Alterations In Autonomic Control Research Articles

Dynamic analysis of cardiac R-R intervals in normal infants and in infants who subsequently succumbed to the sudden infant death syndrome.

Infants who subsequently succumb to the sudden infant death syndrome (SIDS) have higher heart rates and reduced heart rate variation compared with other infants. We examined dynamic changes in cardiac interbeat intervals to explore these differences in cardiac control. Recordings of electrocardiographic activity and respiratory movement were acquired from 13 SIDS victims before their deaths. Moment-to-moment changes in R-R intervals during quiet sleep, rapid eye movement sleep, and waking were compared with values of 13 matched control infants. For each sleep-waking state, every R-R interval was plotted against the previous interval (Poincaré plots), and each change in interbeat interval was plotted against the previous change. Dispersion of interbeat intervals at different heart rates was reduced in SIDS victims, resulting in Poincaré plots markedly different from those of controls. The dispersion, sampled at the 10th and 90th percentiles of heart rates, was reduced across all sleep-waking states in SIDS victims. At high heart rates, the difference between groups disappeared after correcting for basal rate; however, the reduced range at low heart rates was independent of basal rate. SIDS victims also showed smaller beat-to-beat changes in heart rate and fewer sustained runs of consistent heart rate changes during waking relative to controls. The differences in cardiac rate dynamics suggest altered autonomic control in infants who succumb to SIDS. We speculate that the autonomic disturbance may lead to cardiac instability or may indicate CNS alterations with the potential to affect other vital functions.

Development of heart rate variation over the first 6 months of life in normal infants.

Development of heart rate variation in three frequency ranges was examined during sleep-walking states in normal infants over the first 6 mo of life. Extent of all three types of heart rate variation decreased from 1 wk to 1 mo of age. Extent of respiratory sinus arrhythmia increased from 1 mo to 6 mo during all sleep-waking states, with the increase most pronounced during quiet sleep. Variation in two bands of lower frequencies showed increases in extent from 1 to 3 mo, then a slowing or reversal of the increase between 3 and 4 mo of age. During rapid eye movement sleep, the two types of lower frequency heart rate variation decreased in extent from 3 through 6 mo of age. These results suggest that alterations in autonomic control of heart rate occur at several time periods over the first 6 mo of life and that these alterations may have an effect only on particular types of heart rate variation and only during particular sleep-waking states. The diminution of all three types of heart rate variation at 1 mo may indicate a reduction in vagal tone at this age.

Cardiac dimensions and performance after either arm or leg endurance training

We have recently reported improved exercise performance with untrained limbs in 10 men after 11 wk of either arm (N = 5) or leg (N = 5) endurance training. To examine the changes in cardiac function produced by short-term training, we used echocardiography to measure cardiac function at rest, and systolic time intervals (STIs) to measure cardiac function during trained and untrained limb exercise. We repeated all studies after autonomic blockade with atropine and propranolol in order to observe non-autonomic changes in cardiac function. Training had little effect on cardiac size or performance at rest, although with autonomic blockade, cardiac mass increased in the leg-training group and resting left ventricular ejection time (LVET) was prolonged when the two training groups were combined. During submaximal exercise with both trained and undrained limbs and at similar heart rates before and after training, LVET for the combined groups was increased with and without autonomic blockade. This increase in LVET is most consistent with an increased cardiac stroke volume. Short-term endurance training appears to result in improved exercise cardiac function that is in part independent of altered autonomic control or adaptations in trained skeletal muscle.

Altered cardiac responsiveness and regulation in the normal cardiac output type of borderlind hlpertension.

Of 145 patients with borderline hypertension, 30% had increased resting cardiac index (QI), whereas the remainder had normal values. The specific aim of this study was to investigate cardiac regulation in patients who had normal resting QI. Eighty-five control subjects were used for comparison. At rest, patients with normal QI showed evidence of decreased parasympathetic inhibition; the QI after injection of atropine increased less than in control subjects. After complete cardiac autonomic blockade with propranolol and atropine, QI and stroke volume were significantly lower in patients than in control subjects. The mechanism of this low QI was further analyzed. Central blood volume, which strongly correlates with stroke volume, was used as an estimate of the cardiac venous filling. After blockade, stroke volume was decreased in patients, but central blood volume was normal. Patients also showed a decreased heart rate and QI response to infusion of isoproterenol. It is therefore postulated that two components may be responsible for the low QI in the "denervated" heart: patients exhibit a decreased responsiveness to sympathetic stimulation, and they may also be less responsive to venous filling. Behind the facade of cardiac normality in these borderline hypertensive patients with normal cardiac output, there is evidence of altered autonomic control of the heart (decreased vagal inhibition) and of changed cardiac response to sympathetic stimulation and possibly to venous filling.

Effects of altered autonomic control on left ventricular function in conscious dogs.

In eight conscious dogs, effects of beta-adrenergic, vagal, and combined beta-adrenergic and vagal blockage on left ventricular internal diameter, pressure, and outflow were measured at rest and during acute volume loading. At rest, beta-adrenergic blockage resulted in a decrease in heart rate with no change in stroke volume but increased end-diastolic and end-systolic diameters, whereas vagal blockage resulted in an elevated heart rate with reductions in stroke volume, end-diastolic, and end-systolic diameters. Combined blockage, at rest, was associated with elevations in heart rate, diminished stroke volume, and increases in end-diastolic and end-systolic diameters. During acute volume loading, beta-adrenergic blockage reduced peak heart rate and stroke volume, and elevated end-systolic diameter, whereas vagal blockage, despite an elevated heart rate, did not alter peak stroke volume and reduced end-diastolic diameter. The response to acute volume loading in combined blockage was characterized by reduction in peak stroke volume and end-diastolic diameter. Stroke volume was found to be dependent not only on the initial fiber length but also on the sympathetic innervation. This was demonstrated by the increase in end-systolic diameter following beta-adrenergic blockage.

Sweat inhibition by cutaneous cooling in normal sympathectomized and paraplegic man.

ArticleSweat inhibition by cutaneous cooling in normal sympathectomized and paraplegic man.R O Rawson, and J D HardyR O Rawson, and J D HardyPublished Online:01 Feb 1967https://doi.org/10.1152/jappl.1967.22.2.287MoreSectionsPDF (1 MB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat Previous Back to Top Next Download PDF FiguresReferencesRelatedInformation Cited ByHuman temperature regulation under heat stress in health, disease, and injuryMatthew N. Cramer, Daniel Gagnon, Orlando Laitano, and Craig G. Crandall19 August 2022 | Physiological Reviews, Vol. 102, No. 4Integrated fan cooling of the lower back for wheelchair users14 September 2022 | Journal of Rehabilitation and Assistive Technologies Engineering, Vol. 9A Primary Care Provider’s Guide to Autonomic Dysfunction Following Spinal Cord InjuryTopics in Spinal Cord Injury Rehabilitation, Vol. 26, No. 2Heat-related issues and practical applications for Paralympic athletes at Tokyo 202027 June 2019 | Temperature, Vol. 7, No. 1Thermoregulation following spinal cord injuryImplications of altered autonomic control on sports performance in athletes with spinal cord injuryAutonomic Neuroscience, Vol. 209Cooling Athletes with a Spinal Cord Injury15 August 2014 | Sports Medicine, Vol. 45, No. 1Disordered cardiovascular control after spinal cord injuryThermoregulation during Exercise in Individuals with Spinal Cord InjuriesSports Medicine, Vol. 36, No. 10Effects of Spinal Cord Lesion Level upon Thermoregulation during Exercise in the HeatMedicine & Science in Sports & Exercise, Vol. 35, No. 7Thermoregulatory set point in patients with spinal cord injuries (spinal man)Spinal Cord, Vol. 21, No. 4COMPARATIVE PHYSIOLOGY OF SWEATING29 July 2006 | British Journal of Dermatology, Vol. 88, No. 4Experimental hyperthermia in traumatic quadriplegiaInternational Journal of Biometeorology, Vol. 15, No. 2-4 More from this issue > Volume 22Issue 2February 1967Pages 287-91 https://doi.org/10.1152/jappl.1967.22.2.287PubMed6017896History Published online 1 February 1967 Published in print 1 February 1967 Metrics