity ( v ) of conjunctival venules , as previously described 9 .
mean values of d and v were calculated from one randomly selected eye in each subject . based on data in control subjects , 95% normal confidence intervals ( ci ) were calculated for conjunctival d and v. in scd subjects , data from rhc , doppler echocardiography , and laboratory tests were obtained from medical records . pulmonary hemodynamic data including systolic , diastolic , and mean pap ( spap , dpap , mpap ) , pulmonary capillary wedge pressure ( pcwp ) , and cardiac output were obtained from rhc , and trv was documented from doppler echocardiography .
diagnosis of ph was based on a mean pulmonary artery pressure ( mpap ) greater than 25 mm hg 12 .
exercise capacity was assessed using a 6 minute walk distance ( 6mwd ) test ( normal range : 380782 m ) 14 .
the scd subject with ph was categorized according to the world health organization ( who ) clinical classification of ph 15 .
table 3 reports conjunctival hemodynamic properties of control and scd subjects . in control subjects ,
the 95% cis of mean conjunctival d and v were 1723 m ( n = 10 ) and 0.390.59 mm / sec , respectively . demographic and clinical characteristics of healthy control subjects and sickle cell disease subjects with and without pulmonary hypertension ( ph ) .
systolic ( sbp ) and diastolic ( dbp ) blood pressures were available in seven healthy control subjects pulmonary hemodynamic properties in sickle cell disease subjects with and without pulmonary hypertension ( ph ) spap , systolic pulmonary artery pressure ; dpap , diastolic pulmonary artery pressure ; mpap , mean pulmonary artery pressure ; pcwp , pulmonary capillary wedge pressure ; trv , tricuspid regurgitation velocity .
conjunctival hemodynamic properties in healthy control subjects and sickle cell disease subjects with and without pulmonary hypertension ( ph ) .
data in healthy control subjects were reported as 95% confidence intervals case 1 was a 41yearold male with scd and controlled systemic hypertension , cholelithiasis , priapism , and acute chest syndrome during childhood .
the subject was on hydroxyurea treatment , and had not received a blood transfusion within 2 months prior to conjunctival imaging .
the echocardiography data obtained 40 days before conjunctival imaging demonstrated mild pulmonary valve stenosis , with right ventricle systolic pressure of 54 mm hg .
since pulmonary stenosis may confound pulmonary artery hemodynamics , diagnostic rhc was performed for further evaluation of ph , which revealed a normal mpap of 15 mm hg . during the 2month time interval between conjunctival imaging and rhc , the subject had two clinical visits , which indicated an unchanged clinical status and medication list .
mean conjunctival d and v measurements were 19  4 m ( n = 16 venules ) and 0.52  0.22 mm / sec , respectively .
both conjunctival d and v measurements were within the normal 95% cis based on data in control subjects .
case 2 was a 50yearold male with scd and past medical history of ph , controlled systemic hypertension and diabetes , renal insufficiency , chronic leg ulcer , and gout .
this subject was not receiving hydroxyurea treatment and did not have a blood transfusion within 2 months of conjunctival imaging .
the echocardiography data obtained 11 months before conjunctival imaging showed an increased trv of 3.63 m / sec . the initial 6mwd test performed 10 months before conjunctival imaging was 244 m and lower than normal .
the oxygen saturation was measured to be 87% at rest and 88% during activity , and therefore the subject was prescribed supplemental oxygen of 2 l / min at rest and 3 l / min during activity .
rhc revealed postcapillary ph with an elevated mpap of 35 mm hg and pulmonary capillary wedge pressure of 23 mm hg .
the subject was categorized as group 1 of the who clinical classification of ph ( pulmonary arterial hypertension ) . during the 7month time interval between conjunctival imaging and rhc , the subject had six followup clinical visits with one echocardiography which demonstrated persistent increase in trv and pap with negligible improvements in exercise capacity , and shortness of breath .
mean conjunctival d and v measurements were 17  4 m ( n = 8 venules ) and 0.19  0.05 mm / sec , respectively .
conjunctival d was within the normal 95% ci in control subjects , while conjunctival v was lower than normal 95% ci limit .
ph is a prognostic factor in scd and is associated with early mortality 1 and other complications 2 .
rhc is the gold standard for the diagnosis and monitoring of ph , but it is invasive and carries a small , but present risk of mortality and other complications . in contrast , conjunctival microvascular imaging is a noninvasive and noncontact technique to assess hemodynamic properties of the microcirculation .
conjunctival microvascular and hemodynamic abnormalities including abnormal vessel diameter , vessel tortuosity , microaneurysms , and decreased blood velocity have been documented in scd subjects 5 , 6 . decreased conjunctival blood velocity has been associated with scd complications such as stroke 16 and retinopathy 7 . in this study , we reported conjunctival blood velocity in two scd subjects with and without ph .
the mean conjunctival v in the scd subject with ph ( case 2 ) was far below the lower limit of the 95% ci established in healthy control subjects , indicating the potential of conjunctival imaging to detect hemodynamic abnormalities in scd subjects with ph .
the exact mechanism of decreased conjunctival v in the scd subject with ph is not clear .
although scd is associated with microvascular hemodynamics abnormalities which vary based on pathophysiology of the disease complications , the substantially lower conjunctival v observed in case 2 is likely attributed to the combination of ph and scd .
one possible explanation could be higher microvascular network resistance due to increased adherence of red and white blood cells , and platelet to the endothelium and to each other resulting from hypoxia in the scd subjects with ph 17 .
interestingly , the conjunctival d was within the normal range in the scd subject with ph in this study despite lower than normal conjunctival v. this finding may suggest a diminished vasodilatory response to hypoxia in this scd subject due to vasculopathy 18 , increased consumption of nitric oxide , or decreased activity of soluble guanylate cyclase and other downstream messengers in vascular smooth muscle 19 .
future studies in a larger population are required to investigate the relationships between severity of ph and microvascular velocity in scd subjects .
conjunctival v measurements in healthy control subjects in this study were lower than values reported in previous studies 20 , 21 , which may be attributed to differences in ethnicity of the study populations and measurement techniques .
furthermore , decreased dbp in scd subjects as compared to healthy control subjects is consistent with previous studies 22 , 23 , 24 .
this may be attributed to a progressive renal tubular defect in scd subjects , which begins in early childhood ages 23 , 24
assessment of conjunctival microvascular hemodynamics may improve understanding of the pathophysiology of pulmonary hypertension in sickle cell disease .
 key clinical messageconjunctival microvascular hemodynamic alterations were reported for the first time in sickle cell subjects with and without pulmonary hypertension . 
 assessment of the conjunctival microcirculation using noninvasive imaging may improve understanding of microvascular hemodynamic alterations that occur due to pulmonary hypertension in sickle cell disease . 
Introduction
Case Report
Discussion
Conclusions
Conflict of Interest