Exercise as it relates to Disease/The Effects of Exercise on Night Time Blood Pressure Dipping in Adults with Coronary Heart Disease

This article is a critical analysis of the paper “Effects of exercise and stress management training on nighttime blood pressure dipping in patients with coronary heart disease: A randomized, controlled trial” written by, Sherwood, Smith, Hinderliter, Georgiades and Blumenthal (2017).

What is the background to this research?
This research was undertaken because blunted night time blood pressure dipping (NTBPD) in a strong prognostic indicator of cardiovascular morbidity and mortality for both hypertensive and non-hypertensive individuals.

What is blood pressure dipping?
The fall in blood pressure, called the “dip”, is defined as the difference between daytime mean systolic blood pressure (SBP) and night time mean SBP and is expressed as a percentage of the day value. A dip in the range of 10-20% is considered normal, dips less than 10% are referred to as blunted.

What is the link between Coronary Heart Disease and Blunted Dipping?
Patients with coronary heart disease already (CHD) have a heightened risk of cardiovascular events because CHD affects blood vessels supplying the heart muscle. This vulnerability alongside blunted NTBPD may exacerbate the risk of cardiovascular events. Click here to watch a video explaining the cause of CHD and some of the risks associated with the disease.

What interventions have been used to improve the night time blood pressure dip?

 * Chronotherapy


 * Bed time antihypertensive medications (rather than morning does in patients with hypertension)


 * Night time dosing of melatonin


 * Physical activity


 * Managing psychological stress

Where is the research from?
This research was conducted in North Carolina, and has been published in the American Heart Journal. This journal ranks in the top 25 Cardiology and Cardiovascular Medicine Journals globally. The authors of this study work in health faculties at both the University of North Carolina and Duke University. Individually, they have engaged in a large range of research across all aspects of health, particularly cardiology related topics. Extensive expertise knowledge has gone into developing and conducting this study.

CHD is prevalent in both America and Australia, in Australia it affects 1.2 million people, and was the cause of death of 19,777 (12% of all deaths) in 2015. In America CHD is the cause of death for over 370 000 people annually (approx. 14% total deaths). The interventions in this study would be appropriate to apply to the Australian population of CHD.

What kind of research was this?
This study was a clinical investigation, where a randomized, controlled trial was conducted. Meaning the subjects were grouped into interventions randomly and one group underwent usual care in order to compare results of an intervention to the results of no intervention.

Sample and Baseline Testing
This study was conducted from January 1999 to February 2003 and involved 134 patients with CHD and ex-induced myocardial ischemia – 92 male, 42 female (40-84yrs). The patients were required to wear an AccuTracker II in order to provide 24 hour ambulatory blood pressure monitoring (ABPM). Mean SBP and diastolic blood pressure (DBP) were readings taken in both waking hours and night time sleep. SBP and DBP dips were computed continuously and defined as % change between mean day time BP and mean night time BP.

The usage of ABPM is becoming more common, and encouraged in order to avoid the “white coat” effect of clinical cuff measures. ABPM is a more accurate predictor as it provides an average reading over 24 hours. Whilst increased accuracy is a bonus, studies have found that repeat measures don’t necessarily provide the same result. Questioning the reliability of the devices.

Interventions
Following a baseline assessment patients were randomly assigned an intervention group, either exercise training (n=48), stress management (n=44) or usual care (n=42).

Exercise Training: aerobic exercise three times a week for 16 weeks, sessions involved 10 min warm up, and a 35 minute workout training at 70-85% of their calculated heart rate reserve.

Stress Management: 16 weekly 1.5 hour sessions addressing CHD related education, coping skills training and social support.

Usual Care: maintained on regular medical regimens and saw their local cardiologists as needed.

As this study has a control group (usual care) in which they can compare any changes that the interventions result in to this group, and the baseline. This increases the credibility of the study, although a larger sample size could provide more detail and give a clearer indication of the results.

What were the basic results?
Post intervention results showed that both exercise training and stress management interventions resulted in patients being classified as having a normal dip. Whereas those who maintained usual care have their dip classified as blunted. It can be seen that throughout the 16 weeks of usual care, the SBP dip has worsened, this could also be a result of unreliable readings from the ABPM.

What conclusions can we take from this research?
This research suggests that any intervention may be better than no intervention. Sleep quality is directly related to the magnitude of NTBPD. With this in mind, both exercise and stress management showed improved BP dipping, and this may be through improving sleep quality.

This study supports exercise being an intervention which can result in a reduction of psychological distress, furthermore improving sleep quality and the NTBPD. Further study could be done in order to understand what mechanisms are behind these changes. Previous research suggests that both exercise and stress management training improve other biomarkers of cardiovascular disease, alongside increased blood pressure dipping and reducing psychological stress. Indicating that the results of these behavioural interventions align with previous research and should reduce the risks for more severe CHD outcomes.

There is also potential to explore the effects of a combination of both stress management and physical activity training in cardiac rehabilitation patients.

Practical advice
If you have been diagnosed with CHD, complete stage 1 of the Adult Pre-Exercise Screening Tool, before commencing any physical activity and present to your general practitioner or cardiologist for clearance to commence exercise. Your doctor may also be able to provide you with possible avenues to address stress management techniques.