The issue of pulsatile VADs versus non-pulsatile VADs is definitely controversial. If non-pulsatile VADs can be commercialized, they would have definite advantages over pulsatile devices - they would be smaller, lighter and have fewer moving parts. However, the heart is a pulsatile organ and many question whether a non-pulsatile VAD can ever be commercialized. Should this be possible, WorldHeart believes that the HeartSaver could be converted to a non-pulsatile device.
Here are a few abstracts from technical papers presented on the subject, representing both points of view. When time permits I plan to research it further.
Artif Organs 1997 Aug;21(8):922-928
The importance of pulsatile and nonpulsatile flow in the design of blood pumps.
Allen GS, Murray KD, Olsen DB
Department of Surgery, University of Texas Health Science Center, Houston, USA.
The traditional approach of total artificial heart (TAH) and ventricular assist device (VAD) development has been the
mimicking of the native heart. Nonpulsatile flow using cardiopulmonary bypass has provided evidence of short-term
physiologic tolerances. The design of nonpulsatile TAHs and VADs has eliminated the need for valves, flexing diaphragms, and
large ventricular volumes. However, these devices require high efficiency power sources and reliable bearing seals or
electromagnetic bearings while simultaneously attempting to avoid thromboemboli. The physiologic response to nonpulsatile
flow is complex and variable. When compared to a pulsatile device, a nonpulsatile TAH or VAD needs to produce increased
flow and higher mean intravascular pressures to maintain normal organ function. Despite its maintaining normal organ function,
nonpulsatile flow does cause alterations in biochemical functions and organ specific blood flow. The combination of
bioengineering superiority and the maintenance of physiologic homeostasis has directed future TAH and VAD research
towards nonpulsatile systems.
Publication Types:
Review
Review, tutorial
PMID: 9247182, UI: 97388348
Artif Organs 1996 Jun;20(6):467-474
Can we develop a nonpulsatile permanent rotary blood pump? Yes, we
can.
Nose Y, Kawahito K, Nakazawa T
Baylor College of Medicine, Department of Surgery, Houston, Texas 77030, USA.
For many years, it was thought that nonpulsatile perfusion produced physiological and circulatory abnormalities. Since 1977,
Yukihiko Nose and his colleagues have challenged this misconception. Toward that end, they did show that if a 20% higher
blood flow uses more than that required for a pulsatile blood pump, then there would be no circulatory of physiological
abnormalities. These experimental findings confirm that there is no difference in clinical outcome using either a pulsatile or
nonpulsatile blood pump. Furthermore, the nonpulsatile rotary blood pump demonstrates efficient and reliable performance in
various clinical situations. The nonpulsatile blood pump is a simple and reliable design that is manufactured easily and that has
several desirable features. There is no need to incorporate heart valves, which are the most thrombogenic and blood
trauma-inducing components. A continuous flow pump does not require a large orifice inflow conduit and proves to be easier
to implant in patients with minimal damage to the myocardium. There is no need to incorporate a compliance volume-shifting
device, which is essential for a pulsatile blood pump. The nonpulsatile device is a continuous blood pumping system; therefore,
the control system is simpler and more reliable than that of a pulsatile pump. Because of the rotary blood pump's structure,
only one moving part is necessary for the blood-pumping motion. By using durable components for this moving part, a durable
system becomes possible. Because the electrical motor operates continuously, the on-and-off motion required for a pulsatile
pump is not necessary; therefore, it is a more efficient and durable system. Thus, this group is working on the development of a
nonpulsatile blood pump as a permanently implantable assist device. To achieve this goal, it is necessary to incorporate seven
features into the system: small size, atraumatic features, antithrombogenic features, antiinfection features, a simple and durable design, and low energy requirement with easy controllability.
Publication Types:
Historical article
Review
Review, tutorial
PMID: 8817941, UI: 96414940
Eur J Cardiothorac Surg 1997 Apr;11 Suppl:S32-S38
Development of a non-pulsatile permanent rotary blood pump.
Nose Y, Kawahito K
Baylor College of Medicine, Department of Surgery, Houston, TX 77030, USA.
For many years, a common belief was that non-pulsatile perfusion produced physiological and circulatory abnormalities. Since
1977 our group has reported, if a 20% higher blood flow was used more than required for a pulsatile blood pump, there
would be no circulatory or physiological abnormalities. These experimental findings confirmed that there was no difference in
clinical outcome when using a pulsatile or non-pulsatile blood pump. Furthermore, the non-pulsatile rotary blood pump has
demonstrated efficient and reliable performance in various clinical situations. The non-pulsatile blood pump is a simple and
reliable design, that can be easily manufactured, and has the following desirable features. There is no need to incorporate heart
valves, a large orifice inflow conduit, or a compliance volume-shifting chamber. Since an electrical motor operates
continuously, the on-and-off motion required for a pulsatile pump is not necessary; therefore, it becomes a more efficient and
durable system. Further, the control algorism is simpler and more reliable than a pulsatile pump. Considering these factors, the
non-pulsatile blood pump can be selected for a permanently implantable assist device. To develop an implantable non-pulsatile
cardiac device, it is necessary to incorporate seven features in the system such as: small size, atraumatic features,
anti-thrombogenic features, anti-infection features, durable and simple design, and low energy requirement with easy
controllability.
PMID: 9271179, UI: 97415380
Artif Organs 1996 Feb;20(2):139-142
Comparison studies of major organ microcirculations under pulsatile- and
nonpulsatile-assisted circulations.
Sezai A, Shiono M, Orime Y, Nakata K, Hata M, Nemoto M, Saitoh T, Sezai Y
Second Department of Surgery, Nihon University School of Medicine, Tokyo, Japan.
In these comparison studies, we examined changes in major organ microcirculations during circulatory support using pulsatile
and nonpulsatile pumps. Acute myocardial infarction was created by left anterior descending (LAD) branch ligation. After the
animals in these studies fell into cardiogenic shock, they were supported by mechanical assist devices: a pulsatile ventricular
assist device (VAD) in 4 pigs, a nonpulsatile VAD in 4 pigs, and an intraaortic balloon pumping (IABP) plus nonpulsatile VAD
in 4 pigs. Each group was supported for 3 h with an identical mean aortic pressure being maintained. As for parameters, the
stomach mucosa, liver regional blood flow, stomach mucosal pH, and arterial blood keton body ratio (AKBR) were
measured. Both regional blood flow and AKBR increased in the pulsatile group as compared with the nonpulsatile group.
There were no differences in the stomach mucosal pH among the 3 groups. These results suggest that pulsatile assist rather
than the nonpulsatile assist plays a significant role in the recovery of deteriorated splanchnic organs due to cardiogenic shock.
PMID: 8712958, UI: 96282124
J Thorac Cardiovasc Surg 1996 Feb;111(2):478-484
The effects of pulsatile and nonpulsatile systemic perfusion on renal
sympathetic nerve activity in anesthetized dogs.
Fukae K, Tominaga R, Tokunaga S, Kawachi Y, Imaizumi T, Yasui H
Division of Cardiovascular Surgery, Faculty of Medicine, Kyushu University, Fukuoka, Japan.
It is still controversial whether to pulse or not to pulse for the establishment of ideal extracorporeal circulation. We directly
measured the renal sympathetic nerve activity in mongrel dogs (n = 10, weighing from 13 to 21 kg) to determine the effects of
pulsatile and nonpulsatile systemic perfusion on the control of the sympathetic nerve activity during left ventricular assistance.
Pulsatile perfusion was generated with an air-driven, diaphragm-type blood pump, and nonpulsatile perfusion was generated
with a centrifugal pump. Renal sympathetic nerve activity and the blood flow of the descending aorta were then recorded
during pulsatile and nonpulsatile systemic perfusion. Other variables, such as mean arterial pressure, central venous pressure,
left atrial pressure, and blood gas levels, were kept constant. At the same mean arterial pressure, renal sympathetic nerve
activity during pulsatile perfusion decreased significantly to 80% of renal sympathetic nerve activity during nonpulsatile
perfusion (26.8 +/- 2.4 vs 33.4 +/- 2.9 spikes/sec, p < 0.01). Total systemic vascular resistance during pulsatile perfusion
decreased significantly to 85% of that during nonpulsatile perfusion (5700 +/- 580 vs 6667 +/- 709 dynes.sec.cm-5, p <
0.05). These results suggest that pulsatile systemic perfusion, compared with nonpulsatile systemic perfusion, reduces
sympathetic nerve activity and peripheral vascular resistance and thus may improve both microcirculation and organ function.
PMID: 8583823, UI: 96160837
Artif Organs 1996 Jun;20(6):681-684
Effect of pulsatile and nonpulsatile assist on heart and kidney
microcirculation with cardiogenic shock.
Nakata K, Shiono M, Orime Y, Hata M, Sezai A, Saitoh T, Sezai Y
Second Department of Surgery, nihon University School of Medicine, Tokyo, Japan.
To estimate microcirculation of the heart and kidney in pulsatile and nonpulsatile-assisted circulation, a comparison study was
done using a swine model. Acute myocardial infarction was made by ligation of the left coronary artery branches. After
cardiogenic shock, animals were divided into 3 groups as follows: Group C (n = 6), no assist provided; Group NP (n = 6),
assisted by a nonpulsatile pump (Bio-Medicus BP-80); Group P (n = 6), supported by a pulsatile pump (Nippon Zeon). left
coronary artery flow, endocardial and epicardial regional flows, and renal cortex and medulla tissue blood flows were
measured. Left coronary artery flow and endocardial and epicardial tissue blood flows decreased in cardiogenic shock, and
they recovered to the control level soon after support in both Group N and Group P. Renal medulla and cortex tissue blood
flows decreased in cardiogenic shock, and these flows did not recover in either Group N or P. However, cortex blood flow in
Group P did improve, but it did not improve in Group N. These results suggested that pulsatile assist was more effective than
nonpulsatile assist for microcirculation after cardiogenic shock to avoid deterioration of major organ functions.
PMID: 8817977, UI: 96414976
Microvasc Res 1994 Nov;48(3):316-327
Evaluation of pulsatile and nonpulsatile flow in capillaries of goat skeletal
muscle using intravital microscopy.
Lee JJ, Tyml K, Menkis AH, Novick RJ, Mckenzie FN
Division of Cardiovascular-Thoracic Surgery, University Hospital, London, Ontario, Canada.
It is commonly believed that pulsatile flow generated by the pumping action of the heart is dampened out by the time it reaches
the microcirculation. In clinical practice, most of the cardiopulmonary bypass pumps and ventricular assist devices are
nonpulsatile. To test the hypothesis that pulsatile flow generated by the heart does exist at the microvascular level, intravital
microscopy of a large animal model (goat) was developed to visualize and to videorecord the surface microcirculation of the
flexor carpi ulnaris muscle from the right forelimb. Density of perfused capillaries and red blood cell velocity in capillaries were
measured in five goats during pulsatile perfusion provided by the heart and during a subsequent 3-hr period of nonpulsatile
perfusion provided by a centrifugal ventricular assist device (Centrimed, Sarns 3M) that bypassed the heart. Throughout the
experiment, the heart rate, innominate artery mean blood pressure, and flow remained unchanged. During the pulsatile regimen,
velocities showed regular fluctuations that coincided with the period of the cardiac cycle (range of periods: 0.5-0.8 sec). The
peak velocity amplitudes (range: 0.25-0.55 mm/sec) correlated directly with the amplitude of the pulse pressure. During the
nonpulsatile regimen, no such correlations were seen. During pulsatile flow and during the 3-hr nonpulsatile period, capillary
density remained stable at 24 capillaries/mm of test line but there were significant increases in red cell velocity, from 0.8 to 1.2
mm/sec (P < 0.05), and in coefficient of variation of velocity (used as an index of flow heterogeneity), from 19 to 34% (P <
0.05). We conclude that (1) pulsatility exists in the capillary bed and that it directly correlates with the pumping action of the
heart and (2) nonpulsatile flow produced by the ventricular assist device does not cause an acute deterioration in microvascular
perfusion. We interpret the increase in heterogeneity of flow as an early sign of microvascular dysfunction. Prolonged use of the
nonpulsatile device may, therefore, lead to deterioration in perfusion that could compromize the function of the organ.
PMID: 7731396, UI: 95248912 |
