Vascular resistance quantification in high flow resistance areas using the Doppler method

Vascular resistance index and the immediate hemodynamic success of lower limb distal artery revascularization

Background

Revascularization surgery is used to attempt to restore blood flow to the foot in patients with critical ischemia (CI) caused by peripheral arterial occlusive disease of the lower limbs (LL). Ultrasonography with Doppler (USD) SAH emerged in recent years as a highly valuable method for planning this surgical intervention.

Objectives

To evaluate the relationship between the resistance index (RI), measured with USD, and immediate hemodynamic success of LL revascularization surgery in patients with CI.

Methods

The study design was a prospective cohort assessing 46 patients with LL CLI who underwent operations to perform infrainguinal revascularization by angioplasty or bypass from August 2019 to February 2022. All patients underwent preoperative clinical vascular assessment with USD including measurement of the RI of distal LL arteries, LL arteriography, and measurement of the ankle-brachial index (ABI). All patients had their ABI measured again in the immediate postoperative period.

Results

Forty-six patients were assessed, 25 (54.3%) of whom were male. Age varied from 32 to 89 years (mean: 67.83). Hemodynamic success was assessed by comparison of preoperative and postoperative ABI, showing that hemodynamic success was achieved in 31 (67.4%) patients after revascularization surgery (ABI increased by 0.15 or more). A positive correlation (p ≤ 0.05) was observed between the RI of the distal revascularized LL artery and immediate hemodynamic success assessed by ABI (lower RI and hemodynamic success).

Conclusions

This study observed a positive correlation between the resistance index of the distal artery and immediate hemodynamic success of lower limb revascularizations, as assessed by the ankle-brachial index, so that the lower the RI the greater the hemodynamic success achieved.

Exploring the role of a time-efficient MRI assessment of the placenta and fetal brain in uncomplicated pregnancies and these complicated by placental insufficiency

INTRODUCTION

The development of placenta and fetal brain are intricately linked. Placental insufficiency is related to poor neonatal outcomes with impacts on neurodevelopment. This study sought to investigate whether simultaneous fast assessment of placental and fetal brain oxygenation using MRI T2* relaxometry can play a complementary role to US and Doppler US.

METHODS

This study is a retrospective case-control study with uncomplicated pregnancies (n = 99) and cases with placental insufficiency (PI) (n = 49). Participants underwent placental and fetal brain MRI and contemporaneous ultrasound imaging, resulting in quantitative assessment including a combined MRI score called Cerebro-placental-T2*-Ratio (CPTR). This was assessed in comparison with US-derived Cerebro-Placental-Ratio (CPR), placental histopathology, assessed using the Amsterdam criteria [1], and delivery details.

RESULTS

Pplacental and fetal brain T2* decreased with increasing gestational age in both low and high risk pregnancies and were corrected for gestational-age alsosignificantly decreased in PI. Both CPR and CPTR score were significantly correlated with gestational age at delivery for the entire cohort. CPTR was, however, also correlated independently with gestational age at delivery in the PI cohort. It furthermore showed a correlation to birth-weight-centile in healthy controls.

DISCUSSION

This study indicates that MR analysis of the placenta and brain may play a complementary role in the investigation of fetal development. The additional correlation to birth-weight-centile in controls may suggest a role in the determination of placental health even in healthy controls. To our knowledge, this is the first study assessing quantitatively both placental and fetal brain development over gestation in a large cohort of low and high risk pregnancies. Future larger prospective studies will include additional cohorts.

Ultrasound assessments of organs and blood vessels before and after 40 days isolation in a cavern (deep time experiment 2021)

Introduction: Spaceflight simulation studies like confinement in small volume habitat with limited physical activity have reported even after 60 days an abnormal arterial wall adaptation with increase thickness or stiffness. The purpose of the current study was to determine the effects on blood vessel and organ structure of 40 days of isolation in a huge habitat with intensive physical activity. Method: Data were collected from 14 individuals (7 male) who isolated in a cavern for 40-days while performing normal daily activities without time references. Ultrasound assessments were performed pre- and post-isolation using a teleoperated system with eight different acoustic windows to obtain 19 measurements on 12 different organ/vascular structures which included the common carotid artery, femoral artery, tibial artery, jugular vein, portal vein, bile duct, kidney, pancreas, abdominal aorta, cervical and lumbar vertebral distance, and Achilles tendon. Results: Common carotid artery measures, including the intima media thickness, stiffness index, and the index of reflectivity measured from the radiofrequency signal, were not changed with isolation. Similarly, no differences were found for femoral artery measurements or measurements of any of the other organs/vessels assessed. There were no sex differences for any of the assessments. Discussion: Results from this study indicate a lack of physiological effects of 40-days of isolation in a cavern, contrary to what observed in previous 60 days confinement. This suggests a potential protective effect of sustained physical activity, or reduced environmental stress inside the huge volume of the confined facility.

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.

WISE 2005: responses of women to sublingual nitroglycerin before and after 56 days of 6° head-down bed rest

This study tested the hypothesis that cardiovascular effects of sublingual nitroglycerin (NG) would be exaggerated after 56 days of 6° head-down bed rest (HDBR) in women, and that an aerobic and resistive exercise countermeasure (EX, n = 8) would reduce the effect compared with HDBR without exercise (CON, n = 7). Middle cerebral artery maximal blood flow velocity (CBFV), cardiac stroke volume (SV), and superficial femoral artery blood flow (Doppler ultrasound) were recorded at baseline rest and for 5 min following 0.3 mg sublingual NG. Post-HDBR, NG caused greater increases in heart rate (HR) in CON compared with EX (+24.9 ± 7.7 and +18.8 ± 6.6 beats/min, respectively, P < 0.0001). The increase in HR combined with reductions in SV to maintain cardiac output. Systolic, mean, and pulse pressures were reduced 5-10 mmHg by NG, but total peripheral resistance was only slightly reduced at 3 min after NG. Reductions in CBFV of -12.5 ± 3.8 cm/s were seen after NG, but a reduction in the Doppler resistance index suggested dilation of the middle cerebral artery with no differences after HDBR. The femoral artery dilated with NG and blood flow was reduced ∼50% with the appearance of large negative waves suggesting a marked increase in downstream resistance, but there were no effects of HDBR. In general, responses of women to NG were not altered by HDBR; the greater increase in HR in CON but not EX was probably a consequence of cardiovascular deconditioning. These results contrast with the hypothesis and a previous investigation of men after HDBR by revealing no change in cardiovascular responses to exogenous nitric oxide.

Influence of weight bearing and hoof position on Doppler evaluation of lateral palmar digital arteries in healthy horses

OBJECTIVE

To describe the pulsed-wave Doppler tracing of the equine lateral palmar digital artery and its modification in relation to standardized changes in posture.

ANIMALS

17 healthy Saddlebred horses.

PROCEDURES

Pulsed-wave Doppler examinations of left and right lateral palmar digital arteries of the horses were performed. The baseline examination was performed on each forelimb while horses were standing squarely with the body weight equally distributed among the 4 limbs (BED position). For each forelimb, the examination was repeated during 3 standardized modifications of the horse's posture (non-weight-bearing [NWB] position, full weight-bearing [FWB] position, and a position involving hyperextension of the distal interphalangeal joint [HE position]). In each position, mean values of systolic peak velocity, first and second diastolic peak velocity, end-diastolic velocity, mean velocity, and resistive index were calculated. Data obtained in each different posture were compared statistically.

RESULTS

No significant differences in blood flow variables were detected between the left and right forelimbs. However, significant differences were detected in values of first diastolic velocity, second diastolic velocity, mean velocity, and resistive index between the NWB position and FWB position. Also, end-diastolic velocity in the NWB position was significantly different from that recorded in the HE position.

CONCLUSIONS AND CLINICAL RELEVANCE

The pulsed-wave Doppler tracing of the equine lateral palmar digital artery was modified considerably with changes in posture. This suggests that the use of a precisely standardized posture for horses is required to obtain repeatable data.

Uterine artery blood flow velocity waveforms during uterine contractions

OBJECTIVE

No quantitative or qualitative Doppler velocimetry classification of vascular flow resistance covering all stages of forward and reversed flows exists. The objective of this study was to characterize uterine artery (UtA) flow velocity waveforms (FVWs) obtained during an oxytocin challenge test (OCT) and compare them to FVWs in spontaneous normal labor.

METHODS

Uterine artery Doppler velocimetry was performed during and between uterine contractions in 61 high-risk pregnancies subjected to an OCT and in 20 normal pregnancies undergoing spontaneous labor. FVWs were classified relative to the presence of forward/absent/reversed flow during systole and diastole, and the time-averaged flow velocity over the heart cycle.

RESULTS

Eleven different FVW classes were identified. No relationship between FVWs recorded during uterine inertia and contractions was found (P >/= 0.2). In both groups, only forward FVWs were recorded between contractions, whereas during contractions flow reversal was more common in the OCT group (P </= 0.002). In cases of predominantly reversed flow, a reciprocal relationship to FVW classes recorded in the contralateral artery was found.

CONCLUSIONS

UtA FVW patterns recorded during uterine contractions were not predicted by flow patterns recorded during uterine inertia. Reversal of flow direction was more common during oxytocin-induced uterine contractions than during spontaneous contractions. In cases of predominantly reversed flow, domains of the uterus may be supplied by blood from the contralateral UtA. These observations give new insights into the circulatory dynamics of the uterus during labor, and also point to a possible vasoconstrictory effect in the UtAs of oxytocin at high concentrations.

Doppler monitoring of the vascular resistance in the lower limbs during dipyridamole test in preparation for myocardial tomoscintigraphy

OBJECTIVE

the aim of this work was to quantify the intensity of the vasodilation induced by dipyridamole used to simulate a stress test during a myocardial tomoscintigraphy.

METHODS

Doppler measurements of the femoral artery and the thoracic aorta were made on 26 patients (11 men, 15 women), using transducers attached to the skin, measurements being performed every 2 min during the 10 min of the stress test. The following parameters were measured: (a) the vascular resistance index of the lower limbs defined as R(fa)=D/S with S and D, respectively, the maximum amplitude of the systolic wave and the maximum amplitude of the diastolic reflux measured on the Doppler femoral spectrogram; (b) the aortic and femoral blood flows obtained from the mean velocity on the Doppler spectrogram.

RESULTS

14 of the 26 patients (54%) showed a significant vasodilation (i.e. a decrease of R(fa) of more than 10%). Eighty-seven percent of the patients with a positive myocardial scintigraphy showed a vasodilation. Sixty-six percent of patients who had prior vasodilator treatment showed no vasodilation. A slight decrease in blood pressure was observed for vasodilated patients but also for non-vasodilated patients. The aortic flow increased slightly for all patients.

CONCLUSIONS

Doppler monitoring of femoral vascular resistance is a useful method for quantifying the dipyridamole-induced vasodilation, and hence the stress level upon which the diagnostic efficiency of myocardial scintigraphy is depending. Our study demonstrates that testing with dipyridamole was inconclusive in 66% of patients who had already vasodilator treatment.

Influences of thigh cuffs on the cardiovascular system during 7-day head-down bed rest

Thigh cuffs, presently named “bracelets,” consist of two straps fixed to the upper part of each thigh, applying a pressure of 30 mmHg. The objective was to evaluate the cardiac, arterial, and venous changes in a group of subjects in head-down tilt (HDT) for 7 days by using thigh cuffs during the daytime, and in a control group not using cuffs. The cardiovascular parameters were measured by echography and Doppler. Seven days in HDT reduced stroke volume in both groups (−10%; P < 0.05). Lower limb vascular resistance decreased more in the cuff group than in the control group (−29 vs. −4%; P < 0.05). Cerebral resistance increased in the control group only (+6%; P < 0.05). The jugular vein increased (+45%; P < 0.05) and femoral and popliteal veins decreased in cross-sectional area in both groups (−45 and −8%, respectively; P < 0.05). Carotid diameter tended to decrease (−5%; not significant) in both groups. Heart rate, blood pressure, cardiac output, and total resistance did not change significantly. After 8 h with thigh cuffs, the cardiac and arterial parameters had recovered their pre-HDT level except for blood pressure (+6%; P < 0.05). Jugular vein size decreased from the pre-HDT level (−21%; P < 0.05), and femoral and popliteal vein size increased (+110 and +136%, respectively; P < 0.05). The thigh cuffs had no effect on the development of orthostatic intolerance during the 7 days in HDT.

Influences of thigh cuffs on the cardiovascular system during 7-day head-down bed rest

Thigh cuffs, presently named "bracelets," consist of two straps fixed to the upper part of each thigh, applying a pressure of 30 mmHg. The objective was to evaluate the cardiac, arterial, and venous changes in a group of subjects in head-down tilt (HDT) for 7 days by using thigh cuffs during the daytime, and in a control group not using cuffs. The cardiovascular parameters were measured by echography and Doppler. Seven days in HDT reduced stroke volume in both groups (-10%; P < 0.05). Lower limb vascular resistance decreased more in the cuff group than in the control group (-29 vs. -4%; P < 0.05). Cerebral resistance increased in the control group only (+6%; P < 0.05). The jugular vein increased (+45%; P < 0.05) and femoral and popliteal veins decreased in cross-sectional area in both groups (-45 and -8%, respectively; P < 0.05). Carotid diameter tended to decrease (-5%; not significant) in both groups. Heart rate, blood pressure, cardiac output, and total resistance did not change significantly. After 8 h with thigh cuffs, the cardiac and arterial parameters had recovered their pre-HDT level except for blood pressure (+6%; P < 0.05). Jugular vein size decreased from the pre-HDT level (-21%; P < 0.05), and femoral and popliteal vein size increased (+110 and +136%, respectively; P < 0.05). The thigh cuffs had no effect on the development of orthostatic intolerance during the 7 days in HDT.

Cardiovascular echographic and Doppler parameters for the assessment of orthostatic intolerance

OBJECTIVE

To quantify the hemodynamic changes associated with orthostatic intolerance.

METHODS

The aortic flow, the cerebral and lower limb arterial flow and resistance, the flow redistribution between these two areas, and the femoral vein distension were assessed during two orthostatic tests (tilt-up and LBNP:lower body negative pressure) by echography and doppler. Eight subjects stayed 4 days in HDT (head down tilt) in order to induce orthostatic intolerance, and 1 month later, 4 days in confinement. Tilt and LBNP were performed pre- and post-HDT and confinement.

RESULTS

Orthostatic intolerance was significantly more frequent after HDT (63%) than after confinement (25%). At rest, the stroke volume was significantly decreased after HDT (-16%, P<0.01) but not after confinement. Cardiac and cerebral hemodynamic responses to tilt-up and LBNP were similar pre- and post-HDT or confinement. Conversely, during both tilt and LBNP the femoral resistances increased less (P<0.002), and the femoral flow reduced less (P<0.001) after HDT than before HDT or after confinement. The cerebral to femoral flow ratio increased less after HDT than before (P<0.002) but remained unchanged before and after confinement. This ratio was significantly more disturbed on the tilt test non-finisher subjects. The femoral superficial vein was more distended during post-HDT LBNP than pre-HDT or after confinement (IP<0.01). In conclusion, 4 days in HDT were enough to alter the lower limb arterial and venous response to tilt-up and LBNP and reduced the flow redistribution in favor of the brain in all subjects. Confinement did not alter significantly the hemodynamic response to orthostatic tests.

CONCLUSION

The femoral resistance index, and the cerebral to femoral flow ratio measured by doppler during LBNP were the best predictors for orthostatic intolerance.

Doppler sensors and harnesses for cardiac and peripheral arterial flow monitoring

The objective of the present work was to design Doppler sensors and harnesses for monitoring in real time the cardiac stroke volume and output, the cerebral flow volume and resistance and the lower limb arterial flow and resistance changes. For the middle cerebral artery investigation we used a 2-MHz transcranial pulsed wave (PW) Doppler probe (commercial probe) mounted on a rotula, fixed on the horizontal branch of a headset designed like an audio headset. The arch of the headset passed over the top of the skull. For the common carotid investigation, a 4-MHz continuous-wave (CW) or PW flat Doppler probe was inserted in a circular silicone support of 5-cm diameter and 0.6-cm thickness. This soft support could adapt to the irregular surface of the neck, and the silicone material, which is fairly adhesive to the skin, made the system stable. The transducers were preoriented at 45 degrees from the support, which provided an acceptable orientation of the Doppler beam. The aortic Doppler harness consisted of a 2-MHz PW Doppler probe, mounted on a rotula fixed on a plastic rigid support 7 x 1.5 cm2 in area (parallel to the sternum) whose length could be changed (4-7 cm) to localize the rotula and its sensor on the suprasternal area. This flat segment was fixed on a rotating platform, part of a solid square plastic support (10 x 10 cm2) placed on the upper part of the sternum. This system was maintained by elastic bands passing around the shoulder and the chest. The femoral Doppler harness consisted of a 4-MHz CW or PW flat Doppler probe, inserted in a flat and rectangular rigid plastic support 10 x 3 cm2 in area. This rigid support was well adapted to the flat surface of the internal part of the thigh, which made the system stable. Two elastic bands passed around the thigh and the abdomen, which avoided any translation of the support and kept the sensor in contact with the skin. The transducers were preoriented at 45 degrees from the support, which provided an acceptable orientation of the Doppler beam. The whole Doppler monitoring system was successfully tested during orthostatic tests, such as lower body negative pressure or tilt table tests performed in pre and post head-down tilt experiments and space flights, with the objective of assessing and quantifying the cardiac and peripheral arterial hemodynamic changes associated with orthostatic intolerance.

A noninvasive method to estimate arterial impedance by means of assessment of local diameter change and the local center-line blood flow velocity using ultrasound

Vascular impedance is defined as the ratio between the frequency components of the local blood pressure waveform and those of the local blood volume flow waveform. Assessment of vascular impedance is, for example, important to study heart load and distal vascular bed vasomotricity. However, only a few studies on vascular impedance have been performed in humans because pulsatile pressure and volume flow waveforms, simultaneously recorded at the same location, are difficult to obtain noninvasively. The noninvasive assessment of arterial impedance as described in this study is based on the replacement of the pressure waveform by the distension (change in diameter) waveform and the volume flow waveform by the center-line blood flow velocity waveform. Both waveforms can simultaneously and accurately be assessed by means of pulsed ultrasound. It will be shown that, depending on the Womersley number, the volume flow waveform may be replaced by the center-line blood flow velocity waveform for a given frequency range and that the pressure waveform may be replaced by the distension waveform for a wide frequency range. The validation of the proposed ultrasound method was performed through an in vitro study in a flow model with a distensible tube terminated with a hydraulic load (modified windkessel model). It is shown that, in vitro, the proposed method gives the same results as the local spectral pressure-flow relationship.