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, published in the Sleep Medicine journal in 2017.[1]

What is the background to this research?[edit | edit source]

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 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] [4] The background 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] 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 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 has current importance.

Where is this research from?[edit | edit source]

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. The authors have multiple published articles on physical activity as it relates to chronic conditions and declared no conflict of interest with the subject matter of the paper. Funding was from the Ministry for Health with no conflict of interest. Until comparable studies are done in other countries this research has limited relevance outside of the Czech Republic.

What kind of research was this?[edit | edit source]

This was a cross-sectional study involving patients that were diagnosed as having narcolepsy with cataplexy, a group with narcolepsy without cataplexy as well as a control trial group that had neither. A cross-sectional study in the field of health, disease and exercise involves collecting data on a group with a particular health condition and then comparing this group to individuals who exist within a defined population;[6] in this study the control group was age and gender matched to the trial group. The patients with narcolepsy were diagnosed and treated at the Charles University hospital and it is assumed that they are generally healthier than the narcoleptic population who remain untreated. This means the study may not be relevant to people with narcolepsy who are not undergoing medical interventions.

This study was based on results from research conducted in Germany using a telephone survey, the survey 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 using data obtained from a German population and their results would hold more validity. This research better suits a longitudinal study that would involve monitoring whether a long term physical activity intervention improved cardiovascular fitness and subsequently improved quality of life in those with 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 in the cardiovascular fitness of the research population.

What did the research involve?[edit | edit source]

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

Table 1: Subject number, BMI and age.[edit | edit source]
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 | edit source]

This research involved all participants undergoing an exercise stress test (CPX). The control group was recruited from a preventative exercise program for the general population, a limitation of choosing control participants from this group is that it can be assumed they are healthier than the general public. Two weeks prior to the CPX, participants used an accelerometer to gather data on step count. Narcolepsy patients 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 from the researchers own institute there were complete treatment profiles on each narcolepsy participant, increasing the validity of this study.

What were the basic results?[edit | edit source]

The following table outlines the difference between narcolepsy and control VO2 peak.

Table 2: Results VO2 peak.[edit | edit source]
Power 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. 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 | edit source]

As this was not a longitudinal study it is hard to definitively conclude that cardiovascular fitness was inversely related to cataplexy episodes and sleepiness. However, during the two-week step counting procedure done at 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 outlining the amount of people who achieve 10,000 steps a day in the Czech Republic. A similar problem exists around the third conclusion, not enough time passed for any of the participants to age significantly therefore it is unclear what new information this statement is based on. 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 cardiovascular fitness can worsen narcolepsy symptoms but to what extent remains unclear.

Practical advice[edit | edit source]

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 and reduction of chronic disease symptoms.

Further information/resources[edit | edit source]

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 quality 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 | edit source]

  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].