Estimation of spontaneous baroreflex sensitivity using transfer function analysis: effects of positive pressure ventilation.

To determine the short-term effects of non-invasive positive pressure ventilation (PPV) on spontaneous baroreflex sensitivity, we acquired time series of RR interval and beat-to-beat blood pressure in 55 healthy volunteers (mean age 46.5+/-10.5 years), who performed breathing tests on four occasions at frequencies of 12 and 15/min, with application of PPV of 5 mbar, and without positive pressure (control). Using spectral and transfer function analysis, we estimated RR interval variability (HRV) and systolic blood pressure variability (SBPV), as well as the gain (alpha-index) and phase shift (Phi) of the baroreceptor reflex for low- (LF) and high-frequency (HF) bands. Compared to control breathing, PPV at 12 and 15/min led to an increase in mean RR (p<0.001) and blood pressure (p<0.05). The alpha-index in the HF band increased significantly due to PPV for both respiratory frequencies (p<0.05). Phase shifts did not show significant changes in response to pressure ventilation. These results indicate that short-term administration of PPV in normal subjects elicits significant enhancement in the HF index of baroreflex gain. These findings may contribute to understanding the mechanisms, indications, and effectiveness of positive pressure breathing strategies in treating cardiorespiratory and other disease conditions.

Age and gender difference in ST height at rest and after double autonomic blockade in normal adults.

BACKGROUND: ST elevation is commonly seen in young, healthy men. The exact mechanisms that cause ST height to be greater in young men are not yet completely understood. The purpose of the present study was to determine whether autonomic tone is responsible for age and gender differences in ST height. METHODS: Gender and age differences in ST height were studied at rest and after double autonomic blockade (DAB) with atropine and propranolol. Fifty healthy men and women were included (16 men, 14 women, age 23-32 years; 9 men, 11 women, age 65-79 years). Twelve-lead ECGs were registered at rest and after DAB. Leads II and V(1)-V(4) were chosen for analysis. ST height (in mm) was measured manually at the J-point, and 40 ms and 80 ms after the J-point. Values were corrected for QRS amplitude. RESULTS: Gender and age differences in ST height were seen in both rest and DAB data. Men had greater ST height compared to women at J-point, 40 and 80 ms after the J-point (P < or = 0.0001), and younger subjects had greater ST height than older subjects at J-point (P = 0.0140), 40 and 80 ms after the J-point (P < or = 0.0001). DAB did not change ST height at J-point or at 40 ms, but increased ST height at 80 ms. Women had less of an increase in ST height following DAB than men did. CONCLUSIONS: ST elevation in the absence of structural or electrical heart disease is mainly seen in young men. Age and gender difference persist after DAB and thus are not due to differences in autonomic tone.

Menstrual cycle and ST height.

BACKGROUND: Sex hormones and menstrual cycle effects on ST height have not yet been clearly identified. METHODS: Twenty-two young, healthy women (aged 22-32 years) were included in this study. Twelve-lead ECGs were registered during menses, follicular and luteal phase of the menstrual cycle at baseline, and after double autonomic blockade (DAB). Chest leads V2-V4 and limb leads I and II were chosen for analysis. ST height was measured manually at J-Point and 40 ms after the J-Point, and values were corrected for QRS amplitude (J-Point/QRS, 40 ms/QRS). Repeated measure ANOVA was used to analyze differences in ST height among the three phases of the menstrual cycle. A P-value < 0.05 was considered as significant. RESULTS: At baseline, ST height, QTc, and T wave amplitude were not significantly different among the three phases of the menstrual cycle. After double autonomic blockade, ST height at 40 ms, J-Point/QRS, and 40 ms/QRS was significantly higher during follicular versus luteal phase (0.152 +/- 0.413 mm versus -0.007 +/- 0.427 mm, P = 0.0059 at 40 ms; -0.001 +/- 0.030 versus -0.015 +/- 0.032, P = 0.0039 at J-Point/QRS; 0.013 +/- 0.031 versus -0.004 +/- 0.032, P = 0.0005 at 40 ms/QRS) as was the QTc. ST height differences at J-Point were not significantly different (-0.046 +/- 0.395 mm follicular, -0.167 +/- 0.448 mm luteal, and -0.083 +/- 0.492 mm menses, P = 0.1014). CONCLUSION: ST height and QTc varied among the three phases of the menstrual cycle, predominantly after double autonomic blockade. Female sex hormones that vary throughout the menstrual cycle may modulate measures of repolarization.

Effects of positive-pressure ventilation on the spontaneous baroreflex in healthy subjects.

To determine the short-term effects of noninvasive positive-pressure ventilation (PPV) on spontaneous baroreflex sensitivity, we acquired time series of R-R interval and beat-to-beat blood pressure in 55 healthy volunteers (mean age 46.5 +/- 10.5 yr) who performed breathing on four occasions at frequencies of 12 and 15 breaths/min without positive pressure (control) and also using PPV of 5 mbar. By using spectral and cross-spectral analysis, R-R interval variability and systolic blood pressure variability as well as the gain (alpha-index) of the baroreceptor reflex were estimated for the low-frequency and high-frequency (HF) bands. Compared with control breathing, PPV at 12 breaths/min and 15 breaths/min led to an increase in mean R-R (P < 0.001) and blood pressure (P < 0.05). The alpha-index of the HF band increased significantly for both respiratory frequencies (P < 0.05) due to PPV. These results indicate that short-term administration of PPV in normal subjects elicits a significant enhancement in the HF index of the baroreflex gain. These findings may contribute to understanding the mechanisms, indications, and effectiveness of positive pressure breathing strategies in treating cardiorespiratory and other disease conditions.