Clinical testing of thermally stimulated cardiovascular oscillations in man

STUDY OBJECTIVE--The study assessed the physiological validity of an automatic thermal stimulation method to induce synchronised oscillations in the neural cardiovascular control system. DESIGN--Automatic alternating rhythmic warm and cool immersion of different skin areas of 18 males was done at different frequencies and water temperatures. The neurally mediated responses to the periodic thermal stimulation were measured from skin blood flow and heart rate and compared to those of a sham stimulation. Respiration was monitored for control purposes. The reproducibility of the stimulation and responses was examined. SUBJECTS--18 young males volunteered for the study. MEASUREMENTS AND MAIN RESULTS--The water bath method produced reproducible thermal stimulation and responses of skin blood flow and heart rate. Rhythmic thermal stimulation at 0.013-0.096 Hz synchronised the oscillations of the forearm skin blood flow when the thermal stimulus amplitude exceeded 10 degrees C. The increase in the stimulus amplitude or enlargement of the stimulus area did not further increase the oscillatory response of skin blood flow. Sham stimulation or mean temperature of the periodic thermal stimulation in the range 23-33 degrees C did not influence the oscillations of skin blood flow. Local cooling of the stimulated lower legs attenuated the response of skin blood flow. Both thermal stimulation and sham stimulation affected heart rate, but no stable synchronisation of the periodic heart rate variability was found at supine rest. Thermal stimulation of the sitting subjects' forearm instead of legs increased the synchronisation of the periodic heart rate variability. CONCLUSIONS--The response of skin blood flow agreed with the theory of the thermal entrainment. In a supine man, both thermal stimulation and non-specific central nervous influences induced significant and reproducible interactions with periodic heart rate variability and respiration.     

Effects of posture on stimulated ventilation in quadriplegia

Quadriplegics are able to compensate for alterations of operational length of the diaphragm by reflexly increasing neural drive to the diaphragm. This increase in neural drive is adequate to maintain required tidal volume and minute ventilation during quiet breathing in these patients with limited inspiratory muscle function. It is not known, however, if this neural compensation is sufficient to preserve ventilation when the diaphragm is stressed by simultaneously changing its operational length and increasing ventilatory demands. This issue was explored in 7 quadriplegics whose vital capacity was reduced to 15 to 53% of predicted. The diaphragm was stressed by shortening its length from the supine to a 60 degree tilted position, and also by inducing hyperventilation by having the subjects rebreathe 7% CO2. Response to this stress was recorded by monitoring the ventilatory response to rebreathing CO2 (delta VE/delta PCO2), and also by measuring mouth pressure 0.1 s after occluding the airway at the start of inspiration during CO2 rebreathing (delta P0.1/delta PCO2). A change from the supine to the tilted position caused an increase in resting end-expiratory volume of 0.8 +/- 0.2 L (SD) and therefore shortened the diaphragm. Despite this shortening of diaphragm length and the stress of CO2 rebreathing, there was no significant change in delta VE/delta PCO2 and delta P0.1/delta PCO2 with changes in posture. The delta VE/delta PCO2 was 0.82 +/- 0.42 L/min/mm Hg supine versus 0.95 +/- 0.65 L/min/mm Hg when tilted. The delta P0.1/delta PCO2 was 0.18 +/- 0.08 cm H2O/mm Hg supine versus 0.20 +/- 0.10 cm H2O/mm Hg tilted.(ABSTRACT TRUNCATED AT 250 WORDS)     

Intracortical and corticothalamic coherency of fast spontaneous oscillations.

We report that fast (mainly 30- to 40-Hz) coherent electric field oscillations appear spontaneously during brain activation, as expressed by electroencephalogram (EEG) rhythms, and they outlast the stimulation of mesopontine cholinergic nuclei in acutely prepared cats. The fast oscillations also appear during the sleep-like EEG patterns of ketamine/xylazine anesthesia, but they are selectively suppressed during the prolonged phase of the slow (<1-Hz) sleep oscillation that is associated with hyperpolarization of cortical neurons. The fast (30- to 40-Hz) rhythms are synchronized intracortically within vertical columns, among closely located cortical foci, and through reciprocal corticothalamic networks. The fast oscillations do not reverse throughout the depth of the cortex. This aspect stands in contrast with the conventional depth profile of evoked potentials and slow sleep oscillations that display opposite polarity at the surface and midlayers. Current-source-density analyses reveal that the fast oscillations are associated with alternating microsinks and microsources across the cortex, while the evoked potentials and the slow oscillation display a massive current sink in midlayers, confined by two sources in superficial and deep layers. The synchronization of fast rhythms and their high amplitudes indicate that the term "EEG desynchronization," used to designate brain-aroused states, is incorrect and should be replaced with the original term, "EEG activation" [Moruzzi, G. & Magoun, H.W. (1949) Electroencephalogr. Clin. Neurophysiol. 1, 455-473].     

Influence of Cheyne-Stokes respiration on cardiovascular oscillations in heart failure

In patients with congestive heart failure, Cheyne-Stokes respiration is accompanied by oscillations in blood pressure and heart rate at a very low frequency. It is not known whether these cardiovascular oscillations are primarily related to oscillations in ventilation or oxyhemoglobin saturation. We hypothesized that abolition of the ventilatory oscillations of Cheyne-Stokes respiration by CO2 inhalation would eliminate accompanying oscillations in blood pressure and heart rate but that elimination of hypoxic dips by supplemental O2 would not. We studied 10 subjects with heart failure and Cheyne-Stokes respiration during sleep using frequency spectral analysis. During Cheyne-Stokes respiration, heart rate and blood pressure oscillated in association with respiratory oscillations at very low frequency. Inhalation of CO2 abolished Cheyne-Stokes respiration and associated oscillations in both blood pressure and heart rate. In contrast, inhalation of O2 sufficient to eliminate hypoxic dips had no significant effect on Cheyne-Stokes respiration, blood pressure (n = 6), or heart rate (n = 5). We conclude that ventilatory oscillations during Cheyne-Stokes respiration rather than oscillations in oxygenation per se powerfully induce heart rate and blood pressure oscillations. Cheyne-Stokes respiration is therefore one of the mechanisms that contributes to the very low-frequency oscillations in heart rate and blood pressure observed in patients with heart failure.     

Effects of barium on spontaneous mechanical and electrical oscillations in rat papillary muscle

In experiments on isolated rat papillary muscles the effects of Ba2+ (0.2-1 mM) on spontaneous resting tension oscillations (RTO) and membrane potential oscillations (MPO) were investigated. In normal Tyrode's solution the muscles were not spontaneously active, however, the addition of barium (1 mM) after a delay of 3-5 min induced the spontaneous excitations of the preparations. During this time period the amplitudes of RTO and MPO of the quiescent muscle increased gradually, and just before the first spontaneous beat their values were many fold above control levels. It was noted that just before the first spontaneous excitation the RTO became very synchronous and resembled the sinusoidal oscillations. By means of a special transducers the displacements of two adjacent points (distance, 1.0 mm) on a muscle surface were continuously recorded at the resting state. The correlation coefficient between these displacement signals was shown to increase from zero (before Ba2+ addition) to 0.5-0.7 (just before the first spontaneous beat). It was suggested that the enhancement of the RTO and MPO is a result of the synchronization of subthreshold electrical and mechanical activities of all muscle cells after the addition of barium.     

'Respiratory' oscillations of cardiovascular parameters during voluntary apnea

The aim of this study was to ascertain the persistence of heart rate and blood pressure oscillations at the onset of voluntary apnea in humans. In 24 young subjects (10 males, 14 females, mean age 20.4 years) RR intervals, systolic blood pressure (SBP) and diastolic blood pressure (DBP) during controlled breathing (CB) of atmospheric air followed by voluntary apnea on FRC level were recorded continuously. The cosine functions were then fitted by nonlinear regression analysis to heart rate, SBP and DBP oscillations during CB and at the onset of apnea. During apnea, the changes of base of RR intervals indicate primary tachycardic reaction followed by a decrease in heart rate. The base of the blood pressure oscillations was higher (hypertensive reaction) in apnea. At least one cosine-like wave oscillation was present at the onset of apnea in heart rate, SBP and DBP and the second wave was present in all assessed parameters at least in 70% of recordings. There were no significant gender differences neither in the duration of breath holding nor in the RR and SBP oscillations parameters.     

标准体位图联合口诀宣教法对提高内镜下逆行胰胆管造影术体位摆放效果的影响

目的评价标准体位图联合口诀宣教法对提高内镜下逆行胰胆管造影术(ERCP)体位摆放效果的影响。 方法采用便利抽样方法,选取2021年11~12月经解放军总医院第一医学中心消化内镜中心行ERCP的患者为研究对象,其中,11月的72例设为对照组,12月75例设为试验组。对照组采用常规口头宣教方式进行ERCP体位摆放宣教,试验组采用标准体位图进行宣教,评价并比较两组患者的体位摆放配合度及宣教至体位摆放完成所需要的时间,同时采用Likert量表调查试验组医护人员对标准体位图的评价及患者对宣教满意度的评价。 结果试验组患者体位摆放配合度高于对照组,试验组患者的宣教至体位摆放完成时间少于对照组,差异均有统计学意义(P<0.01)。71.33%以上医护人员认为应用标准体位图可减轻护士工作量、提高工作效率、提高体位准确性、缩短准备时间、提高服务质量、调动护士工作积极性,其中提高工作效率、缩短准备时间方面均得到100%的认可。92%以上患者认为提前看图示利于配合护士、图示容易理解,68%患者认为图片吸引力强、护理服务质量高。 结论应用标准体位图联合口诀进行ERCP体位摆放宣教,能明显提高患者配合度,缩短摆放时间,医护患评价及满意度高,利于提升护理服务质量。     

Nervous mechanisms of spontaneous oscillations of systolic blood pressure and heart rate

The phenomenon of rhythmic fluctuations in cardiovascular variables such as heart rate (HR) or arterial blood pressure (BP) has attracted the attention of workers in both pure and applied research. In recent years, the possibility of quantifying these oscillations by using power spectral analysis has aroused a growing interest. We investigated the fluctuations which underly the spontaneous variability of BP and HR in conscious rats. Intrafemoral pulsatile BP was computed to generate evenly spaced signals (systolic, diastolic, mean BP, HR) at 200 ms intervals. This equidistant sampling allowed a direct spectral analysis using a Fast Fourier Transform algorithm. Systolic Blood Pressure (SBP) and HR exhibited low frequency oscillations (Mayer waves, 20-605 mHz) and a high frequency oscillation related to respiration (1,855 mHz). The respiratory fluctuations in HR were almost abolished by vagal blockade (atropine). HR fluctuations in the low frequency regime were diminished by vagal blockade or cardiac sympathetic blockade (atenolol). The respiratory frequency fluctuations in SBP were markedly increased by alpha sympathetic blockade (prazosin). On the contrary the low frequency oscillations in SBP were reduced by alpha sympathetic blockade. These data indicate that in conscious rats: 1) the HR oscillation with respiration is vagally mediated, 2) the HR fluctuation in the low frequency regime is jointly mediated by beta sympathetic and parasympathetic activities, 3) the respiratory oscillation in SBP depends on fluctuations in cardiac output and is normally counteracted by the sympathetic tone, 4) the low frequency oscillations in SBP reflect the sympathetic activity to the resistance vessels.     

Effect of body posture on serum concentration of lipids

The purpose of this study was to evaluate the effects of body postural changes (supine-upright), upon the serum concentration of cholesterol (CT), triglycerides (TG), high density lipoproteins (HDL), low density (LDL) and very low density lipoproteins (VLDL) and hemoglobin, hematocrit, and plasma proteins (to calculate delta% change in plasma y volume). Nine healthy men participated as subjects. Their age ranged from 32 +/- 3 years old, and 16 +/- 4% body fat (X +/- SD). After 10-12 hours post absorptive and appropriate rest, they performed a standard orthostatic maneuver: subjects remained supine for 30 minutes, then assumed the standing position (unsupported and with minimal movement) for additional 30 minutes. Blood samples were obtained after 30 minutes supine and at 10, 20 and 30 minutes of standing. At 10 minutes of orthostatism, CT, TG, HDL and VLDL had a significant increase as compared to supine values; these changes were associated with a reduction of 8.9% on plasma volume (PV) (p less than 0.05). After 30 minutes of orthostatism CT, TG, HDL and VLDL showed increments of 8.5%, 33.3%, 20.1% and 32% respectively, in relation to the supine values (p less than 0.05). Changes on serum lipids were associated with PV reductions until 20 minutes of orthostatism. However, there was not a significant association between these variables at 30 minutes of standing. These data indicated that the body position and the time in which blood samples are obtained significantly influence lipid and lipoprotein serum level. Therefore, in any study related to lipids, such variables should be considered and properly controlled.     

Effect of posture on regional ventilation in children.

Little information has been published concerning the pattern of regional ventilation in children, yet many differences in lung and chest wall mechanics in childhood, supported by clinical observation, have led to the hypothesis that the pattern of regional ventilation seen in children may not be the same as in adults. Forty-three children and 16 adult volunteers underwent Krypton (Kr) 81m radionuclide ventilation lung scans in the supine and right and left decubitus postures. In children aged 2-10 years mean fractional ventilation to the right lung (VfR) was 46.1%. This fell to 36% when dependent and rose to 56.1% in the uppermost position. Redistribution of ventilation away from the dependent towards the uppermost lung was seen in all children. In children aged 10-18 years VfR was 57.2% (supine), 48.0% (dependent), and 62.9% (uppermost). An identical pattern was seen in children with normal or abnormal pulmonary function tests (peak expiratory flow rate, and FEV1: FVC ratio). In subjects over 18 years of age a different pattern was seen: mean VfR was 52.4% (supine), rising to 53.4% (dependent), and falling to 48.9% (uppermost). Postural redistribution of ventilation, as assessed by Kr81m ventilation imaging, changes late in the second decade of life. This will have clinical consequences in the management of children with unilateral lung disease.     

Effect of body posture on radionuclide measurements of gastric emptying

The purpose of this investigation was to compare the effect of body posture on gastric emptying measurements of radiolabeled meals. Eight healthy male subjects were studied on four separate days. During each study subjects were fed a standardized meal of beef stew labeled with technetium-99m sulfur colloid, and orange juice. Measurements of solid-phase gastric emptying rates were obtained by a gamma camera. Subjects were studied in the lying, sitting, standing, or combined sitting-standing postures. The results demonstrated that the lying position significantly slowed gastric emptying compared to all other positions. Conversely, a decrease in emptying times of 51% and 35% occurred in the combined sitting-standing position compared to the lying and sitting position. These results support a marked effect of body posture on the radionuclide measurement of gastric emptying.The authors wish to acknowledge the Salt Lake City Veterans Administration Medical Center, Department of Research for support of this work.