III. The effect of fasting Ramadan on the heart rate
variability
Ramadan fasting has a significant effect on RR duration (ms)
and sympathovagal balance at rest and during exercise. Indeed, under these
conditions, there is a lower heart rate (bpm) from one session to another
(Table VII); supine (59.94 Versus 56.92 Versus 55.50), standing (72.99 Versus
68.80 Versus 67.95) and during the effort interval (122.19 Versus 115.16 Versus
110,29) associated with an increase in parameter values representing
parasympathetic activity (HF« ms2», HF«nu»,
RMSSD, PNN50) (Tables IV, V, VI): (Akselrod et al., 1981; et al., 1991,
Camm, 1996) and the decrease in the values of the parameters
representing the sympathetic activity (HF« ms2»,
HF«nu») (Tables IV, V, VI) (Rimoldi et al., 1990; , 1991,
Kamath & Fallen, 1993, Montano et al., 1994), and consequently a
decrease in the LF / HF ratio; some authors have adapted this ratio as an
indicator of sympathetic activity (Yamamoto et al., 1991),
others as an index of sympathovagal balance (Pagani et al.,
1986).
This significant increase in RR (ms) duration, which reflects
a decrease in mean heart rate, is confirmed with the study by Hussain
et al., (1987); these authors found a significant decrease in heart
rate at rest throughout the month of fasting in male subjects. Similarly,
Karli et al.,
52
(2007) found a nonsignificant decrease heart
rate at rest during Ramadan compared to before Ramadan.
In addition, Zoladz et al., (2005) found a
decrease in heart rate of 10 beats / min during exercise at each workload that
starts at 30 W and ends at 150 W of fasting overnight. Similarly,
Ramadan et al., (1999) found a decrease in heart rate at
submaximal exercise during the month of Ramadan compared to the control
session.
Explanations of this phenomenon differ from one researcher to
another. Husain et al., (1987) explained this decrease in
heart rateat rest by the decrease in metabolic activity which is under the
influence of reduced sympathetic activity; these authors added that the
increase in religious devotion during Ramadan results from a solicitation of
the mental state which tends to lower metabolic rate and heart rate.
Zoladz et al., (2005) explained the
significant decrease in heart rate following a fasting night by increasing the
plasma level of noradrenaline leading to an increase in systemic vascular
resistance, and thus, the solicitation of arterial baroreceptors leading to
vagal stimulation (Schachinge et al., 2001 and Malpas, 2004 cited by
Zoladz et al., 2005). It is also known that diet can influence
cardiovascular regulation in healthy subjects at rest (Hoost et al.,
1996, Karpovich & Sinning, 1980). On the other hand, it has been
shown that the effect of diet (abstention or food intake) can influence the
cardiorespiratory activity by neuronal or hormonal pathways (Kearney et
al., 1996).
Other research has also shown that the secretion of leptin
(satiety hormone) and ghrelin (the hormone of hunger) can influence
cardiovascular activity (Haynes et al., 1987). According to
Matsumura, (2002, 2003) the injection of leptin activates the
sympathetic nervous system, and on the contrary, the injection of ghrelin
significantly decreases the heart rate in rabbits.
The decrease in resting and exercise heart rate can be
explained by increased secretion of ghrelin and a decrease in leptin secretion
during Ramadan, so that Zoladz et al.(2005) found no
significant difference between the secretion of these two fasting hormones
compared to the control session. According to Zoladz, this is probably due to
the short duration of fasting (one night) observed during this protocol.
Through the study of cardiac variability, our results
reflected a modulation of the autonomic nervous system by the decrease of the
parameters reflecting the sympathetic activity on the frequency plane (LF
« ms2 », LF « nu ») (FIG. 4)
and the increase of the parameters
53
reflecting the frequency-domain activity of the
parasympathetic system ("HF « ms2 », HF
« nu ») and their temporal correspondences (PNN50, RMSSD) (FIGS. 5,
6) (Neto et al., 2005) during the month of Ramadan.
We also found a significant decrease in the LF / HF ratio (FIG
9), which reflects sympathovagal activity or also the variation in sympathetic
activity, this decrease is explained by the decrease of the LF values (Tables
IV, V, VI) and the increase of the HF values (Tables IV, V, VI) during the holy
month.
These results may be a good explanation for the decrease in
heart rate during Ramadan and confirm the hypotheses of Husain et al.,
(1987). These authors explained the decrease in heart rate during the
holy month by a reduction in sympathetic tone.
These results may be consistent with the explanation given by
Zoladz et al., (2005) who attribute the decrease in heart rate
observed during exercise during abstinence by increasing systemic vascular
resistance and vagal stimulation via the baroreceptors.
We can also add the change in the daily habits of Muslims
during Ramadan, favoring sedentarism because Muslims tend to sleep late by
watching television, praying or reading (Afifi et al.,
1997).
In addition, general fatigue, reduced feeling of well-being,
and impaired cognitive function are the result of changes in eating habits and
sleep deprivation during Ramadan (Kadri et al., 2000; Leiper et al.
2003, Roky et al., 2004). It has also been shown that the month of
fasting is accompanied by a decrease in alertness, probably because of the
absence of lunch, which usually leads to falling asleep (El Kalifi,
1998).
The major changes in the rhythm of life in Ramadan, mainly
affecting food intake and sleep (Chaouachi et al., 2008, Maughan et
al., 2008a, Leiper et al., 2008) can also explain this increase in
tone. parasympathetic identified in our results. Indeed, fasting reduces the
basic metabolism in the absence of digestion. In addition, it has already been
shown that digestion accelerates the heart rate for 2 or 3 hours
(Karpovich, Sinning, 1980).
It is known that digestion activates the sympathetic
tone (Guyton, 2006) so fasting tilts the sympathovagal balance
towards parasympathetic tone which is confirmed by the study of
Al-Hazmi et al., (2009) who found a decrease in LF / HF ratio
during the holy month compared
54
to the control session according to Ramadan. They also
concluded that fasting protects the heart and minimizes the risk of heart
attacks.
Nerve modulation on the heart causes a change in heart rate,
called a chronotropic effect. It should also be noted that the heart rate is
also influenced by hormonal control mediated through the bloodstream, but
hormonal control is less rapid and less powerful than direct nerve control
(Pocock & Richards, 2004). This may explain the findings
found in some studies that show a decrease in heart rate despite the increase
in noradrenaline levels (Zoladz et al., 2005).
Indeed, fasting is a phenomenon of long duration; therefore
the decrease in heart rate may also be related to the decrease in the secretion
of the accelerating hormones of the heart rate during Ramadan; this mechanism
remains to be verified.
Our results show a modulation of the autonomic system by the
increase of the participation of the parasympathetic system (HF, HF nu, PNN50,
NN50) and the decrease of the sympathetic effect (SDNN, LF, LF nu) during the
month of fasting on the whole organism, and especially on the heart. The
explanation of this phenomenon can be attributed to two essential factors
related to the changes of life rhythm during Ramadan:
1. Sleep deprivation observed at night and,
2. The food intake.
There will consequently be a hormonal and nervous response to
these two major changes that are accentuated by the psychological factor
related to the specific spiritual environment, and the typical religious
climate created by the holy month of the Muslims.
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