title: The effect of deep hypothermia on the human pulmonary circulation.
abstract: OBJECTIVE
  Acute rises in pulmonary artery pressures following complex cardiac surgery are associated with high morbidity and mortality. We hypothesised that periods of deep hypothermia predispose to elevated pulmonary pressures upon rewarming. We investigated the effect of this hypothermic preconditioning on isolated human pulmonary arteries and isolated perfused lungs.
  
  
  METHODS
  Isometric tension was measured in human pulmonary artery rings (n=24). We assessed the constriction and dilation of these arteries at 37 °C and 17 °C. Isolated perfused human lung models consisted of lobes ventilated via a bronchial cannula and perfused with Krebs via a pulmonary artery cannula. Bronchial and pulmonary artery pressures were recorded. We investigated the effect of temperature using a heat exchanger.
  
  
  RESULTS
  Rewarming from 17 °C to 37 °C caused a 1.3 fold increase in resting tension (p<0.05). Arteries constricted 8.6 times greater to 30 nM KCl, constricted 17 times greater to 1 nM Endothelin-1 and dilated 30.3 times greater to 100 μM SNP at 37 °C than at 17 °C (p<0.005). No difference was observed in the responses of arteries originally maintained at 37 °C compared to those arteries maintained at 17 °C and rewarmed to 37 °C. Hypothermia blunted the increase in pulmonary artery pressures to stimulants such as potassium chloride as well as to H-R but did not precondition arteries to higher pulmonary artery pressures upon re-warming.
  
  
  CONCLUSIONS
  Deep hypothermia reduces the responsiveness of human pulmonary arteries but does not, however, precondition an exaggerated response to vasoactive agents upon re-warming.
authors.affiliation: Department of Cardiothoracic Surgery, Castle Hill Hospital, Cottingham HU16 5JQ, UK. Electronic address: priyadariyaratnam@yahoo.co.uk.
authors.forename: Priyadharshanan
authors.initials: P
authors.lastname: Ariyaratnam
authors.affiliation: Department of Cardiothoracic Surgery, Castle Hill Hospital, Cottingham HU16 5JQ, UK.
authors.forename: Mahmoud
authors.initials: M
authors.lastname: Loubani
authors.affiliation: Department of Cardiothoracic Surgery, Castle Hill Hospital, Cottingham HU16 5JQ, UK.
authors.forename: Alexander R J
authors.initials: AR
authors.lastname: Cale
authors.affiliation: Department of Cardiothoracic Surgery, Castle Hill Hospital, Cottingham HU16 5JQ, UK.
authors.forename: Mubarak
authors.initials: M
authors.lastname: Chaudhry
authors.affiliation: Department of Cardiothoracic Surgery, Castle Hill Hospital, Cottingham HU16 5JQ, UK.
authors.forename: Michael E
authors.initials: ME
authors.lastname: Cowen
authors.affiliation: Department of Cardiothoracic Surgery, Castle Hill Hospital, Cottingham HU16 5JQ, UK.
authors.forename: Martin A
authors.initials: MA
authors.lastname: Jarvis
authors.affiliation: Department of Cardiothoracic Surgery, Castle Hill Hospital, Cottingham HU16 5JQ, UK.
authors.forename: Steven
authors.initials: S
authors.lastname: Griffin
authors.affiliation: Department of Academic Medicine, Castle Hill Hospital, Cottingham HU16 5JQ, UK.
authors.forename: Alyn H
authors.initials: AH
authors.lastname: Morice
mesh_terms: D003080:Cold Temperature; D006801:Humans; D007035:Hypothermia / Q000503:physiopathology*; D066298:In Vitro Techniques; D008954:Models, Biological; D011651:Pulmonary Artery / Q000502:physiology*; D011652:Pulmonary Circulation; D014661:Vasoconstriction
keywords: Hypothermia; Pulmonary hypertension