Exercise as it relates to Disease/The role of cardiovascular fitness in patients with narcolepsy

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This wiki provides a critique on the original journal article Cardiovascular fitness in narcolepsy is inversely related to sleepiness and the number of cataplexy episodes.[1]

What is the background to this research?[edit]

Narcolepsy is a chronic neurological condition that is identified by excessive sleepiness during the daytime and can be categorised into two different subclasses; narcolepsy with cataplexy and narcolepsy without cataplexy.[2] Cataplexy is distinguished by the sudden loss of muscle tone, making a person who was otherwise awake unexpectedly lose voluntary control. Attacks of cataplexy are often triggered by excitement, stress and other strong or sudden emotions.[3] Narcolepsy with cataplexy is caused by a degeneration and loss of hypocretin neurons in the hypothalamus, which play a vital role in the cycle of sleep and wakefulness. Unlike narcolepsy with cataplexy, narcolepsy without cataplexy is not categorised by a loss of hypocretin neurons and is much less understood.[4] The background reasoning to this research comes from another study in which it was concluded that patients with narcolepsy have a lower quality of living compared with other people suffering from neurological disorders.[5] Moreover, patients diagnosed as having narcolepsy with cataplexy are more likely to avoid engaging in physical activity and social sporting activities due to the risk of cataplexy attacks. The research in this study was conducted with the aim to observe whether cardiovascular fitness could reduce sleepiness and the number of cataplexy episodes in those with narcolepsy, and thus improve their overall quality of life. There are few studies exploring the quality of life of patients with narcolepsy as well as evaluating ways in which their symptoms could be alleviated, therefore this research is exploring important questions about improving quality of life via methods of symptom reduction.

Where is this research from?[edit]

This study was conducted by researchers from the Department of Endocrinology and Metabolism, and the Department of Neurology and Centre of Clinical Neurosciences at Charles University in Prague, Czech Republic. The authors declared that none of them had a conflict of interest with the subject matter of the paper, funding was from the government Ministry for Health also with no conflicts of interest. The research was conducted within the Czech Republic and tested patients diagnosed and treated at the Charles University Hospital, thus this research is only pertinent with the methodology and treatment used at the Charles University Hospital.

What kind of research was this?[edit]

This was a cross-sectional study involving patients that were diagnosed as having narcolepsy with cataplexy and a group of those with narcolepsy without cataplexy as well as a control trial group that had neither. A cross-sectional study in the field of health, exercise and disease involves collecting data on a group with a particular health condition or state, and then comparing this group to individuals who all exist within a defined population;[6] in this study the control group was age and gender matched to the trial group. As the patients with narcolepsy were all diagnosed and treated in the same hospital it may be assumed that they are generally more healthy and proactive in controlling their narcolepsy than the narcoleptic population who remain untreated, and do not wish to participate in studies. This may account for lower BMI ratings and higher cardiovascular fitness in the narcoleptic group of this study, and thus may not be able to account for the majority of those with the condition.

This study was based on the results from research conducted in Germany using telephone surveys, it was concluded that patients with narcolepsy had a lower quality of life than the general German population. [5] The researchers completing this paper could have completed a similar survey with their own patients rather than use data obtained from a German population and their results would hold more validity. This cross-sectional study would have worked better as a longitudinal study that involved monitoring whether a long term physical activity intervention improved cardiovascular fitness and thus improved the symptoms and therefore quality of life in those suffering from narcolepsy. It is hard to conclude that cardiovascular fitness is inversely related to sleepiness and cataplexy episodes when there has been no increase or decrease to cardiovascular fitness and measurements retaken; there are only current cardiovascular fitness measures as well as current sleepiness and cataplexy attack measures taken in this study.

What did the research involve?[edit]

The details of the subjects included in this study are in the table below.

Table 1: Subject number, BMI and age.[edit]
Narcolepsy w/ Cataplexy Narcolepsy w/o Cataplexy Control
Number 32 10 36
BMI 30.6 ± 5.6 27.6 ± 5.7 28.1 ± 6.2
Age (y) 35.0 ± 10.0 34.6 ± 10.6 35.3 ± 10.2

Methods for Study Population Data Collection[edit]

This research involved patients with narcolepsy and the control group undergoing an exercise stress test (CPX). The control group were recruited from participants a part of a preventative exercise program for the general population, a limitation of choosing control participants from this population is that it can be assumed they are more healthy than the general public. Two weeks prior to the CPX, participants used an accelerometer to gather data on step count. All of the narcolepsy patients were diagnosed at the Charles University Hospital according to the International Sleep Disorders Classification. Narcolepsy patients participating in the research underwent a night polysomnography (8 hours) and the 5-nap multiple sleep latency test (MSLT), these tests were performed without any existing treatments that could influence symptoms. As this study was conducted on patients with narcolepsy from the researchers own institute there were complete treatment profiles on each participant, increasing the validity of this study.

Method for Cardiopulmonary Exercise Stress Test[edit]

The CPX were completed on a cycle ergometer. The work rate was calculated based off of body weight, and work rate corresponded to 0.5 Watts/kg increasing to 1.0 W/kg in the second work period. From then the test increased 5 Watts every 10 seconds corresponding to 30 Watts every minute which was not based off of body weight.

What were the basic results?[edit]

The following table outlines the difference between narcolepsy and control VO2 max

Table 2: Results VO2 max.[edit]
Narcolepsy VO2 mL/kg/min Control VO2 mL/kg/min
0.5W/kg 12.3 ± 1.4 12.6 ± 1.1
1.0W/kg 18.9 ± 1.7 20.2 ± 1.5
Peak 30.1 ± 7.5 36.0 ± 7.8

There were no significant differences between results from the group of narcolepsy with cataplexy patients and narcolepsy without cataplexy patients, accounting for their joint results table. VO2 peak was higher in the control group compared to those with narcolepsy which was expected. This was the first study to provide data on the cardiovascular fitness of patients with narcolepsy, the three main findings of this study include;

  1. Cardiovascular fitness is inversely related to sleepiness in both narcolepsy populations, and a reduced number of cataplexy attacks in patients with narcolepsy with cataplexy.
  2. Those with narcolepsy have a lower cardiovascular fitness than control subjects and the general Czech Republic population.
  3. As patients with narcolepsy age their cardiovascular fitness becomes closer to those in the general population.

What conclusions can we take from this research?[edit]

As this was not a longitudinal study it hard to definitively conclude that cardiovascular fitness was inversely related to cataplexy episodes and sleepiness. However during the two week step counting procedure done in the beginning of this research it was found that patients with narcolepsy took 35% less steps than the recommended 10,000 steps per day which could potentially be from sleepiness - however this finding does not carry many implications as no normative data was given as to the amount of people who achieve 10,000 steps a day in the Czech Republic. A similar problem exists around the third conclusion of this study, not enough time passed for any of the participants to age significantly therefore it is unclear what new information this conclusion is based off of. This research reliably demonstrates that people suffering from narcolepsy do have a lower VO2 peak than individuals in the general population, it can be assumed that reduced physical activity can be attributed to excessive daytime sleepiness and cataplexy episodes from the work done with accelerometers, however to what extent remains somewhat unclear.

Practical advice[edit]

Patients with narcolepsy could potentially improve their symptoms of excessive daytime sleepiness, as well as cataplexy episodes if they were to undertake a physical activity intervention which aimed to increase their cardiovascular fitness. By suggesting exercise and cardiovascular fitness as a potential symptom alleviator this study joins a plethora of others suggesting exercise may lead to an increase in quality of life, reduction of disease or chronic disease symptoms and be the key to longevity, which holds huge implications for how practitioners treat disease states now and in the future.

Further information/resources[edit]

Starting tips on how to increase cardiovascular fitness - https://www.lifestyle.com.au/health/how-to-improve-your-cardio-fitness.aspx

Narcolepsy Australia: latest news and events concerning narcolepsy in Australia - http://www.narcolepsysupportaustralia.com/

Sleep Disorders Australia: more about narcolepsy and its diagnosis - https://www.sleepoz.org.au/disorders/narcole

Study conducted in Germany on health related qualities of life of patients with narcolepsy (used in this research) - https://www.ncbi.nlm.nih.gov/pubmed/17512797

Longitudinal study on increased mortality in those with narcolepsy - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3920308/

References[edit]

  1. Matoulek M, Tuka V, Fialova M, Nevsimalova S, Sonka K. Cardiovascular fitness in narcolepsy is inversely related to sleepiness and the number of cataplexy episodes. Sleep Med [Internet]. 2017 Mar 11 [cited 2018 Sept 4];34(1):7-12.
  2. Thorpy MJ. Classification of sleep disorders. Neurotherapeutics [Internet]. 2012 Sep 14 [cited 2018 Sept 4];9(4):687-701.
  3. National Institute of Neurological Disorders and Stoke. Narcolepsy Fact Sheet [Internet]. USA: NINDS; last updated 2018 [cited 2018 Sept 4].
  4. Burgess CR, Scammell TE. Narcolepsy: neural mechanisms of sleepiness and cataplexy. J Neurosci [Internet]. 2012 Sept 5 [cited 2018 Sept 4];32(36).
  5. a b Dodel R, Peter H, Spottke A, et al. Health related quality of life in patients with narcolepsy.Sleep Med [Internet]. 2007 Nov [cited 2018 Sept 4];8(7-8):733-741.
  6. Public Health Action Support Team. Introduction to study designs - cross-sectional studies [Internet].England: PHAST; 2017 [cited 2018 Sept 6].