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Biomedical subjects

D S Miles

Publications and source records attributed to D S Miles.

At least 19 recordsLinked to original sources
PubMed1991

Cardiothoracic variables measured by bioelectrical impedance in preterm and term neonates.

OBJECTIVE: To report the range of normal values for impedance-derived cardiac output, stroke volume, and the baseline transthoracic impedance in the healthy preterm and term neonate over the weight range generally found in the intensive care nursery. DESIGN: Prospective, case-referent study. SETTING: University medical center special care and term nurseries. PATIENTS: Twenty-seven preterm and 25 term newborns with no evidence of cardiovascular problems. INTERVENTIONS: We determined the values for impedance cardiac output and stroke volume to be used as reference values. Also measured was the baseline transthoracic impedance, a number that reflects the air/fluid ratio of the thorax. MEASUREMENTS AND MAIN RESULTS: Stroke volume and stroke volume index were, respectively, 2.0 +/- 0.8 (SD) mL and 1.4 +/- 0.5 mL/kg for preterm infants, and 5.0 +/- 2.0 mL and 1.6 +/- 0.7 mL/kg for term neonates. Cardiac output and cardiac index were, respectively, 304 +/- 114 mL/min and 214 +/- 68 mL/min.kg for preterm newborns, and 648 +/- 244 mL/min and 205 +/- 78 mL/min.kg in term newborns. These values compared favorably with published values utilizing other techniques for these populations. Both cardiac output and stroke volume were linearly correlated to body weight, being largest in the heavier neonates. Transthoracic impedance values were 42.7 +/- 9.0 ohms and 6.7 +/- 1.7 ohms/cm for preterm infants and 32.3 +/- 4.3 ohms and 3.9 +/- 0.6 ohms/cm for term infants. Transthoracic impedance and transthoracic impedance/cm values were correlated negatively to body weight and were curvilinearly related to body weight. CONCLUSIONS: These values for transthoracic impedance and transthoracic impedance/cm are the first reported using the standard electrode lead configuration in neonates.

Cardiac Output↗
PubMed1991

Acute recovery profile of lung volumes and function after running 5 miles.

The purpose of this study was to characterize the acute changes and recovery profile of lung volumes and function subsequent to strenuous aerobic exercise. Eight experienced runners (X age = 25 yrs; wt = 73 kg; ht = 181 cm) completed three identical 5 mile runs. Determinations were made of forced vital capacity (FVC), residual volume (RV), closing capacity (CC), and pulmonary diffusion capacity (DLCO). Measurement of cardiac output (Q) and stroke volume (SV) occurred simultaneously with the 10 second DLCO breathhold maneuver. Measurements were obtained before and 5, 15 and 25 minutes after each run. FVC was reduced (-4.5%) 5 min post-run with a return to pre-run values by 15 min. CC (+16%) and RV (+18%) remained elevated for at least 30 min post-run. DLCO did not appear to be effected by the run. However, the single-breath DLCO breathhold maneuver consistently caused a fall in SV at rest and during recovery. The hypothesis has been forwarded that an increase in central blood volume post-run accounted for the acute reduction in FVC. The sustained elevation in RV resulted from early closure of the small airways possibly due to an increase in extra-vascular lung water.

Adult↗
PubMed1991

Weight control and exercise.

Obesity in the United States can truly be called a national epidemic. The associated health risks and diseases present a tremendous drain to the economy. The most effective program to lose and maintain a desirable body weight incorporates a combination of restriction in caloric intake with an increase in caloric expenditure through exercise. A gradual approach of losing 1 or 2 pounds per week has proved to be the most effective. Men should strive to maintain approximately 15% body fat and women 25% body fat. Weight-reduction programs that demonstrate phenomenal weight loss in a short period will not work over the long term and may represent a significant health risk. The ability to lose fat and maintain a desirable body weight is not easy but can be attained through a firm commitment to a healthy life style.

Adipose Tissue↗
PubMed1990

Impedance cardiography fails to measure accurately left ventricular ejection fraction.

The purpose of this study was to describe the technique proposed to measure left ventricular ejection fraction (LVEF) with the impedance cardiogram and to compare these values with those measured by radionuclide angiocardiography. Characteristics (mean +/- SE) of the healthy control group were: age, 32 +/- 3 yr; weight, 75 +/- 6 kg; and height, 177 +/- 3 cm. Characteristics of the patient population of 46 men and 49 women were: age, 63 +/- 1 yr; weight 74 +/- 2 kg; and height, 170 +/- 1 cm. LVEF was measured by impedance (ZEF) and multiple-gated scans (MEF) while in the supine position. The control group ZEF averaged 72% (range 67% to 78%) and the MEF averaged 71% (range 65% to 77%). There were no differences between the average ZEF (56 +/- 1%) and MEF (53 +/- 2%) in the patients. Correlations, however, between ZEF and MEF were unacceptably low for the several clinical populations within this group (-0.17 to 0.16). Furthermore, MEF correlated well with regional wall motion (r = .84) while ZEF did not (r = .00). Subdividing the patients according to heart function as determined by regional wall motion failed to improve the correlation between MEF and ZEF. The use of a previously published regression equation to predict LVEF from the systolic time interval ratio of pre-ejection period/left ventricular ejection time derived from the impedance cardiogram also proved ineffective. These data suggest that the previously proposed analysis of the impedance cardiogram to measure LVEF should not be used to make a clinical diagnosis.

Adult↗
PubMed1989

Comparison of two impedance cardiographic techniques for measuring cardiac output.

The purpose of the present study was to compare cardiac outputs obtained by both the Kubicek (MIC) and Sramek (NCCOM3) impedance cardiographic techniques with thermodilution (TD) in critically ill patients. The two impedance techniques were also compared in normal subjects. Seven healthy subjects and ten patients in the intensive care unit were enlisted in the study. Only those subjects with successful measurements by all three methods were used in the data analysis. Three measurements of cardiac output were made in each subject. In patients, there were no significant differences in cardiac outputs as measured by TD (6.61/min), MIC (6.3 1/min), NCCOM3 (6.4 1/min). MIC and NCCOM3 cardiac outputs were correlated and approximated the line of identify when compared to TD. In normals, however, the NCCOM3 overestimated the cardiac output (NCCOM3, 9.2 1/min; MIC, 6.2 1/min). Because of these inconsistent results, caution is urged when interpreting the values obtained by the NCCOM3. In contrast, the use of the MIC in both populations has been reaffirmed.

Adolescent↗
PubMed1989

Noninvasive assessment of cardiac output by impedance cardiography in the newborn canine.

Currently, critical care monitoring of cardiac function in the newborn human consists mainly of measuring heart rate and BP. A noninvasive technique for assessing cardiac output routinely in the critically ill neonate would facilitate clinical management. Impedance cardiography (IC) is a noninvasive technique which measures stroke volume on a beat-by-beat basis. This study compared cardiac output as measured by thermodilution (TD) to that measured by IC in seven canine pups 6 to 7 days old weighing 0.66 to 0.86 kg. Cardiac output was altered by the withdrawal and reinfusion of blood. There were no significant differences between the two methods for either the absolute value of cardiac output (r = .96) or the percent change in cardiac output (r = .97). Coefficients of variation were 3.0% for TD and 3.6% for IC. These results indicate that IC can be used to assess serially cardiac function in the newborn.

Animals↗
PubMed1989

Comparison of two impedance cardiographic techniques for measuring cardiac output in critically ill patients.

The purpose of the present study was to compare cardiac output (Q) values obtained by both the Kubicek (MIC) and Sramek (NCCOM3) impedance cardiographic techniques with thermodilution (TD) in critically ill patients. The two impedance techniques were also compared in normal subjects. Seven healthy subjects and ten ICU patients were enlisted in the study. Three Q measurements were made in each subject. In the ICU patients, there were no significant differences in Q values as measured by TD (6.6 L/min), MIC (6.3 L/min), and NCCOM3 (6.4 L/min). Both MIC and NCCOM3 Q values were comparable to TD in patients. In normals, however, the NCCOM3 estimated larger values for Q than did the MIC (NCCOM3, 9.2 L/min; MIC, 6.2 L/min). Q values obtained with MIC in normals were comparable with published values for supine normals. Thus, the two techniques agreed in the patients but not in the normals. The reasons for these results are not obvious from the data, but are attributable to the measurements by the NCCOM3. Because of this, caution is suggested when interpreting absolute Q values obtained by the NCCOM3.

Adult↗
PubMed1989

Modified head-up tilt test for orthostatic challenge of critically ill patients.

The purpose of this study was to assess the cardiovascular response to a modified head-up tilt test for use with the bedridden, critically ill patient. The cardiovascular responses of seven normals and ten critically ill patients to 45 degrees head-up tilt with the legs horizontal (0 degrees) were analyzed. Stroke volume index (SI) and cardiac index (CI) were measured with thoracic electric bioimpedance (TEB). The baseline TEB (Z0) was measured to monitor fluid shift out of the thorax during tilt. BP was measured and systemic vascular resistance index (SVRI) was calculated. Normals responded to the modified head-up tilt with a decreased SI (59 to 44 ml/m2 and CI (3.7 to 2.8 L/min.m2), and an increased SVRI and Z0 (25.5 to 27.9). As a group, the patients showed no significant change with tilt. However, individual analysis revealed a heterogeneous response by the patients. Those patients who demonstrated a caudal shift of blood (increased Z0) had decreased SI. Those with no indication of a caudal shift of blood, presumably due to decreased venous compliance, did not change SI. Thus, this type of modified head-up tilt can be used in the ICU to study more intensely cardiovascular function and control in the bedridden subject.

Adult↗
PubMed1989

Cardiopulmonary effects of high frequency positive-pressure ventilation versus jet ventilation in respiratory failure.

Conventional ventilators are frequently used at high rates in the intensive care nursery to achieve adequate oxygenation and ventilation with reduced peak inspiratory pressure. The efficacy and limitations of high frequency positive-pressure ventilation (HFPPV) using a conventional ventilator were studied by comparing the cardiopulmonary effects of HFPPV with those of high frequency jet ventilation (HFJV) in an animal model of respiratory failure. Sixteen saline-lavaged rabbits were ventilated with either HFPPV or HFJV for 2 h using rates of 200 breaths/min, inspiratory to expiratory ratio of 1:2, and FIO2 of 1.0. As controls an additional eight lavaged rabbits were ventilated at conventional rates (40 to 60 breaths/min). Proximal peak inspiratory pressure as indicated on the ventilator manometer or drive pressure was adjusted to maintain acceptable blood gases. Cardiac output (CO) was measured by thermodilution. Although there was a significant decrease in cardiac function over time, there were no significant differences between the groups in CO or stroke volume. Satisfactory oxygenation and ventilation were maintained in all groups. Static respiratory system compliance and mean airway pressure were similar among the groups. Histologic examination of the lungs revealed no differences between the three ventilator groups. The results of this study indicate that both HFPPV and HFJV are effective in short-term maintenance of normal blood gases in respiratory failure without any discernable differences in their effects on cardiovascular function. At very high rates, however, increases in VT are not possible with HFPPV, which limits its usefulness and flexibility in respiratory failure.

Animals↗
PubMed1989

Cardiovascular responses to upper body exercise in normals and cardiac patients.

This review summarizes and contrasts the cardiovascular responses elicited during dynamic upper body exercise (UBE) with those associated with lower body exercise (LBE). Information was obtained from studies which utilized arm-crank and/or cycle ergometers. At any given submaximal oxygen uptake (VO2), cardiac output (Q) is similar for UBE and LBE; however, heart rate (HR) is higher and stroke volume (SV) lower during UBE. Peripheral resistance and systolic and diastolic blood pressure are greater during UBE. Maximal Q, HR, SV, workload, and VO2 are less for UBE. As observed with healthy individuals, cardiac patients experience greater physiological stress for any given VO2 during UBE. UBE offers a satisfactory but perhaps not equivalent alternative to LBE for evaluation of angina and ischemic responses to exercise. The central and peripheral responses to either upper or lower body exercise appear to be independent of the muscle mass but directly related to the ergometer specific relative exercise intensity. The control mechanisms which govern these responses appear to be a centrally mediated activation of medullary centers coupled with a chemoreflex arising in the exercising skeletal muscle.

Arm↗
PubMed1988

Accuracy of electrical impedance cardiography for measuring cardiac output in children with congenital heart defects.

This study determined whether noninvasive electrical impedance cardiography accurately measures systemic blood flow (cardiac output) in children with congenital heart defects. A total of 37 patients ranging in age from 2 to 171 months underwent complete right- and left-sided heart catheterizations that included simultaneous Fick and impedance measurement of cardiac output. Based on the diagnosis, 4 groups were formed consisting of a control group (n = 11) with no shunts, a group with intracardiac left-to-right shunting and an atrial septal defect (n = 7), another with a ventricular septal defect (n = 12) and an extracardiac left-to-right shunting with patent ductus arteriosus group (n = 7). Impedance values for systemic blood flow were compared with systemic and pulmonary blood flow obtained by the direct Fick method with measured oxygen consumption. The difference between impedance and Fick systemic blood flow was less than or equal to 5% in each of the 4 groups. The highest correlation between impedance and Fick systemic blood flow was with the atrial septal defect group (r = 0.89) and lowest with the ventricular septal defect and control (r = 0.69) groups. Fick pulmonary blood flow was significantly greater than impedance or Fick systemic flow in all 3 shunt groups. Impedance cardiography accurately measured systemic blood flow in children without shunts or valvular insufficiency. Likewise, systemic blood flow was accurately measured by impedance in the presence of intracardiac left-to-right shunts (atrial and ventricular septal defects) and extracardiac left-to-right shunts (patent ductus arteriosus).(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Circulation↗
PubMed1988

Single-breath DLCO maneuver causes cardiac output to fall during and after cycling.

The purpose of this study was to evaluate the influence of the single-breath pulmonary diffusing capacity (DLCO) breath-hold maneuver on central hemodynamics. Ten men (mean age 24 yr) were studied at rest, during 40 min of cycling at 40 and 60% of peak O2 uptake, and 10 min into recovery. DLCO was measured in the seated position during a 10-s breath hold at total lung capacity. At rest the breath hold caused a significant fall in stroke volume (SV, -16%) and an increase in heart rate (HR, +20%) with no change in cardiac output (Q). The resting DLCO of 36.5 ml.min-1.mmHg-1 increased by 28 and 48%, respectively, during the low- and moderate-intensity cycling. The breath hold while cycling caused a significant decrease in SV and Q, but HR did not change. Likewise, during recovery SV and Q fell with the breath hold but again HR did not change. A significant fall in systolic (-17%), diastolic (-12.5%), and mean arterial pressure (-15%) occurred during the breath hold at rest and during and after the exercise. The reduction observed in SV and blood pressure most likely reflected a decrease in venous return. The differences observed in the HR response before, compared with during and after exercise, were consistent with a resetting or shift in the operating point of the arterial baroreflex. Because blood flow fell during the exercise and recovery breath-hold maneuver, the "true" DLCO may have been underestimated during and after cycling.

Adult↗
PubMed1988

Running-induced changes in lung function are not altered by acute moderate hypoxia.

The purpose of this study was to describe the acute changes in pulmonary function and volumes induced by running in a simulated normobaric hypoxic environment. Eleven men (X- = 26 years, 78 kg) ran 5 miles (run time approximately equal to 40 min) under normoxic (N) and hypoxic (H) conditions. A PO2 Aerobic Exerciser was used to approximate an altitude of 2286 m (PIO2 = 113 mm Hg). Impedance cardiography was used to measure cardiac output and segmental transthoracic impedance (Zo) was used to identify thoracic fluid shifts. Similar reductions in vital capacity (7%) and increases in residual volume (10%) occurred after the N and H runs with no change in total lung capacity. Flow rates breathing air or He/O2, closing volume, and closing capacity did not change. The DLCO breathhold maneuver caused a significant fall in pulmonary blood flow after running but diffusing capacity appeared to be unaffected. No changes occurred in Zo at the apex, middle, or base of the lung after either run. The hypoxic pulmonary pressor response failed to modify the pulmonary changes observed after equivalent normoxic exercise. The lung volume changes subsequent to either run were due to expiratory limitation. Previous speculation of an exercise-induced interstitial edema could not be confirmed.

Adult↗
PubMed1986

Oscillatory cardiopulmonary effects of high-frequency jet ventilation.

The cardiovascular effects of high-frequency jet ventilation (HFJV) were compared with conventional volume ventilation in the anesthetized dog. A unique effect of HFJV on stroke volume and cardiac output was observed when stroke volume was analyzed on a beat-by-beat basis with impedance cardiography. A pronounced amplitude modulation of stroke volume, as well as of pulmonary and arterial pressure, occurred when the frequency of the HFJV approached the heart rate. The beat frequency of these amplitude oscillations was equal to that predicted based upon the frequency of the HFJV and the heart rate. Cardiac outputs obtained by techniques which average several beats will not detect these oscillations in cardiac output. These findings suggest that HFJV can generate an oscillation in thoracic hemodynamics which affects ventricular output in a similar manner.

Animals↗
PubMed1979

Post-competition blood lactate concentrations in collegiate swimmers.

The purpose of this investigation was to quantitate post-competition lactate (LA) concentrations of swimmers during a competitive collegiate meet. Blood LA was measured by an enzymatic method on 23 subjects 5 min after each race event. The largest mean LA concentration of 25.7 mM/L was observed in swimmers after competing in the 200-yd individual medley. Swimmers in the 200-yd butterfly, back, breast and freestyle races had similar mean blood LA concentrations (ranging from 16.4 to 20.6 mM/L). Swimmers in the two longest events, the 500-yd and 1,000-yd free style races, had mean LA concentrations of 15.6 and 10.0 mM/L, respectively. To account for the effects of motivation, LA concentrations were measured following maximal effort noncompetitive 100 and 200-yd swims. LA concentrations were slightly greater in conjunction with faster performances for the competitive as compared to the noncompetitive 100 and 200-yd swims.

Adult↗
PubMed1979

Maximal work capacity of women during acute hypoxia.

Six healthy women (22--34 yr of age) performed maximal bicycle work in a hypobaric chamber at sea level and at simulated altitudes of 2,130 and 3,050 m (barometric pressures, 758, 586, and 523 Torr). Maximal oxygen uptake (VO2max) decreased 10 and 15% from sea-level values at 2,130 and 3,050 m, respectively. At these altitudes minute ventilation (VEBTPS) increased 17 and 22% respectively, a consequence of increased respiratory rate (fR). Respiratory exchange ratios increased 10 and 14%, and oxygen pulse decreased 9 and 12%, respectively, at 2,130 and 3,050 m. Maximal blood lactates, heart rates, cardiac outputs, and plasma volume shifts were unaffected by these altitudes. Although during maximal work the percentage increases in VEBTPS, fR, and R that resulted from altitude exposure were greater in women than those previously reported for men, the decrements in VO2max were comparable to those in men. The results show that relative to their performance at sea level, men and women have equal ability to perform maximal work at altitudes up to 3,050 m.

Acute Disease↗