Age-related changes of cardiac parasympathetic modulation after vasovagal syncope

Age determines vascular reactivity as measured by optical rhinometry

BACKGROUND

Endonasal blood volume depends on autonomous nervous system activation and ultimately vascular reactivity. It can be measured by optical rhinometry, a simple- to-use, subject-compliance independent method. We investigated endonasal perfusion following postural change to determine predictors of vascular response.

MATERIALS AND METHODS

Optical rhinometry was performed in 52 healthy subjects (25 women) with an age range of 21-80 years. Subjects were placed in supine position after 5 min of standing. Optical density (OD) as marker of endonasal blood volume was continuously measured for 30 min after postural change. In addition to age, data on other risk factors for impaired vascular reactivity, such as gender, smoking, level of physical activity, resting heart rate and blood pressure were obtained. To evaluate raw-data curves, integrals over defined time-periods were calculated.

RESULTS

The OD initially increased following the intervention (t(max) at 207 +/- 12 s, mean +/- SEM). Thereafter, a gradual return to baseline levels was observed in young but not in elderly subjects. In multivariate models, age was the most influential parameter for vascular response followed by body mass index. The defined integrals as indicators of curve structure were all significantly influenced by age (P < 0.01 for each interval). Other measured risk factors had no effect on curve characteristics.

CONCLUSIONS

Age is an important predictor of endonasal perfusion. Evaluation of optical rhinometry needs to take age-dependency of results into account. Studies in patients with cardiovascular disease are needed to show if optical rhinometry can provide information about vascular responsiveness as a predictor of cardiovascular morbidity.

Developmental Changes in Electrophysiological Properties and Synaptic Transmission in Rat Intracardiac Ganglion Neurons

We charted postnatal changes in the intrinsic electrophysiological properties and synaptic responses of rat intrinsic cardiac ganglion (ICG) neurons. We developed a whole-mount ganglion preparation of the excised right atrial ganglion plexus. Using intracellular recordings and nerve stimulation we tested the hypothesis that substantial transformations in the intrinsic electrical characteristics and synaptic transmission accompany postnatal development. Membrane potential ( Em) did not change but time constant (τ) and cell capacitance increased with postnatal development. Accordingly, input resistance ( Rin) decreased but specific membrane resistance ( Rm) increased postnatally. Comparison of the somatic active membrane properties revealed significant changes in electrical phenotype. All neonatal neurons had somatic action potentials (APs) with small overshoots and small afterhyperpolarizations (AHPs). Adult neurons had somatic APs with large overshoots and large AHP amplitudes. The range of AHP duration was larger in adults than in neonates. The AP characteristics of juvenile neurons resembled those of adults, with the exception of AHP duration, which fell midway between neonate and adult values. Phasic, multiply adapting, and tonic evoked discharge activities were recorded from ICG neurons. Most neurons displayed phasic discharge at each developmental stage. All neurons received excitatory synaptic inputs from the vagus or interganglionic nerve trunk(s), the strength of which did not change significantly with postnatal age. The changes in the electrophysiological properties of the postganglionic neuron suggest that increased complexity of parasympathetic regulation of cardiac function accompanies postnatal development.

Autonomic dysfunction and impaired cerebral autoregulation in cirrhosis

Cerebral blood flow autoregulation is lost in patients with severe liver cirrhosis. The cause of this is unknown. We determined whether autonomic dysfunction was related to impaired cerebral autoregulation in patients with cirrhosis. Fourteen patients with liver cirrhosis and 11 healthy volunteers were recruited. Autonomic function was assessed in response to deep breathing, head-up tilt and during 24-h Holter monitoring. Cerebral autoregulation was assessed by determining the change in mean cerebral blood flow velocity (MCAVm, transcranial Doppler) during an increase in blood pressure induced by norepinephrine infusion (NE). The severity of liver disease was assessed using the Child-Pugh scale (class A, mild; class B, moderate; class C, severe liver dysfunction).NE increased blood pressure similarly in the controls (27 (24-32) mmHg) and patients with the most severe liver cirrhosis (Child-Pugh C, 31 (26-44) mmHg, p=0.405 Mann-Whitney). However, the increase in MCAVm was greater in cirrhosis patients compared to the controls (Child-Pugh C, 26 (24-39) %; controls, 3 (-1.3 to 3) %; respectively, p=0.016, Mann-Whitney). HRV during deep breathing was reduced in the cirrhosis patients (Child-Pugh C, 6.0+/-2.0 bpm) compared to the controls (21.7+/-2.2 bpm, p=0.001, Tukey' test). Systolic blood pressure fell during head-up tilt only in patients with severe cirrhosis. Our results imply that cerebral autoregulation was impaired in the most severe cases of liver cirrhosis, and that those with impaired cerebral autoregulation also had severe parasympathetic and sympathetic autonomic dysfunction. Furthermore, the degree of liver dysfunction was associated with increasing severity of autonomic dysfunction. Although this association is not necessarily causal, we postulate that the loss of sympathetic innervation to the cerebral resistance vessels may contribute to the impairment of cerebral autoregulation in patients with end-stage liver disease.

Heart rate and blood pressure variability in subjects with vasovagal syncope

Autonomic nervous system control in subjects with vasovagal syncope is controversial. In the present study, we used short-term spectral analysis to evaluate autonomic control in subjects with recurrent vasovagal syncope. We assessed the ability of spectral indices of HR (heart rate) variability to predict tilt-test responses. A series of 47 outpatients with recurrent vasovagal syncope and with positive responses to head-up tilt testing underwent a further study of RR variability during controlled breathing at rest and during tilt testing. During controlled breathing, RR interval variability of total power (TPRR; P<0.001), low-frequency power (LFRR; P<0.05), high-frequency power (HFRR; P<0.001) and HF expressed in normalized units (HFnuRR; P<0.001) were all higher, and LF expressed in normalized units (LFnuRR) and LF/HF ratio were lower in subjects with vasovagal syncope than in controls (P<0.001). To assess the ability of spectral components of RR variability to predict tilt-test responses, we prospectively studied 109 subjects with recurrent vasovagal syncope. The two normalized measures, HFnuRR and LFnuRR, determined during controlled breathing alone predicted a positive tilt-test response (sensitivity, 76%; specificity, 99%; positive predictive value, 96%; and negative predictive value, 90%). During tilting, subjects with vasovagal syncope had lower SBP (systolic blood pressure; P<0.05), LF component of peak SBP variability (LFSBP) and LFnuRR than controls, and higher TPRR, HFRR, HFnuRR and α HF (P<0.001). These spectral data indicate that vagal sinus modulation is increased at rest in subjects with vasovagal syncope. Spectral analysis of RR variability during controlled breathing, a procedure that predicts tilt-test responses, could be a useful guide in choosing the method of tilt testing.