Exercise as it relates to Disease/The impact of varied aerobic exercise on blood pressure in hypertensive patients

This Wikibooks page is a critique of the research article: Moreira WD, Fuchs FD, Ribeiro JP, Appel LJ. The effects of two aerobic training intensities on ambulatory blood pressure in hypertensive patients: results of a randomized trial. Journal of clinical epidemiology. 1999 Jul 1;52(7):637-42.

Background To Research
Hypertension (high blood pressure) has become increasingly prevalent worldwide. It is the highest risk factor associated with heart disease, and among the top 5 leading causes of mortality in Australia. Blood pressure is the amount of force blood puts on the walls of the arteries as it flows through them, measured in millimetres of mercury (mmHg). There are many factors that can increase blood pressure, such as blood composition or artery size, both of which cause the heart to pump harder to output the same amount of blood. Lifestyle factors such as stress, diet, and exercise (or lack of) can have this same effect, causing chronically high blood pressure above the normal range of 90-120mmHg/60-80mmHg. This is known as hypertension. The paper discussed in this critique looked at patients with mild hypertension. Aerobic training is an exercise format commonly characterised by endurance sports such as long distance running or cycling. This type of exercise utilises oxygen to assist in various processes that resynthesise ATP, the energy currency of the body. During aerobic exercise, it is normal for systolic blood pressure to temporarily increase to 160-220mmHg before returning to normal. This is highly taxing to the cardiovascular system and therefore causes the most structural adaptations to the heart. These adaptations include strengthening and thickening of the heart muscle that increases blood pumping efficiency and therefore lowers blood pressure long-term. The paper discussed in this critique investigated the effect of aerobic exercise at 20% and 60% of maximum workload.

The paper discussed in this critique sought to fill a gap in previous hypertension research that solely focused on high intensities. If lower aerobic intensities are found to have the same benefits as high intensity, this could increase the success rate of exercise interventions. By providing patients with a more achievable goal, a greater sense of success is attained and may result in higher compliance and perseverance with treatment. In other words, if the patient feels the challenge they are faced with is within their capacity, they are much more likely to succeed. This effect may have influenced the study being critiqued, as it was mentioned that the only two participants that dropped out once the study was underway were in the higher intensity exercise group.

Where This Research Is From
The paper in question was written by a team of authors led by Wilson D Moreira and was published in the Journal of Clinical Epidemiology in 1999. Research regarding the relationship between hypertension and exercise is ever-growing, therefore this smaller study with no clinical applications is somewhat outdated and irrelevant.

What Kind Of Research This Was
The paper discussed in this critique was a randomised control trial that utilised a double-blind parallel group design. This meant that participants were randomly assigned to one of two conditions: Group 1 who performed at 20% of maximum workload, or Group 2 who performed at 60% of maximum workload. It also meant that the researchers and participants were unaware of which group they were in. The sample size was small (N=28), recruited via non-probability sampling. Convenience sampling (advertisements in local papers) and purposive sampling (volunteers from a hypertension outpatient clinic) were both utilised. Participants tended to be middle-aged with both genders well presented, although race was not mentioned. All had been diagnosed with Stage 1 hypertension and underwent various pre-testing tasks to be eligible for the study. Preferably participants would be recruited using probability sampling to eliminate bias, as volunteer participants may have underlying intentions or beliefs that could effect their results. Generally more participants would have been ideal and would allow for a non-exercise control group.

What The Research Involved
Participants followed a 10 week exercise program on a cycle ergometer under observation. The program included 3 sessions per week consisting of a 5 minute warmup, 30 minute workout, and 5 minute cooldown. The workout was always completed at the same time each day (2:00pm - 3:00pm). Participants were instructed to continue their normal lifestyles, including diet and alcohol intake. Appropriate methodology was used and documented well, increasing the replicability of the study. A limiting factor of the focus study was that the identified gap in previous research was not filled by the evidence provided, given that ‘low intensity’ aerobic exercise is a broad bracket that can not be reduced to two levels of intensity. Ideally, this experiment would be redesigned to incorporate the aspects outlined below and refocus on creating realistic and varied treatment options.

Results Of The Study
The author's of this study claimed to have observed similar decreases in blood pressure between Group 1 and Group 2. In Group 1, blood pressure dropped from 137.2 to 135.2mmHg, and in Group 2 from 144.4 to 138.6mmHg. If anything, it would seem that the difference between the groups was under-emphasised. In the discussion section, it was noted that the p value for both groups was too high. This meant that the data could not be considered statistically or practically relevant. Due to this, the level of evidence is considered inadequate due to the low external validity and inapplicability of the results to patient care.

Conclusions From The Research
Upon critique, it would seem that higher intensity aerobic exercise at 60% of maximum workload is more effective at reducing mild hypertension. Despite the claim that they had a similar effect, the results clearly show that Group 2 reduced blood pressure significantly more than Group 1. The only conclusion that can be drawn from this particular article is that blood pressure can be reduced by aerobic exercise. The most effective modality, intensity, duration, and frequency requires further research. Further research should also investigate patients with stage 2 and 3 hypertension.

Practical advice
Before beginning any unfamiliar exercise, it is recommended to see a medical professional for the most individualised and effective treatment.

Further Resources
(1) How blood pressure works - Wilfred Manzano:

 https://www.youtube.com/watch?v=Ab9OZsDECZw 

(2) Exercise: A drug-free approach to lowering high blood pressure:

 https://www.mayoclinic.org/diseases-conditions/high-blood-pressure/in-depth/high-blood-pressure/art-20045206 

(3) High Blood Pressure - Facts About Hypertension:

 https://www.cdc.gov/bloodpressure/facts.htm#:~:text=Nearly%20half%20of%20adults%20in,are%20taking%20medication%20for%20hypertension 

(4) World Health Organisation - Hypertension:

 https://www.who.int/health-topics/hypertension#tab=tab_1