Students

Name: Peng Zhi-Yong

Post: Full-time Ph.D

Enrolled: 2001-2004

Origin: Mainland China, Wuhau

Supervisor: Prof. Lester Critchley

Title of Thesis:

Development of a canine flow probe model to investigate aspects of cardiac monitors and vasopressor therapies that can not be tested clinically

Outline of the Thesis:

Cardiovascular monitoring and vasopressor therapies are important adjuncts to clinical practice especially in the fields of anaesthesia and critical care. However, the developments of safe and effective methods need rigorous testing that cannot be done solely in the clinical arena because of ethical limitations. In this research I developed an anaesthetized canine model in which cardiac output and contractility were measured using a high-performance flow probe placed on the aorta via a left thoracotomy and renal blood flow was measured by a flow probe placed on the left renal artery. This model also provided gold standard measurements of cardiac contractility (dF/dt (max)) from the aortic flow waveform. Arterial and central venous blood pressure was also measured. The circulation of the canine model was manipulated using vasopressor infusions and halothane.

The model enabled me to evaluate: (i) the performance of a new impedance cardiograph, the RheoCardioMonitor; (ii) the performance of a new ultrasonic Doppler cardiac monitor, the USCOM, and (iii) the circulatory effects of five commonly used vasopressor agents on the systemic and renal circulation under normal and septic conditions.

My main findings were that: (i) impedance cardiography cardiac output measurements were affected by changes in peripheral resistance, so that it underestimated at low peripheral resistance and overestimated at high peripheral resistance; (ii) impedance cardiac contractility was better assessed using indices based on the slope of the impedance waveform, rather than the timing intervals of cardiac cycle; (iii) the USCOM reliably detected changes in cardiac output over a wide range of values; and (iv) noradrenaline, which showed a powerful vasopressor effect without decreasing of cardiac output and renal blood flow, was the best choice of vasopressors in septic shock, but the effects of all catecholamine vasopressors were attenuated in septic shock, and with the exception of vasopressin which probably was the alternative choice in refractory septic shock.

In conclusion, the canine flow probe model proved a valuable asset for testing cardiac monitors and evaluating vasopressor therapies, particularly in sepsis. It enabled me to answer a number of clinically relevant questions relating to these devices and therapies, and set up the foundation for future studies.

Publications arising from his thesis:

(A) Scientific Papers:

1. Peng ZY, Critchley LAH, Fok BSP, James AE. Evaluation of Impedance based indices of cardiac contractility in dogs. Journal of Clinical Monitoring and Computing 2004; 18: 103-109.
   
   
2. Critchley LAH, Peng ZY, Fok BS, James AE. An investigation to show the effect of peripheral resistance on impedance cardiography measurements in the anaesthetized dog. Anesthesia and Analgesia 2005; 100: 1708-1712.
   
   
3. Critchley LAH, Peng ZY, Fok BS, Flach J, Wong SC, Lee A, Phillips RA. Testing the reliability of a new ultrasonic cardiac output monitor, the USCOM, using aortic flow probes in anaesthetized dogs. Anesthesia and Analgesia 2005; 100: 748-753.
   
   
4. Peng ZY, Critchley LAH, Fok BS. The effects of increasing doses of noradrenaline on systemic and renal circulations in septic dogs. Intensive Care Medicine 2005; 11:1558-1563 (supplementary data & editorial)
   
   
5. Peng ZY, Critchley LAH, Fok BSP. An investigation to show the effect of lung fluid on impedance cardiography measurements in the anaesthetized dog. British Journal of Anaesthesia 2005; 95: 458-464.
   
   
6. Peng ZY, Critchley LAH, James AE, Aortic flow probe placement for the non-surgeon. Scandinavian Journal of Laboratory Animal Science 2006; 33: 227-235.
   
   
7. Peng ZY, Critchley LAH, Joynt GM, Gruber PC, Jenkins CR, Ho AM. Effects of noradrenaline during intra-abdominal hypertension on renal blood flow in bacteremic dogs. Critical Care Medicine 2007 (Pending acceptance)
   

(B) Conference Abstracts:

8. 2003. Euroanaesthesia Glasglow. Peng ZY, Critchley LAH, Fok BSP, James AE. The effects of phenylephrine on cardiac function as blood pressure increases.
   
   
9. 2003. 27^th Congress SSAIC Helsinki. Acta Scandanivica Anaesthiologica (Suppl 116).2003: 47; 110. Critchley LAH, Peng ZY, Fok BSP, James AE. Evaluation of bioimpedance derived indices of cardiac contractility in anaesthetized dogs.
   
   
10. 2004. 13^th World Congress of Anaesthesiologists. Paris. Critchley LAH, Peng ZY, Flach J, Wong SC. Validation of a new ultrasonic cardiac output monitor. The USCOM.
    
    
11. 2004. 13^th World Congress of Anaesthesiologists. Paris. Lim BK, Peng ZY, Critchley LAH. A comparison of the effects of vasopressin and adrenaline on the systemic circulation and renal blood flow.
    
    
12. 2004. 13^th World Congress of Anaesthesiologists. Paris. Fok BS, Critchley LAH, Peng ZY, James ZE. The effect of changes in peripheral resistance on bioimpedance cardiac output measurements.
    
    
13. 2004. 13^th World Congress of Anaesthesiologists. Paris. Peng ZY, Critchley LAH, Fok BS, James AE. The dose-response effects of noradrenaline on renal blood flow in normal and septic dogs.
    
    
14. 2004. 24^th Int. Symposium in Intens Care and Em. Med., Brussels. Critical Care 2004; 8(Suppl): 177. Peng ZY, Critchley LAH. The effects of five vasopressors on renal blood flow in septic dogs.
    
    
15. 2004. SEYMF PG Conference Model Organism Research and Human Disease. Hong Kong. Peng ZY, Critchley LAH. A flow probe model for investigating sepsis.
    

(C) Prizes and Awards:

16. The Harry M Vars Research Award (2006) by the American Society for Parenteral and Enteral
    
    
17. The Promising Investigator Award (2006) by thr American Society for Parenteral and Enteral
    
    
18. 2009 Annual Scientific Awards by the Society of Critical Care Medicine(USA)