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Resting Hemodynamics and Response to Exercise Using the 6-Minute Walk Test in Late Pregnancy: An International Prospective Multicentre Study

Dennis, Alicia Therese MBBS, PhD, MIPH, PGDipEcho, FANZCA*,†; Salman, Marwa MBBCh, FRCA, MSc, LLM, EDRA; Paxton, Emma BSc, MD*; Flint, Margot BSc, MSc, PhD§,‖,**; Leeton, Liz BAppSc, BAppSc, GradDipMid, RN*; Roodt, Francois MBChB, FCA (SA)§,‖,**; Yentis, Steve BSc, MBBS, FRCA, MD, MA¶,#; Dyer, Robert Anthony BSc, MBChB, FCA (SA), PhD§,‖,**

doi: 10.1213/ANE.0000000000003818
Obstetric Anesthesiology: Original Clinical Research Report
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BACKGROUND: Cardiac disease is the leading cause of maternal death. Assessment of cardiovascular fitness is important in pregnant women because it is linked to increased risk of cardiac disease but is rarely undertaken or studied. The 6-Minute Walk Test (6MWT) is a safe exercise test but is not used in pregnancy. We determined the 95% reference interval for resting heart rate (HR) and distance walked for the 6MWT, as well as hemodynamic recovery variables, and quantified expectations and actual experiences of exertion and breathlessness with exercise in late pregnancy.

METHODS: After institutional research board approval (Australian and New Zealand Clinical Trials Registry Number: 12615000964516), 300 healthy term nulliparous pregnant women performed the 6MWT at 3 tertiary referral obstetric hospitals using a standardized protocol. Each woman underwent two 6MWT with maximum 15-minute recovery period after each test. Hemodynamic variables were measured at rest and after exercise. Participants were asked 4 questions, 2 regarding expectation and 2 regarding actual experience, using the Rating of Perceived Exertion scale and Modified Borg Dyspnea scale.

RESULTS: Participant characteristics and resting variables were mean (standard deviation [SD]); age, 31 years (4.2 years); body mass index, 27 kg/m2 (2.9 kg/m2); gestational age, 37 weeks (1.3 weeks); HR, 85 bpm (10.8 bpm) with 95% reference interval 64–106 bpm; systolic blood pressure, 112 mm Hg (10.2 mm Hg); diastolic blood pressure, 72 mm Hg (8.6 mm Hg); oxygen saturation, 98% (0.9%); and respiratory rate, 18 breaths/min (5.7 breaths/min). The mean (SD) average distance walked was 488 m (94.9 m) with a speed of 3.0 mph (0.64 mph) with a 95% reference interval of 302–674 m. The mean (SD) HR increase with exercise was 12 bpm (11.0 bpm) with a median [quartile] recovery time of 5.0 minutes [1–8 minutes]. A lower resting HR was associated with increased distance walked (r = −0.207; 95% confidence interval, −0.313 to −0.096; P < .001). A greater HR change with exercise was associated with increased recovery time from exercise (r = 0.736; 95% confidence interval, 0.697–0.784; P < .001). Sixty-three percent and 83% of participants, respectively, expected to be more exerted and breathless than they actually were with exercise.

CONCLUSIONS: The 6MWT is feasible and applicable in term pregnant women. The reference intervals for resting HR and distance walked in the 6MWT have been generated. HR increases by approximately 12 bpm with submaximal exercise, and half of the women recovered within 5 minutes of submaximal exercise. Women expected to be more exerted and breathless than they actually were with exercise.

From the *Department of Anaesthesia, Royal Women’s Hospital, Parkville, Australia

Departments of Pharmacology, Obstetrics and Gynaecology, and Medicine and Radiology, The University of Melbourne, Parkville, Australia

Department of Anaesthesia, Guy’s & St Thomas’ Hospital, Lambeth, United Kingdom

§Groote Schuur Hospital, Cape Town, South Africa

Mowbray Maternity Hospital, Cape Town, South Africa

Department of Anaesthesia, Chelsea and Westminster Hospital, London, United Kingdom

#Imperial College London, London, United Kingdom

**Department of Anaesthesia and Perioperative Medicine, University of Cape Town, Cape Town, South Africa.

Published ahead of print 22 August 2018.

Accepted for publication August 22, 2018.

Funding: This work was supported by the Obstetric Anaesthetists’ Association Project Grant 2016. A.T.D. receives funding from the National Health and Medical Research Council Australia (NHMRC ECF Medical Professional APP1108598).

The authors declare no conflicts of interest.

Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal’s website.

Preliminary data from this study were presented as posters and published abstracts: Dennis AT, Salman M, Paxton E, Flint M, Leeton L, Yentis SM, Dyer RA. The 6 Minute Walk test in pregnant women: an international multicentre exercise and haemodynamic study. Int J Obstet Anesth. 2017;31;P43:(suppl 1):S33; and Salman M, Yentis SM, Paxton E, Flint M, Leeton L, Dyer RA, Dennis AT. Exertion and breathlessness in pregnant women: an international multicentre prospective cohort study using the 6-Minute Walk Test. Int J Obstet Anesth. 2017;31(suppl 1):P44:S33.

Clinical trials number: Australian and New Zealand Clinical Trials Registry Number: 12615000964516.

Reprints will not be available from the authors.

Address correspondence to Alicia Therese Dennis, MBBS, PhD, MIPH, PGDipEcho, FANZCA, Department of Anaesthesia, Royal Women’s Hospital, Locked Bag 300, Corner Grattan St and Flemington Rd, Parkville, Australia 3052. Address e-mail to alicia.dennis@thewomens.org.au.

Copyright © 2018 International Anesthesia Research Society
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