Effect of arterial compliance on systolic blood pressure and cardiac function

Electrical modelling of tissue experiments confirms precise locations of resistance and compliance in systemic arterial tree-they are mutually exclusive

This study presents electrical modelling of the arterial system to understand the effect of adrenaline on the aortae and small arteries in terms of their resistance and compliance. There is no categorical documentation in the current literature on the precise locations of arterial resistance (R) and compliance (C) in vasculature. Knowledge of their exact locations in the arterial tree enables re-assessment of the differential action of vasoactive drugs on resistance versus compliance vessels once we resolve beat-to-beat changes in R and C in response to these drugs. Isolated goat aortae and small arteries were perfused with a pulsatile pump and lumen pressures were recorded before and after addition of adrenaline. Equivalent electrical models were simulated, and biological data was compared against the electrical equivalents to derive interpretations. In the aortae, systolic pressure increased, diastolic pressure decreased, pulse pressure increased (P = .018); but the mean pressure remained the same (P = .357). Whereas in small artery, vasoconstriction caused an increase in systolic, diastolic, and mean pressures (P = .028). Simulations allow us to infer that vasoconstriction in the aorta leads to a reduction in compliance, but an increase in resistance if any, is not sufficient to alter the mean aortic pressure. Whereas vasoconstriction in small arteries increases resistance, but a decrease in compliance, if any, does not affect any of the pressure parameters measured. The presented study is first of its kind to give experimental evidence that large arteries and aorta are the only compliance vessels and small arteries are the only resistance vessels.

Differences in cardiovascular function comparing prior preeclamptics with nulliparous controls

OBJECTIVE

The objective of the current study was to evaluate cardiovascular function; including blood pressure, cardiac output, pulse wave velocity and vascular compliance in nonpregnant nulliparous women compared to women with a history of preterm preeclampsia.

STUDY DESIGN

This was a case control study. Blood pressure was measured using the Finapres Pro. Baseline cardiac output was determined by echocardiography. Pulse wave velocity was estimated using simultaneous electrocardiographic tracings and ultrasound determined arterial flow waveforms and calculated as estimated distance divided by the time interval between EKG r-wave peak and ultrasound derived peak popliteal artery flow. During volume challenge, 500mL of lactated Ringers solution was infused through an indwelling antecubital catheter over 10min. Cardiac output and blood pressure during and 15min after the infusion were estimated using the Finapres Pro.

MAIN OUTCOME MEASURES

Indices of arterial stiffness and vascular compliance.

RESULTS

Previous preeclamptics exhibited a significant increase in pulse pressure and cardiac output in response to volume challenge when compared with nulliparous controls. Prior preeclamptics had a strong positive correlation between blood pressure indices (r=0.50-0.68, p⩽0.01) and pulse pressure (r=0.58, P=0.008) with pulse wave velocity that was not evident in control women.

CONCLUSIONS

In women with prior preterm preeclampsia a relationship between blood pressure, intravascular volume and arterial stiffness, is evident in the nonpregnant state and in the absence of hypertension or overt cardiovascular disease. This supports an overarching hypothesis that nonpregnant physiology is an important contributor to pregnancy adaptations.

Effect of diet and exercise on pulse pressure and cardiac function in morbid obesity: analysis of 24-hour ambulatory blood pressure

Blood pressure is a major risk factor for cardiovascular events, although the role of pulse pressure, an independent predictor of arterial stiffness, has recently been emphasized. This study examines the baseline relationship between body mass index (BMI) and blood pressure indexes in 215 obese African Americans enrolled in a diet-exercise program. The subject population was 77% female, with a mean +/- SD age of 46.7+/-10.7 years and a mean BMI of 42.5+/-7.5 kg/m2. In addition, the authors prospectively examined the effect of weight loss on cardiovascular parameters in a subset of 25 participants. The results show a closer significant correlation between pulse pressure and BMI (b=1.97 kgm-1; p=0.001) than between systolic blood pressure and BMI (b=1.58 kgm-1; p=0.020). After 3 months of diet and exercise, average reductions were as follows: BMI, 4.2 kg/m2 (p<0.01); systolic blood pressure, 7.2 mm Hg (p<0.01); pulse pressure, 4.8 mm Hg (p<0.01); and cardiac output, 975 mL/min (p<0.01). Compliance index increased by 0.1 mL/mm Hg/m2 (p=0.03). The results highlight the potential value to cardiovascular health of a modest reduction in body weight in obese individuals.

Total arterial compliance estimated by stroke volume-to-aortic pulse pressure ratio in humans

On the basis of the windkessel model, the stroke volume-to-aortic pulse pressure ratio (SV/PP) has been proposed as an estimate of total arterial compliance, but recent studies have questioned this approximation. Aortic pressure was obtained at rest in 31 adults undergoing cardiac catheterization (47 +/- 14 yr): controls (n = 7), patients with dilated cardiomyopathy (n = 10), and patients with other cardiac diseases (n = 14). We calculated PP, mean aortic pressure (MAoP), heart period (T), SV (thermodilution cardiac output/heart rate), total peripheral resistance (R), total arterial compliance estimated by area method (Carea), and the time constant of aortic pressure decay in diastole (RCarea). In the overall population (n = 31), there was no significant difference between SV/PP and Carea. SV/PP was linearly related to Carea (SV/PP = 0.99Carea + 0.05; r = 0.98; P < 0.001); the slope and intercept did not differ from unity and zero, respectively. Similar results were obtained in the three subgroups. These results implied that PP/MAoP and T/RCarea were proportionally related (T/RCarea = 1.18PP/MAoP - 0.07; r = 0.96; P < 0.001). We conclude that for humans at rest 1) SV/PP gave a reliable estimate of Carea, and 2) T normalized by the time constant of aortic pressure decay in diastole was proportionally related to PP/MAoP. This last relationship could be considered an aspect of the coupling between the left ventricle and its load.

A blood pressure independent index of aortic distensibility

A non-invasive Doppler ultrasound technique for the assessment of aortic compliance based on the in vivo measurement of pulse wave velocity along the thoraco-abdominal aortic pathway is described. An approach for correcting for the effect of blood pressure on aortic compliance is considered. The derivation of an index of distensibility, Cp, which is independent of blood pressure is provided and applied to data collected from 58 normal, healthy volunteers. Medical disorders such as atherosclerosis, diabetes mellitus and familial hypercholesterolaemia have all been shown to affect arterial distensibility. We suggest that the clinical measurement of Cp may be a useful, non-invasive tool for assessing such patients' susceptibility to atheromatous arterial disease as well as for monitoring their response to therapy.

Systolic and diastolic blood pressures as predictors of coronary heart disease mortality in the Whitehall study

Systolic and diastolic blood pressures were compared as predictors of death due to coronary heart disease using data on the 10 year mortality outcome from the 18 403 male civil servants, aged 40-64, in the Whitehall study. There were 727 deaths due to coronary heart disease. At entry to the study the systolic pressure in these men was significantly higher than the diastolic pressure, and a standardised index of relative risk for death from coronary heart disease was greater for systolic blood pressure. After adjustment for age the top quintile of systolic pressure (greater than 151 mm Hg) identified 5% more men at risk of death from coronary heart disease than for the top diastolic quintile (greater than 95 mm Hg). The findings suggested that clinicians should pay more attention to systolic levels as a criterion for making diagnostic and therapeutic decisions.