| Summary: | Background: Measurement of wave intensity (WI) requires simultaneous or quasi-simultaneous measurement of pressure and flow limiting its use. Previous work in dogs [1] and humans [2] has shown that the excess pressure waveforms calculated using reservoir analysis correspond closely with aortic flow waveforms. This offers a potential method to estimate WI using only pressure waveforms (pWI). We investigated the feasibility of this approach and agreement with established methods.
Methods: 262 participants (68.3 (SD = 5.5); 74% male) without aortic stenosis or heart failure were recruited from a UK-based longitudinal study, Southall and Brent Revisited. Central pressure waveforms, aortic flow velocity and carotid WI were measured using tonometry (Sphygmocor, AtCor), echocardiography (iE33, Philips) and ultrasonography (SSD-5500, Aloka) respectively. Reservoir analysis was performed as previously described [2] and excess pressure waveforms were calibrated to flow velocity assuming a peak velocity of 1 m/s. Method agreement was assessed as mean difference (MD), limits of agreement (LOA) and concordance coefficient (CC).
Results: Analysis failed in 9 individuals; results for those with analysable data are shown in Table 1. Aortic pWI was higher than aortic WI but showed good concordance (logW1: MD(LOA) = −0.41(−0.73, −0.09) CC = 0.7; logW2: MD(LOA) = −0.41 (−0.73, −0.09); CC = 0.7). Agreement of pWI with carotid WI showed no bias and concordance was fair to poor (logW1: MD (LOA) = −0.16 (−1.30, 0.99) CC = 0.3; logW2: MD (LOA) = −0.02 (−1.23, 1.2); CC = 0.1).
Table 1Results
Variables
N
Median/(%)
p25
p75
Age, y
207
67.9
63.6
71.9
BMI, kg/m2
207
26.6
24.1
30.1
Systolic BP, mmHg
207
139
126
148
Diastolic BP, mmHg
207
76
70
82
Heart rate, bpm
207
66
59
74.5
Male sex, %
150
72.5
Ethnicity
European
88
(42.5%)
South Asian
75
(36.2%)
African Caribbean
44
(21.3%)
Current smoker
18
(8.8%)
Diabetes
65
(31.4%)
Hypertension
130
(62.8%)
Aorta
W1, mmHg.m.s−3
207
7103
5041
9910
W2, mmHg.m.s−3
207
1637
1147
2518
pW1, mmHg.m.s−3
207
10,526
7677
14,336
pW2, mmHg.m.s−3
207
2491
1779
3560
time W1 to W2, s
207
0.25
0.23
0.27
Peak velocity, m/s
207
1.34
1.2
1.46
Carotid artery
W1, mmHg.m.s-3
207
8714
6550
12,883
W2, mmHg.m.s-3
207
2327
1471
3227
time W1 to W2, s
207
0.29
0.27
0.31
Peak velocity, m/s
207
1.10
0.92
1.30
BMI, body mass index; BP, blood pressure; p25, 25th centile; p75, 75th centile; pW1, peak intensity of initial forward compression wave (W1) estimated using pressure only; pW2, peak intensity of initial forward compression wave (W2) estimated using pressure only; W1, peak intensity of initial forward compression wave (W1) calculated using aortic velocity; W2, peak intensity of initial forward compression wave (W2) calculated using aortic velocity.
Conclusion: Estimation of aortic WI from pressure waveforms using reservoir analysis is feasible.
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