Total sleep deprivation elevates blood pressure through arterial baroreflex resetting: a study with microneurographic technique

STUDY OBJECTIVES: Sleep deprivation has a profound effect on cardiovascular regulation through the autonomic nervous system. This study examined the effect of 24-hour total sleep deprivation on muscle sympathetic nerve activity (MSNA), which is a direct measurement of the postganglionic sympathetic efferent innervating the vascular bed in the skeletal muscle and other circulatory structures. DESIGN: The study was performed on 6 young healthy men. The factors exerting influence on MSNA, such as aging, obesity, body posture, activity, intensity of illumination, and food and beverage consumption were strictly controlled. Burst rate and burst incidence were used as parameters of MSNA. The burst rate, burst incidence, heart rate, and systolic and diastolic blood pressure were measured after total sleep deprivation and control sleep. To perform a linear regression analysis of arterial baroreflex (ABR), the incidence of MSNA bursts corresponding to a given diastolic blood pressure (%MSNA) was examined. MEASUREMENT AND RESULTS: The diastolic blood pressure was significantly higher after total sleep deprivation than after control sleep (66.5 +/- 1.7 vs 57.4 +/- 3.3 mm Hg). The burst rate (9.6 +/- 1.8 vs 13.3 +/- 2.7 bursts/min) and burst incidence (21.6 +/- 4.5 vs 30.3 +/- 8.9 bursts/100 heart beats) of MSNA were significantly lower after total sleep deprivation than after control sleep (P < .05). Analysis of the ABR disclosed a significant linear regressive relation between %MSNA and diastolic blood pressure in every subject after both total sleep deprivation and control sleep. This result implies that the ABR regulates the occurrence of MSNA bursts under different diastolic blood pressure conditions. The threshold (X-axis intercept) of the blood pressure regression line (ie, an indicator of the ABR set point) shifted by 12 +/- 4.3 mm Hg toward a higher blood pressure level after total sleep deprivation (P < .05). The ABR sensitivity, or the slope of the regression line, tended to be less steep after total sleep deprivation than after control sleep, although it was not statistically significant (P = .09). CONCLUSIONS: The diastolic blood pressure increased and both burst rate and burst incidence of MSNA decreased after total sleep deprivation. The results show that resetting of the ABR toward a higher blood pressure level occurred after total sleep deprivation. This ABR resetting probably brings about an increase in arterial blood pressure after total sleep deprivation.     

Hormone replacement therapy reduces mean 24-hour blood pressure and its variability in postmenopausal women with treated hypertension

BACKGROUND: The rate and severity of hypertension increase dramatically after menopause. Complications seem to be more frequent and marked in hypertensive patients with greater blood pressure (BP) variability, and antihypertensive treatment does not easily reduce this variability. The effect of hormone replacement therapy (HRT) on BP and its variability is not well understood in moderate to severe hypertension, but estrogen may have calcium channel-blocking properties. Cardiovascular events occur more frequently in the morning, likely in part because of a rise in BP. DESIGN: We prospectively studied 34 postmenopausal women with treated hypertension (mean age = 53 years) and receiving a cyclic combination of estradiol and norgestrel for 19 weeks with 24-h ambulatory BP monitoring. RESULTS: Mean daily BP and its variability decreased significantly with HRT (149.3 +/- 6.1 mm Hg vs. 140.3 +/- 8.5 mm Hg [p < 0.001]; diastolic: 95.4 +/- 4.7 mm Hg vs. 92.4 +/- 7.2 mm Hg [p < 0.05]). There was also a significant decrease in the early morning BP values after HRT (154.0 +/- 6.9 mm Hg vs. 145.6 +/- 11.0 mm Hg [p < 0.001]; diastolic: 98.0 +/- 4.8 mm Hg vs. 95.1 +/- 10.0 mm Hg [p < 0.05]). Subjects who were taking calcium channel blockers (n = 11) had only half the reduction in 24-h systolic BP compared with those who were not taking calcium channel blockers (5.3 mm Hg vs. 10.5 mm Hg), and the reduction in those who were taking calcium channel blockers failed to reach statistical significance. CONCLUSIONS: Our results demonstrate that HRT may have a role in decreasing the severity of hypertension, and the mechanism of its action might be through calcium channels.     

Initial cardiovascular response on change of posture from squatting to standing

Summary The immediate cardiovascular responses on active change from the squatting (control) to the standing position differ from those obtained in the lying-to-standing manoeuvre. Without exception, the first beat after changing from squatting to standing showed a decrease in systolic, diastolic and mean pressure by 2.0±1.1 kPa (14.6±8.3 mm Hg), 1.4±1.7 kPa (10.6±12.6 mm Hg) and 1.9±1.0 kPa (13.9±7.3 mm Hg), respectively. During the 4^th or 5^th pulse after standing the pulse pressure was significantly higher than when lying (P<0.01). Mean pressure reached a minimum of 7.7±1.9 kPa (57.8±14.4 mm Hg) after 7.1±1.1s. Thereafter the blood pressure increased to a new level within about 15 s. 11 of 16 subjects demonstrated a biphasic heart rate (HR) response. The maximum HR was reached after 11.0±2.4 s of standing. In all experiments, the peaks in HR were distinctly delayed after the blood pressure clips. We conclude that an arterial baroreflex could be implicated in the immediate HR increase after a squatting-tostanding manoeuvre. The subsequent time course of the initial HR response, however, might be induced by other mechanisms.     

Assessment of Baroreceptor Reflex Function During Mental Stress and Relaxation

This paper describes a method of measuring baroreceptor cardiac reflex sensitivity noninvasively from spontaneous patterns of blood pressure and interbeat interval, and the application of this technique in psychophysiology. Baroreflex function was assessed in 24 female volunteers during relaxation and performance of the cold pressor test and a non-verbal mental arithmetic task. Blood pressure and interbeat interval were monitored continuously from the finger using the vascular unloading technique. Sequences of three or more cardiac cycles were identified over which systolic blood pressure increased progressively in conjunction with lengthening interbeat interval, or systolic blood pressure decreased as interbeat interval was reduced. The regression between systolic blood pressure and interbeat interval was computed as an index of baroreflex sensitivity. Relaxation was associated with a small prolongation of interbeat interval, whereas baroreflex sensitivity increased from 17.1 to 19.8 ms/mmHg. Baroreflex sensitivity was reduced significantly during mental arithmetic (mean 14.2 ms/mmHg) but not during the cold pressor test (mean 17.4 ms/mmHg). The difference between mental arithmetic and the cold pressor test may be related to the relative intensity of cardiac and vascular responses in the two situations. The implications of these results for the understanding of behavioural influences on haemodynamic function are discussed and the advantages of noninvasive methods are considered.     

Elevated arterial blood pressure in cardiac tamponade.

BACKGROUND. In cardiac tamponade cardiac output falls, but peripheral vascular resistance increases, so that systemic blood pressure may be maintained at normal or near-normal levels. We recently observed a patient with cardiac tamponade whose blood pressure was markedly elevated. METHODS. To determine the frequency of elevated blood pressure in patients with cardiac tamponade and their hemodynamic characteristics, we studied 18 consecutive patients with cardiac tamponade from a variety of causes using right heart catheterization. RESULTS. Six of the 18 patients had systolic arterial blood pressures ranging from 150 to 210 mm Hg (mean [+/- SD], 176 +/- 26) and diastolic pressures ranging from 100 to 130 mm Hg (mean, 113 +/- 14). All six had previously been hypertensive. After pericardiocentesis there was a significant decrease in blood pressure (to 139 +/- 13 mm Hg systolic, P less than 0.05; and 83 +/- 6 mm Hg diastolic, P less than 0.01) and peripheral vascular resistance (from 2150 +/- 588 to 1207 +/- 345 dyn.sec.cm-5, P less than 0.01). Cardiac output increased in all six. The other 12 patients, 3 of whom had a history of hypertension, had significant increases in cardiac output and systolic blood pressure (from 119 +/- 13 to 127 +/- 7 mm Hg, P less than 0.05) after pericardiocentesis, whereas peripheral vascular resistance decreased. Both groups had similar degrees of cardiac tamponade, as indicated by measurements of cardiac output and intrapericardial, right atrial, and pulmonary-artery wedge pressures. CONCLUSIONS. Elevated blood pressure may occur in some patients with cardiac tamponade who have preexisting hypertension. Moreover, blood pressure may fall after pericardiocentesis in patients who have elevated blood pressure associated with tamponade.     

Relationship of blood pressure and pump flow in an implantable centrifugal blood pump during hypertension

The purpose of this study was to evaluate the real time relationship between pump flow and pump differential pressure (D-P) during experimentally induced hypertension (HT). Two calves (80 and 68 kg) were implanted with the EVA-HEART centrifugal blood pump (SunMedical Technology Research Corp., Nagano, Japan) under general anesthesia. Blood pressure (BP) in diastole was increased to 100 mm Hg by norepinephrine to simulate HT. Pump flow, D-P, ECG, and BP were measured at pump speeds of 1,800, 2,100, and 2,300 rpm. All data were separated into systole and diastole, and pump flow during HT was compared with normotensive (NT) conditions at respective pump speeds. Diastolic BP was increased to 99.3+/-4.1 mm Hg from 66.5+/-4.4 mm Hg (p<0.01). D-P in systole was under 40 mm Hg (range of change was 10 to 40 mm Hg) even during HT. During NT, the average systolic pump flow volume was 60% of the total pump flow. However, during HT, the average systolic pump flow was 100% of total pump flow volume, although the pump flow volume in systole during HT decreased (33.1+/-5.7 vs. 25.9+/-4.0 ml/systole, p<0.01). In diastole, the average flow volume through the pump was 19.6+/-6.9 ml/diastole during NT and -2.2+/-11.1 ml/diastole during HT (p<0.01). The change in pump flow volume due to HT, in diastole, was greater than the change in pump flow in systole at each pump speed (p<0.001). This study suggests that the decrease of mean pump flow during HT is mainly due to the decrease of the diastolic pump flow and, to a much lesser degree, systolic pump flow.     

Energy equivalent pressure and total hemodynamic energy associated with the pressure-flow waveforms of a pediatric pulsatile ventricular assist device

A pulsatile pediatric ventricular assist device (VAD) with a dynamic stroke volume of approximately 12 ml was tested to quantify the effect of flowrate and systolic duration on pulsatility as quantified by the energy equivalent pressure (EEP), defined as the hemodynamic energy per unit volume of fluid pumped. The VAD was tested on a mock circulatory loop, adjusted to maintain a systemic arterial pressure of approximately 90/60 mm Hg (systolic/diastolic) and a mean of 75 mm Hg. The EEP was calculated for each beat for 1 minute at both the proximal end of the pump outlet cannula and at the distal end (arterial EEP). Nominal mean flowrates were 0.50, 0.75, 1.00, and 1.25 l/min. Systolic duration was set at either 230 or 400 milliseconds. With a rapid systolic ejection (230 milliseconds), the arterial EEP ranged from 5.58% to 8.41% relative to the mean arterial pressure. The highest EEP occurred at the lowest flowrate. With a slower (400 milliseconds) systolic ejection, the arterial EEP ranged from 2.33% to 4.20%. Hemodynamic energy loss in the outlet cannula was also quantified by the differential EEP and shown to increase markedly as systolic duration was decreased, but was relatively insensitive to mean flowrate.     

Acute and chronic stress influence blood pressure variability in mice

There is evidence that alterations in heart rate and blood pressure variability (BPV) are associated with cardiovascular disease. We used a mice model to investigate the effects of acute and chronic stress on blood pressure variability (BPV) and heat rate variability (HRV). Shaker stress was given acutely (5 min, 150 cycles/min) and chronically (3 days, 2 min stress, 150 cycles/min, 45 sessions/day) in male C57BLJ mice. Systolic arterial pressure (SAP) and pulse interval (PI) time series were submitted to autoregressive spectral analysis with variability measured in the low-frequency (LF, 0.1-1.0 Hz) and high-frequency (HF, 1-5 Hz) ranges. In the acute experiment, MAP was increased significantly in the first 10 min poststress period (99+/-2 vs. 113+/-2 mm Hg) and returned to control levels 30 min poststress. HR was significantly higher in the initial poststress period (537+/-12 vs. 615+/-20 bpm). These alterations were associated with a marked increase in BPV (21+/-4 vs. 55+/-11 mm Hg2) and in power of LF oscillations (18+/-3 vs. 42+/-7 mm Hg2). On the other hand, chronic stress exposure produced a reduction in BPV (16+/-4 vs. 6+/-1 mm Hg2) and LF oscillations (11+/-3 vs. 3+/-1 mm Hg2). HRV was not altered after either acute or chronic stress. Spontaneous baroreflex sensitivity (SBS), determined by cross-spectral analysis between PI and BP, was reduced significantly in acute stress (-50%), but unchanged in chronic stress. Our results show that acute stress produced changes in BPV that may be associated with increased sympathetic activity and a reduction in blood pressure buffering. Under chronic conditions, there is no alteration in baroreflex sensitivity while BPV is reduced. This is likely related to the combination of sympathetic activation in the face of vasculature alterations.     

Blood pressure perturbations caused by subclinical sleep-disordered breathing

We studied the acute effects of apneas and hypopneas on blood pressure in a nonclinic population of middle-aged adults. Arterial pressure was measured noninvasively (photoelectric plethysmography) during an overnight, in-laboratory polysomnographic study in 72 men and 23 women enrolled in the Wisconsin Sleep Cohort Study, a population-based study of sleep-disordered breathing. Sleep-disordered breathing events (272 apneas and 1469 hypopneas) were observed in 92% of subjects. The across-subject mean decreases in arterial O2 saturation were 9+/-8% (SD) for apneas (17+/-8 seconds duration) and 4+/-3% for hypopneas (21+/-6 seconds duration; 41+/-17% of baseline ventilation). In both apneas and hypopneas, even those with only 1% to 3% O2 desaturations, blood pressure decreased during the event, followed by an abrupt increase in the postevent recovery period. Mean values for peak changes in blood pressure (difference between the maximum during the recovery period and the minimum during the event) were 23+/-10 mm Hg for systolic and 13+/-6 mm Hg for diastolic pressure. The strongest predictors of the pressor responses to apneas and hypopneas were (in order of importance): magnitude of the ventilatory overshoot, length of the event, magnitude of changes in heart rate and arterial O2 saturation, and presence or absence of electroencephalographic arousal. We speculate that these fluctuations may play a role in the pathogenesis of hypertension in individuals with subclinical sleep-disordered breathing.     

Association of breathing movements to the variability of heart rate and blood pressure in foetal lambs

Heart rate (HR) variability and arterial blood pressure (BP) variability were analysed as functions of foetal breathing movements (FBMs) by means of power spectral analysis in seven foetal lambs during the third trimester of gestation. No evidence of FBM-related changes, either in mean HR, mean systolic or diastolic arterial pressures, were found. Mean arterial pulse pressure, HR variability, and BP variability increased during FBMs. The increase in BP variability occurred at frequencies higher than 0.35 Hz, i.e. those of FBMs. The increase in HR variability occurred at 0.07-1.0 Hz, i.e. at every frequency band except the lowest one. Thus, the increase in HR variability was not frequency-specifically related to FBMs. During FBMs the periodic variability of HR at frequencies > 0.35 Hz was only 10% of total HR variability. We suggest that the FBM-related changes of BP variability may be mediated by direct peripheral, hydraulic mechanisms. HR changes involve autonomic control systems: the vagal component of baroreflex seems to be relatively insensitive, whereas the very slow vasomotor component of HR variability is dominant.     

Optimized veno-venous bypass with the affinity pump

Veno-venous bypass (VVBP) is increasingly used to avoid acute venous hypertension and low cardiac output after clamping the vena cava. Air embolism upon accidental decannulation of the inflow line and endothelial damage due to suction of the blood collecting cannula to the vessel wall are known complications specific to the currently used roller and centrifugal pumps, because they generate negative pressure at the inflow site of the pump. The Affinity pump has a unique chamber design with an occlusive segment, that collapses in low filling states preventing negative pressure at the inflow site of the pump chamber. This device was tested for VVBP in three pigs (each weighing 52.3 +/- 5.1 kg) with hepatic vascular exclusion. Blood was pumped from the femoral and portal veins to the external jugular vein and perfusion was maintained for 6 hours. The hemodynamic state of the animals was assessed by recording heart rate; systolic, mean arterial, and diastolic pressure; as well as central venous pressure. Mean pump flow during the experiment was 1,629.3 +/- 372.2 ml/min. After clamping, the inflow line of the pump mean arterial pressure significantly decreased (from 69.5 +/- 4.4 to 43.1 +/- 3.5 mm Hg), and mean pressure in the femoral vein increased significantly (from 16.1 +/- 2.6 to 26.8 +/- 5.9 mm Hg), whereas the mean pressure in the internal jugular vein did not significantly change (from 6.0 +/- 1.7 to 5.0 +/- 2.1 mm Hg). There was no suction by the blood collecting cannula on the vessel wall, and neither bubbles nor air emboli were detected and no operator intervention was needed. In conclusion, the Affinity pump eliminates device related complications due to negative pressure generated at the inlet, and guarantees stable hemodynamics. Its application is simple and safe and minimal operator intervention is needed, making the Affinity pump particularly suited for veno-venous bypass.     

Effect of celiprolol treatment in hypertensive patients with sleep apnea.

The effects of a beta-blocker, celiprolol, on sleep and arterial blood pressure (BP) were evaluated during a single-blind study in seven hypertensive patients with sleep apnea. Diurnal ambulatory BP measurements with an automatic cuff-inflation device and polysomnography with simultaneous Finapres BP recording were performed separately on consecutive days at the end of two 21-day treatment periods involving placebo followed by celiprolol (200 mg/day). Age was 59 +/- 2.5 yr (m +/- sem) and body mass index 33.2 +/- 2.3 kg. m-2. Diurnal ambulatory BP was significantly lower with celiprolol than with placebo (systolic 139 +/- 4 vs 152 +/- 5 mmHg, diastolic 86 +/- 2 vs 96 +/- 2 mmHg). The apnea-hypopnea index was similar under celiprolol and placebo (48 +/- 7.4 vs 53 +/- 7.8, respectively), as were the total sleep time and percent of duration of the different sleep stages. Individual average BP values were significantly lower during REM sleep under celiprolol but remained similar under celiprolol and placebo in the other sleep stages. Variability of nocturnal BP (assessed by the SD of distribution of BP variations) was not affected by celiprolol. In conclusion, celiprolol which decreased daytime BP, did not affect sleep pattern or respiratory disturbances, or nocturnal BP variability related to apnea.     

The pathogenesis of acute pulmonary edema associated with hypertension

BACKGROUND: Patients with acute pulmonary edema often have marked hypertension but, after reduction of the blood pressure, have a normal left ventricular ejection fraction (> or =0.50). However, the pulmonary edema may not have resulted from isolated diastolic dysfunction but, instead, may be due to transient systolic dysfunction, acute mitral regurgitation, or both. METHODS: We studied 38 patients (14 men and 24 women; mean [+/-SD] age, 67+/-13 years) with acute pulmonary edema and systolic blood pressure greater than 160 mm Hg. We evaluated the ejection fraction and regional function by two-dimensional Doppler echocardiography, both during the acute episode and one to three days after treatment. RESULTS: The mean systolic blood pressure was 200+/-26 mm Hg during the initial echocardiographic examination and was reduced to 139+/-17 mm Hg (P< 0.01) at the time of the follow-up examination. Despite the marked difference in blood pressure, the ejection fraction was similar during the acute episode (0.50+/-0.15) and after treatment (0.50+/-0.13). The left ventricular regional wall-motion index (the mean value for 16 segments) was also the same during the acute episode (1.6+/-0.6) and after treatment (1.6+/-0.6). No patient had severe mitral regurgitation during the acute episode. Eighteen patients had a normal ejection fraction (at least 0.50) after treatment. In 16 of these 18 patients, the ejection fraction was at least 0.50 during the acute episode. CONCLUSIONS: In patients with hypertensive pulmonary edema, a normal ejection fraction after treatment suggests that the edema was due to the exacerbation of diastolic dysfunction by hypertension--not to transient systolic dysfunction or mitral regurgitation.     

The relationships of resting baroreflex sensitivity, heart rate variability and measures of impulse control in children and adolescents.

The objectives of the present study were to assess: (1) the feasibility of using a non-invasive method to measure baroreflex sensitivity in children and adolescents; (2) the relationships of resting baroreflex sensitivity with resting levels of other cardiovascular variables; and (3) whether baroreflex sensitivity and heart rate variability, two indices of cardiac vagal control at rest, were related to measures of impulse control. Ninety-one Black and White children (ages 8-10) and adolescents (ages 15-17), both female and male, participated in the study. Baroreflex sensitivity, auscultatory blood pressure, EKG-derived heart rate, and the mean successive difference of interbeat intervals were collected during a 10-min rest period. Measures of impulse control came from the Interview for Antisocial Behavior. Baroreflex sensitivity was strongly positively correlated with mean successive difference and negatively correlated with heart rate for all participant groups; baroreflex sensitivity was negatively correlated with diastolic blood pressure, but only for children, males, and Blacks. Increased problems with impulse control was associated with decreased cardiac vagal control, but only in males. The usefulness of this technique as a measure of vagal activation is discussed.     

Arterial stiffness increases during obstructive sleep apneas

STUDY OBJECTIVES: Obstructive sleep apnea (OSA) appears to be an independent risk factor for diurnal systemic hypertension, but the specific biologic markers for this association have not been well established. Increased arterial stiffness is an important measure of increased left ventricular load and a predictor of cardiovascular morbidity and may precede the onset of systemic hypertension in humans. However, arterial stiffness has not been measured in association with obstructive apneas in patients with OSA, nor related to systemic blood pressure (BP) activity in this setting. Our objective was to test the hypothesis that arterial stiffness may be utilized as a sensitive measure of arterial vasomotor perturbation during obstructive events in patients with OSA, by demonstrating that (1) arterial stiffness increases acutely in association with obstructive apnea and hypopnea, and that (2) such increased stiffness may occur in the absence of acute BP increase. DESIGN: Prospective, cross-sectional. SETTING: A tertiary-care university-based sleep and ventilatory disorders center. PATIENTS: Forty-four normo- and hypertensive adult patients (11 women, 33 men) with polysomnographically diagnosed moderate to severe OSA. INTERVENTIONS: N/A. MEASUREMENTS AND RESULTS: Beat-to-beat BP was recorded from the radial artery by applanation tonometry during nocturnal polysomnography. Arterial augmentation index (AAI), a measure of arterial stiffness, was calculated as the ratio of augmented systolic BP (SBP) to pulse pressure and expressed as a percentage for the following conditions: awake, the first 10 ("early apnea") and last 10 ("late apnea") cardiac cycles of obstructive events, and the first 15 cardiac cycles following apnea termination ("post apnea"). Mean AAI (+/-SD) for the group was significantly increased during NREM sleep from early apnea to late apnea (12.02 +/- 2.70% vs 13.35 +/- 3.54%, p<0.05, ANOVA). During REM (analyzed in 20 patients), MI again significantly increased from early apnea to late apnea (11.75 +/- 2.81% vs 13.43 +/- 4.97%). Conversely, neither mean SBP nor mean arterial BP was significantly changed from early apnea to late apnea in NREM (SBP 130 +/- 14 mmHg vs 129 +/- 14 mmHg) or REM (SBP 128 +/- 22 mmHg vs 127 +/- 21 mmHg). CONCLUSIONS: Arterial stiffness increases acutely during obstructive apneas in both NREM and REM sleep, in the absence of measurable BP change. These data suggest that arterial stiffness may be a sensitive measure of acute arterial vasomotor perturbation in this setting and may have implications concerning cardiovascular sequelae in patients with OSA.     

The effect of balloon angioplasty on hypertension in atherosclerotic renal-artery stenosis. Dutch Renal Artery Stenosis Intervention Cooperative Study Group

BACKGROUND: Patients with hypertension and renal-artery stenosis are often treated with percutaneous transluminal renal angioplasty. However, the long-term effects of this procedure on blood pressure are not well understood. METHODS: We randomly assigned 106 patients with hypertension who had atherosclerotic renal-artery stenosis (defined as a decrease in luminal diameter of 50 percent or more) and a serum creatinine concentration of 2.3 mg per deciliter (200 micromol per liter) or less to undergo percutaneous transluminal renal angioplasty or to receive drug therapy. To be included, patients also had to have a diastolic blood pressure of 95 mm Hg or higher despite treatment with two antihypertensive drugs or an increase of at least 0.2 mg per deciliter (20 micromol per liter) in the serum creatinine concentration during treatment with an angiotensin-converting-enzyme inhibitor. Blood pressure, doses of antihypertensive drugs, and renal function were assessed at 3 and 12 months, and patency of the renal artery was assessed at 12 months. RESULTS: At base line, the mean (+/-SD) systolic and diastolic blood pressures were 179+/-25 and 104+/-10 mm Hg, respectively, in the angioplasty group and 180+/-23 and 103+/-8 mm Hg, respectively, in the drug-therapy group. At three months, the blood pressures were similar in the two groups (169+/-28 and 99+/-12 mm Hg, respectively, in the 56 patients in the angioplasty group and 176+/-31 and 101+/-14 mm Hg, respectively, in the 50 patients in the drug-therapy group; P=0.25 for the comparison of systolic pressure and P=0.36 for the comparison of diastolic pressure between the two groups); at the time, patients in the angioplasty group were taking 2.1+/-1.3 defined daily doses of medication and those in the drug-therapy group were taking 3.2+/-1.5 daily doses (P<0.001). In the drug-therapy group, 22 patients underwent balloon angioplasty after three months because of persistent hypertension despite treatment with three or more drugs or because of a deterioration in renal function. According to intention-to-treat analysis, at 12 months, there were no significant differences between the angioplasty and drug-therapy groups in systolic and diastolic blood pressures, daily drug doses, or renal function. CONCLUSIONS: In the treatment of patients with hypertension and renal-artery stenosis, angioplasty has little advantage over antihypertensive-drug therapy.     

Evaluation of the harmonized alert sensing technology device for hemodynamic monitoring in chronic hemodialysis patients

The Harmonized Alert Sensing Technology (HASTE) device was developed to overcome the primary shortcomings of interval based noninvasive blood pressure (BP) monitoring. This study was conducted to assess the reliability of the HASTE system compared with standard cuff BP values in patients on hemodialysis. A total of 1,370 HASTE measurements were compared with oscillometric standard cuff systolic BP values in 42 sessions of 15 patients on hemodialysis. The average discrepancy between the HASTE and cuff systolic BP was 1.41 +/- 16.90 mm Hg. Compared with cuff measurements, 31% of systolic BP fell within a range of 5 mm Hg difference, 57% of systolic BP fell within 10 mm Hg, and 73% of systolic BP fell within a 15 mm Hg band. According to British Hypertension Society standards or Association for the Advancement of Medical Instrumentation criteria, the current HASTE method did not perform well. Technology to provide noninvasive hemodynamic monitoring is, however, in its developmental stage. The effort at continuous systolic pressure monitoring using existing, readily available, and frequently used techniques is exciting. Although the HASTE system as currently configured and calibrated did not adequately perform, variations in site analysis and conversion factors may increase pressure sensitivity and tracking over the course of a standard dialysis treatment.     

Oral appliance therapy reduces blood pressure in obstructive sleep apnea: a randomized, controlled trial

STUDY OBJECTIVE: To investigate the short-term effect (4 weeks) of oral appliance therapy for obstructive sleep apnea on blood pressure. DESIGN: Randomized, controlled, crossover trial. SETTING: Multidisciplinary sleep disorders clinic in a university teaching hospital. PATIENTS: Sixty-one patients diagnosed with obstructive sleep apnea on polysomnography (apnea hypopnea index > or = 10 per hour and at least 2 of the following symptoms--daytime sleepiness, snoring, witnessed apneas, fragmented sleep; age > 20 years; and minimum mandibular protrusion of 3 mm). INTERVENTION: A mandibular advancement splint (MAS) and control oral appliance for 4 weeks each. MEASUREMENTS AND RESULTS: Polysomnography and 24-hour ambulatory blood pressure monitoring were carried out at baseline and following each 4-week intervention period. Patients showed a 50% reduction in mean apnea hypopnea index with MAS compared with the control and a significant improvement in both minimum oxygen saturation and arousal index. There was a significant reduction with the MAS in mean (+/- SEM) 24-hour diastolic blood pressure (1.8 +/- 0.5 mmHg) compared with the control (P = .001) but not in 24-hour systolic blood pressure. Awake blood-pressure variables were reduced with the MAS by an estimated mean (+/- SEM) of 3.3 +/- 1.1 mmHg for systolic blood pressure (P = .003) and 3.4 +/- 0.9 mmHg for diastolic blood pressure (P < .0001). There was no significant difference in blood pressure measured asleep. CONCLUSION: Oral appliance therapy for obstructive sleep apnea over 4 weeks results in a reduction in blood pressure, similar to that reported with continuous positive airway pressure therapy.     

Experimental testing of a new left ventricular assist device--the microdiagonal blood pump

All existing ventricular assist devices are associated with a considerable number of serious complications. This article reports on the first animal tests with a newly developed microdiagonal blood pump (MDP). Six adult female sheep weighing 80 to 90 kg underwent implantation of the microdiagonal blood pump. The inflow and outflow conduits were anastomosed to the left atrium and the descending aorta. Pump flow was adjusted to 2-3 L/minute. Hemodynamic and echocardiographic data, as well as blood samples, were measured over the entire test period of 7 days. All internal organs and the pump were explanted for thorough examination at the end of the trial. Mean arterial (range 88.5 +/- 13.1-103.7 +/- 10.7 mm Hg) and mean pulmonary arterial (18.3 +/- 2.7-21.6 +/- 20.5 mm Hg) pressures, as well as the pulmonary capillary wedge pressure (14.2 +/- 3.0 - 16.6 +/- 4.0 mm Hg), remained stable during the whole test period. Cardiac output (4.9 +/- 0.7 --> 3.2 +/- 0.5 L/minute) decreased postoperatively caused by partial unloading of the heart. Left ventricular end diastolic (4.1 +/- 0.5 --> 3.6 +/- 0.3 cm) and end systolic (3.2 +/- 0.4 --> 2.8 +/- 0.5 cm) diameters, as well as the ejection fraction (57 +/- 9 --> 42 +/- 5%), decreased after MDP implantation and did not change during the test period. Mean number of platelets (428 +/- 54 --> 286 +/- 66 x 10(3)/microL) and hemoglobin (9.8 +/- 1.3 --> 6.3 +/- 0.8 g/dL) decreased perioperatively because of surgical reasons and increased continuously in the postoperative course (platelet count and hemoglobin on day 7:441 +/- 74 x 10(3)/microL and 7.2 +/- 1.1 g/dL, respectively). Free hemoglobin was not enhanced in the postoperative course (mean value during the test period: 18.8 mmoL/L). Histologic examination of the organs did not demonstrate any infarctions of internal organs other than typical operative sequelae such as chronic pericarditis and some degree of atelectasis of the left lungs. These results demonstrate that the microdiagonal pump may be a promising alternative to the currently used ventricular assist devices, if long-term trials support these results.     

Foetal placental blood flow in the lamb

1. Fifteen sheep foetuses of 1.5-5.2 kg body weight were prepared with indwelling arterial and venous catheters for experimentation one to six days later.2. Unanaesthetized foetuses were found to have mean arterial and central venous blood pressures of 40 +/- 1.5 (S.E. of mean) and 2.0 +/- 0.3 (S.E. of mean) mm Hg respectively, compared to intra-uterine pressure. Intra-uterine pressure was 16 +/- 0.8 (S.E. of mean) mm Hg with respect to atmospheric pressure at mid-uterine level.3. Mean placental blood flow of the foetuses was 199 +/- 20 (S.E. of mean) ml./(min.kg body wt.). Mean cardiac output in eleven of the foetuses was 658 +/- 102 (S.E. of mean) ml./(min.kg).4. Mean foetal and maternal colloid osmotic pressures were 17.5 +/- 0.7 (S.E. of mean) and 20.5 +/- 0.6 (S.E. of mean) mm Hg respectively at 38 degrees C.5. Intravenous infusions into six ewes of 1.8 mole of mannitol and 0.4 mole of NaCl resulted in significant increases in foetal plasma osmolarity, sodium, potassium, and haemoglobin concentrations, without detectable transfer of mannitol to the foetal circulation.6. In the sheep placenta there is osmotic and hydrostatic equilibration of water. As a consequence, there should be an interaction between foetal placental blood flow and foetal water exchange with the maternal circulation. It was concluded that this interaction tends to stabilize foetal placental blood flow.