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|Title: ||Pulse transit time and the pulse wave contour as measured by photoplethysmography: the effect of drugs and exercise|
|Authors: ||Payne, Rupert Alistair|
|Supervisor(s): ||Maxwell, Simon|
|Issue Date: ||7-Jul-2009|
|Publisher: ||The University of Edinburgh|
|Abstract: ||Photoplethysmography (PPG) is a simple means of measuring the pulse wave in
humans, exploitable for the purposes of timing the arrival of the pulse at a particular
point in the arterial tree, and for pulse contour analysis. This thesis describes a
methodology for measuring arterial pulse transit time (PTT) from cardiac ejection to
pulse arrival at the finger. It describes the effect on PTT of drug and exercise induced
changes in BP. The nature of the relationship between the PPG and arterial pressure
is also examined, and the PTT technique extended to assessment of conduit vessel
pulse wave velocity (PWV) during exercise.
PTT measured from ECG R-wave to PPG finger wave (rPTT) had a negative
correlation (R2=0.39) with systolic BP (SBP), unaffected by vasoactive drugs in
some but not all persons. rPTT showed similar beat-to-beat variability to SBP,
unaffected by drugs. rPTT correlated weakly with diastolic (DBP) and mean (MAP)
pressure. Cardiac pre-ejection period (PEP) formed a substantial and variable part of
rPTT (12% to 35%). Transit time adjusted for PEP (pPTT) correlated better with
DBP (R2=0.41) and MAP (R2=0.45), than with SBP. The PPG wave tracked changes
in the peripheral pressure wave. Drugs had little effect on the generalised transfer
function (GTF) describing the association between arterial and PPG waves.
Strenuous exercise induced a large decrease in rPTT, mainly accounted for by
decreases in PEP (53% of the total change in rPTT) and in transit time from aorta to
distal brachial artery (33%). In contrast, minimal change in transit time from wrist to
finger tip occurred with exercise.
Simultaneous ear-finger PPG signals were used to measure conduit artery PWV
during exercise. Ear-finger PWV (PWVef) overestimated carotid-radial PWV
throughout exertion (overall bias 0.81±1.05ms-1, p<0.001), but the degree of
difference remained constant. The increase in PWVef with exercise, was greater
(1.18±0.54ms-1, p=0.035) in healthy subjects with a positive cardiovascular family
history compared to those without.
PPG enables analysis of the pulse contour during exercise, but estimation of the
radial pressure wave from finger PPG by use of a GTF derived at rest, resulted in inaccuracy following exertion. These effects were variable and relatively short-lived.
Furthermore, a resting GTF used to determine central pressure from the peripheral
wave, resulted in underestimation of SBP (-5.9±2.1mmHg) and central pressure
augmentation index (-8.3±2.9%), which persisted for 10 minutes post-exercise.
rPTT had a negative linear association with SBP (R2=0.94) during strenuous exercise,
slightly stronger than during recovery (R2=0.85). Differences existed in area-undercurve
of the rPTT/SBP relationship between exercise and recovery, due to
discrepancies in rate and degree of recovery of SBP and PEP. The linear relationship
between the rPTT/SBP during exercise was affected by aerobic capacity, and the
regression slope was less in the anaerobic compared to aerobic phase of exercise due
to minimal change in PEP during anaerobic exertion. The correlation between
rPTT/SBP did not change with prolonged aerobic exercise. Finally, measures of
baroreflex sensitivity during exercise, were not significantly different between actual
beat-to-beat SBP and SBP estimated using rPTT.
In conclusion, absolute BP cannot be reliably estimated by measurement of rPTT
following administration of drugs and during exercise. However, rPTT may have a
role in measuring BP variability and in the assessing exercise capacity. PPG may
also be useful in determining the effects of exercise on arterial stiffness, and for
estimating the pressure wave contour, although its use during exercise for the latter
purpose must be treated with caution.|
|Sponsor(s): ||Edinburgh Technology Fund|
|Keywords: ||blood pressure|
|Appears in Collections:||School of Clinical Sciences thesis and dissertation collection|
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