Nocturnal blood pressure during apnoeic and ventilatory periods in patients with obstructive sleep apnoea.
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The exact nature of asleep blood pressure in relation to awake blood pressure is still unclear in patients with obstructive sleep apnoea. This study aimed: 1) to investigate the asleep blood pressure in both apnoeic and ventilatory periods; 2) to determine the diurnal and nocturnal factors correlated with the changes in blood pressure from apnoea to ventilatory periods during sleep. Thirty-two patients, newly diagnosed as moderate to severe obstructive sleep apnoea with a standard nocturnal polysomnography, were enrolled. The blood pressure was monitored by using the noninvasive continuous monitoring method during polysomnographic study. The mean blood pressures in ventilatory periods during nonrapid eye movement (NREM) and rapid eye movement (REM) sleep were 117.5+/-17.9 mm Hg and 128.8+/-21.9 mm Hg, and those in apnoea periods were 94.5+/-15.4 mm Hg and 102.7+/-19.0 mm Hg. The average blood pressure during NREM sleep (103.0+/-16.1 mm Hg) was higher than the awake blood pressure (97.0+/-15.7 mm Hg). The blood pressure during REM sleep was greater than that during NREM sleep. The changes in the nocturnal blood pressure from apnoea to ventilatory periods were inversely correlated with the age and nocturnal mean nadir saturation. In conclusion, patients with obstructive sleep apnoea have higher asleep blood pressure than awake blood pressure. (+info)
Reproducibility of the hyperbaric index as a measure of blood pressure excess.
(42/1099)
The approach of establishing a time-specified tolerance limit reflecting the circadian variability in blood pressure and then determining the hyperbaric index, the area of blood pressure excess above the upper limit of the tolerance interval, has been proposed for diagnosing hypertension as well as for evaluating the patient's response to treatment. The retrospective evaluation of this test provided high sensitivity and specificity in the diagnosis of hypertension, with a threshold value for the hyperbaric index of 15 mm Hg. h. To evaluate the stability and reproducibility of this tolerance-hyperbaric test, we studied 332 previously untreated subjects (218 men) who underwent sequential 48-hour ambulatory blood pressure monitoring for 2 years, providing a total of 1337 blood pressure profiles. Diagnosis of hypertension was established for each subject on the restricted basis of presenting at least 1 blood pressure profile with a hyperbaric index above the previously defined threshold. Sensitivity of this tolerance-hyperbaric test was 98.6%, with a negative predictive value of 99.7%. For the same subjects, the blood pressure load (percentage of values >140/110/90 mm Hg for systolic/mean arterial/diastolic blood pressure during activity or >120/95/80 mm Hg during resting hours) had a sensitivity of 49% and specificity of 25%. The 24-hour mean, still the most common approach for diagnosing hypertension on the basis of ambulatory monitoring, had sensitivities of 40% and 31% for systolic and diastolic blood pressure, respectively. Despite the limitations of ambulatory blood pressure monitoring, the tolerance-hyperbaric test represents a reproducible, noninvasive, and high-sensitivity test for the identification of subjects in need of prophylactic or therapeutic intervention. (+info)
Effect of continuous positive airway pressure on blood pressure : a placebo trial.
(43/1099)
This study examined the effect of continuous positive airway pressure (CPAP) treatment on blood pressure in patients with obstructive sleep apnea. Thirty-nine patients with sleep apnea were studied. Ambulatory blood pressure monitoring was obtained before and after patients were randomized to receive either 1 week of CPAP or placebo CPAP (CPAP administered at ineffective pressure). Blood pressure was examined over daytime hours (6 AM to 10 PM) and during nighttime hours (10 PM to 6 AM). Daytime mean arterial blood pressure decreased significantly but equally in both the active treatment group and the placebo treatment group (P=0.001). Nighttime mean arterial pressure levels decreased to a much greater extent over time in the patients who received active CPAP treatment (P=0. 032). CPAP does appear to decrease nighttime blood pressure. However, the decrease in daytime blood pressure may reflect a nonspecific response (ie, placebo), since both the active treatment group and the placebo treatment group developed comparable decreases in blood pressure. (+info)
Renin-angiotensin system genetic polymorphisms and salt sensitivity in essential hypertension.
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We evaluated the association between salt-sensitive hypertension and 3 different genetic polymorphisms of the renin-angiotensin system. Fifty patients with essential hypertension were classified as salt sensitive or salt resistant, depending on the presence or absence of a significant increase (P<0.05) in 24-hour ambulatory mean blood pressure (BP) after high salt intake. The insertion/deletion (I/D) angiotensin-converting enzyme (ACE) gene, the M235T angiotensinogen (AGT) gene, and the A1166C angiotensin II type 1 (AT1) receptor gene polymorphisms were determined with the use of standard polymerase chain reaction methods. Twenty-four (48%) patients with significantly increased (P<0.05) 24-hour mean BP with high salt intake (from 107.3+/-9.4 to 114.8+/-10.6 mm Hg) were classified as salt sensitive. In the remaining 26 patients (52%), high salt intake did not significantly modify 24-hour mean BP (from 107.6+/-10 to 107. 8+/-9 mm Hg), and they were classified as having salt-resistant hypertension. We did not find any significant association between either M235T AGT or A1166C AT1 receptor genotypes and the BP response to high salt intake. However, patients with essential hypertension homozygous for the insertion allele of the ACE gene (II) had a significantly higher BP increase with high salt intake (9. 8+/-8.1 mm Hg for systolic BP and 5.2+/-4.2 mm Hg for diastolic BP) than that observed in patients homozygous for the deletion allele (DD) (1.2+/-5.9 mm Hg for systolic BP; P=0.0118 and -0.2+/-4.2 mm Hg for diastolic BP; P=0.0274). Heterozygous patients (ID) exhibited an intermediate response. The prevalence of salt-sensitive hypertension also was significantly higher (P=0.012) in II (67%) and DI patients (62%) compared with DD hypertensives (19%). We conclude that a significant association exists between the I/D polymorphism of the ACE gene and salt-sensitive hypertension. Patients with II and DI genotypes have significantly higher prevalence of salt sensitivity than DD hypertensives. (+info)
Attenuation of the "white-coat effect" by antihypertensive treatment and regression of target organ damage.
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This study assessed whether 2 common surrogate measures of the "white-coat effect," namely the clinic-daytime and the clinic-home differences in blood pressure (BP), were attenuated by long-term antihypertensive treatment and whether this attenuation is relevant to the treatment-induced regression of left ventricular hypertrophy, thus having clinical significance. We considered data from 206 patients with essential hypertension (aged 20 to 65 years) who had a diastolic BP between 95 and 115 mm Hg and echocardiographic evidence of left ventricular hypertrophy. In each patient, clinic BP, 24-hour ambulatory BP, and left ventricular mass index were assessed at baseline, after 3 and 12 months of treatment with an angiotensin-converting enzyme inhibitor, and after a final 4-week placebo run-off period. At baseline, the clinic-daytime differences in systolic and diastolic BP were 12.1+/-15.4 and 6.8+/-10.1 mm Hg, respectively; the corresponding values for the clinic-home differences were 5.7+/-10.6 and 2.9+/-6.1 mm Hg, respectively. These differences were reduced by 57.6% and 77.1% (P<0.01) and by 65.7% and 64.3% (P<0.01), respectively, after 12 months of treatment, with a partial return toward the pretreatment differences after the final placebo period. The observed treatment-induced reductions in left ventricular mass index and those in the clinic-daytime or clinic-home differences for systolic and diastolic BP showed no significant relationship when tested by multiple regression analysis. This provides the first longitudinal evidence that clinic-daytime and clinic-home differences in BP have no substantial value in predicting the regression of target organ damage, such as left ventricular hypertrophy, that has prognostic relevance. (+info)
Long-term telemetric recording of arterial pressure and heart rate in mice fed basal and high NaCl diets.
(46/1099)
Research examining the control of arterial pressure in mice has primarily relied on tail-cuff plethysmography and, more recently, on tethered arterial catheters. In contrast, the radiotelemetry method has largely become the "gold standard" for long-term monitoring of arterial pressure and heart rate in rats. Whereas smaller telemetry probes have recently been developed, no published studies have used radiotelemetric monitoring of arterial pressure in mice, largely because of a relatively low success rate in small mice (ie, <30 g body weight). We report on the development of a protocol for the use of these probes to continuously monitor arterial pressure and heart rate in mice as small as 19 g body weight. To test the accuracy and reliability of this method, adult C57/BL6 mice were monitored for 3 weeks during exposure to a basal followed by a high NaCl diet. The results demonstrate that carotid and aortic placements of the telemetry probe provide equally accurate monitoring of arterial pressure and heart rate, but the carotid placement has a much greater rate of success. Exposure to a high NaCl diet increases both the amplitude of the arterial pressure rhythm (+ 6.0+/-0.6 mm Hg, approximately 32%) and the average mean arterial pressure (+ 8.6+/-1.1 mm Hg, approximately 8%), as would be predicted from previous studies in NaCl-resistant rats. Thus, the data demonstrate that telemetric recording of long-term arterial pressure and heart rate provides a powerful tool with which to define the mechanisms of cardiovascular control in mice. (+info)
Endothelin-1 plasma levels are not elevated in patients with obstructive sleep apnoea.
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Endothelin-1 (ET-1), a potent vasoconstrictor, is released mainly by vascular endothelial cells under the influence of hypoxia and other stimuli. ET-1 is related to endothelial dysfunction, as well as arterial and pulmonary hypertension, all of which are thought to be associated with obstructive sleep apnoea (OSA). This study evaluated venous plasma concentrations of ET-1 and noradrenaline and 24-h systemic blood pressure in 29 patients with OSA (age=56.9+/-1.6 yrs; body mass index=29.5+/-0.7 kg x m2 (mean+/-SEM)). Blood samples were taken in the morning, evening and during sleep. In the same way, the patients were assessed during a night of continuous positive airway pressure (CPAP) and after 13.9+/-1.4 months while still on CPAP. ET-1 levels were compared to those of control subjects, who were selected from in- and outpatients and were matched to patients for age, sex, presence of arterial hypertension and coronary artery disease. ET-1 plasma levels were not elevated in the patients compared to the controls (41.6+/-2.2 and 44.9+/-1.3 pg x mL(-1), respectively, p=0.20). The ET-1 concentration did not change significantly, neither during sleep nor in the first night on CPAP therapy, nor under long-term treatment with CPAP. ET-1 neither correlated to the severity of OSA nor to that of systemic hypertension. The results suggest that endothelin-1 does not play a crucial role in the pathophysiology of obstructive sleep apnoea. (+info)
Glomerular hyperfiltration in hypertensive African Americans.
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The incidence of end-stage renal disease attributable to hypertension is 5-fold greater in African Americans than in whites. To determine whether glomerular hyperfiltration is an antecedent to renal failure, we compared responses of renal blood flow and glomerular filtration rate to graded infusions of norepinephrine (0. 01, 0.025, and 0.05 microg. kg(-1). min(-1) for 30 minutes each) in 29 African Americans and 33 age-matched French Canadian whites with essential hypertension. Renal blood flow and glomerular filtration rate were measured by using a constant-infusion technique of PAH and inulin, respectively. Studies were conducted on an inpatient clinical research center, and antihypertensive medications had been discontinued for at least 1 week. Based on 24-hour blood pressure monitoring, nighttime blood pressures decreased (P<0.01) in the French Canadians but not in the African Americans. Baseline renal blood flow was higher (P<0.05) in the African Americans (1310+/-127 mL. min(-1) per 1.73 m(2)) than in the French Canadians (1024+/-42 mL. min(-1) per 1.73 m(2)); baseline glomerular filtration rate was also higher (P<0.01) in the African Americans (140+/-4 versus 121+/-4 mL. min(-1) per 1.73 m(2)). In response to norepinephrine-induced blood pressure increases, renal blood flow was autoregulated and did not change in either patient group. In the African Americans, glomerular filtration rate increased (P<0.01) to 167 mL. min(-1) per 1.73 m(2) during the first norepinephrine infusion, without subsequent change. In contrast, glomerular filtration rate did not change with norepinephrine-induced increases of blood pressure in the French Canadians. In the African Americans, the elevation of baseline glomerular filtration rate, with a further increase in response to norepinephrine, may be indicative of glomerular hyperfiltration. Glomerular hyperfiltration and lack of nocturnal blood pressure decline may contribute to the higher incidence of end-stage renal disease in hypertensive African Americans. (+info)