title: Pulmonary hypertension leads to a loss of gravity dependent redistribution of regional lung perfusion: a SPECT/CT study.
abstract: OBJECTIVE
  Pre-capillary pulmonary hypertension (PHT) is characterised by progressive pulmonary vascular obliteration and loss of vascular reserves. In health, regional lung perfusion redistributes under the influence of gravity due to the presence of recruitable vessels. We investigated a combined single photon emission computed tomography/CT (SPECT/CT) method for assessing the pulmonary circulation by quantifying the gravity dependent redistribution of lung perfusion.
  
  
  METHODS
  Characterisation of patients versus healthy controls.
  
  
  METHODS
  15 patients with pre-capillary PHT and 11 healthy controls.
  
  
  METHODS
  University hospital clinic.
  
  
  METHODS
  Regional lung perfusion was measured using SPECT/CT in two different postures (supine vs upright). A perfusion redistribution index (PRI) was used to quantify the cranial-caudal shift in regional lung perfusion resulting from gravitational (postural) change.
  
  
  METHODS
  PRI was compared between cases and controls, and correlated with markers of disease severity in cases.
  
  
  RESULTS
  Patients with pre-capillary PHT had notably reduced PRI compared to controls (0.02±0.06 vs. 0.28±0.15 normalised perfusion/cm, p<0.0001). PRI was significantly associated with prognostic parameters such as 6 min walk distance (r=0.60, p=0.018), functional class (p=0.008), and tricuspid annular plane systolic excursion (r=0.58, p=0.022). The receiver operating characteristic curve showed that PRI differentiated patients with pre-capillary PHT from controls with AUC=0.94 (p<0.001).
  
  
  CONCLUSIONS
  With SPECT/CT, gravity dependent redistribution of lung perfusion can be quantified using the PRI derived from supine and upright perfusion analysis. The potential utility of PRI for the non-invasive detection of PHT and assessment of disease severity warrants further study.
authors.affiliation: Department of Medicine, Sydney Medical School, University of Sydney, , Camperdown, Australia.
authors.forename: Edmund Mt
authors.initials: EM
authors.lastname: Lau
authors.forename: Dale L
authors.initials: DL
authors.lastname: Bailey
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Bailey
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Torzillo
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Roach
authors.forename: Geoffrey P
authors.initials: GP
authors.lastname: Schembri
authors.forename: Tamera J
authors.initials: TJ
authors.lastname: Corte
authors.forename: David S
authors.initials: DS
authors.lastname: Celermajer
mesh_terms: D005260:Female; D006112:Gravitation; D006801:Humans; D006976:Hypertension, Pulmonary / Q000175:diagnosis* / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D011187:Posture / Q000502:physiology*; D011652:Pulmonary Circulation / Q000502:physiology*; D012372:ROC Curve; D012720:Severity of Illness Index; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods*; D014057:Tomography, X-Ray Computed / Q000379:methods*