Effect Of Upright Posture Research Articles

Effect of Upright Posture on Endothelial Function in Women and Men.

Women are more prone to orthostatic intolerance compared to men and have a greater vasodilatory capacity. We investigated the hypothesis that women would have greater peripheral flow-mediated dilation (FMD) while in the upright posture compared to men, which could contribute to this phenomenon. In young healthy women (age: 20 ± 3, BMI: 27 ± 5 kg/m2, n = 10) and men (age = 21 ± 2, BMI: 27 ± 8 kg/m2, n = 8), we assessed FMD of the brachial artery and hemodynamics to determine endothelial function during the supine and 70° head-up tilt postures (randomized). The brachial artery was kept at heart level in both trials. We observed that FMD increased in both sexes during tilt (Women: 11.9 ± 5.3 to 15.7 ± 5.6%; Men: 8.4 ± 3.2 to 14.6 ± 3.4%, Main effect of tilt p = 0.005) which was not due to changes in blood pressure or shear stress. There were no interaction effects between sex and posture. In a second cohort of women (age: 22 ± 3, BMI: 23 ± 3 kg/m2, n = 9) and men (age: 22 ± 2, BMI: 25 ± 8 kg/m2, n = 8), we investigated reactive hyperemia by peripheral arterial tonometry (LnRHI) via EndoPAT. Interestingly, we found that the EndoPAT response was decreased in both sexes during tilt (LnRHI: Men: 0.70 ± 0.28 to 0.59 ± 0.40, Women: 0.52 ± 0.23 to 0.30 ± 0.32, Main effect of tilt p = 0.037). We previously found that FMD is related to coronary responses to acetylcholine and adenosine whereas EndoPAT is related to coronary responses to dobutamine. Therefore, we suggest that sympathetic mediated dilation is attenuated in the upright posture while the increased vasodilatory response as measured by FMD in the tilt posture could be attributed to increasing metabolite production from postural muscles.

Effect of upright posture on central wave reflection in 637 volunteers not using medications with direct cardiovascular influences: Description of different phenotypes

BackgroundThe effect of upright posture on the level of augmentation index (AIx) remains controversial [1–3]. Phenotypic differences in AIx responses to upright posture are unknown.MethodsAltogether 323 women and 315 men without cardiovascular disease and medications with direct cardiovascular influences were subjected to passive head-up tilt (5-min supine, 5-min upright). Haemodynamics were recorded using continuous tonometric pulse wave analysis and whole-body impedance cardiography.ResultsMean (SD) age was 45.6 (1.2) years, BMI 26.8 (4.4) kg/m2, and average blood count, plasma lipids and creatinine were normal. AIx decreased from supine 22.7% (11.9) to upright 13.8% (12.2) (p < 0.001), while heart rate related AIx@75 decreased from 17.9% (11.8) to 13.9% (11.0) (p < 0.001), respectively. In stepwise linear regression analyses, the explanatory variables for upright reduction in AIx were changes in ejection duration (β = 0.744), aortic reflection time (β = −0.491), and stroke volume (β = 0.117); and supine ejection duration (β = 0.312), systemic vascular resistance (SVR) (β = −0.271), pulse wave velocity (PWV) (β = −0.203), and systolic blood pressure (β = 0.081) (p≤0.001 for all). When divided to quartiles according to the supine-to-upright change in AIx 1) the quartile with lowest supine AIx had highest upright AIx, lowest supine SVR and PWV, and lowest upright heart rate; 2) the quartile with highest supine AIx had lowest upright AIx, highest supine SVR and PWV, and highest upright heart rate.ConclusionsThe level of AIx is decreased in the upright position. The phenotypic differences in the supine-to-upright change in AIx may explain why this variable has not predicted cardiovascular events in all endpoint studies.

Effect of upright posture on tonsillar level in adolescent idiopathic scoliosis

Results In AIS patients, the cerebellar tonsil position was significantly lower in the upright than the supine position (-0.7 +/-1.5 vs +1.2+/-1.7, p<0.00001) while in normal subjects, there was no change in cerebellar tonsil position between upright and supine positions (mean +2.1+/-1.7 vs +2.2 +/-1.8, p = 0.93). AIS patients also had a greater degree of tonsillar excursion between upright and supine positions compared to normal subjects (mean -1.9 +/-1.6 vs -0.1 +/-1.7, p<0.00001). More AIS patients tended to have tonsillar descent in the upright position rather than the supine position though this did not reach statistical significance (28% in supine position vs 48% in standing position, p=0.15). There is slightly better correlation between tonsillar level and Cobb angle in upright position (r = 0.45, p = 0.01) than those in supine position (r= 0.31, p=0.03) in AIS patients. Conclusion AIS patients have more tonsillar descent in the upright position and a greater degree of tonsillar excursion between supine and upright positions compared to matched control subjects. Apart from supporting the hypothesis of relative cord tethering in AIS, the results also enhance the likelihood of more significant chronic dynamic compression of the brainstem and upper cervical cord in AIS. Whether this will lead to chronic insult with subclinical neurophysiological disturbance, affecting both dynamic postural balance and SSEP, and contributing to the etiopathogenesis of AIS, warrants further study.

Effect of upright posture and physical exercise on endogenous neurohormonal systems in cirrhotic patients with sodium retention and normal supine plasma renin, aldosterone, and norepinephrine levels

It is well known that sodium retention occurs in a significant proportion of patients with cirrhosis despite normal supine plasma levels of renin, aldosterone (ALDO), and norepinephrine (NE). The current study was performed to assess whether this subset of patients also present normal activity of the renin-aldosterone and sympathetic nervous systems during upright posture in sitting position and moderate physical exercise. Nine healthy controls, 14 patients with compensated cirrhosis and 10 patients with cirrhosis, ascites, sodium retention, and normal supine plasma renin activity (PRA) and ALDO and NE concentration were sequentially studied after 60 minutes in supine rest, 30 minutes in sitting position, and 30 minutes of cycloergometric exercise (3-METs). Sitting position and exercise were associated with similar stimulation of the renin-aldosterone and sympathetic nervous systems in the three groups of subjects. Consequently, cirrhotic patients with ascites showed values of PRA and plasma concentration of ALDO and NE similar to healthy subjects and patients with compensated cirrhosis during supine rest (renin: 1.4 +/- 0.3, 0.8 +/- 0.2, and 0.8 +/- 0.3 ng/mL; aldosterone: 24.3 +/- 4.7, 20.2 +/- 3.9 and 21.4 +/- 3.4 ng/dL; norepinephrine: 252 +/- 23, 250 +/- 16, and 255 +/- 23 pg/mL), sitting position (renin: 2.1 +/- 0.5, 1.1 +/- 0.3, and 1.6 +/- 0.4; aldosterone: 32.2 +/- 7.3, 23.7 +/- 5.3, and 26.2 +/- 4.5; norepinephrine: 356 +/- 38, 401 +/- 63, and 420 +/- 35), and exercise (renin: 2.9 +/- 0.8, 1.6 +/- 0.4, and 2.2 +/- 0.5; aldosterone: 43 +/- 6.4, 34.9 +/- 8.5, and 38.2 +/- 5.3; norepinephrine: 481 +/- 35, 499 +/- 54, and 534 +/- 48).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of upright posture and physical exercise on endogenous neurohormonal systems in cirrhotic patients with sodium retention and normal supine plasma renin, aldosterone, and norepinephrine levels

It is well known that sodium retention occurs in a significant proportion of patients with cirrhosis despite normal supine plasma levels of renin, aldosterone (ALDO), and norepinephrine (NE). The current study was performed to assess whether this subset of patients also present normal activity of the renin-aldosterone and sympathetic nervous systems during upright posture in sitting position and moderate physical exercise. Nine healthy controls, 14 patients with compensated cirrhosis and 10 patients with cirrhosis, ascites, sodium retention, and normal supine plasma renin activity (PRA) and ALDO and NE concentration were sequentially studied after 60 minutes in supine rest, 30 minutes in sitting position, and 30 minutes of cycloergometric exercise (3-METs). Sitting position and exercise were associated with similar stimulation of the renin-aldosterone and sympathetic nervous systems in the three groups of subjects. Consequently, cirrhotic patients with ascites showed values of PRA and plasma concentration of ALDO and NE similar to healthy subjects and patients with compensated cirrhosis during supine rest (renin: 1.4 ± 0.3, 0.8 ± 0.2, and 0.8 ± 0.3 ng/mL.hr; aldosterone: 24.3 ± 4.7, 20.2 ± 3.9 and 21.4 ± 3.4 ng/dL; norepinephrine: 252 ± 23, 250 ± 16, and 255 ± 23 pg/mL), sitting position (renin: 2.1 ± 0.5, 1.1 ± 0.3, and 1.6 ± 0.4; aldosterone: 32.2 ± 7.3, 23.7 ± 5.3, and 26.2 ± 4.5; norepinephrine: 356 ± 38, 401 ± 63, and 420 ± 35), and exercise (renin: 2.9 ± 0.8, 1.6 ± 0.4, and 2.2 ± 0.5; aldosterone: 43 ± 6.4, 34.9 ± 8.5, and 38.2 ± 5.3; norepinephrine: 481 ± 35, 499 ± 54, and 534 ± 48). Plasma atrial natriuretic peptide concentration was significantly ( P < .05) higher in cirrhotic patients with ascites than in healthy subjects during supine rest (5.69 ± 1.1 vs. 21.0 ± 3.3 fmol/L) and exercise (9.1 ± 2.2 vs. 28.3 ± 6.6). These results indicate that sodium retention in cirrhosis may occur in the setting of a normal activity of the endogenous neurohormonal antinatriuretic systems and high plasma levels of ANP.

Paradoxical Hemodynamic Responses to Orthostasis in Patients with Dual Chamber Pacemakers

The effect of upright posture on hemodynamics of patients with dual chamber (DDD) pacemakers has been largely unexplored. The postural hemodynamic responses in 27 patients with DDD pacemakers were assessed by impedance cardiography calculations of stroke volume and sphygmomanometer measurements of blood pressure. Twenty patients with complete heart block (5 with heart failure) were studied in the YDD mode and 7 patients with sick sinus syndrome and severe chronotropic incompetence (fixed heart rate) were assessed in DVI (4) or VDD (3) modes. In contrast to the responses observed in normals, pacemaker patients’ orthostatic responses included: (1) a reduction in systolic, diastolic and mean blood pressures; (2) fixed stroke volume in sick sinus syndrome or heart failure patients, and only modest stroke volume reductions in the remaining patients, and (3) a reduction in systemic vascular resistance. Thus, when assuming the upright position, DDD patients develop a hypotensive response with paradoxical maintenance of stroke volume. Even when AV synchrony is preserved, orthostatic hemodynamic abnormalities are detectable independently of the underlying heart disease. We assume that these abnormalities occur because of the altered autonomic state (autonomic dysfunction) induced by the abnormally depolarized ventricles.

Effects of upright posture on anterograde and retrograde atrioventricular conduction in patients with coronary artery disease, mitral valve prolapse or no structural heart disease

To assess the effects of posture on anterograde and retrograde atrioventricular conduction, electrophysiologic testing was performed in 25 patients in both the supine and 45 ° upright positions on a tilt table. Retrograde conduction was present during ventricular pacing in 17 patients in the supine position; all 17 continued to manifest retrograde conduction in the upright position. In all patients with absent retrograde conduction while supine, retrograde conduction could not be demonstrated while upright. Upright posture significantly (p < 0.05) shortened the sinus cycle length (from 808 ± 34 to 678 ± 26 ms, mean ± standard error of the mean), AH interval during sinus rhythm (78 ± 6 to 69 ± 6 ms), and AH interval during atrial pacing at cycle length 500 ms (123 ± 13 to 91 ± 9 ms). Total atrioventricular conduction time during atrial pacing shortened significantly (from 169 ± 1.3 to 136 ± 10 ms), as did ventriculoatrial conduction time during ventricular pacing (from 192 ± 9 to 178 ± 7 ms). Upright posture also significantly shortened both anterograde block cycle length (390 ± 20 to 328 ±17 ms) and retrograde block cycle length (466 ±27 to 354 ± 18 ms). However, the effect of upright posture on retrograde block cycle length was significantly greater than on anterograde block cycle length: a 21% decrease retrograde vs a 14% decrease anterograde (p < 0.05). These effects may produce clinically important changes in characteristics of arrhythmias that depend on the properties of anterograde and retrograde conduction. Electrophysiologic testing in both the supine and upright positions may better define retrograde conduction properties than supine testing alone.

Effect of short-term upright posture on plasma angiotensin II in man.

The effect of upright posture on radioimmunologically measured venous plasma angiotensin II was studied in healthy volunteers, using active (continuous walking) and passive (head-up tilting) types of upright posture. Blood samples were drawn 1, 3, 10, 30 and 90 minutes after assumption of an upright posture. Significantly increased concentrations of angiotensin II were found 10 minutes after the change of posture. In the active test the initial rise was more marked, whereas at 90 minutes significantly more angiotensin II was found in the passive test. The initial rise in the active test was slightly slower in subjects over 60 years of age. During the conditions used the diurnal variation of angiotensin II was not found to affect markedly the response of angiotensin II to upright posture. The present data suggest that angiotensin II does not play any significant role in the maintenance of blood pressure right after the change of posture from supine to upright. Later, angiotensin II is obviously linked to t...

Effect of Upright Posture and Isoproterenol Infusion on Cyclic Adenosine Monophosphate Excretion in Control Subjects and Patients with Labile Hypertension.1

Labile hypertension is often characterized by β-adrenergic hyperactivity accompanied by an increased responsiveness of renin to upright posture. β-adrenergic receptors are related to the cyclic AMP generating enzyme, adenylate cyclase. In order to evaluate a possible relationship between cyclic AMP, the circulatory hyperactivity, and renin hyperresponsiveness, urinary excretion of cyclic AMP was measured by radioimmunoassay in 12 control subjects and 14 patients with labile hyperkinetic hypertension. Four-hr urines were collected at the same time of the day in recumbent and upright positions and after isoproterenol stimulation. The excretion of cyclic AMP in upright posture decreased in control subjects and increased significantly in labile hypertensive patients. Similar response was observed after isoproterenol infusion in both groups of subjects.

The effect of upright posture on right ventricular volumes in patients with and without heart failure

The effects of posture on stroke volume, right ventricular end-diastolic and end-systolic volumes, cardiac output, and heart rate were studied in subjects without heart disease and patients with congestive heart failure. Cardiac catheterization was performed, and right ventricular volumes were measured by combining a direct Fick cardiac output determination with a thermodilution technique, while the subjects were supine and after they had been tilted to a 60-degree upright position. In the normal subjects, upright tilting resulted in a profound fall in stroke volume, an increase in heart rate, and a significant decrease in the size of the right ventricle, although the residual fraction increased. In contrast, in subjects with congestive heart failure, tilting to the upright position caused no significant changes.