Effect of age, cardiovascular disease, and vasomotor changes on transmission of arterial pressure waves through the lower extremities

Endothelium function dependence of acute changes in pulse wave velocity and flow-mediated slowing

Flow-mediated slowing (FMS), defined as the minimum pulse wave velocity (PWVmin) during reactive hyperemia, is potentially a simple, user-objective test for examining endothelial function. The purpose of the current study was to determine the effects of a known endothelial dysfunction protocol on arm PWV and PWVmin. Complete data were successfully collected in 22 out of 23 healthy adults (23.8 years [SD 4.1], 16 F, 22.8 kg/m2 [SD 2.8]). Local endothelial dysfunction was induced by increasing retrograde shear stress in the upper arm, through inflation of a distal (forearm) tourniquet to 75 mmHg, for 30 min. Pre- and post-endothelial dysfunction, PWV was measured followed by simultaneous assessment of PWVmin and flow-mediated dilation (FMD). PWV was measured between the upper arm and wrist using an oscillometric device, and brachial FMD using ultrasound. FMD (%) and PWVmin (m/s) were calculated as the maximum increase in diameter and minimum PWV during reactive hyperemia, respectively. Endothelial dysfunction resulted in a large effect size (ES) decrease in FMD (∆ = -3.10%; 95% CI: -4.15, -2.05; ES = -1.3), and a moderate increase in PWV (∆ = 0.38 m/s; 95% CI: 0.07, 0.69; ES = 0.5) and PWVmin (∆ = 0.16 m/s; 95% CI: 0.05, 0.28; ES = 0.6). There was a large intra-individual (pre- vs post-endothelial dysfunction) association between FMD and PWVmin (r = -0.61; 95% CI: -0.82, -0.24). In conclusion, acute change in PWV and PWVmin are at least partially driven by changes in endothelial function.

Velocity acceleration as a determinant of flow-mediated dilation

Shear stress is the established stimulus for flow-mediated dilation (FMD). In vivo, shear stress is typically estimated using mean blood velocity. However, mean blood velocity may not adequately characterize the shear stimulus. Pulsatile flow results in large shear gradients (velocity acceleration) at the onset of flow. The purpose of this study was to determine the importance of velocity acceleration to FMD. We define FMD as the brachial artery shear rate-diameter slope. Fourteen physically active, young (26 ± 5 years), male subjects were tested. Progressive forearm heating and handgrip exercise elicited steady-state increases in shear rate. FMD was measured prior to and following induced increases in velocity acceleration. Velocity acceleration was increased by inflating a tourniquet around the forearm to 40 mm Hg. Hierarchical linear modeling was used to estimate change in diameter with repeated measures of shear stress nested within each subject. Averaged across conditions, the 40 mm Hg cuff resulted in a 14% increase in velocity acceleration (p = 0.001). FMD was attenuated by 11.0% (p = 0.015) for the acceleration vs. control condition. However, after specifying velocity acceleration as a covariate, FMD was no longer significantly (p = 0.619) different between acceleration and control conditions. This finding suggests that mean blood velocity alone may not adequately characterize the shear stimulus.

Exercise ankle brachial index adds important prognostic information on long-term out-come only in patients with a normal resting ankle brachial index

BACKGROUND

The clinical value of exercise ankle brachial index (ABI) is still unclear, especially in patients with normal resting ABI.

METHOD

2164 patients performed a single-stage treadmill exercise test to diagnose or evaluate PAD. The population was divided into two groups: a normal resting ABI (resting ABI≥0.90) and PAD (resting ABI<0.90). Patients with a normal resting ABI were divided into 4 exercise ABI groups: exercise ABI<0.90, 0.90-0.99, 1.00-1.09 and 1.10-1.29 (reference).

RESULTS

Mean follow-up was 5 years. Exercise ABI added significant prognostic information on all cause long-term mortality only in patients with normal resting ABI (p-value 0.014, HR 0.99 95% CI (0.98-0.99)), not in patients with PAD. Fifty years or older (OR 2.93 95% CI (1.65-5.20)) and resting systolic blood pressure>140 mmHg (OR 2.18 95% CI (1.35-3.55)) were associated with an abnormal exercise ABI in patients with a normal resting ABI. Mortality rate increased when the exercise ABI became worse (p trend 0.0001) with a 2.5-fold increase mortality risk in patients with a normal resting ABI but exercise ABI <0.90 (HR 2.56, 95% CI (1.11-5.91)).

CONCLUSION

In patients with a normal resting ABI, treadmill exercise ABI added important prognostic information on long-term mortality. Based on our results we recommend that at least all patients suspected for PAD, with a resting ABI≥0.90, who are 50 years or older and having hypertension should undergo treadmill exercise testing.

Low-dose sodium nitrite vasodilates hypoxic human pulmonary vasculature by a means that is not dependent on a simultaneous elevation in plasma nitrite

Inorganic nitrite has recently been recognized to possess vascular activity that is enhanced in hypoxia. This has been demonstrated in humans in the forearm vascular bed. In animal models nitrite reduces pulmonary vascular resistance, but its effects upon the pulmonary circulation of humans have not yet been demonstrated. This paradigm is of particular interest mechanistically since the pulmonary vasculature is known to behave differently to the systemic. To investigate, 18 healthy volunteers were studied in a hypoxic chamber (inspired oxygen, 12%) or while breathing room air. Each received an infusion of sodium nitrite (1 micromol/min) or 0.9% saline. Three protocols were performed: nitrite/hypoxia (n = 12), saline/hypoxia (n = 6), and nitrite/normoxia (n = 6). Venous blood was sampled for plasma nitrite, forearm blood flow was measured by strain-gauge plethysmography, and pulmonary arterial pressure was measured by transthoracic echocardiography. Plasma nitrite doubled and clearance kinetics were similar whether nitrite was infused in hypoxia or normoxia. During hypoxia, nitrite increased forearm blood flow (+36%, P < 0.001) and reduced three separate indirect indexes of pulmonary arterial pressure by 16%, 12%, and 17% (P < 0.01). Pulmonary, but not systemic, arterial effects persisted 1 h after stopping the infusion, at a time when plasma nitrite had returned to baseline. No effects were observed during normoxia. Therefore, in hypoxic but not normoxic subjects, sodium nitrite causes arterial and pulmonary vasodilatation. In addition, hypoxia-induced pulmonary vasoconstriction was attenuated for a prolonged period and not dependent on a simultaneous elevation of plasma nitrite. This finding is consistent with the direct extravascular metabolism of nitrite to nitric oxide to effect hypoxia-associated bioactivity.

Year in review 2006: Critical Care--Cardiology

This review summarizes key research papers published in the fields of cardiology and intensive care during 2006 in Critical Care and, where relevant, in other journals within the field. The papers have been grouped into categories: haemodynamic monitoring, vascular access in intensive care, microvascular assessment and manipulation, and impact of metabolic acidosis on outcome.

Abdominal vascular sonography

This is an introductory article on abdominal vascular ultrasound in dogs. An overview of the hemodynamics of venous and arterial blood flow and Doppler principles, spectral analysis, and velocity waveforms is given. The anatomic and Doppler features of major abdominal vessels that can be examined routinely with ultrasonography are discussed. Select cases of vascular pathology affecting various abdominal vessels in the dog and cat are described.

The correlation of ankle oscillometric blood pressures and segmental pulse volumes to Doppler systolic pressures in arterial occlusive disease

PURPOSE

This study was designed to evaluate the accuracy and failure rates of automatically collected oscillometric ankle systolic pressures (Psys) and pulse volumes (Pvol) using a new algorithm as compared with Psys obtained by standard manual Doppler-and-cuff technique.

METHODS

One hundred ten consecutive patients at a vascular laboratory had brachial and ankle Psys measured with the two methods. Pvol at or near the mean arterial pressure was also obtained automatically by the oscillometric device.

RESULTS

Both methods showed a 6.6% failure rate when measuring Psys at the ankle. Oscillometric Psys measurement was possible when Doppler Psys failed as a result of nonoccluding arteries. No difference was found between the two methods in occluding limbs with ankle-brachial indexes of 1.30 or more. Sequential brachial Psys values had a mean difference (Doppler-oscillometric) or 2 +/- 10.9 mm Hg and a correlation coefficient (r) of 0.92. Measurements at the ankle had a mean difference of -8.4 +/- 16.8 mm Hg and r = 0.90. These differences were not statistically significant. Mean arterial pressure Pvol recorded at the ankle also correlated with ankle Doppler Psys (r = 0.71) and showed a 1.9% failure rate.

CONCLUSION

Both automatic oscillometric plethysmographic Psys and Pvol at the ankle are shown to correlate well with Doppler-and-cuff Psys in patients with vascular disease. Oscillometric measurements can replace Doppler measurements in most clinical situations.

Arm and ankle blood pressure response to treadmill exercise in normal people

Nineteen healthy volunteers, 10 men and nine women (mean age 38 and 30 years), exercised on a treadmill. The systolic blood pressure (BP) was measured at the ankle and in the arm after submaximal (8 min with a final load of 2 W kg-1 body weight) and maximal exercise. The BP was measured for 10 min after exercise, or until the elimination of a negative pressure difference between ankle and arm. The pre-study resting systolic arm and ankle pressures were 122 +/- 11 and 144 +/- 13 mmHg. One minute after submaximal exercise, arm and ankle BP were 147 +/- 18 and 159 +/- 19 mmHg (ankle-arm pressure difference 12 +/- 13 mmHg); 1 min after maximal exercise the corresponding figures were 182 +/- 26 and 153 +/- 35 mmHg (ankle-arm pressure difference -29 +/- 33 mmHg). We conclude that maximal exercise, but not an appropriately chosen submaximal exercise level, causes a negative BP difference between ankle and arm in normal people.

A comparison of brachial, femoral, and aortic intra-arterial pressures before and after cardiopulmonary bypass

Following recent evidence that brachial and femoral artery pressures are more reliable than radial artery pressures after cardiopulmonary bypass, thirty-one adults had simultaneous pre- and post-bypass measurements of brachial, femoral, and ascending aortic pressures. Two minutes after cardiopulmonary bypass, brachial artery systolic pressure and mean arterial pressure fell significantly below corresponding pressures in the femoral artery and aorta. Five minutes after cardiopulmonary bypass, only brachial artery systolic pressure was still less than femoral and aortic systolic pressures. By ten minutes after bypass, all significant pressure differences had resolved except between brachial and femoral artery systolic pressures. Clinically significant (greater than or equal to 5 mmHg) aortic-to-brachial reductions in mean arterial pressures occurred in six (19%) patients at two minutes and in three (10%) patients at five and ten minutes after bypass. Equivalent aortic-to-femoral mean pressure diminution occurred in two (6%) patients at two minutes and one (3%) patient at five and ten minutes after bypass. Neither systemic vascular resistance nor body temperatures contributed significantly to post-bypass central-to-peripheral pressure reductions. Immediately following bypass, femoral artery pressures reproduce central aortic pressures more reliably than do radial or brachial artery pressures.

A comparison of radial, brachial, and aortic pressures after cardiopulmonary bypass

Previous investigations have identified falsely low radial artery pressures after cardiopulmonary bypass (CPB). The present study investigates the relationship among radial, brachial, and aortic arterial pressures in 33 cardiac surgical patients following CPB. Two minutes after separation from CPB, clinically important (greater than or equal to 10 mmHg) underestimation of systolic aortic pressures occurred in 17 of 33 (52%) radial artery catheters, while occurring in seven of 33 (21%) brachial artery catheters. Radial artery mean pressure underestimated aortic mean pressure by greater than or equal to 5 mmHg in 21 of 33 (61%) patients two minutes after CPB, while an equivalent aortic-to-brachial artery mean arterial pressure difference occurred in nine of 33 (27%) patients. The incidence of aortic-to-radial mean arterial pressure differences greater than or equal to 5 mmHg decreased to 40% (four of ten patients) by ten minutes after CPB, although interpretation is complicated by decreased availability of aortic pressure measurements. Multivariate analysis failed to identify factors predisposed to central-to-peripheral pressure gradients. Radial and brachial arterial pressures were compared both before and after CPB in all 33 patients. Brachial artery systolic and mean pressures were higher than corresponding radial artery measurements two minutes after CPB (P less than 0.05), followed by gradual resumption of a normal brachial-to-radial pressure relationship over 60 minutes. Either vasospasm in the brachial and radial arteries or profound arteriolar vasodilation in the upper extremity might cause the observed central-to-peripheral arterial pressure differences. The progressive central-to-peripheral decrease in mean arterial pressure favors the latter mechanism.(ABSTRACT TRUNCATED AT 250 WORDS)

Age- and sex-related changes in the ratio between ankle and brachial systolic pressure in normal subjects

The ratio between ankle (ASP) and brachial (BSP) systolic pressure was studied by using Doppler ultrasound in 198 normal subjects aged between twenty and ninety years: 97 males and 101 females. The ASP/BSP ratio decreased significantly with age both in males (r = -0.64; p less than 0.001) and in females (r = -0.72; p less than 0.001). In males, the decrease in the ratio with age was due to a significant decrease in ASP with age (r = -0.52; p less than 0.001), whereas BSP did not increase significantly with age. In females, a different result was observed, since only BSP (and not ASP) was significantly (and positively) correlated with age. In both sexes, the diameter of the terminal abdominal aorta measured by echocardiography was significantly increased with age, and full examination with Doppler ultrasound excluded any significant arterial stenosis of the lower limbs. The study provided evidence that age- and sex-related changes in arterial wave transmission do exist in normal subjects.

Toe pulse wave analysis in obliterating atherosclerosis

photoplethysmographic measurements were carried out in 61 limbs with angiographically documented obliterating atherosclerosis (OA) and in 72 limbs with OA. The distance P was measured between the ascending and descending limbs of the pulse wave at the border of the upper and middle thirds of the amplitude. To standardize the measurements the P value was divided by the length L of the pulse wave (P/L ratio). Using 95% confidence limit in the group of healthy young individuals, 80.8% of the lower limbs with obliterating atherosclerosis without occlusion (OAWO) and 100% of those with complete occlusion (OAWCO) were revealed. In the group of healthy individuals (average age 50 years), 69.8% of lower limbs with OAWO and 100% of those with OAWCO were found. This method showed the higher number of detected OAWO when compared with peripheral systolic pressure measurements.

Difference in systolic blood pressure between arm arm and ankle region in children 0-15 years old

Arm and ankle systolic blood pressure was measured in a supine position in 95 children aged between 2 days and 16 years using either the ultrasound Doppler technique (0-6 years) or the strain-gauge technique (7-16 years). Among children below 1 year of age, the ankle systolic blood pressure was significantly lower than the arm blood pressure and lowest when recorded over the dorsal pedal artery as compared to the post-tibial artery. Children over 1 year of age had a higher ankle systolic blood pressure compared to the arm which corresponds to earlier findings among adults. The study indicates that lower limb systolic pressure is greater than upper limb systolic pressure but first demonstrable at the time when the babies begin to stand or walk. These findings might be used in evaluation of children suspected for aortic coarctation.

Blood flow in the diabetic neuropathic foot

The mechanisms which underlie the development of Charcot joints and foot ulceration are poorly understood. The present study using non-invasive Doppler techniques demonstrates that in the neuropathic leg, the arteries are rigid, peripheral blood flow is increased and associated with arteriovenous shunting. We studied 10 diabetics with severe neuropathy (including five with Charcot changes), 16 diabetics without neuropathy and 10 control subjects. Markedly abnormal blood velocity profiles (sonograms) were demonstrated only in those patients with severe neuropathy. They showed increased diastolic flow (indicated by a reduced Pulsatility Index of 2.88 +/- 0.8 (mean +/- SD) compared with 9.53 +/- 4.0 (p less than 0.001) in the diabetics without neuropathy and 10.8 +/- 3.7 (p less than 0.001) in the control subjects) suggesting arteriovenous shunting. Increased rigidity was indicated by decreased transit times -57 +/- 6.3 ms (mean +/- SD) in the diabetics with neuropathy compared with 66 +/- 7.6 ms (p less than 0.01) in the diabetics without neuropathy and 67 +/- 9.1 ms (p less than 0.05) in the control subjects. This was accompanied by raised ankle systolic pressures -199 +/- 22 mmHg (mean +/- SD) in the diabetics with neuropathy compared with 151 +/- 15 mmHg, (p less than 0.001) in the diabetics without neuropathy and 146 +/- 18 mmHg (p less than 0.001) in the control subjects. Medial wall calcification occurred almost exclusively in the neuropathic subjects. These alterations in blood flow which include arteriovenous shunting may be important in the pathogenesis of complications of the neuropathic leg.