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ORIGINAL PAPER
Distinct load dependence of relaxation rate and diastolic function
in
Oryctolagus cuniculus
and
Ratus norvegicus
Accepted: 12 March 2003 / Published online: 23 May 2003
Springer-Verlag 2003
Abstract This study investigated potential differences
on load dependence of relaxation rate and diastolic
function between Oryctolagus cuniculus and Ratus nor-
vegicus, which have constitutive differences in the
mechanisms involved in myocardial inactivation. Load
dependence of relaxation rate and diastolic function
were evaluated with the response of left ventricular time
constant sand diastolic pressure-dimension relation to
beat-to-beat aortic constrictions in open-chest rabbits
and rats. Afterload levels were normalized, being ex-
pressed as a percentage of peak isovolumetric pressure
(relative load). In control heartbeats, relaxation rate and
diastolic function were similar in the two animal species.
They presented, however, distinct responses to afterload
elevations. In rabbits, time constant decreased 7% and
diastolic pressure-dimension relation remained un-
changed when afterload was elevated to a relative load
of 73–76%. Above this afterload level, a significant
deceleration of relaxation rate (increase of time con-
stant) and an upward shift of diastolic pressure-dimen-
sion relation were observed. In rats, afterload elevations
accelerated pressure fall up to a relative load of
97–100% and no afterload-induced shift of the diastolic
pressure-dimension relation was observed. This study
provides, therefore, evidence that Oryctolagus cuniculus
has lower afterload reserve of myocardial relaxation and
diastolic function than Ratus norvegicus.
Keywords End-diastolic pressure-volume relation Æ
Rabbits ÆRats ÆTime constant s
Abbreviations ED End-diastolic ÆLV Left ventricular Æ
LVP Left ventricular pressure ÆNCX Na
+
/Ca
2+
exchanger ÆPV Pressure-volume ÆSERCA2 Sarcoplas-
mic reticulum Ca
2+
-ATPase
Introduction
Myocardial relaxation is an important determinant of
both early (Shintani and Glantz 1994) and late (Leite-
Moreira et al. 1999a; Leite-Moreira and Correia-Pinto
2001) left ventricular (LV) diastolic filling. It is mod-
ulated by non-uniformity, inactivation and load
(Gillebert et al. 2000). Non-uniformity refers to the
temporal and spatial asynchronous distribution of load
and inactivation during myocardial relaxation
(Brutsaert 1987; Leite-Moreira and Gillebert 1996).
Inactivation refers to the processes whereby Ca
2+
is
transported out of the cytosol (Bers 2002), in order to
achieve its diastolic levels, and cross-bridge detachment
occurs. The four pathways involved in the first are
phospholamban (PLB)-modulated uptake of Ca
2+
by
the sarcoplasmic reticulum Ca
2+
-ATPase (SERCA2a),
Ca
2+
extrusion via the Na
+
/Ca
2+
exchanger (NCX),
mitochondrial Ca
2+
-uniport and sarcolemmal Ca
2+
-
ATPase, with the two latter being responsible for only
about 1% of total (Bers 2002). The quantitative
importance of the two first major routes varies between
species (Negretti et al. 1993; Bassani et al. 1994; Hove-
Madsen and Bers 1993; Lewartowski et al. 1992). In
rabbit ventricular myocytes, SERCA2a removes 70%
of the free intracellular Ca
2+
concentration ([Ca
2+
]
i
),
while NCX removes 28%. On the other hand,
SERCA2a activity is higher in rat ventricular myocytes,
being responsible for the uptake of 92% of [Ca
2+
]
i
,
whilst NCX contributes to the removal of only 7%
(Bers 2002). In addition, rat hearts express predomi-
nantly the faster myosin heavy chain (MHC)-aisoform
(Meehan et al. 1999), while rabbit hearts express pre-
dominantly the slower MHC-bisoform, which has a
higher affinity for Ca
2+
(Reiser and Kline 1998).
J Comp Physiol B (2003) 173: 401–407
DOI 10.1007/s00360-003-0347-7
J. Correia-Pinto ÆT. Henriques-Coelho
S.-M. Oliveira ÆA. F. Leite-Moreira
Communicated by G. Heldmaier
J. Correia-Pinto ÆT. Henriques-Coelho ÆS.-M.Oliveira
A. F. Leite-Moreira (&)
Department of Physiology, Faculty of Medicine,
University of Porto, 4200-319 Porto, Portugal
E-mail: amoreira@med.up.pt
Tel.: +351-22-5508452
Fax: +351-22-5519194
Load changes influence calcium regulatory mecha-
nisms and myofilament properties. In rabbits, it was
previously demonstrated that afterload elevations have a
biphasic effect on relaxation rate and end-diastolic (ED)
pressure-volume (PV) relation (Leite-Moreira et al.
1999a). In this regard, afterload elevations up to a certain
level accelerate LV relaxation and do not affect the
ED-PV relation, reflecting a compensatory response and
the presence of afterload reserve. Greater elevations of
afterload slow LV relaxation and upward shift the
ED-PV relation, resulting in diastolic dysfunction
because afterload reserve has been exhausted. The level of
afterload above which a decompensatory response occurs
may be shifted by pharmacological agents such as caf-
feine (Leite-Moreira et al. 1999b) and b-adrenergic
stimulation (Leite-Moreira et al. 2001). Caffeine, which
decreases [Ca
2+
]
i
uptake by SERCA2a and increases
myofilament Ca
2+
sensibility (Wendt and Stephenson
1983), shifts the transition to a decompensatory response
towards smaller afterload levels. On the other hand,
b-adrenergic stimulation, which enhances SERCA2a
activity and decreases myofilament Ca
2+
sensibility,
thereby shifts the transition to a decompensatory re-
sponse toward higher afterload levels. Diastolic distur-
bances induced by afterload are therefore attenuated.
These results are highly suggestive of a relation between
SERCA2a activity and the occurrence of afterload-
induced disturbances of relaxation and diastolic function.
Additionally, it was also documented that afterload-
induced diastolic disturbances are related not only with
relaxation rate but also with the available time to relax
(Leite-Moreira and Correia-Pinto 2001). The time
available to relax is altered by heart rate, which is sig-
nificantly higher in rats. Taking into account these
molecular and heart rate differences between rabbits and
rats, it would be interesting to investigate how rats
handle all these factors without compromising normal
cardiac diastolic physiology.
As Oryctolagus cuniculus and Ratus norvegicus have
different heart rate and constitutive differences in gene
expression and activity of SERCA2a and NCX, we
hypothesized that load dependence of relaxation and
diastolic function would also be significantly different.
Materials and methods
The investigation conforms to the Guide for the Care and Use of
Laboratory Animals published by the US National Institutes of
Health (NIH Publication No. 85-23, revised 1996). The study was
carried out in 36 male adult healthy animals: 19 New Zealand white
rabbits (O. cuniculus, 12 weeks old) and 17 Wistar rats (R. nor-
vegicus, 7 weeks old).
Experimental preparation
The rabbits were premedicated with ketamine hydrochloride
(50 mg kg
)1
, i.m.) and xylazine hydrochloride (5 mg kg
)1
, i.m.),
while rats were anaesthetized with pentobarbital (6 mg/100 g, i.p.).
A tracheostomy was performed and mechanical ventilation
initiated (Harvard Small Animal Ventilator, Model 683), delivering
oxygen-enriched air. Respiratory rate and tidal volume were
adjusted, according to species, in order to keep arterial blood gases
and pH within physiological limits. Anaesthesia was maintained
with ketamine hydrochloride (33 ml kg
)1
h
)1
i.m.), pentobarbital
sodium (12.5 mg kg
)1
i.v. before opening the chest and then
2.5 mg kg
)1
i.v. as needed), and vecuronium bromide (0.5 mg h
)1
i.v.) for rabbits and with an additional bolus of pentobarbital
(2 mg/100 g) as needed for rats. A central vein was cannulated and
a pre-warmed solution 20 mEq KCl and 40 mEq NaHCO
3
in
500 ml 0.9% NaCl was then administrated to compensate for
perioperative fluid losses.
In both animal species, the heart was exposed through a median
sternotomy and the pericardium widely opened. The ascending
aorta was dissected and a silk suture (1-0 in rabbits and 3-0 in rats)
was placed around it to allow its external occlusion during the
experimental protocol. Left ventricular pressure (LVP) was mea-
sured with a high-fidelity micromanometer (3-F, SPR-524, Millar
Instruments, Houston, Tex., USA) inserted through an apical
puncture wound into the LV cavity. The manometers were cali-
brated against a mercury column and zeroed after stabilization for
30 min in a water bath at body temperature. LV dimensions were
measured with miniaturized ultrasonic dimension gauges using a
sonomicrometer amplifier (Triton Electronics, San Diego, Calif.,
USA). In rabbits, one pair of crystals (3 mm) was sutured in place
onto the LV anterior and posterior epicardial surfaces to measure
LV external anterior-posterior diameter and a third crystal (1 mm)
was tunnelled at a 30–45º angle into the subendocardial facing the
LV anterior epicardial crystal. The anterior epicardial crystal and
the subendocardial crystal were combined to measure wall thick-
ness. In rats, one crystal was placed in the interventricular septum
(1 mm) and another one on the epicardial surface of the LV free
wall (2 mm), allowing the direct measurement of LV septal-free
wall dimension. In all animals, a limb ECG (II) was recorded
throughout. At the end of the experiment, the animals were sacri-
ficed with an overdose of anaesthetics and the position of crystals
and manometers verified at necropsy.
Experimental protocol
After complete instrumentation, the animal preparation was
allowed to stabilize for 30 min before the beginning of the experi-
mental protocol, which consisted in randomly performing multiple
graded left ventricular pressure elevations, by abruptly narrowing
or occluding the ascending aorta during the diastole separating two
heartbeats. The preceding beat is control and the following beat is
test heartbeat. The analysed intervention, therefore, was a selective
alteration of afterload without changes in preload or long-term
load history (Gillebert et al. 1997). Systolic LVP of the first
heartbeat following the intervention varied as a function of the
extent of aortic constrictions. The animal was stabilized for several
beats before another intervention was performed. The animals were
not paced, but heart rate did not vary significantly during the
experimental protocol (214±9 and 295±16 beats min
)1
for rab-
bits and rats, respectively).
Data acquisition and analysis
Recordings were made with respiration suspended at end expi-
ration and parameters were converted on-line to digital data with
a frequency of 500 Hz. To distinguish between ED at the begin-
ning and at the end of the analysed cardiac cycle, ED at the
beginning was referred to as ED(pre), while ED at the end was
referred to as ED(post). Peak rates of LVP rise (dP/dt
max
) and
fall (dP/dt
min
) were measured. LVP was measured at the begin-
ning of the cardiac cycle (LVP
ED(pre)
), at peak systole (LVP
max
),
at its protodiastolic nadir (LVP
min
), and at the end of the cardiac
cycle (LVP
ED(post)
). Afterload levels were presented as relative
load, which consists in peak systolic LVP of a given heartbeat
402
expressed as percentage of peak pressure of the corresponding
isovolumetric beat (Leite-Moreira and Gillebert 1994). Time
intervals were measured from ED(pre) to dP/dt
min
and from dP/
dt
min
to ED(post). Rate of pressure fall was evaluated with dP/
dt
min
and the time constant s. For calculating s, the portion of the
LVP tracing between dP/dt
min
and a pressure equal or below the
value of ED(post) was selected. The curve was fitted (SigmaPlot
5.0 SPSS) to a monoexponential model with a non-zero asymp-
tote, given by the following equation:
PtðÞ¼P0et=sþP1
where P
¥
is a non-zero asymptote (mmHg), P
0
is an amplitude
constant (mmHg), tis time (ms), and sis the time-constant of the
exponent (ms). The correlation coefficient (r
2
) yielded values
>0.97. According to this formula, relaxation will be 97% complete
after a time interval of 3.5s(ms) starting at the onset of LVP fall
(Weisfeldt et al. 1978; Leite-Moreira et al. 1999a). LV dimension
was measured at the beginning of the cardiac cycle (LVP
ED(pre)
), at
its minimal value (LVD
min
) and at the end of the cardiac cycle
(LVP
ED(post)
).
Statistical analysis
Group data are presented as mean±SEM. To compare the mul-
tiple afterload levels in rats and rabbits, we performed two-way
repeated-measures ANOVA. When treatments were significantly
different, the Student-Newman-Keuls test was selected to perform
pairwise multiple comparisons. Statistical significance was set at
P<0.05.
Results
For both species and from multiple available interven-
tions we selected for further analysis, in addition to
control heartbeats, cardiac cycles whose relative loads
were closer to 70% (rabbits, 69±1%; rats, 70±1%),
80% (rabbits, 81±1%; rats, 82±1%), 90% (rabbits,
90±1%; rats, 91±1%) and 100% (isovolumetric
heartbeats). In both species dP/dt
max
did not change
significantly with afterload interventions. Relative load
of the control beats was significantly higher in rabbits
(56±1%) than in rats (49±2%).
Effects of LV afterload elevations on LVP fall
and diastolic function
Effects of LV afterload elevations on LVP fall and dia-
stolic function are illustrated in Figs. 1 and 2 and sum-
marized in Tables 1 and 2. At baseline, both species
presented similar relaxation rates as measured by
dP/dt
min
and time constant s. As illustrated in Fig. 1,
effects of afterload elevations on relaxation rate were
assessed with the fractional changes in the time constant
s. Although in both species, spresented biphasic
response to afterload elevations, they were not identical.
In rats, s
test
/s
control
decreased (s
test
/s
control
<1, accel-
eration of pressure fall) over almost the entire range of
afterload elevations from control to isovolumetric beats.
This acceleration was maximal at a relative load of 80%.
Above this afterload level acceleration of pressure
fall became smaller and was no more observed in
isovolumetric beats (relative load of 100%). On the
other hand, in rabbits, relaxation rate accelerated up to
a relative load of 70%, while afterload elevations
reaching or exceeding a relative load of 80% resulted in
a progressive and significant increase of s
test
/s
control
(s
test
/s
control
>1, deceleration of pressure fall). The
transition from acceleration to deceleration occurred at
relative loads of 73–76% and 97–100% for rabbits and
rats, respectively.
ED LV pressures and dimensions showed distinct
responses to afterload elevations. Whereas LVP
ED(pre)
,
ID
ED(pre)
and ID
ED(post)
were not affected, LVP
ED(post)
increased significantly with afterload elevations in rab-
bits, but only marginally in rats. As ID
ED(post)
did not
change with afterload in rabbits and rats that means that
in the first diastole after an elevation of the afterload
there was no significant filling beyond ID
ED(pre)
.
Therefore, the difference between ED LVP at the end
and beginning of the cardiac cycle (LVP
ED(post)
)LV-
P
ED(pre)
) reflects the magnitude of the upward shift of
the ED LVP-ID relation and the occurrence of diastolic
dysfunction, which was observed in rabbits but not in
rats (Fig. 2).
In rabbits diastolic dysfunction became apparent
when relaxation rate decelerated (s
test
/s
control
>1). In
rats, this never occurred since afterload elevations elic-
ited almost always acceleration of myocardial relaxation
(s
test
/s
control
<1).
Evaluation of LV completeness of myocardial relaxation
In Fig. 3, afterload-induced upward shift of the ED
LVP-ID relation (diastolic dysfunction) is plotted
against the difference between available and predicted
times for the LV to relax. Available time for the ven-
tricle to relax corresponds to the measured time inter-
val from onset of left ventricular pressure fall till the
next end-diastole. On the other hand, the predicted
time was computed as 3.5s(Leite-Moreira et al. 1999a;
Leite-Moreira and Correia-Pinto 2001), which esti-
mates 97% completion of relaxation. When the differ-
ence between available and predicted times was
negative, this means that there was a deficit in time for
the ventricle to relax. In rats, such deficit only occurred
in isovolumetric beats, while in rabbits an significantly
bigger deficit was present not only in isovolumetric
beats but also for the relative load of 90%. Interest-
ingly, when such a deficit in time for the ventricle to
relax occurred a significant afterload-induced diastolic
dysfunction was observed.
Discussion
In the current study, we tested the hypothesis that load
dependence of relaxation and diastolic function in
O. cuniculus and R. norvegicus, which have different
403
heart rate and constitutive gene expression of sarco-
plasmic reticulum Ca
2+
-ATPase (SERCA2a) and Ca
2+
extrusion via the NCX (Negretti et al. 1993; Bassani et al.
1994; Hove-Madsen and Bers 1993; Lewartowski et al.
1992), would be distinct. We could demonstrate that,
although myocardial relaxation rate at baseline was
similar in both animal species, they showed a distinct
response to afterload elevations, with rats having a
higher afterload reserve of diastolic function than rab-
bits. This could have a biological meaning since heart
rate is significantly higher in rats than in rabbits. In fact,
with the pronounced afterload-induced acceleration of
relaxation, rats could compensate the shortest time
available that its LV has to relax.
Investigation of load dependence of relaxation rate
and diastolic function, in the in situ intact heart, must be
performed with beat-to-beat load manipulations in the
presence of a widely opened pericardium, as we did in
the present study, in order to exclude several con-
founding factors, such as neurohumoral activation,
pericardial constraint, preload changes and long-term
load history (Gillebert et al. 2000).
Myocardial relaxation is an important determinant of
diastolic function. It is essentially modulated by the
interaction of afterload with the underlying mechanisms
involved in the decline of [Ca
2+
]
i
to its diastolic levels
(Leite-Moreira and Gillebert 1996; Leite-Moreira et al.
1999b). Quantitative importance of the various mecha-
nisms involved in this process varies amongst animal
species (Hove-Madsen and Bers 1993; Bassani et al.
1994), namely rabbits and rats, as outlined in the Intro-
duction. Relaxation rate, as assessed by dP/dt
min
and s,
seems to be highly dependent of SERCA2a activity as
previously demonstrated either in a transgenic mouse line
overexpressing SERCA2a (He et al. 1997) and NCX
knockout mice (Yao et al. 1997, 1998). As rat hearts have
significantly higher SERCA2a activity than rabbit hearts
(Negretti et al. 1993; Bassani et al. 1994; Hove-Madsen
and Bers 1993; Lewartowski et al. 1992) we expected
myocardial relaxation to be faster in rats than in rabbits.
Interestingly, the present study showed that, at baseline,
relaxation rate was similar in the two species and that the
Fig. 1A–C Effects of selective afterload elevations on left ventric-
ular (LV) pressure time-courses (A, B) and relaxation rate (C)in
both species. In the A(rabbit) and B(rat), a representative example
of five superposed heartbeats with increasing afterloads are
displayed. In contrast to rat, in rabbits diastolic LV pressures at
the end of highly afterloaded heartbeats were significantly higher
than end-diastolic (ED) LV pressures at the beginning of the
cardiac cycles. In C, relaxation rate was assessed with the fractional
changes in the time constant s(s
test
/s
control
). In rats, afterload
elevations elicited acceleration of myocardial relaxation with
transition from acceleration to deceleration occurring at a relative
load of 97–100%. In rabbits, acceleration of myocardial relaxation
was evident only from control to 70% relative load (s
test
/s
control
<1), whereas afterload elevations reaching or exceeding a relative
load of 80% progressively decreased relaxation rate (s
test
/s
control
>1). In rabbits, transition from acceleration to deceleration
occurred at a relative load of 73–76%. In Cresults are
mean±SEM. Significant differences between animal species,
P<0.05: rabbit versus rat. Significant differences between
afterload levels, P<0.05: * versus control; § versus 70%; –versus
80%; # versus 90%
b
404
differences only became manifest in response to an
afterload challenge. Indeed, rabbit hearts revealed lower
afterload reserve of diastolic function than rats.
Afterload reserve of diastolic function was previously
defined on the basis of the response of rate of pressure
fall and position of the diastolic pressure-volume rela-
tion to acute beat-to-beat afterload elevations. As
already described in previous studies, this response was
biphasic in dogs (Leite-Moreira and Gillebert 1994) and
rabbits (Leite-Moreira et al. 1999a; Leite-Moreira and
Correia-Pinto 2001). In both these species, smaller
afterload elevations, up to a relative load of 81–84% in
dogs (Leite-Moreira and Gillebert 1994), and 73–76% in
rabbits (Leite-Moreira et al. 1999a, Leite-Moreira and
Correia-Pinto 2001), accelerated LV relaxation rate and
did not affect the LV end-diastolic pressure-volume
relation, indicating a compensatory response and the
presence of afterload reserve of diastolic function. On
the contrary, afterload elevations exceeding those rela-
tive loads markedly slowed LV relaxation rate and
shifted the end-diastolic pressure-volume relation
upwards. This traduces a decompensatory response,
indicating that afterload reserve of diastolic function has
exhausted. The present study confirmed the results pre-
viously observed in rabbits but showed that rat hearts
respond to afterload elevations in a compensatory way
almost during the entire range of afterloads between
control and isovolumetric beats.
Decompensatory response was either not observed,
or present only in isovolumetric and beats very close
to isovolumetric. Transition from compensation to
decompensation could be estimated in rats at a relative
load of 97-100%. These findings nicely fit our hypothesis
of a relation between this transition that determines
afterload reserve of diastolic function and SERCA2a
activity, which is significantly higher in rats than in
rabbits. Another potential mechanism for this finding is
the distinct isoform of MHC predominantly expressed
by each of these animal species. In fact, while rat hearts
express predominantly the faster MHC-aisoform
(Meehan et al. 1999), rabbit hearts predominantly ex-
press the slower MHC-bisoform, which has a higher
affinity for Ca
2+
(Reiser and Kline 1998). It should be
remembered, however, that changes in MHC isoforms
have a bigger impact on contraction than on relaxation
(Perez et al. 1999). This could explain why indices of
contractility, such as dP/dt
max
and peak isovolumetric
pressure, were significantly higher in rats than in rabbits,
Fig. 2A–C Effects of afterload elevations on the position of the
diastolic pressure-dimension relation. In A(rabbit) and B(rat), a
representative example of five superposed heartbeats with increas-
ing afterloads are displayed. In contrast to the rat, in the rabbit the
diastolic portion of the pressure-dimension loops was upward
shifted in highly afterloaded heartbeats. In Cthe upward shift of
the diastolic pressure-dimension relation (diastolic dysfunction) is
presented as a function of the relative load either in rats and
rabbits. Significant diastolic dysfunction was observed when
afterload exceeded a relative load of 73–76% in rabbits and
97–100% in rats. In Cresults are mean±SEM. Significant
differences between animal species, P<0.05: rabbit versus Rat.
Significant differences between afterload levels, p<0.05: * versus
Control; § versus 70%; versus 80%; # versus 90%
b
405
while relaxation rate in control beats was similar in the
two animal species.
The observations reported in this study reflect,
therefore, the different expression of regulatory calcium
proteins between studied species. It should be emphas-
ised that calcium regulatory proteins (Tate et al. 1990,
1996) and myosin isoforms (Farrar et al. 1988) are to
some degree dependent on age and previous endurance
performance. In our study this aspect can be excluded
since all animals were instrumented at matched devel-
opmental ages and all animals had similar husbandry
conditions.
Distinct load dependence of relaxation expressed by
rats and rabbits might have a biological relevance. In
fact, if the rat presented a relaxation behaviour similar
to the rabbit, rats would develop serious diastolic
intolerance to increased afterload, because the higher
heart rate of rats means that they have significantly
shorter time available for the ventricle to relax than do
rabbits. This does not happen because the rat’s molec-
ular machinery allows myocardial relaxation to respond
to afterload elevations essentially with acceleration and
not with deceleration as observed in larger animal spe-
cies such as rabbits and dogs. This issue might be par-
ticularly relevant to physiological adaptation to physical
exercise. In fact, we can speculate that given their ele-
vated physiological heart rate, rats will presumably
respond to exercise using preferentially preload reserve
rather than contractility and heart rate augmentation.
This study, therefore, provided evidence that O. cuniculus
has a lower afterload reserve of myocardial relaxation
and diastolic function than R. norvegicus. These data
could have a biological significance since heart rate in
rats is considerably higher than in rabbits. Additionally,
as these are two of the most commonly used animal
species in cardiovascular physiology, the differences de-
scribed in the present study should be taken in account
when drawing conclusions about physiological and/or
Results presented as mean±SEM; rabbits, n=19; rats, n=17
(LVP
max
peak systolic left ventricular pressure; dP/dt
max
,dP/dt
min
peak rates of LVP rise and fall, respectively)
Significant differences between animal species: P<0.05:
a
versus
rabbit
Significant differences between afterload levels P<0.05: *versus
control; §versus 70%; –versus 80%; #versus 90%
Results presented as mean±SEM; rabbits, n=19; rats, n=17
(LVP
ED(pre)
and LVP
ED(post)
end-diastolic left ventricular pressures
at the beginning and at the end of the heartbeat, respectively;
ID
ED(pre)
and ID
ED(post)
end-diastolic internal diameters at the
beginning and the end of the heartbeat, respectively; LVP
min
,
minimal left ventricular pressure; ID at LVP
min
internal diameter at
minimal left ventricular pressure)
Significant differences between animal species, P<0.05:
a
versus
rabbit
Significant differences between afterload levels, P<0.05: *versus
control; §versus 70%; –versus 80%; #versus 90%
Table 1 Effects of afterload on parameters of left ventricular contraction and relaxation
Parameter Species Afterload elevations
Control 70% 80% 90% 100%
LVP
max
(mmHg)
Rabbit 85.6±2.8 102.0±3.1* 116.5±3.8
*, §
132.8±3.5
*, §
145.9±4.6
*, §, #, –
Rat 96.2±4.3 137.6±2.9
a,*
161.8±3.7
a,*, §
179.7±3.9
a,*, §
196.9±4.8
a,*, §, #, –
dP/dt
max
(mmHg/s)
Rabbit 3381±135 3234±134 3124±151 3139±134 3306±169
Rat 5068±343 5104±303
a
5131±290
a
5184±275
a
5247±277
a,#, –
dP/dt
min
(mmHg/s)
Rabbit )2790±136 )2897±110* )2604±107* )2181±93* )1830±95
Rat )3403±343 )3735±235
a
)3972±412
a
)3886±353
a,*, §
)3585±529
a,*, §, –
Time to dP/
dt
min
(ms)
Rabbit 160.3±3.8 161.9±4.7 175.2±5.3 181.2±6.4 187.5±7.2
Rat 108.9±6.7
a
124.4±8.6
a
132.5±8.5
a
140.6±8.6
a
143.6±9.3
a,–
Time constant
s(ms)
Rabbit 18.2±9.8 16.0±1.1 20.2±1.5 30.1±2.7
*, §
44.2±3.3
*, §, #, –
Rat 24.8±2.3 19.3±1.4 18.7±1.6* 20.3±1.8
a
24.9±2.2
a
Table 2 Effects of afterload changes on LV diastolic parameters
Parameter Species Afterload elevations
Control 70% 80% 90% 100%
LVP
ED(pre)
(mmHg) Rabbit 5.6±0.5 5.7±0.6 5.9±0.6 6.3±0.7 6.1±0.7
Rat 7.0±1.3 6.9±1.3 6.9±1.2 7.6±1.2 7.4±1.1
ID
ED(pre)
(mm) Rabbit 12.5±0.7 12.1±0.7 12.0±0.7 12.2±0.7 11.9±0.7
Rat 9.2±0.6
a
9.2±0.6
a
9.3±0.6
a
9.3±0.6
a
10.0±0.6
a
LVP
ED(post)
)LVP
ED(pre)
(mmHg) Rabbit 0.24±0.17 0.16±0.07 1.33±0.27
*, §
2.65±0.4
*, §, –
5.95±0.67
*, §, –,#
Rat )0.32±0.13 0.11±0.08 0.241±0.13
a
0.54±0.17
a
0.72±0.15
a
ID
ED(post)
(mm) Rabbit 12.4±0.7 12.1±0.7 12.1±7.3 12.4±0.7 12.2±0.6
Rat 9.3±0.7
a
9.2±0.6
a
9.2±0.6
a
9.3±0.6
a
9.3±0.6
a
406
pathophysiological observations on relaxation and dia-
stolic function.
Acknowledgements Supported by Portuguese grants from FCT
(PRAXIS/SAU/11301/98; partially funded by FEDER), from
Calouste Gulbenkian Foundation and from Comissa
˜o de Fomento
da Investigac¸ a
˜o em Cuidados de Sau´ de (Ministry of Health),
through Unidade I&D Cardiovascular (51/94-FCT).
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Fig. 3 The upward shift of the diastolic pressure-dimension
relation (diastolic dysfunction) was plotted as function of the
difference between the available and the predicted time for the
ventricle to relax (time deficit) in both species. Results are presented
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