Wrist band photoplethysmography in detection of individual pulses in atrial fibrillation and algorithm-based detection of atrial fibrillation.

AIMS: Atrial fibrillation (AF) is the most common tachyarrhythmia and a significant cause of cardioembolic strokes. Atrial fibrillation is often intermittent and asymptomatic making detection a major clinical challenge. We evaluated a photoplethysmography (PPG) wrist band in individual pulse detection in patients with AF and tested the reliability of two commonly used algorithms for AF detection. METHODS AND RESULTS: A 5-min PPG was recorded from patients with AF or sinus rhythm (SR) with a wrist band and analysed with two AF detection algorithms; AFEvidence and COSEn. Simultaneously registered electrocardiogram served as the golden standard for rhythm analysis and was interpreted by two cardiologists. The study population consisted of 213 (106 AF, 107 SR) patients. The wrist band PPG achieved individual pulse detection with a sensitivity of 91.7 ± 11.2% and a positive predictive value (PPV) of 97.5 ± 4.6% for AF, with a sensitivity of 99.4 ± 1.5% [7.7% (95% confidence interval, 95% CI 5.5% to 9.9%); P < 0.001] and PPV of 98.1 ± 4.1% [0.6% (95% CI -0.6% to 1.7%); P = 0.350] for SR. The pulse detection sensitivity was lower 86.7 ± 13.9% with recent-onset AF (AF duration <48 h, n = 43, 40.6%) as compared to late AF (≥48 h, n = 63, 59.4%) with 95.1 ± 7.2% [-8.3% (95% CI -12.9% to -3.7%); P = 0.001]. For the detection of AF from the wrist band PPG, the sensitivities were 96.2%/95.3% and specificity 98.1% with two algorithms. CONCLUSION: The wrist band PPG enabled accurate algorithm-based detection of AF with two AF detection algorithms and high individual pulse detection. Algorithms allowed accurate detection of AF from the PPG. A PPG wrist band provides an easy solution for AF screening.

Stroke recurrence in patients with atrial fibrillation: concomitant carotid artery stenosis doubles the risk.

BACKGROUND AND PURPOSE: Atrial fibrillation (AF) and significant carotid artery stenosis (CAS) often coexist in patients with acute stroke but whether CAS affects the stroke recurrence rate in anticoagulated AF patients is largely unknown. The effect of concomitant CAS on both short- and long-term prognosis after stroke in patients with AF was evaluated. METHODS: The multicentre, retrospective FibStroke registry included AF patients with an ischaemic stroke or transient ischaemic attack (TIA) during 2003-2012. In this sub-study, 165 AF patients with ischaemic stroke or TIA with significant (>50%) CAS (CAS group) and 734 AF patients without CAS (non-CAS group) were identified. The median follow-up time after an index event was 3.5 (interquartile range 3.9) years. Long-term stroke recurrence rate, 30-day mortality, CHA2 DS2 -VASc score, other risk factors and the use and intensity of anticoagulation were assessed. RESULTS: The recurrence rate of ischaemic stroke (21.2% vs. 12.7%, P = 0.005, 8.1 vs. 3.6 events per100 follow-up years) was significantly higher in CAS patients compared to the non-CAS group despite similar anticoagulation/antithrombotic therapy. CAS patients had higher mean CHA2 DS2 -VASc scores than non-CAS patients (4.3 vs. 3.3, P < 0.001). However, in a multivariate analysis CAS was shown to be an independent risk factor for stroke recurrence (hazard ratio 2.02, 95% confidence interval 1.37-3.01, P = 0.001). The 30-day all-cause mortality was significantly higher in CAS patients (7.9% vs. 1.9%, P < 0.001) and CAS was an independent risk factor also for 30-day mortality (odds ratio 3.34, 95% confidence interval 1.51-7.38, P = 0.003). CONCLUSIONS: In patients with AF, concomitant CAS was an independent risk factor for both long-term stroke recurrence and 30-day mortality.

Underuse of anticoagulation in stroke patients with atrial fibrillation--the FibStroke Study.

BACKGROUND AND PURPOSE: Current guidelines recommend oral anticoagulation (OAC) for patients with atrial fibrillation (AF) and increased risk of thromboembolic events. The reasons for not using OAC in AF patients suffering stroke or transient ischaemic attack (TIA) were assessed. METHODS: This retrospective registry included 3404 patients with previously diagnosed AF who suffered a total of 2955 ischaemic strokes and 895 TIAs during 2003-2012. RESULTS: A CHA2DS2-VASc score ≥2 and a CHADS2 score ≥2 was observed in 3590 (93.2%) and in 2784 (72.3%) of the events, respectively. Of the high-risk patients (CHADS2 ≥2) only 55.1% were on OAC before the onset of stroke or TIA. The most frequently documented reasons for withholding OAC were infrequent paroxysms of AF (14%), previous bleeding episodes (13%) and the patient's decline/independent discontinuation of treatment (9%). Moreover, patients with paroxysmal AF (40% using OAC), previous bleeding (26% using OAC) and alcohol abuse (30% using OAC) were using OAC significantly less often than patients without these characteristics. A significant increase in the proportion of high-risk patients using OAC from 49% in 2003 to 65% in 2012 was seen. CONCLUSIONS: Underuse of anticoagulation is a common contributor to ischaemic strokes and TIA episodes in patients with AF. Infrequent AF episodes, previous bleeds, patient preference and alcohol abuse were the most common reasons for not using OAC.

Three-dimensional respiratory-gated coronary MR angiography with reference to X-ray coronary angiography.

PURPOSE: To assess the clinical value of three-dimensional coronary MR angiography (CMRA) in the detection of significant coronary artery stenosis using conventional X-ray angiography as the standard reference. MATERIAL AND METHODS: Sixty-nine patients underwent X-ray coronary angiography and CMRA because of suspected or previously diagnosed coronary artery disease. MRI was performed with a 1.5-T whole body imaging system using ECG-triggered 3D gradient echo sequence with retrospective navigator echo respiratory gating and fat suppression. RESULTS: A total of 276 coronary artery segments were analyzed. The X-ray coronary angiography was normal in 22 patients. Significant proximal stenoses (exceeding 50%) or occlusions were present in 102 coronary artery segments. In all, 120 stenoses or occlusions were identified in CMRA. Sixteen percent of the coronary artery segments had to be excluded because of poor image quality. The overall sensitivity and specificity for MRA for identification of significant stenosis were 75% and 62%, respectively. CMRA correctly detected 89% of patients with at least one vessel disease, but 6 patients with coronary artery disease would have been missed. CONCLUSIONS: Because of the high data exclusion and false- negative case rate, CMRA with retrospective navigator echo triggering is at present not suitable as a clinical screening method in coronary artery disease.

Repeated 3D coronary MR angiography with navigator echo gating: technical quality and consistency of image interpretation.

The purpose of this study was to evaluate the technical quality of 3D coronary MR angiography (CMRA) with navigator echo and the consistency of image interpretation in repeated imaging sessions. Fourteen subjects underwent CMRA, 10 of whom were imaged twice. The coronary arteries (96 segments) were analyzed twice for hemodynamically significant stenoses. Signal-to-noise and contrast-to-noise ratios varied considerably between the two imagings. Fat saturation was poor or satisfactory in 37%; in 15% of the slabs, the severity of artifacts was moderate; and the overall quality was good to excellent in only 42% of the imagings. The intraobserver reproducibility was good (kappa = 0.54), but the consistency of interpretation for repeated CMRA was only satisfactory (kappa = 0.43). Sensitivities of 84 and 84% and specificities of 70 and 62% were obtained for the two readings. Although the reproducibility of image reading is good, 3D CMRA with navigator echo provides only fair technical consistency, and the frequently compromised image quality impairs the clinical utility of this technique.

Complications related to permanent pacemaker therapy.

This study evaluates complications related to permanent endocardial pacing in the era of modern pacemaker therapy. There is only limited information available about the complications related to modern cardiac pacing. Most of the existing data are based on the 1970s and are no longer valid for current practice. The recent reports on pacemaker complications are focused on some specific complication or are restricted to early complications. Thus, there are no reports available providing a comprehensive view of complications related to modern cardiac pacing. Four hundred forty-six patients, who received permanent endocardial pacemakers between January 1990 and December 1995 at Kuopio University Hospital, were reviewed retrospectively using patient records. Attention was paid to the occurrence of any complication during the implantation or follow-up. An early complication was detected in 6.7%, and 4.9% of patients were treated invasively due to the early complication. Late complication developed in 7.2% and reoperation was required in 6.3% of the patients. Complications related to the implantation procedure occurred in 3.1%. Inadequate capture or sensing was observed in 7.4% of the patients. Pacemaker infection was detected in 1.8% and erosion in 0.9% of the patients. An AV block developed in 3.6% (1.6%/year) patients who received an AAI(R)-pacemaker due to sick sinus syndrome. There was no mortality attributable to pacemaker therapy. A great majority (68%) of the complications occurred within the first 3 months after the implantation. Complications associated to modern permanent endocardial pacemaker therapy are not infrequent. Eleven percent of patients needed an invasive procedure due to an early or late complication.

Power spectral analysis of heart rate variability during hyperinsulinemia in nondiabetic offspring of type 2 diabetic patients: evidence for possible early autonomic dysfunction in insulin-resistant subjects.

Sympathetic activation has been considered as a link between insulin resistance, hyperinsulinemia, and hypertension. However, little is known about the association between insulin sensitivity and autonomic regulation or about the effect of acute hyperinsulinemia on cardiac sympathovagal balance. The aim of this study was to investigate heart rate variability (HRV) during the euglycemic-hyperinsulinemic clamp in nondiabetic offspring of patients with type 2 diabetes. We studied 35 nondiabetic offspring of patients with type 2 diabetes and 19 control subjects. Probands were chosen from a 10-year follow-up study of patients with well-characterized type 2 diabetes according to their fasting C-peptide level (selected from both ends of the distribution) and from control subjects to form three groups: 1) a group including subjects who were offspring of type 2 diabetic patients with low C-peptide levels (deficient insulin secretion group [IS group], n = 17), 2) a group including subjects who were offspring of type 2 diabetic patients with high C-peptide levels (insulin-resistant group [IR group], n = 18), and 3) a control group without a history of type 2 diabetes in first-degree relatives (n = 19). HRV was assessed at baseline and at the steady state during the euglycemic-hyperinsulinemic clamp. Rates of whole-body glucose uptake (M value) were lower in the IR group than in the IS group and the control group (41+/-3 vs. 54+/-2 vs. 60+/-4 micromol x kg(-1) x min(-1), P < 0.01 and P < 0.01, respectively). In all groups, heart rate increased significantly during hyperinsulinemia. In the IR group, insulin infusion increased total power of HRV [from 7.70+/-0.15 to 8.05+/-0.15 ln(ms2), P < 0.01] and the low frequency-to-high frequency ratio (from 0.62+/-0.14 to 1.14+/-0.18, P < 0.01) and decreased power of the high frequency spectral component (from 5.73+/-0.17 to 5.43+/-0.16 ln(ms2), P < 0.05), whereas in other groups, changes in HRV were not significant. We conclude that the HRV response to acute hyperinsulinemia in the offspring of type 2 diabetic probands was likely to be modulated by the type 2 diabetic phenotype of the parent. In insulin-resistant subjects, autonomic dysfunction may be an earlier defect than hitherto acknowledged.

Lipid peroxidation products and antioxidant capacity in portal venous and systemic arterial plasma during gradual intestinal ischemia and reperfusion in pigs.

Intestinal ischemia may evoke an inflammatory response and eventually multiple organ failure. We investigated whether intestinal ischemic injury induces systemic lipid peroxidation and changes in the plasma antioxidant capacity in a pig model. Together with cardiovascular parameters, arterial and portal venous blood of 7 pigs were measured for thiobarbituric acid-reactive material diene conjugates, fluorescent chromolipids and plasma antioxidant capacity during graded occlusion of superior mesenteric artery and reperfusion. Plasma levels of lipid peroxidation products did not change significantly during graded ischemia and reperfusion. Portal venous plasma antioxidant capacity increased slightly during reperfusion (from 96.16 +/- to 3.91 to 142.49 +/- 12.01 mumol/l, p < 0.05). Although elevated levels of free radical reaction products have been found in ischemia-reperfusion, we found no evidence of systemic lipid peroxidation in our intestinal ischemia model.

Analogue and digital electrocardiogram recordings in the assessment of heart rate variability.

We compared analogue and digital 24-h electrocardiogram (ECG) recordings in the assessment of heart rate variability (HRV) in 41 patients with suspected coronary artery disease. The patients underwent ambulatory ECG recordings simultaneously with analogue (A) (Marquette 8500) and digital (D) (Oxford Medilog FD-3) recorders. Digital ECG recordings were analysed with the Excel Medilog II system (DE) and analogue recordings were analysed with both Marquette (AM) and Excel Medilog II (AE) systems. SDNN, SDANN, rMSSD and pNN50 were calculated for the assessment of time domain measures of HRV, and powers of low (0.04-0.15 Hz) and high (0.15-0.40 Hz) spectral components of HRV for the assessment of frequency domain measures of HRV. Correlations between time domain measures of HRV derived from AM, AE and DE recording and analysis techniques were high (r = 0.803-0.999, P < 0.001). SDANN and pNN50 assessed with AM and DE were equal, whereas SDNN and rMSSD values differed slightly but significantly from each other (P < 0.01 for both). All time domain measures of HRV assessed with AE differed significantly from AM (P < 0.001) and from DE (P < 0.01). Correlations between frequency domain measures of HRV derived from AM, AE and DE were also high (r = 0.973-0.992, P < 0.001). Despite this, frequency domain measures of HRV assessed with AM, AE and DE differed significantly from each other (P < 0.001). In conclusion, when analysed with their own analysis systems, analogue and digital recordings provided almost identical time domain, but not frequency domain, measures of HRV. In addition, analysis of an ECG recording with an analysis system of different manufacturer should be avoided.

The effects of reflex parasympathetic stimulation on the QT interval and QT dispersion.

The effect of phenylephrine-induced reflex parasympathetic stimulation on QT interval and its dispersion was studied in 16 healthy subjects with a history of paroxysmal supraventricular tachycardia, both during sinus rhythm and during atrial pacing. Results demonstrate that rapid reflex parasympathetic stimulation does not influence QT interval duration or QT dispersion, and also emphasize the inappropriateness of Bazett's formula, the need for comparison of QT intervals during identical heart rates, and the importance of analyzing all 12 leads of a standard electrocardiogram when assessing the effects of various interventions on the QT interval.

Sympathetic predominance of cardiac autonomic regulation in patients with left free wall accessory pathway and orthodromic atrioventricular reentrant tachycardia.

AIMS: The aim of this study was to compare cardiac autonomic regulation in patients with a history of paroxysmal supraventricular tachyarrhythmias, such as atrioventricular nodal reentrant tachycardia and atrioventricular reentrant tachycardia, and healthy controls. METHODS AND RESULTS: Seventeen patients with paroxysmal atrioventricular nodal reentrant tachycardia (atrioventricular nodal reentrant tachycardia group), 14 patients with overt preexcitation and paroxysmal atrioventricular reentrant tachycardia caused by a left free wall accessory pathway (atrioventricular reentrant tachycardia group) and 14 healthy control subjects, were studied. The patients and the controls were age and gender matched. Cardiac autonomic regulation was assessed by means of frequency domain analysis of heart rate variability at rest, during head-up tilt, active standing, treadmill exercise and after exercise. The high frequency component (0.15-0.5 Hz) of heart rate variability tended to be lower and the low frequency component (0.04-0.15 Hz) tended to be higher among the atrioventricular reentrant tachycardia patients than in atrioventricular nodal reentrant tachycardia patients and controls. The difference reached statistical significance at rest (P < 0.05) and during standing (P < 0.05 atrioventricular reentrant tachycardia vs atrioventricular nodal reentrant tachycardia and P < 0.01 atrioventricular reentrant tachycardia vs controls). Accordingly, the low-to-high frequency ratio--the marker of cardiac sympathetic regulation--was higher in atrioventricular reentrant tachycardia patients than in atrioventricular nodal reentrant tachycardia patients (P < 0.05 at rest and during standing) and controls (P < 0.01 during standing). CONCLUSION: The cardiac autonomic status in atrioventricular reentrant tachycardia patients was suggestive of a higher sympathetic tone than in atrioventricular nodal reentrant tachycardia patients or healthy controls. This may be related to inhomogeneous ventricular activation in the presence of antegrade conduction via the accessory atrioventricular pathway.

Effects of upright posture on filtered QRS parameter of the signal-averaged electrocardiogram in healthy volunteers.

The effects of upright posture on signal-averaged electrocardiography were studied together with short-term spectral analysis of heart rate variability (HRV) in 20 healthy volunteers (mean age 34 +/- 10 years). Filtered QRS duration from 5-minute epochs and corresponding spectral measures of HRV were computed from digital ambulatory electrocardiographic recordings both at supine rest and during upright tilt (60 degrees). Upright tilt was associated with a significant shortening of filtered QRS (88.2 +/- 8 vs 82.6 +/- 8 msec, p < 0.0001) and with an increase in its maximum amplitude (78.8 +/- 39 vs 87 +/- 48 microV, p < 0.004), whereas the average noise level remained unchanged. In the same time the ratio between low- and high-frequency components of HRV shifted in favor of sympathetic predominance (1.4 +/- 1.2 vs 3.4 +/- 2.9, p < 0.003). No correlation was found between changes in signal-averaged electrocardiography and HRV parameters associated with upright tilt. These data suggest that upright tilt-induced shortening in filtered QRS duration is rather vector-related and does not reflect changes in cardiac autonomic tone. This result must be considered when dynamic analysis of signal-averaged electrocardiography is attempted.

Arterial baroreflex sensitivity assessed from phase IV of the Valsalva maneuver.

To assess the feasibility of 2 noninvasive methods for arterial baroreflex sensitivity testing based on phase IV of the Valsalva maneuver, the performance of a simple arterial baroreflex sensitivity index compared with a slope method and reproducibility of repeated measurements of either parameter were evaluated in 36 subjects without structural heart disease. The study showed feasibility and reproducibility of both these methods for arterial baroreflex sensitivity assessment and demonstrated the importance of an appropriate rest period between repeated Valsalva maneuvers, giving a basis for prospective testing of noninvasive determination of arterial baroreflex sensitivity together with phenylephrine method in survivors of myocardial infarction.

Distinction between arrhythmic and nonarrhythmic death after acute myocardial infarction based on heart rate variability, signal-averaged electrocardiogram, ventricular arrhythmias and left ventricular ejection fraction.

OBJECTIVES: We investigated whether heart rate variability, the signal-averaged electrocardiogram (ECG), ventricular arrhythmias and left ventricular ejection fraction predict the mechanism of cardiac death after myocardial infarction. BACKGROUND: Postinfarction risk stratification studies have almost exclusively focused on predicting the risk of arrhythmic death. The factors that identify and distinguish persons at risk for arrhythmic and nonarrhythmic death are poorly known. METHODS: Heart rate variability, the signal-averaged ECG, ventricular arrhythmias and left ventricular ejection fraction were assessed in 575 survivors of acute myocardial infarction. The patients were followed up for 2 years; arrhythmic and nonarrhythmic cardiac deaths were used as clinical end points. During the follow-up period, 47 cardiac deaths occurred, 29 (62%) arrhythmic and 18 (38%) nonarrhythmic. RESULTS: All risk factors were associated with cardiac mortality in univariate analysis. With the exception of left ventricular ejection fraction, they were also predictors of arrhythmic death. Depressed heart rate variability (p < 0.001), ventricular ectopic beats (p < 0.001) and low ejection fraction (p < 0.001) were related to nonarrhythmic death. In multivariate analysis, depressed heart rate variability (p < 0.001) and runs of ventricular tachycardia (p < 0.05) predicted arrhythmic death. Nonarrhythmic death was associated with depressed heart rate variability (p < 0.001), ventricular ectopic beats (p < 0.001) and low ejection fraction (p < 0.01). By selecting patients with depressed heart rate variability, long filtered QRS duration or ventricular arrhythmias and excluding patients with the lowest ejection fraction, we identified a group in which 75% of deaths were arrhythmic. Similarly, by selecting patients with a low ejection fraction and excluding patients with the lowest heart rate variability, we identified a group in which 75% of deaths were nonarrhythmic. CONCLUSIONS: Arrhythmic death was associated predominantly with depressed heart rate variability and ventricular tachycardia runs, and nonarrhythmic death with low ejection fraction, ventricular ectopic beats and depressed heart rate variability. A combination of risk factors identified patient groups in which a majority of deaths were either arrhythmic or nonarrhythmic.

The high frequency component of heart rate variability reflects cardiac parasympathetic modulation rather than parasympathetic 'tone'.

This study was designed to evaluate the effect of modulating cardiac parasympathetic input on the high frequency component of heart rate variability. We stimulated the right vagus nerve with three different stimulation patterns in anaesthetized, vagotomized and spinal anaesthetized dogs. We kept the mean stimulation frequency constant; controlled the amplitude of modulation with programmed stimulation patterns, and analysed the resulting heart rate variability by power spectral analysis. Constant frequency vagal stimulation increased the cardiac interval, but did not change heart rate variability markedly. There was a slight increase, from 11 +/- 2 to 27 +/- 11 ms2, in the high frequency component. However, when the instantaneous stimulation frequency oscillated between 4 and 17 Hz during 5 s period, we could produce a marked heart rate variation, with 91 +/- 9% of the variation corresponding to the frequency of the modulation (0.20 Hz). The high frequency component was 12932 +/- 7701 ms2. With an increased magnitude of modulation, i.e. the difference between minimum and maximum instantaneous frequency, the high frequency component increased to 32711 +/- 17943 ms2. Thus, the high frequency component of heart rate variability reflects the magnitude of fluctuation in the cardiac parasympathetic input rather than parasympathetic 'tone'.

Effect of sympathetic modulation and sympatho-vagal interaction on heart rate variability in anaesthetized dogs.

Changes in the function of the autonomic nervous system underlying changes in heart rate variability are not fully understood. Furthermore, decreased heart rate variability has been found to be related to poor prognosis, for example, in patients with coronary artery disease. Our aim was to study how modulation in sympathetic stimulation at various frequencies is transferred into heart rate variation, and how the interaction between sympathetic and parasympathetic inputs can affect the high-frequency component of heart rate variability. We stimulated electrically cardiac sympathetic and vagal nerves in anaesthetized, vagotomized, spinal anaesthetized dogs. We controlled the frequency and magnitude of the modulation in programmed stimulation patterns and analysed the resulting changes in heart rate variability by power spectral analysis. We found that modulations in sympathetic stimulation were reflected in the high-frequency component of heart rate variability, as well as in the low- and medium-frequency components. In addition, a novel finding was that sympathetic stimulation reduced the magnitude of the high-frequency variations caused by vagal stimulation. This suggests that, although the high-frequency component of heart rate variability is mainly under parasympathetic regulation, it may also be influenced by the sympathetic nervous system.

Simultaneous invasive and noninvasive evaluations of baroreflex sensitivity with bolus phenylephrine technique.

Estimation of baroreflex sensitivity (BRS) is receiving increasing attention in clinical and experimental cardiology. Until recently, in most studies BRS has been assessed on the basis of invasive blood pressure measurement, which limits its use in large-scale studies and in clinical practice. The development of continuous noninvasive blood pressure monitoring has made it possible to assess BRS noninvasively. We compared central invasive and peripheral noninvasive techniques in the assessment of BRS during cardiac catheterization in 40 patients with possible coronary artery disease. The correlation between noninvasive and invasive BRS was high (r = 0.92; p < 0.001). However, the noninvasive method resulted in significantly higher BRS values than did the invasive method (7.1 +/- 6.5 msec/mm Hg vs 5.1 +/- 4.3 msec/mm Hg, respectively; p < 0.001) because of the smaller increase in systolic blood pressure after phenylephrine injection by the noninvasive technique than by the invasive technique (18.9 +/- 6.8 mm Hg vs 25.2 +/- 7.8 mm Hg, respectively; p < 0.01). The difference between noninvasive and invasive BRS correlated positively with invasive BRS (r = 0.54; p < 0.001) and inversely with age (r = -0.39; p < 0.01) and resting systolic blood pressure (r = -0.30, p < 0.05). A noninvasive BRS value of < 4.0 ms/mm Hg showed a sensitivity of 94%, a specificity of 91%, and an accuracy of 93% in identifying cases of reduced invasive BRS (< 3.0 msec/mm Hg). Our findings encourage the use of finger-cuff method in the assessment of BRS. However, noninvasive BRS values were slightly but significantly higher than invasive BRS values, a difference that should be taken into account when BRS is measured by the noninvasive approach.

Valsalva manoeuvre in the assessment of baroreflex sensitivity in patients with coronary artery disease.

The overshoot rise in arterial pressure after release of Valsalva strain is a natural challenge for baroreflex regulation of heart rate. To assess the feasibility of the Valsalva manoeuvre in the determination of baroreflex sensitivity (BRS), we measured the slope of the linear relationship between the length of the RR interval and preceding systolic blood pressure value during the overshoot phase after the strain and compared this index of BRS to a standard phenylephrine test in 64 subjects, of whom 58 had coronary artery disease. The BRS slopes obtained with the Valsalva manoeuvre showed a good linear correlation with the phenylephrine test (r = 0.77 in the 27 patients with two Valsalva and phenylephrine tests and r = 0.56 in the whole cohort). The correlation coefficients of the BRS slopes were better than in the phenylephrine test (r = 0.89 vs r = 0.85, P < 0.05). The rise in systolic blood pressure in the slope calculation area was higher than with phenylephrine (41 +/- 18 vs 30 +/- 10 mmHg, P < 0.01). The reproducibility of BRS slopes in successive tests was comparable with both methods. These results suggest that non-invasive assessment of BRS using Valsalva strain to induce blood pressure rise is possible in patients with coronary artery disease.

Power spectral analysis of heart rate and blood pressure variability in anaesthetized dogs.

Short-term oscillation of heart rate and blood pressure are mainly regulated by the automatic nervous system. It has been proposed that non-neural factors, such as changes in intrathoracic pressure, can strongly modulate this rhythmicity. Our aim was to evaluate the effect of changing intrathoracic pressure and central autonomic nervous activity on heart rate and blood pressure variability. Evaluation was performed by using spectral analysis techniques with autoregressive modelling. The variability in heart rate and blood pressure remained in animals with open chest or paralysed respiratory muscles. After vagotomy, the variability in heart rate decreased, but not that of blood pressure. Total spinal anaesthesia elicited a decrease in the variability in blood pressure. The pharmacological blockade of alpha- and beta-receptors further decreased both variabilities. It was concluded that in anaesthetized dogs heart rate and blood pressure variability are mainly of central origin and non-neural factors have only minor effect on these central rhythms. High (> 0.15 Hz), medium (0.07-0.15 Hz) and, obviously low (0.00-0.07 Hz) frequency variations in heart rate are mostly mediated vagally. In blood pressure, medium and obviously low frequency variations are modulated by sympathetic nervous system, whereas high frequency variations are secondary to the heart rate variation.