Pavel Jurák

Sex-selective QT prolongation during rapid eye movement sleep.

Background—We examined the effects of the various sleep stages on RR and QT intervals in healthy subjects and tested the hypothesis that there is a differential effect of sleep stage on QT interval in women compared with men. Methods and Results—Eighteen healthy subjects (9 women, age 22 to 45 years) underwent polysomnography and simultaneous recording of ECG, blood pressure, and respiration. RR interval, RR variability, and QT values were measured in stable conditions (no abrupt changes of heart rate or blood pressure, stable breathing pattern) during inactive wakefulness during stages 2 and 3 to 4 of non-REM sleep and during REM sleep. The absolute QT interval was normalized for variations of RR (QTc). In men, RR interval and RR variability increased through all sleep stages. The QTc remained stable from wakefulness through all sleep stages. In women, however, RR interval increased only during non-REM and was virtually identical in wakefulness and in REM. RR variability remained very stable from wakefulness through all stages of sleep. Also, during REM in women, both absolute QT interval and QTc, regardless of the correction maneuver used, increased compared with wakefulness. Conclusions—The influence of sleep on RR, RR variability, and QTc is sex-dependent. We speculate that these differential sex effects on cardiac rate and repolarization may have important implications for sleep-selected cardiac arrhythmias in women.

Sympathetic neural responses to smoking are age dependent.

Objective Smoking is an important risk factor for cardiovascular disease. Sympathetic responses to cigarette smoking may be implicated in the link between smoking and cardiovascular disease. We tested the hypothesis that the sympathetic neural responses to smoking are age dependent. Methods We examined the effects of cigarette smoking and sham smoking on muscle sympathetic nerve activity, blood pressure and heart rate in 14 normotensive middle-aged (49 ± 4 years) and 12 young (29 ± 4 years) habitual smokers matched for body mass index (25 ± 2 kg/m2 in both groups). Results Sham smoking had no significant effect on sympathetic drive, blood pressure or heart rate in either group. Cigarette smoking increased heart rate in both middle-aged subjects and young subjects. In comparison to younger subjects, middle-aged smokers showed similar smoking-related increases in systolic blood pressure (SBP) [10 ± 3 versus 12 ± 2 mmHg, respectively, not significant (NS)]. Smoking decreased sympathetic nerve activity by 28 ± 12% of baseline values (P < 0.01) in young subjects. However, muscle sympathetic nerve activity did not change significantly after smoking in middle-aged subjects (5 ± 8%, NS), despite the increased blood pressures, which would be expected to inhibit sympathetic activity. By contrast, in young subjects, the heart rate increase (22 ± 2 bpm) was greater than that seen in middle-aged subjects (13 ± 2 bpm, P < 0.01). Conclusions The autonomic responses to smoking are age dependent. While blood pressure increases are similar in both groups, young subjects respond to smoking by marked increases in heart rate and suppression of central sympathetic outflow. In middle-aged subjects, the heart rate increase is less marked, but sympathetic vasoconstrictor activity is not suppressed.

Heightened acute circulatory responses to smoking in women.

Objective. Smoking, a major risk factor for cardiovascular morbidity and mortality, may be particularly harmful to women. Sympathetic and hemodynamic responses to cigarette smoking may be implicated in the link between smoking and acute cardiovascular events. We tested the hypothesis that acute effects of smoking on cardiovascular function are potentiated in women compared with men. Methods. We examined the effects of cigarette smoking and sham smoking on muscle sympathetic nerve activity, blood pressure and heart rate in 20 female and 20 male middle‐aged healthy habitual smokers. Results. Sham smoking had no effect on muscle sympathetic nerve activity, blood pressure, or heart rate. Although cigarette smoking increased average systolic blood pressure and heart rate in both females and males, systolic blood pressure increased more in women (12±2 mmHg) than in men (6±2 mmHg; p = 0.02), as did heart rate (16±2 beats/min in women vs 9±2 beats/min in men; p = 0.002). Female smokers also had greater smoking‐related increases in systolic blood pressure variability compared with males (2.2±0.6 vs 0.4±0.4 mmHg, respectively; p = 0.01) and greater decreases in RR variability (−28±5 vs −7±4 ms; p = 0.002). Despite the potentiated blood pressure increase in females, which would be expected to inhibit sympathetic activity to a greater extent in females than in males, changes in muscle sympathetic nerve activity during smoking were similar in both sexes. Conclusions. Acute pressor and tachycardic effects of smoking are potentiated in women compared with men. These findings may have important implications for understanding increased vulnerability to acute cardiovascular events in women who smoke.

EARLY AUTONOMIC CHANGES IN PATIENTS WITH NEWLY DIAGNOSED ARTERIAL HYPERTENSION: PP.25.05

Objective: The autonomic nervous system plays a key role in the regulation of blood circulation and its abnormal function is a major factor involved in the early phases of essential arterial hypertension. The objective of the study was to assess the differences between short-term variation in heart rate and blood pressure in healthy individuals and in a group of patients with newly diagnosed mild essential arterial hypertension. Design and Method: Three continuous 5-minute measurements of the ECG and blood pressure in supine position with different breathing patterns (spontaneous breathing, paced breathing 0.1 Hz and 0.33 Hz), were applied at 2 groups of subjects: young healthy (YH, 31 subjects, 13 female) and patients with newly diagnosed mild arterial hypertension (HT, 29 subjects, 12 female). Analyzed parameters: heart rate (HR), heart rate variability spectral power in low frequency (HRVlf) and high frequency (HRVhf) power bands, systolic pressure (SBP), diastolic pressure (DBP) and baroreflex sensitivity (BRS). Results: Mean HR [beat/min] over groups YH/HT at 0.1Hz breathing is 69.9/73.2 (p = NS), during spontaneous breathing 66.1/72.9 (p = NS), and 0.33Hz breathing 67.1/72.8 (p = NS); mean HRVlf [ms2/1000] at 0.1Hz is 17.9/8.5 (p < 0.01), during spontaneous breathing 3.8/2.0 (p = NS) and at 0.33Hz 2.2/0.8 (p < 0.05); mean HRVhf [ms2/1000] at 0.1 Hz is 2.4/1.3 (p = NS), during spontaneous breathing 2.6/1.3 (p = NS) and at 0.33 Hz 2.1/0.7 (p = NS); mean BRS [ms/mmHg] at 0.1 Hz is 17.3/11.2 (p < 0.01), during spontaneous breathing 10.6/8.3 (p = NS) and at 0.33 Hz 9.9/5.9 (p < 0.05). Conclusions: Increased risk of cardiac mortality is closely connected to decreased HRV and BRS as the markers of the short-term circulation control dysfunction. There are no significant differences between both groups in HRVlf, HRVhf and BRS during spontaneous breathing. Group differences in HRVlf and BRS are more significant (p < 0.01) at 0.1Hz breathing than during 0.33Hz breathing (p < 0.05). The 0.1Hz paced breathing is simple and convenient approach to amplify inter-groups differences of the cardiovascular control detected by the HRVlf and BRS in early stages of hypertension.