PubMed Health⌕ Search

Biomedical subjects

T J Ebert

Publications and source records attributed to T J Ebert.

87 records · Page 5Linked to original sources
PubMed1985

Determination of cardiac output using ensemble-averaged impedance cardiograms.

Although impedance cardiography provides safe and reliable noninvasive estimates of stroke volume in humans, its usefulness is limited by the necessity for subjects to be apneic and motionless. In an effort to circumvent this restriction we studied the validity of ensemble-averaging of impedance data in exercising normal subjects and in intensive-care patients. The correlation coefficient (r value) between 128 ensemble-averaged and standard hand-digitized determinations of stroke volume index from the same records taken during rest and exercise in six normal male subjects was +0.97 (P less than 0.001). The r value for ensemble-averaged stroke volume indices during free breathing and breath hold in the same subjects was +0.92 (P less than 0.001), suggesting that breath hold did not significantly affect the stroke volume estimation. In 14 freely breathing hospital intensive-care patients the r value between simultaneous thermodilution cardiac output readings and ensemble-averaged impedance determinations was +0.87 (P less than 0.01). The results indicate that ensemble-averaging of transthoracic impedance data provides waveforms from which reliable estimates of cardiac output can be made during normal respiration in healthy human subjects at rest and exercise and in critically ill patients.

Adult↗
PubMed1984

Primary dysfunction of the afferent limb of the arterial baroreceptor reflex system in a patient with severe supine hypertension and orthostatic hypotension.

A 33 year old man with a history of recurrent episodes of orthostatic dizziness since adolescence was noted to have a supine blood pressure of 200/120 mm Hg and a standing blood pressure of 90/60 mm Hg. Results of extensive laboratory studies for secondary hypertension were negative. Studies of the autonomic nervous system function revealed normal plasma catecholamines, cold pressor test and response to 4 minute 30% of maximal static handgrip contraction and an appropriate increase in heart rate on intravenous injection of atropine. In contrast, the heart rate response to phenylephrine and sodium nitroprusside infusion, carotid massage and graded neck suction with an airtight chamber was very abnormal, indicating marked dysfunction of the afferent limb of the arterial baroreceptor reflex system. Methyldopa decreased the supine hypertension and increased the standing blood pressure.

Adult↗
PubMed1984

Impedance cardiograms reliably estimate beat-by-beat changes of left ventricular stroke volume in humans.

Linear regression was used to compare stroke volumes calculated from tetrapolar impedance cardiograms and simultaneous left ventriculograms in 14 patients undergoing diagnostic left heart catheterisation. We calculated three to five consecutive stroke volumes from each ventriculogram. Left ventricular stroke volumes estimated by the two methods correlated closely: the correlation coefficients from pairs of data obtained from individual patients ranged between 0.77 and 1.00 (average = 0.91), and the correlation coefficient for pooled data (all pairs from all subjects) was 0.79 (p less than 0.001). Changes in left ventricular stroke volume measured with the two methods also correlated well (r = 0.89 for pooled data, p less than 0.001). The results suggest that impedance cardiograms provide reliable estimates of changes of beat-by-beat left ventricular stroke volumes and reasonable estimates of absolute levels of beat-by-beat stroke volumes in humans.

Aged↗
PubMed1984

Baroreceptor reflex control of heart rate during isoflurane anesthesia in humans.

The effect of isoflurane alone (Group 1) and isoflurane following thiopental (Groups 2 and 3) on baroreflex control of heart rate in humans was investigated in this study. Phenylephrine (the pressor test) and sodium nitroprusside (the depressor test) were used to induce moderate changes in arterial blood pressure and to alter the stimulation of baroreceptor sites. In addition, graded neck suction was employed to examine carotid baroreflex control of heart rate. In Group 3 subjects, phenylephrine was infused continuously during anesthesia to maintain mean arterial blood pressure near control levels. The pressor- and neck-suction-derived baroreflex slopes were decreased progressively from awake to 1.0 and 1.5 MAC isoflurane. The slopes of the depressor responses were decreased at 1.0 MAC but showed little further depression at 1.5 MAC. For each method, the depression of baroreceptor slopes from control to 1.0 MAC and 1.5 MAC was similar among the three groups. Maintenance of arterial blood pressure (Group 3) and the utilization of thiopental (Group 2) did not significantly alter the depression of baroreflex responses during increasing levels of isoflurane anesthesia. Neck suction derived slopes compared favorably with the pressor test slopes (r = 0.75, P less than 0.001). This study indicates that the depression of arterial baroreflex heart rate responses under isoflurane anesthesia are less pronounced than the depression of baroreflex responses noted by other investigators for halothane or enflurane. The neck suction technique appears to be a sensitive method useful in assessing the carotid sinus reflex in awake and anesthetized humans.

Adult↗
PubMed1984

Baroreceptor reflex control of heart rate during morphine sulfate, diazepam, N2O/O2 anesthesia in humans.

The effect of morphine, diazepam, N2O/O2 anesthesia on baroreflex control of heart rate in humans was investigated in this study. Group 1 subjects (n = 11) received morphine 0.5 mg/kg, diazepam 0.25 mg/kg, and 70% N2O with O2. Group 2 subjects (n = 10) received morphine 0.75 mg/kg, diazepam 0.25 mg/kg, and 70% N2O with O2. Phenylephrine (the pressor test), sodium nitroprusside (the depressor test), and graded neck suction were employed to alter the stimulation of baroreceptor sites. The pressor, the depressor, and neck suction baroreflex slopes declined significantly in both groups from awake to anesthetized. There was no significant difference in the degree of depression between the two groups for all three tests. Neck suction derived slopes compared favorably to the pressor test slopes (r = 0.70, P less than 0.01). This study indicates that the depression of arterial baroreflex-heart rate responses under morphine, diazepam, N2O/O2 anesthesia is similar to that seen with potent inhalational anesthetics such as isoflurane. Furthermore, there was no difference between the two morphine doses that were studied.

Adult↗
PubMed1984

Repetitive ramped neck suction: a quantitative test of human baroreceptor function.

Bolus intravenous injection of an alpha-agonist is a widely accepted method used for studying baroreceptor function. However, the method is invasive, multiple baroreceptor regions are stimulated, and there are diverse direct effects of these pharmacologic agents, e.g., direct effects on the carotid sinus region. A recently described noninvasive neck suction technique may be highly specific for assessing the carotid sinus to sinoatrial node baroreflex. We compared neck suction-derived baroslopes with those obtained from the standard, invasive phenylephrine infusion method. These techniques were applied to 15 adult volunteers while awake and during 1.34 and 2% isoflurane anesthesia. The correlation coefficients between the two methods were 0.74 (P = 0.002) in awake subjects and 0.75 (P = 0.001) overall. The neck suction method of repetitive, ramped carotid stimuli yielded results that were qualitatively and quantitatively similar to those of the standard phenylephrine method. The neck suction method is simple, noninvasive, and can be repeated at frequent intervals. This method may be highly specific for determining carotid baroreceptor-cardiac reflex physiology in humans.

Adult↗
PubMed1983

Carotid baroreceptor reflex regulation of forearm vascular resistance in man.

The carotid baroreflex regulation of forearm vascular resistance in man is uncertain. Forearm vascular resistance, blood pressure and R-R interval responses to carotid sinus stimulation were therefore measured in seven healthy men. Carotid stimuli were delivered by gradually applying neck pressure, neck suction or neck suction during simultaneous low-level lower-body negative pressure. Mean arterial blood pressure and R-R interval responses to neck suction and pressure were immediate and were sustained throughout the periods of stimulation. In contrast, forearm vascular responses, were transient. During simultaneous mild lower-body negative pressure (which decreases cardiopulmonary baroreceptor stimulation and increases forearm vascular resistance), neck-suction-induced forearm vasodilation was exaggerated and sustained throughout the entire period of neck suction. There was a linear relationship between the level of resting forearm vascular resistance and the change in resistance produced by carotid stimuli. It is concluded that reflex changes in forearm vascular resistance provoked by carotid baroreceptor stimuli are immediate and evanescent in man. Simultaneous reduction of cardiopulmonary baroreceptor activity heightens the magnitude and duration of forearm vasodilation induced by carotid baroreceptor stimulation.

Adaptation, Physiological↗
PubMed1982

Summated circulatory responses of thermal and baroreflexes in humans.

Baroreceptor and thermal receptor mediated reflexes are important neural control systems that can markedly alter blood pressure in humans. These two systems have different afferent limbs and are integrated at different central sites. Although the circulatory effects of activating these individual reflexes have been examined, the effects of simultaneous activation of two or more separate reflexes have received relatively little attention. We used noninvasive methods in 13 normal men (20-27 yr) to examine the responses mediated by cardiopulmonary and arterial baroreceptors; the reflexes were elicited by alterations in central blood volume [lower body negative pressure (LBNP) and leg elevation (LE)] in the presence or absence of local thermal receptor stimulation induced by hand immersion (HI) in 10 degree C water. During all levels (-10, -25, and -40 Torr) of LBNP and during LE, forearm vascular resistance (FVR) was altered. At the two higher levels of LBNP, stroke volume, cardiac index, and blood pressure (BP) decreased, and heart rate (HR) and total peripheral resistance (TPR) increased. TPR, FVR, and BP increased during HI. Our analyses indicated that responses to combined stimuli, i.e., local cold during LBNP or LE, resulted in simple additive responses in all variables except HR. A central interaction between thermal and baroreflex control of HR is possible.

Adult↗
PubMedDate not supplied

Muscarinic cholinergic receptors modulate vagal cardiac responses in man.

Respiratory sinus arrhythmia (peak-valley P-P interval changes during controlled breathing) and carotid baroreceptor-cardiac reflex responses (provoked by neck suction) were studied before and after low (0.725 microgram/kg) or high (0.043 mg/kg) dose atropine sulfate infusions in 22 healthy young adults. There was a highly significant (r = 0.78, P = 0.002) correlation between resting respiratory sinus arrhythmia and baroreflex responses. Low dose atropine increased the magnitude of sinus arrhythmia and baroreflex responses. Large dose atropine reduced sinus arrhythmia and baroreflex responses in an exponential fashion. Our results link respiratory sinus arrhythmia with baroreflex responsiveness and provide inferential evidence that vagal cardiac efferent activity is modulated by inhibitory cholinergic receptors. We speculate that blockade of these receptors by low doses of atropine amplifies vagal motoneuron responses to incoming baroreceptor information, and thereby increases average maximum and minimum levels of vagal cardiac outflow during breathing.

Adult↗
PubMedDate not supplied

Intraoperative use of bolus doses of esmolol to treat tachycardia.

UNLABELLED: A randomized, double-blind, parallel, placebo-controlled study was conducted to determine the safety and efficacy of intravenous (IV) bolus administration of esmolol in treating intraoperative tachycardia in patients undergoing noncardiac general surgery. Forty-eight ASA II-IV patients were randomized into three equal groups to receive either placebo, esmolol 50 mg, or esmolol 100 mg. Premedication (lorazepam) and anesthetic induction techniques (thiopental sodium and succinylcholine) were identical between groups. Approximately 20 minutes after intubation, during isoflurane/N2O/O2 maintenance anesthesia, patients with systolic pressure (SBP) greater than or equal to 110 mmHg were advanced into a 10-minute study drug period if one of two conditions were met: (1) heart rate (HR) was greater than or equal to 95 beats/minute, or (2) an increase in HR of greater than 20% above preinduction baseline occurred. After two consecutive recordings of HR and blood pressure (BP), the study drug (or placebo) was injected. HR was recorded every 30 seconds and BP was recorded every minute during the ensuing 10-minute period. Compared to placebo responses, HR was significantly reduced with both doses of esmolol within 1 minute of bolus injection and remained below placebo levels for 5 minutes after 50 mg of esmolol and for 9.5 minutes after 100 mg of esmolol. There were, however, only minor differences among groups with respect to SBP, diastolic blood pressure (DBP), and mean blood pressure (MBP) changes. CONCLUSION: Bolus administration of esmolol can produce a rapid reduction of HR with relatively few adverse effects in an unhealthy surgical population.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic beta-Antagonists↗
PubMedDate not supplied

Attenuation of hemodynamic responses to rapid sequence induction and intubation in healthy patients with a single bolus of esmolol.

The effectiveness of a single preinduction intravenous (IV) bolus of esmolol in blunting hemodynamic responses to rapid sequence induction and tracheal intubation was evaluated. In a randomized double-blind study, 32 ASA I and II healthy patients scheduled for surgery were monitored with electrocardiography (EKG) lead V5, arterial cannulation, and impedance cardiography. After preoxygenation and a priming dose of vecuronium (0.01 mg/kg), patients received either saline (n = 12), esmolol 100 mg (n = 10), or esmolol 200 mg (n = 10) as an IV bolus (20 ml volume). This procedure was immediately followed by a 5 ml IV saline flush, cricoid pressure, thiopental sodium 5 mg/kg, and succinylcholine 1.5 mg/kg. Patients receiving 200 mg of esmolol had a 50% reduction in the usual tachycardia associated with induction and a greater decline in systolic blood pressure (SP) (by 50%) prior to intubation as compared with the placebo group (p less than 0.05). The increase in diastolic blood pressure (DP) and the reduction in stroke volume (SV) produced by induction and intubation were similar in all the groups. Plasma norepinephrine levels at 1.5 minutes after intubation increased in the esmolol groups about 130% above that measured in the placebo group. This finding was associated with a more gradual return of peripheral resistance to baseline following tracheal intubation. However, both doses of esmolol effectively attenuated heart rate (HR), SP, and rate pressure product (RPP) increases (p less than 0.05 vs placebo) produced by laryngoscopy and tracheal intubation.

Adrenergic beta-Antagonists↗
PubMedDate not supplied

Captopril potentiates chronotropic baroreflex responses to carotid stimuli in humans.

Angiotensin II is a potent vasoconstrictor and has profound effects on autonomic neural mechanisms in experimental animals. Human carotid baroreflex control of arterial pressure and heart period was examined before and after acutely decreasing angiotensin II levels by administering 50 mg of oral captopril, an angiotensin converting enzyme inhibitor. Carotid baroreceptor stimuli were delivered by a neck chamber worn by 14 normotensive volunteers. Four subjects received placebo. Arterial pressure responses to carotid distention and tachycardia in response to carotid compression were not changed in captopril or placebo groups; however, there was an augmented bradycardic response to carotid stretch in captopril-treated subjects. These results indicate that captopril has an asymmetrical effect on carotid baroreflex function and suggest that enhanced baroreflex mediated bradycardia is due to a reduction in central nervous system angiotensin II levels by captopril, which augments vagal-cardiac responses to carotid stimuli.

Adult↗
PubMedDate not supplied

A comparison of epidural narcotics, with and without a test dose, to epidural lidocaine for extracorporeal shock wave lithotripsy.

We sought to compare epidural lidocaine to several short-acting epidural narcotics for their efficacy in controlling pain during extracorporeal shock wave lithotripsy (ESWL), hemodynamic changes, side effects and patient acceptance. To determine what contribution, if any, the local anesthetic test dose makes to the above factors, we also compared epidural sufentanil with and without a preceding test dose of local anesthetic with epinephrine. One hundred ASA I-III patients scheduled for elective ESWL were divided equally into five groups to receive one of the following epidural drugs through an epidural catheter: 2% lidocaine with 1:200,000 epinephrine (Group L), 1000 micrograms alfentanil (Group A), 200 micrograms fentanyl (Group F) or 60 micrograms sufentanil (Groups S and S-). Group S- differed from all other groups in omission of the test dose and direct injection of the opioid through the epidural needle. Significant hypotension occurred in 20% of patients in Group L compared to 0% in the narcotic groups (p less than 0.01). Clinically significant respiratory depression was not observed in any group. Mild pruritus was observed in up to 60% of patients in the narcotic groups (p less than 0.01). Sedation was observed in all of the narcotic groups, particularly in Group S-, in which more than half of patients were drowsy (p less than 0.05). Requirements for adjuvant analgesics during ESWL were highest in Group A. Patient acceptance was high throughout the study. We conclude that epidural alfentanil, fentanyl and sufentanil are as effective as epidural lidocaine plus epinephrine in providing analgesia during ESWL.(ABSTRACT TRUNCATED AT 250 WORDS)

Alfentanil↗