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Brain & Heart Sleep and limb vasodilation
higher during daytime compared to nighttime, probably a plethysmographic fluximeter. Through a large-caliber
influenced by mental and physical activity during waking tube connected to an under-pressure air reservoir, the
hours. technique incorporates periodic and automatic occlusion/
deflation phases at over-venous-under-diastolic pressure
While BP rhythms have received considerable attention, 42
other aspects of limb hemodynamics, such as arterial flow (usually 50 mmHg). This methodology facilitates the
measurement of arterial flow in various body segments
and resistance, have been addressed to a lesser extent. This (for instance, legs and forearms) by analyzing the deflation
limited exploration is primarily attributed to the technical slope coefficient according to automatic interpolation of
challenges associated with continuous 24-h monitoring the angle (α) of the initial deflation slope (Equation I),
of peripheral arterial flow – a prerequisite for resistance where x and y represent the experimental points, and n is
calculations. i i
their number. 34,35,38,42 Any measured values deviating from
Furthermore, to distinguish between circadian rhythms the norm are rectified by inner software.
resulting from diurnal activity and those that are intrinsic
2
−
˘˘˘
(independent of activity), it is imperative to maintain ( ) ( ) ( ) ( i i i 2 )
ii
ii
ii
subjects in a supine posture for 24 h. This protocol involves = tg ∝= 2 2 Coefficient (I)
( )
the stringent requirement of preventing any partial / ny − x
ii
i i
movements while in bed, effectively inhibiting involuntary
movements during sleep – a task that proves challenging The presence of a professional observer throughout the
to realize. 24-h study obviated the need for electroencephalographic
ascertainment of sleep – a procedure that would have
2. Methods added complexity to the study procedure.
Several years ago, our systematic exploration into the
sleep/wake rhythm in limbs commenced, prompted by 3. Results
prior attempts in studies to monitor 24-h arterial flow 3.1. Circadian rhythm in healthy volunteers
in limbs. In animals, the attempt involved measuring In a pilot experiment conducted on subjects confined to bed
the capillary diameter and erythrocyte speed, while within a controlled environment – featuring a light blanket,
21
in humans, the approach utilized radioactive isotope a comfortable room with a stable temperature, and limbs
clearance ( Na, Xe). 22-26 Unfortunately, these techniques immobilized by orthopedic devices – we demonstrated, for
14
133
solely measure skin and subcutaneous flow, neglecting the first time, the existence of a circadian rhythm in limb
27
hemodynamically predominant muscular flow at rest. arterial flow and resistance directly influenced by sleep,
Although it was feasible to measure total limb arterial flow utilizing strain-gauge plethysmography. 46,47
(skin + subcutaneous + muscular) by directly cannulating
a large artery, this method posed challenges for human Sixty young and healthy volunteers underwent
28
application and encountered difficulties in obtaining continuous recording of leg and forearm arterial flow while
approval from bioethic committees. confined to bed for a 24-h period. Resistance was calculated
in units of resistance (UR = mmHg × ml × min × dl )
−1
tissue
The optimal non-invasive method for continuous derived from the mean BP to arterial flow ratio. Systolic and
monitoring of total limb arterial flow is venous-occlusion diastolic BP (in mmHg) were measured contemporaneously
plethysmography. While water plethysmography offers with every arterial flow detection using an automatic
29
precision, it proves impractical for 24-h recordings. device, and mean BP was calculated from Equation II. All
Furthermore, drawing from previous studies, we found procedures were automated yet constantly controlled by an
30
31
that air-, impedance-, and photo-plethysmography are expert researcher. Importantly, the natural sleep of study
32
either imprecise or present difficulties in standardization. subjects, visually monitored by researchers constantly
Our pilot experiments have highlighted strain-gauge present next to the examined subjects and responsible
venous-occlusion plethysmography as the optimal method for measuring sleeping hours, remained undisturbed
for conducting 24-h studies in subjects confined to throughout the study.
bed. Our particular proficiency lies in the application of Mean = (systolic + 2 diastolic)/× 3 (II)
indium-gallium-in-silicone venous-occlusion strain-gauge
plethysmography, a technique deeply ingrained in our With no a priori knowledge of the anticipated results,
experiments within the realm of human physiology. 33-41 our observations in healthy subjects yielded a surprising
This method, whose accuracy was unequivocally revelation: arterial flow demonstrated a significant
demonstrated, 42-45 employs a non-invasive approach using increase during sleep, both in the leg (39.1%, P < 0.0001)
Volume 2 Issue 1 (2024) 2 https://doi.org/10.36922/bh.1886
