Micro Medical Limited. PO Box 6, Rochester Kent ME1 2AZ England T +44 (0) F +44 (0)

Transcription

1 Limited PO Box 6, Rochester Kent ME1 2AZ England T +44 (0) F +44 (0) micromedical@viasyshc.com

2 Contents What is PulseTrace? How does it work? What determines the pulse contour? Definition of RI? Definition of SI? Do I need particular skills to do the measurement? Can I use PulseTrace on everybody? How are results presented? What is the reproducibility of the measurement? How is RI used to measure endothelial function? How does SI compare with other measurements of large artery stiffness? Does the measurement change with blood pressure? What are the normal values for SI and RI? References

3 What is PulseTrace? How does it work? Pulse Trace is a desktop instrument providing rapid non-invasive assessment of vascular structure and function:!! Stiffness index, SI, is a measure of large artery stiffness. Large artery stiffness is an important independent risk factor for cardiovascular events. Reflection index, RI, is a measure of vascular tone of small arteries. Endothelial function can be assessed by measuring the change in RI in response to an endothelium-dependent stimulus e.g. the vasoactive drug salbutamol (albuterol). RI can also be used to examine effects of other vasoactive drugs. A digital volume pulse is obtained by measuring the transmission of infra-red light through the finger pulp. The amount of light is proportional to the volume of blood in the finger pulp. Pulse Trace calculates the average pulse from a short recording (10-30 seconds) to produce a typical pulse waveform, as shown, from which RI and SI are derived. 2 3

4 The reflected component is formed by pressure transmitted from the heart to the lower body where it is reflected back up the aorta and thence to the finger. What determines the pulse contour? The reflected component (in green) is delayed relative to the direct component by a time closely related to pulse wave velocity (PWV) in the aorta and large arteries. PWV is determind by large artery stiffness. The relative amplitude of the two components depends upon the amount of reflection in the lower body. This, in turn, depends on vascular tone (the degree of vasodilation / constriction) of small arteries. To a first approximation the digital volume pulse can be considered to be the summation of a direct and a reflected component. The direct component (in blue) is due to transmission of a pressure wave from the left ventricle to the finger via the most direct route. So the amplitude of the reflected wave is related to reflection and hence to vascular tone, whereas the time between the direct and the reflected wave is related to PWV and large arteries stiffness. 4 5

5 Definition of RI? Definition of SI? RI is a measure of reflection. SI is a measure of large artery stiffness. RI can be used to assess endothelial function by measuring its change in response to an endothelium - dependent vasodialator. Subject height is included in the formula for SI to take into account the path length traversed by the reflected component and gives a value similar to aortic PWV. 6 7

6 Do I need particular skills to do the measurement? How are results presented? No. You just have to put a finger probe on the patient. This probe is similar to the one used for pulse oximetry. PulseTrace and its straightforward software will guide you through the recording and provide you with the results. Can I use the PulseTrace on everybody? Pretty much, yes. The only limitation is that a poor signal may be obtained in patients with poor peripheral perfusion. Patients with very cold hands or Raynaud's syndrome may have a poor signal, difficult to analyse. This can be overcome by studying patients in a warm room. In patients with exceptionally high values of arterial stiffness (such as elderly hypertensive subjects) accurate measurements may be difficult to obtain because the direct and reflect components of the pulse overlap too much. Certain types of dysrythmia may also affect the accuracy. PulseTrace has an integrated printer which gives a full or summary report. In addition, PulseTrace is provided with a PC-software programme, PTUpload. PTUpload uploads all your measurements from the PulseTrace into a database on your PC. You can navigate through this database using PTUpload or Microsoft Access. 8 9

7 What is the reproducibility of the measurement? Depending upon the exact setting the within subject coefficient of variation of SI is between 5 to 10% and RI between 10 to 15%. How is RI used to measure endothelial function? The change in RI in response to an endothelium dependent vasodilator can be used to measure endothelial function. The ß 2 -sympathomimetic agonist salbutamol (albuterol) is one such vasodilator and has the advantage that it may be administered by inhalation. This makes a particularly simple measure of endothelial function and has been used in a number of studies. How does SI compare with other measurements of large artery stiffness? The most widely used measurement of large artery stiffness is aortic pulse wave velocity (PWV). SI is closely correlated with PWV. SI is influenced by age and blood pressure (the major physiological determinants of PWV) in a similar manner to PWV. Does the measurement change with blood pressure? SI is influenced by blood pressure as noted above. RI varies less with blood pressure but does vary with heart rate. In part this is because reduced reflection is usually associated with a tachycardia

8 What are the normal values for SI and RI? RI is a measure of peripheral vasodilation. So anything influencing peripheral vascular tone, for example caffeine intake or exercise may influence RI. RI varies between 60-90% in normal subjects SI varies with age in a similar manner to PWV. Typical values for a healthy subject, in his twenties should lie between 5 and 8 m/s. For a sixty year old subject, a typical value would be between 6 and 10 m/s

9 References Digital volume pulse - general Chowienczyk PJ, Kelly RP, MacCallum H, Millasseau SC, Andersson TLG, Gosling RG, Ritter JM, Änggård EE. Photoplethysmographic assessment of pulse wave reflection. Blunted response to endothelium-dependent beta2-adrenergic vasodilation in type II diabetes mellitus. J Am Coll Cardiol 1999; 34: Millasseau SC, Guigui FG, Kelly RP, Prasad K, Cockcroft JR, Ritter JM, Chowienczyk PJ. Non-invasive assessment of the digital volume pulse: comparison with the peripheral pressure pulse. Hypertension 2000; 36: Wilkinson IB, Hall IR, MacCallum H, Mackenzie IS, McEniery CM, van der Arend BJ, ShuYE, MacKay LS, Webb DJ, Cockcroft JR. Pulse-wave analysis: clinical evaluation of a noninvasive, widely applicable method for assessing endothelial function. Arterioscler Thromb Vasc Biol 2002; 22: [This method applies a similar principle but utilises the radial pressure rather than the digital volume waveform]. Large artery stiffness Millasseau SC, Kelly RP, Bland J, Ritter JM, Chowienczyk PJ. An index of large artery stiffness derived from the digital volume pulse. Circulation 2001; 102: 3782 Suppl. S (Abstract). Millasseau SC, Kelly RP, Ritter JM, Chowienczyk PJ. Analysis of increases in large artery stiffness by digital pulse contour analysis. Clin Sci (Colch) 2002; in press. Endothelial function Chowienczyk PJ, Kelly RP, MacCallum H, Millasseau SC, Andersson TLG, Gosling RG, Ritter JM, Änggård EE. Photoplethysmographic assessment of pulse wave reflection. Blunted response to endothelium-dependent beta2-adrenergic vasodilation in type II diabetes mellitus. J Am Coll Cardiol 1999; 34: Gopaul N.K, Manraj M.D, Hebe A, Lee Kwai,Yan S, Johnston A, Carrier,M.J, Änggård EE. Oxidative stress could precede endothelial dysfunction and insulin resistance in Indian Mauritians with impaired glucose metabolism. Diabetologia; 2001; 44: Beeton I, Leatham E. Bedside digital plethysmography detects endothelial dysfunction in recent onset angina. Eur Heart J 2001; 22: Suppl. S (Abstract)