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  • Oral presentation
  • Open Access

Assessing the hemodynamic response to exercise - a novel MR approach

  • Jennifer A Steeden1,
  • David Atkinson1,
  • Andrew M Taylor2 and
  • Vivek Muthurangu2
Journal of Cardiovascular Magnetic Resonance201012(Suppl 1):O67

https://doi.org/10.1186/1532-429X-12-S1-O67

Published: 21 January 2010

Keywords

Cardiac OutputSystemic Vascular ResistanceHemodynamic ResponseLeft Ventricular VolumeHigh Temporal Resolution

Introduction

Exercise is a powerful stimulator of the cardiovascular system. Therefore, it can be used to unmask subtle vascular changes in early hypertensive disease. Routinely only blood pressure and heart rate response to exercise are measured. However measuring cardiac output (CO), systemic vascular resistance (SVR) and arterial compliance would increase the sensitivity of exercise testing. MRI is a proven method of measuring CO and deriving SVR and compliance at rest. Unfortunately the lack of appropriate sequences has made it difficult to perform MRI during exercise.

Purpose

We hypothesize that measuring the hemodynamic response to exercise is feasible using a novel high temporal resolution, real-time, spiral MRI flow sequence.

Methods

Twenty healthy volunteers (21.9-49.2 years) underwent aortic flow quantification using real-time spiral PC-MR (8 interleaves, 4-fold SENSE acceleration, 40 ms temporal resolution). Aortic flow quantification was carried out at rest and during supine exercise (at 4 W and 8 W). The novel sequence was validated against a standard gated flow sequence at rest and against a real-time sequence to measure left ventricular volume during exercise. The real-time flow data was combined with simultaneous oscillometric blood pressures to calculate systemic vascular resistance (SVR) and arterial compliance.

Results

A good agreement of the flow volumes calculated from our real-time flow sequence was found against the standard flow sequence and also against the left ventricular volumes calculated Table 1.
Table 1

Validation of real-time flow sequence at rest and during exercise

Validation

Bland Altman Assessment

Correlation coefficient

 

Bias (ml/cycle)

Limits of agreement (ml/cycle)

 

Standard flow sequence Vs.

Real-time flow sequence, at rest

-0.58

-0.58

-4.71

0.994 (p < 0.005)

Real-time ventricular volume Vs. Real-time flow volume, at rest

-2.04

-8.29

4.21

0.988 (p < 0.005)

Real-time ventricular volume Vs. Real-time flow volume, at 8 W

0.83

-4.18

5.84

0.984 (p < 0.005)

The real-time flow volumes calculated were combined with simultaneous blood pressure measurements to calculate SVR and compliance.
Table 2

Hemodynamic response to exercise

 

Rest+

4 W+

8 W +

P*

(0 W-4 W)

P*

(4 W-8 W)

P*

(0 W-8 W)

Heart rate (bpm)

68.2 (12.5)

99.2 (15.8)

108.6 (21.2)

<.001

< .001

< .001

Cardiac output (L.min-1)

5.8 (1.4)

8.3 (1.6)

9.1 (1.7)

< .001

0.002

< .001

Systolic BP (mmHg)

112.5 (10.4)

137.2 (15.2)

134.6 (21.0)

< .001

.50

< .001

Diastolic BP (mmHg)

64.8 (6.0)

66.3 (12.3)

64.3 (13.1)

.54

.46

.85

Mean BP (mmHg)

83.9 (6.8)

95.5 (9.4)

95.3 (8.9)

< .001

.91

< .001

Vascular resistance (WU)

15.2 (2.9)

11.8 (2.5)

10.7 (1.7)

< .001

.007

< .001

Arterial compliance (mL.mmHg-1)

1.00 (0.23)

0.62 (0.23)

0.63 (0.21)

< .001

.80

< .001

+ Mean from all volunteers (std) * Paired t-test

At 4 W, heart rate, cardiac output, and systolic and mean blood pressure significantly increased, whilst SVR and compliance decreased, as expected (Table 2). Apart from heart rate and cardiac output, there was no significant change in these parameters between 4 W and 8 W. There was no change in diastolic blood pressure during either stage of exercise.

Conclusion

We have demonstrated the feasibility of measuring the hemodynamic response to exercise using a novel real-time flow MRI sequence. The high temporal resolution of this sequence ensures accuracy at the high heart rates present during exercise. This technique is relatively simple to perform and could be made available in a large number of centers. This raises the possibility of assessing exercise response in large populations and linking it to cardiovascular risk. Understanding this link should improve identification of at-risk groups and increase understanding of the early development of vascular disease.

Authors’ Affiliations

(1)
UCL Department of Medical Physics & Bioengineering, London, UK
(2)
UCL Institute of Child Health, London, UK

Copyright

© Steeden et al; licensee BioMed Central Ltd. 2010

This article is published under license to BioMed Central Ltd.

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