Discussion
Movement, physical activity and position are known to influence a broad
spectrum of mechanisms in the human body. Therefore, we set out to
explore the impact movement may have on urine production. There is ample
existing body of literature showcasing the effects of movement, physical
activity and position, however, there is no existing data on the impact
on urine production 9-11.
Our study was performed in a population of healthy patients with age
varying from 26 years to 54 years with a mean of 35 years old. Due to
multiple variables and the complex interaction between these, we opted
for mixed model statistical analysis, A positive association was found
between diuresis and physical activity, movement and position for all
three timeframes i.e. 24 hours, daytime and night-time. Negative
associations were found between osmolality and creatinine and physical
activity, movement and position. The association between creatinine and
physical activity, movement and position were significant for all three
timeframes, however, this was not the case for osmolality where the
association was only significant for 2 timeframes being 24-hours and
night-time. Furthermore, there were no significant associations between
sodium and physical activity, movement and position except a very slight
statistically significant value for the model of daytime.
As this is a pilot study, there is a paucity of data exploring the topic
of movement and urine production. There are, however, other studies
exploring the association of physical activity and glomerular filtration
rate (GFR) as well as kidney function. The general consensus states a
positive association between physical activity and GFR as well as kidney
function 9,12-14. Moreover, Wolin et al. state that
physical activity may provide a strategy for the management of benign
prostatic hyperplasia related outcomes, particularly nocturia11.
Physical activity is known to increase blood pressure in the acute
setting. An increase in blood pressure would theoretically increase the
blood flow to the kidneys, without counting for any diversion of blood
flow to skeletal muscle or cerebrum in cases of flight-and-fright
responses. Nonetheless, an increase in renal blood flow, would increase
the flow within the glomerulus. This would result in an increased
glomerular filtration rate, which could be a potential hypothesis for
increased urine production. Nonetheless, one must account for processes
of reabsorption and filtration that occur within the renal tubules,
which brings us to our second hypothesis 15,16.
The renin-angiotensin-aldosterone system (RAAS) is a hormone system that
regulates fluid balance and blood pressure and works by increasing blood
volume and hence blood pressure. With increased physical activity, blood
pressure rises likely due to a combination of the baroreceptor reflex,
increased cardiac output and increased systemic vascular resistance
secondary to the effect of the sympathetic nervous system. As such,
there is a possibility that RAAS activity may not be as required by the
body’s physiology since the blood pressure is already autoregulated and
no increase in blood volume is required to increase blood pressure.
Nonetheless, a simple increase in blood pressure causing an increased
glomerular filtration rate with unchanged reabsorption dynamics, could
very well be the principle cause of an increased diuresis associated
with physical activity, movement and position. This would clarify the
phenomenon of increased urinary excretion without impacting on urinary
sodium, however, it is likely it is a combination of multiple systems
that play a role 10,15-17.
The strengths of our study are that it has been performed in a
well-designed sample that is representative of the general population.
Furthermore, the study design is prospective, and the research topic is
completely novel; hence the pilot study. However, some limitations must
be noted such as the lack of data on serum. Due to this, we could not
calculate the GFR and an estimate was made using BMI and age, however,
we felt this would be too vague and not accurate enough. Furthermore, as
the initial objective of the questionnaires was to compare the basic and
extended urine sampling, targeted data for the movement was not
specifically outlined. Urine samples were taken every 3 hours and were
objectified; whereas, the data on movement was given a subjective score
every hour by the patient. This data was then transformed to make the
analysis more transparent. In addition, the sample of our study might be
considered too small to note all the differences between certain
confounders. As such it is difficult to amplify the results to larger
patient groups. It is important to note that calculating the low level-1
variations of the different mixed models may have led to the loss of
matching previous results within the same patient. As such all the data
and its results could only be made with relation to intraindividual
differences.
It remains clear that more research is necessary within this domain. As
many studies have suggested physical activity is a very easy,
non-invasive way to improve quality of life 9-11,13.
Here it is vital to focus on a larger and more varied sample, as this
could lead to more exact data. As there are many unanswered questions
within this field of research, we must try and find a better
understanding of the pathology and increase the methods and tools
available to analyse the same. In an ideal situation, the researcher
must gain information on the exact timing of movement, the exact
intensity of movement, and finally how this impacts the renal system.
In the future, the use of automated monitoring devices for factors like
voiding, urine production and residual volume, but also for diet, blood
pressure, pulse and sleep will be necessary. In addition to this,
fitting applications, such as bladder diaries and intake diaries, will
be needed as well in support of these new monitoring devices. Technology
is already available in the form of a smart flow, a smart diaper, but
also a smart mattress that can supply the required information.
Furthermore, the necessary applications are available or easy to make.
The main problems to solve are validation of the applications and
devices for the purpose of exploring nocturnal LUTS and the financial
incentive for companies to this low-volume work. However,
community-driven sponsoring might be a solution for this.