Evaluation of transcutaneous Doppler ultrasonography for the measurement of blood flow in the femoral artery of pigs

Evaluation of a new model of hind limb ischemia in rabbits

OBJECTIVE

Various animal models of critical limb ischemia have been developed in the past. However, there is no animal model that can undergo endovascular treatment, while providing reproducible true critical limb ischemia with arterial ulcers and rest pain. We evaluated the efficacy of a new model of rabbit hindlimb ischemia created through a percutaneous approach using embolization with calibrated particles.

METHODS

Through a percutaneous transauricular artery approach and selective catheterization of the superficial femoral artery, embolization of distal limb vessels was performed using a mixture of 300- to 500-μm calibrated microparticles (Embosphere, Merit Medical, Salt Lake City, Utah), saline solution, and iodine contrast. Clinical and ultrasound imaging-based blood flow evaluation was performed before embolization and during follow-up. Histologic evaluation was performed at humane killing 14 days after the procedure.

RESULTS

The model was successfully created in 10 rabbits (10 limbs). One rabbit died of sudden death at 8 days after the procedure. The nine surviving rabbits developed hind ulcers. All rabbits had a higher pain score in the follow-up compared to baseline value (P < .0001). Blood flow in the saphenous artery decreased significantly after the procedure and later at 14 days follow-up (baseline value 63.4 ± 31.3 μL per cardiac cycle vs 32.0 ± 28.4 μL per cardiac cycle postprocedure [P = .0013] and 32.0 ± 28.4 μL per cardiac cycle at 14 days [P = .0015]). Pathology showed signs of severe limb ischemia in all rabbits with subacute and chronic injury patterns.

CONCLUSIONS

A rabbit hind limb ischemia model created by percutaneous transauricular distal femoral artery embolization with calibrated particles may overcome some of the limitations of existing animal models. As such, this model could prove useful for assessing therapies designed to improve arterial perfusion and collateral growth.

Spectral analysis of femoral artery blood flow waveforms of conscious domestic cats

The qualitative and quantitative aspects of femoral artery blood flow waveform spectra were evaluated in 15 male and 15 female Persian and mixed breed domestic cats (Felis catus), which were healthy and not sedated, using duplex Doppler ultrasonography (DDU). Spectral Doppler demonstrated a biphasic characteristic in 16 (53.34%) of the animals evaluated, and a triphasic characteristic in the 14 (46.66%) remaining animals. The systolic blood pressure and heart rate values were within the normal range for the species. The quantitative parameters evaluated, based on the spectral Doppler, were as follows: systolic velocity peak (SVP), recent diastolic velocity peak (RDVP), end diastolic velocity peak (EDVP), mean velocity (MV), integral velocity time (ITV), artery diameter (AD), femoral flow volume (FFV), pulsatility index (PI), resistive index (RI), systolic peak acceleration time (AT) and deceleration time (DT). The respective mean values were: 36.41 ± 7.33 cm/s, 4.69 ± 0.90 cm/s, 10.74 ± 2.74 cm/s, 23.06 ± 4.86 cm/s, 3.91 ± 1.05 cm, 0.17 ± 0.04 cm, 0.11 ± 0.08 cm(3), 3.85 ± 0.19, 1.40 ± 0.20, 39.84 ± 7.38 ms, and 114.0 ± 22.15 ms. No significant differences were found between males and females. The analyses carried out on the femoral artery flow spectrum obtained by DDU showed that it is easy to use and highly tolerated in non-sedated, healthy cats. It appears that DDU may be a useful diagnostic technique, but further studies are needed to evaluate how it compares with invasive telemetric methodology or high-definition oscillometric waveform analytic techniques.

Muscular arterial impedance in dogs with chronic degenerative mitral valve disease

Systemic vascular impedance represents the retrograde strength of the blood flow to the left ventricle, thus it is one of the main compounds of afterload. Mitral regurgitation is markedly sensitive to afterload alterations. The purpose of this study was to evaluate muscular arterial impedance in dogs with chronic degenerative mitral valve disease (CDMVD) by use of duplex Doppler ultrasonography (DDU), since its technique there was not used before to determine impedance index in dogs with CDMVD. For this purpose, ten healthy dogs and ten dogs with CDMVD were used. Some parameters related to blood flow impedance in the common femoral artery were measured by DDU: pulsatility index (PI), resistance index (RI), high-resistance index (HRI), and acceleration velocity (AC) and deceleration velocity (DC) of the systolic peak. The results showed that RI and HRI were significantly higher in animals with CDMVD than in healthy animals. These findings showed that DDU provides quantitative data related to vascular impedance. Broader studies may therefore provide new aspects related to physiopathology and therapy in CDMVD patients.

Effects of sedation with acepromazine maleate and buprenorphine hydrochloride on femoral artery blood flow in healthy dogs

The purpose of this study was to qualify and quantify the femoral artery blood flow by duplex Doppler ultrasonography (DDU) in healthy dogs, before and after the administration of a combination of acepromazine maleate and buprenorphine hydrochloride (ACP-BPN). Seven healthy adult mongrel dogs and three adult beagles were used. Heart rate, arterial blood pressure and measurement of femoral artery blood flow by DDU were also recorded. The DDU measurements were: femoral artery diameter (FAD), peak systolic velocity (PSV), early retrograde (EDV) and end diastolic velocities (EnDV), mean velocity (BMV), pulsatility index (PI), flow velocity integral (FVI) and femoral blood flow (FBF). After 30 min, combination ACP-BPN was administered intramuscularly, and all the measurements were recorded again. The ACP-BPN protocol induced a significant decrease in systolic, mean, and diastolic arterial blood pressure, and heart rate. A significant increase in peak systolic velocity and integral flow velocity integral of the femoral blood were obtained. The Doppler spectra of the blood flow in the femoral artery revealed a spectral dispersion pattern after ACP-BPN administration in all the dogs. These results demonstrate that despite quantitative and qualitative changes, the overall femoral blood flow (FBF) is not significantly modified.

Alterations in the large peripheral circulation in dogs with heart failure

The femoral artery is responsible for perfusion of a large muscular region that can be involved in the exercise intolerance shown by dogs with spontaneous heart failure. The objective of the present study was to evaluate blood flow in the femoral artery by transcutaneous duplex Doppler ultrasonography (TDU) in 50 healthy dogs and 50 dogs with spontaneous heart failure. The group of dogs with heart disease was divided according to the functional class of the heart failure. The TDU measurements were: peak systolic velocity (PSV), early retrograde (EDV) and end diastolic velocities (EnDV), mean velocity (MV), pulsatility index (PI), resistivity index (RI) and femoral flow volume (FFV). In healthy dogs, PSV and FFV were significantly higher than in dogs with heart disease. FFV was reduced mainly in patients with moderate and severe heart failure. TDU allowed for non-invasive detection and quantification of pathological alterations in peripheral hemodynamics.

Evaluation of aging on muscle blood flow in conscious healthy dogs by duplex Doppler ultrasonography

According to a study conducted on a population of 9,248 subjects, cardiac diseases are the second most prevalent cause of death in the dog. During the last decades, a common scenario has been the increase on life expectancy of dogs. The exact relationship between the negative modifications of cardiovascular function and the development of specific cardiovascular diseases is difficult to ascertain, and also, the effect of age per se on vascular impedance is important. It may result in limited cardiovascular reserve under conditions of increase demand in senescent animals. To evaluate the effect of age on the peripheral vasculature specifically, the objective of this study was to compare parameters of the regional blood flow as well as compliance and resistance indexes in the femoral arterial system of younger and older conscious healthy dogs by duplex Doppler ultrasonography. The data were collected from 16 mixed-breed dogs divided into two groups: young and old healthy dogs. In all dogs Doppler spectra blood flow patterns of the femoral artery were triphasic. Significant differences were not found between the parameters measured for young and old groups. Despite this, the average value of femoral flow volume in the older group was approximately 50% lower than the younger group. This finding could play an important role in limiting exercise response with age. In order to validate these speculations, further studies should be performed in aged dogs.

Evaluation of Doppler ultrasonography for the measurement of blood flow in young loggerhead sea turtles (Caretta caretta)

The aim of this study was to identify ultrasound accessible blood vessels in the loggerhead sea turtle (Caretta caretta) and describe their Doppler waveform patterns, peak systolic velocity, mean velocity, systolic/diastolic ratio as well as pulsatility and resistive indices. B-mode, colour and pulsed-wave Doppler examinations were performed on 10 turtles. Flow measurements were recorded for the left and right aorta, epigastric and internal iliac arteries, and right hepatic vein. Additionally, the large blood vessels of three dead turtles were injected with latex and dissected for anatomical support. A parabolic flow velocity profile was observed in all arteries. The waveforms of the right and left aortic arteries showed an unusual pattern when compared with mammals. The hepatic vein flow velocity waveform of the loggerhead sea turtle was found to be similar to that in the dog, although the flow velocity in the C-wave was higher than that in the A-wave. The low resistance flow pattern observed suggests that the loggerhead sea turtle's organs require a continuous blood supply.

Use of a flow-mediated vasodilation technique to assess endothelial function in dogs

OBJECTIVE

To develop and assess the reproducibility of a protocol to noninvasively test endothelial function in dogs on the basis of the flow-mediated vasodilation (FMD) procedure used in humans.

ANIMALS

5 healthy spayed female dogs.

PROCEDURES

Luminal arterial diameter and blood flow velocity in the brachial and femoral arteries were measured with ultrasonography. The within-dog reproducibility of these ultrasonographic measurements was tested. An occlusion period of 1, 3, or 5 minutes with an inflatable cuff was used to create the FMD response. Measurements made at 15, 30, and 60 seconds following release of the occlusion were compared with measurements made immediately prior to each occlusion to assess the FMD response.

RESULTS

Within-dog reproducibility of measurements revealed moderate to high correlations. Change from baseline in luminal arterial diameter was most substantial when measured at 30 seconds following release of occlusion, whereas blood flow velocity changes were maximal when measured at 15 seconds following release. The brachial imaging site provided a larger number of significant FMD responses than the femoral site. The 3-minute occlusion period provided equal or better responses than the 5-minute occlusion period.

CONCLUSIONS AND CLINICAL RELEVANCE

Ultrasonographic measurement of the FMD responses was a feasible and reproducible technique and significant changes from baseline were detected. The FMD responses in dogs were most substantial when performed at the brachial artery with blood flow velocity and luminal arterial diameter changes from baseline measured at 15 and 30 seconds, respectively, following release of a 3-minute occlusion period.

Exercise training improves femoral artery blood flow responses to endothelium-dependent dilators in hypercholesterolemic pigs

We tested two hypotheses: 1) that the effects of hypercholesterolemia on endothelial function in femoral arteries exceed those reported in brachial arteries and 2) that exercise (Ex) training enhances endothelium-dependent dilation and improves femoral artery blood flow (FABF) in hypercholesterolemic pigs. Adult male pigs were fed a normal fat (NF) or high-fat/cholesterol (HF) diet for 20 wk. Four weeks after the diet was initiated, pigs were Ex trained or remained sedentary (Sed) for 16 wk, thus yielding four groups: NF-Sed, NF-Ex, HF-Sed, and HF-Ex. Endothelium-dependent vasodilator responses were assessed in vivo by measuring changes in FABF after intra-arterial injections of ADP and bradykinin (BK). Endothelium-dependent and -independent relaxation was assessed in vitro by measuring relaxation responses to BK and sodium nitroprusside (SNP). FABF increased in response to ADP and BK in all groups. FABF responses to ADP and BK were not impaired by HF but were improved by Ex in HF pigs. BK- and SNP-induced relaxation of femoral artery rings was not altered by HF or Ex. To determine whether the mechanism(s) for vasorelaxation of femoral arteries was altered by HF or Ex, BK-induced relaxation was assessed in vitro in the absence or presence of N(G)-nitro-l-arginine methyl ester [l-NAME; to inhibit nitric oxide synthase (NOS)], indomethacin (Indo; to inhibit cyclooxygenase), or l-NAME + Indo. BK-induced relaxation was inhibited by l-NAME and l-NAME + Indo in all groups of femoral arteries. Ex increased the NOS-dependent component of endothelium-dependent relaxation in NF (not HF) arteries. Indo did not inhibit BK-induced relaxation. Collectively, these results indicate that hypercholesterolemia does not alter endothelial function in femoral arteries and that Ex training improves FABF responses to ADP and BK; however, the improvement cannot be attributed to enhanced endothelial function in HF femoral arteries. These data suggest that Ex-induced improvements in FABF in HF arteries are mediated by vascular adaptations in arteries/arterioles downstream from the femoral artery.