Introduction

The Physiology in Critical Illness Group carries out a wide range of research into physiological processes related mainly to acute cardiorespiratory illness. We are interested in the experimental study, application and mathematical modelling of physiology in the critically ill.

A list of publications is available.

Research areas

Heliox

Heliox is a mixture of oxygen and helium for respiratory applications. The comparatively low density of helium reduces the Reynolds number of the flowing gas and suppresses the onset of turbulent flow. This enhanced laminar flow reduces the resistance to gas movement, particularly in airway obstruction.

• Heliox administration. Heliox is increasingly used in the treatment of upper airway obstruction. However, traditional methods of administration are of questionable efficiency. By developing  tracheal gas sampling and mass spectrometer analysis techniques, we have demonstrated that significant air entrainment occurs in spontaneously breathing individuals unless the delivery system is carefully designed. We are studying optimal methods for the administration of Heliox. We have developed methods for blood helium analysis and are investigating their potential role in assessing the effectiveness of Heliox delivery.
• Heliox as an adjunct to extubation. Critically ill patients who have been mechanically ventilated may fail to breathe adequately when the ventilator is withdrawn due to the increased work of breathing. It may be that Heliox, by decreasing the resistance to gas flow, reduces the need to re-institute mechanical ventilation in such patients. We are studying the effect of optimal methods of Heliox administration to see if we can reduce the incidence of failed tracheal extubation in critical care patients.

Selected references

• Room air dilution of heliox given by facemask. Standley TDA, Smith HL, Brennan LJ, Wilkins IA, Bradley PG, Groba CB, Davey AJ, Menon DK, Wheeler DW. Intensive Care Medicine 2008;34:1469-1476. [PubMed]

Cardiovascular coupling

Maintaining adequate organ perfusion is central to perioperative and critical care medicine. Yet, the coupling of the heart to the vascular system, the relationship between pressure and flow and the propagation of the arterial impulse through a branching structure is complex and still poorly understood.

• Arterial pulse wave evolution. We are developing non-linear numerical models of arterial pulse evolution with a view to elucidating the effects of mechanical parameters which may have important clinical correlate
• Time resolved cardiovascular pharmacophysiology. A number of commercial instruments allow beat-to-beat measurement of cardiac output and systemic vascular resistance. We are developing combined pharmacokinetic / pharmacodynamic numerical models of the effects of pharmacological agents on cardiovascular physiology on these new ultrashort timescales.

Critical Care Provision

Critical care services may be vulnerable to surges in demand. The influenza A (H1N1) pandemic has heightened concerns that, under certain circumstances, critical care provision may become overstretched. We have modelled potential adult and paediatric intensive care occupancy under pandemic conditions.

Selected references

• Modelling the impact of pandemic influenza A(H1N1) on UK paediatric intensive care demand. Ercole A, Menon DK, O’Donnell R. Archives of Disease in Childhood 2009;94(12):962-4. [PubMed]
• Modelling the impact of an influenza A/H1N1 pandemic on critical care demand from early pathogenicity data: the case for sentinel reporting. Ercole A, Taylor BL, Rhodes A, Menon DK. Anaesthesia. 2009;64(9):937-941. [PubMed]