J. Biomedical Science and Engineering, 2011, 4, 529-534
doi:10.4236/jbise.2011.48068 Published Online August 2011 (http://www.SciRP.org/journal/jbise/ JBiSE ).
Published Online August 2011 in SciRes. http://www.scirp.org/journal/JBiSE
Pattern of respiratory-induced changes in fingertip blood
volume measured by light transmission
Meir Nitzan1, Daniel Dayan1, Eran Shalom1, Yu val Slovik2, Alan Murray3
1Department of Applied Physics/Medical Engineering, Jerusalem College of Technology, Jerusalem, Israel;
2Department of Otorhinolaringology, Head and Neck Surgery, Soroka University Medical Center, Beer Sheva, Israel;
3Department of Medical Physics Freeman Hospital, Newcastle, UK.
Received 16 May 2011; revised 13 June 2011; accepted 5 July 2011.
ABSTRACT
Respiratory-induced fluctuations in heart rate and
arterial blood pressure have been intensively investi-
gated, but there is little information on the effect of
respiration on peripheral blood volume. In the cur-
rent study, blood volume changes in the finger, ob-
tained by light transmission measurements, were
measured during regular breathing (6 s periods) and
long breathing (12 s periods). Respiratory chest-cir-
cumference changes were simultaneously measured
in order to associate the pattern of tissue blood vol-
ume change with the respiratory cycle. Sixteen sub-
jects were studied, and in fourteen finger blood vol-
ume increased during inspiration and decreased
during expiration in the long-breathing periods. In
all 14 subjects the start of blood volume decrease was
significantly delayed from the start of expiration by
mean ± SD 1.00 ± 0.65 s (p < 0.001, range 0 - 2.3 s).
The start of blood volume increase was significantly
delayed from the end of expiration by 3.45 ± 1.76 s (p <
0.005). In eight, finger blood volume started to in-
crease more than 2 s before the start of inspiration.
For the 6 s breathing period, blood volume decreased
during inspiration in five examinations, and in-
creased in seven. The increase in peripheral blood
volume during inspiration could be attributed to the
higher abdominal pressure during inspiration, and to
the decrease in sympathetic activity during inspira-
tion and the subsequent vasodilatation. The decrease
in peripheral blood volume during inspiration is
probably due to the negative thoracic pressure dur-
ing inspiration and its mechanical effect on thoracic
vessels.
Keywords: Light Absorption; Deep Breathing;
Sympathetic Nervous system; Tissue Blood Volume
1. INTRODUCTION
Respiratory-induced fluctuations in heart rate—respira-
tory sinus arrhythmia—and similar fluctuations in arte-
rial blood pressure have been intensively investigated,
but in only a few studies the pattern of the chang e during
inspiration and during expiration was investigated. Heart
rate increases and systolic blood pressure decreases dur-
ing inspiration [1-3] but there is strong variability in the
relationship between heart rate or systolic blood pressure
and the respiratory changes in chest circumference. The
origin of these respiratory-induced fluctuations is not
decisively known. They have been attributed to fluctua-
tions in central autonomic activity caused by spontane-
ous oscillations in respiratory center activity or by resp i-
ratory-induced mechanical effects on the aortic baro-
receptors and the pulmonary stretch receptors [2-4]. The
direct mechanical effect of respiratory-induced thoracic
pressure changes on arterial blood pressure and on cen-
tral veins may also be significant [5-7].
Respiratory-ind uced flu ctuatio ns hav e also been fo und
in the peripheral circulatory system. Deep inspiration
reduces skin blood flow, measured by skin temperature
[8,9] and by laser Doppler flowmetry [9-12], and this
reduction has been attributed to higher sympathetic ac-
tivity. Peripheral blood volume, as measured by light
transmission through the tissue, has been shown to fluc-
tuate at the respiratory rate [13-18], as it does with each
heart beat, and so induces the photoplethysmographic
(PPG) signal.
Two possible mechanisms have been suggested for
the origin of tissue blood fluctuations with respiration:
mechanical influence of the negative thoracic pressure
during inspiration on the arteries and veins in the thorax
[14-17] and respiratory changes in sympathetic activity
[15-18]. The effect of respiration on sympathetic activity
has been demonstrated by several studies [19-21], which
showed higher muscle sympathetic nerve activity

M. Nitzan et al. / J. Biomedical Science and Engineering 4 (2011) 529-534 530
(MSNA) during expiration and very low MSNA at
end-inspiration, when lung volume is maximal. Since
sympathetic activity generally constricts skin blood ves-
sels, the decrease of sympathetic activity during inspira-
tion is expected to in crease fingertip blood volume.
The mechanical effect of respiration on the tissue
blood volume also depends on the relative contributions
of abdominal respiration and thoracic respiration. The
negative thoracic pressure during inspiration decreases
blood pressure in the arteries and veins in the thorax , and
consequently decreases peripheral tissue blood volume
during inspiration. The higher abdominal pressure dur-
ing inspiration increases blood pressure in the arteries
and veins in the abdomen and consequently increases
peripheral tissue blood volume during inspiration
[22,23]. In particular, finger blood volume is expected to
increase due to the higher blood pressure in the abdomi-
nal aorta, resulting in higher blood flow from the heart to
the upper part of the body.
The respiratory changes in the peripheral blood vol-
ume can therefore exhibit different patterns. In the cur-
rent study we measured the temporal relationship be-
tween changes in finger blood volume and the respira-
tory phase.
2. MATERIALS AND METHODS
2.1. Subjects and Examination
Sixteen non-smoker male subjects aged 21 - 63 years,
with no known cardiovascular or neurological disease
were studied. During the examination the subjects sat
with their right hand comfortably laid on the table, at
about heart level. A PPG probe was attached to the right
index finger for the measurement of light transmission
though the finger tissue, and an op tic-fiber sensor for the
measurement of the respiratory chest-circumference
changes (see later) was applied around their chest. Fin-
gertip skin temperature was measured before the start of
the examination by an alcohol thermometer held by the
index finger and the two adjacent fingers. Room tem-
perature was 21˚C - 24˚C; fingertip temperature was
29˚C - 35˚C.
After a rest period of five min the subjects were asked
to breath three series of 5 regular and 5 long respiration
periods, where inspiration and expiration time were de-
termined by a light point moving on a computer screen
in the form of triangular waves. Regular respiration con-
sisted of inspiration of 2 s and expiration of 2 s followed
by 2 s of no-breath, and long breathing consisted of in-
spiration of 4 s and expiration of 3 s followed by 5 s of
no-breath. It should be noted that in our study there were
no constraints on the tidal volume, and it was allowed to
change between long and regular breathing.
2.2. The Light Transmission and the Chest
Circumference Sensors
The PPG probe consisted of an infrared light-source and
photodetector of a pulse-oximeter probe (Oxisensor N25,
Nelcor), mounted on the same plane (reflection PPG
probe). The probe was attached to the ind ex finger of the
right hand of the subject. A low-pass filter (0 - 40 Hz)
reduced high frequency noise. The signal was inverted
so that a higher signal level corresponded with a higher
blood volume. The signals were sampled at a rate of 500
Hz (16 bit) and digita l l y store d fo r of fl i ne pr ocessi n g.
In order to obtain the relationship between the light
transmission changes and time of inspiration and expira-
tion, we used an optic-fiber sensor previously developed
by us [24] for the measurement of respiratory-induced
changes in chest-circumference. The sensor is based on
the dependence of light transmission through a bent op-
tic-fiber on its radius of curvature, and on the change of
the latter when chest circumference changes. Some light
rays, which are totally reflected by the core-cladding
surface when the fiber is straight or slightly bent, may
escape through the cladding when the fiber bending is
higher, if the angle to the surface normal becomes lower
than the critical angle. The details of the sensor were
described elsewhere [24].
3. RESULTS
In 14 out of the 16 long-breathing period examinations
(12 s each, including 5 s pause), tissue blood volume
increased during inspiration and decreased during expi-
ration. Figure 1 shows the tissue blood-volume and
chest-circumference change as a function of time for one
of these examinations. In this examination, finger blood
volume started to decrease about two s after the start of
expiration, while the increase of finger blood volume
started before the start of inspiration, and continued to
increase during inspiration. In two examinations, the
pattern of blood volume change during long breathing
was not in direct relationship with chest-circumference
change. In one of these, an inverse pattern was found for
the long breathing periods: the tissue blood volume in
the finger decreased during inspiration and increased
during expiration. In the other, the finger blood volume
displayed double bloo d volume pulses for each breath.
Figure 2 shows two examples from the 14, showing
the pattern of direct relationship between tissue blood
volume and chest-circumference change for the long-
breathing period examinations. In all those examinations
the finger blood volume started to decrease after the start
of expiration (range 0 - 2.3 s). In ten cases finger blood
volume started to increase before the start of inspiration,
and continued to increase during inspiration, indicating
that the blood volume increase was also related to the
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M. Nitzan et al. / J. Biomedical Science and Engineering 4 (2011) 529-534 531
end of the previo us phase of expiration. In 8, the changes
started more than 2 s before inspiration, and in 2, just
before. To allow the relationship between tissue blood
volume and chest-circumference change to be seen more
clearly, the pulses in tissue blood volume were elimi-
nated by depicting only the diastolic (minimal) blood
volume for each pulse, and Figure 3 shows the results
for the same examinations as in Figure 2.
The time of the increase and decrease of the blood
volume pulse relative to respiratory phase was charac-
terized by two parameters: the time-difference TDI from
the end of expiration to the start of blood volume in-
crease, and the time-difference TDD from the start of
expiration to the start of blood volume decrease, as
shown in Figure 1. The time of the start of expiration
was taken as the time of the maximum of the chest-cir-
cumference change curve; the time of the end of expira-
tion was taken as the time of the end of the breathing
instruction triangle (BG in Figure 2).
Figure 1. The changes in tissue blood volume (TBV) and
chest-circumference (CC) as a function of time. TDI is the time
difference between the end of decrease of CC and the start of
increase of TBV; TDD is the time difference between the start
of decrease of CC and the start of decrease of TBV.
(a)
(b)
Figure 2. Two examinations showing, for long breathing peri-
ods, a direct relationship between tissue blood volume (TBV)
increase (upper curve) and chest circumference (CC) increase
(middle curve). TBV changes during regular breathing show an
inverse relationship (a) and a direct relationship (b) with chest
circumference increase. Upward direction indicates increase in
TBV and chest circumference. The lower curve in each ex-
amination (denoted by BG—breathing graph) shows the trian-
gular waves displayed on the computer screen for breathing
instruction.
(a)
(b)
Figure 3. The two examinations of Figure 2, showing the
changes in the minimal (diastolic) blood volume (upper curve)
and chest circumference increas e (lower curve) .
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M. Nitzan et al. / J. Biomedical Science and Engineering 4 (2011) 529-534 532
Figure 4. The time of the start of tissue blood volume increase,
TDI, relative to the end of expiration (empty circles) and the
time of the start of tissue blood volume decrease, TDD, relative
to the start of expiration (full circles) for the long breathing
periods. Each pair of circles presents the values of TDI and
TDD for one of the 14 subjects, displaying a direct relationship
between tissue blood volume change and chest circumference
change.
Figure 4 presents the detailed results for the mean
values of TDI and TDD for each of the 14 subject ex-
aminations. These mean values were obtained by aver-
aging, for each subject, the values for all the long-
breathing pulses, not including the first in each group.
The increase in blood volume was significantly delayed
from the end of expiration by TDI 3.45 ± 1.76 s (mean ±
SD, p < 0.005) and the decrease in blood volume was
significantly delayed from the start of expiration by
TDD 1.00 ± 0.65 s (p < 0.001).
Figures 2 and 3 also present results of blood volume
measurements with regular breathing of the 6 s period. A
pattern of direct relationship between tissue blood vol-
ume change and chest-circumference change (i.e. in-
crease of tissue blood volume during inspiration and
decrease during expiration) was found in some subjects
as shown in Figure 2(b) for one examination, while for
other subjects it was an inverse relationship (as in Fig-
ure 2(a)). For the 14 examinations, seven showed a di-
rect relationship, five an inverse relationship and in two
the relationship was not clearly defined. No quantitative
results could be derived from the examinations of regu-
lar breathing due to the low signal-to-noise ratio in the
blood volume measurement.
4. DISCUSSION
In the current study we measured the blood volume
changes in the finger, as obtained by light transmission
measurements, during regular breathing (6 s periods) and
during long breathing (12 s periods). The examinations
were performed simultaneously with measurement of
chest-circumference change, in order to see whether in-
spiration was associated with an increase or decrease in
tissue blood volume. The main finding of the study was
that in all except two long-breathing examinations of
finger blood volume changes, tissue blood volume in-
creased during inspiration and decreased during expira-
tion (direct relationship). In only one examination did
tissue blood volume decrease during inspiration and in-
crease during expiration (inverse relationship). This in-
verse relationship was also found in some regular-
breathing examinations, even though the long-breathing
examinations in these subjects were associated with a
direct relationship pattern.
An important finding was the relative timing of blood
volume change. The start of the decrease in finger blood
volume followed the start of expiration, suggesting that
the former was induced by the latter. On the other hand
the start of the increase in finger blood volume preceded
the start of inspiration in the majority of the examina-
tions. Though the increase in finger blood volume re-
lated to inspiration, it is likely to have been initiated by
the end of previous expirat i o n .
As presented in the Background Section, two possible
mechanisms have been suggested as the origin of the
tissue blood volume fluctuations with respiration: me-
chanical influence of the thoracic pressure on the tho-
racic blood vessels [14-17] and sympathetic activity os-
cillations [15-18]. The sympathetic activity has been
shown to decrease during inspiration [19-21], which can
explain the increase in fingertip blood volume during
inspiration, found in almost all of our long-breathing
results. Though those studies on sympathetic activity
(measured by MSNA) were performed with spontaneous
breathing, with a respiration frequency which was even
higher than our regu lar breathing, it seems reasonable to
suggest that sympathetic activity is similarly modulated
by the respiratory pattern of our long-breathing exami-
nations.
In former publications the mechanical effect of
breathing on the peripheral blood volume was attributed
to the negative internal thoracic pressure during inspira-
tion which decreases blood pressure in the thoracic ar-
teries and increases blood volume in the thoracic veins.
These two effects are expected to decrease peripheral
tissue blood volume during inspiration. However, inspi-
ration is generally also accompanied with increased ab-
dominal pressure, which increases the blood pressure in
the abdominal arteries and veins and diverts blood to the
peripheral tissue [22,23]. This effect increases the blood
volume in the peripheral blood vessels during inspiration
and can explain the increase in tissue blood volume dur-
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M. Nitzan et al. / J. Biomedical Science and Engineering 4 (2011) 529-534 533
ing inspiration and its decrease during expiration (direct
relationship) in long breathing. In addition to the effect
of sympathetic activity decrease during inspiration, the
respiratory change in tissue blood volume is probably
affected by the two opposing effects of thoracic and ab-
dominal breathing on the peripheral tissue blood volume.
5. CONCLUSIONS
While in most long-breathing examinations finger blood
volume increased when chest-circumference increased,
an inverse relationship between the two parameters was
found in one long-breathing examination and also in
several examinations of regular breathing. It is likely
that different mechanisms are involved in the effect of
respiration on peripheral blood volume, probably in-
cluding lower thoracic pressure, higher abdominal pres-
sure and lower sympathetic activity during inspiration.
6. ACKNOWLEDGEMENTS
The study was supported by E.W. Joseph Fun d.
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