Blood pressure monitoring during exercise: Comparison of pulse transit time and volume clamp methods

Figures & data

Table I. Subject characteristics.

Characteristic
Subjects	18
Age (years)	59.8 ± 12.9
Male	11 (61)
Body height (cm)	169.1 ± 9.1
Body mass index (kg/m²)	26.8 ± 7.7
Underlying disease
Interstitial lung disease	5 (28)
COPD	9 (50)
Pulmonary hypertension	2 (11)
Congestive heart failure	2 (11)
History of smoking	10 (56)
Arterial hypertension	6 (33)
Diabetes mellitus	0 (0)
Rhythm
Sinus rhythm	18 (100)
Pacemaker	0 (0)
Current medication
β-Blockers	4 (22)
ACE inhibitors or AT1b	4 (22)
Diuretics	7 (39)
Calcium channel blockers	3 (17)
Nitrates	0 (0)

Data are shown as mean ± SD or n (%).

COPD, chronic obstructive pulmonary disease; ACE, angiotensin-converting enzyme; AT1b, angiotensin receptor-1 blockers.

Table II. Exercise test results.

Parameter
Maximum workload (W)	76 ± 38
Limitations to maximum exercise
Dyspnea	9 (50)
Muscle (fatigue/cramps)	5 (28)
Dyspnea and muscle	4 (22)
No. of reference points	10.1 ± 1.4
Pulse transit time (ms)
Rest	258 ± 33
Maximum exercise	197 ± 27
Recovery	245 ± 30
SBP, sphygmomanometer (mmHg)
Rest	125 ± 24
Maximum exercise	185 ± 36
Recovery	128 ± 21
SBP, PTT-derived (mmHg)
Rest	125 ± 24
Maximum exercise	185 ± 34
Recovery	132 ± 20
SBP, Portapres (mmHg)
Rest	148 ± 33
Maximum exercise	193 ± 36
Recovery	144 ± 37

Data are shown as mean ± SD or n (%).

SBP, systolic blood pressure; PTT, pulse transit time.

Figure 1. Plot of the 18 nonlinear calibration functions derived from the 18 individual data sets of systolic blood pressure and pulse transit time.

Figure 2. Box plot of pulse transit time (PTT) and corresponding sphygmomanometer systolic blood pressure (SBP), PTT-derived SBP estimate and volume clamp (Portapres) SBP at reference points P1–P11. The line through the box indicates the median, the box represents the interquartile range, and the whiskers represent the full range of values.

Table III. Bland–Altman comparisons: agreement between sphygmomanometer systolic blood pressure (SBP) values and pulse transit time (PTT)-derived SBP estimates, and between sphygmomanometer SBP values and volume-clamp derived SBP (Portapres).

			Sphygmomanometer and PTT-derived SBP		Sphygmomanometer and volume-clamp SBP
Subject	No. of reference points	Calibration curve: goodness of fit R²	Bias (mmHg)	Limits of agreement (mmHg)	Bias (mmHg)	Limits of agreement (mmHg)
1	11	0.66	−1.6 ± 15.0	−31.1 to 27.8	12.5 ± 24.8	−36.0 to 61.1
2	11	0.99	−0.1 ± 6.2	−12.31 to 12.13	−1.5 ± 12.2	−25.4 to 22.4
3	11	0.91	−0.1 ± 11.6	−22.9 to 22.7	35.1 ± 21.2	−6.6 to 76.7
4	11	0.84	−2.8 ± 13.3	−28.8 to 23.2	21.8 ± 41.3	−59.1 to 102.7
5	8	0.97	−2.8 ± 10.2	−22.7 to 17.2	10.6 ± 19.0	−26.6 to 47.8
6	10	0.27	−2.5 ± 15.1	−32.1 to 27.1	19.2 ± 21.6	−23.2 to 61.6
7	10	0.83	−3.2 ± 17.4	−37.3 to 30.9	10.8 ± 17.5	−23.6 to 45.2
8	11	0.91	0.4 ± 6.3	−12.1 to 12.7	−3.5 ± 8.8	−20.8 to 13.7
9	11	0.98	0.5 ± 9.3	−17.7 to 18.6	−30.3 ± 28.0	−85.1 to 24.5
10	10	0.89	−0.2 ± 10.5	−20.7 to 20.3	−4.6 ± 17.9	−39.7 to 30.5
11	10	0.89	0.0 ± 7.7	−15.1 to 15.1	29.6 ± 8.5	13.0 to 46.2
12	8	0.89	−1.1 ± 12.1	−24.8 to 22.5	3.6 ± 12.4	−20.8 to 28.0
13	11	0.62	−1.0 ± 19.5	−39.2 to 37.2	28.4 ± 12.8	3.2 to 53.5
14	6	0.29	3.1 ± 18.43	−33.0 to 39.3	48.3 ± 31.4	−13.2 to 109.9
15	10	0.73	−0.6 ± 12.9	−25.8 to 24.6	52.8 ± 18.0	17.5 to 88.1
16	11	0.90	2.1 ± 14.1	−25.4 to 29.6	0.6 ± 15.0	−28.8 to 30.1
17	11	0.88	1.6 ± 18.7	−35.2 to 38.3	12.9 ± 30.2	−46.3 to 72.0
18	11	0.97	−0.1 ± 6.4	−12.6 to 12.4	14.5 ± 27.3	−39.1 to 68.0
All	182	N/A	−0.3 ± 12.4	−24.7 to 24.1	14.0 ± 28.6	−42.0 to 70.1

Data are shown as mean ± SD.

N/A, not applicable.

Figure 3. Bland–Altman plots. The outer lines indicate the limits of agreement, the inner line represents the mean difference. (a) Bias (–0.3 ± 12.4 mmHg) and limits of agreement (–24.7 to 24.1 mmHg) between systolic blood pressure measured by arm cuff sphygmomanometer (SBP_Sphy) and pulse transit time (PTT)-derived systolic blood pressure estimate (SBP_PTT). (b) Bias (14.0 ± 28.5 mmHg) and limits of agreement (–42.0 to 70.1 mmHg) between systolic blood pressure measured by arm cuff sphygmomanometer (SBP_Sphy) and systolic blood pressure measured by volume clamp technique using Portapres Model-2 (SBP_Portapres).