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Biomedical subjects

G M London

Publications and source records attributed to G M London.

At least 91 records · Page 5Linked to original sources
PubMed1993

Wave reflections and cardiac hypertrophy in chronic uremia. Influence of body size.

Arterial wave reflections (AWRs), an important determinant of cardiac afterload, are increased in hemodialysis patients. However, an association between AWRs and left ventricular hypertrophy has not been established in these subjects. We therefore sought an association between these two parameters in a cross-sectional study of two outpatient hemodialysis populations. AWRs were quantified (augmentation index, percent) as the ratio of the height of the late systolic peak to the total height of the carotid pulse wave recorded with a micromanometer-tipped probe. AWRs were determined in 44 hemodialysis patients, 22 with pronounced AWRs (group A: augmentation index > 12%), and 22 with small or moderate AWRs (group B: augmentation index < 12%). The groups were matched for age, sex, blood pressure, and hemodialysis duration. Left ventricular size was determined by echocardiography. Despite lower body size (P < .005) and similar blood pressure, cardiac output, peripheral resistance, and aortic pulse wave velocity, group A patients had greater left ventricular mass (P < .01). For the population as a whole, left ventricular mass and AWRs were positively correlated (P < .0001) independent of age, blood pressure, hemodialysis duration, or body size. Lesser body height was the principal factor associated with increased AWRs in group A (P < .001). We conclude that in hemodialysis patients AWRs are associated with the development of left ventricular hypertrophy and that small body height is a risk factor for long-term cardiovascular complications.

Adult↗
PubMed1993

Arterial compliance and blood pressure.

As a result of the dual function of arteries, the conduit and cushioning functions, arterial pressure has 2 components: the steady component, characterised by mean blood pressure, and the pulsatile component, characterised by pulse pressure. Arterial compliance mostly depends on arterial intrinsic elastic properties, and is a determinant of the propagation speed of the pulse pressure wave. Decreased arterial compliance is responsible for both an increase in the incident pressure wave and the higher effect of reflected pressure waves. This increases systolic pressure and ventricular afterload, and generates left ventricular hypertrophy. Arterial structural changes that accompany the aging process result in a loss of distensibility and compliance. In essential as well as in secondary hypertension, arterial compliance is reduced, and age-related structural changes of the arterial wall are accelerated. Whether the change in arterial compliance is a passive consequence of the increase in blood pressure or is related to changes in the arterial wall structure remains unclear. Calcium antagonists improve the distensibility and compliance of large and small arteries, contributing significantly to the improvement in the management of essential and secondary hypertension.

Animals↗
PubMed1993

Cardiac hypertrophy and arterial alterations in end-stage renal disease: hemodynamic factors.

Left ventricular (LV) hypertrophy is the most common cardiovascular alteration observed in end-stage renal disease patients. LV hypertrophy results from chronic flow and pressure overload and combines features of concentric and eccentric hypertrophy. The causes of chronic flow overload are the presence of AV shunt, salt and water overload, and anemia. The pressure overload is related to alterations of physical properties of large arteries characterized by an increased arterial and aortic stiffness. The systolic function of hypertrophied ventricle is preserved, but the diastolic filling is impaired. The ventricular hypertrophy progresses over the time on hemodialysis together with a progressive worsening of both systolic and diastolic functions.

Arteries↗
PubMed1992

Hysteresis of the venous pressure-volume relationship in the forearm of borderline hypertensive subjects.

1. The forearm venous pressure-volume relationship was studied in 14 young men with borderline hypertension and in 16 control subjects of the same age and sex. Strain-gauge plethysmography was used to evaluate volume changes after slow increases and decreases in distention, in order to estimate the amplitude of the hysteresis curve. 2. Compared with normotensive control subjects, subjects with borderline hypertension had significantly higher values of blood pressure, heart rate and forearm blood flow. 3. Baseline forearm venous tone was slightly, but not significantly, increased in borderline hypertensive subjects (21.35 +/- 6.53 versus 18.75 +/- 5.95 mmHg ml-1 100 ml-1) and was significantly enhanced after a cold pressor test. The increase was no higher in the borderline hypertensive subjects than in the normotensive control subjects. 4. The area of the hysteresis curve was significantly decreased (7.58 +/- 3.58 versus 10.34 +/- 5.67 arbitrary units; P = 0.0092) as was the extent of isotonic relaxation (creep) (0.28 +/- 0.11 versus 0.39 +/- 0.22 ml/100 ml; P = 0.0098) in borderline hypertensive subjects compared with control subjects. Both parameters were unaffected by the cold pressor test. 5. The study suggests that the viscous component of the venous wall is altered in young patients with borderline hypertension, indicating intrinsic changes in vascular segments which are not exposed to increased intraluminal pressure.

Adult↗
PubMed1992

Carotid arterial haemodynamics after mild degrees of lower-body negative pressure in man.

1. Pulsatile changes in the diameter of the common carotid artery were studied transcutaneously using an echo-tracking technique in 15 normal subjects: eight subjects before and during application of graded lower-body negative pressure from -5 to -15 mmHg, and seven subjects before and during weight-bearing head-up tilt at 30 and 60 degrees. 2. In concomitant studies of changes in forearm vascular resistance, it was seen that mild lower-body negative pressure produced deactivation of cardiopulmonary receptors without changes in systemic blood pressure or heart rate. 3. After lower-body negative pressure, a significant decrease in carotid arterial diastolic diameter [from 0.662 +/- 0.028 to 0.624 +/- 0.033 cm (lower-body negative pressure -10 mmHg) and 0.640 +/- 0.030 cm lower-body negative pressure -15 mmHg), P < 0.001 and < 0.05] was observed. 4. After head-up tilt, carotid arterial diameter was also significantly decreased at 30 and 60 degrees, whereas a significant increase in heart rate occurred only at 60 degrees and mean blood pressure did not change. 5. The study provides evidence that the geometry of the arterial wall is substantially modified by non-invasive manoeuvres such as head-up tilting and lower-body negative pressure. The latter is assumed to selectively deactivate human cardiopulmonary receptors, but the present data suggest that local changes may also influence carotid baroreceptors.

Adult↗
PubMed1992

Arterial structure in hypertension and the effects of angiotensin converting enzyme inhibition.

BACKGROUND: In hypertension, structural changes in the cardiovascular system affect not only small arteries and the heart but also the large arteries, particularly in elderly people. It has been suggested that structural alterations to the small arteries are responsible for the elevation in mean arterial pressure seen in hypertension, as a result of increased vascular resistance. However, the amplitude of pressure oscillation (pulse pressure) is influenced by other haemodynamic mechanisms that involve large arteries including a decrease in compliance and an increase in wave reflection. EFFECTS OF STRUCTURAL ALTERATIONS TO LARGE ARTERIES ON BLOOD PRESSURE: Structural alterations to the large arteries may, in hypertensive subjects, be responsible for an increase in the amplitude of pressure oscillation, leading to a disproportionate increase in systolic over diastolic blood pressure because of arterial (not arteriolar) changes. These findings not only contribute to a better understanding of the relationship between vascular structure and blood pressure levels but also to a better interpretation of hypertensive complications, particularly those related to the heart and large vessels. APPLICATION TO TREATMENT: The reversal of structural arterial changes may become a goal in long-term antihypertensive treatment. Angiotensin converting enzyme (ACE) inhibitors in particular can reverse structural arterial changes, increase arterial compliance and produce a more pronounced decrease in systolic than in diastolic blood pressure.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1992

Arterial calcinosis, chronic renal failure and calcium antagonism.

A progressive rise in arterial calcium content is the most characteristic age-associated alteration in the arterial wall and the decisive factor in arteriosclerotic degeneration. Experimental studies have demonstrated that calcium antagonists can prevent or retard the development of arterial calcinosis associated with vitamin D overload, hypertension or alloxan-induced diabetes. Although similar effects are more difficult to observe in humans, they have been demonstrated in patients with coronary artery disease and in patients with end-stage renal disease, which is characterised by an acceleration of the normal arterial aging process.

Aging↗
PubMed1992

Effects of antihypertensive agents on carotid pulse contour in humans.

The aim of this study was to assess the influence of antihypertensive agents on arterial wave reflections (AWR) and carotid pulse pressure (PP) in humans. Twenty patients with hypertension (predominantly systolic) were studied. After one month of placebo therapy they were randomly assigned to atenolol (At) 50 mg/day or to nitrendipine (Ni) 40 mg/day. Carotid pressure waveform was recorded noninvasively by applanation tonometry using a Millar micromanometer-tipped probe. Arterial wave reflections were quantified as the ratio of the height of the late systolic peak (delta P) to the total height of carotid pulse pressure wave as an augmentation index (delta P/PP). Travel time of the reflected wave (delta tp) was timed from the foot of the pressure wave to the foot of the late systolic peak. Atenolol and Ni were equally effective in reducing sphygmomanometric brachial artery blood pressure (BP). Whereas At (p < 0.05) and Ni (p < 0.01) reduced the carotid PP, Ni (p < 0.01) but not At significantly reduced delta P/PP. Both agents increased the delta tp (p < 0.01) and decreased aortic PWV (p < 0.01). Nitrendipine was associated with a decrease in left ventricular ejection time (LVET) (p < 0.01), while At increased heart period (p < 0.01) and LVET. The LVET/delta tp ratio decreased after Ni (from 3.25 +/- 0.77 to 2.42 +/- 0.73; p < 0.01) but did not change after At. The study shows, that for the same effect on peripheral BP, Ni has a more pronounced effect on pressure wave in central arteries, resulting from an improvement in the timing between the ventricular ejection and AWRs.

Antihypertensive Agents↗
PubMed1992

Sodium, large arteries and diuretic compounds in hypertension.

BACKGROUND: Clinical and experimental data have shown that different antihypertensive drugs do not cause similar changes in arterial compliance for an equipotent blood pressure reduction. There are no clear data on the effects of sodium and diuretics on the visco-elastic properties of the hypertensive arterial wall. DATA ANALYSIS: Cross-sectional epidemiological studies suggest that for given values of age and blood pressure, pulse wave velocity is lower in the presence than in the absence of a low sodium intake. Longitudinal studies indicate that in hypertensive subjects, a low sodium intake is associated with a larger brachial artery diameter than that seen with a high sodium intake. In hypertension in the elderly and in severe hypertension with end-stage renal disease, a sodium overload reduces arterial compliance and distensibility independently of blood pressure changes. In animal studies, the diuretic compounds cycletanine and indapamide increase systemic and carotid compliance independently of blood pressure changes. In contrast, in a crossover study in hypertensive subjects, the diuretic agent hydrochlorothiazide did not change arterial compliance and pulse wave velocity while the calcium entry-blocker felodipine did improve these hemodynamic parameters. CONCLUSION: The studies reviewed indicate that sodium may act on the arterial wall independently of blood pressure changes. the contribution made by counter-regulatory mechanisms, which may be related to the renin-angiotensin and the sympathetic nervous systems, might explain the differences between the clinical and the experimental changes observed with diuretic compounds.

Animals↗
PubMed1992

Body height as a determinant of carotid pulse contour in humans.

AIM: The aim of this study was to assess the effect of body height on arterial wave reflections and the carotid pulse pressure contour in humans. METHODS: In 85 men, the carotid pulse wave and arterial wave reflections were determined from the common carotid artery pulse contour as recorded by applanation tonometry using a Millar micromanometer-tipped probe. The arterial wave reflection was calculated as the ratio of the height of the late systolic peak to the total height of the carotid pulse wave. The reflected wave was timed from the foot of the pressure wave to the foot of the late systolic peak. RESULTS: Multiple regression analysis showed that body height and aortic pulse wave velocity were the principal determinants of travel time of the reflected wave and of arterial wave reflections (P < 0.0001), short stature being associated with a short travel time and increased reflections (P < 0.0001). CONCLUSIONS: Body height is a determinant of arterial wave reflections and peak systolic blood pressure in humans.

Adolescent↗
PubMed1991

Glomerular hypertension in renovascular hypertensive patients.

Split intrarenal hemodynamics in stenotic and contralateral kidneys of unilateral renovascular hypertension (RVH) were estimated by Gomez's formulae. Forty patients with essential hypertension and 40 patients with RVH were studied. Split para-amino hippurate and inulin clearances were measured by ureteral catheterization as indexes for effective renal plasma flow and glomerular filtration rates, allowing the estimation of intrarenal hemodynamics such as afferent arteriolar resistance (RA), efferent arteriolar resistance (RE) and glomerular hydrostatic pressure (PG) in each kidney. Normal values of intrarenal hemodynamic parameters were obtained in 24 normotensive subjects without ureteral catheterization, assuming each kidney had the half function of both kidneys. Systemic mean arterial pressure did not differ between essential and renovascular hypertension (141 +/- 3 vs. 148 +/- 3 mm Hg). Effective renal plasma flow and glomerular filtration rates were decreased in the stenotic kidney of RVH (98 +/- 8, 24 +/- 2 ml/min/m2), while increased in the contralateral kidney (195 +/- 11, 48 +/- 2), compared with the right kidney of essential hypertension (162 +/- 8, 33 +/- 1). Although effective renal plasma flow rate was not different from normal (191 +/- 8), glomerular filtration rate was significantly higher in the contralateral kidney of RVH than in normal (38 +/- 1). RA was elevated due to the stenotic lesion in the stenotic kidney (28,500 +/- 1,900 dyns.sec.cm-5), while the elevation in the contralateral kidney (10,800 +/- 600) was less than in the right kidney of essential hypertension (14,900 +/- 1,200). RE (5,800 +/- 300) in both kidneys of RVH was higher than in the right kidney of essential hypertension (4,500 +/- 200).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Influence of sex and body weight on forearm hemodynamics in patients with sustained essential hypertension.

Forearm hemodynamics using pulsed Doppler flowmeter measurements were studied in 60 hemodynamics men (30 nonobese and 30 obese) and in 45 hypertensive women (15 nonobese and 30 obese subjects). Age and blood pressure of nonobese and obese patients were identical in men as well as in women. Blood flow, expressed in milliliters/minute or corrected for body surface area, was significantly higher in obese hypertensive patients. When blood flow was expressed per unit liter of forearm volume, the difference was no longer present. The increased blood flow in milliliters/minute in obese hypertensive patients was due to an increased blood velocity, while arterial diameter was similar in nonobese and obese hypertensive patients. Forearm vascular resistance, expressed either in absolute values or in normalized values was significantly higher in nonobese than in obese hypertensive patients. When men and women with similar body weight and mean arterial pressure were compared, women were characterized by lower values of arterial diameter, body surface area and forearm volume, whereas vascular resistance in absolute value or corrected for body surface area was higher. This increase was no longer present when vascular resistance was normalized for forearm volume. This study provides evidence that body composition and body mass index evolve as determinants of arterial blood velocity whereas the gender of the patient seems to influence the arterial diameter.

Adult↗
PubMed1991

Twenty-four hours of bed rest with head-down tilt: venous and arteriolar changes of limbs.

The hemodynamic changes after 24 h of bed rest with -5 degree head-down tilt were studied in six normal subjects as a condition causing an intrathoracic shift of blood volume with a resulting urinary sodium and water loss and a subsequent reduction in total intravascular volume. Vascular resistance and venous tone of the upper and the lower limbs were investigated as were systemic hemodynamics throughout the procedure. Whereas systemic hemodynamic parameters did not change significantly, vascular resistance and venous tone of the upper and lower limbs decreased significantly up to the sixth h and then returned toward baseline values at 24 h. Systemic and forearm vasoconstriction responses to lower body negative pressure (LBNP) were studied just before and at the end of the study period. With LBNP, -5, -10, and -15 mmHg pressure levels were used to investigate mechanoreceptors in the low-pressure system, whereas the -40 mmHg pressure level was used to explore baroreceptors both in low and high pressure systems. Changes in vascular resistance in response to LBNP did not differ at the beginning and at the end of the head-down tilt, whereas an exaggerated heart rate response was observed at -40 mmHg at the end of 24 h of bed rest. The study showed that after 24 h of bed rest with -5 degree head-down tilt, the adaptative changes in venous tone and vascular resistance to blood volume reduction were altered. A dissociation between cardiac and vascular baroreflex response was observed in situations simulating tilting.

Adult↗
PubMed1991

Arteriosclerosis and antihypertensive response to calcium antagonists in end-stage renal failure.

The relationship between the presence of arterial calcinosis and the antihypertensive response to calcium blockers was studied in 40 hypertensive patients with end-stage renal failure (ESRF) on chronic hemodialysis, before and during 16 weeks after administration of nitrendipine in monotherapy. In a double-blind, placebo-controlled, randomized study, nitrendipine reduced systolic blood pressure regardless of the presence or absence of arterial calcifications. The antihypertensive effect was significantly more pronounced in subjects with aortic calcium deposits in comparison with patients without clinical signs of arteriosclerosis (p less than 0.01). The diastolic blood pressure was significantly reduced only in patients with aortic calcifications, and remained unchanged in subjects with noncalcified aorta. The aortic pulse wave velocity decreased significantly in patients with aortic calcifications (p less than 0.001), but remained unaffected in patients with noncalcified vessels. Multivariate regression analysis showed that the antihypertensive action of nitrendipine was correlated to the presence of aortic calcium deposits independent of age or baseline blood pressure levels. The results of the present study indicate that an overt arteriosclerosis as demonstrated by the presence of aortic calcifications on abdominal radiographs is a good indication for the use of dihydropyridines in patients with ESRF.

Adult↗
PubMed1991

Cardiac hypertrophy and arterial compliance following drug treatment in hypertension.

The load of the heart in hypertension is related both to increased peripheral vascular resistance and decreased aortic compliance. From noninvasive studies involving determinations of pulse-wave velocity and systolic-diastolic variations of aortic arch diameter, it can be shown that increased aortic elastic modulus is strongly related to increased cardiac mass. The relationship is observed even after adjustment for the level of mean arterial pressure. It is suggested that decreased aortic compliance in hypertension causes a disproportionate increase in systolic pressure and end-systolic stress, thus contributing to promote cardiac hypertrophy. Such a possibility may have consequences for long-term antihypertensive therapy. Following converting enzyme inhibition and calcium blockade, important dissociations may be observed between the antihypertensive effect and the cardiac and arterial changes.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1991

Arteriosclerosis and antihypertensive response to calcium antagonists in end-stage renal failure.

The relationship between the presence of arterial calcinosis and the antihypertensive response to calcium blockers was studied in 40 hypertensive patients with end-stage renal failure (ESRF) on chronic hemodialysis, before and during 16 weeks after administration of nitrendipine in monotherapy. In a double-blind, placebo-randomized study, nitrendipine reduced systolic blood pressure regardless of the presence or absence of arterial calcifications. The antihypertensive effects were significantly more pronounced in subjects with aortic calcium deposits in comparison with patients without clinical signs of arteriosclerosis (p less than 0.01). Diastolic blood pressure was significantly reduced only in patients with aortic calcifications, and remained unchanged in subjects with noncalcified aorta. Aortic pulse wave velocity decreased significantly in patients with aortic calcifications (p less than 0.001), but remained unaffected in patients with noncalcified vessels. Multivariate regression analysis showed that antihypertensive action of nitrendipine was correlated with the presence of aortic calcium deposits independently of age or baseline blood pressure levels. The results of the present study indicate that an overt arteriosclerosis as demonstrated by the presence of aortic calcifications on abdominal radiographs is a good indication for use of dihydropiridines in patients with ESRF.

Administration, Oral↗
PubMed1991

Split intrarenal hemodynamics in renovascular hypertension.

Split intrarenal hemodynamics in stenotic and contralateral kidneys of unilateral renovascular hypertension (RVH) were estimated by Gomez's formulae. Ten patients with RVH were studied. Split para-amino hippurate and inulin clearances were measured by ureteral catheterization as indexes for renal plasma flow and glomerular filtration rates, allowing the estimation of intrarenal hemodynamics such as preglomerular arteriolar resistance, postglomerular arteriolar resistance and glomerular hydrostatic pressure in each kidney. Renal plasma flow and glomerular filtration rates were lower in the stenotic kidney (83 +/- 12, 19 +/- 2 ml/min/m2) than in the contralateral kidney (170 +/- 19, 43 +/- 4). Preglomerular arteriolar resistance was elevated due to the stenotic lesion in the stenotic kidney (30,900 +/- 4,500 dyns.sec.cm-5) while the elevation in the contralateral kidney (11,300 +/- 1,000) was less. Postglomerular arteriolar resistance was high in both kidneys. Glomerular pressure was lowered in the stenotic kidney (54 +/- 1 mmHg), while elevated in the contralateral kidney (71 +/- 3). Although the stenotic kidney of RVH was protected from systemic hypertension (138 +/- 6 mmHg) by stenosis of the renal artery, the increase in preglomerular arteriolar resistance in the contralateral kidney was not sufficient, making glomerular pressure elevated. Thus, glomerular hypertension and hyperfiltration were demonstrated in the contralateral kidney of RVH.

Adult↗