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At least 289 records · Page 16Linked to original sources
PubMed2002

Role of resting pressure gradient in the investigation of idiopathic fecal incontinence.

PURPOSE: One-third of patients who suffer from idiopathic fecal incontinence are found to have maximum mean resting pressures within the normal range. The objective of this study was to determine whether measuring the gradient of pressure at rest throughout the anal canal is a more sensitive predictor of incontinence in these patients. METHODS: Anorectal physiology measurements were retrospectively reviewed in patients referred over an 18-month period. Two patient groups were selected for the study: Group 1, continent patients (n = 80); and Group 2, patients with idiopathic fecal incontinence (n = 47). Maximum resting pressures, vector volumes, and resting pressure gradients were all contrasted, sensitivities and specificities were calculated, and receiver operating characteristic curve analyses were performed. Reproducibility studies were also performed for the calculation of the pressure gradient. RESULTS: Patient demographics were similar in the two groups. The resting pressure gradient, maximum mean resting pressure, and vector volumes were significantly lower in incontinent patients compared with the normal patients (P < 0.0001, all comparisons). The sensitivity (and specificity) of resting pressure gradient, maximum mean resting pressure, and vector volumes were 89 percent (96 percent), 55 percent (98 percent), and 53 percent (88 percent), respectively. CONCLUSION: The resting pressure gradient is the most accurate in detecting fecal incontinence. The authors conclude that this test is simple, reproducible, and identifies an abnormality in the majority of patients with idiopathic fecal incontinence.

Adult↗
PubMed1985

The relation between myocardial ischemia and the ejection fraction response to exercise in patients with normal or abnormal resting left ventricular function.

This study examines the relation between myocardial ischemia and the left ventricular (LV) ejection fraction (EF) response to exercise in patients with normal or abnormal resting EF. We studied 69 patients aged 25 to 78 years (mean 52 years) by radionuclide ventriculography (at rest and during peak upright exercise) and by exercise thallium-201 imaging. In 27 patients with resting EF less than 50%, the EF response to exercise was normal (greater than or equal to 5% increase) in 13 patients and abnormal in 14. The thallium scans showed reversible defects in 11 of the 14 patients (79%) with abnormal response but none in any of the patients with normal responses (p = 0.0001). In the 42 patients with resting EF greater than or equal to 50%, the EF response to exercise was normal in 23 and abnormal in 19. Reversible defects were present in 13 of the 19 patients (68%) with abnormal response and in only 3 of 23 patients (13%) with normal response (p = 0.0001). Therefore, an abnormal EF response to exercise was seen in 11 of 11 patients with resting EF less than 50% and in 13 of 16 patients (81%) with resting EF greater than or equal to 50% who had reversible thallium defects; normal EF responses were seen in 13 of the 16 patients (81%) with resting EF less than 50% and in 20 of 26 patients (77%) with resting EF greater than or equal to 50% who had no reversible thallium defects. Thus, in patients with abnormal resting LV function an abnormal EF response to exercise suggests the presence of myocardial ischemia rather than a nonspecific response to stress.

Adult↗
PubMed1985

Baseline rest electrocardiographic abnormalities, antihypertensive treatment, and mortality in the Multiple Risk Factor Intervention Trial. Multiple Risk Factor Intervention Trial Research Group.

The overall results of the Multiple Risk Factor Intervention Trial (MRFIT) showed a nonsignificant 7% lower coronary artery disease (CAD) mortality rate in the special-intervention (SI) as compared to the usual-care (UC) group. The initial results also suggested that the SI program was more effective than UC in the community in reducing the CAD mortality rate in nonhypertensive persons than in hypertensive persons, and that the SI program used was more effective in reducing CAD deaths among men without than men with electrocardiographic (ECG) abnormalities at rest. Furthermore, an unfavorable mortality trend in hypertensive SI men with ECG abnormalities at rest compared with UC men was noted (adjusted relative risk of 1.67). Further analyses in baseline-defined subgroups indicated that (1) the most common ECG abnormalities at rest were high R waves and ST-T changes, (2) the CAD mortality differential (SI/UC) was similar in the subgroup with these abnormalities and in the subgroup with other abnormalities at rest, (3) the apparent excess CAD mortality among hypertensive SI men with ECG abnormalities at rest was manifested chiefly as sudden death within 1 hour, and (4) the association between ECG abnormalities at rest and the CAD mortality rate among hypertensive men was independent of the baseline level of blood pressure or of the findings on the exercise electrocardiogram. However, CAD mortality in those with abnormalities on the electrocardiogram both at rest and during exercise was lower in the SI than the UC group. A possible explanation for the difference in outcome in the baseline-defined subgroup was an unexpectedly low UC mortality rate. However, within-group analysis revealed an interaction between ECG abnormalities at rest and diuretic treatment in the SI group, with the risk of CAD death for men prescribed diuretic drugs relative to men not prescribed diuretic drugs estimated as 3.34 among men with baseline ECG abnormalities at rest and as 0.95 among men without such abnormalities. No such effect was found in the UC group, in which men generally were prescribed lower doses of hydrochlorothiazide and chlorthalidone than SI men. However, analyses do not suggest an effect of diuretic dose or of hypokalemia on the CAD mortality rate in treated SI participants. Although subgroup analyses must be interpreted with caution, particularly those that go beyond the randomized clinical trial design by the MRFIT, these findings pose hypotheses for investigation by other researchers in systemic hypertension and may have implications for therapy.

Antihypertensive Agents↗
PubMedDate not supplied

Shift length and on-duty rest patterns in rotor-wing air medical programs.

INTRODUCTION: Air medical teams provide around-the-clock critical care, a pattern at risk of inducing performance-altering fatigue from circadian disruption and sleep deprivation. Safety is an essential issue in the air medical industry, but little data are available on shift length and on-duty rest practices. We report the results of a survey concerning those practices and analyze the relationships to crew duty practices by program model (hospital-operated, vendor-operated, independent, or public safety), base location, flight volume, and job requirements. METHODS: A survey was mailed to 182 Association of Air Medical Services-member rotor-wing air medical programs in the United States that complete scene flights with a flight nurse. One-hundred-twenty-nine programs (70.9%) returned anonymous surveys, all of which were used for data analysis. Results were analyzed with descriptive and nonparametric statistics. RESULTS: All pilots work shifts between 10 and 14 hours. For medical team members the shift distribution is: </= 8 hours, 0.4%; 9 to 12 hours, 44.2%; 12 to 16 hours, 7.0%; 17 to 24 hours, 45%; > 24 hours, 3.5%. An independent association exists between shift length greater than 12 hours and each of the following: flight volume per-aircraft under 731 flights/year, program model other than hospital operated, and nonhospital base (Fisher's exact test with Bonferroni correction, P < .01 for each). All pilots are allowed on-duty rest on both day and night shifts. On-duty rest is permitted for 67.4% of medical team members: 18.2% only at night, and 49.2% at any time of day. The presence of any period of on-duty crew rest is significantly associated with nonhospital base, program model other than hospital-operated, and shift length exceeding 12 hours (Fisher's exact test with Bonferroni correction, P < .01 for each). The presence of a nonflight clinical assignment while on flight duty is associated with a prohibition against on-duty rest (Fisher's exact test with Bonferroni correction, P < .05). CONCLUSION: Notable differences arose between on-duty work and rest patterns for pilots and medical team members. Medical team members generally work longer shifts than pilots do, with shifts exceeding 12 hours as the most common staffing pattern. Medical team members also have less access to on-duty rest than do pilots. Traditional hospital-operated programs are more likely to use shorter shifts and prohibit on-duty rest for the medical teams, whereas vendor-operated, independent, or public safety programs are more likely to use longer shifts and permit on-duty rest. As the industry works toward a unified approach to mitigating the impact of fatigue on safe operation, variable practices based on job description and program style may be a factor.

Air Ambulances↗
PubMed2000

Comparison of electrocardiographic-gated technetium-99m sestamibi single-photon emission computed tomographic imaging and rest-redistribution thallium-201 in the prediction of myocardial viability.

Although the combined assessment of perfusion and function using rest electrocardiographic (ECG)-gated technetium-99m (Tc-99m) sestamibi single-photon emission computed tomographic (SPECT) imaging has been shown to improve sensitivity and accuracy over perfusion alone in the prediction of myocardial viability, no data are available comparing this technique with rest-redistribution thallium-201. Thirty patients with coronary artery disease and left ventricular dysfunction (ejection fraction < or = 40%) underwent rest-redistribution thallium-201 and rest ECG-gated Tc-99m sestamibi SPECT imaging before revascularization and rest ECG-gated Tc-99m sestamibi SPECT imaging at 1 or 6 weeks after revascularization. All thallium-201 and Tc-99m sestamibi images were interpreted by a consensus agreement of 3 experienced readers without knowledge of patient identity or time of imaging with Tc-99m sestamibi (before or after revascularization) using a 17-segment model. Concordance between techniques for the prediction of viability was 89% (kappa 0.556 +/- 0.109). With rest-redistribution thallium-201, sensitivity, specificity, positive predictive value, negative predictive value, and predictive accuracy were 95%, 59%, 88%, 78%, and 86%, respectively. With rest ECG-gated Tc-99m sestamibi SPECT imaging, sensitivity, specificity, positive predictive value, negative predictive value, and predictive accuracy were 96%, 55%, 87%, 80%, and 86%, respectively (p = NS vs rest-redistribution thallium-201). Although both techniques are comparable for detecting viable myocardium, rest ECG-gated Tc-99m sestamibi SPECT imaging allows direct assessment of both myocardial perfusion and ventricular function, which may be clinically useful in patients who require assessment of myocardial viability.

Coronary Disease↗
PubMed2003

Comparison of the binding character of triflavin on resting and activated alpha(IIb)beta(3) integrin in human platelets by electron microscopy.

Triflavin, an Arg-Gly-Asp (RGD)-containing disintegrin purified from venom peptide inhibited platelet aggregation by interfering with the interaction of fibrinogen with alpha(IIb)beta(3) integrin. Using an immunostaining technique and electron microscopy, we investigated and compared the distribution of triflavin binding in both resting and activated platelets. Triflavin uniformly and strongly stained the plasma membrane and the open canalicular system (OCS), whereas a lesser extent of staining was seen on alpha-granules in both resting and activated platelets. Furthermore, resting unfixed platelets were incubated with triflavin for 10 min at 4 degrees C, and then rewarmed at 30 degrees C for 0, 10, and 30 min to advance internalization. At 0 min, platelets showed an extensive rim-staining pattern of bound triflavin on the surface membrane, which was then gradually internalized into the cytoplasmic OCS with prolonging of incubation times. However, triflavin bound fewer to alpha-granules than to the OCS within the 0-30-min period of internalization in both resting and activated platelets. Furthermore, triflavin did not influence physiological endocytosis in resting platelets. Comparing the 3D structures of triflavin and another disintegrin, echistatin, we found that the spatial differences between the RGD motif and the C-termini of structures of disintegrins may mediate functional differences of binding activity towards alpha(IIb)beta(3) integrin in resting platelets. These data indicate that (1) triflavin binds effectively to alpha(IIb)beta(3) on the platelet membrane and cytoplasmic OCS, but a relative lesser extent to alpha-granules in both resting and activated platelets; (2) triflavin is internalized in resting platelets independent of cellular activation; and (3) spatial differences between the RGD motif and the C-termini of disintegrins may play an important role in mediating disintegrin binding to alpha(IIb)beta(3) in resting platelets.

Blood Platelets↗
PubMed1999

Changes in the tibialis anterior tendon moment arm from rest to maximum isometric dorsiflexion: in vivo observations in man.

OBJECTIVE: In the present study, we examined the hypothesis that the tibialis anterior tendon moment arm increases during maximum isometric dorsiflexion as compared with rest. BACKGROUND: In musculoskeletal modelling applications, moment arms from passive muscles at rest are assumed representative of those measured during isometric muscle contraction. The validity of this assumption is questionable in musculotendon actuators enclosed by retinacular systems as in tibialis anterior. DESIGN AND METHODS: Sagittal-plane magnetic resonance images of the right ankle were taken in six subjects at rest and during maximum isometric dorsiflexion at six ankle angles between dorsiflexion and plantarflexion having the body placed in the supine position and the knee flexed at 90 degrees. Instant centres of rotation in the tibio-talar joint, tibialis anterior tendon action lines and moment arms were identified in the sagittal plane at ankle angles of -15 degrees, 0 degrees,+15 degrees and +30 degrees at rest and during maximum isometric dorsiflexion. RESULTS: At any given ankle angle, the tibialis anterior tendon moment arm during maximum isometric dorsiflexion increased by 0.9-1.5 cm (P<0.01) compared with rest. This was attributed to a displacement of both tibialis anterior tendon action line by 0.8-1.2 cm (P<0.01) and all instant centres of rotation by 0.3-0.4 cm (P<0. 01) distally in relation to their corresponding resting positions. CONCLUSIONS AND IMPLICATIONS: The assumption that the tibialis anterior tendon moment arm does not change from rest to maximum isometric dorsiflexion is invalid. Erroneous tendon forces, muscle stresses and joint moments by as much as 30% would be calculated using resting tibialis anterior tendon moment arms in the moment equilibrium equation around the ankle joint during maximum isometric dorsiflexion. RELEVANCE: A substantial increase in the tibialis anterior tendon moment arm occurs from rest to maximum isometric dorsiflexion. This needs to be taken into consideration when using planimetric musculoskeletal modelling for analysing maximal static ankle dorsiflexion loads.

Adult↗
PubMed2000

The effect of resting ST segment depression on the diagnostic characteristics of the exercise treadmill test.

OBJECTIVES: The aim of this study is to demonstrate the effect of resting ST segment depression on the diagnostic characteristics of the exercise treadmill test. BACKGROUND: Previous studies evaluating the effect of resting ST segment depression on the diagnostic characteristics of exercise treadmill test have been conducted on relatively small patient groups and based only on visual electrocardiogram (ECG) analysis. METHODS: A retrospective analysis of data collected prospectively was performed on consecutive patients referred for evaluation of chest pain. One thousand two hundred eighty-two patients without a prior myocardial infarction underwent standard exercise treadmill tests followed by coronary angiography, with coronary artery disease defined as a 50% narrowing in at least one major epicardial coronary artery. Sensitivity, specificity, predictive accuracy and area under the curve of the receiver operating characteristic (ROC) plots were calculated for patients with and without resting ST segment depression as determined by visual or computerized analysis of the baseline ECG. RESULTS: Sensitivity of the exercise treadmill test increased in 206 patients with resting ST segment depression determined by visual ECG analysis compared with patients without resting ST segment depression (77 +/- 7% vs. 45 +/- 4%) and specificity decreased (48 +/- 12% vs. 84 +/- 3%). With computerized analysis, sensitivity of the treadmill test increased in 349 patients with resting ST segment depression compared with patients without resting ST segment depression (71 +/- 6% vs. 42 +/- 4%) and specificity decreased (52 +/- 9% vs. 87 +/- 3%) (p < 0.0001 for all comparisons). There was no significant difference in the area under the curve of the ROC plots (0.66-0.69) or the predictive accuracy (62-68%) between the four subgroups. CONCLUSIONS: The diagnostic accuracy and high sensitivity of the exercise treadmill test in a large cohort of patients with resting ST segment depression and no prior myocardial infarction support the initial use of the test for diagnosis of coronary artery disease. The classification of resting ST segment depression by method of analysis (visual vs. computerized) did not affect the results.

Chest Pain↗
PubMed2002

Thyrothymic thyroid rests: incidence and relationship to the thyroid gland.

BACKGROUND: Rests of thyroid tissue within the thyrothymic area are relatively common and might be of clinical importance. The purpose of this study is to define the incidence and anatomy of thyroid tissue located in the line of the thyrothymic ligament, referred to here as "rests." STUDY DESIGN: Prospective descriptive intraoperative evaluation of 100 consecutive thyroid or parathyroid procedures was undertaken to identify the incidence and anatomical location of thyrothymic thyroid rests. Photographs and histologic confirmation of the thyroid remnants were obtained. RESULTS: One hundred eighty sides of the thyroid gland are examined in 100 consecutive patients. Thyroid rests in the thyrothymic area were found in 53 patients, or on 83 separate sides of the thyroid (46%). In patients who had rests identified, 30 (57%) had bilateral rests, with 16 (30%) only on the right, and 7 (13%) only on the left. Eighty percent of identified rests were still attached to the thyroid proper by a pedicle of thyroid tissue but 20% were entirely separate. Most rests were small, with 88% being less than 1 cm in diameter. CONCLUSION: Rests of thyroid tissue within the thyrothymic area, either as entirely separate nodules or as prolongations from the thyroid lobe, are relatively common and might be of clinical importance during thyroid or parathyroid surgery.

Adolescent↗
PubMed1997

Reproductive hormonal responses to maximal exercise in endurance-trained men with low resting testosterone levels.

A cross-sectional study was conducted to compare the changes from rest and in response to a maximal exercise bout for select reproductive hormones between age matched groups of endurance trained (ET; distance runners) men with low resting testosterone and untrained (UT) men. Both ET and UT men completed two evaluation sessions: (a) resting hormonal profiling, and (b) a maximal treadmill exercise test to exhaustion. Serial blood samples were taken for four hours at each of the evaluation sessions. Resting and exercise hormonal concentrations were plotted and the area under the response curve (AUC) measured. Percentage change in AUC values were also calculated and compared (exercise vs. resting AUC values). Resting testosterone (16.6 +/- 2.4 vs. 23.9 +/- 3.1 nmol x 1(-1)) and prolactin (3.3 +/- 1.4 vs. 6.0 +/- 2.0 micrograms x 1(-1)) concentrations in the ET men were significantly lower (p < 0.05) than those in the UT men. All other resting hormonal levels did not differ between the groups (p > 0.05). Exercise produced a significant increase (p < 0.05) in the ET men for testosterone, LH, and prolactin AUC values, when compared to resting values. In the UT men the only significant change was a reduction (p < 0.05) in the exercise LH AUC versus the resting AUC value. AUC percentage change values showed between-group differences (p < 0.05) for testosterone, LH and prolactin. The level of change in each of these hormones was found to be greater in the ET than UT group (approximately 20 to 75%). The hormonal changes of the UT men were viewed as "control--reference" responses within a functioning hypothalamo-pituitary-testicular regulatory axis; therefore, it was concluded that the ET men displayed an "atypical" response to exercise to that of UT men relative to this axis.

Adult↗
PubMed1993

Charybdotoxin-sensitive K+ channels regulate the myogenic tone in the resting state of arteries from spontaneously hypertensive rats.

1. To determine the possible role of Ca(2+)-activated K+ (KCa) channels in the regulation of resting tone of arteries from spontaneously hypertensive rats (SHR), the effects of agents which interact with these channels on tension and 86Rb efflux were compared in endothelium-denuded strips of carotid, femoral and mesenteric arteries from SHR and normotensive Wistar-Kyoto rats (WKY). 2. Strips of carotid, femoral and mesenteric arteries from SHR exhibited a myogenic tone; that is, the resting tone decreased when either the Krebs solution was changed to a 0-Ca2+ solution or 10(-7) M nifedipine was added. 3. The addition of charybdotoxin (ChTX, 10(-9)-10(-7) M), a blocker of large conductance KCa channels, to the resting strips of these arteries produced a concentration-dependent contraction, which was significantly greater in SHR than in WKY. Relatively low concentrations of tetraethylammonium (0.05-5 mM) produced a concentration-dependent contraction which was similar to the ChTX-induced contraction in these strips. 4. The ChTX-induced contractions in SHR were greatly attenuated by 10(-7) M nifedipine and by 3 x 10(-6) M cromakalim, a K+ channel opener. Cromakalim alone abolished the myogenic tone in SHR. 5. The addition of apamin (a blocker of small conductance KCa channels, up to 10(-6) M), or of glibenclamide (a blocker of ATP-sensitive K+ channels, up to 5 x 10(-6) M), to the resting strips failed to produce a contraction. 6. In resting strips of carotid, femoral and mesenteric arteries preloaded with 86Rb, the basal 86Rb efflux rate constants were significantly greater in SHR than in WKY. The addition of 10-7 M nifedipine to the resting strips decreased the basal 86Rb efflux rate constants only in SHR.7. The cellular Ca2+ uptake in the resting state of carotid and femoral arteries from SHR was significantly increased when compared to WKY, and this increase in SHR was significantly reduced by 10-7M nifedipine.8. These results suggest that the ChTX-sensitive KCa channels were highly activated to regulate the myogenic tone in the resting state of carotid, femoral and mesenteric arteries from SHR. The increased Kca channel functions in SHR arteries appeared to be secondary to the increased Ca2' influx via L-type voltage-dependent Ca2+ channels in the resting state of these arteries.

Animals↗
PubMed2006

The pH change after HCl titration into resting and stimulated saliva for a buffering capacity test.

BACKGROUND: Saliva collection can provide clinical information about individual patients. However, a correlation between ranking buffering capacity using resting and stimulated saliva is still unknown. The aim of this study was to evaluate the pH change after HCl titration into resting and stimulated saliva for a salivary buffering capacity test. METHODS: Resting and stimulated saliva (by chewing paraffin wax) were collected from 80 patients. After the pH of both saliva samples was measured using a hand-held pH meter, the saliva samples were titrated with 0.1N HCl to evaluate the buffering capacity. Correlations of ranking buffering capacity (high, medium, low) between stimulated saliva and resting saliva with 30 microL HCl titration and between stimulated saliva and resting saliva with 40 microL HCl titration were statistically analysed by Spearman Rank Correlation Test (p < 0.05). RESULTS: At 50 microL HCl titration, stimulated saliva buffering capacities were ranked into high (above pH 5.5), medium (pH from 5.5 to 4.5) and low (below pH 4.5). At 30-40 microL HCl titration, the resting saliva buffering capacities were ranked into the same categories. Spearman Rank Correlation indicated significant positive coefficients for the stimulated saliva and resting saliva buffering capacity at 30 microL titration and the stimulated saliva and resting saliva at 40 microL titration. CONCLUSION: Stimulated saliva is more resistant to variation in pH change during HCI titration than resting saliva. Stimulated saliva sampling is a good method to determine buffering capacity during a comprehensive oral health assessment.

Adolescent↗
PubMed1979

Phosphate efflux and oxygen consumption in small non-myelinated nerve fibres at rest and during activity.

1. The oxygen consumption and the movements of labelled phosphate were measured in garfish olfactory nerve at rest and during activity.2. In solutions with 2.5 mM-K and 0.2 mM-phosphate the resting oxygen consumption was 0.206 m-mole/kg.min; activity at 2 sec(-1) produced an extra oxygen consumption of 2.46 mumole/kg.impulse. The extra oxygen consumption declined exponentially with a time constant of 2.62 min at 22-26 degrees C.3. The phosphate efflux, measured simultaneously, had a resting efflux rate constant of 1.24 x 10(-3) min(-1); activity at 2 sec(-1) produced an extra fractional loss of 9.38 x 10(-6) impulse(-1). The increase in phosphate efflux followed almost the same time course as the increase in oxygen consumption.4. Increasing the frequency of stimulation from 2 sec(-1) to 3 or 5 sec(-1) decreased both the extra oxygen consumption and the extra fractional loss of phosphate. When the frequency was decreased to 0.5 or 1 sec(-1) the extra oxygen consumption per impulse increased, while the extra phosphate liberation was lowered.5. Changing the phosphate concentration did not much affect the extra oxygen consumption; on the other hand, lowering or increasing the phosphate from the standard 0.2 mM decreased both the resting and the stimulated phosphate efflux.6. Lowering the K from the standard 2.5 mM did not affect the extra oxygen consumption, but increased both the resting and the extra loss of phosphate. At higher K concentrations the extra oxygen consumption and the extra fractional loss of phosphate decreased without much change in the resting phosphate efflux.7. Application of 1-20 muM-strophanthidin produced a transient decrease in the resting phosphate efflux without much change in resting oxygen consumption. With 10 or 20 muM-strophanthidin the extra fractional loss of phosphate and the extra oxygen consumption were both lowered in approximately the same proportions.8. The findings are consistent with the hypothesis that the increase in intracellular inorganic phosphate that results from increased break-down of ATP after activity, is the main cause for the increased phosphate efflux. A fraction of the increase in intracellular phosphate only appears to be liberated to the outside, the value of the fraction depending on the resting phosphate efflux before activity.9. The initial increase in intracellular inorganic phosphate after an impulse, estimated from the oxygen consumption or the phosphate fluxes, appears to be about 12-19 mumole/kg nerve, remarkably close to the value known from chemical analysis.

Animals↗
PubMed1987

Diffusion and electrogenic components of the resting potential in explanted neonatal rat ventricle cells.

Spontaneously beating explanted neonatal rat ventricle cells stop beating and show a steady potential (the mean resting potential, -46.2 mV at 6.0 mM Ko) when exposed to 10 mM Cao or 4 mM Mn. When Ko was increased, resting potential changed only slightly between 3 and 15 mM, but the resting potential versus Ko characteristically approached the slope of a K electrode at high Ko. Elimination of Cl from the medium did not alter the K dependence of the resting potential. However, a hyperpolarization of 9 mV per 10-fold change was observed when Nao was decreased from 50 to 4 mM. Ouabain (10(-4) M) depolarized the membrane within 2 min to a stable level of about -30 mV in spontaneously beating cells and in those treated with Ca channel blockers. This potential was considered as the diffusion component of the membrane potential, Vdiff. Consequently the difference between resting potential and Vdiff represents the ouabain-sensitive or the electrogenic component of the resting potential. Using linearized versions of the Mullins and Noda as well as the Goldman - Hodgkin - Katz equations, we calculated that a PNa/PK between 0.25 and 0.35, a Na/K exchange ratio of 2.0, and a Ki of 160 mM adequately described the K dependence of the resting potential. We demonstrated the contribution of electrogenic Na extrusion to the resting potential of mammalian cardiac cells in culture. Therefore the existence of a composite resting potential precludes the direct comparison of potential measurements obtained under conditions liable to independently modify either the diffusion or the electrogenic component.

Animals↗
PubMed2006

Coronary MR imaging: breath-hold capability and patterns, coronary artery rest periods, and beta-blocker use.

PURPOSE: To prospectively evaluate breath-hold capability and patterns, coronary artery rest periods, and beta-blocker use in coronary magnetic resonance (MR) imaging. MATERIALS AND METHODS: Ethics committee approval and informed consent were obtained. In 210 consecutive patients (mean age, 61.8 years +/- 10.3 [standard deviation]; 146 men, 64 women), breath-hold patterns and maximal capability were assessed at expiration with dynamic navigator MR imaging (temporal resolution, 1 second). Left coronary artery (LCA) and right coronary artery (RCA) rest periods were determined at transverse cine imaging (steady-state free precession, retrospective gating, 40 phases per cycle). Before and after beta-blockade, rest periods were assessed in 25 additional patients (mean age, 61.4 years +/- 7.1; 20 men, five women). Differences were tested within groups with paired Student t test and between groups with unpaired Student t test (continuous variables) and chi(2) test (categoric variables). Pearson correlation was used to test the relationship between rest period and heart rate. RESULTS: Four distinct breath-hold patterns, characterized by diaphragmatic motion, were identified: pattern 1, steady plateau (55% of patients); 2, initial drift followed by plateau (12%); 3, continuous drift (19%); and 4, irregular, unsteady behavior (14%). Mean breath-hold capability with patterns 1 and 2 was 29 seconds +/- 13 (range, 10-64 seconds). The rest period of LCA was longer than that of RCA (163 msec +/- 75 vs 123 msec +/- 60; P < .01) and began earlier in the cardiac cycle (521 msec +/- 149 vs 540 msec +/- 160; P < .01); In a minority of patients, LCA rest period began later (21%) or was shorter (14%). With no pharmacologic intervention, correlation between rest period duration and heart rate was weak (LCA, r = -0.52; RCA, r = -0.38; P < .01). However, beta-blockade significantly lowered heart rate (61.3 beats/min +/- 7.2 vs 82.6 beats/min +/- 12.5, P < .001) and increased rest duration (LCA, 201.8 msec +/- 83.6 vs 111.8 msec +/- 44.55; RCA, 134.8 msec +/- 57.3 vs 83.1 msec +/- 35.8; P < .001). CONCLUSION: In 33% of patients (patterns 3 and 4), breath-hold pattern was unsuitable for high-spatial-resolution breath-hold MR imaging. LCA and RCA rest periods showed large variability in starting point and duration, with no correlation to heart rate.

Adrenergic beta-Antagonists↗
PubMed1980

Rest and exercise hemodynamic effects of oral hydralazine in patients with coronary artery disease and left ventricular dysfunction.

To determine the hemodynamic effects of afterload reduction at rest and during upright exercise in patients with coronary artery disease and left ventricular dysfunction, 12 patients were studied before and after taking 50-75 mg of oral hydralazine every 6 hours for 48 hours. Oxygen consumption and heart rate were unchanged from control both at rest and during two work loads on a bicycle ergometer. Cardiac output was significantly increased at rest and during both workloads. The arteriovenous oxygen difference was significantly reduced at rest and during exercise. Pulmonary capillary wedge pressure was also significantly lower at rest and during exercise. Systemic vascular resistance was reduced at rest, and exercise-induced vasodilation was augmented by the administration of hydralazine. Left ventricular end-diastolic volume and ejection fraction assessed by radionuclide angiocardiography were not significantly changed at rest or during exercise after hydralazine. Seven of the 12 patients have maintained clinical improvement during a follow-up of 6-12 months. Hemodynamic improvement provided by oral hydralazine at rest is maintained during moderate exertion in patients with coronary artery disease and left ventricular dysfunction. In selected patients, chronic afterload reduction with oral hydralazine may result in increased cardiac reserve, decreased pulmonary congestion or decreased myocardial oxygen demands, thereby improving or abolishing resting or exertional dyspnea or angina.

Aged↗
PubMed1982

Rest and exercise hemodynamics after the Fontan procedure.

Sixteen consecutive patients (12 with tricuspid atresia) underwent a Fontan procedure, with no operative deaths. There were three late deaths. Eleven of the survivors were electively catheterized 4-25 months postoperatively. Rest and exercise hemodynamics were measured in five patients, and resting hemodynamics alone were measured in three. All exercised patients were New York Heart Association class I Cardiac index was low at rest (2.3 +/- 0.61/min/m2) and during exercise (4.9 +/- 1.11/min/m2) due to a low stroke index both at rest (28 ml) and exercise (35 ml). Accordingly, mixed venous oxygen saturations were decreased (66% at rest and 31% during exercise). These values are significantly lower than those at rest and during exercise from 23 control patients of similar age and size. Heart rates, pulmonary vascular resistances, and left ventricular filling pressures appeared normal both at rest and during exercise. High right atrial pressure at rest (15 mm Hg) was associated with minimal conduit gradient (2 mm Hg). However, exercise increased the mean conduit gradient to 8 mm Hg, demonstrating significant functional conduit obstruction. As expected, the cardiovascular response to exercise is abnormal after the Fontan procedure, even in asymptomatic patients. This abnormal response may be exacerbated by conduit obstruction, and conduit obstruction may not be apparent during resting studies.

Adolescent↗
PubMed1994

Predicting recovery of severe regional ventricular dysfunction. Comparison of resting scintigraphy with 201Tl and 99mTc-sestamibi.

BACKGROUND: Regional 201Tl activity after resting injection, imaged early and after redistribution, reflects viable myocardium and can predict improved isotope uptake as well as regional and global ventricular function after revascularization. 99mTc-sestamibi, a perfusion tracer with favorable imaging characteristics, has distinct kinetics compared with 201Tl, demonstrating minimal redistribution; this property may give 201Tl an advantage for detecting viable myocardium, particularly in segments with resting hypoperfusion. The purpose of this study was to compare regional activities of 201Tl and 99mTc-sestamibi after resting injections in patients with coronary artery disease and regional or global left ventricular dysfunction and to assess their comparative abilities for predicting recovery of severe regional ventricular dysfunction after revascularization. METHODS AND RESULTS: Qualitative and quantitative comparisons of rest and redistribution 201Tl activity and sestamibi activity 1 hour after rest injection were performed in 31 patients with coronary artery disease and left ventricular dysfunction. Quantitative analysis of three short-axis tomograms per patient was performed by use of circumferential profiles that allowed analysis of 12 segments per patient. Two-dimensional echocardiography was used to assess wall motion and thickening in segments corresponding to the single photon emission computed tomography data. Concordance between regional 201Tl activity at redistribution imaging and regional sestamibi activity by semiquantitative visual analysis demonstrated concordant regional activity in 87% of segments; among discordant segments, no significant skew was seen, indicating enhanced uptake of one agent over the other. Quantitative analysis for all segments showed significant correlation (r = .86, P < .001) between quantitative regional 201Tl redistribution activity and 1-hour post-rest injection sestamibi activity in individual segments. Eighteen of these patients were revascularized, and echocardiography was repeated 20 +/- 16 days later; segments exhibiting significant regional ventricular dysfunction before revascularization were classified as having reversible or irreversible dysfunction on the basis of the change in wall motion and thickening. 201Tl and sestamibi regional activities were similar in those segments with reversible (72 +/- 11% [percent of peak activity] versus 75 +/- 9%, respectively, P = NS) as well as irreversible ventricular dysfunction (51 +/- 11% versus 50 +/- 8%, P = NS). Positive (75% versus 80% for 201Tl and sestamibi, respectively) and negative (92% versus 96%, respectively) predictive values for recovery of regional ventricular dysfunction after revascularization were similar for the two agents. CONCLUSIONS: In patients with coronary artery disease and left ventricular dysfunction, quantified sestamibi activity 1 hour after rest injection parallels redistribution 201Tl activity after a resting injection, suggesting that uptake and subsequent handling of sestamibi are more complex than can be explained by a pure flow tracer with no redistribution. Quantitative analysis of regional activities of both 201Tl and sestamibi after resting injections can differentiate viable from nonviable myocardium, and the two agents comparably predict reversibility of significant regional wall motion abnormalities after revascularization in such patients to a similar degree.

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