Heart Rate Plateau Research Articles

Identifying Trends of Dysautonomia Signs and Symptoms Associated with Protracted Concussion Recovery during the Buffalo Concussion Treadmill Test: A Retrospective Study

Abstract Objective: To identify trends of provoked dysautonomia signs and symptoms during the Buffalo Concussion Treadmill Test (BCTT). Subjects: This is a retrospective cohort study of 101 patient charts post-concussion who were screened for suspected dysautonomia. Methods: Patients with suspected dysautonomia were assessed for exercise intolerance using a BCTT. Symptoms and rate of perceived exertion were recorded on a standardized form. Digital pulse oximetry was used to collect heart rate (HR) and oxygen saturation. Descriptive analyses were conducted on BCTT results. Results: Of 101 patient charts, 57 were excluded from analysis, including four patients who completed the BCTT by asymptomatically reaching the target HR zone for their estimated HR max. The remaining 44 patients demonstrated: 35 (79.5%) poor HR stabilization defined as a drop or plateau in HR during exercise, 28 (63.8%) exacerbated concussion symptoms, 13 (29.5%) autonomic nervous system response such as hot flushed sensation, 12 (27.3%) rebound symptoms during recovery phases, and 8 (18.2%) desaturation of 90% or below. The mean delta (80% expected HR max – 80% achieved HR max) on the initial test was 80.66 (± 23.08) beats per minute. Conclusions: This study is the first to identify trends of signs and symptoms during the BCTT in an expanded population with suspected dysautonomia after concussion. Future studies are indicated to validate these findings and contribute to development of modified termination criteria for the BCTT in individuals with suspected dysautonomia associated with protracted concussion recovery.

Identifying Trends of Dysautonomia Signs and Symptoms Associated with Protracted Concussion Recovery during the Buffalo Concussion Treadmill Test: A Retrospective Study

Objective: To identify trends of provoked dysautonomia signs and symptoms during the Buffalo Concussion Treadmill Test (BCTT). Subjects: This is a retrospective cohort study of 101 patient charts post-concussion who were screened for suspected dysautonomia. Methods: Patients with suspected dysautonomia were assessed for exercise intolerance using a BCTT. Symptoms and rate of perceived exertion were recorded on a standardized form. Digital pulse oximetry was used to collect heart rate (HR) and oxygen saturation. Descriptive analyses were conducted on BCTT results. Results: Of 101 patient charts, 57 were excluded from analysis, including four patients who completed the BCTT by asymptomatically reaching the target HR zone for their estimated HR max. The remaining 44 patients demonstrated: 35 (79.5%) poor HR stabilization defined as a drop or plateau in HR during exercise, 28 (63.8%) exacerbated concussion symptoms, 13 (29.5%) autonomic nervous system response such as hot flushed sensation, 12 (27.3%) rebound symptoms during recovery phases, and 8 (18.2%) desaturation of 90% or below. The mean delta (80% expected HR max – 80% achieved HR max) on the initial test was 80.66 (± 23.08) beats per minute. Conclusions: This study is the first to identify trends of signs and symptoms during the BCTT in an expanded population with suspected dysautonomia after concussion. Future studies are indicated to validate these findings and contribute to development of modified termination criteria for the BCTT in individuals with suspected dysautonomia associated with protracted concussion recovery.

Identifying Trends of Dysautonomia Signs and Symptoms Associated with Protracted Concussion Recovery during the Buffalo Concussion Treadmill Test: A Retrospective Study

Objective: To identify trends of provoked dysautonomia signs and symptoms during the Buffalo Concussion Treadmill Test (BCTT). Subjects: This is a retrospective cohort study of 101 patient charts post-concussion who were screened for suspected dysautonomia. Methods: Patients with suspected dysautonomia were assessed for exercise intolerance using a BCTT. Symptoms and rate of perceived exertion were recorded on a standardized form. Digital pulse oximetry was used to collect heart rate (HR) and oxygen saturation. Descriptive analyses were conducted on BCTT results. Results: Of 101 patient charts, 57 were excluded from analysis, including four patients who completed the BCTT by asymptomatically reaching the target HR zone for their estimated HR max. The remaining 44 patients demonstrated: 35 (79.5%) poor HR stabilization defined as a drop or plateau in HR during exercise, 28 (63.8%) exacerbated concussion symptoms, 13 (29.5%) autonomic nervous system response such as hot flushed sensation, 12 (27.3%) rebound symptoms during recovery phases, and 8 (18.2%) desaturation of 90% or below. The mean delta (80% expected HR max – 80% achieved HR max) on the initial test was 80.66 (± 23.08) beats per minute. Conclusions: This study is the first to identify trends of signs and symptoms during the BCTT in an expanded population with suspected dysautonomia after concussion. Future studies are indicated to validate these findings and contribute to development of modified termination criteria for the BCTT in individuals with suspected dysautonomia associated with protracted concussion recovery.

Does heart rate response confirm the attainment of maximal oxygen uptake in adults 45years and older?

To test the efficacy of a plateau in heart rate (HRplat) as an effective indicator for confirming [Formula: see text]max attainment in a middle-aged to older sample. Nine men and eleven women (age 60 ± 8.5 years, [Formula: see text]max 35.9 ± 9.4ml/kg/min, N = 20) completed a single [Formula: see text]max test on both the treadmill and cycle ergometer.[Formula: see text]max was confirmed using a plateau in [Formula: see text] ([Formula: see text]plat) of ≤ 150ml/min, a verification bout, and HRplat (≤ 4bpm). [Formula: see text]plat occurred in 100% and 95% of participants on the treadmill and cycle ergometer, respectively. Verification criteria ([Formula: see text]max during verification ≤ 2% of [Formula: see text]max during incremental test) were met by 80% of participants on both modalities. HRplat was achieved by 90% and 70% of participants on the treadmill and cycle ergometer, respectively. These results suggest that a verification bout is reliable for confirming [Formula: see text]max in older adults on both modalities. In our sample of middle-aged and older adults, [Formula: see text]plat was the most robust method to assess [Formula: see text]max when indirect calorimetry is available. Although more research is warranted, when indirect calorimetry is not available, a HRplat of ≤ 4bpm may be a useful alternative to get an accurate representation of maximal effort in middle-aged and older adults.

Does Heart Rate Response Confirm The Attainment Of Maximal Oxygen Uptake In Adults 45 Years And Older?

Heart rate plateau (HRplat) is an effective indicator for confirming V˙O2max attainment. However, it is unknown if this criterion holds for older populations. PURPOSE: Test the efficacy of HRplat for confirming V˙O2max in older individuals. METHODS: Twelve males and twelve females (60±8 years, N=24) completed individualized ramp and staged protocols to volitional fatigue on the cycle ergometer (CE) and treadmill (TM), respectively. Participants then performed verification protocols at 105% of their peak workload from each V˙O2max test. V˙O2max was confirmed using a plateau in V˙O2 (V˙O2plat = largest V˙O2 value – closest neighboring point ≤150 ml/min), a V˙O2max verification criterion of a V˙O2 not greater than 2% higher than the incremental phase, and two different criteria for HRplat (≤2 bpm or ≤4 bpm). Secondary criteria for establishing maximal effort were RERmax ≥1.10, HRmax ±10 bpm of APHRmax, RPE ≥17, and [BLa-] ≥ 8mM. RESULTS: Data are presented (Table 1) as sex-specific percentages. All attained V˙O2plat on both modalities. The verification criterion was met by ≥ 67% of females and ≥ 92% of males in our sample regardless of modality. HRplat (≤2 bpm) was met by ≤ 67% of females and ≤ 44% of males in our sample regardless of modality. Males more frequently attained HRplat (≤4 bpm) than did females; females attained HRplat (≤4 bpm) more frequently on TM as compared to CE. CONCLUSION: A verification bout is reliable for confirming V˙O2max in older males on both modalities and for females on the TM. HRplat (≤4 bpm) may serve as a standalone criterion for TM V˙O2max attainment for males and females. V˙O2plat was the most robust method for confirming V˙O2max attainment in older adults. Due to wide variability in the literature regarding V˙O2plat criteria and indirect calorimetry processing methods, agreement on a standardized definition for V˙O2plat and clear data processing procedures are needed.Table 1: V˙O2max attainment criteria for all tests across sex and modality (N=24)

Differential cardiovascular responses to cutaneous afferent subtypes in a nociceptive intersegmental spinal reflex

Electrical stimulation to segmental dorsal cutaneous nerves (DCNs) activates a nociceptive sensorimotor reflex and the same afferent stimulation also evokes blood pressure (BP) and heart rate (HR) responses in rats. To investigate the relationship between those cardiovascular responses and the activation of nociceptive afferents, we analyzed BP and HR responses to electrical stimulations at each DCN from T6 to L1 at 0.5 mA to activate A-fiber alone or 5 mA to activate both A- and C-fibers at different frequencies. Evoked cardiovascular responses showed a decrease and then an increase in BP and an increase and then a plateau in HR. Segmentally, both cardiovascular responses tended to be larger when evoked from the more rostral DCNs. Stimulation frequency had a larger effect on cardiovascular responses than the rostrocaudal level of the DCN input. Stimulation strength showed a large effect on BP changes dependent on C-fibers whereas HR changes were dependent on A-fibers. Additional A-fiber activation by stimulating up to 4 adjacent DCNs concurrently, but only at 0.5 mA, affected HR but not BP. These data support that cutaneous nociceptive afferent subtypes preferentially contribute to different cardiovascular responses, A-fibers to HR and C-fibers to BP, with temporal (stimulation frequency) and spatial (rostrocaudal level) dynamics.

Evaluation of a rat model of exercise-induced fatigue using treadmill running with progressively increasing load.

The mechanism behind exercise-induced fatigue is a significant topic in the field of sports physiology. Therefore, establishing and evaluating an acute exercise-induced fatigue animal model that explores the limits of the motor system may provide greater insight into these mechanisms. Heart rate is an important quantitative parameter that accurately reflects the immediate change in physical function due to exercise load. And there is likely to be an important correlation between heart rate and behavioral performance. In this study, changes in heart rate and behavioral indexes during exercise-induced fatigue were quantitatively analyzed in rats using heart rate telemetry and video methods respectively. The behavioral indexes were used as independent variables and the degree of fatigue was used as the forecast value. Ternary quadratic function curve fitting was used to deduce a formula to calculate a fatigue score: Y = 15.2548+0.4346∙xa-0.1154∙xb+0.6826∙xc+0.0044∙xa∙xb-0.0021∙xb∙xc-0.0013∙xc∙xa-0.0023∙xa2-0.0016∙xb2 (r2=0.906). It identified a linear relationship between heart rate and exercise intensity, with a plateau in heart rate occurring during difference periods. It will serve as an effective reference for the modeling of exercise-induced fatigue. In addition, it also provides a theoretical method for analyzing the correlation between peripheral and central parameters.

Heart Rate Responses in the Diving Reflex among Aerobically Trained and Untrained Men

The mechanisms of the diving reflex involve the simultaneous activation of the sympathetic and parasympathetic nervous systems (PNS). The enhanced PNS capabilities as achieved through aerobic training has been investigated in the diving reflex, specifically vagally-mediated bradycardia, and the research remains controversial. PURPOSE: The current study was conducted to evaluate heart rate responses associated with the diving reflex in aerobically trained and untrained men. METHODS: Using 2 x 3 mixed factorial ANOVA, lowest heart rate achieved, percent heart rate reduction, and time course of heart rate reduction were compared between aerobically untrained (n = 7) and trained (n = 9) men while breath holding in air, water at 15 °C, and water at 0 °C. RESULTS: Results showed that trained men did not differ in percent heart rate reduction or lowest heart rate achieved, although there was a tendency for lowest heart rate achieved in the trained group (p = .06). A significant interaction was found for time course (p = .01), where trained men took significantly longer to reach a plateau in heart rate in the air compared to untrained men. No differences in training status were found for time course in the two water conditions. However, a linear increase in time course for untrained men in the water conditions indicated a potentially delayed response by the PNS with the diving reflex. CONCLUSION: No additional clarification on the impact of training status on the diving reflex has been made except that an effect may lie in the timing of the response of the PNS.

Confirming Maximal Oxygen Uptake: Is Heart Rate the Answer?

This study investigates heart rate (HR), in 11 young adults (22.4±3.21yr), at V̇O2max, to ascertain whether measured maximal heart rate (HRmax), as determined by a plateau in HR (HRplat), can reliably confirm V̇O2max. V̇O2max and HRplat were determined, using the parameters of a V̇O2≤50 ml•min-1 and a ∆HR≤2b•min-1, respectively, over the final 60 s of sampling. V̇O2 was also independently determined using a verification phase protocol. A HRplat was achieved by 91% of participants (∆HR=1.3±1b•min-1) and critically the time at which HRmax was reached coincided with that at which V̇O2max was achieved. Moreover RER and ΔRER criteria were reached significantly earlier (p<0.05) than V̇O2max, whilst age-related heart rate maximums (HRage), were not achieved by many participants. The results suggest that a HRplat ≤2 b•min-1 is a more accurate method, within the group tested, to determine whether a 'true' V̇O2max has been achieved, than other secondary criteria and potentially avoids the requirement for an additional verification phase.

Acute Effect of Central Administration of Urotensin II on Baroreflex and Blood Pressure in Conscious Normotensive Rabbits.

In the present study, we examined the effects of central administration of Urotensin II on blood pressure, heart rate, and baroreceptor heart rate reflexes in conscious normotensive rabbits. Preliminary operations were undertaken to implant a balloon cuff on the inferior vena cava for baroreflex assessments and to implant cannula into the lateral and fourth ventricle. After 2 weeks of recovery cumulative dose response curves to Urotensin II (10, 100 ng, 1, 10, and 100 μg) given into the ventricles, or Ringer's solution as a vehicle were performed on separate days. Injections were given each hour and baroreflex assessments were made 30 min after each administration. Analysis of the dose response curves to Urotensin II compared to vehicle administered into the lateral or fourth ventricle, indicated little change to blood pressure or heart rate. Analysis of the time course to the highest dose over a 30 min period revealed a small (−5 mmHg) depressor response maximal at 10 min when injected into the fourth ventricle but no effect when injected into the lateral ventricle. Baroreflex assessments made at each dose showed that there was no change in baroreflex sensitivity but that an increase in the upper plateau was observed when Urotensin was injected into the lateral ventricle and a tendency for a reduced lower heart rate plateau was observed after fourth ventricle administration. Clonidine administration in the fourth ventricle decreased blood pressure and heart rate, thus confirming catheter patency. In conclusion, our findings suggest that Urotensin II in the forebrain and brainstem may play a role in modulating cardiac sympathetic and vagal baroreflexes but only during large acute changes in blood pressure.

Time-to-Fatigue During Incline Treadmill Running: Implications for Individualized Training Prescription.

Uphill running has been touted as a key interval training tactic for distance runners despite few scientifically derived recommendations for individualized training prescription. To date, a majority of uphill training research has focused on shorter, faster training bouts; however, longer, slower bouts based on an individual's velocity at maximum oxygen consumption (Vmax) may prove more effective. One potential longer bout length may be associated with the time Vmax can be maintained (Tmax), an approach proven effective in level-grade interval training. Therefore, the purpose of this investigation included examining the Tmax, heart rate, and test-retest reliability of incline treadmill running (INC) on a 10% grade at 65, 70, 75, 80, and 85%Vmax compared with level-grade running at Vmax. Twelve moderately trained distance runners (age, 26.4 ± 4.8; body mass, 64.3 ± 12.9 kg; height, 171.2 ± 9.3 cm; and V̇O2max, 56.6 ± 7.6 ml·min⁻¹·kg⁻¹) completed 2 Tmax INC trials at each submaximal Vmax and a level-grade Tmax at Vmax. The dependent variables were Tmax, heart rate plateau (HR(Plateau)), and half-time to heart rate plateau (½HR(Plateau)) of each condition. Statistical significance was set to p ≤ 0.05. Student's t-test revealed no significant differences in Tmax, HR(Plateau), and ½HR(Plateau) between trials 1 and 2 at any INC condition. One-way analysis of variance revealed significant differences in (a) Tmax during INC at 75, 80, and 85%Vmax and level-grade at Vmax and (b) ½HR(Plateau) during INC at 80 and 85%Vmax and all other conditions. In conclusion, Tmax and heart rate dynamics during INC proved reliable, and simple regression analysis revealed ∼68%Vmax during INC yields the same level-grade Tmax at Vmax.

Cardiovascular baroreceptor activity and selective inhibition of monoamine oxidase

Cardiovascular baroreceptor responsiveness of conscious rats treated with selective inhibitors of monoamine oxidase (MAO) types A and B was determined by measurement of blood pressure (BP) and heart rate (HR) responses to intravenous injection of phenylephrine and sodium nitroprusside. Treatment with selegiline (1 or 5mg/kg p.o. daily for 7days) did not significantly modify resting levels of BP and HR, lower or upper HR plateau levels, or HR/BP gain. Treatment with clorgyline (2mg/kg p.o. daily for 7days) increased HR/BP gain but also did not modify resting BP or HR, or lower and upper plateau levels of HR. The results are compatible with an effect of MAO-A inhibition to modify monoamine levels in medullary areas participating in CNS control of blood pressure.

Micro-CT imaging assessment of dobutamine-induced cardiac stress in rats

Introduction Dobutamine (DOB) stress in animal models of heart disease has been imaged so far using echocardiography and magnetic resonance imaging. The purpose of this study was to assess normal response to DOB stress in rats using anatomical and functional data using micro-computed tomography (CT). Methods Ten normal adult male rats were first injected with a liposomal-based blood pool contrast agent and next infused with DOB via a tail vein catheter. Using prospective gating, 5 pairs of systole/diastole micro-CT images were acquired (a) pre-infusion baseline; (b) at heart rate plateau during infusion of 10 μg/kg/min DOB; (c) at post-DOB infusion baseline; (d) at heart rate plateau during infusion of 30 μg/kg/min DOB; and (e) after post-infusion return to baseline. Heart rate, peripheral and breathing distensions were monitored by oximetry. Micro-CT images with 88-μm isotropic voxels were segmented to obtain cardiac function based on volumetric measurements of the left ventricle. Results DOB stress increased heart rate and cardiac output with both doses. Ejection fraction increased above baseline by an average of 35.9% with the first DOB dose and 18.4% with the second dose. No change was observed in the relative peripheral arterial pressures associated with the significant increases in cardiac output. Discussion Micro-CT proved to be a robust imaging method able to provide isotropic data on cardiac morphology and function. Micro-CT has the advantage of being faster and more cost-effective than MR and is able to provide higher accuracy than echocardiography. The impact of such an enabling technology can be enormous in evaluating cardiotoxic effects of various test drugs.

The Onset And Magnitude Of Cardiovascular Drift Depend On Exercise Intensity In Recreational Runners

Cardiovascular drift (CVD) is a gradual increase in heart rate (HR) during prolonged steady-state exercise. Despite considerable research on the etiology of this complex phenomenon, little is known as to the effects of CVD on energy consumption. PURPOSE: To examine the potential effects of CVD on aerobic and anaerobic metabolism. METHOD: Recreational runners (n=10, age 40.3±8.3 years, height 176±7 cm, weight 71.29±10.76 kg, VO2max 57.29±5.96 ml·kg-1·min-1) volunteered for this study and signed informed consent forms. Each participant performed 5 running tests 2-4 days apart: a maximal oxygen consumption (VO2max) test (2-min stages to exhaustion), a Maximal Lactate Steady State test (MLSS), and 3 prolonged submaximal bouts (45 min duration each) at intensities corresponding to 95%, 100%, and 105% of the MLSS velocity (1% grade). HR and VO2 were recorded continuously throughout all tests; blood lactate was measured at the end of each stage during the first 2 tests, and every 10 minutes for the 3 prolonged bouts. All protocols were approved by the IRB. RESULTS: Only 3 runners were able to complete the 105% MLSS bout. Onset of CVD was different for every participant, often with no HR plateau in the 105% MLSS bout. Small differences in exercise intensity (0.22 m·sec-1) yielded statistically significant (p < 0.05) differences across the three intensities in the amplitude of CVD (increases of 7 BPM, 14 BPM, and 18 BPM for the 95%, 100%, and 105% respectively), VO2 (1.42 ml·kg-1·min-1, 1.8 ml·kg-1·min-1, and 1.39 ml·kg-1·min-1 respectively), and blood lactate (0.25 mmol·L-1, 0.88 mmol·L-1, and 1.08 mmol·L-1 respectively) between steady state and minute 40. CONCLUSION: We successfully measured the small changes associated with the metabolic cost of exercise during CVD. Our data conclusively indicate that the onset of CVD is affected by the intensity of exercise and the amplitude of CVD is greater as exercise intensity increases. Supported by the Mary Stuart Rogers Foundation and an NSF grant (DUE 0511219).

Effects of soft-water acclimation on the physiology, swimming performance, and cardiac parameters of the rainbow trout, Oncorhynchus mykiss

Rainbow trout acclimated to soft water were submitted to an incremental velocity trial, and exhibited a 14% decrease in critical swimming speed (U(crit) * 1.37 +/- 0.055 vs. 1.54 +/- 0.044 m s(-1)) compared to fish kept in hard water. After a standardized swimming protocol, soft-water-acclimated fish had higher blood lactate concentrations (6.5 +/- 0.66 and 6.0 +/- 0.64 mmol L(-1) (soft water) vs. 5.0 +/- 0.46 and 3.9 +/- 0.32 mmol L(-1) (hard water)), revealing a greater use of anaerobic metabolism for the same exercise. Cardiovascular parameters were investigated while fish were swimming at increasing water velocities, revealing that soft-water-acclimated fish had lower increases in heart rate (105% vs. 118% of pre-exercise values), due to higher heart rates observed during acclimation and during the first 10 min of the swimming trial. This was also reflected by the plateau in heart rate and stroke volume observed during the swimming protocol, which can be attributed to increased cardiovascular function in response to soft-water acclimation. These results are in accord with previously reported increases in blood-to-water diffusion distance, due to proliferation of chloride cells at the gills in response to soft-water conditions, and underscore the costs and limitations of soft-water acclimation.

高血圧自然発症ラットにおけるβ遮断薬と運動の併用効果

We investigated the effects of long-term administration of bisoprolol (β-blocker), exercise and their combination on blood pressure, heart rate, and baroreflex function in spontaneously hypertensive rats (SHR).SHR aged 5 week were randomly assigned to control group (C), bisoprolol-treated group (Biso), exercise group (Exer), and combination group (Biso+Exer)(n=8/each group). In Biso and Biso+Exer, bisoprolol (20 mg/kg/day) was administered. In Exer and Biso+Exer, exercise training was performed on treadmill 5 days/week for 12 weeks. Systolic blood pressure (SBP) and heart rate (HR) were measured using the tail-cuff method under restraint from 5 to 16 weeks of age. After 12-week intervention period, sigmoidal mean artery pressure (MAP) and HR reflex curve were obtained by intravenous injections of various doses of phenylephrine and nitroprusside under non-restraint condition. To determine vagal component of baroreflex function, baroreflex MAP-HR relation were also examined after intravenous injections of atenolol (β-blocker). After measurements of all baroreflex function, atropine was additionally injected to determine intrinsic HR.At 15 and 16 weeks of age, SBP and HR in Biso and Exer were significantly lower than those in C. SBP and HR in Biso+Exer were further reduced compared with Biso. Before atenolol, resting MAP, HR and upper and lower HR plateaus in the sigmoid curve were lower in Biso, Exer, and Biso+Exer compared with C. There were no significant differences in these parameters between Biso and Biso+Exer. There were no significant differences in baroreflex gain before atenolol among the four groups except for between Biso and Biso+Exer. After atenolol, baroreflex gain and HR range in Biso, Exer, and Biso+Exer were significantly higher than those in C. HR range of sympathetic component (upper HR plateau before atenolol-itrinsic HR) was significantly reduced in Biso, Exer, and Biso+Exer compared with C. There were no significant differences in baroreflex gain of vagal component or HR range of vagal and sympathetic component between Biso and Biso+Exer.These findings suggest that both chronic treatment with β-blocker and exercise decrease resting blood pressure and HR in SHR, associated with reduced sympathetic component and increased vagal component of baroreflex function. The additive effects of β-blocker and exercise are not evident under non-stressful conditions, but could be obtained in the presence of stress such as restraint.

Cardiopulmonary exercise test evidence of isolated right coronary artery disease

Isolated right coronary artery disease is usually difficult to diagnose because of frequent negativity of standard exercise stress test. We report a case of isolated coronary artery stenosis which was not detected by standard ECG stress testing. The cardiopulmonary exercise test showed a peculiar pattern: abrupt flattening in VO2/Work relationship, plateau in O2 pulse and 90 s afterwards a plateau in heart rate, probably related to vagal afferent stimulation by ischaemia of the postero-inferior wall of the left ventricle. Multidetector computed tomography of coronary vessels and coronary angiography confirmed isolated critical stenosis of middle right coronary artery. After revascularization by PTCA, normalization of cardiopulmonary exercise test was obtained.

Isoflurane depresses baroreflex control of heart rate in decerebrate rats.

Isoflurane inhibits baroreflex control of heart rate (HR) by poorly understood mechanisms. The authors examined whether suprapontine central nervous system cardiovascular regulatory sites are required for anesthetic depression. The effects of isoflurane (1 and 2 rat minimum alveolar concentration [MAC]) on the baroreflex control of HR were determined in sham intact and midcollicular-transected decerebrate rats. Intravenous phenylephrine (0.2-12 microg/kg) and nitroprusside (1-60 microg/kg) were used to measure HR responses to peak changes in mean arterial pressure (MAP). Sigmoidal logistic curve fits to HR-MAP data assessed baroreflex sensitivity (HR/MAP), HR range, lower and upper HR plateau, and MAP at half the HR range (BP50). Four groups (two brain intact and two decerebrate) were studied before, during, and after isoflurane. To assess sympathetic and vagal contributions to HR baroreflex, beta-adrenoceptor (1 mg/kg atenolol) or muscarinic (0.5 mg/kg methyl atropine) antagonists were administered systemically. Decerebration did not alter resting MAP and HR or baroreflex parameters. Isoflurane depressed baroreflex slope and HR range in brain-intact and decerebrate rats. In both groups, 1 MAC reduced HR range by depressing peak reflex tachycardia. Maximal reflex bradycardia during increases in blood pressure was relatively preserved. Atenolol during 1 MAC did not alter maximum reflex tachycardia. In contrast, atropine during 1 MAC fully blocked reflex bradycardia. Therefore, 1 MAC predominantly depresses sympathetic components of HR baroreflex. Isoflurane at 2 MAC depressed both HR plateaus and decreased BP50 in both groups. Isoflurane depresses HR baroreflex control by actions that do not require suprapontine central nervous system sites. Isoflurane actions seem to inhibit HR baroreflex primarily by the sympathetic nervous system.

The effects of central administration of omega-conotoxin GVIA on cardiovascular parameters and autonomic reflexes in conscious rabbits.

1. The effects of central administration of omega-conotoxin GVIA (omega-CTX), an N-type calcium channel blocker, were examined in conscious rabbits implanted with lateral intracerebroventricular (i.c.v.) cannulae. 2. Experiments were performed over 4 consecutive days. On day 1, the baroreceptor heart rate (induced by glyceryl trinitrate and phenylephrine) and Bezold-Jarisch like (elicited by serotonin) reflexes were measured before (0 h) and 2 h after central administration of omega-CTX (3 or 30 pmol/kg, i.c.v.) or vehicle. On days 2-4, resting parameters and reflexes were again monitored but no further omega-CTX was administered. 3. No change in heart rate (HR) was observed in any rabbit treatment group during the experimental period. In the vehicle (n = 6) and omega-CTX 3 pmol/kg (n = 6) groups, small falls in mean arterial pressure (MAP) of 6 +/- 2 and 10 +/- 3 mmHg, respectively, occurred between 0 and 24 h; MAP then remained stable. Baroreceptor-heart rate reflex curve parameters did not change in either of these groups during the 4 day period. 4. Following administration of omega-CTX 30 pmol/kg (n = 7), MAP decreased progressively and by 48 h had fallen by 19 +/- 4 mmHg. Also at 48 h, a 20% decrease in HR range of the baroreceptor-heart rate reflex curve was seen without any change in the lower HR plateau from the 0 h control. This indicates that there was an attenuation of the sympathetically mediated upper component of the curve while the vagally mediated component was unaffected.(ABSTRACT TRUNCATED AT 250 WORDS)

Central effects of endothelin on baroreflex of spontaneously hypertensive rats

To study the contribution made by central endothelin to cardiovascular regulation in spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) controls. Central endothelin binding was measured with receptor autoradiography. The baroreceptor heart rate reflex was measured by sigmoidal curve-fitting of the mean arterial pressure and heart rate responses evoked by alternating intravenous injections of nitroprusside or phenylephrine. The baroreflex gain was derived as a function of the heart rate range and the curvature coefficient. Autoradiographic experiments with [125I]-endothelin-1 showed low to moderate binding in various medullary nuclei involved in cardiovascular regulation, such as the nucleus tractus solitarius and the ventrolateral medulla. A moderate binding density was found in regions such as the hypoglossal nucleus and the spinal trigeminal nucleus, whereas a high binding density was observed in the molecular layer of the cerebellum. The binding density was significantly lower in the ventrolateral medulla of SHR than in that of WKY rats, but there were no differences in other medullary regions. Compared with WKY rats, the SHR had higher mean arterial pressures and heart rates but tended to have a reduced baroreceptor heart rate reflex gain. This latter change was entirely attributed to a significantly lower heart rate range, caused by an elevated lower heart rate plateau in SHR. The intracisternal injection of endothelin-1 at 25 pmol/kg did not influence the resting mean arterial pressure or heart rate, but it caused a significant increase in baroreflex gain, in both SHR and WKY rats. The extent of the effect was similar in the two strains and was attributed to a significant increase in the curvature coefficient of the sigmoidal baroreflex curve. Consequently, the range over which blood pressure changes evoked reflex changes in the heart rate was reduced by endothelin-1 treatment in both SHR and WKY rats. The heart rate range was not affected and remained different between SHR and WKY rats after the endothelin-1 injection. The intracisternal injection of endothelin-3 at 25 pmol/kg, but not at 2.5 pmol/kg, had effects similar to those of endothelin-1 on the baroreflex. These results show that binding sites for endothelin-1 are present in various regions of the hindbrain of SHR and WKY rats and that central administration of endothelin-1 sensitizes the baroreceptor heart rate reflex. However, this latter effect is similar in SHR and WKY rats and is mediated by a mechanism which is distinct from that underlying the difference in reflex sensitivity between these strains.